Tungiasis
Encyclopedia
Tungiasis is an inflammatory skin disease caused by infection of the female ectoparasitic Tunga penetrans
flea
(also known as chigoe flea
, jigger, nigua or sand flea), found in the tropical parts of Africa, the Caribbean, Central and South America, and India. Tunga penetrans is the smallest flea in the world, measuring 1mm across. It is also known in Latin America as the nigua and bicho de pie.,.
Tungiasis causes skin inflammation
, severe pain, itching, and a lesion
at the site of infection that is characterized by a black dot at the center of a swollen red lesion, surrounded by what looks like a white halo. Desquamation
of the skin is always seen, especially after the flea expands during hypertrophy.
As of 2009, tungiasis is present worldwide in 88 countries with varying degrees of incidence. This disease is of special public health concern in highly endemic areas like Nigeria, Trinidad, Tobago, and Brazil where its prevalence, especially in poor communities, has been known to approach 50%.
The chigoe flea is properly classified as a member of the order Siphonaptera as it is a flea
. Although commonly referred to as chiggers, true chiggers are mites
which are minute arachnids. Mites penetrate the skin to drink blood but they do not lay eggs as T. penetrans does. Moreover, in mites, the adult and the larval forms both feed on other animals. This is not the case with T. penetrans as only the adults feed on mammals and it is only the female that stays attached to the host.
after they were shipwrecked on Haiti. Through ship routes and further expeditions, the chigoe flea was spread to the rest of the world, particularly to the rest of Latin America and Africa. The spread to greater Africa occurred throughout the 17th and 19th centuries, specifically in 1873 when the infected crewmen of the ship Thomas Mitchell introduced it into Angola having sailed from Brazil.,
Left untreated, secondary infections such as bacteremia
, tetanus
, and gangrene
can occur.
(The term transmission does not apply in tungiasis case because T. penetrans causes the condition, does not transmit it.) It has been written that the explanation for the preponderance of tungiasis lesions on the toes is because chigoe flea is a poor jumper, attaining only a high of 20 cm http://www.dermato.med.br/publicacoes/artigos/2007Tungiasis-and-Myiasis.pdf. But the reality is more complex; for example, the jumping ability cannot explain why hands are the second most affected body part. Lesions on the hands are better explained by playing in the sand and nothing that hands are oftenused to remove sand from other parts of the body. The occurrence of tungiasis lesions on the toes, between them, on the soles can easily explained by the fact that most of the victims are poor, walk barefoot, and live in places where the sand (home to chigeo fleas) constitutes the floor. Rate of incidence therefore is greatly increased in poor communities and populations because of the lack of adequate housing. This occurs in significantly higher proportions during the peak of the dry season in local communities.
About 6–8 days after hatching, the larva pupates and builds a cocoon around itself. Because it lives mostly on and below the surface of sand, sand is used to stabilize the cocoon and it helps to promote its development. An environmental disturbance such as rain or a lack of sand have been shown to decrease incidence, most likely due to decreasing the environmental factors (i.e., sand) that the flea depends on for overall growth. Barring any disturbances to the cocoon, an adult flea will emerge from the puparium after 9–15 days.
In the adult phase, the flea will occasionally feed on unsuspecting animals. Only once the female burrows into the skin can reproduction occur, as the male and female show no interest in each other in the wild. The next phase of life for the female flea, as the male flea dies after copulation, is in vivo ecto-developmental, and it is commonly referred to as the Fortaleza Classification of tungiasis, though it seems rather appropriate to make a distinction and refer to the in vivo development of the T. penetrans organism as the Fortaleza Cycle.
Stage 1 is characterized by the penetration of the skin by the female chigoe flea. Running along the body, the female uses its posterior legs to push its body upward by an angle between 45–90 degrees. Penetration then starts, beginning with the proboscis
going through the epidermis.
By stage 2 (day 1–2), penetration is complete and the flea has burrowed most of its body into the skin. Only the anus, the copulatory organs, and four rear air holes in fleas called stigmatas remain on the outside of the epidermis. The anus will excrete feces that is thought to attract male fleas for mating, described in a later section. The hypertrophic zone between tergites 2 and 3 in the abdominal region begins to expand a day or two after penetration and takes the appearance of a life belt. During this time, the flea begins to feed on the host’s blood.
Stage 3 is divided into two substages, the first of which being 2–3 days after penetration is complete. In 3a, maximum hypertrophy
is achieved and the flea’s midsection swells to the size of a pea. Due to the expanding flea, the outer layer of the skin is stretched thin, resulting in the appearance of a white halo around the black dot (rear end of the flea) at the center of the lesion. In 3b, the chitin exoskeleton of tergites 2 and 3 increase in thickness and gives the structure the look of a mini caldera. Egg release is common in substage 3b, as are fecal coils. The eggs tend to stick to the skin.
At about the 3rd week after penetration, stage 4 begins, which is also divided into two substages. In 4a, the flea loses its signs of vitality
and appears near death. As a result, the lesion shrinks in size, turns brown, and appears wrinkled. The death of the flea marks the beginning of substage 4b (around day 25 post-penetration) as the body begins to eliminate the parasite through skin repair mechanisms (e.g. shedding and subsequent skin repair). At this phase, the lesion is seen as brown or black.
By the 5th stage of tungiasis, the carcass of the T. penetrans flea has been expelled and there are circular skin residues of the infection that remain. There are only lingering symptoms at this time, described in the next section.
enzyme secreted during stage 1.
The patient with a single flea may present as early as stage 2 when, though the erythema
is barely perceptible, a boring pain and the curious sensation of pleasant itching occur. This inflammatory reaction is the initial immunological response to the infestation. Heavily infested patients may not notice a stage 2 infection due to the other fleas’ causing irritation as well. Feces may be seen, but this is more common in the 3rd stage.
Around the third day after penetration, erythema and skin tenderness are felt, accompanied by pruritus (severe itching) and a black furuncular nodule surrounded by a white halo of stretched skin caused by the expansion of the flea. Fecal coils may protrude from the center of the nodule where the flea’s anus
is facing upward. They should be washed off quickly as the feces may remain in the skin unless removed. During this 3a substage, pain can be severe, especially at night or, if the nodule is on the foot, while walking. Eggs
will also begin to be released and a watery secretion can be observed. The radical metamorphosis
during the 3rd to 6th day after penetration, or neosomy, precedes the formation of a small caldera-like rim rampart as a result of the increased thickness of the flea’s chitin
exoskeleton
. During the caldera formation, the nodule shrinks a bit and it looks as if it is beginning to dry out; this takes 2 weeks and comprises substage 3b.
At the third week after penetration and substage 4a, the eggs’ release will have stopped and the lesion
will become smaller and more wrinkled. As the flea is near death, fecal and water secretion will stop altogether. Pain, tenderness, and skin inflammation will still be present. Around the 25th day after penetration, the lesion looks like a black crust and the flea’s carcass is removed by host repair mechanisms and the skin begins to heal. With the flea gone, inflammation may still persist for a while.
Although patients would not present with in the 5th stage of tungiasis as the flea would be dead and no longer in the body, this stage is characterized by the reorganization of the skin (1–4 weeks) and a circular residue of 5–10 mm in diameter around the site in penetration. An intraepithelial abscess
, which developed due to the presence of the flea, will drain and later heal. Although these disease residues would persist for a few months, tungiasis is no longer present.
In severe cases, ulcers are common, as well as complete tissue and nail deformation. A patient may be unable to walk due to severe pain if too many of the lesions are present in the feet. Suppuration (pus formation), auto-amputation of digits (via ainhum), and chronic lymphedema
may also be seen.
If the patient is not vaccinated, tetanus
if often a complication due to secondary infection. Gangrene is another common complication of severe infestation and superinfection. Staphylococcus aureus
and Wolbachia
endobacteria can be transmitted by the chigoe flea, as well as nearly 150 other different pathogens. For these reasons, the chigoe flea should be removed as soon as possible.
e to develop on the surface of the sand and the deeper sand does not have enough oxygen. This preferred ecological niche
offers a way to decrease transmission among humans by investing in concrete grounds as opposed to the sand that is usually used in shacks and some favelas. Indeed, Nany et al. (2007) report that “In shacks with concreted ground being cleaned every day with water, Tunga [penetrans] larvae were hardly found.”
In a longitudinal study
conducted from March 2001 to January 2002, incidence of tungiasis was found to vary significantly with the local seasons of an endemic community in Brazil
. In particular, the study found that “occurrence of tungiasis varies throughout the year and seems to follow local precipitation patterns. Maximum and minimum prevalence rates differed by more than a factor of three.” The authors suggest that the correlation
is due to the high humidity in the soil impairing larval development during the rainy season, as well as the more obvious reason that rain may simply wash away all stages of T. penetrans due its small size of 1mm.
Acting as both biological vectors and definitive hosts, humans have spread Tunga penetrans from its isolated existence in the West Indies to all of Latin America
and most of Africa
via sea travel. Since the chigoe flea technically has no reservoir species and the female will cause tungiasis to any mammalian organism it can penetrate, this means the flea will have a relatively large amount of hosts and victims. Epidemiologically, this is important as tungiasis often causes secondary infections.,,
Investigators have also found that adult T. penetrans have different morphologies with respect to the shape of their head. Some have a rounded head, others have head shapes that resemble ski ramps more than anything else; still others demonstrate head shapes that are very linear with a slight bulge at the nose. These morphologies were seen to be host-specific, as only fleas of some head-types were found in specific hosts. This, along with genetic differences among the T. penetrans fleas that infect different host animals, may suggest that there are several species of closely related species have been grouped taxonomically under one binomial nomanclature.
Though the chigoe flea resembles most others in morphology, the flea has a hypertrophic region between tergites 2 and 3. As stated in Eisele et al. (2003), tergites 2 and 3, as well as the abdominal sternites, stretch considerably and are bent apart. Chitinous clasps that are built for the abdominal enlargement surround these regions and hold onto the hypertrophic zone, giving them the appearance of a three-leafed clover. (See image 7 of the life cycle diagram.) Surprisingly, the rest of the flea, including the head and the thorax, do not change in shape.,
With the rapid expansion of the flea, the morphology of the flea is now vastly different. It has gone from the smallest flea in the world to a bulging mass that measures 5–10mm in diameter. This results in a volume that is 2000 to 3000 times what it used to be.
The chigoe flea eggs’ average length is 604 μm and the just hatched larvae, in their first instar, have an average length of 1,500 μm. At the second and last instar (T. penetrans is unique among the fleas in that it only has two, instead of three, instars.) the larvae decreases in size to 1,150 μm after growing to at least 2,900 μm. The development from instar 1 to instar 2 lasts less than one day.
On the whole, Tunga penetrans does not do very well in terms of its Darwinian fitness. In a laboratory setting in which different mediums were provided for larval growth, the rate of survival from egg to adult in the best medium was 1.05%. Only 15% of the eggs were found to develop into larvae, and of those, only 14% formed a cocoon. Moreover, only half of the pupae reached the adult phase, resulting in gender disequilibrium. Although these results reflect a laboratory setting, the general lack of success for T. penetrans’s reproductive (opportunistic) R-strategy is surprising given the number of fleas that a single person can attract. The low survival rate suggests that a concentrated public health effort directed at any point in the flea’s life cycle is likely to deal a crippling blow to the overall population of the flea in the area.
There is no drug that has proven to be effective against embedded fleas. Oral niridazole
was once considered a therapeutic drug, but well-designed studies are lacking and, given the severe adverse effects, this is one drug that is likely to cause more harm than good. However, it has some anecdotal evidence of lysing the fleas altogether. Oral ivermectin is considered by some in endemic areas to be a panacea against the fleas but studies using high doses have failed to validate this hypothesis. Other drugs such as topical ivermectin and metrifonate
have been somewhat successful, but not enough to be significant. [2,5] For superinfections, trimethoprim
, sulfamethoxazole
, metronidazole
, amoxicillin
, (with/without clavulanate) have been used successfully, though these treat only secondary infections.
Successful topical treatments also include cryotherapy
and electrodesiccation of the lesion. If formaldehyde
, chloroform
, or DDT
are used topically, care should be taken when dealing with the resulting morbidity. The T. penetrans flea can also be suffocated using occlusive petrolatum, while Vaseline will kill the organism as well, most likely due to suffocation as the stigmatas would be covered. The gum of the mammee apple
, a fruit that also goes by the name Saint Domingo Apricot, has also been used to kill the chigoe flea, though this has not been reported in the main T. penetrans literature.
Even without treatment, the burrowed fleas will die within five weeks and are naturally sloughed off as the skin sheds.
Though vaccines would be useful, due to the ectoparasitic nature of chigoe flea, they are neither a feasible nor an effective tool against tungiasis. Nevertheless, due to the high incidence of secondary infection, those at risk of tungiasis should get vaccinated against tetanus. A better approach is to use repellents that specifically target the chigoe flea. One very successful repellent is called Zanzarin, a derivative of coconut oil, jojoba oil, and aloe vera. In a recent study involving two cohorts, the infestation rates dropped 92% on average for the first one and 90% for the other. Likewise, the intensity of the cohorts dropped by 86% and 87% respectively. The non-toxic nature of Zanzarin, combined with its “remarkable regression of the clinical pathology” make this a tenable public health tool against tungiasis.
The use of pesticide
, like DDT, has also led to elimination of the Tunga penetrans, but this control/prevention strategy should be utilized very carefully, if at all, because of the possible side effects such pesticides can have on the greater biosphere. In the 1950s, there was a worldwide effort to eradicate malaria. As part of that effort, Mexico
launched the Campaña Nacional para la Erradicación de Paludismo, or the National Campaign for the Eradication of Malaria. By spraying DDT
in homes, the Anopheles
genus of mosquitoes known to carry the deadly Plasmodium falciparum
was mostly eliminated. As a consequence of this national campaign, other arthropods were either eliminated or significantly reduced in number, including the reduviid big responsible for Chagas disease
(American Trypanosomiasis) and T. penetrans. Controlled, in-home spraying of DDT is effective as it gives the home immunity against arthropods while not contaminating the local water supplies and doing as much ecological damage as was once the case when DDT was first introduced.
While other species gradually gained resistance to DDT and other insecticides that were used, T. penetrans did not; as a result, incidences of tungiasis in Mexico are very low when compared to the rest of Latin America, especially Brazil, where rates in poor areas have been known to be as high or higher than 50%. There was a 40-year period with no tungiasis cases in Mexico. It was not until August 1989 that three Mexican patients presented with the disease. Though there were other cases of tungiasis reported thereafter, all were acquired in Africa
.
Chigoe flea
The chigoe flea or jigger is a parasitic arthropod found in most tropical and sub-tropical climates, not to be confused with the larval form of Trombiculidae found in more temperate climates. In Brazil, the parasite is referred to as bicho-de-pé . At 1 mm long, the chigoe flea is the smallest...
flea
Flea
Flea is the common name for insects of the order Siphonaptera which are wingless insects with mouthparts adapted for piercing skin and sucking blood...
(also known as chigoe flea
Chigoe flea
The chigoe flea or jigger is a parasitic arthropod found in most tropical and sub-tropical climates, not to be confused with the larval form of Trombiculidae found in more temperate climates. In Brazil, the parasite is referred to as bicho-de-pé . At 1 mm long, the chigoe flea is the smallest...
, jigger, nigua or sand flea), found in the tropical parts of Africa, the Caribbean, Central and South America, and India. Tunga penetrans is the smallest flea in the world, measuring 1mm across. It is also known in Latin America as the nigua and bicho de pie.,.
Tungiasis causes skin inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
, severe pain, itching, and a lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
at the site of infection that is characterized by a black dot at the center of a swollen red lesion, surrounded by what looks like a white halo. Desquamation
Desquamation
Desquamation , also called skin peeling, is the shedding of the outermost membrane or layer of a tissue, such as the skin.-Skin:Normal, nonpathologic desquamation of the skin occurs when keratinocytes, after moving apically over about 14 days, are individually shed unnoticeably...
of the skin is always seen, especially after the flea expands during hypertrophy.
As of 2009, tungiasis is present worldwide in 88 countries with varying degrees of incidence. This disease is of special public health concern in highly endemic areas like Nigeria, Trinidad, Tobago, and Brazil where its prevalence, especially in poor communities, has been known to approach 50%.
Classification
The classification of T. penetrans is as follows:- Kingdom: AnimalAnimalAnimals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
ia - Phylum: ArthropodArthropodAn arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
a - Class: InsectInsectInsects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
a - Order: Siphonaptera
- Family: HectopsyllidaeHectopsyllidaeHectopsyllidae is a small family of fleas, containing only the chigoe fleas and the sticktight fleas. They were formerly known as Tungidae, and by authorities that demote the Pulicoidea to family rank they are treated as subfamily Hectopsyllinae...
- Genus: TungaTungaTunga may refer to:* Tunga River, a river in India* Tunga, Leyte, a municipality in the Philippines* Tunga, Trondheim, a location in Trondheim, Norway* Tunga , a Unicode typeface included in Windows XP that displays Kannada script...
- Species: penetrans
The chigoe flea is properly classified as a member of the order Siphonaptera as it is a flea
Flea
Flea is the common name for insects of the order Siphonaptera which are wingless insects with mouthparts adapted for piercing skin and sucking blood...
. Although commonly referred to as chiggers, true chiggers are mites
MITES
MITES, or Minority Introduction to Engineering and Science, is a highly selective six-week summer program for rising high school seniors held at the Massachusetts Institute of Technology. Its purpose is to expose students from minority, or otherwise disadvantaged backgrounds, to the fields of...
which are minute arachnids. Mites penetrate the skin to drink blood but they do not lay eggs as T. penetrans does. Moreover, in mites, the adult and the larval forms both feed on other animals. This is not the case with T. penetrans as only the adults feed on mammals and it is only the female that stays attached to the host.
Synonyms
Tunga penetrans is also known by the following names: chigoe flea, sand flea, nigua, chigger flea, jigger flea, bicho de pé, pico, sikka, kuti, and piqui, among many others.History
From the existing literature, it seems T. penetrans is native to the West Indies. The first case of tungiasis was described in 1526 by Gonzalo Fernández de Oviedo y Valdés where he discussed the skin infection and its symptoms on crew members from Columbus’s Santa MariaSanta María (ship)
La Santa María de la Inmaculada Concepción , was the largest of the three ships used by Christopher Columbus in his first voyage. Her master and owner was Juan de la Cosa.-History:...
after they were shipwrecked on Haiti. Through ship routes and further expeditions, the chigoe flea was spread to the rest of the world, particularly to the rest of Latin America and Africa. The spread to greater Africa occurred throughout the 17th and 19th centuries, specifically in 1873 when the infected crewmen of the ship Thomas Mitchell introduced it into Angola having sailed from Brazil.,
Symptoms
The symptoms of this disease include:- Severe pruritus
- Pain
- InflammationInflammationInflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
and swelling - Lesions and ulcerations, with black dots in the center
Left untreated, secondary infections such as bacteremia
Bacteremia
Bacteremia is the presence of bacteria in the blood. The blood is normally a sterile environment, so the detection of bacteria in the blood is always abnormal....
, tetanus
Tetanus
Tetanus is a medical condition characterized by a prolonged contraction of skeletal muscle fibers. The primary symptoms are caused by tetanospasmin, a neurotoxin produced by the Gram-positive, rod-shaped, obligate anaerobic bacterium Clostridium tetani...
, and gangrene
Gangrene
Gangrene is a serious and potentially life-threatening condition that arises when a considerable mass of body tissue dies . This may occur after an injury or infection, or in people suffering from any chronic health problem affecting blood circulation. The primary cause of gangrene is reduced blood...
can occur.
Etiology
Tungiasis is strictly caused by chigoe fleas Chigoe fleaChigoe flea
The chigoe flea or jigger is a parasitic arthropod found in most tropical and sub-tropical climates, not to be confused with the larval form of Trombiculidae found in more temperate climates. In Brazil, the parasite is referred to as bicho-de-pé . At 1 mm long, the chigoe flea is the smallest...
(The term transmission does not apply in tungiasis case because T. penetrans causes the condition, does not transmit it.) It has been written that the explanation for the preponderance of tungiasis lesions on the toes is because chigoe flea is a poor jumper, attaining only a high of 20 cm http://www.dermato.med.br/publicacoes/artigos/2007Tungiasis-and-Myiasis.pdf. But the reality is more complex; for example, the jumping ability cannot explain why hands are the second most affected body part. Lesions on the hands are better explained by playing in the sand and nothing that hands are oftenused to remove sand from other parts of the body. The occurrence of tungiasis lesions on the toes, between them, on the soles can easily explained by the fact that most of the victims are poor, walk barefoot, and live in places where the sand (home to chigeo fleas) constitutes the floor. Rate of incidence therefore is greatly increased in poor communities and populations because of the lack of adequate housing. This occurs in significantly higher proportions during the peak of the dry season in local communities.
Reservoirs and Transmission
T. penetrans has been documented to use various mammals as reservoir hosts, including humans, pigs, dogs, cats, rats, sheep, cattle, donkeys, monkeys, birds, and elephants. These hosts indirectly propagate the disease by being the origin of the next generation of fleas. Once the female flee expels 100-200 eggs, the cycle of transmission begins again.Incubation Period
Because of the relatively rapid onset of tungiasis, the incubation period tends to be short. Although there is some reddening around the site of penetration, the first symptoms are perceived in stage 2 as itching and severe pain, usually a day after penetration.Life Cycle / Ex vivo Development
Tunga penetrans starts off its life as a small egg that has just been released from a gravid female. On average, it is 604 μm long and the larva will hatch from the egg within 1–6 days, assuming the environmental conditions (e.g., moisture, humidity, etc.) are favorable. After hatching, the flea will progress through two instar phases. This is unique in that most fleas go through three instead. Over the course of that development, the flea will first decrease in size from its just-hatched size of 1,500 μm to 1,150 μm (first instar) before growing to 2,900 μm (second instar).About 6–8 days after hatching, the larva pupates and builds a cocoon around itself. Because it lives mostly on and below the surface of sand, sand is used to stabilize the cocoon and it helps to promote its development. An environmental disturbance such as rain or a lack of sand have been shown to decrease incidence, most likely due to decreasing the environmental factors (i.e., sand) that the flea depends on for overall growth. Barring any disturbances to the cocoon, an adult flea will emerge from the puparium after 9–15 days.
In the adult phase, the flea will occasionally feed on unsuspecting animals. Only once the female burrows into the skin can reproduction occur, as the male and female show no interest in each other in the wild. The next phase of life for the female flea, as the male flea dies after copulation, is in vivo ecto-developmental, and it is commonly referred to as the Fortaleza Classification of tungiasis, though it seems rather appropriate to make a distinction and refer to the in vivo development of the T. penetrans organism as the Fortaleza Cycle.
Fortaleza Classification / In vivo Development
In a seminal paper on the biology and pathology of Tunga penetrans, Eisele et al. (2003) provided and detailed the five stages of tungiasis, thereby detailing the in vivo development of the female chigoe flea for the first time. In dividing the natural history of the disease, the Fortalez Classification formally describes the last part of the female flea’s life cycle where it burrows into its host’s skin, expels eggs, and dies. Due to the nature of the discussion, overlap with other sections, particularly the one on symptoms, is unavoidable.Stage 1 is characterized by the penetration of the skin by the female chigoe flea. Running along the body, the female uses its posterior legs to push its body upward by an angle between 45–90 degrees. Penetration then starts, beginning with the proboscis
Proboscis
A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...
going through the epidermis.
By stage 2 (day 1–2), penetration is complete and the flea has burrowed most of its body into the skin. Only the anus, the copulatory organs, and four rear air holes in fleas called stigmatas remain on the outside of the epidermis. The anus will excrete feces that is thought to attract male fleas for mating, described in a later section. The hypertrophic zone between tergites 2 and 3 in the abdominal region begins to expand a day or two after penetration and takes the appearance of a life belt. During this time, the flea begins to feed on the host’s blood.
Stage 3 is divided into two substages, the first of which being 2–3 days after penetration is complete. In 3a, maximum hypertrophy
Hypertrophy
Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It should be distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number...
is achieved and the flea’s midsection swells to the size of a pea. Due to the expanding flea, the outer layer of the skin is stretched thin, resulting in the appearance of a white halo around the black dot (rear end of the flea) at the center of the lesion. In 3b, the chitin exoskeleton of tergites 2 and 3 increase in thickness and gives the structure the look of a mini caldera. Egg release is common in substage 3b, as are fecal coils. The eggs tend to stick to the skin.
At about the 3rd week after penetration, stage 4 begins, which is also divided into two substages. In 4a, the flea loses its signs of vitality
Vitality
-Vitality:Etymology: From Latin vita , which means life.Outside of its own existence or source, life is only recognized through some form of expression or dynamic...
and appears near death. As a result, the lesion shrinks in size, turns brown, and appears wrinkled. The death of the flea marks the beginning of substage 4b (around day 25 post-penetration) as the body begins to eliminate the parasite through skin repair mechanisms (e.g. shedding and subsequent skin repair). At this phase, the lesion is seen as brown or black.
By the 5th stage of tungiasis, the carcass of the T. penetrans flea has been expelled and there are circular skin residues of the infection that remain. There are only lingering symptoms at this time, described in the next section.
Clinical presentation in humans
In all cases, tungiasis by itself only caused morbidity, though secondary infection may lead to mortality. The life cycle section presents the Fortaleza stages from the flea’s developmental perspective. It should be noted that the discussion is specific to symptoms of human infection. The clinical presentation in humans follows the Fortaleza Classification as the stage of infection will determine the symptoms present. The following discussion will give an overview of the symptoms beginning in stage 2 because patients are not likely to present themselves at the early stages of infection, mostly because the flea’s burrowing is usually not felt. This may be due to a keratolyticKeratolytic
Keratolytic therapy is treatment to remove warts and other lesions in which the epidermis produces excess skin. In this therapy, acid medicine, such as salicylic acid is put on the lesion. Keratolytic therapy thins the skin on and around the lesion. It causes the outer layer of the skin to loosen...
enzyme secreted during stage 1.
The patient with a single flea may present as early as stage 2 when, though the erythema
Erythema
Erythema is redness of the skin, caused by hyperemia of the capillaries in the lower layers of the skin. It occurs with any skin injury, infection, or inflammation...
is barely perceptible, a boring pain and the curious sensation of pleasant itching occur. This inflammatory reaction is the initial immunological response to the infestation. Heavily infested patients may not notice a stage 2 infection due to the other fleas’ causing irritation as well. Feces may be seen, but this is more common in the 3rd stage.
Around the third day after penetration, erythema and skin tenderness are felt, accompanied by pruritus (severe itching) and a black furuncular nodule surrounded by a white halo of stretched skin caused by the expansion of the flea. Fecal coils may protrude from the center of the nodule where the flea’s anus
Anus
The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...
is facing upward. They should be washed off quickly as the feces may remain in the skin unless removed. During this 3a substage, pain can be severe, especially at night or, if the nodule is on the foot, while walking. Eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
will also begin to be released and a watery secretion can be observed. The radical metamorphosis
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
during the 3rd to 6th day after penetration, or neosomy, precedes the formation of a small caldera-like rim rampart as a result of the increased thickness of the flea’s chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
exoskeleton
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
. During the caldera formation, the nodule shrinks a bit and it looks as if it is beginning to dry out; this takes 2 weeks and comprises substage 3b.
At the third week after penetration and substage 4a, the eggs’ release will have stopped and the lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
will become smaller and more wrinkled. As the flea is near death, fecal and water secretion will stop altogether. Pain, tenderness, and skin inflammation will still be present. Around the 25th day after penetration, the lesion looks like a black crust and the flea’s carcass is removed by host repair mechanisms and the skin begins to heal. With the flea gone, inflammation may still persist for a while.
Although patients would not present with in the 5th stage of tungiasis as the flea would be dead and no longer in the body, this stage is characterized by the reorganization of the skin (1–4 weeks) and a circular residue of 5–10 mm in diameter around the site in penetration. An intraepithelial abscess
Abscess
An abscess is a collection of pus that has accumulated in a cavity formed by the tissue in which the pus resides due to an infectious process or other foreign materials...
, which developed due to the presence of the flea, will drain and later heal. Although these disease residues would persist for a few months, tungiasis is no longer present.
In severe cases, ulcers are common, as well as complete tissue and nail deformation. A patient may be unable to walk due to severe pain if too many of the lesions are present in the feet. Suppuration (pus formation), auto-amputation of digits (via ainhum), and chronic lymphedema
Lymphedema
Lymphedema , also known as lymphatic obstruction, is a condition of localized fluid retention and tissue swelling caused by a compromised lymphatic system....
may also be seen.
If the patient is not vaccinated, tetanus
Tetanus
Tetanus is a medical condition characterized by a prolonged contraction of skeletal muscle fibers. The primary symptoms are caused by tetanospasmin, a neurotoxin produced by the Gram-positive, rod-shaped, obligate anaerobic bacterium Clostridium tetani...
if often a complication due to secondary infection. Gangrene is another common complication of severe infestation and superinfection. Staphylococcus aureus
Staphylococcus aureus
Staphylococcus aureus is a facultative anaerobic Gram-positive coccal bacterium. It is frequently found as part of the normal skin flora on the skin and nasal passages. It is estimated that 20% of the human population are long-term carriers of S. aureus. S. aureus is the most common species of...
and Wolbachia
Wolbachia
Wolbachia is a genus of bacteria which infects arthropod species, including a high proportion of insects , as well as some nematodes. It is one of the world's most common parasitic microbes and is possibly the most common reproductive parasite in the biosphere...
endobacteria can be transmitted by the chigoe flea, as well as nearly 150 other different pathogens. For these reasons, the chigoe flea should be removed as soon as possible.
Epidemiology
For the most part, the chigoe flea lives 2–5 cm below sand, an observation which helps explains its overall distribution. The temperature is generally too hot for the larvaLarva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e to develop on the surface of the sand and the deeper sand does not have enough oxygen. This preferred ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
offers a way to decrease transmission among humans by investing in concrete grounds as opposed to the sand that is usually used in shacks and some favelas. Indeed, Nany et al. (2007) report that “In shacks with concreted ground being cleaned every day with water, Tunga [penetrans] larvae were hardly found.”
In a longitudinal study
Longitudinal study
A longitudinal study is a correlational research study that involves repeated observations of the same variables over long periods of time — often many decades. It is a type of observational study. Longitudinal studies are often used in psychology to study developmental trends across the...
conducted from March 2001 to January 2002, incidence of tungiasis was found to vary significantly with the local seasons of an endemic community in Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
. In particular, the study found that “occurrence of tungiasis varies throughout the year and seems to follow local precipitation patterns. Maximum and minimum prevalence rates differed by more than a factor of three.” The authors suggest that the correlation
Correlation
In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....
is due to the high humidity in the soil impairing larval development during the rainy season, as well as the more obvious reason that rain may simply wash away all stages of T. penetrans due its small size of 1mm.
Acting as both biological vectors and definitive hosts, humans have spread Tunga penetrans from its isolated existence in the West Indies to all of Latin America
Latin America
Latin America is a region of the Americas where Romance languages – particularly Spanish and Portuguese, and variably French – are primarily spoken. Latin America has an area of approximately 21,069,500 km² , almost 3.9% of the Earth's surface or 14.1% of its land surface area...
and most of Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
via sea travel. Since the chigoe flea technically has no reservoir species and the female will cause tungiasis to any mammalian organism it can penetrate, this means the flea will have a relatively large amount of hosts and victims. Epidemiologically, this is important as tungiasis often causes secondary infections.,,
Morphology
In a study of 1000 freshly ejected T. penetrans eggs, it was found that females are generally smaller than males for all criteria. In some cases though, females had a bigger epipharynx and maxillar palpus. Due to its burrowing activity, the chigoe flea has developed a well-developed lacinia and epipharynx that is used to penetrate the skin. Overall, the fleas’ head is relatively flattened, which again aids in burrowing through the epidermal and dermal layers.Investigators have also found that adult T. penetrans have different morphologies with respect to the shape of their head. Some have a rounded head, others have head shapes that resemble ski ramps more than anything else; still others demonstrate head shapes that are very linear with a slight bulge at the nose. These morphologies were seen to be host-specific, as only fleas of some head-types were found in specific hosts. This, along with genetic differences among the T. penetrans fleas that infect different host animals, may suggest that there are several species of closely related species have been grouped taxonomically under one binomial nomanclature.
Though the chigoe flea resembles most others in morphology, the flea has a hypertrophic region between tergites 2 and 3. As stated in Eisele et al. (2003), tergites 2 and 3, as well as the abdominal sternites, stretch considerably and are bent apart. Chitinous clasps that are built for the abdominal enlargement surround these regions and hold onto the hypertrophic zone, giving them the appearance of a three-leafed clover. (See image 7 of the life cycle diagram.) Surprisingly, the rest of the flea, including the head and the thorax, do not change in shape.,
With the rapid expansion of the flea, the morphology of the flea is now vastly different. It has gone from the smallest flea in the world to a bulging mass that measures 5–10mm in diameter. This results in a volume that is 2000 to 3000 times what it used to be.
Reproduction and Darwinian Fitness
Females have a depression or groove at their abdominal end whereas the males have their protrusive copulatory organs in that same region. These morphological differences reflect the way the male and female copulate. In the first step toward copulation, the female penetrates an organism in an ungravid state. It is only there that the male will find her and copulate. Copulation of adults has not been observed in the wild. With the female reproductive organs pointing outward, the male will place his reproductive organs “in direction to the upright abdominal end of the female” to copulate. Having copulated for only a few seconds to 2 minutes, the male will then take search for another female. After copulation is complete, the male will die, although sometimes he will take a blood meal before doing so. Interestingly, eggs will be expelled whether or not they have been fertilized.The chigoe flea eggs’ average length is 604 μm and the just hatched larvae, in their first instar, have an average length of 1,500 μm. At the second and last instar (T. penetrans is unique among the fleas in that it only has two, instead of three, instars.) the larvae decreases in size to 1,150 μm after growing to at least 2,900 μm. The development from instar 1 to instar 2 lasts less than one day.
On the whole, Tunga penetrans does not do very well in terms of its Darwinian fitness. In a laboratory setting in which different mediums were provided for larval growth, the rate of survival from egg to adult in the best medium was 1.05%. Only 15% of the eggs were found to develop into larvae, and of those, only 14% formed a cocoon. Moreover, only half of the pupae reached the adult phase, resulting in gender disequilibrium. Although these results reflect a laboratory setting, the general lack of success for T. penetrans’s reproductive (opportunistic) R-strategy is surprising given the number of fleas that a single person can attract. The low survival rate suggests that a concentrated public health effort directed at any point in the flea’s life cycle is likely to deal a crippling blow to the overall population of the flea in the area.
Diagnostic Tests
There are no diagnostic tests for tungiasis. This is most likely because the parasite is ectoparasitic with visible symptoms. Identification of the parasite through removal, and a patient’s traveling history, should suffice for diagnosis, though the latter is clearly more useful than the former. Localization of the lesion may be a useful diagnostic method for the clinician. A biopsy may be done, though again, it is not required for diagnosis.Management and Treatment
As the disease is self-limiting, at least when exposure to the parasite is limited, management is mostly confined to treatment. Due to the secondary infection that can cause serious medical issues, the recommended course of action upon diagnosis is surgical extraction of the flea followed by the application of a topical antibiotic. Care should be taken to avoid tearing the flea during the extraction procedures as severe inflammation will result. The same will occur if part of the flea is left behind. Sterile equipment should always be used, as contaminated instruments could act as mechanical vectors for pathogens to enter the body.There is no drug that has proven to be effective against embedded fleas. Oral niridazole
Niridazole
Niridazole is a schistosomicide. It is used to treat schistosomiasis, the helmintic disease caused by certain flatworms from the genus Schistosoma . It is also known by its trade name Ambilgar. It is usually is given as tablets. Niridazole has central nervous system toxicity and can cause...
was once considered a therapeutic drug, but well-designed studies are lacking and, given the severe adverse effects, this is one drug that is likely to cause more harm than good. However, it has some anecdotal evidence of lysing the fleas altogether. Oral ivermectin is considered by some in endemic areas to be a panacea against the fleas but studies using high doses have failed to validate this hypothesis. Other drugs such as topical ivermectin and metrifonate
Metrifonate
Metrifonate or trichlorfon is an irreversible organophosphate acetylcholinesterase inhibitor.it is a prodrug which is activated non-enzymatically into 2,2-dichlorovinyl dimethyl phosphate ....
have been somewhat successful, but not enough to be significant. [2,5] For superinfections, trimethoprim
Trimethoprim
Trimethoprim is a bacteriostatic antibiotic mainly used in the prophylaxis and treatment of urinary tract infections.It belongs to the class of chemotherapeutic agents known as dihydrofolate reductase inhibitors...
, sulfamethoxazole
Sulfamethoxazole
Sulfamethoxazole is a sulfonamide bacteriostatic antibiotic.It is most often used as part of a synergistic combination with trimethoprim in a 5:1 ratio in co-trimoxazole , also known under trade names such as Bactrim, Septrin, or Septra; in Eastern Europe it is marketed as Biseptol...
, metronidazole
Metronidazole
Metronidazole is a nitroimidazole antibiotic medication used particularly for anaerobic bacteria and protozoa. Metronidazole is an antibiotic, amebicide, and antiprotozoal....
, amoxicillin
Amoxicillin
Amoxicillin , formerly amoxycillin , and abbreviated amox, is a moderate-spectrum, bacteriolytic, β-lactam antibiotic used to treat bacterial infections caused by susceptible microorganisms. It is usually the drug of choice within the class because it is better absorbed, following oral...
, (with/without clavulanate) have been used successfully, though these treat only secondary infections.
Successful topical treatments also include cryotherapy
Cryotherapy
Cryotherapy is the local or general use of low temperatures in medical therapy or the removal of heat from a body part. The term "cryotherapy" comes from the Greek cryo meaning cold and the word therapy meaning cure...
and electrodesiccation of the lesion. If formaldehyde
Formaldehyde
Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...
, chloroform
Chloroform
Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...
, or DDT
DDT
DDT is one of the most well-known synthetic insecticides. It is a chemical with a long, unique, and controversial history....
are used topically, care should be taken when dealing with the resulting morbidity. The T. penetrans flea can also be suffocated using occlusive petrolatum, while Vaseline will kill the organism as well, most likely due to suffocation as the stigmatas would be covered. The gum of the mammee apple
Mammee apple
Mammea americana, commonly known as mammee, mammee apple, mamey, mamey apple, Santo Domingo apricot or South American apricot, is an evergreen tree of the family Calophyllaceae, whose fruit is edible...
, a fruit that also goes by the name Saint Domingo Apricot, has also been used to kill the chigoe flea, though this has not been reported in the main T. penetrans literature.
Even without treatment, the burrowed fleas will die within five weeks and are naturally sloughed off as the skin sheds.
Public Health and Prevention Studies
Due to the high number of hosts, eradication of tungiasis is not feasible, at least not easily so. Public health and prevention strategies should then be done with elimination as the target. Better household hygiene, including having a cemented rather than a sand floor, and washing it often, would lower the rates of tungiasis significantly.Though vaccines would be useful, due to the ectoparasitic nature of chigoe flea, they are neither a feasible nor an effective tool against tungiasis. Nevertheless, due to the high incidence of secondary infection, those at risk of tungiasis should get vaccinated against tetanus. A better approach is to use repellents that specifically target the chigoe flea. One very successful repellent is called Zanzarin, a derivative of coconut oil, jojoba oil, and aloe vera. In a recent study involving two cohorts, the infestation rates dropped 92% on average for the first one and 90% for the other. Likewise, the intensity of the cohorts dropped by 86% and 87% respectively. The non-toxic nature of Zanzarin, combined with its “remarkable regression of the clinical pathology” make this a tenable public health tool against tungiasis.
The use of pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
, like DDT, has also led to elimination of the Tunga penetrans, but this control/prevention strategy should be utilized very carefully, if at all, because of the possible side effects such pesticides can have on the greater biosphere. In the 1950s, there was a worldwide effort to eradicate malaria. As part of that effort, Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
launched the Campaña Nacional para la Erradicación de Paludismo, or the National Campaign for the Eradication of Malaria. By spraying DDT
DDT
DDT is one of the most well-known synthetic insecticides. It is a chemical with a long, unique, and controversial history....
in homes, the Anopheles
Anopheles
Anopheles is a genus of mosquito. There are approximately 460 recognized species: while over 100 can transmit human malaria, only 30–40 commonly transmit parasites of the genus Plasmodium, which cause malaria in humans in endemic areas...
genus of mosquitoes known to carry the deadly Plasmodium falciparum
Plasmodium falciparum
Plasmodium falciparum is a protozoan parasite, one of the species of Plasmodium that cause malaria in humans. It is transmitted by the female Anopheles mosquito. Malaria caused by this species is the most dangerous form of malaria, with the highest rates of complications and mortality...
was mostly eliminated. As a consequence of this national campaign, other arthropods were either eliminated or significantly reduced in number, including the reduviid big responsible for Chagas disease
Chagas disease
Chagas disease is a tropical parasitic disease caused by the flagellate protozoan Trypanosoma cruzi. T. cruzi is commonly transmitted to humans and other mammals by an insect vector, the blood-sucking insects of the subfamily Triatominae most commonly species belonging to the Triatoma, Rhodnius,...
(American Trypanosomiasis) and T. penetrans. Controlled, in-home spraying of DDT is effective as it gives the home immunity against arthropods while not contaminating the local water supplies and doing as much ecological damage as was once the case when DDT was first introduced.
While other species gradually gained resistance to DDT and other insecticides that were used, T. penetrans did not; as a result, incidences of tungiasis in Mexico are very low when compared to the rest of Latin America, especially Brazil, where rates in poor areas have been known to be as high or higher than 50%. There was a 40-year period with no tungiasis cases in Mexico. It was not until August 1989 that three Mexican patients presented with the disease. Though there were other cases of tungiasis reported thereafter, all were acquired in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
.
External links
- Health in Plain English - Tungiasis with pictures
- http://emedicine.medscape.com/article/1109335-overview
- http://www3.interscience.wiley.com/cgi-bin/fulltext/118926772/HTMLSTART
- Afro-Nets - Tungiasis
- Seasonal variation of Tungiasis in an endemic community. The American Journal of Tropical Medicine and Hygiene. Also contains background about the parasite.
- Tungiasis: A Neglected Health Problem in Rural Cameroon. International Journal of Collaborative Research on Internal Medicine & Public Health
- Periungual Tungiasis Muehlstaedt M (2008) Images in clinical medicine. Periungual tungiasis. N Engl J Med 359(24):e30.
- http://www.springerlink.com/content/e3515q55028m8054/ (by subscription)
- http://www.springerlink.com/content/j1wpn7jtlxm6ketj/?p=9c35517ae80743098ef50aec88672c36&pi=2 (by subscription)