Lymphatic filariasis.

Lymphatic filariasis* 1. Brief description of the condition/disease Lymphatic filariasis is a tropical discase caused by the parasitic wonns Wurchereria bancrofur Oi Brugia inalayz. Intection witlh these parasites leads to a variety of clinical manifestations. includtng lymphoedema and elephantiasis of tlle leg. aenital disease (including hydroccIc, chylocele and cl- ephantiasis of the scrotum and penis) and recurient acute secondarv bactenal infections. commonlv known as *acuLe attacks" The majority of infected persons are asymnptomatic. but vii tually all have subclinical lymphatic damage. and approximatelv 40% have relnal involvement (proteinuria and hae- maturia). Tropical pulmonary eosinophilia. a rare progressive lung disease, is caused by inflammatory rcactions against thc parasite in the lunas When an infccted mosquito takes a blood meal. the larval form of the parasite eniters the skin. migrates to the lymphiatic % essels. and devrelops over 6-12omonths into adult worms. whlch cause damage and dilatation of the lymphatic vessels Fertile adult females, during theii 4-6 year life span. ielease mil- lions ot microfilariae into the blood. wlliclh are takien up by mosquitos: furtlier development inside the mosquito is rcquired before the parasite larva is again infectiouts for humans 2. Current global burden and rating within the overall burden of disease Although lymphatic filariasis infrequentlI causes death, it is a nmajor cause of clinical morbidity and disability WHO ranks lymphatic filariasis as the sec- ond leading cause of disability worldwide The eco- nomic buiden of the discasc is poorly defined, but the costs to India alone ate estimated al US$ 15()0 million. In 1990, the estimated burden of disease was 850000 disability-adjusted life years (DALYs). Approximately 120 million persons in tropical areas of the wvorld are actuallv infected withd the parasite. but those at-risk arc estimated at 1100 mil- lion Of these iilfections. 90%,"O are caused b% WV bancrofti: B. mnala r (10%) is linmited to Asia and parts ot the South Pacific. An estimated 25 million men suffer from genital disease (niost commonlv Conlnbuted by David Addiss, Centers for Disease Control and Prevention, Atlanta, GA, USA. hydrocele); an estimated 15 million persons, the mna- jority of whom are wvomen, have lymphoedema or elepliantiasis of the leg. The devastating social and psychological impact of these disfiguring condiLions is only beginning to be undcrstood. 3. Feasibility (biological) of elimination/eradication The InLernational T'ask Force tor Disease Eradica- tLion considels lymphatic fiiarlasis to be one of onzly six "eradicable or potentially eradicable" diseases. Factors favounng eradicatioil include inefficient transmission (several hundred infective mosquito bites are required to produce a fertile adult woimi pair) and, at least for W. banci ofi. tie absence of a nonhumnan rcscrvoir. Because nicw drugs and drug combinations are now available that profoundly sup- prcss microfilaria levels in Lhe blood for . 12 months after a singlc dose elimination is possible with an- nual single-dose mass treaLmenl In 1997, tile World Health Assembly called tor global elimLnation of lymphatic filariasis as a public health problcm Lym- phatic filariasis has already been elinminated from several countnes. both as a result ot targeted pro- grammes (e g. Japan and parts of Chinia) and im- proved sanitation (e.g. the USA where W'. banciofti was endemic in South CalcolLna until the I930s) 4. Estimated costs and benefits of elimination/eradication Anilual costs for mass treatmlent witlh available dlug combinations aie approximately US$ 0.05-0. lO per person. These efforts may have to be sustaincd for 5 years or longer to assure interruption of Lransmis- sion. Benefits wvould include prevecntion ot tremen- dous social and psychological suffering from chironic diseasc and imnproved ecolomic productivity. lI the estimated costs of lymplhatic filariasis in India (US$ 1500 million) are similar to those in the resL of the woild the global economic bencfit of lymphatic filariasis elinmination could approach $4000 million per year. 5. Key strategies to accomplish the objectives Global elimination of lymphiatic filariasis mcans in- terrupting transmission of infection, and reducing Bulletin of the WoNd Health Organrzaion. 1,995 76 (SJop' 2) -45-146 145 Lymphatic filariasis the suffering of persons with chronic disease. includ- ing appropriate treatment of lymphoedema and el- ephantiasis. The main strategy recommended for interruption ot transmission is annual mass treat- ment of at-risk populations in endemic areas with single doses of albendazole in combination with ei- ther ivermectin or DEC; ancillary vector control can be helpful but is not required. To alleviate the suffer- ing. the principal strategy is health education and training so that affected individuals learn the impor- tance of scrupulous hygienc and other measures and the techniques necessary to achieve them. 6. Research needs Diagnostic and therapeutic tools are already avail- able tor global elimination of lymphatic filariasis. Additional research is nieeded to identify and evalu- ate techniques for rapid assessment and mapping of the disease, to develop mechanisms for surveillance and for monitoring the effectiveness of interven- tions, to identify optimal drug-deliver, systems, and to assess the cost-effectiveness of intervention strat- egies. Research is also needed to optimize the effec- tiveness of drugs and drug combinations in killing the adult stagc of the parasite 7. Status of elimination/eradication efforts to date Recognizing the availability of these new tools and a proven strategy for using them, the World Healtb Assembly in 1997 defined an international political will for this initiative by resolving to elinminate lvm- phatic filanasis as a public health problem globally. By November 1997, 13 countries in Asia. South America, and Africa had announced national plans for elimination of lymphatic filariasis, and seven of these countnes had already begun implementing these plans. For example. in India alone. 40 million people have been targeted to receive a single dose of DEC o.n "National Filanasis Day." 8. Principal challenges to elimination/eradication Challenges include: developing and sustaining the global, regional, and national will required for filariasis elimination; and developing accuratC and efficient methods to certify elimination. WHO Bulletn OMS Vol 76. Suppl 2 1998146