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Filariasis (Philariasis) is a parasitic and infectioustropical disease, that is caused by
thread-like filarial nematode worms in the superfamily Filarioidea, also known as "filariae".
There are 9 known filarial nematodes which use humans as the 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''. Theseworms occupy the lymphatic system, including thelymph nodes, and in chronic cases these
worms lead to the diseaseElephantiasis. Subcutaneous Filariasis is caused by ''Loa loa'' (the
African eye worm), ''Mansonella streptocerca'', ''Onchocerca volvulus'', and ''Dracunculus
medinensis'' (the guinea worm). These worms occupy the subcutaneous layer of the skin,
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 either blood sucking insects (fly or mosquito) or Copepod
crustaceans in the case of ''Dracunculus medinensis''.
Human filarial nematode worms have a complicated life cycle, which primarily consists of
five stages. After the male and female worm mate, the female gives birth to live
microfilariae 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 our skin. After approximately one
year the larvae molt through 2 more stages, maturing into the adult worm.
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.
Filariasis Symptoms
The most spectacular symptom of lymphatic filariasis is elephantiasisedemawith
thickening of the skin and underlying tissueswhich 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 ears, 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, and breasts, while ''Brugia timori'' rarely affects the genitals. Interestingly,
those who develop the chronic stages of elephantiasis are usually amicrofilaraemic, and
often have adverse immunlogical reactions to the microfilaria as well as the adult worm.
The subcutaneous worms present with skin rashes, urticarial papules, andarthritis, as well
as hyper- and hypopigmentation macules. ''Onchocerca volvulus'' manifests itself in the
eyes causing "river blindness"(onchocerciasis), the 2nd leading cause of blindness in the
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world. Serous cavity filariasis presents with symptoms similar to subcutaneous filariasis, in
addition toabdominal painbecause these worms are also deep tissue dwellers.
Filariasis Diagnosis
Filariasis is usually diagnosed by identifying microfilariae on a Giemsa stained thick bloodfilm. Blood must be drawn at night, since the microfilaria circulate at night(nocturnal
periodicity), when their mosquito vector is most likely to bite. Also,decreased peripheral
temperature may attract more microfilariae.
Concentration Methods
Various concentration methods are applied:
i. Membrane filter ii. Knott's concentration method
iii. Sedimentation technique
Polymerase chain reaction (PCR) and antigenic assays are also available for making the
diagnosis. The latter are particularly useful in amicrofilaraemic cases.
Lymph Node aspirrate,Chylus fluid may also yield Microfilriae.
Imaging like CT,MRI may reveal "Filarial Dance Sign" in Chylus fluid.
X-ray can show calcified adult worm in lymphatics.
DEC provokation test is performed to obtain satisfying number of parasite in day-time
samples.
Circulating Filarial Antigen (CFA) may be detected by PCR.
Xenodiagnosis is now obsolete
EOsinophilia is a non-specific primary sign.
Filariasis Prevention
In 1993, the International Task Force for Disease Eradication declared lymphatic filariaisis to
be one of six potentially eradicable diseases. With consistent treatment, the reduction of
microfilariae means the disease will not be transmitted, the adult worms will die out, and
the cycle will be broken.
The efforts of the Global Programme to Eliminate LF are estimated to have already
prevented 6.6 million new filariasis cases from developing in children, and to have stopped
the progression of the disease in another 9.5 million people who have already contracted it.
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Dr Mwele Malecela, who chairs the programme, said: "We are on track to accomplish our
goal of elimination by 2020."
Filariasis Treatment
The recommended treatment for killing adult filarial worms in patients outside the UnitedStates is albendazole (a broad spectrum anthelmintic) combined with ivermectin.
Filarial parasites have symbiotic bacteria in the genus Wolbachia, which live inside the
worm. When the symbiotic bacteria are killed by the antibiotic, the worms themselves also
die.
Clinical trials in June 2005 by the Liverpool School of Tropical Medicine reported that an 8
week course almost completely eliminated microfilaraemia.
Filariasis Epidemiology
Filariasis is endemic in tropical and sub-tropical regions of Asia, 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 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 possibleelephantiasissymptoms. The first clear reference to the disease occurs in
ancient Greek literature, where scholars differentiated the often similar symptoms of
lymphatic filariasis from those ofleprosy.
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 began to develop until centuries later.
In 1866, Timothy Lewis, building on the work of Jean-Nicolas Demarquay and Otto Henry
Wucherer, 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.
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This article is licensed under theCreative Commons Attribution-ShareAlike License. It uses
material from the Wikipedia article on "Filariasis" All material adapted used from Wikipedia
is available under the terms of theCreative Commons Attribution-ShareAlike License.
Wikipedia itself is a registered trademark of the Wikimedia Foundation, Inc.
Recent Filariasis News
LSTM professor awarded The Manson Medal for outstanding contribution in field of tropical medicineTheLiverpool School of Tropical Medicine (LSTM) is delighted that Emeritus Professor and Senior Professional
Fellow, David Molyneux, has been awarded The Manson Medal, the Royal Society of Tropical M...
Low-cost intervention reduces transmission of lymphatic filariasis to undetectable levelsAn internationalteam of scientists have demonstrated that a simple, low-cost intervention holds the potential to eradicate a
debilitating tropical disease that threatens nearly 1.4 billion people in ...
DFID awards 5-year grant to DNDi to advance research and development for neglected diseasesThe UKDepartment for International Development (DFID) has announced its renewed support to the Drugs forNeglected Diseases initiative (DNDi), allocating a total of - 30 million (- 35 million) over t...
Human filariasis research: an interview with Professor Mark Taylor, Liverpool School of TropicalMedicineFilariasis refers to a group of diseases caused by parasitic worms, which are transmitted by blood
feeding insects. Two species infect the lymphatic and blood systems causing lymphatic filariasis, whi...
UC Riverside researchers develop easy-to-wear patch that makes humans invisible to mosquitoesTechnologythat hampers mosquitoes' host-seeking behavior, identified at the University of California, Riverside in 2011,
has led to the development of the world's first product that blocks mosquitoe...
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