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PubMed1994

[The necessity of conducting to the end the activities of vector control in the onchocerciasis control program in west Africa: recall of the stakes and proposal of a minimum budget for the period 1998-2002].

After a brief presentation of the Onchocerciasis Control Programme in West Africa (OCP), the authors realize the health and socioeconomic consequences that could follow a cessation of larvicide treatment before 2002 in the south-eastern and western extensions of the Programme. Taking into account that OCP activities are theoretically supported until 1997, but aware of financial constraints that will probably increase from now to 2002, this paper proposes an a minima estimation of the residual vector control activities for a "phasing out" spread out for five years (1998-2002). These estimations essentially concern the larvicide coverage, the insecticides used, the entomological surveillance, the logistical support and their financial aspects. As far as 48 U.S. $ million amount for 5 years are concerned, the budget allocated for vector control activities should not exceed the third of the global amount allocated to OCP for the actual fourth financial phase of the Programme (1992-1997).

Africa, Western↗
PubMed1995

Development by injection in Simulium damnosum s.l. of two Onchocerca species from the wart hog to infective larvae resembling type D larvae (Duke, 1967).

Four wart hogs (Phacochoerus aethiopicus) examined in the Sudan savanna of North-Cameroon were all found infected with two types of skin microfilariae. One was O. ramachandrini Bain, Wahl and Renz, 1993, the adult worms of which live in the subcutaneous tissues of the feet. The other, smaller type belongs to a new Onchocerca species, the adult worms of which were not yet found. O. ramachandrini-microfilariae were evenly distributed across the whole body surface, those of Onchocerca sp. were concentrated on the back. The two species of microfilariae were isolated from an infected hide separated under the dissecting microscope and injected into the thorax of pupae-hatched S. squamosum and S. damnosum s.slr. females. Both filariae developed in both flies at high rates (33-47% of injected microfilariae) and without pathological forms to infective larvae L3). Both L3-species had a caudal tip, were long, slender and very motile and had a conspicuous glandular oesophagus. L3 from O. ramachandrini-microfilariae had a long glandular oesophagus (55% of total L3 length), a round head and measured an average of 955 microns long and 19.2 microns wide. L3 from the other microfilaria-species were shorter (845 microns, P < 0.001) and thinner (16.7 microns, P < 0.001) and had a shorter glandular oesophagus (36%, P < 0.001), a shorter tail (P < 0.01) and a conical head. Both L3-species, by their caudal tip, their long and slender silhouette, their great motility and their conspicuous glandular oesophagus resemble non-O. volvulus filarial L3 known, since many years, to occur in "wild" S. damnosum s.l. in Cameroon (Type D larvae, Duke, 1967) and in Liberia (Agamofilaria Type VI, Voelker and Garms, 1972). During our study, L3 such larvae were found in 12 wild S. damnosum s.l. from two geographically different areas of North Cameroon and all identified as O. ramachandrini. The excellent development of the two Onchocerca species from the wart hog in S. damnosum s.l. after artificial infection, and the identification of all recently examined wild Type D larvae as O. ramachandrini suggest that S. damnosum s.l. is a natural vector of O. ramachandrini and that most (if not all) of the Type D larvae in onchocerciasis vectors in North-Cameroon originate from wart hogs.

Animals↗
PubMed2002

Onchocerciasis in West Africa after 2002: a challenge to take up.

Initially planned for a 20 year life time, the Onchocerciasis Control Programme in West Africa (OCP) will have finally continued its activities for nearly three decades (vector control alone from 1975 to 1989, then vector control and/or therapeutic treatment until 2002). Although onchocerciasis is no longer a problem of public health importance nor an obstacle to socio-economic development in the OCP area, the control of this filariasis is not over because OCP never aimed at eradication, neither of the parasite (Onchocerca volvulus), nor of its vector (Simulium damnosum s.l.). In 2003, the eleven Participating countries of OCP will take over the responsibility of carrying out the residual activities of monitoring and the control of this disease. This mission is of great importance because any recrudescence of the transmission could lead in the long run to the reappearance of the clinical signs of onchocerciasis, if not its most serious manifestations. For epidemiological and operational reasons, and given the disparity in national health policies and infrastructures, the capacities of the countries to take over the residual activities of monitoring and control of onchocerciasis are very unequal. Indeed, the interventions to be carried out are very different from one country to another and the process of integrating the residual activities into the national health systems is not taking place at the same pace. This inequality among the countries vis-a-vis the challenges to be met does not, however, prejudge the epidemiological situation after 2002 whose evolution will also depend on the effectiveness of the provisions made before that date by OCP, then after 2002, by the Regional Office for Africa of the World Health Organization which is currently setting up a sub-regional multidisease surveillance centre.

Africa, Western↗
PubMed2006

[African Program for Onchocerciasis Control (APOC): Onchocerca volvulus transmission by Simulium damnosum s. l. in two regions of the Central African Republic].

Entomological baseline data were collected in the villages of Zinga and Boali-Falls in Central African Republic (CAR) in view of the long term impact assessment of community-directed treatment with ivermectin (CDTI). Morphological determinations revealed that flies caught in both sites belong to the sub-group Sou/Sq. In Boali, the nuisance was relatively high with biting rates averaging 243 bites/man/day, with a parous rate of 61.6% and a crude annual transmission potential (ATP) of 8,259 infective larvae/man/year; and the average number of infective larvae per 1,000 parous flies was 177. In Zinga, the mean biting rate was 191 bites/man/day, with a parous rate of 51.6%, a crude ATP of 3,422, and 86 infective larvae per 1,000 porous flies. In conclusion, the vectorial capacity and the entomological indices recorded are characteristic of high onchocerciasis transmission zones. However, some of the infective larvae found, maybe of animal origin, need identification to better determine the real level of endemicity.

Animals↗
PubMedDate not supplied

Onchocerca ochengi transmission dynamics and the correlation of O. ochengi microfilaria density in cattle with the transmission potential.

The intensity of natural transmission of Onchocerca ochengi and Onchocerco volvulus by anthropo-boophilic Simulium damnosum s.l. was studied longitudinally in two cattle watering sites of a cattle ranch within a predominantly cattle populated area of the Guinea savanna of Cameroon and related to cattle O. ochengi skin microfilaria abundance. During the 12 months study period, a total of 4696 flies was individually dissected to examine the monthly transmission potential (MTP) of O. ochengi and O. volvulus. The estimated Simulium damnosum s.l. annual biting rates (ABR) on human baits were 47529 flies at the bank of the Vina "du sud" river. The ABR at the lake, which was situated at about 2 km upland from the perennial river, was 8579. The monthly parous rate was highly correlated with monthly biting rate. The annual transmission potentials (ATP) of O. ochengi were calculated to be 7732 and 1669 at the riverbank and the lake, respectively. Transmission occurred mainly in the dry season, peaking in the months of January to mid-March when dermal microfilaria density in the animals was also the highest. The O. ochengi microfilaria uptake by the fly vectors was host microfilaria density-dependent. The MTP of O. ochengi was positively correlated with dermal microfilaria density. The mean number of microfilariae per fly taken up during a blood meal was high during the dry season as was the mean number of infective larvae per fly but declined significantly with the onset of the early rains. A similar seasonality of transmission was also observed for O. volvulus that was concurrently transmitted by the same vector flies, but its ATP was comparatively much lower: 1332 infective larvae per man per year at the riverbank and 107 around the lake. The population dynamics of cattle microfilariae therefore plays an important role in the regulation of O. ochengi transmission.

Animals↗