Enteroaggregative Escherichia coli: a public health hazard in Yaounde; Cameroon?

The prevalence of various pathotypes of Escherichia coli was investigated during a case-control study conducted in children diarrhoea in Yaounde. Isolates obtained from the stools samples of children aged 6 months to 5 years were selected on phenotypic basis; and identified by virulence genes detection using polymerase chain reactions. The most prevalent pathotype was enteroaggregative Escherichia coli (25.8). Enteropathogenic Escherichia coli (3.6); enterotoxigenic Escherichia coli (1); and enteroinvasive Escherichia coli (0.2) followed. No shiga toxin-producing Escherichia coli were identified. Enteroaggregative Escherichia coli was not associated with diarrhoea (cases 26.1; controls 25.5; P=0;887); unlike enteropathogenic Escherichia coli (cases 6.7; controls 1; P=0.003). Investigations into documented potentials of enteroaggregative Escherichia coli in causing diarrhoea and other related pathologies indicated that it could be a major public health threat in Cameroon despite the fact that it was not found associated with clinical diarrhoeal cases in this study

[Comparative titration of three antivenin serums used against sub-Saharan African snakes]. / Titrage comparatif de trois sérums antivenimeux utilisés contre les serpents d'Afrique sub-saharienne.

The standardisation of serotherapy is necessary in Africa mainly because of the frequency of envenomations and the lack of alternative treatments. Comparative titrations of FAV-Afrique (Aventis Pasteur), Polyvalent serum (Serum Institute of India = SII) and Polyvalent antivenin (South African Vaccine Fabricants Ltd = SAIMR) were carried out on venoms of Echis ocellatus from Cameroun, E. ocellatus from Mali, E. leucogaster and Naja melanoleuca. The 50% protective doses (ED50) of the antivenoms were given according either to i) the in vitro method which consists of inoculating 5 batches of 5 mice with a mixture containing 3 DL50 of venom and increasing volumes of antivenom incubated for 30 mn at 37 degrees C and ii) the in vivo method which consists of successive administration of venom and then antivenom after a 30 to 60 mn interval. The three antivenoms showed a similar efficacy against all the Echis venoms. Interestingly, the SAIMR proved to be effective against the venom of E. leucogaster and E. ocellatus although no venom of Echis was used to immunise horses during the preparation of antivenom. Conversely, this paraspecificity did not exist with the Naja melanoleuca venom against which FAV Afrique showed a higher efficacy. The electrophoresis pattern of FAV-Afrique performed on acetate gel strips showed only one protein fraction (76 g.l-1), whereas both the SII and SAIMR antivenoms showed four fractions whose protein concentrations was respectively 64 g.l-1 and 145 g.l-1.

Single-tube and nested reverse transcriptase-polymerase chain reaction for detection of Rift Valley fever virus in human and animal sera.

Rift Valley fever (RVF) is an anthropozoonosis caused by a Phlebovirus (Bunyaviridae family) that has re-emerged recently in East and West Africa in 1997-1998. This emphasizes the need for early and rapid detection of the virus and an efficient surveillance system. To this goal, a single tube or a nested reverse transcriptase-polymerase chain reaction (RT-PCR) method focusing on the NSs coding region of the S segment was developed and used to detect the RVF virus (RVFV) genome, resulting respectively in the synthesis of 810 and 662 bp DNA amplimers. The assay was specific for RVFV and did not amplify any other phleboviruses known to circulate in sub-Saharan Africa. When serial dilutions of RVFV were artificially mixed with human normal serum, the minimal detection limits were 50 and 0.5 plaque forming units respectively using the simple and the nested RT-PCR. The RT-PCR method was efficient for the detection of RVFV RNA in the blood from experimentally RVFV-infected mice and lamb and the nested RT-PCR was found more sensitive than the virus isolation method. Additionally, this detection method was applied successfully for the diagnosis of human cases during the 1998 Mauritanian outbreak.

Vertical transmission of the yellow fever virus by Aedes aegypti (Diptera, Culicidae): dynamics of infection in F1 adult progeny of orally infected females.

Vertical transmission of yellow fever virus from orally infected females to their progeny was experimentally demonstrated in 2 Aedes aegypti colonies from the Dakar and Koungheul regions in Senegal. A total of 10,530 F1 adult mosquito progeny were tested. The overall vertical transmission rate was 0.97%, with no significant difference between the Dakar and Koungheul colonies. The infection rates were significantly higher in females (1.15%) than in males (0.74%) in both colonies. The virus was not isolated from the progeny of the first oviposition cycle (OVC1). The true infection rates were 0.27% and 1.99%, respectively, for the OVC2 and OVC3 progeny in the Dakar colony, and 1.1% and 1.48%, respectively, for the OVC2 and OVC3 progeny in the Koungheul colony. The infection rates increased with extrinsic incubation in both male and female offspring of the 2 colonies, reaching 5.2% in 20-day-old OVC3 female progeny in the Dakar colony. The epidemiologic consequences of these results are discussed.

Rift valley fever surveillance in the lower Senegal river basin: update 10 years after the epidemic.

After the Rift valley fever (RVF) epidemic of 1987 in the Senegal River Basin, RVF surveillance based on serosurveys has been conducted for 10 years. Serum samples were obtained from 1336 persons and from sheep and goats in selected areas, and these were tested for IgG/IgM RVF antibodies by ELISA. After a period of regular decrease in RVF prevalence in domestic animals until 1993, an epizootic was observed in all herds in 1994-95 with increases in IgM levels and abortions. During the same period, no human cases or RVF IgM were detected. The RVF IgG prevalence significantly correlated with date of birth: children born after 1987 have a low prevalence (5%) in clear contrast to the older population (25.3%) in Podor district. A retrospective analysis of rainfall and RVF prevalence in small domestic animals over the last 10 years showed that the re-emergence correlated with heavy rainfall. A general analysis of the risk of re-emergence and the efficiency of this RVF surveillance system are presented.

[Experimental transmission of Crimean-Congo hemorrhagic fever virus by Rhipicephalus evertsi evertsi (Acarina:Ixodidae)]. / Transmission expérimentale du virus de la fièvre hémorragique de Crimée-Congo par la tique Rhipicephalus evertsi evertsi (Acarina: Ixodidae).

We have conducted experiments to assess the ability of Rhipicephalus evertsi evertsi tick to transmit the Crimean-Congo haemorrhagic fever (CCHF) and determine their reproductive cycle. The Rh. e. evertsi was infected by intracoelomic (transparietal and intra-anal) inoculation during the imaginal stases and by oral feeding on an infected viremic goat during imaginal and nymphal stases. The infection rate, transovarial and trans-stasial CCHF virus transmission were monitored for virus reisolation after suckling mice inoculation and the virus identified by ELISA and IFA for antigen detection. After intracoelomic inoculation, unfed adults had viral titers ranging from 0.67 to 2.9 log DL50/0.02 ml and had transmitted the virus to their vertebrate hosts by blood feeding. After 8 to 10 days of blood feeding duration, infection rates were respectively 36% and 100% for male and female ticks. In two instances out of seven transovarial transmission was observed and the virus reisolated from larvae of first generation. However, the virus was not detected after nymphal metamorphosis. After blood feeding on viremic goats, 71% of the nymphae were infected. After metamorphoses 22% of the males and 42% of the females had a low virus titer. Rh. e. evertsi appears to have a limited efficacy in transmitting and replicating the CCHF virus but must be not neglected as a potential vector during an epizootic manifestation.

[Chikungunya virus outbreak in Senegal in 1996 and 1997]. / Epidémies à virus Chikungunya en 1996 et 1997 au Sénégal.

Chikungunya disease is generally recognized in Africa by serosurveys conducted in rural areas. Epidemics are rarely documented. We report two outbreaks in Senegal: one having occurred near Kaffrine in 1996 during an epidemic of yellow fever (YF), the second in Niakhar in 1997. Both diagnoses were conducted by IgM antibodies captures and confirmed by virus isolations. In Kaffrine, a randomised study was carried out on 447 blood donors whose serum was systematically tested for the most frequently encountered arboviruses in Senegal. The incidence rate was higher for the unrecognized Chikungunya infection (35.3%) than for the notified YF infection (21%). In Niakhar, Chikungunya infection was initially detected through three cases having occurred in health workers. A serosurvey was then conducted to define the area of prevalence. We report the clinical forms of Chikungunya virus infections, the interest in detecting IgM for recent arbovirus infections and the duration of these IgM. The difficulties of diagnosis of Chikungunya infection in malaria endemic areas are stressed. The occurrence of arbovirus infections, Yellow fever and Chikungunya viruses, transmitted by the same vectors (Aedes aegypti) in Kaffrine are also discussed.

[Phlebotomus of Senegal: survey of the fauna in the region of Kedougou. Isolation of arbovirus]. / Phlébotomes du Sénégal: inventaire de la faune de la région de Kédougou. Isolements d'arbovirus.

Phlebotomine sand-flies were captured on a bimonthly basis from April 1995 to March 1996 in the Kedougou district of south-east Senegal. In all, 6,642 specimens were identified belonging to 25 species. Eleven species were captured in tree holes, 17 in termites hills, 19 in rodent burrows and 23 on grass. Sergentomyia buxtoni, S. clydei, S. dubia, S. squamipleuris et S. schwetzi were the most abundant. Species from the genus Sergentomyia accounted for 99.3% versus 0.7% for the genus Phlebotomus, Phlebotomus duboscqi, the leishmaniasis vector in Senegal, was very rare. The male of S. edentula and S. herollandi were recorded for the first time. The sand-fly population was observed to peak in April. The most populated resting sites were, in decreasing order, termite-hills, burrows and tree-holes. Thirty virus strains from 5 different viruses (Saboya, Chandipura, Tete, ArD 95737, ArD 111740) were isolated from 30,482 specimens tested.

Vectors of Chikungunya virus in Senegal: current data and transmission cycles.

Chikungunya fever is a viral disease transmitted to human beings by Aedes genus mosquitoes. From 1972 to 1986 in Kédougou, Senegal, 178 Chikungunya virus strains were isolated from gallery forest mosquitoes, with most of them isolated from Ae. furcifer-taylori (129 strains), Ae. luteocephalus (27 strains), and Ae. dalzieli (12 strains). The characteristics of the sylvatic transmission cycle are a circulation periodicity with silent intervals that last approximately three years. Few epidemics of this disease have been reported in Senegal. The most recent one occurred in 1996 in Kaffrine where two Chikungunya virus strains were isolated from Ae. aegypti. The retrospective analysis of viral isolates from mosquitoes, wild vertebrates, and humans allowed to us to characterize Chikungunya virus transmission cycles in Senegal and to compare them with those of yellow fever virus.

Yellow fever outbreak in Kaffrine, Senegal 1996: epidemiological and entomological findings.

In November 1996 a yellow fever (YF) outbreak occurred near Kaffrine in the central part of Senegal. Thirty-six deaths were notified, all children under 15 years of age. The YF diagnosis was confirmed by MAC-ELISA or by virus isolation. The immune status against YF virus of a sample population of 449 individuals was determined, and 31 confirmed cases and 69 asymptomatic cases were reported. Distribution of YF cases and incidence rate decreased with age, while the attack rate was stable in all age groups. Larva indices were high and Aedes aegypti was common in all villages, causing man-to-man transmission. The greatest risk of YF disease was lack of immunity, especially in individuals <20 years of age. The outbreak was rapidly controlled by an emergency immunization campaign. YF epidemics occurred in Senegal over two consecutive years. The last outbreak reached the main road to Dakar and the risk of spread to urban areas has increased.

[Phlebotomines of Senegal (Diptera: Psychodidae): population and population dynamics of the Mont-Rolland region]. / Phlébotomes du Sénégal (Diptera-Psychodidae): peuplement et dynamique des populations de la région de Mont-Rolland.

Phlebotomine sandflies were captured on a monthly basis from May 1995 to April 1996 in the Mont-Rolland district in Western Senegal. The objectives were to study the population dynamics of sandflies and to make an inventory of the viruses they transmit. Among 10,315 specimens captured, belonging to 14 species, Sergentomyia dubia (35.9%), S. schwetzi (27.7%) and S. buxtoni (24.5%) were the most abundant. Species from the genus Sergentomyia accounted for 99.6% versus 0.4% for the genus Phlebotomus. The sandflies population was observed to peak in February. The most populated resting sites of the captured insects were in decreasing order tree-holes, termite-hills and burrows. S. dubia was the most abundant species captured in tree-holes. It was S. buxtoni in termite-hills, while S. schwetzi was found to dwell most often in burrows. No virus was isolated from 2,114 specimens tested.

Re-emergence of yellow fever in Senegal in 1995.

An outbreak of yellow fever (YF) occurred in the central part of Senegal during October 1995. Thirty-one probable cases were detected and 79 cases were confirmed either by IgM ELISA or by virus isolation (30 strains isolated). The case fatality rate was 18.9%. Incidence of the infection was evaluated by a serosurvey in the area. Males 10-29 years old belonging to the Peul ethnic group were more affected. Moreover, 28 YF virus strains were isolated from mosquitoes and larvae pools and vertical transmission of YF virus by Aedes aegypti was also demonstrated for the first time in the field. This outbreak occurred after the major amplification of the wild cycle of YF virus in 1993 in West Africa. This epidemic represented a typical example of intermediate transmission of YF: both humans and wild vertebrates are involved in the virus cycle through wild mosquitoes with semidomestic habits, mainly Ae. furcifer, Ae. luteocephalus, and domestic vector Ae. aegypti. It was controlled by a prompt immunization campaign. The impact of inclusion of YF vaccine in the Expanded Program of Immunization, which has been conducted in Senegal for eight years, is discussed.

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. In 1974 and 1983, the virus had been isolated from Ae. dalzieli. Although these vectors differ from the main vectors in East and South Africa, they use the same type of breeding sites and also feed on cattle and sheep. Although enzootic vectors have now been identified in West Africa, the factors causing outbreaks remain unclear.

First evidence of natural vertical transmission of yellow fever virus in Aedes aegypti, its epidemic vector.

Entomological investigations were conducted in 1995 in Senegal, following a yellow fever (YF) outbreak. A total of 1125 mosquitoes collected in the field, including males, females and 12-48 h old newly emerged adults reared from wild-caught larvae, were tested for YF virus. Among the 22 species captured, Aedes aegypti was the most common. 'Wild' vectors of YF were also captured, including A. furcifer, A. metallicus and A. luteocephalus. In all, 28 YF virus isolations were made: 19 from A. aegypti females, including 2 from newly emerged specimens; 5 were obtained from A. aegypti males, including one from a pool of newly emerged specimens, 2 from A. furcifer females, and one each from a female A. metallicus and a female A. luteocephalus. The true infection rates (TIRs) were much higher in adult A. aegypti than in specimens reared from larvae--8.2% and 31.4% for female and male A. aegypti captured on human volunteers, respectively (P < 0.0001). The TIRs for A. aegypti reared from larvae were 1.4% and 0.5% for females and males, respectively (P > 0.05). This outbreak was an intermediate YF epidemic, involving 4 vector species. Our data provide the first evidence of vertical transmission of YF virus in nature by A. aegypti, its main vector to humans, and strongly suggest that vertical transmission played a major role in the spread of the epidemic.

[Ngari virus (Bunyaviridae: Bunyavirus). First isolation from humans in Senegal, new mosquito vectors, its epidemiology]. / Le virus Ngari (Bunyaviridae: Bunyavirus). Premiers isolements chez l'homme au Sénégal, nouveaux vecteurs culicidiens, le point sur son épidémiologie.

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. The large diversity of Culicidae vectors and feeding patterns showed a large heterogeneity of vertebrate hosts. The wide geographical distribution of NRI virus in different bioclimatic areas indicated an important adaptability of the virus. Ngari virus epidemiology will need further investigations in order to approach the real pathogenicity of such emerging virus.

[Post-vaccination anti-poliomyelitis seroprevalence in an urban setting in Abidjan]. / Séroprévalence antipoliomyélitique post-vaccinale en milieu urbain à Abidjan.

In order to determine the antipoliomyelitis seroprevalence of children in Abidjan, we checked the presence of antipoliovirus antibodies in 48 children received in the South Abobo's vaccination center for vaccination against measles. According to the vaccination schedule and rules applied in Côte d'Ivoire: 12.5% of the children have received less than three doses or oral polio vaccine (OPV), 87.5% have received the three doses. Antibody titration results indicated that 78.6, 93 and 76.2% of the children have been immunized against Poliovirus type I, type II and type III, respectively; 71.4% of the children showed antibodies against the three poliovirus serotypes and 4.8% had no antipoliovirus antibodies at all. The children which showed an antibodies titer less than 1/8 were considered unprotected: the proportion of unprotected was 21.4, 7 and 23.8% against Poliovirus type I, type II and type III, respectively. Although these results showed that the level of protection against poliomyelitis in Abidjan is acceptable (> 75%), the efforts for vaccination program in Côte d'Ivoire need to be improved in order to eradicate poliomyelitis.

[Evaluation of the immunological and entomological indices of yellow fever in the subprefecture of Taï, Ivory Coast]. / Evalation des indices immunologiques et entomologiques de la fièvre jaune dans la sous-préfecture de Taï, Côte-d'Ivoire.

The authors report the results of a serological sample survey managed to evaluate the prevalence of yellow fever antibodies, connected with an entomological survey, in the area of Taï in Côte d'Ivoire. The refugee population has a high rate of non protected people, contrary to the Ivory population especially under 15 years old, because Côte d'Ivoire has included YF vaccine in his Expanded Programme on Immunization. A campaign of vaccination has been carried out.