Onchocerciasis.

Onchocerciasis* 1. Brief description of the condition/disease Onclhocerca volvi{h(s infectioii (i.e. "'nver blind- ness"). which is caused by filariid parasites that are long-lived (8-15 years), is characterized by cbronic skin and eye lesions. It is transmitted by Simuldiun blackflies that breed in rapidly flowing rivers and streams. The emiibryonic stage (microfilaria). rc- leased by female worms causes most of thle pathol- ogy. Human infection occurs from the bite of a blackfly that harbours one or more infectious (third- stage) 0 voliutrlzis larvae. Male and fcmale wvorms gather in groups of five or six. intertwined and en- cased in a fibrous capsule that forms a palpable nod- ule The female worms produce thousands ot microfilartae (each about the size of a period oii this page). which leave the nodule and migrate into the host's skin, cyes, and other organls. Persons with many fertilized female voi ms can harbour as many as 200 million microfilanae. The microfilariae live for 9-18 months but canniot develop into adult worms without first passing through the Sinhunte blackfly vectol. In these insects, the microfilarlac transfonr in the course of 6-12 days into the third-stage larvae that aie infective to humans. There is nlo known animal reservoir for 0. iolvildus. Several aspects of this life-cycle aftect potential eradicability. First, only the few microfilaiiae tliat succeed in passing throuogh both human and blackfly hosts reach adulthood. Second. the blackflv must bite at least twice to transmiit the infection: once to acquire microfilariae from an infected person, and again to transmit the infectious larvae to another person Finially, rarely do more tlhani 5%n of blackflies harbour infectious larvae at a' given time. and most of these flies have only one or two such larvae ready to inoculate Theretore. the transmission cycle has only one point of amplification (tlhrough humans) and is relatively susceptiblc to interruption. Contnbuled by Frank 0 Richards, Centers for Disease Conlrol and Prevention Atlanta, GA, USA; Emanuel Min, The Carter Center of Emory University, Atlanta, GA. USA, Stefanie Meredith Task Force for Child Survival and Development, CDC, Atlanta, GA USA, Flonald Guderian, (forrnerly) Ecuador Onchocerciasis Con- trol Program, Seattle WA USA; Mauricio Sauerbrey, Oncho- cerciasis Elimination Program of the Americas, Guatemala; Hans Remme. Tropical Disease Research Programme WHO Geneva Switzerland; Randall Packard. Emory University Ro,lins School of Public Health. Atanta, GA, USA. Jean-Michel Ndiaye. Africa Re- gional Advisor in Health/Guinea-worm, UNICEF, Abidjan, C6te d'lvoire. 2. Current global burden and rating within the overall burden of disease Onchocerciasis is known to be endemic in 37 couin- tries Tn 1995, the WHO Expcrt Committee on Onchocerciasis estimated that l23 million persons were at nsk of contracting the discase, and 17-18 million were infected, of whom about 270000 were blind and another 500 000 severely visually impaircd. About 95°0/ of infected persons iesidc in Africa. where the disease is most severe along the major rivers in 30 countries in a belt spanning the northern and central part of the continent. Outside Atrica, onchocerciasis occurs in Mcxico. Guatemala, Ecua- dor. Colombia, Venezuela, and Brazil in the Amen- cas. and in Yemen in Asia. 3. Feasibility (biological) of elimination/eradication In 1993, the International Task Force for Disease Elimination did not list onchocerciasis as one of the six diseases suitable for eradication. However, onclhocerciasis was listed as a disease, one aspect of whlich (blindness) could be eliminated. The diffMcul- tlies in eradication include. the lone life-span of the adult worms. thc occurrence of reinfections; and lack of vaccines and acceptable drugs to kill the adult woNarms (macrofilaricide). HoWvc cr. reconsideration of these difficulties is now appropriate given the considerable progress made towards elimination of all morbidity from onchocerciasis In the Onchocerciasis Control Pro- gramme (OCP) areas in West Africa) and in the Aimericas Using vector control, the OCP has been very successful in interrupting transmission of this disease. After 20 years, onchocerciasis is no longer a public health problem in the original OCP area. Whereas infection rates in the programme's most severely affected country. Burkina Faso. weic 80- 90% wbhen the programme began. the highest rates in 1995 were <2%. All 30 million persons at risk in the 11 countries of the OCP are being protccted. and 125000 to 200000 have beeni picvented from becom- ino blind. About 10 million children born since the programme began are free from onchocerciasis, and 2 million hectares of land - enough to support 17 million persons- along West African rivers are now available for rcscttlernent In the Americas. data strongly suggest that semiannual mass distribution of Butetrn of the Worfd Health Organizaion. 1998, 76 (Suppl 2) 147-149 147 Onchocerciasis ivermectin, without vector control, has interrupted transmission in 7 of 14 known focL, including those in Colombia and Ecuador. where one of the most effi- cient vectors in the world (Sinuhium exiqgaum) exists. If transmission can be interrupted with a free anid easily deliverable medicine, the disease could poten- tially be eradicable. Furtlhermore. computer mod- els and observations suggest that repeaLcd ivemiectin treatment might affect the tecundity of adult females or longevity of adult males, thus reduc- ing the duration of mass treatment programmes to less than the life span of the adult parasites (8-15 years). Nongovernmental development organiza- tions (NGDOs). bilateral and multilateral institu- tions, and national governments are providing the international momentum behind major programmnes. and industry (Merck & Co.) is donating the drug. Finally, the problem is, unlike lymphatic filariasis, restricted to rural Africa and Latin Amenca. Thlus, onchocerciasis may now be eligible to be included on the list of discascs for potential eradication 4. Estimated costs and benefits of elimination/eradication In African conununities with severe (hyperendemic) onchiocerciasis of the savanna type, 15% of the popu- lation can be blind and up to 40°% of adults can be visually impaired. Visual impairment is a major oc- cupational and social obstacle and reduces the life span of affected persons by an average of 10 years. Agncultural production decreases, young childrcn are torced to care for their parents, and adolescents emiorate because ot the tear of becoming blind. Ultimately, the village is turther impoverislhed or completely abandoned. In areas where blinding onchocerciasis is rare, onchocercal skm disease oc- curs in up to 30% of the population; 8 million per- sons suffer from troublesome itching associated with dermal onchocerciasis, making it difficult for them to work, study. or interact socially. The unsightly skin changes may result in poor self-esteem and social ostracism. Intensive research is under way on the economic impact of onchocercal skin disease. 5. Key strategies to accomplish the objectives The OCP. which began in seven countries in 1974, used a strategy of interrupting transmission via vector control. The programme comrpnsed aerial larviciding, supplemented by ground and water- based handspraymng of blackfly breeding sites in rivers over a vast area of West Africa. In 1986, opera- tions were extended to parts of four other countries to prevent reinvasion of the core area by blackflies. Replication of the OCP was not practical tor 87% of the onchocerciasis-affected population living outside the OCP area. In 1987. the introduction of ivermectin (Mectizan) resulted in a new strategy that enabled assistance to be extended to other populations. The drug kills Onchocerca microfilariac with almost no serious side-effects, and its effects atter one oral dose last for approximately a year. In 1987, Merck & Co. announced its decision to provide the drug wvithout cost in whatever quantities were needed and for as long as necessary to treat and prevent onchocerciasis. Merck also establislhed an independ- ent group of international scientists. the Mectizan Expert Committee, to evaluate applications for sup- plies of thle drug. The donation by Mcrck & Co. prompted na- tional anid intcrnational health workers in the af- fected countries to develop systems capable of distributing thc orally administered drug once or twice a year to persons in remote villages. Many programmes for communitv-based distribution of Mectizan are assisted by NGDOs, which have dem- onstrated their flexibility, creativity. and rapid re- sponse to the challenge. The NGDOs have used delivery of what has become a popular drug in the communities as an] entry point for developing broader health care services. A 10-member NGDO coalition has been established internationally. and national coalitions of NGDOs have been established In some countries. In December 1995 the World Bank, encour- aged by these successes, launched another region al programme - the Afrncan Programme for Oncho- cerciasis Control (APOC)- tor the remaining areas of Atrica. The primary goal ofAPOC is to eliminate onchocerciasis as a public health problem in these areas of Africa by the year 2007 by ieachmg the remaining 50-60 million persons at nsk of poten- tially blinding onchocerciasis and/or severe skin disease. Unlike the OCP, APOC will use annual community-based distribution of Mlectizan as its pri- nmary control strategy. Sinmilarly, the Onchocerciasis Elmination Program for the Americas (OEPA), es- tablished after a Pan Amerncan Health Organization resolution in 1991 and aided by the InterAmerican Development Bank, also aims to eliminate onchocerciasis as a public health problem in the Americas by 2007 through Mectizan delivery. On both continents, the strategy entails rapidly determining the severity and distribution of oncho- cerciasis in remote areas and communities by testing a carefully selected sample of the populations and communities using new microcomputer-based map- WHO Bulletin OMS Vol 76, Suppl 2 199814a Onchocerciasis ping techniques and noninvasive. field-based diag- nostic methods. Rapid-assessment field teclhniques are based on classification of communities by the prevalence of nodules (hyperendemicity is generally defined as rates 40,%) Once the at-nsk" commu- nities are identified, Mectizan is offered annually (or in some countries in the Amcricas. biannually) for an indefinite period to all healthy persons except motlh- ers who are nursing <1-week-old infants. 6. Research needs Research is needed concerning the followvmg: mechanisms of survelJlance. GIS (geographic infor- mation system) applications: conmputer-modelling, of transmission of the parasite. PCR!DNA probes lor infectivc larvae in blackflies: impact of prolonged ivcrmectin treatment on onchocercal skin disease: adult woim longevity/fecundity (through antigen detection techniques); monitoring of transnmission: aspects of sustainiabiity: econiomic impact develop- ment of netw macrofilaricides: aild adapting the programme (without dis;upting tlc currcnt momen- tum) to olher suitable drugs that can be used at the community level to control or eradicate other widespread diseases, suchi as conmbination therapy for lymphatic filariasis or praziquantel for schistosomiasis. 7. Status of elimination/eradication efforts The progressive increase in thc nunmbers treated with iveimectin has been impressive - trom 500000 per- sons in 19S8 to >20 million in 1997. The World Banik signed a declaration of intent to reach thc remaining 50-60 million persons at risk of potentially blinding onclhoccrciasis aild/or severe skin disease and elimi- nate onchocerciasis as a public health problem in Afrnca by 2007. Similarly, the Onchocerciasis Elimination Program for the Americas aims to elimi- nate onchocerciasis as a public problemn in the Amnericas by 200-7. Mlore than 95% of known hyperenideinic comlmunities in the Americas are un- der treatment. Merck & Co. vill provide 410 million tablets of Meclizani. valued at several hundred million US$. during the initiative: over 100-million doses of Mectizan have safely been given since the donation began in 1987. 8. Principal challenges to elimination/eradication Challenges to elimination include the following: adequate funding: establishment by APOC arid OEPA of effective and lasting partnerships Nwith the coalition participants; continued refinement of the model of sustainable conniuunity-based distribution of Mectizan to control onchocerciasis: surveillance mechanisms for '"sustainabilty,", man- agement traininicg at the ministr ot health level; dcvelopment of new macrolilaricides: difficulties as- socialed with iInpoiting the drug: the relatively short shelf-life t2 veals) of vcrmnectin; and certification cijteria that are internationally accepted for elimina- tion of morbiditv and transmission. WHO Bulletn OMS Vol 76, Suppl 2 1998 149