Myiasis
Encyclopedia
Myiasis is a general term for infection by parasitic fly
larvae feeding on the host
's necrotic or living tissue
. Colloquialisms for myiasis include flystrike, blowfly strike, and fly-blown. In Greek, "myia" means fly.
Myiasis is a serious problem for livestock
industries, causing severe economic losses worldwide. Although infestation by fly larvae is much more prevalent in animals, it is a relatively frequent occurrence in humans in rural, tropical and subtropical regions.
Myiasis can come in all sorts of variations, depending on the fly species and where the larvae are located. Some flies may lay eggs in open wounds, other larvae may invade unbroken skin or enter the body through the nose or ears, and still others may be swallowed if the eggs are deposited on the lips or on food.
coined the term myiasis in 1840 to refer to diseases resulting from dipterous larvae as opposed to those caused by other insect larvae (the term for this was scholechiasis). Hope described several cases of myiasis from Jamaica caused by unknown larvae, one of which resulted in death.
Even though the term myiasis was first used in 1840, the disease has been around for far longer than that. Ambroise Paré
, the chief surgeon to Charles IX and Henri III, observed that maggots often infested open wounds.
, especially in areas where there are hot and wet conditions. The life cycle in sheep is typical of the disease. The female flies
lay their eggs on the sheep in damp, protected areas of the body that are soiled with urine and faeces, mainly the sheep's breech (buttocks
). It takes approximately eight hours to a day for the eggs to hatch, depending on the conditions. This results in sores as the larva
e lacerate the skin; this is the primary reason for the early removal of lambs' tails. The larvae then tunnel into the host's tissue
, causing irritating lesion
s. After about the second day, bacteria
l infection
occurs and, if left untreated, causes toxemia
or septicemia. This leads to anorexia
and weakness and, if untreated, will lead to death. Blowfly strike accounts for over A$
170 million a year in losses in the Australia
n sheep industry so preventive measures such as mulesing
are practised. Infestation of vulvar area with larvae and maggots is called vulvar myiasis
.
entomologist
Fritz Zumpt
describes myiasis as "the infestation of live human and vertebrate animals with dipterous larvae, which at least for a period, feed on the host's dead or living tissue, liquid body substances, or ingested food". For modern purposes however, this is too vague. For example, feeding on dead tissue is not generally a problem except when larvae such as those of flies in the familiy Piophilidae
attack stored food such as cheese or preserved meats; such activity suggests saprophagy
rather than parasitism; it even may be medically beneficial in maggot debridement therapy (MDT)
.
Currently myiasis commonly is classified according to aspects relevant to the case in question:
Accidental myiasis commonly is enteric, resulting from swallowing eggs or larvae with one's food. The effect is called pseudomyiasis. One traditional cause of pseudomyiasis was the eating of maggots of cheese flies
in cheeses such as Stilton. Depending on the species present in the gut, pseudomyiasis may cause significant medical symptoms, but it is likely that most cases pass unnoticed.
families causing economically important myiasis in livestock and also, occasionally, in humans:
Other families occasionally involved are:
Flesh flies, or sarcophagids, can cause intestinal
myiasis in humans if the females lay their eggs on meat or fruit.
The adult flies are not parasitic, but when they lay their eggs in open wound
s and these hatch into their larva
l stage (also known as maggot
s or grubs), the larvae feed on live and/or necrotic tissue, causing myiasis to develop. They may also be ingested or enter through other body apertures.
Several different presentations of myiasis and their symptoms:
Nosocomial Myiasis refers to myiasis in a hospital setting. It is quite frequent, as patients with open wounds or sores can be infested if flies are present. To prevent nosocomial myiasis, hospital rooms must be kept free of flies.
Human ophthalmomyiasis, both external and internal, has been caused by botfly
larvae.
Clues that myiasis may be present include recent travel to an endemic area, one or more non-healing lesions on the skin, itchiness, movement under the skin or pain, discharge from a central punctum (tiny hole), or a small, white structure protruding from the lesion. Serologic testing has also been used to diagnose the presence of botfly larvae in human ophthalmomyiasis.
. The second control method is the treatment once the infestation is present, and concerns the infected animals (or humans).
applications in the environment where the target livestock is kept. Organophosphorus
or organochlorine
compounds may be used, usually in a spraying formulation. One alternative prevention method is the SIT
(Sterile Insect Technique) where a significant number of artificially reared sterilized (usually through irradiation) male flies are introduced. The male flies compete with wild bred males for females in order to copulate and thus cause females to lay batches of unfertilized eggs which can't develop into the larval stage.
One prevention method involves removing the environment most favourable to the flies, such as by docking
(removal of the tail). Another example is the crutching
of sheep, which involves the removal of wool from around the tail and between the rear legs, which is a favourable environment for the larvae. Another more permanent practice which is used in some countries is mulesing
, where skin is removed from young animals to tighten remaining skin – leaving it less prone to fly attack. PETA
have been campaigning to have farmers cease mulesing. Celebrities such as Pink
, Toni Collette
and Chrissie Hynde
have also participated in PETA's campaign against the mulesing practice; However, Collette has since changed her stance and Pink has said she was misled by PETA and had not done enough research herself into mulesing.
To prevent myiasis in humans, there is a need for general improvement of sanitation, personal hygiene, and extermination of the flies by insecticides. Clothes should be washed thoroughly, dried away from flies, and ironed. The heat of the iron kills the eggs of myiasis-causing flies.
It is also possible to treat livestock with the use of slow release bolus
es containing ivermectin which can provide long term protection against the larvae development.
Sheep may be dipped
, which involves drenching the sheep in insecticide to prevent the growth of the larvae.
in order to clean out necrotic wound
s, a method known as maggot therapy
.
Fly larvae that feed on dead tissue can clean wounds and may reduce bacterial activity and the chance of a secondary infection. They dissolve dead tissue by secreting digestive enzymes onto the wound as well as actively eat the dead tissue with “mouth hooks,” two probing appendages near their toothless mouth. Maggot therapyalso known as maggot debridement therapy (MDT), larval therapy, larva therapy, or larvae therapyis the intentional introduction by a health care practitioner of live, disinfected green bottle fly
maggots or larvae into the non-healing skin and soft tissue wound(s) of a human or other animal for the purpose of selectively cleaning out only the necrotic (dead) tissue within a wound in order to promote wound healing.
Maggot therapy has a long history. The indigenous people of Australia used maggot therapy, as well as the Hill Peoples of Northern Burma, and possibly the Mayans of Central America. Surgeons in Napoleon’s armies recognized that wounded soldiers with myiasis were more likely to survive than those without the infestation. In the American Civil War, army surgeons treated wounds by allowing blowfly maggots to clean away the decayed tissue.
Dr. William Baer, an orthopedic surgeon at Johns Hopkins during the late 1920s, used maggot therapy to treat a series of patients with osteomyelitis, an infection of bone or bone marrow and published his findings. Dr. Baer first got the idea when, during World War I, two soldiers presented to him with broken femurs after having lain on the ground for seven days without food and water. Dr. Baer could not figure out why neither man had a fever or signs of sepsis, and he got an unexpected surprise: “On removing the clothing from the wounded part, much was my surprise to see the wound filled with thousands and thousands of maggots, apparently those of the blow fly. The sight was very disgusting and measures were taken hurriedly to wash out these abominable looking creatures.” However, he then realized that the wounds were filled with “beautiful pink granulation tissue” and were healing well. Dr. Baer was onto something that many had discovered before him: the healing power of maggots.
Maggot therapy was common in the United States during the 1930s. However, during the second half of the twentieth century, after the introduction of antibiotics, maggot therapy was only used as a last resort for very serious wounds. Lately maggots have been making a comeback due to the increased resistance of bacteria to antibiotics.
Although maggot therapy has been used in the US for the past 80 years, it was approved by the FDA as a “medical device” only in 2004 (along with leeches in the same year). Maggots were the first live organism to be marketed in the US according to FDA regulations, and are approved for treating neuropathic (diabetic) foot ulcers, pressure ulcers, venous stasis ulcers, and traumatic and post-surgical wounds that are unresponsive to conventional therapies. Before this, maggots were being used but were unregulated. Richard Sherman, a doctor in Irvine, CA, is the most well-known maggot therapy advocate and began treating patients with maggots in 1990. He is now the laboratory director of Monarch Labs, the first and only commercial producer of medical grade maggots. This lab has provided maggots and maggot therapy supplies since 1935.
Today, there is an ever-increasing demand for medical maggots. In the US, demand for these fly larvae has increased by 20% over the last ten years, and doubled since the FDA ruling. Maggot therapy is now used in more than 300 sites across the country. The American Medical Association and Centers for Medicare and Medicaid Services recently clarified the reimbursement guidelines to the wound care community for medicinal maggots, and this therapy may soon be covered by insurance. The larvae of the green bottle fly
(a type of blow-fly) are now used exclusively for this purpose, since they preferentially devour only necrotic tissue, leaving healthy tissue intact. This is an important distinction, as most other major varieties of myiasitic fly larvae attack both live and dead wound tissue indiscriminately, effectively negating their benefit in non-harmful wound debridement. Medicinal maggots are placed on the wound and covered with a sterile dressing of gauze and nylon mesh. Too many larvae placed on the wound could result in healthy tissue being eaten.
Fly
True flies are insects of the order Diptera . They possess a pair of wings on the mesothorax and a pair of halteres, derived from the hind wings, on the metathorax...
larvae feeding on the host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
's necrotic or living tissue
Biological tissue
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
. Colloquialisms for myiasis include flystrike, blowfly strike, and fly-blown. In Greek, "myia" means fly.
Myiasis is a serious problem for livestock
Livestock
Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...
industries, causing severe economic losses worldwide. Although infestation by fly larvae is much more prevalent in animals, it is a relatively frequent occurrence in humans in rural, tropical and subtropical regions.
Myiasis can come in all sorts of variations, depending on the fly species and where the larvae are located. Some flies may lay eggs in open wounds, other larvae may invade unbroken skin or enter the body through the nose or ears, and still others may be swallowed if the eggs are deposited on the lips or on food.
History of discovery
The Reverend Frederick William HopeFrederick William Hope
Frederick William Hope was an English entomologist and founder of the Hope Department of Entomology at the University of Oxford....
coined the term myiasis in 1840 to refer to diseases resulting from dipterous larvae as opposed to those caused by other insect larvae (the term for this was scholechiasis). Hope described several cases of myiasis from Jamaica caused by unknown larvae, one of which resulted in death.
Even though the term myiasis was first used in 1840, the disease has been around for far longer than that. Ambroise Paré
Ambroise Paré
Ambroise Paré was a French surgeon. He was the great official royal surgeon for kings Henry II, Francis II, Charles IX and Henry III and is considered as one of the fathers of surgery and modern forensic pathology. He was a leader in surgical techniques and battlefield medicine, especially the...
, the chief surgeon to Charles IX and Henri III, observed that maggots often infested open wounds.
Life cycle
Myiasis, known as blowfly strike, is a common disease in sheepDomestic sheep
Sheep are quadrupedal, ruminant mammals typically kept as livestock. Like all ruminants, sheep are members of the order Artiodactyla, the even-toed ungulates. Although the name "sheep" applies to many species in the genus Ovis, in everyday usage it almost always refers to Ovis aries...
, especially in areas where there are hot and wet conditions. The life cycle in sheep is typical of the disease. The female flies
Fly
True flies are insects of the order Diptera . They possess a pair of wings on the mesothorax and a pair of halteres, derived from the hind wings, on the metathorax...
lay their eggs on the sheep in damp, protected areas of the body that are soiled with urine and faeces, mainly the sheep's breech (buttocks
Buttocks
The buttocks are two rounded portions of the anatomy, located on the posterior of the pelvic region of apes and humans, and many other bipeds or quadrupeds, and comprise a layer of fat superimposed on the gluteus maximus and gluteus medius muscles. Physiologically, the buttocks enable weight to...
). It takes approximately eight hours to a day for the eggs to hatch, depending on the conditions. This results in sores as the larva
Larva
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 lacerate the skin; this is the primary reason for the early removal of lambs' tails. The larvae then tunnel into the host's tissue
Tissue (biology)
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
, causing irritating 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 :...
s. After about the second day, bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
l infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
occurs and, if left untreated, causes toxemia
Toxemia
Toxemia may refer to:* A generic term for the presence of toxins in the blood, see Bacteremia* An outdated medical term for Pre-eclampsia...
or septicemia. This leads to anorexia
Anorexia (symptom)
Anorexia is the decreased sensation of appetite...
and weakness and, if untreated, will lead to death. Blowfly strike accounts for over A$
Australian dollar
The Australian dollar is the currency of the Commonwealth of Australia, including Christmas Island, Cocos Islands, and Norfolk Island, as well as the independent Pacific Island states of Kiribati, Nauru and Tuvalu...
170 million a year in losses in the Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n sheep industry so preventive measures such as mulesing
Mulesing
Mulesing is a skilled surgical task that involves the removal of strips of wool-bearing skin from around the breech of a sheep to prevent flystrike in regions where it is common....
are practised. Infestation of vulvar area with larvae and maggots is called vulvar myiasis
Vulvar myiasis
Myiasis is a parasitic infestation caused by larvae of several fly species. Diagnosis and treatment are generally quite simple. This infestation is, however, rarely seen in the vulvar area. Infestation of vulvar area with larvae and maggots is called Vulvar myiasis...
.
Classifications
GermanGermany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
entomologist
Entomology
Entomology is the scientific study of insects, a branch of arthropodology...
Fritz Zumpt
Fritz Konrad Ernst Zumpt
Fritz Konrad Ernst Zumpt was a German entomologist who worked mainly in Africa . He is best known for his work on Diptera and the associations between insects and African mammals. Also for his work on myiasis.Amongst Zumpt’s works are...
describes myiasis as "the infestation of live human and vertebrate animals with dipterous larvae, which at least for a period, feed on the host's dead or living tissue, liquid body substances, or ingested food". For modern purposes however, this is too vague. For example, feeding on dead tissue is not generally a problem except when larvae such as those of flies in the familiy Piophilidae
Cheese fly
Cheese flies are members of the family Piophilidae of flies. Most are scavengers in animal products and fungi. The best-known member of the family is Piophila casei. It is a small fly, about four mm long, found worldwide. The fly's larva infests cured meats, smoked fish, cheeses, and decaying...
attack stored food such as cheese or preserved meats; such activity suggests saprophagy
Saprotrophic nutrition
Saprotrophic nutrition is a process of chemoheterotrophic extra-cellular digestion involved in the processing of dead or decayed organic matter that occurs in saprotrophs or heterotrophs, and is most often associated with fungi, for example Mucor and Rhizopus...
rather than parasitism; it even may be medically beneficial in maggot debridement therapy (MDT)
Maggot therapy
Maggot therapy is a type of biotherapy involving the intentional introduction of live, disinfected maggots into the non-healing skin and soft tissue wound of a human or animal for the purpose of cleaning out the...
.
Currently myiasis commonly is classified according to aspects relevant to the case in question:
- The classical description of myiasis is according to the part of the host that is infected. This is the classification used by ICD-10ICDThe International Statistical Classification of Diseases and Related Health Problems is a medical classification that provides codes to classify diseases and a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or disease...
. For example:- dermalDermisThe dermis is a layer of skin between the epidermis and subcutaneous tissues, and is composed of two layers, the papillary and reticular dermis...
- sub-dermalSubcutaneous tissueThe hypodermis, also called the hypoderm, subcutaneous tissue, or superficial fascia is the lowermost layer of the integumentary system in vertebrates. Types of cells that are found in the hypodermis are fibroblasts, adipose cells, and macrophages...
- cutaneous (B87.0)
- Creeping, where larvae burrow through or under the skin
- FuruncularBoilA boil, also called a furuncle, is a deep folliculitis, infection of the hair follicle. It is always caused by infection by the bacterium Staphylococcus aureus, resulting in a painful swollen area on the skin caused by an accumulation of pus and dead tissue...
, where a larva remains in one spot, causing a boil-like lesion
- nasopharyngeal nose, sinuses or pharynx. (B87.3)
- OphthalmicOphthalmicOphthalmic means pertaining to the eye, and can refer to:* Ophthalmology* Ophthalmic nerve* Ophthalmic artery* Ophthalmic veins* Ophthalmic drug administration, as with eye dropsSee also:* Ophthalmia...
or ocularHuman eyeThe human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
in or about the eye (B87.2) - AuricularEarThe ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
in or about the ear - gastricStomachThe stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
, rectalRectumThe rectum is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long...
, or intestinal/enteric for the appropriate part of the digestive system(B87.8) - urogenital (B87.8).
- dermal
- Another aspect is the relationship between the host and the parasite and provides insight into the biology of the fly species causing the myiasis and its likely effect. Thus the myiasis is described as either:
- ObligatoryObligate parasiteAn obligate parasite is a parasitic organism that cannot complete its life cycle without dependence on its host.-See also:*Obligate intracellular parasite*Parasitism*Parasitic plant*Facultative parasite...
, where the parasite cannot complete its life cycle without its parasitic phase, which may be Specific, Semispecific, or Opportunistic. - FacultativeFacultative parasiteA facultative parasite is an organism that may resort to parasitic activity, but does not absolutely rely on any host for completion of its life cycle....
, incidental, or accidental, where it is not essential to the life cycle of the parasite; perhaps a normally free-living larva accidentally gained entrance to the host.
- Obligatory
Accidental myiasis commonly is enteric, resulting from swallowing eggs or larvae with one's food. The effect is called pseudomyiasis. One traditional cause of pseudomyiasis was the eating of maggots of cheese flies
Cheese fly
Cheese flies are members of the family Piophilidae of flies. Most are scavengers in animal products and fungi. The best-known member of the family is Piophila casei. It is a small fly, about four mm long, found worldwide. The fly's larva infests cured meats, smoked fish, cheeses, and decaying...
in cheeses such as Stilton. Depending on the species present in the gut, pseudomyiasis may cause significant medical symptoms, but it is likely that most cases pass unnoticed.
Vectors in humans
There are three main flyDiptera
Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...
families causing economically important myiasis in livestock and also, occasionally, in humans:
- Calliphoridae (blowflies)
- OestroideaOestroideaOestroidea is a superfamily of Calyptratae....
(botfliesBotflyA botfly is any fly in the family Oestridae, which includes all the members of the former families Cuterebridae, Gasterophilidae, and Hypodermatidae. It is the only family of flies whose larvae live as obligate parasites within the bodies of mammals, with the exception of a few screwworm flies in...
) - Sarcophagidae (fleshflies)
Other families occasionally involved are:
- AnisopodidaeAnisopodidaeAnisopodidae is a small cosmopolitan family of gnat-like flies known as wood gnats or window-gnats with 154 described extant species in 15 genera, and several described fossil taxa. Some species are saprophagous or fungivorous. They are mostly small to medium-sized flies, except the genera...
- Piophilidae
- StratiomyidaeStratiomyidaeThe soldier flies , are a family of flies . The family contains about 1,500 species in about 400 genera worldwide. Adults are found near larval habitats...
- Syrphidae
Specific myiasis
Caused by flies that need a host for larval development- Dermatobia hominis (human botfly)
- Cordylobia anthropophagaCordylobia anthropophagaCordylobia anthropophaga, the mango fly, tumbu fly, tumba fly, putzi fly or skin maggot fly is a species of blow-fly common in East and Central Africa. It is a parasite of large mammals during its larval stage .C...
(tumbu fly) - Oestrus ovis (sheep botfly)
- Hypoderma spp. (cattle botflies or ox warbles)
- GasterophilusGasterophilusGasterophilus is a genus of parasitic flies in the family Oestridae which includes the horse bot flies. They lay eggs on horses, caribou, donkeys, and similar animals, usually equines. The eggs are laid depending on the species of gasterophilus. There are two species - Gasterophilus nasalis, and...
spp. (horse botfly) - Cochliomyia hominivoraxCochliomyia hominivoraxCochliomyia hominivorax, the New World screw-worm fly, or screw-worm for short, is a species of parasitic fly that is well known for the way in which its larvae eat the living tissue of warm-blooded animals. It is present in the New World tropics...
(new world screwworm fly) - Chrysomya bezzianaChrysomya bezzianaChrysomya bezziana, also known as the Old World screwworm fly or screwworm, is an obligate parasite of mammals. Obligate parasitic flies require a host to complete their development. Named to honor the Italian entomologist Mario Bezzi, this fly is widely distributed in Asia, tropical Africa, India,...
(old world screwworm fly) - Auchmeromyia senegalensis (Congo floor maggot)
- Cuterebra spp. (rodent and rabbit botfly)
Semispecific myiasis
Caused by flies that usually lay their eggs in decaying animal or vegetable matter, but that can develop in a host if open wounds or sores are present- Lucilia spp. (green-bottle fly)
- CochliomyiaCochliomyiaCochliomyia is a genus in the family Calliphoridae, known as blowflies, in the order Diptera. Cochliomyia are commonly referred to as the New World screwworm fly. There are four species in this genus: Cochliomyia macellaria, Cochliomyia hominivorax, Cochliomyia aldrichi, and Cochliomyia minima...
spp. (blue-bottle fly) - Phormia spp. (black-bottle fly)
- CalliphoraCalliphoraCalliphora is the type genus of blow flies, the family Calliphoridae.-Species in the genus Calliphora:...
spp. (blowfly) - SarcophagaSarcophagaSarcophaga is a genus of true flies, the type of the flesh-fly family .This genus occurs essentially worldwide. These flies are generally well-sized and of a greyish color; like many of their relatives, the typical patterns are lengthwise darker stripes on the thorax and dark and light square dots...
spp. (flesh fly or sarcophagids)
Flesh flies, or sarcophagids, can cause intestinal
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
myiasis in humans if the females lay their eggs on meat or fruit.
Accidental myiasis
Also called pseudomyiasis. Caused by flies that have no preference or need to develop in a host but that will do so on rare occasions. Transmission occurs through accidental deposit of eggs on oral or genitourinary openings, or by swallowing eggs or larvae that are on food.- Musca domestica (housefly)
- FanniaFannia (genus)Fannia is a very large genus of approximately 288 species of flies. The genus was originally described by the French entomologist Jean-Baptiste Robineau-Desvoidy in 1830...
spp. (latrine flies) - Eristalis tenaxEristalis tenaxEristalis tenax is a European hoverfly, also known as the drone fly . It has been introduced into North America and is widely established....
(rat-tailed maggots) - MuscinaMuscinaMuscina is a genus of flies that belongs to the family Muscidae, currently consisting of 27 species. They are worldwide in distribution and are frequently found in livestock facilities and outside restrooms. The most common species are M. stabulans , M. levida, and M. prolapsa...
spp.
The adult flies are not parasitic, but when they lay their eggs in open wound
Wound
A wound is a type of injury in which skin is torn, cut or punctured , or where blunt force trauma causes a contusion . In pathology, it specifically refers to a sharp injury which damages the dermis of the skin.-Open:...
s and these hatch into their larva
Larva
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...
l stage (also known as maggot
Maggot
In everyday speech the word maggot means the larva of a fly ; it is applied in particular to the larvae of Brachyceran flies, such as houseflies, cheese flies, and blowflies, rather than larvae of the Nematocera, such as mosquitoes and Crane flies...
s or grubs), the larvae feed on live and/or necrotic tissue, causing myiasis to develop. They may also be ingested or enter through other body apertures.
Clinical presentation in humans
How myiasis affects the human body depends on where the larvae are located. Larvae may infect necrotic (dead) or living tissue in various sites: the skin, eyes, ears, stomach and intestinal tract, or in genitourinary sites. They may invade open wounds and lesions or unbroken skin. Some enter the body through the nose or ears. Larvae or eggs can reach the stomach or intestines if they are swallowed with food and cause gastric or intestinal myiasis.Several different presentations of myiasis and their symptoms:
| Syndrome | Symptoms |
|---|---|
| Cutaneous Myiasis | Painful, slow-developing ulcers or furuncle- (boil-) like sores that can last for a prolonged period. |
| Nasal Myiasis | Obstruction of nasal passages and severe irritation. In some cases facial edema and fever can develop. Death is not uncommon. |
| Aural Myiasis | Crawling sensations and buzzing noises. Smelly discharge is sometimes present. If located in the middle ear, larvae may get to the brain. |
| Ophthalmomyiasis | Fairly common, this causes severe irritation, edema, and pain. |
Nosocomial Myiasis refers to myiasis in a hospital setting. It is quite frequent, as patients with open wounds or sores can be infested if flies are present. To prevent nosocomial myiasis, hospital rooms must be kept free of flies.
Human ophthalmomyiasis, both external and internal, has been caused by botfly
Botfly
A botfly is any fly in the family Oestridae, which includes all the members of the former families Cuterebridae, Gasterophilidae, and Hypodermatidae. It is the only family of flies whose larvae live as obligate parasites within the bodies of mammals, with the exception of a few screwworm flies in...
larvae.
Diagnostics
Myiasis is often misdiagnosed in the United States because it is extremely rare and its symptoms are not specific. Intestinal myiasis and urinary myiasis are especially difficult to diagnose.Clues that myiasis may be present include recent travel to an endemic area, one or more non-healing lesions on the skin, itchiness, movement under the skin or pain, discharge from a central punctum (tiny hole), or a small, white structure protruding from the lesion. Serologic testing has also been used to diagnose the presence of botfly larvae in human ophthalmomyiasis.
Control methods
The first control method is preventive and aims to eradicate the adult flies before they can cause any damage and is called vector controlVector control
Vector control is any method to limit or eradicate the mammals, birds, insects or other arthropods which transmit disease pathogens. The most frequent type of vector control is mosquito control using a variety of strategies.-Methods of Control:...
. The second control method is the treatment once the infestation is present, and concerns the infected animals (or humans).
Prevention
The principal control method of adult populations of myiasis inducing flies involves insecticideInsecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
applications in the environment where the target livestock is kept. Organophosphorus
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
or organochlorine
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
compounds may be used, usually in a spraying formulation. One alternative prevention method is the SIT
Sterile insect technique
The sterile insect technique is a method of biological control, whereby overwhelming numbers of sterile insects are released. The released insects are normally male as it is the female that causes the damage, usually by laying eggs in the crop, or, in the case of mosquitoes, taking a bloodmeal from...
(Sterile Insect Technique) where a significant number of artificially reared sterilized (usually through irradiation) male flies are introduced. The male flies compete with wild bred males for females in order to copulate and thus cause females to lay batches of unfertilized eggs which can't develop into the larval stage.
One prevention method involves removing the environment most favourable to the flies, such as by docking
Docking (animals)
Docking is the removal of portions of an animal's tail. While space docking and bobbing are more commonly used to refer to removal of the tail, the term cropping is used in reference to the ears. Tail docking occurs in one of two ways. The first involves constricting the blood supply to the tail...
(removal of the tail). Another example is the crutching
Crutching
Crutching refers to the removal of wool from around the tail and between the rear legs of a sheep. It can also refer to removing wool from the heads of sheep or from the bellies of male sheep .-Motivation:...
of sheep, which involves the removal of wool from around the tail and between the rear legs, which is a favourable environment for the larvae. Another more permanent practice which is used in some countries is mulesing
Mulesing
Mulesing is a skilled surgical task that involves the removal of strips of wool-bearing skin from around the breech of a sheep to prevent flystrike in regions where it is common....
, where skin is removed from young animals to tighten remaining skin – leaving it less prone to fly attack. PETA
Peta
Peta can refer to:* peta-, an SI prefix denoting a factor of 1015* Peta, Greece, a town in Greece* Peta, the Pāli word for a Preta, or hungry ghost in Buddhism* Peta Wilson, an Australian actress and model* Peta Todd, English glamour model...
have been campaigning to have farmers cease mulesing. Celebrities such as Pink
Pink (singer)
Alecia Beth Moore , better known by her stage name Pink , is an American singer-songwriter, musician and actress....
, Toni Collette
Toni Collette
Antonia "Toni" Collette is an Australian actress and musician, known for her acting work on stage, television and film as well as a secondary career as the lead singer of the band Toni Collette & the Finish....
and Chrissie Hynde
Chrissie Hynde
Christine Ellen "Chrissie" Hynde is an US musician best known as the leader of the rock/new wave band the Pretenders. She is a singer, songwriter, and guitarist, and has been the only constant member of the band throughout its history.-Early life and career:Hynde is the daughter of a part-time...
have also participated in PETA's campaign against the mulesing practice; However, Collette has since changed her stance and Pink has said she was misled by PETA and had not done enough research herself into mulesing.
To prevent myiasis in humans, there is a need for general improvement of sanitation, personal hygiene, and extermination of the flies by insecticides. Clothes should be washed thoroughly, dried away from flies, and ironed. The heat of the iron kills the eggs of myiasis-causing flies.
Treatment
This applies once an infestation is underway. First the larvae must be eliminated through pressure around the lesion and the use of forceps. Secondly the wound must be cleaned and disinfected. Further control is necessary to avoid further reinfestation.It is also possible to treat livestock with the use of slow release bolus
Bolus (medicine)
In medicine, a bolus is the administration of a medication, drug or other compound that is given to raise its concentration in blood to an effective level...
es containing ivermectin which can provide long term protection against the larvae development.
Sheep may be dipped
Sheep dip
Sheep dip is a liquid formulation of insecticide and fungicide which shepherds and farmers may use to protect their sheep from infestation against external parasites such as itch mite , blow-fly, ticks and lice...
, which involves drenching the sheep in insecticide to prevent the growth of the larvae.
Use of myiasitic maggots in medicine
Throughout time maggots have been used as medicineMedicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
in order to clean out necrotic wound
Wound
A wound is a type of injury in which skin is torn, cut or punctured , or where blunt force trauma causes a contusion . In pathology, it specifically refers to a sharp injury which damages the dermis of the skin.-Open:...
s, a method known as maggot therapy
Maggot therapy
Maggot therapy is a type of biotherapy involving the intentional introduction of live, disinfected maggots into the non-healing skin and soft tissue wound of a human or animal for the purpose of cleaning out the...
.
Fly larvae that feed on dead tissue can clean wounds and may reduce bacterial activity and the chance of a secondary infection. They dissolve dead tissue by secreting digestive enzymes onto the wound as well as actively eat the dead tissue with “mouth hooks,” two probing appendages near their toothless mouth. Maggot therapyalso known as maggot debridement therapy (MDT), larval therapy, larva therapy, or larvae therapyis the intentional introduction by a health care practitioner of live, disinfected green bottle fly
Green bottle fly
The common green bottle fly is a common blow-fly found in most areas of the world, and the most well-known of the numerous green bottle fly species. It is 10–14 mm long, slightly larger than a housefly, and has brilliant, metallic, blue-green or golden coloration with black markings. It has...
maggots or larvae into the non-healing skin and soft tissue wound(s) of a human or other animal for the purpose of selectively cleaning out only the necrotic (dead) tissue within a wound in order to promote wound healing.
Maggot therapy has a long history. The indigenous people of Australia used maggot therapy, as well as the Hill Peoples of Northern Burma, and possibly the Mayans of Central America. Surgeons in Napoleon’s armies recognized that wounded soldiers with myiasis were more likely to survive than those without the infestation. In the American Civil War, army surgeons treated wounds by allowing blowfly maggots to clean away the decayed tissue.
Dr. William Baer, an orthopedic surgeon at Johns Hopkins during the late 1920s, used maggot therapy to treat a series of patients with osteomyelitis, an infection of bone or bone marrow and published his findings. Dr. Baer first got the idea when, during World War I, two soldiers presented to him with broken femurs after having lain on the ground for seven days without food and water. Dr. Baer could not figure out why neither man had a fever or signs of sepsis, and he got an unexpected surprise: “On removing the clothing from the wounded part, much was my surprise to see the wound filled with thousands and thousands of maggots, apparently those of the blow fly. The sight was very disgusting and measures were taken hurriedly to wash out these abominable looking creatures.” However, he then realized that the wounds were filled with “beautiful pink granulation tissue” and were healing well. Dr. Baer was onto something that many had discovered before him: the healing power of maggots.
Maggot therapy was common in the United States during the 1930s. However, during the second half of the twentieth century, after the introduction of antibiotics, maggot therapy was only used as a last resort for very serious wounds. Lately maggots have been making a comeback due to the increased resistance of bacteria to antibiotics.
Although maggot therapy has been used in the US for the past 80 years, it was approved by the FDA as a “medical device” only in 2004 (along with leeches in the same year). Maggots were the first live organism to be marketed in the US according to FDA regulations, and are approved for treating neuropathic (diabetic) foot ulcers, pressure ulcers, venous stasis ulcers, and traumatic and post-surgical wounds that are unresponsive to conventional therapies. Before this, maggots were being used but were unregulated. Richard Sherman, a doctor in Irvine, CA, is the most well-known maggot therapy advocate and began treating patients with maggots in 1990. He is now the laboratory director of Monarch Labs, the first and only commercial producer of medical grade maggots. This lab has provided maggots and maggot therapy supplies since 1935.
Today, there is an ever-increasing demand for medical maggots. In the US, demand for these fly larvae has increased by 20% over the last ten years, and doubled since the FDA ruling. Maggot therapy is now used in more than 300 sites across the country. The American Medical Association and Centers for Medicare and Medicaid Services recently clarified the reimbursement guidelines to the wound care community for medicinal maggots, and this therapy may soon be covered by insurance. The larvae of the green bottle fly
Green bottle fly
The common green bottle fly is a common blow-fly found in most areas of the world, and the most well-known of the numerous green bottle fly species. It is 10–14 mm long, slightly larger than a housefly, and has brilliant, metallic, blue-green or golden coloration with black markings. It has...
(a type of blow-fly) are now used exclusively for this purpose, since they preferentially devour only necrotic tissue, leaving healthy tissue intact. This is an important distinction, as most other major varieties of myiasitic fly larvae attack both live and dead wound tissue indiscriminately, effectively negating their benefit in non-harmful wound debridement. Medicinal maggots are placed on the wound and covered with a sterile dressing of gauze and nylon mesh. Too many larvae placed on the wound could result in healthy tissue being eaten.
External links
- Myiasis reviewed and published by WikiVetWikiVetWikiVet is a wiki of veterinary content, run using the MediaWiki software. The project is a collaborative initiative involving UK veterinary schools with external support...
- University of Sydney
- fly blown sheep
- Human oral myiasis, two cases and general remarks
- pdf A collective analysis of 54 cases of human myiasis in China from 1995–2001.Chinese Medical Journal
- NHM Identification key to myiasis causing fly larvae.