Isolations of West Nile and Bagaza viruses from mosquitoes (Diptera: Culicidae) in central Senegal (Ferlo).

During October-November 1990, 31,497 mosquitoes consisting of 25 different species were collected in Barkedji, Ferlo area (Senegal), and tested for virus infection. Viruse were isolated from 55 of 407 pools. Eighteen pools were found positive for both Bagaza virus (BGA) and West Nile virus (WN). One alphavirus (Babanki [BBK] and 72 flaviviruses (19 BGA, 53 WN) were isolated from Culex poicilipes Theobald (29 WN, 8 BGA), C. neavei Theobald (3 WN, 1 BGA), Mimomyia hispida Theobald (8 WN, 6 BGA, and 1 BBK), M. lacustris Edwards (4 WN, 1 BGA), M. splendens Theobald (6 WN, 2 BGA), Mimomyia. spp. (2 WN), and Aedeomyia africana Neveu-Lemaire (1 WN). These were the first isolations of arboviruses from A. africana and Mimomyia species. C. poicilipes and possibly Mimomyia spp. may be involved in an avian-mosquito cycle of West Nile virus transmission in Senegal.

Dengue 2 outbreak in southeastern Senegal during 1990: virus isolations from mosquitoes (Diptera: Culicidae).

During 1990, Dengue-2 (DEN-2) virus was isolated for the first time from mosquitoes (Aedes furcifer, six isolates; Ae. taylori, six isolates; Ae. luteocephalus, seven isolates) collected during an epidemic in which DEN-2 virus also was isolated from humans. Numerous isolations have been made previously from mosquitoes in the absence of human infection. In Senegal, DEN-2 virus appears to be maintained in an enzootic cycle and, therefore, plays an expanding role in human disease and increases the need for effective surveillance in mosquito populations.

Rift Valley fever in rural northern Senegal: human risk factors and potential vectors.

To investigate past infection in and transmission of Rift Valley fever (RVF) virus to humans within an endemic focus, we undertook a retrospective cohort study of the seminomadic Peul people living in sub-Saharan northcentral Senegal. Residents of the rural settlement of Yonofere five years of age or older were studied during February-May 1989. Anti-RVF virus IgG was found in blood samples of 22.3% of 273 persons who responded to a standard questionnaire; none had IgM antibodies. Seropositivity was similar for males (25.4%) and females (21.1%), increased markedly with age for both sexes, and varied considerably among compounds (groups of huts) (0-37.5%). Risk factors for past RVF virus infection were nursing sick people, assisting animals during abortions/births, and treating sick animals. In all age groups, odds ratios (ORs) for RVF viral antibody among females who reported treating sick animals were three to six times greater than for those who did not. The ORs for males who reported assisting with animal births/abortions and nursing sick people were approximately five times those for males who did not. Serologic prevalence of RVF viral antibody among sheep averaged 30.1% overall (0.8% IgM), but varied among compounds (0-66.7%) in a manner different from that of humans. The seasonal abundance and relative density of potential mosquito vectors were estimated by monthly samples captured in Centers for Disease Control and Prevention-type traps. Mosquito abundance varied seasonally with rainfall (> 90% captures during four months). Species diversity was large (28 spp.), dominated by Aedes and Culex. Rift Valley fever virus was not isolated from 142 pools of 2,956 unengorged mosquitoes tested, although three other arboviruses were found. Results indicate that RVF is endemic in this region, people are at considerable risk of infection, and that a heretofore unrecognized mode of human infection under nonepizootic conditions may be transmission via contact with infected animals or humans.

[Surveillance of the circulation of arbovirus of medical interest in the region of eastern Senegal]. / Surveillance de la circulation des arbovirus d'intérêt médical dans la région du Sénégal oriental (1988-1991).

A study about the circulation of arboviruses of medical interest in southeastern Senegal was conducted from 1988 to 1991, during and around the periods of transmission. Specific IgM antibodies were detected by ELISA test in human sera, as a sign of a recent infection within 2 to 5 months. The comparison of the serological IgM results from human surveys in different villages, and the isolations of arboviruses from mosquitoes during the same period of time permitted a rapid and global evaluation of the circulation of these viruses. A low level of yellow fever virus activity was detected both in humans and mosquitoes in 1988 to 1990. A dengue 2 epizootic occurred in 1989-1990. Dengue 2 virus was isolated from humans and mosquitoes in 1990. Some dengue 2 outbreak may occur in the upcoming years. A Zika virus epizootic outbreak was observed each year. A human strain was isolated in 1990. The other flaviviruses (West-Nile, Kedougou, Wesselsbron), Chikungunya virus, Rift Valley Fever virus and Crimean-Congo Hemorrhagic Fever virus did not seem to present a major public health concern in southeastern Senegal.

[The effect of 2 chloroquine-based drug strategies (prevention and therapy of febrile cases] on malaria transmission]. / Influence de deux stratégies médicamenteuses par chloroquine (prophylaxie et thérapie des accès fébriles) sur la transmission du paludisme.

A 3 years study was decided in 12 villages of the South-West Burkina Faso to compare the chemoprophylaxis and the chemotherapy of febrile cases as potential malaria control strategies. During the first year pretreatment data were collected. During the two following years a programme carried out (I) prophylaxis (10 mg chloroquine/kg body weight) was given weekly to all children under 14 years old in 5 villages, and (II) therapy (10 mg chloroquine/kg body weight) was given in a single dose to all febrile cases in 7 other villages. Chloroquine tablets were distributed by health workers belonging to the community. Both prophylaxis and therapy reduced the gametocyte rate in children (2-9 years) respectively of 63% and 45%. The analysis of the evolution after the first year of the sporozoite rate of anopheline was made difficult by concomitant natural variations of mosquitoes longevity and by mosquitoes displacements. Significant variations of sporozoite rate can be explained by natural variations of mosquitoes longevity. But data from the rice field villages support evidence that reduction of the pool of parasite infective for vectors induced the decrease of Anopheles gambiae s. l. sporozoite rate. Therefore our results reflect a trend more than a strict reduction of malaria transmission.

[Sylvatic yellow fever in Africa recent advances and present approach (author's transl)]. / La fièvre jaune selvatique en Afrique: donnees récentes et conceptions actuelles.

Recent works carried out in west and central Africa resulted in numerous yellow fever virus isolations from sylvatic mosquitoes in the forest-savanna transitional zone. This virus was also obtained from monkeys, whereas studies on sequence and duration of the observed epizootics permitted a previsional approach of the yellow fever mechanisms in the same belt, the epidemiological importance of which was stressed ("emergence zone"). In the same course of research and publications, the prevalent part of the involved mosquitoes as virus-reservoirs was constantly emphasized ("reservoir-vector"). Recent investigations on transovarial transmission and yellow fever isolations from male mosquitoes caught in the field, provide decisive support to such a conception. It can explain that epizootics may be locally observed several years in succession, despite the fact that yellow fever virus circulation seems to be fundamentally of a dynamic character. Yellow fever virus was recently obtained from ticks and tick-eggs.

[The control of Aedes (Stegomyia) and related species involved in transmission of human arbovirus infections in tropical Africa (author's transl)]. / Le côntrole des Aedes (Stegomyia) et espèces voisines vecteurs d'arboviroses humaines, en Afrique tropicale.

In Africa, many Aedes mosquitos are involved in yellow fever and dengue transmission. Their control can be carried out either in a "prophylactic" way, when no disease occurs, or in a "curative" one, when virus is detected in the human community. In the first event, control is confounded with sanitation measures; in the second event, insecticidal control is needed against both larvae and adults. Larvae populations are destroyed by means of insecticidal deposits in the breeding-sites. Control of adults is achieved by thermal fogs or U.L.V. applications of organophosphorous compounds dispensed from ground or aerial generators. The insecticide susceptibility level of every Aedes populations involved in arbovirus transmission must be periodically determined with all the insecticides available.