Studies of the long-term impact of CDTI on transmission

t African Programme for Onchocerciasis Control (APOC) Programme africain de lutte contre l'onchocercose JAF-FAC l JOINT ACTION FORUM Office of the Chairman JOINT ACTION FORUM Third session Livemool. 4-5 December 1997 FORUM D'ACTION COMMUNE Bureau du Prdsident JAF3/INF/DOC.3 ORIGINAL: ENGLISH October 1997I STUDIES OF THE LONG-TERM IMPACT OF CDTI ON TRANSMISSION Introduction The information available to date indicates that large scale ivermectin treatment reduces transmission and the incidence of infection by some 45%o-75o/o after the first rounds of treatmentr-r. Furthermore, the post-treatment paffem of repopulation of the skin by microfilariae indicates that repeated treatment may have a cumulative effect on the reproduction capacrty (fecundity) of the adult wormsa. On the basis of these results, it has been suggested that CDTI could lead to the intemrption of transmission and elimination of infection. However, it is unlikely that total intemrption of transmission will occur, and that CDTI will need to be continued for decades to sustain the control of the disease as a public health problem. Given the unceftainty about this issue, the likely and geographical variability in the impact of CDTI on transmission and because of the important operational implications if intemrption of transmission were to be achieved, APOC will study the impact of CDTI on transmission. To this end, base line data require to be collected and studies of the reduction in vector infectivity after 5-10 years of CDTI will be undertaken in a selected number of sites representative of the main epidemiological pattems and the principal vector- parasite complexes in APOC. To evaluate the impact of ivermectin based Control on Transmission, the methodology need to be defined. It was considered that the most appropriate indicator was level of Infectivity of the vector. The changes over a 4-5 year period in any selected area should be available to APOC. General objective To determine the long term effect of CDTI on O. volvuhzs transmission. Specific objective: To determine the long term reduction in vector infectivity as measured by the number of infective flies (flies with L3 larvae in the head) per thousand flies. JAF3/INF/DOC.3 Page 2 METHODOLOGY Fly collection should take place over three month period when transmission is at its peak. For each site, 3 teams each of 2 capturers will work for an 1 t hours day (an all-day catch is necessary so that the proportion of parous flies in the catch is approximately the same during Pre-control and Post-control catche. If flies are numerous then 10 days of catching over 2-3 days per week would be carried out each month for 3 months. If flies are numerous and there are no transport problems, one team of 2 capturers could collect daily (5 days a week) throughout the three-month-period. For ethical reasons the capturers must be fully clothed except for the legs where the flies can land. SAMPLE SIZE OF FLIES To obtain a reasonable number of parous flies, a sample of 10,000 flies but at least 5,000 flies is required. PRESERVATION & TRANSPORTATION Flies should be preserved in either 100% ethanol or propanol and transported to the processing laboratory for DNA assays on pools of blackflies to determine the level of infectivity. INTERPRETATION OF RESTJLTS Analysis of the vector infectivity data in the OCP using the model onchosim indicates that transmission is unlikely to take place at a level which instin:tes a public health risk when vector Infectivity is less than one L3 in the head/1000 parous flies. This result applies to S.W Savanna oncho and the vectors S. damnosum or sirbanum. For other vector parasite complexes, the same threshold may be appropriate and further analysis of Transmission data for other vector species is required to guide interpretation of the results of the studies on the acceptable level of Transmission. SITE SELECTION CRITERIA This should be done with regard to the following 1) Different vectors (biting in different countries) 2) Different seasonality 3) Different climate/vegetation 4) Endemicity of the site - hyperendemic area LIST OF SITES COI.INTRY N'SITES REMARKS 1. Cameroon SW in Kumba area -forest with diffuse transmission I { t 2 J Ethiopia Tanzania A S. damnosum focus near border A S.damnosum focus Mahenge possibly I 1 t JAI/INF/DOC.3 Page 3 4. Uganda J A S. neavei focus in S.W and another in Nile Region. S. damnosum focus perhaps only mesoendemic in Gupa/Apac or Kitgum (i.e. the North Central) I 5 6 7 Democratic Rep. of Congo (ex-Zaire) 3 CAR 1 Congo and/or Gabon 2 Probably a S. neavei focus i A Savanna focus Perhaps 1 forest and 1 Savanna but mesoendemic 8. Sudan (S) 1 Savanna of severe blinding oncho in S.W of country probably RAGA. 9. Nigeria 2 1 forest and 1 Savanna. The Savanna to be a Taraba State or Hawal valley Total = 15 sites in 9 countries (Map attached). BTIDGET PER SITE US DOLLAR 1. PERSONNEL Six fly catchers @ $5 per day - 6 x 5x 90 days One driver @ $10 x 90 days 2,700 900 2. TRANSPORTATION Vehicle hire for 4hrs per day @ $20 x 90 days Fuel and oil/ lubricant 1,800 200 3. SUPPLIES Bottles for flies x 1000 Preservatives - 100% ethanol or propanol s00 4. STATIONERY 20 I Ream of ,{4 paper Accessories - Files 5. COST OF PROCESSING 1O,OOO FLIES IN BOUAKE @ $0.007 per fly + Other Reagents TOTAL COST OF STUDY PER SITE: 1s0 6270 JAF3/INF/DOC.3 Page 4 References l. Taylor HR, Pacque M, Munoz B, Greene BM. Impact of mass treatment of onchocerciasis with ivermectin on the transmission of infection. Science 1990;250:l l6-8. 2. Remme J, Baker RH, De Sole G, et al. A community trial of ivermectin in the onchocerciasis focus of Asubende, Ghana. I. Effect on the microfilarial reservoir and the transmission of Onchocerca vol',ulus. Trop Med Parasitol 1989;40:367 -7 4. t 3. Boussinesq M, Chippaux IP, Ernould JC, Quillevere D, Prod'hon J. Effect of repeated treatments with ivermectin on the incidence of onchocerciasrs in northern Cameroon. Am J Trop Med Hyg 1995;53:63-7. 4. Plaisier AP, Alley ES, Boatin BA, et al. Irreversible effects of ivermectin on adult parasites in onchocerciasis patients in the Onchocerciasis Control Programme in West Africa. J Infect Dis 1995;172:204-10. r JAF3/rNF /DOC.3 , l o(,) oo o fo ,U U otg ooe 'l (t, TU6f at) z o oo =U,z t t oIL o IUF CD a q uJ :)I dI o tuFo .uJ J ul U) F oz <J) TU EFzl oo() o(L i]|,.::i.rli ;t: olF @ ulIF Z o UJo :) Joz U)g tFzl oo() o(L :: *], 'tij.:a oo =3tt I EC o)(,)(l) J s UI Zf(, J E. oF fa TU {\ t h q- u ! ij t: t l+,t I\ J ) 4 I a I tl l! r