Tonate virus infection in French Guiana: clinical aspects and seroepidemiologic study.

Two recent cases of human infection with Tonate virus, one of which was a fatal case of encephalitis, have renewed interest in these viruses in French Guiana. The clinical aspects of confirmed and probable cases of infection with this virus indicate that it has pathogenic properties in humans similar to those of other viruses of the Venezuelan equine encephalitis complex. To determine the prevalence of antibodies to Tonate virus in the various ethnic groups and areas of French Guiana, 3,516 human sera were tested with a hemagglutination inhibition test.

[Present status of an arbovirus infection: yellow fever, its natural history of hemorrhagic fever, Rift Valley fever].

In the early 20th century, when it was discovered that the yellow fever virus was transmitted in its urban cycle by Aedes aegypti, measures of control were introduced leading to its disappearance. Progressive neglect of the disease, however, led to a new outbreak in 1927 during which the etiological agent was isolated; some years later a vaccine was discovered and yellow fever disappeared again. In the 1960s, rare cases of encephalitis were observed in young children after vaccination and the administration of the vaccine was forbidden for children under 10 years.

Genetic reassortment of Rift Valley fever virus in nature.

Rift Valley fever virus (RVFV), a phlebovirus of the Bunyaviridae family, is an arthropod-borne virus which emerges periodically throughout Africa, emphasizing that it poses a major threat for animal and human populations. To assess the genetic variability of RVFV, several isolates from diverse localities of Africa were investigated by means of reverse transcription-PCR followed by direct sequencing of a region of the small (S), medium (M), and large (L) genomic segments. Phylogenetic analysis showed the existence of three major lineages corresponding to geographic variants from West Africa, Egypt, and Central-East Africa.

New vectors of Rift Valley fever in West Africa.

After an outbreak of Rift Valley fever in Southern Mauritania in 1987, entomologic studies were conducted in a bordering region in Sénégal from 1991 to 1996 to identify the sylvatic vectors of Rift Valley fever virus. The virus was isolated from the floodwater mosquitoes Aedes vexans and Ae. ochraceus.

Variability of the NS(S) protein among Rift Valley fever virus isolates.

Eighteen strains of Rift Valley fever (RVF) virus collected over a period of 38 years and isolated from diverse localities in Africa and from various hosts (human, animal and arthropod) were investigated by RT-PCR followed by sequencing of the NS(S) protein coding region. This region was chosen to analyse variability because, in contrast to the N protein, the NS(S) protein differs in various phleboviruses and there exists an RVF virus (clone 13) in which 70% of the NS(S) ORF is deleted, suggesting that this sequence is under a weak selective pressure. Sequence data indicated that percentage divergence among isolates ranged from 0 to 9.

Extensive nucleotide changes and deletions within the envelope glycoprotein gene of Euro-African West Nile viruses.

We compared the sequence of an envelope protein gene fragment from 21 temporally distinct West Nile (WN) virus strains, isolated in nine African countries and in France. Alignment of nucleotide sequences defined two groups of viruses which diverged by up to 29%. The first group of subtypes is composed of nine WN strains from France and Africa.

Enzootic activity of Rift Valley fever virus in Senegal.

In two areas of Senegal where previous evidence of Rift Valley fever (RVF) virus circulation was detected, Barkedji in the Sahelian bioclimatic zone and Kedougou in the Sudano-Guinean zone, a longitudinal study of the enzootic maintenance of RVF virus was undertaken from 1991 to 1993. Mosquitoes, sand flies, and ticks were collected and domestic ungulates were monitored with serologic surveys. Rift Valley fever virus was not isolated in Kedougou.

Surveillance for yellow fever virus in eastern Senegal during 1993.

During the 1993 rainy season, 15,806 mosquitoes, including 14,304 Aedes ssp., were collected and tested for virus infection in 702 and 547 pools, respectively. Aedes furcifer (Edwards) was the most abundant species collected throughout the survey period.

[Ngari virus (Bunyaviridae: Bunyavirus). First isolation from humans in Senegal, new mosquito vectors, its epidemiology].

Ngari virus (NRI) (Bunyaviridae, genus Bunyavirus) was isolated first from male Aedes simpsoni mosquitoes in Southeastern Senegal in 1979. Then, it was recovered from several mosquito species in Senegal, Burkina Faso, Central African Republic and Madagascar. A potential pathogenicity of NRI virus in humans was suspected when the virus was isolated from two patients in Dakar in October and November 1993.

Short report: Rift Valley fever in western Africa: isolations from Aedes mosquitoes during an interepizootic period.

Thirteen strains of Rift Valley fever virus were isolated from Aedes vexans and Ae. ochraceus mosquitoes collected in October and November 1993 in northern Senegal. Entomologic and serologic data show that the risk of a new epizootic is increasing in this region.

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).

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.

First isolations of arboviruses from phlebotomine sand flies in West Africa.

For the first time in West Africa, arboviruses were isolated from phlebotomine sand fly pools. One strain of Chandipura virus (a Vesiculovirus), four strains of Saboya virus (a Flavivirus), and one strain of a not yet identified virus were isolated. Three hundred twenty-two pools were established from a population of 33,917 sand flies caught in CO2 light traps in the Ferlo Sahelian region of Senegal from November 1991 to December 1992.

Geographic distribution and evolution of yellow fever viruses based on direct sequencing of genomic cDNA fragments.

We have compared the nucleotide sequence of an envelope protein gene fragment encoding amino acids 291 to 406 of 22 yellow fever (YF) virus strains of diverse geographic and host origins isolated over a 63 year time span. The nucleotide fragment of viral RNA was examined by direct sequencing of a PCR product derived from complementary DNA. Alignment with the prototype Asibi strain sequence showed divergence of 0 to 21.

Simian immunodeficiency viruses from central and western Africa: evidence for a new species-specific lentivirus in tantalus monkeys.

Although up to 50% of African green monkeys (AGMs) are infected by simian immunodeficiency viruses (SIV) in their natural habitat, they remain asymptomatic carriers of these lentiviruses. They provide an attractive model to study not only the origin but also the link among genetic variation, host-virus adaptation, and pathogenicity of primate lentiviruses. SIVagm have been isolated from three species of AGM: the vervet (Cercopithecus pygerythrus), the grivet (Cercopithecus aethiops), and the sabaeus (Cercopithecus sabaeus) monkey.

[Yellow fever epidemic in the extreme North of Cameroon in 1990: first yellow fever virus isolation in Cameroon].

Some two years ago, suspicious cases of yellow fever (YF) were reported in northern Cameroon. A deadly epidemic broke out during the second half of the rainy season (from 15 September to 22 December 1990) with 180 known cases, of which 125 died. The real figures could have been between 5000 and 20,000 cases with between 500 and 1000 deaths.

[Yellow fever virus, dengue 2 and other arboviruses isolated from mosquitos, in Burkina Faso, from 1983 to 1986. Entomological and epidemiological considerations].

An arbovirus surveillance was carried out in Burkina Faso from 1983 to 1986. It was based on crepuscular catches of mosquitoes on human bait in some wooded areas and in one town. The total collection was 228 catches with an average of 8 men per catch.

Arbovirus isolations from mosquitoes collected during 1988 in the Senegal River basin.

During August and September 1988, we collected adult mosquitoes from 14 locations in the Senegal River basin to search for evidence of Rift Valley fever (RVF) viral activity one year after the 1987 outbreak, which occurred along the Senegal-Mauritania border. More than 62,000 specimens representing 18 species in seven genera were collected with carbon dioxide-baited, solid-state Army miniature light traps and sheep-baited traps. Twenty virus isolations from Culex, Aedes, and Anopheles mosquitoes were recovered from six locations: Fanaye Diery (11), Bode (four), Matam (two), Diongui (one), Ndialene (one), and Ngoui (one).

Continuous cell lines and immune ascitic fluid pools in arbovirus detection.

Successive experiments led us to use two cellular systems, MOS61 (Aedes pseudoscutellaris cells) and Vero cells, among the continuous cell lines recommended by the WHO Collaborating Center for systematic research and isolation of arboviruses. Virus detection in cell cultures is carried out with 7 mixtures containing 10 hyperimmune ascitic fluids made with the reference viruses. This technique enables the detection of 70 of the 80 arboviruses transmitted by mosquitoes in Africa and very easily detects arbovirus associations by using either monospecific or monoclonal immune ascitic fluids (dengue-1-2-3-4 and yellow fever viruses) used in the indirect immunofluorescence technique.