J.P. Digoutte

Electron microscopic and antigenic studies of uncharacterized viruses. II. Evidence suggesting the placement of viruses in the family Bunyaviridae

SummaryThis is the second of three papers describing the use of electron microscopy and antigenic analyses intended to characterize and place in taxa more than 60 previously unclassified viruses. The first paper of the series describes the viruses we classified as provisional members of the familiesArenaviridae, Paramyxoviridae, orPoxviridae; another paper, published separately, discusses theRhabdoviridae. In this paper we report that electron microscopy provided sufficient evidence to place 17 of these viruses (Belem, Erve, Estero Real, Mojui dos Campos, Nyando, Odrenisrou, Okola, Pacora, Para, Santarem, Tanga, Telok Forest, Termeil, Thiafora, Thottapalayam, Wanowrie, and Yacaaba) in the familyBunyaviridae and to support the observations of others that Yogue and Kasokero viruses are members of this virus family. Subsequent antigenic studies allowed us to place some of these viruses in recognized antigenic groups and to establish new antigenic groups for others.

Rift valley fever among domestic animals in the recent west African outbreak

Severe haemorrhagic disease among the human population of the Senegal River Basin brought the Rift Valley fever virus (RVFV) outbreak of 1987 to the attention of science. As in previous RVFV outbreaks, local herdsmen reported a high incidence of abortion and disease in their livestock. Serum samples were obtained from domestic animal populations from areas near Rosso, the best studied focus of human infection, as well as other areas distant from known human disease. Among animals from the area of high incidence of human disease, antibody prevalence was as high as 85%, with approximately 80% of the sera positive for both RVFV IgG- and viral-specific IgM antibodies. In contrast, human populations in the same area had lower RVFV antibody prevalences, 40% or less, with 90% also being IgM-positive. Sera from livestock in coastal areas 280 km south of the epidemic area were negative for RVFV antibodies. Thus, the detection of RVFV specific IgG and IgM antibodies provided evidence of recent disease activity without the requirement to establish pre-disease antibody levels in populations or individuals and without viral isolation. Subsequently, detection of modest levels of IgG and IgM in the Ferlo region, 130 km south of the Senegal River flood plain, established that RVFV transmission also occurred in another area of the basin. Similar serological testing of domestic ungulates in The Gambia, 340 km south of Rosso, demonstrated antibody prevalence consistent with a lower level of recent transmission of RVFV, i.e., 24% IgG-positive with 6% of the positive sera also having RVFV-specific IgM.

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.

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.

Rapid diagnosis of Rift Valley fever: a comparison of methods for the direct detection of viral antigen in human sera.

Human sera collected during the 1987 Rift Valley fever (RVF) epidemic in the Senegal River basin were analysed using three enzyme immunoassays to establish the best method for rapid diagnosis of RVF. A biotin-avidin-enhanced antigen detection method utilizing monoclonal antibodies proved most sensitive. Eighty-two viremic human sera were tested, and this assay detected antigen in 29.3% of the samples.

Isolement de 96 souches de virus dengue 2 à partir de moustiques capturés en cote-d'ivoire et Haute-Volta

Summary The authors give some historical data and the geographical distribution of dengue fever in Africa. They describe circumstances in which they isolated 96 strains of dengue 2 virus from wild mosquitoes collected in Ivory Coast and Upper Volta, during the dry or semi-humid savanna from May to November, 1980. Aedes luteocephalus and Aedes furcifer/taylori were the two main species from which the virus was isolated by the classical inoculation technique in newborn mice. Identification was carried out by haemagglutination inhibition and complement fixation tests, and further characterization was performed by the immunofluorescence test with monoclonal specific antibodies, at the WHO Collaborating Center for Arboviruses Reference and Research in Dakar. Epidemiological serosurveys carried out in Ivory Coast after the finding of the epizootic showed the absence of human infection. Possible animal reservoirs, such as monkeys, have not yet been studied. The isolation of virus from one pool of male mosquitoes, A. furcifer/taylori, could at least partially explain the maintenance of the virus in wilderness areas.

Antigenic and biological properties of Rift Valley fever virus isolated during the 1987 Mauritanian epidemic.

The antigenic and biological properties of three strains of Rift Valley fever virus (RVFV) isolated during the 1987 epidemic in Mauritania were compared with those of strains isolated previously in West Africa and with other selected African strains. Neither the antigenic characteristics of the Mauritanian isolates, as monitored by the binding of 59 monoclonal antibodies, nor the electrophoretic migration of the virus-specific structural and non-structural proteins were significantly different from other strains of RVFV isolated in this region or elsewhere in sub-Saharan Africa. Biological and antigenic traits which distinguished the strains isolated from the 1977 Egyptian epidemic were not associated with the Mauritanian isolates.

Characterization of the Palyam Serogroup Viruses (Reoviridae: Orbivirus)

31 Palyam serogroup viruses were examined by complement-fixation and plaque-reduction neutralization tests and by PAGE of the segmented, double-stranded (ds) RNA genome. Although the viruses were indistinguishable by complement-fixation tests, 10 distinct virus serotypes were identified by plaque-reduction neutralization methods. Palyam group viruses which were distinct by the neutralization test had unique dsRNA profiles, whereas those agents which were indistinct by the neutralization test had identical dsRNA profiles. 20 isolations of 3 Palyam serotypes were made from bovines and Culicoides midges in Australia over a 9-year period. When the genome of these isolates was examined electrophoretically, the dsRNA profiles of virus isolates within a given serotype were identical.

Comparative immunochemical and biological analysis of African and South American yellow fever viruses

SummaryFour geographic variants (topotypes) of yellow fever (YF) virus from Africa and South America previously determined by RNA oligonucleotide mapping were analyzed for their structural, antigenic and virulence characteristics. The electrophoretic migration mobility and carbohydrate content of the envelope protein E characterized YF virus strains of South America. The NS 1 protein of South American and Central African YF virus strains was not precipitated by anti-NS 1 monoclonal antibodies (MAB) that precipitated NS 1 of West African strains. No distinction could be made among the YF virus strains on the basis of the neutralizing capacity of available MAB. South American, but not African YF virus strains were virulent for 8-day-old mice upon intraperitoneal inoculation. The results permitted characterization of topotypes of Central Africa and South America but failed to differentiate YF strains from West Africa.

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.