Eric Leroy

Ebola and Marburg haemorrhagic fever viruses: major scientific advances, but a relatively minor public health threat for Africa

Ebola and Marburg viruses are the only members of the Filoviridae family (order Mononegavirales), a group of viruses characterized by a linear, non-segmented, single-strand negative RNA genome. They are among the most virulent pathogens for humans and great apes, causing acute haemorrhagic fever and death within a matter of days. Since their discovery 50 years ago, filoviruses have caused only a few outbreaks, with 2317 clinical cases and 1671 confirmed deaths, which is negligible compared with the devastation caused by malnutrition and other infectious diseases prevalent in Africa (malaria, cholera, AIDS, dengue, tuberculosis …). Yet considerable human and financial resourses have been devoted to research on these viruses during the past two decades, partly because of their potential use as bioweapons. As a result, our understanding of the ecology, host interactions, and control of these viruses has improved considerably.

A limited outbreak of Ebola haemorrhagic fever in Etoumbi, Republic of Congo, 2005

Ebolavirus has caused highly lethal outbreaks of haemorrhagic fever in the Congo basin. The 2005 outbreak in the Republic of Congo occurred in the Etoumbi district of Cuvette Ouest Department between April and May. The two index cases were infected while poaching. The sanitary response consisted of active surveillance and contact tracing, public awareness campaigns and community mobilization, case management and safe burial practices, and laboratory confirmation. Twelve cases and ten deaths were reported (lethality 83%). A transmission tree was constructed from a sample collected by a medical team. This outbreak was remarkable by its short duration and limited size. Increased awareness among these previously affected populations and the rapid response of the healthcare system probably contributed to its extinction.

Prevalence of Plasmodium falciparum infection in asymptomatic rural Gabonese populations

BackgroundMalaria may be perennial or epidemic in sub-Saharan Africa, and its transmission may be stable or unstable, depending on the region. The prevalence of asymptomatic Plasmodium falciparum carriage is poorly documented in Gabon. A large survey of P. falciparum infection was conducted in asymptomatic individuals living in rural Gabon.MethodsTwo hundred and twenty-two villages were randomly selected in the nine administrative regions. With the participants informed consent, blood samples were collected for thick and thin blood film examination after 20% Giemsa staining. Prevalence rates were calculated per village, per region and per ecosystem, and nationwide. Demographic risk factors were identified with STATA software version 9.0. Significance was assumed at p < 0.05.Results and discussionThe prevalence of P. falciparum in adults was 6.2% (269/4342) nationwide, with a maximum of 37.2% in one village; a linear decrease was observed with increasing age (p = 0.045). Only 5% of the 399 children from forest areas tested positive. The prevalence was significantly higher in forest areas (7%) than in savannah (4%) and lakeland (2.5%). Within the forest region, the prevalence was significantly higher in forest grassland (10.9%) than in the mountain forest (3.5%), interior forest (6.8%) and north-eastern forest (4.5%).ConclusionPlasmodium falciparum carriage remains high among adults in rural Gabon. Control measures must be adapted to the region and ecosystem. Routine treatment of asymptomatic individuals should be considered.

New STLV-3 strains and a divergent SIVmus strain identified in non-human primate bushmeat in Gabon

BackgroundHuman retroviral infections such as Human Immunodeficiency Virus (HIV) or Human T-cell Lymphotropic Virus (HTLV) are the result of simian zoonotic transmissions through handling and butchering of Non-Human Primates (NHP) or by close contact with pet animals. Recent studies on retroviral infections in NHP bushmeat allowed for the identification of numerous Simian Immunodeficiency Viruses (SIV) and Simian T-cell Lymphotropic Viruses (STLV) to which humans are exposed. Nevertheless, today, data on simian retroviruses at the primate/hunter interface remain scarce. We conducted a pilot study on 63 blood and/or tissues samples derived from NHP bushmeat seized by the competent authorities in different locations across the country.ResultsSIV and STLV were detected by antibodies to HIV and HTLV antigens, and PCRs were performed on samples with an HIV or/and HTLV-like or indeterminate profile. Fourteen percent of the samples cross-reacted with HIV antigens and 44% with HTLV antigens. We reported STLV-1 infections in five of the seven species tested. STLV-3 infections, including a new STLV-3 subtype, STLV-1 and -3 co-infections, and triple SIV, STLV-1, STLV-3 infections were observed in red-capped mangabeys (C.torquatus). We confirmed SIV infections by PCR and sequence analyses in mandrills, red-capped mangabeys and showed that mustached monkeys in Gabon are infected with a new SIV strain basal to the SIVgsn/mus/mon lineage that did not fall into the previously described SIVmus lineages reported from the corresponding species in Cameroon. The same monkey (sub)species can thus be carrier of, at least, three distinct SIVs. Overall, the minimal prevalence observed for both STLV and SIV natural infections were 26.9% and 11.1% respectively.ConclusionsOverall, these data, obtained from a restricted sampling, highlight the need for further studies on simian retroviruses in sub-Saharan Africa to better understand their evolutionary history and to document SIV strains to which humans are exposed. We also show that within one species, a high genetic diversity may exist for SIVs and STLVs and observe a high genetic diversity in the SIVgsn/mon/mus lineage, ancestor of HIV-1/SIVcpz/SIVgor.