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  • Title: [Mechanisms of viral emergence and interspecies transmission: the exemple of simian foamy viruses in Central Africa].
    Author: Gessain A.
    Journal: Bull Acad Natl Med; 2013 Dec; 197(9):1655-67; discussion 1667-8. PubMed ID: 26137812.
    Abstract:
    A large proportion of viral pathogens that have emerged during the last decades in humans are considered to have originated from various animal species. This is well exemplified by several recent epidemics such as those of Nipah, Severe Acute Respiratory Syndrome, Avian flu, Ebola, Monkeypox, and Hantaviruses. After the initial interspecies transmission per se, the viruses can disseminate into the human population through various and distinct mechanisms. Some of them are well characterized and understood, thus allowing a certain level of risk control and prevention. Surprisingly and in contrast, the initial steps that lead to the emergence of several viruses, and of their associated diseases, remain still poorly understood. Epidemiological field studies conducted in certain specific high-risk populations are thus necessary to obtain new insights into the early events of this emergence process. Human infections by simian viruses represent increasing public health concerns. Indeed, by virtue of their genetic andphysiological similarities, non-human primates (NHPs) are considered to be likely the sources of viruses that can infect humans and thus may pose a significant threat to human population. This is well illustrated by retroviruses, which have the ability to cross species, adapt to a new host and sometimes spread within these new species. Sequence comparison and phylogenetic studies have thus clearly showed that the emergence of human immunodeficiency virus type 1 (HIV-1) and HIV-2 in humans have resulted from several independent interspecies transmissions of different SIV types from Chimpanzees and African monkeys (including sooty mangabeys), respectively, probably during the first part of the last century. The situation for Human T cell Lymphotropic virus type 1 (HTLV-1) is, for certain aspects, quite comparable. Indeed, the origin of most HTLV-1 subtypes appears to be linked to interspecies transmission between STLV-1-infected monkeys and humans, followed by variable periods of evolution in the human host. In this review, after an introduction on emerging viruses, we will briefly present the results of a large epidemiological study performed in groups of Bantus and Pygmies living in villages and settlements located in the rain forest of the South region of Cameroon. These populations are living nearby the habitats of several monkeys and apes, often naturally infected by different retroviruses including SIV, STLV and simianfoamy virus. Most of the persons included in this study were hunters of such NHPs, thus at high risk of contact with infected body fluids (blood, saliva,...) during hunting activities. After reviewing the current available data on the discovery, cross-species transmission from monkeys and apes to humans of the simian foamy retroviruses, we will report the results of our study. Such infection is a unique natural model to study the different mechanisms of restriction of retroviral emergence in Humans. La plupart des agents viraux pathogènes, ayant émergé durant les dernières décennies chez l’Homme, est d’origine animale (Coronavirus du SRAS, virus de la grippe aviaire, Hantavirus, virus Ebola, virus Marburg, virus Nipah, etc.). Après le contact initial qui a conduit à la transmission inter-espèces per se, ces virus, principalement à ARN, se sont ensuite, souvent adaptés à leur nouvel hôte par des mécanismes variés, puis ont disséminé dans l’espèce humaine par différentes voies. Alors que ces mécanismes évolutifs d’adaptation et ces voies de dissémination inter-humaine ont été largement étudiées, les connaissances concernant les premières étapes de l’émergence virale (comment, par quels moyens, dans quelles conditions, etc.) demeurent encore souvent rudimentaires. La veille microbiologique, associant des travaux épidémiologiques de terrain à des études sérologiques et viromoléculaires, dans des populations à haut risque de transmission inter-espèces, est donc nécessaire pour mieux comprendre les premières étapes de l’émergence virale. Les primates non-humains représentent une importante source potentielle d’agents infectieux transmissibles à l’Homme. Cela a été bien démontré pour les virus de l’immunodéficience simienne (SIV) et les rétrovirus T lymphotropes simiens (STLV). Nous présenterons ici les résultats d’enquêtes sérologiques et moléculaires, réalisées parmi des populations humaines du Sud-Cameroun, pour découvrir et caractériser de nouveaux rétrovirus chez l’Homme. Ces études multidisciplinaires, associant médecins, épidémiologistes, anthropologues et virologues, ont été menées dans des populations villageoises, soit d’origine Bantou, soit d’origine Pygmée, vivant dans la grande forêt équatoriale, dans des régions très proches des habitats des populations de primates non-humains, en particulier chimpanzés, gorilles, mandrills, cercopithèques, etc. La première étude concerne la découverte d’un nouveau rétrovirus humain ; l’HTLV-3, ainsi que sa caractérisation viro-moléculaire. La seconde étude, que nous détaillerons davantage dans cet article, concerne la mise en évidence de la transmission fréquente de rétrovirus foamy simiens aux Hommes, en particulier par des morsures de gorilles et de chimpanzés et la caractérisation des facteurs de risque de cette transmission.
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