Filariasis

Filariasis
Classification & external resources

ICD-10	B74.
ICD-9	125.0-125.9
MeSH	D005368

See special page for Filariasis in domestic animals

Lymphatic Filariasis is a parasitic and infectious tropical disease, caused by three thread-like parasitic filarial worms, Wuchereria bancrofti, Brugia malayi, and Brugia timori, all transmitted by mosquitoes. It is extremely rare in Western countries. Loa loa is another filarial parasite of humans, transmitted by the deer fly.

Presentation

The most spectacular symptom of lymphatic filariasis is elephantiasis—thickening of the skin and underlying tissues—which was the first disease discovered to be transmitted by insects. Elephantiasis is caused when the parasites lodge in the lymphatic system.

Elephantiasis affects mainly the lower extremities, whereas ears, mucus membranes, and amputation stumps are rarely affected; however, it depends on the species of filaria. W. bancrofti can affect the legs, arms, vulva, breasts, while Brugia timori rarely affects the genitals. Infection by Onchocerca volvulus and the migration of its microfilariae through the cornea is a major cause of blindness (Onchocerciasis).

Incidence/prevalence

Filariasis is endemic in tropical regions of Asia, Africa, Central and South America with 120 million people infected.

In endemic areas of the world (e.g., Malaipea in Indonesia), up to 54% of the population may have microfilariae in their blood.^[1]

History

Lymphatic Filariasis is thought to have affected humans since approximately 1500-4000 years ago, though an exact date for its origin is unknown. The first clear reference to the disease occurs in ancient Greek literature, where scholars discuss diagnosis of lymphatic filariasis vs. diagnosis of similar symptoms that can result from leprosy.

The first documentation of symptoms occurred in the 16th century, when Jan Huygen Linschoten wrote about the disease during the exploration of Goa. Soon after, exploration of other parts of Asia and Africa turned up further reports of disease symptoms. It was not until centuries later than an understanding of the disease began to develop.

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. Not long after, in 1876, Joseph Bancroft discovered the adult form of the worm, and finally 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.^[2]

Diagnosis

The diagnosis is made by identifying microfilariae on a Giemsa stained thick blood film. Blood must be drawn at night, since the microfilaria circulate at night, when their vector, the mosquito, is most likely to bite.

There are also PCR assays available for making the diagnosis.

Treatment

Medicines to treat lymphatic filariasis are most effective when used soon after infection, but they do have some toxic side effects. In addition, the disease is difficult to detect early. Therefore, improved treatments and laboratory tests are needed.

Antibiotics as a possible treatment

In 2003 it was suggested that the common antibiotic doxycycline might be effective in treating elephantiasis.^[3] The parasites responsible for filariasis have a population of symbiotic bacteria, Wolbachia, that 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 microfilariaemia.^[4][5]

• Diethylcarbamazine Citrate (Hetrazan)

References

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Filariasis

1. ^ Aupali T, Ismid IS, Wibowo H, et al. (2006). "Estimation of the prevalence of lymphatic filariasis by a pool screen PCR assay using blood spots collected on filter paper". Tran R Soc Trop Med Hyg 100 (8): 753–9. 
2. ^ http://www.stanford.edu/class/humbio103/ParaSites2006/Lymphatic_filariasis/Discovery.htm Accessed 7-3-2007
3. ^ Hoerauf A, Mand S, Fischer K, Kruppa T, Marfo-Debrekyei Y, Debrah AY, Pfarr KM, Adjei O, Buttner DW (2003). "Doxycycline as a novel strategy against bancroftian filariasis-depletion of Wolbachia endosymbionts from Wuchereria bancrofti and stop of microfilaria production". Med Microbiol Immunol (Berl) 192 (4): 211-6. PMID 12684759. 
4. ^ Taylor MJ, Makunde WH, McGarry HF, Turner JD, Mand S, Hoerauf A (2005). "Macrofilaricidal activity after doxycycline treatment of Wuchereria bancrofti: a double-blind, randomised placebo-controlled trial". Lancet 365 (9477): 2116-21. PMID 15964448. 
5. ^ Outland, Katrina. "New Treatment for Elephantitis: Antibiotics", The Journal of Young Investigators, 2005 Volume 13. 

External links

• (2005) "Special issue". Indian Journal of Urology 21 (1). 

• BBC News article on Lymphatic filariasis

• Filariasis Research at the University of Tuebingen

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