Lassa fever in Guinea: II. Distribution and prevalence of Lassa virus infection in small mammals.

Rodents of the genus Mastomys form the reservoir for Lassa virus (LV), an arenavirus that causes a potentially severe hemorrhagic illness, Lassa fever (LF). Although Mastomys rodents exist throughout sub-Saharan Africa, areas of human LF appear to be quite focal. The distribution of small mammals and LV-infected Mastomys has been assessed in only a few countries. We conducted a survey of small mammals in selected regions of Guinea to assess the degree to which LV poses a public health risk in that country. A total of 1,616 small mammals, including 956 (59%) Mastomys, were captured from 444 households and seven bush sites. Mastomys made up > 90% of the captured animals in the savannah, savannah-forest transition, and forest regions of Guinea, while Mus musculus dominated in coastal and urban sites. Animals were analyzed via enzyme-linked immunosorbent assay (ELISA) for LV-specific antigen (blood and spleen homogenate) and IgG antibody (blood only). Virus isolation from spleen homogenates was also performed on a subset of animals. Lassa antibody and antigen were found in 96 (11%) and 46 (5%), respectively, of 884 tested Mastomys. Antibody and antigen were essentially mutually exclusive and showed profiles consistent with vertical transmission of both LV and antibody. LV was isolated only from Mastomys. ELISA antigen constituted an acceptable surrogate for virus isolation, with a sensitivity and specificity when performed on blood of 78% (95% confidence interval: 68-83%) and 98% (95-99%), respectively. The proportion of LV-infected Mastomys per region ranged from 0 to 9% and was highest in the savannah and forest zones. The proportion of infected animals per village varied considerably, even between villages in close proximity. Infected animals tended to cluster in relatively few houses, suggesting the existence of focal "hot spots" of LV-infected Mastomys that may account for the observed heterogeneous distribution of LF.

Persistent measles virus infection in vero and McCoy cell lines.

Persistent measles virus infection was established in two cell lines: Vero and McCoy. Vero cells were infected with a virus that had been propagated five times from an undiluted inoculum. Measles virus infection of McCoy cells caused no cytopathic lesions but led to the establishment of persistent infection. Haemadsorption (HA) and immunofluorescence (IF) results indicated that the majority of Vero and McCoy cells carried measles virus antigen localized in the cell membranes. Both cell lines released infectious virus into the medium. In Vero cells, the virus yield diminished with the number of cell passages. Our results suggest that the presence of defective interfering particles in Vero cells and an antiviral factor in the supernatant of McCoy cells contributed to the maintenance of persistent infection.

[Vaccination against measles at 6 months of age]. / Etude de la vaccination contre la rougeole a six mois.

Measles immunization with the Edmonston Zagreb stain was carried out in 71 six-month-old infants. Proportions of subjects with immunity were 91% among the 47 subjects retested before one year of age and 100% among the 28 subjects retested between two and three years of age. These results support the WHO recommendation that measles immunization should be given at the age of six months. The concerns expressed by some about possible adverse effects of early measles immunization (decreased immune defenses) are discussed, as well as the transfer of maternal antibodies and persistence of these antibodies in the child. The obstacles to such studies in developing countries, including the need for repeated phlebotomies with centrifugation of specimens and freezing of sera, could be circumvented by the use of filter paper dried blood spot samples which seem to provide reliable results although with values somewhat lower than those found in frozen sera.

Evidence for high genetic diversity and long-term endemicity of hepatitis C virus genotypes 1 and 2 in West Africa.

During 1994 and 1995, the prevalence of hepatitis C virus (HCV) and its genotypes were studied in several rural and urban populations in three West African countries: Guinea, Burkina Faso, and Benin. The following groups were screened for antibodies to HCV (anti-HCV): 459 villagers in the forest region of Guinea; 965 individuals in urban, suburban, and rural populations of the Bobo Dioulasso area, Burkina Faso; and 582 blood donors in Cotonou, Benin. In Benin, 60 patients with sickle cell anemia (30 with and 30 without history of multiple transfusion) and 13 hospital patients with liver disease were also tested. RT-PCR detection of HCV-RNA was carried out on all anti-HCV positive samples, followed by genotyping and sequencing of unrecognized subtypes. The prevalence rates of anti-HCV were 1.1% in the Guinean population group, 1.4% among blood donors in Benin, and 4.9% in residents of Burkina Faso. In patients with sickle cell anemia, five of the 30 polytranfused patients (17%) had anti-HCV, whereas none of the patients without a history of blood transfusion had anti-HCV (P < 0.05). Among the 13 patients with liver disease, five had anti-HCV, of whom four had history of blood transfusion. HCV-RNA was detected in 41 anti-HCV positive sera. All belonged to genotypes 1 or 2, with a high genomic diversity; 18 different subtypes were identified, including 2c, 2d, and 16 new subtypes. Such genetic diversity poses a challenge for vaccine development and also implies that HCV infection is long-established in these West African regions.