J.F. Saluzzo

Rift Valley fever on the east coast of Madagascar.

In March 1990, a Rift Valley fever virus (RVFV) outbreak was suspected in the district of Fenerive on the east coast of Madagascar after an abnormally high incidence of abortions and disease in livestock. Sera from humans and cattle were tested for RVFV antibodies by immunofluorescence assay (IFA) and ELISA-IgM capture. Sera and mosquitoes collected in the same area were tested for virus isolation by tissue culture and suckling mouse intracerebral inoculation, and for antigen detection by an ELISA antigen capture assay. Among cattle from the area, RVFV antibody prevalence was 58.6% by IFA and 29.6% by ELISA-IgM. In contrast, human populations in the same area had a lower RVFV antibody prevalence, with 8.01% IFA and 5.4% IgM-positive sera. No RVFV antigen was detected and virus isolation was unsuccessful from the sera and mosquito pools tested. Different hypotheses concerning the emergence and diffusion of RVFV in this area and the occurrence of the outbreak are discussed.

Isolation of dengue 2 and dengue 4 viruses from patients in Senegal

Dengue 2 and dengue 4 viruses were isolated and re-isolated by inoculation into Aedes pseudoscutellaris continuous cell line (Mos 61) and/or Toxrhynchites brevipalpis. The strain of dengue 2 had been isolated from a patient returning from Casamance (south-western Senegal) and two strains of dengue 4 from patients who lived in Dakar and had not been outside the town in the 15 days before becoming ill. Serological evidence of dengue 4 infection was found in another patient living in Casamance.

Premier isolement du virus Mokola à partir d'un rongeur (Lophuromys sikapusi)

Summary An isolate of Mokola virus (AnRB3247) was obtained from the brain of a wild rodent Lophuromys sikapusi caught in the Central African Republic. This was the first isolation of Mokola virus from a rodent and the first isolation of this virus in the Central African Republic. This isolate was identified with Mokola virus by complement fixation and seroneutralization tests. The antigenic pattern of this isolate was determined with a panel of monoclonal antibodies, and was compared to those of Mokola isolates from Nigeria and Cameroun, of Lagos bat virus and of Duvenhage virus.

Intérêt du titrage par ELISA des IgM spécifiques pour le diagnostic et la surveillance de la circulation selvatique des flavivirus en Afrique

Summary The complement-fixation (CF) test and IgM antibody-capture enzymelinked immunosorbent assay (ELISA) were compared for the serological diagnosis of medically important flavivirus infections in Africa. The specificity and kinetics of antibody development were studied using serum specimens from humans during investigation of the 1983 yellow fever epidemic in Burkina Faso, from monkeys and young children in eastern Senegal, and from persons with clinical flavivirus infections. IgM antibodies detected by ELISA showed complete specificity in cases of yellow fever, Zika and Wesselsbron infection, whereas extensive crossreactions were noted by ELISA in dengue infections and by the CF test in the case of all flaviviruses. The combined use of end-point IgM ELISA and virus isolation permitted a specific diagnosis in all cases of yellow fever studied during the epidemic in Burkina Faso. These techniques thus provided a means of rapid diagnosis using a single serum sample, and should be applied in programs of surveillance and epidemic investigation. The persistence of IgM antibodies to yellow fever and Zika is relatively brief (1–3 months). Tests on a small number of cases of dengue 2 and 4 also indicated the brief duration of specific IgM compared to CF antibodies. The IgM ELISA has also been applied to the surveillance of sylvatic flavivirus transmission in eastern Senegal. With the successive isolation of yellow fever and Zika viruses in two years, the sensitivity and limits of the serological technique have been elucidated. The best approach for detection of flavivirus transmission is timely serological surveillance of young children; a minimum of one survey should be conducted at the end of the rainy season. Moreover, routine surveillance of wild monkeys for specific IgM antibodies allows early detection of flavivirus activity. This approach is especially useful for the planning and initiation of field studies to assess the occurrence of clinical infections, particularly those due to dengue virus. Two techniques for measurement of IgM antibodies by ELISA were compared. The indirect assay using peroxidase appears to be the most sensitive.

Comparaison de différentes techniquespour la détection du virus de la fièvre jaune dans les prélèvements humains et les lots de moustiques: Intérêt d'une méthode rapide de diagnostic par ELISA

Summary During the 1983 yellow fever (YF) epidemic in Burkina Faso (formerly Upper Volta), blood samples and liver specimens from patients and mosquito pools were collected. Five methods for the isolation or detection of the YF virus were used and compared. These methods included intracerebral inoculation of the newborn mouse, inoculation of mosquito cell lines (Aedes pseudoscutellaris Mos-61 and Ae. aegypti C20), intrathoracic inoculation of the mosquito Toxorhynchites brevipalpis and an ELISA method for the detection of YF antigen. From 17 blood samples, 5 strains of YF virus were isolated. Furthermore, the detection of IgM antibody by ELISA allowed us to diagnose YF infection in 10 patients tested. From 13 liver specimens, 11 YF strains were isolated. Twenty-six YF strains were isolated from 121 mosquito pools: 25 from Ae. furcifer and 1 from Ae. metallicus. The Ae. pseudoscutellaris cell line (Mos-61) has the advantage of sensitivity and a relatively short—3 to 6 days—delay when virus identification was performed using a monoclonal antibody. Antigen capture ELISA was positive for 11 human specimens (16 strains isolated) but YF antigen was detected only four times in mosquito pools (26 strains isolated). The rapidity with which the test can be performed provides clinical relevance to the diagnosis of infection with YF virus. This procedure can also be applied when the specimens are stored in unfavourable conditions. The studies demonstrate that antigen detection by ELISA or the IgM capture ELISA could be useful for the rapid diagnosis of YF infection. During this study, one strain of Crimean-Congo haemorrhagic fever(CCHF) was also isolated from the blood of a patient who presented with haemorrhagic syndrome and jaundice. The CCHF virus was isolated by inoculation into newborn mice. This isolation raises the question of the handling of specimens collected from patients with haemorrhagic fever. Inactivation of the virus in the sera and detection of antigen or IgM by ELISA is considered.

Le virus pétévo, un nouvel arbovirus du groupe palyam isolé en république centrafricaine à partir de la tique Amblyomma variegatum

Summary A new arbovirus, Petevo virus (ArTB-2032) has been isolated from a pool of 20 male Amblyomma variegatum collected from cattle at the slaughterhouses in Bangui. Chemical properties of Petevo virus, especially its resistance to lipid solvents and sensitivity to pH 3.0 were identical to that of orbiviruses. Its group relation was established by complement fixation tests with other viruses of the Palyam group. Its distinctness from other Palyam group viruses was determined by neutralization test. This isolation extends the distribution of Palyam group viruses to Africa. For the first time a tick appears as vector of a Palyam group virus. Neutralizing antibodies were found in cattle sera but not in 69 human sera tested.

Étude écologique du virus Orungo en Afrique Centrale

Summary Orungo virus was isolated in the Central African Republic from Culex perfuscus group, Anopheles gambiae, Aedes africanus and A. opok . An epizootic was shown to have occurrel during the 1978 rainy season. The virus was isolated on several occasions from pools of A. africanus and A. opok mosquitoes collected inside a forest-gallery near the village of Bozo, in the semi-humid savannah belt bordering the Congolese forest block. In addition to the virus isolations, sentinel-monkeys exhibited serological conversions. These observations suggest a sylvatic cycle for Orungo virus. Studies on the geographic distribution of antibodies in the human population from Gabon, Cameroon and the Central African Republic using the complement fixation test, showed d widespread distribution of Orungo virus in Central Africa. Antibodies were frequently found in the sera of monkeys. These data confirm the part played by monkeys in the ecology of Orungo virus. Antibodies were also demonstrated in rabbit serum samples, but were not present in a small number of tested sera from cattle, guineapigs, dogs, birds and rodents. Two serological conversions were observed in patients with fever and headache. The detection of Orungo virus over four consecutive years inside the same forest-gallery poses an interesting question as to the persistence of arboviruses in a given phytogeographical zone. The existence of different serotypes for Orungo virus is discussed.

Le virus Bozo (ArB 7343) : un nouvel arbovirus du groupe Bunyamwera isolé en République Centrafricaine; sa transmission expérimentale par Aedes aegypti

Summary Bozo virus (ArB 7343), a new arbovirus, was isolated in 1975 from a pool of 100 Aedes opok collected near the village of Bozo in a forest-gallery of semi-humid savannahs in the south of Central African Republic. Its group relation was established by complement fixation test within the Bunyamwera group; its distinctness from other Bunyamwera viruses was determined by neutralisation test. Subsequently 55 strains were isolated from Aedes gr. africanus (52 strains) Culex pruina (2 strains) and Anopheles funestus (1 strain). Transmission of Bozo in suckling mice by orally infected A. aegypti was demonstrated. Virological and serological studies in the Bozo region established the existence of a selvatic cycle for Bozo virus in which principally Aedes gr. africanus and monkeys occur. The support mechanism which maintains the Bozo virus in the gallery-forests is discussed.

Intérêt de la technique d'inoculation intrathoracique à Aedes aegypti dans l'isolement et le réisolement des arbovirus

Summary Direct intrathoracic inoculation of Aedes aegypti with wild Central Africa mosquito pools was used for primary multiplication of viruses. The systematic use of this method permitted the isolation of 4 yellow fever strains in December 1978. The virus titration during the isolation exhibited a minimal increase of 3 log 10 DL 50 with this technique as compared to direct inoculation of suckling mice. The strains studied belonged to yellow fever, Zika, West-Nile, Orungo, Chikungunya and Bunyamwera serogroup viruses.

Isolements du virus de la fièvre jaune à partir de moustiques du groupe Aedes (Stegomyia) Africanus (theobald) en République Centrafricaine au cours de l'année 1978

Summary Ten strains of yellow fever virus were isolated during the year 1978, from 24 977 Aedes africanus and A. opok alloted in 906 pools, collected in the field station of Bozo (Central African Republic). Eight strains were isolated using direct inoculation into suckling mice; two more were obtained by multiplication in A. aegypti before inoculation into suckling mice. This method was used for reisolation of strains. Its interest is discussed. The present report describes the virological and immunological properties of this strains. The average survival time (5 days) is the same as that of all yellow fever viruses isolated in Central Africa.