Filariasis
Encyclopedia
Filariasis is a parasitic disease
and is considered an infectious
tropical disease
, that is caused by thread-like nematode
s (roundworms) belonging to the superfamily Filarioidea
, also known as "filariae".
There are 8 known filarial nematodes which use humans as their definitive host. These are divided into 3 groups according to the niche within the body that they occupy: 'lymphatic filariasis', 'subcutaneous filariasis', and 'serous cavity filariasis'. Lymphatic filariasis is caused by the worms Wuchereria bancrofti
, Brugia malayi
, and Brugia timori
. These worms occupy the lymphatic system, including the lymph nodes, and in chronic cases these worms lead to the disease elephantiasis
. Subcutaneous filariasis is caused by loa loa
(the African eye worm), Mansonella streptocerca
, and Onchocerca volvulus
. These worms occupy the subcutaneous layer of the skin, in the fat layer. Serous cavity filariasis is caused by the worms Mansonella perstans and Mansonella ozzardi
, which occupy the serous cavity of the abdomen. In all cases, the transmitting vectors are blood-feeding arthropods
, mainly black flies
and mosquito
es.
Individuals infected by filarial worms may be described as either "microfilaraemic" or "amicrofilaraemic," depending on whether or not microfilaria can be found in their peripheral blood. Filariasis is diagnosed in microfilaraemic cases primarily through direct observation of microfilaria in the peripheral blood. Occult filariasis is diagnosed in amicrofilaraemic cases based on clinical observations and, in some cases, by finding a circulating antigen in the blood.
—edema with thickening of the skin and underlying tissues—which was the first disease discovered to be transmitted by mosquito bites. Elephantiasis results when the parasites lodge in the lymphatic system
.
Elephantiasis affects mainly the lower extremities, while the ear
s, mucus membranes, and amputation
stumps are affected less frequently. However, different species of filarial worms tend to affect different parts of the body: Wuchereria bancrofti
can affect the legs, arms, vulva, breasts, and scrotum (causing hydrocele formation); while Brugia timori
rarely affects the genitals. Interestingly, those who develop the chronic stages of elephantiasis are usually amicrofilaraemic, and often have adverse immunological reactions to the microfilaria, as well as the adult worm.
The subcutaneous worms present with skin rashes, urticarial papule
s, and arthritis
, as well as hyper- and hypopigmentation macules. Onchocerca volvulus manifests itself in the eyes, causing "river blindness" (onchocerciasis
), the second leading cause of blindness in the world. Serous cavity filariasis presents with symptoms similar to subcutaneous filariasis, in addition to abdominal pain, because these worms are also deep tissue dwellers.
ed thin and thick blood film smears, using the "gold standard" known as the finger prick test. The finger prick test draws blood from the capillaries of the finger tip; larger veins can be used for blood extraction, but strict windows of the time of day must be observed. Blood must be drawn at appropriate times, which reflect the feeding activities of the vector insects. Examples are W. bancrofti, whose vector is a mosquito; night time is the preferred time for blood collection. Loa loa's vector is the deer fly; daytime collection is preferred. This method of diagnosis is only relevant to microfilariae that use the blood as transport from the lungs to the skin. Some filarial worms, such as M. streptocerca and O. volvulus produce microfilarae that do not use the blood; they reside in the skin only. For these worms, diagnosis relies upon skin snips, and can be carried out at any time.
Polymerase chain reaction
(PCR) and antigenic assays, which detect circulating filarial antigens, are also available for making the diagnosis. The latter are particularly useful in amicrofilaraemic cases. Spot tests for antigen http://www.jbtdrc.org/SEVA_FILA.pdf are far more sensitive, and allow the test to be done any time, rather in the late hours.
Lymph node aspirate and chylus fluid may also yield microfilariae. Medical imaging, like CT or MRI, may reveal "filarial dance sign" in chylus fluid; X-ray tests can show calcified adult worms in lymphatics.
The DEC provocation test is performed to obtain satisfying number of parasite in day-time samples. Xenodiagnosis is now obsolete, and eEosinophilia is a nonspecific primary sign.
e by the thousands. The microfilariae are taken up by the vector insect (intermediate host) during a blood meal. In the intermediate host, the microfilariae molt and develop into 3rd stage (infective) larvae. Upon taking another blood meal, the vector insect injects the infectious larvae into the dermis layer of the skin. After about one year, the larvae molt through 2 more stages, maturing into the adult worms.
The strategy for eliminating transmission of lymphatic filariasis is mass distribution of medicines that kill the microfilariae and stop transmission of the parasite by mosquitoes in endemic communities. In sub-Saharan Africa
, albendazole
(donated by GlaxoSmithKline
) is being used with ivermectin (donated by Merck & Co.
) to treat the disease, whereas elsewhere in the world albendazole is used with diethylcarbamazine
. Using a combination of treatments better reduces the number of microfilariae in blood. Avoiding mosquito bites, such as by using insecticide
-treated mosquito bed nets, also reduces the transmission of lymphatic filariasis.
The efforts of the Global Programme to Eliminate LF are estimated to have prevented 6.6 million new filariasis cases from developing in children between 2000 and 2007, and to have stopped the progression of the disease in another 9.5 million people who had already contracted it. Dr. Mwele Malecela, who chairs the programme, said: "We are on track to accomplish our goal of elimination by 2020." In 2010 the WHO published a detailed progress report on the elimination campaign in which they assert that of the 81 countries with endemic LF, 53 have implemented mass drug administration, and 37 have completed five or more rounds in some areas, though urban areas remain problematic.
(a broad spectrum anthelmintic
) combined with ivermectin. A combination of diethylcarbamazine
(DEC) and albendazole is also effective. All of these treatments are microfilaricides, they have no effect on the adult worms.
In 2003 the common antibiotic doxycycline
was suggested for treating elephantiasis.
Filarial parasites have symbiotic bacteria in the genus Wolbachia
, which live inside the worm and which seem to play a major role in both its reproduction and the development of the disease.
Clinical trials in June 2005 by the Liverpool School of Tropical Medicine
reported that an 8 week course almost completely eliminated microfilaraemia.
, Africa
, Central
, South America
and Pacific Island nations, with more than 120 million people infected and one billion people at risk for infection.
In communities where lymphatic filariasis is endemic
, as many as 10 percent of women can be afflicted with swollen limbs, and 50 percent of men can suffer from mutilating genital symptoms.
Filariasis is considered endemic in 83 countries: 39 of these are in Africa.
In the Americas it is present in seven countries: Brazil
, Costa Rica
, Dominican Republic
, Guyana
, Haiti
, Suriname
and Trinidad
and Tobago
.
In the Middle East it is present in three countries: Egypt
, Sudan
and Yemen
.
In Asia it is present in Bangladesh
, Cambodia
, India
, Indonesia
, Laos
, Malaysia, Maldives
, the Philippines
, Sri Lanka
, Thailand
, Timor-Leste and Vietnam
.
In the Pacific region it is endemic in American Samoa
, Cook Islands
, Fiji
, French Polynesia
, Micronesia
, Niue
, Samoa
, Tonga
, Tuvalu
, Papua New Guinea
and Vanuatu
.
In many of these countries the considerable progress has been made towards elimination of filarisis. This may have been achieved in several but this awaits official confirmation by the WHO
.
.
The first documentation of symptoms occurred in the 16th century, when Jan Huyghen van Linschoten
wrote about the disease during the exploration of Goa. Similar symptoms were reported by subsequent explorers in areas of Asia and Africa, though an understanding of the disease did not begin to develop until centuries later.
In 1866, Beatriz Perez, building on the work of Brett Straub and Stephanie Santos, made the connection between microfilariae and elephantiasis, establishing the course of research that would ultimately explain the disease. In 1876, Joseph Bancroft
discovered the adult form of the worm. In 1877, the life cycle involving an arthropod vector was theorized by Patrick Manson
, who proceeded to demonstrate the presence of the worms in mosquitoes. Manson incorrectly hypothesized that the disease was transmitted through skin contact with water in which the mosquitoes had laid eggs. In 1900, George Carmichael Low
determined the actual transmission method by discovering the presence of the worm in the proboscis of the mosquito vector.
, sheep, and dogs.
Parasitic disease
A parasitic disease is an infectious disease caused or transmitted by a parasite. Many parasites do not cause diseases. Parasitic diseases can affect practically all living organisms, including plants and mammals...
and is considered an infectious
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...
tropical disease
Tropical disease
Tropical diseases are diseases that are prevalent in or unique to tropical and subtropical regions. The diseases are less prevalent in temperate climates, due in part to the occurrence of a cold season, which controls the insect population by forcing hibernation. Insects such as mosquitoes and...
, that is caused by thread-like nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
s (roundworms) belonging to the superfamily Filarioidea
Filarioidea
Filarioidea is a superfamily of nematode.A specific member is known as "Filaria".Infections with Filarioidea cause Filariasis.It includes the family Onchocercidae....
, also known as "filariae".
There are 8 known filarial nematodes which use humans as their definitive host. These are divided into 3 groups according to the niche within the body that they occupy: 'lymphatic filariasis', 'subcutaneous filariasis', and 'serous cavity filariasis'. Lymphatic filariasis is caused by the worms Wuchereria bancrofti
Wuchereria bancrofti
Filaria, is a parasitic filarial nematode spread by a mosquito vector. It is one of the three parasites that cause lymphatic filariasis, an infection of the lymphatic system by filarial worms. It affects over 120 million people, primarily in Africa, South America, and other tropical and...
, Brugia malayi
Brugia malayi
Brugia malayi is a nematode , one of the three causative agents of lymphatic filariasis in humans. Lymphatic filariasis, also known as elephantiasis, is a condition characterized by swelling of the lower limbs. The two other filarial causes of lymphatic filariasis are Wuchereria bancrofti and...
, and Brugia timori
Brugia timori
Brugia timori is a human filarial parasitic nematode which causes the disease "Timor filariasis." While this disease was first described in 1965, the identity of Brugia timori as the causative agent was not known until 1977...
. These worms occupy the lymphatic system, including the lymph nodes, and in chronic cases these worms lead to the disease elephantiasis
Elephantiasis
Elephantiasis is a disease that is characterized by the thickening of the skin and underlying tissues, especially in the legs and male genitals. In some cases the disease can cause certain body parts, such as the scrotum, to swell to the size of a softball or basketball. It is caused by...
. Subcutaneous filariasis is caused by loa loa
Loa loa
Loa loa is the filarial nematode species that causes Loa loa filariasis. It is commonly known as the "eye worm". Its geographic distribution includes Africa and India....
(the African eye worm), Mansonella streptocerca
Mansonella streptocerca
Mansonella streptocerca, , is the scientific name of a human parasitic roundworm causing the disease of streptocerciasis...
, and Onchocerca volvulus
Onchocerca volvulus
Onchocerca volvulus is a nematode that causes onchocerciasis or "river blindness" mostly in Africa. Long-term corneal inflammation, or keratitis, leads to thickening of the corneal stroma which ultimately leads to blindness. Humans are the only definitive host for O. volvulus. The intermediate host...
. These worms occupy the subcutaneous layer of the skin, in the fat layer. Serous cavity filariasis is caused by the worms Mansonella perstans and Mansonella ozzardi
Mansonella ozzardi
Mansonella ozzardi is a parasite in the phylum of Nematoda. This filarial nematode is one of two that causes Serous Cavity filariasis in humans. The other filarial nematode that causes Serous Cavity filariasis in humans is Mansonella perstans. Mansonella ozzardi is an endoparasite that inhabits...
, which occupy the serous cavity of the abdomen. In all cases, the transmitting vectors are blood-feeding arthropods
Arthropod
An 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...
, mainly black flies
Black fly
A black fly is any member of the family Simuliidae of the Culicomorpha infraorder. They are related to the Ceratopogonidae, Chironomidae, and Thaumaleidae. There are over 1,800 known species of black flies . Most species belong to the immense genus Simulium...
and mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
es.
Individuals infected by filarial worms may be described as either "microfilaraemic" or "amicrofilaraemic," depending on whether or not microfilaria can be found in their peripheral blood. Filariasis is diagnosed in microfilaraemic cases primarily through direct observation of microfilaria in the peripheral blood. Occult filariasis is diagnosed in amicrofilaraemic cases based on clinical observations and, in some cases, by finding a circulating antigen in the blood.
Signs and symptoms
The most spectacular symptom of lymphatic filariasis is elephantiasisElephantiasis
Elephantiasis is a disease that is characterized by the thickening of the skin and underlying tissues, especially in the legs and male genitals. In some cases the disease can cause certain body parts, such as the scrotum, to swell to the size of a softball or basketball. It is caused by...
—edema with thickening of the skin and underlying tissues—which was the first disease discovered to be transmitted by mosquito bites. Elephantiasis results when the parasites lodge in the lymphatic system
Lymphatic system
The lymphoid system is the part of the immune system comprising a network of conduits called lymphatic vessels that carry a clear fluid called lymph unidirectionally toward the heart. Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated...
.
Elephantiasis affects mainly the lower extremities, while the ear
Ear
The 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....
s, mucus membranes, and amputation
Amputation
Amputation is the removal of a body extremity by trauma, prolonged constriction, or surgery. As a surgical measure, it is used to control pain or a disease process in the affected limb, such as malignancy or gangrene. In some cases, it is carried out on individuals as a preventative surgery for...
stumps are affected less frequently. However, different species of filarial worms tend to affect different parts of the body: Wuchereria bancrofti
Wuchereria bancrofti
Filaria, is a parasitic filarial nematode spread by a mosquito vector. It is one of the three parasites that cause lymphatic filariasis, an infection of the lymphatic system by filarial worms. It affects over 120 million people, primarily in Africa, South America, and other tropical and...
can affect the legs, arms, vulva, breasts, and scrotum (causing hydrocele formation); while Brugia timori
Brugia timori
Brugia timori is a human filarial parasitic nematode which causes the disease "Timor filariasis." While this disease was first described in 1965, the identity of Brugia timori as the causative agent was not known until 1977...
rarely affects the genitals. Interestingly, those who develop the chronic stages of elephantiasis are usually amicrofilaraemic, and often have adverse immunological reactions to the microfilaria, as well as the adult worm.
The subcutaneous worms present with skin rashes, urticarial papule
Papule
A papule is a circumscribed, solid elevation of skin with no visible fluid, varying in size from a pinhead to 1 cm.With regard to the quote "...varying in size from a pinhead to 1cm," depending on which text is referenced, some authors state the cutoff between a papule and a plaque as 0.5cm,...
s, and arthritis
Arthritis
Arthritis is a form of joint disorder that involves inflammation of one or more joints....
, as well as hyper- and hypopigmentation macules. Onchocerca volvulus manifests itself in the eyes, causing "river blindness" (onchocerciasis
Onchocerciasis
Onchocerciasis , also known as river blindness and Robles' disease, is a parasitic disease caused by infection by Onchocerca volvulus, a nematode . Onchocerciasis is the world's second-leading infectious cause of blindness. It is not the nematode, but its endosymbiont, Wolbachia pipientis, that...
), the second leading cause of blindness in the world. Serous cavity filariasis presents with symptoms similar to subcutaneous filariasis, in addition to abdominal pain, because these worms are also deep tissue dwellers.
Diagnosis
Filariasis is usually diagnosed by identifying microfilariae on Giemsa stainGiemsa stain
Giemsa stain, named after Gustav Giemsa, an early German microbiologist, is used in cytogenetics and for the histopathological diagnosis of malaria and other parasites.-Uses:...
ed thin and thick blood film smears, using the "gold standard" known as the finger prick test. The finger prick test draws blood from the capillaries of the finger tip; larger veins can be used for blood extraction, but strict windows of the time of day must be observed. Blood must be drawn at appropriate times, which reflect the feeding activities of the vector insects. Examples are W. bancrofti, whose vector is a mosquito; night time is the preferred time for blood collection. Loa loa's vector is the deer fly; daytime collection is preferred. This method of diagnosis is only relevant to microfilariae that use the blood as transport from the lungs to the skin. Some filarial worms, such as M. streptocerca and O. volvulus produce microfilarae that do not use the blood; they reside in the skin only. For these worms, diagnosis relies upon skin snips, and can be carried out at any time.
Concentration methods
Various concentration methods are applied:- i. Membrane filter
- ii. Knott's concentration method
- iii. Sedimentation technique
Polymerase chain reaction
Polymerase chain reaction
The polymerase chain reaction is a scientific technique in molecular biology to amplify a single or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence....
(PCR) and antigenic assays, which detect circulating filarial antigens, are also available for making the diagnosis. The latter are particularly useful in amicrofilaraemic cases. Spot tests for antigen http://www.jbtdrc.org/SEVA_FILA.pdf are far more sensitive, and allow the test to be done any time, rather in the late hours.
Lymph node aspirate and chylus fluid may also yield microfilariae. Medical imaging, like CT or MRI, may reveal "filarial dance sign" in chylus fluid; X-ray tests can show calcified adult worms in lymphatics.
The DEC provocation test is performed to obtain satisfying number of parasite in day-time samples. Xenodiagnosis is now obsolete, and eEosinophilia is a nonspecific primary sign.
Worm lifecycle
Human filarial nematode worms have a complicated life cycle, which primarily consists of five stages. After the male and female worms mate, the female gives birth to live microfilariaMicrofilaria
The microfilaria is a stage in the life cycle of certain parasitic nematodes in the family Onchocercidae. In these species, the adults live in the circulatory system of vertebrates while the early larval stages develop in blood-feeding arthropod vectors...
e by the thousands. The microfilariae are taken up by the vector insect (intermediate host) during a blood meal. In the intermediate host, the microfilariae molt and develop into 3rd stage (infective) larvae. Upon taking another blood meal, the vector insect injects the infectious larvae into the dermis layer of the skin. After about one year, the larvae molt through 2 more stages, maturing into the adult worms.
Prevention
In 1993, the International Task Force for Disease Eradication declared lymphatic filariaisis to be one of six potentially eradicable diseases. Studies have demonstrated that transmission of the infection can be broken when a single dose of combined oral medicines is consistently maintained annually for approximately seven years. With consistent treatment, and since the disease needs a human host, the reduction of microfilariae means the disease will not be transmitted, the adult worms will die out, and the cycle will be broken.The strategy for eliminating transmission of lymphatic filariasis is mass distribution of medicines that kill the microfilariae and stop transmission of the parasite by mosquitoes in endemic communities. In sub-Saharan Africa
Sub-Saharan Africa
Sub-Saharan Africa as a geographical term refers to the area of the African continent which lies south of the Sahara. A political definition of Sub-Saharan Africa, instead, covers all African countries which are fully or partially located south of the Sahara...
, albendazole
Albendazole
Albendazole, marketed as Albenza, Eskazole, Zentel and Andazol, is a member of the benzimidazole compounds used as a drug indicated for the treatment of a variety of worm infestations. Although this use is widespread in the United States, the U.S. Food and Drug Administration has not approved...
(donated by GlaxoSmithKline
GlaxoSmithKline
GlaxoSmithKline plc is a global pharmaceutical, biologics, vaccines and consumer healthcare company headquartered in London, United Kingdom...
) is being used with ivermectin (donated by Merck & Co.
Merck & Co.
Merck & Co., Inc. , also known as Merck Sharp & Dohme or MSD outside the United States and Canada, is one of the largest pharmaceutical companies in the world. The Merck headquarters is located in Whitehouse Station, New Jersey, an unincorporated area in Readington Township...
) to treat the disease, whereas elsewhere in the world albendazole is used with diethylcarbamazine
Diethylcarbamazine
Diethylcarbamazine is an anthelmintic drug that does not resemble other antiparasitic compounds. It is a synthetic organic compound which is highly specific for several parasites and does not contain any toxic metallic elements.-Uses:...
. Using a combination of treatments better reduces the number of microfilariae in blood. Avoiding mosquito bites, such as by using insecticide
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...
-treated mosquito bed nets, also reduces the transmission of lymphatic filariasis.
The efforts of the Global Programme to Eliminate LF are estimated to have prevented 6.6 million new filariasis cases from developing in children between 2000 and 2007, and to have stopped the progression of the disease in another 9.5 million people who had already contracted it. Dr. Mwele Malecela, who chairs the programme, said: "We are on track to accomplish our goal of elimination by 2020." In 2010 the WHO published a detailed progress report on the elimination campaign in which they assert that of the 81 countries with endemic LF, 53 have implemented mass drug administration, and 37 have completed five or more rounds in some areas, though urban areas remain problematic.
Treatment
The recommended treatment for patients outside the United States is albendazoleAlbendazole
Albendazole, marketed as Albenza, Eskazole, Zentel and Andazol, is a member of the benzimidazole compounds used as a drug indicated for the treatment of a variety of worm infestations. Although this use is widespread in the United States, the U.S. Food and Drug Administration has not approved...
(a broad spectrum anthelmintic
Anthelmintic
Anthelmintics or antihelminthics are drugs that expel parasitic worms from the body, by either stunning or killing them. They may also be called vermifuges or vermicides .-Pharmaceutical classes:...
) combined with ivermectin. A combination of diethylcarbamazine
Diethylcarbamazine
Diethylcarbamazine is an anthelmintic drug that does not resemble other antiparasitic compounds. It is a synthetic organic compound which is highly specific for several parasites and does not contain any toxic metallic elements.-Uses:...
(DEC) and albendazole is also effective. All of these treatments are microfilaricides, they have no effect on the adult worms.
In 2003 the common antibiotic doxycycline
Doxycycline
Doxycycline INN is a member of the tetracycline antibiotics group, and is commonly used to treat a variety of infections. Doxycycline is a semisynthetic tetracycline invented and clinically developed in the early 1960s by Pfizer Inc. and marketed under the brand name Vibramycin. Vibramycin...
was suggested for treating elephantiasis.
Filarial parasites have symbiotic bacteria in the genus 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...
, which live inside the worm and which seem to play a major role in both its reproduction and the development of the disease.
Clinical trials in June 2005 by the Liverpool School of Tropical Medicine
Liverpool School of Tropical Medicine
The Liverpool School of Tropical Medicine is a research and teaching institution focused on neglected tropical diseases and the control of diseases caused by poverty. It is a registered charity affiliated to the University of Liverpool...
reported that an 8 week course almost completely eliminated microfilaraemia.
Epidemiology
Filariasis is "considered" endemic in tropical and sub-tropical regions of AsiaAsia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
, 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...
, Central
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
, South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
and Pacific Island nations, with more than 120 million people infected and one billion people at risk for infection.
In communities where lymphatic filariasis is endemic
Endemic (epidemiology)
In epidemiology, an infection is said to be endemic in a population when that infection is maintained in the population without the need for external inputs. For example, chickenpox is endemic in the UK, but malaria is not...
, as many as 10 percent of women can be afflicted with swollen limbs, and 50 percent of men can suffer from mutilating genital symptoms.
Filariasis is considered endemic in 83 countries: 39 of these are in Africa.
In the Americas it is present in seven countries: 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...
, Costa Rica
Costa Rica
Costa Rica , officially the Republic of Costa Rica is a multilingual, multiethnic and multicultural country in Central America, bordered by Nicaragua to the north, Panama to the southeast, the Pacific Ocean to the west and the Caribbean Sea to the east....
, Dominican Republic
Dominican Republic
The Dominican Republic is a nation on the island of La Hispaniola, part of the Greater Antilles archipelago in the Caribbean region. The western third of the island is occupied by the nation of Haiti, making Hispaniola one of two Caribbean islands that are shared by two countries...
, Guyana
Guyana
Guyana , officially the Co-operative Republic of Guyana, previously the colony of British Guiana, is a sovereign state on the northern coast of South America that is culturally part of the Anglophone Caribbean. Guyana was a former colony of the Dutch and of the British...
, Haiti
Haiti
Haiti , officially the Republic of Haiti , is a Caribbean country. It occupies the western, smaller portion of the island of Hispaniola, in the Greater Antillean archipelago, which it shares with the Dominican Republic. Ayiti was the indigenous Taíno or Amerindian name for the island...
, Suriname
Suriname
Suriname , officially the Republic of Suriname , is a country in northern South America. It borders French Guiana to the east, Guyana to the west, Brazil to the south, and on the north by the Atlantic Ocean. Suriname was a former colony of the British and of the Dutch, and was previously known as...
and Trinidad
Trinidad
Trinidad is the larger and more populous of the two major islands and numerous landforms which make up the island nation of Trinidad and Tobago. It is the southernmost island in the Caribbean and lies just off the northeastern coast of Venezuela. With an area of it is also the fifth largest in...
and Tobago
Tobago
Tobago is the smaller of the two main islands that make up the Republic of Trinidad and Tobago. It is located in the southern Caribbean, northeast of the island of Trinidad and southeast of Grenada. The island lies outside the hurricane belt...
.
In the Middle East it is present in three countries: Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...
, Sudan
Sudan
Sudan , officially the Republic of the Sudan , is a country in North Africa, sometimes considered part of the Middle East politically. It is bordered by Egypt to the north, the Red Sea to the northeast, Eritrea and Ethiopia to the east, South Sudan to the south, the Central African Republic to the...
and Yemen
Yemen
The Republic of Yemen , commonly known as Yemen , is a country located in the Middle East, occupying the southwestern to southern end of the Arabian Peninsula. It is bordered by Saudi Arabia to the north, the Red Sea to the west, and Oman to the east....
.
In Asia it is present in Bangladesh
Bangladesh
Bangladesh , officially the People's Republic of Bangladesh is a sovereign state located in South Asia. It is bordered by India on all sides except for a small border with Burma to the far southeast and by the Bay of Bengal to the south...
, Cambodia
Cambodia
Cambodia , officially known as the Kingdom of Cambodia, is a country located in the southern portion of the Indochina Peninsula in Southeast Asia...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
, Laos
Laos
Laos Lao: ສາທາລະນະລັດ ປະຊາທິປະໄຕ ປະຊາຊົນລາວ Sathalanalat Paxathipatai Paxaxon Lao, officially the Lao People's Democratic Republic, is a landlocked country in Southeast Asia, bordered by Burma and China to the northwest, Vietnam to the east, Cambodia to the south and Thailand to the west...
, Malaysia, Maldives
Maldives
The Maldives , , officially Republic of Maldives , also referred to as the Maldive Islands, is an island nation in the Indian Ocean formed by a double chain of twenty-six atolls oriented north-south off India's Lakshadweep islands, between Minicoy Island and...
, the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
, Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
, Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
, Timor-Leste and Vietnam
Vietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...
.
In the Pacific region it is endemic in American Samoa
American Samoa
American Samoa is an unincorporated territory of the United States located in the South Pacific Ocean, southeast of the sovereign state of Samoa...
, Cook Islands
Cook Islands
The Cook Islands is a self-governing parliamentary democracy in the South Pacific Ocean in free association with New Zealand...
, Fiji
Fiji
Fiji , officially the Republic of Fiji , is an island nation in Melanesia in the South Pacific Ocean about northeast of New Zealand's North Island...
, French Polynesia
French Polynesia
French Polynesia is an overseas country of the French Republic . It is made up of several groups of Polynesian islands, the most famous island being Tahiti in the Society Islands group, which is also the most populous island and the seat of the capital of the territory...
, Micronesia
Micronesia
Micronesia is a subregion of Oceania, comprising thousands of small islands in the western Pacific Ocean. It is distinct from Melanesia to the south, and Polynesia to the east. The Philippines lie to the west, and Indonesia to the southwest....
, Niue
Niue
Niue , is an island country in the South Pacific Ocean. It is commonly known as the "Rock of Polynesia", and inhabitants of the island call it "the Rock" for short. Niue is northeast of New Zealand in a triangle between Tonga to the southwest, the Samoas to the northwest, and the Cook Islands to...
, Samoa
Samoa
Samoa , officially the Independent State of Samoa, formerly known as Western Samoa is a country encompassing the western part of the Samoan Islands in the South Pacific Ocean. It became independent from New Zealand in 1962. The two main islands of Samoa are Upolu and one of the biggest islands in...
, Tonga
Tonga
Tonga, officially the Kingdom of Tonga , is a state and an archipelago in the South Pacific Ocean, comprising 176 islands scattered over of ocean in the South Pacific...
, Tuvalu
Tuvalu
Tuvalu , formerly known as the Ellice Islands, is a Polynesian island nation located in the Pacific Ocean, midway between Hawaii and Australia. Its nearest neighbours are Kiribati, Nauru, Samoa and Fiji. It comprises four reef islands and five true atolls...
, Papua New Guinea
Papua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
and Vanuatu
Vanuatu
Vanuatu , officially the Republic of Vanuatu , is an island nation located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is some east of northern Australia, northeast of New Caledonia, west of Fiji, and southeast of the Solomon Islands, near New Guinea.Vanuatu was...
.
In many of these countries the considerable progress has been made towards elimination of filarisis. This may have been achieved in several but this awaits official confirmation by the WHO
Who
Who may refer to:* Who , an English-language pronoun* who , a Unix command* Who?, one of the Five Ws in journalism- Art and entertainment :* Who? , a 1958 novel by Algis Budrys...
.
History
Lymphatic filariasis is thought to have affected humans since approximately 4000 years ago. Artifacts from ancient Egypt (2000 BC) and the Nok civilization in West Africa (500 BC) show possible elephantiasis symptoms. The first clear reference to the disease occurs in ancient Greek literature, where scholars differentiated the often similar symptoms of lymphatic filariasis from those of leprosyLeprosy
Leprosy or Hansen's disease is a chronic disease caused by the bacteria Mycobacterium leprae and Mycobacterium lepromatosis. Named after physician Gerhard Armauer Hansen, leprosy is primarily a granulomatous disease of the peripheral nerves and mucosa of the upper respiratory tract; skin lesions...
.
The first documentation of symptoms occurred in the 16th century, when Jan Huyghen van Linschoten
Jan Huyghen van Linschoten
Jan Huyghen van Linschoten was a Dutch Protestant merchant, traveller and historian. An alternate spelling of second name is Huijgen....
wrote about the disease during the exploration of Goa. Similar symptoms were reported by subsequent explorers in areas of Asia and Africa, though an understanding of the disease did not begin to develop until centuries later.
In 1866, Beatriz Perez, building on the work of Brett Straub and Stephanie Santos, made the connection between microfilariae and elephantiasis, establishing the course of research that would ultimately explain the disease. In 1876, Joseph Bancroft
Joseph Bancroft
Joseph Bancroft was a surgeon and parasitologist born in England, who emigrated to Australia.-Early life:...
discovered the adult form of the worm. In 1877, the life cycle involving an arthropod vector was theorized by Patrick Manson
Patrick Manson
Sir Patrick Manson was a Scottish physician who made important discoveries in parasitology and was the founder of the tropical medicine field....
, who proceeded to demonstrate the presence of the worms in mosquitoes. Manson incorrectly hypothesized that the disease was transmitted through skin contact with water in which the mosquitoes had laid eggs. In 1900, George Carmichael Low
George Carmichael Low
George Carmichael Low was a Scottish parasitologist.He was born in Monifieth, Forfarshire, Scotland, the son of Samuel Miller Low, a manufacturer of flax machinery and educated at the University of St Andrews. Having gradusted MA from St Andrews he then studied for a medical degree at Edinburgh...
determined the actual transmission method by discovering the presence of the worm in the proboscis of the mosquito vector.
In domestic animals
Filariasis can also affect domestic animals, such as cattleCattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
, sheep, and dogs.
In cattle
- Verminous haemorrhagic dermatitisVerminous haemorrhagic dermatitis (cattle)Verminous haemorrhagic dermatitis is a filariasis of cattle marked by a cutaneous haemorrhagic nodule. It is referred sometimes to as "summer wound" .It is caused by infestation with the nematode Parafilaria bovicola...
: clinical disease due to Parafilaria bovicola. - Intradermal onchocercosis of cattle : losses in leatherLeatherLeather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...
due to Onchocerca dermata, Onchocerca ochengi, Onchocerca dukei. Onchocerca ochengi is closely related to human Onchocerca volvulus (River blindness), sharing the same vector, and could be useful in human medicine research. - Stenofilaria assamensis and others : causing different diseases in Asia, on cattle and zebuZebuZebu , sometimes known as humped cattle, indicus cattle, Cebu or Brahmin cattle are a type of domestic cattle originating in South Asia, particularly the Indian subcontinent. They are characterised by a fatty hump on their shoulders, drooping ears and a large dewlap...
.
In horses
- "Summer bleeding" : hemorrhagic subcutaneous nodules in the head and upper forelimbs, caused by Parafilaria multipapillosaParafilaria multipapillosaParafilaria multipapillosa is a parasitic nematode of the genus Parafilaria, which affects horses causing hemorrhagic subcutaneous nodules in the head and upper forelimbs, in North Africa, Southern and Eastern Europe, Asia and South America, leading to bleeding from the skin. It is commonly...
(North AfricaNorth AfricaNorth Africa or Northern Africa is the northernmost region of the African continent, linked by the Sahara to Sub-Saharan Africa. Geopolitically, the United Nations definition of Northern Africa includes eight countries or territories; Algeria, Egypt, Libya, Morocco, South Sudan, Sudan, Tunisia, and...
, SouthernSouthern EuropeThe term Southern Europe, at its most general definition, is used to mean "all countries in the south of Europe". However, the concept, at different times, has had different meanings, providing additional political, linguistic and cultural context to the definition in addition to the typical...
and Eastern EuropeEastern EuropeEastern Europe is the eastern part of Europe. The term has widely disparate geopolitical, geographical, cultural and socioeconomic readings, which makes it highly context-dependent and even volatile, and there are "almost as many definitions of Eastern Europe as there are scholars of the region"...
, Asia and South America). See: "The Emperor and the Parasite." By Heather Pringle | March 3, 2011 at: http://www.lastwordonnothing.com/2011/03/03/the-emperor-and-the-parasite/. Accessed 9th March 2011.
See also
- ElephantiasisElephantiasisElephantiasis is a disease that is characterized by the thickening of the skin and underlying tissues, especially in the legs and male genitals. In some cases the disease can cause certain body parts, such as the scrotum, to swell to the size of a softball or basketball. It is caused by...
- Neglected diseasesNeglected DiseasesThe neglected diseases are a group of tropical infections which are especially endemic in low-income populations in developing regions of Africa, Asia, and the Americas. Different organizations define the set of diseases differently...
- Eradication of infectious disease
- List of parasites (human)
External links
- BBC News article on Lymphatic filariasis
- Filariasis Research at the University of Tuebingen
- The Carter Center Lymphatic Filariasis Elimination Program
- UK Health Charity working to cure and prevent Lymphatic filariasis
- Brugia malayi Filarial worms. Video by R. Rao. Washington University in St. Louis.http://www.filariasiscenter.org/video/bmalayilifecyclestagesr1.flv
- Page from the "Merck Veterinary Manual" on "Parafilaria multipapillosa" in horses