After 8 years of silence, dengue virus serotype 2 (DENV-2) reemerged in southeastern Senegal in 1999. Sixty-four DENV-2 strains were isolated in 1999 and 9 strains in 2000 from mosquitoes captured in the forest gallery and surrounding villages. Isolates were obtained from previously described vectors, Aedes furcifer, Ae. taylori, Ae. luteocephalus, and—for the first time in Senegal—from Ae. aegypti and Ae. vittatus. A retrospective analysis of sylvatic DENV-2 outbreaks in Senegal during the last 28 years of entomologic investigations shows that amplifications are periodic, with intervening, silent intervals of 5–8 years. No correlation was found between sylvatic DENV-2 emergence and rainfall amount. For sylvatic DENV-2 vectors, rainfall seems to particularly affect virus amplification that occurs at the end of the rainy season, from October to November. Data obtained from investigation of preimaginal (i.e., nonadult) mosquitoes suggest a secondary transmission cycle involving mosquitoes other than those identified previously as vectors.

Following an outbreak of Rift Valley fever (RVF) in south-eastern Mauritania during 1998, entomological investigations were conducted for 2 years in the affected parts of Senegal and Mauritania, spanning the Sénégal River basin. A total of 92 787 mosquitoes (Diptera: Culicidae), belonging to 10 genera and 41 species, were captured in light traps. In Senegal, Culex poicilipes (41%) and Mansonia uniformis (39%) were the most abundant species caught, whereas Aedes vexans (77%) and Cx. poicilipes (15%) predominated in Mauritania. RVF virus was isolated from 63 pools of Cx. poicilipes: 36 from Senegal in 1998 and 27 from Mauritania in 1999. These results are the first field evidence of Cx. poicilipes naturally infected with RVFV, and the first isolations of this virus from mosquitoes in Mauritania - the main West African epidemic and epizootic area. Additional arbovirus isolates comprised 25 strains of Bagaza (BAG) from Aedes fowleri, Culex neavei and Cx. poicilipes; 67 Sanar (ArD 66707) from Cx. poicilipes; 51 Wesselsbron (WSL) from Ae. vexans and 30 strains of West Nile (WN) from Ma. uniformis, showing differential specific virus-vector associations in the circulation activity of these five arboviruses.

Dengue virus 2 (DENV-2) strains that circulate in sylvatic habitats of Senegal and other parts of west Africa are believed to represent ancestral forms that evolved into endemic/epidemic strains that now circulate widely in urban areas of the tropics. Previous studies suggested that the evolution of the endemic/epidemic strains was mediated by adaptation to the peridomestic mosquito vectors Aedes aegypti and Ae. albopictus. We conducted experimental infections using sylvatic and peridomestic Senegalese mosquitoes, and both sylvatic and urban DENV-2 strains to determine if endemic DENV-2 adaptation was vector species specific, and to assess ancestral vector susceptibility. Aedes furcifer and Ae. luteocephalus, probable sylvatic vectors, were highly susceptible to both sylvatic and urban DENV-2 strains. In contrast, sylvatic Ae. vittatus and both sylvatic and peridomestic populations of Ae. aegypti were relative refractory to all DENV-2 strains tested. These results indicate that adaptation of DENV-2 to urban vectors did not result in a loss of infectivity for some African sylvatic vectors. Implications for dengue emergence in west Africa are discussed.

Endemic dengue virus (DENV) type 2 strains infect Aedes aegypti and Ae. albopictus more efficiently than ancestral sylvatic strains, which suggests that adaptation to these vectors mediated DENV emergence.

Nucleotide sequences of the central portion of gp120, including the third hypervariable (V3) loop, were obtained from lymphocytes cocultivated with SupT1 cells from 29 AIDS patients in Bangui, Central African Republic. These sequences displayed significantly greater diversity (average distance, 23%) than has been previously observed in isolates from comparably restricted geographical areas. Isolates belonging to four major subtypes of HIV-1 were found; the only subtype not represented was the North American/European subtype B. Unlike the situation in Zaire and Uganda, where subtypes A and D account equally for virtually all isolates of HIV-1, the predominant subtypes in the Central African Republic, accounting for two-thirds of the isolates, were subtypes A (10 isolates) and E (9 isolates). Subtype E represents a group of variants that have previously been found only in Thailand. Only one isolate belonging to subtype D was found. Also recovered were two isolates of subtype C, a subtype associated with southern African and Indian isolates but not previously detected in central Africa. These isolates, although clearly clustering with subtype C, formed a distinct subset, differing from one another by 8.8% and from the Indian and South African subtype C isolates by an average of 22.5%. High interpatient, intrasubtype variation was also seen among the CAR subtype A (average pairwise difference, 19.3%) and subtype E (10.9%) isolates. The diversity of V3 sequences in this set has implications for immunization protocols that rely on the recognition of V3. This study underscores the necessity of basing intervention strategies on knowledge of the particular sequences present in the target population or geographical area.

We investigated whether V3-binding assays might be useful to analyze human immunodeficiency virus type 1 (HIV-1) variants in different geographic regions. We showed that strong cross-reactivity between subtype-specific V3 peptides is almost inevitable in standard indirect enzyme-linked immunosorbent assays (EIA), impairing precise serological subtyping. We therefore developed a subtype-specific EIA (HIV-1 SSEIA) that uses the principle of blocking by an excess of peptide in the liquid phase. Using 231 serum samples collected from HIV-1-infected individuals in 10 different geographical areas from 4 continents, we showed that this approach detected the dominant subtype reactivity in more than 97% of the cases. Internal controls (0 and 100% blocking) were used for every sample such that comparative analysis was possible, independent of both the individual humoral response and the time of collection during the course of infection. This was validated by the excellent concordance of the serological profiles of couples and the temporal stability of the serological profile in individuals. The geographical distribution of the various subtypes in the SSEIA was in agreement with the present knowledge of the distribution of the various genotypes. Although the goal of this study was not an extensive seroepidemiological survey, our results showed that the various profiles in most of the regions were relatively homogeneous, but in central Africa there was a large diversity of serological profiles. Cluster analysis identified a limited number of V3 serogroups of serotypes within the HIV-1 group M. Five serogroups, some of them divided into subgroups, were identified and characterized by a mean serological profile. Our data confirmed that subtypes A and C, although being dissimilar genetic subtypes, present conserved antigenic properties in the V3 region, and that the D subtype is probably the most divergent within the group M (B Korber et al., J Virol 1994;68:6730). Cluster analysis showed a clear correlation between position within the dendrogram and geographical origin of the samples. This is further support for the reliability and thereof the usefulness of the SSEIA. This simple methodology may help facilitate the analysis of the distribution of various HIV-1 subtypes circulating in different populations and regions.

Abstract. Following the reemergence of Rift Valley fever (RVF) virus in southeastern Mauritania in 1998, an entomological survey was undertaken in the boundary area in Senegal to assess the extent of the virus circulation. During this study, RVF virus (36 strains) was isolated for the first time from Culex poicilipes in nature. The possible role of Cx. poicilipes as an RVF vector is discussed regarding its biology and ecology. Rift Valley fever (RVF) is an African viral zoonosis transmitted by mosquitoes. In September and October 1998, hemorrhagic fever cases were reported in the Ayoun El Atrouss zone, Mauritania (Nabeth P, unpublished data). Rift Valley fever virus was diagnosed using IgM capture, reverse transcriptase-polymerase chain reaction (RT-PCR), and virus isolation at the Pasteur Institute, Dakar, Senegal. Following the confirmation of these RVF cases in Mauritania, entomological survey was carried out in Senegal along the river basin in Thille Boubacar, Kanel, Dembankane, and Diawara ( Figure 1) in order to evaluate the extent of virus circulation. These localities are approximately 400 kilometers from the Mauritanian epidemic/epizootic zone.Mosquitoes were collected using the Centers for Disease Control and Prevention (CDC) light traps with CO 2 set nearby temporary ground pools and CDC light traps without CO 2 set in sheepfolds or cowsheds. They were then sorted and classified into monospecific pools and stored in liquid nitrogen before virological isolation attempts were made. Isolations were performed on Vero and AP 61 (Aedes pseudoscutellaris) cell lines. Rift Valley fever virus identification was made by indirect immunofluorescence, 1 then confirmed by complement fixation and seroneutralization tests.In total, 31,944 mosquitoes belonging to 6 genera and 20 species were captured. Culex poicilipes and Mansonia uniformis were the most common species (Table 1). Thirty-six RVF virus strains were isolated from Cx. poicilipes captured in Diawara, the locality in which the highest density of Cx. poicilipes was obtained (Figure 2). The true infection rate was estimated to be 0.37 Ϯ 0.06% in Diawara.To our knowledge, this is the first isolation of RVF virus from Cx. poicilipes in nature. Among mosquitoes collected, Culex antennatus, Anopheles pharoensis, Mansonia africana and Ma. uniformis were already found naturally infected by the RVF virus. 2 Previously, RVF virus isolations were obtained in Senegal from mosquitoes Aedes dalzieli, Aedes vexans, and Aedes ochraceus. 3 Like most RVF virus vectors, Cx. poicilipes is a temporary-ground-pools mosquito well adapted to the Sahelian area. In Barkedji area where an entomological survey has been conducted since 1990, Cx. poicilipes is the most represented species after Ae. vexans. 3 In this area, a high tropism of Cx. poicilipes was observed for

Abstract. An influenza survey was conducted in seven sentinel sites in Dakar, Senegal from June 1996 to December 1998. Throat or nasal swab cultures were randomly collected from 804 patients suffering from influenza-like symptoms. Influenza viruses were isolated at a similar proportion in adults and in children (P ϭ 0.29). Strains of influenza B viruses were isolated from sporadic cases in 1997, whereas type A virus was associated with an isolated peak. Proportions of influenza virus isolation varied from 17.5% to 40.0% between 1996 and 1998 during the peak period (July/September) of acute respiratory infection in Dakar. Rainfall, humidity, and temperatures rose during the same period. Influenza in Dakar seems to be an-all-age groups respiratory infection characterized by high transmission during the hot and rainy season. The antigenic similarity of the A(H3N2) and B viruses to those circulating elsewhere in the world at the same time was confirmed. However, the A(H1N1) strains were found to be more closely related to an Asiatic strain which had not been isolated outside Asia previously. Consequently, the strain close to the A(H1N1)/ Wuhan/371/95 strain isolated in Dakar was included in the composition of the 1998/1999 influenza vaccine. This reinforces the importance of setting up a national influenza control strategy in tropical regions.