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Category: Clinical Microbiology
Emergence of Novel Retroviruses, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815585/9781555813772_Chap08-1.gif /docserver/preview/fulltext/10.1128/9781555815585/9781555813772_Chap08-2.gifAbstract:
Retroviruses are a large and diverse group of enveloped RNA viruses in the family Retroviridae that replicate in a unique way, using a viral reverse transcriptase enzyme to transcribe the RNA genome into linear double-stranded DNA. Among viruses capable of causing zoonotic infections, defined for the purposes of this chapter as primary infections resulting from direct animal exposure, only some are capable of secondary spread. The approach advocated focuses on the study of individuals who are highly exposed to the blood and body fluids of primates, either through contact in laboratories and primate centers or through the hunting and butchering of wild non-human primate (NHP) game, and the detailed follow-up of individuals with zoonotic infections and their contacts for evidence of secondary transmission. The gorilla simian foamy virus (SFV)-infected persons in this study reported having received significant bite wounds from gorillas. Researchers have recently examined the diversity of human T-lymphotropic viruses (HTLVs) among primate bushmeat hunters in Cameroon who had documented SFV infections and who thus may be at risk for infection with additional simian retroviruses. Three new retroviruses previously undocumented in humans, including the simian foamy viruses, HTLV-3, and HTLV-4, have all been identified in persons exposed to the blood and body fluids of NHPs.
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Diagram representing the process of viral emergence. Step 1 (bottom) is primary infection or successful cross-species transmission from the wild-animal reservoir to humans. Step 2 is local secondary transmission between humans, leading to regional spread. Step 3 is pandemic spread from a regional epidemic into the global population. Examples of various zoonotic infections, including simian retroviruses, are shown, with arrows indicating the level of transmission at each step (represented by horizontal dashed lines).
SFVs found in occupationally and naturally exposed persons. Shown is the phylogenetic analysis of SFV polymerase (pol) sequences derived from peripheral blood lymphocytes by PCR and sequence analysis described in detail elsewhere ( 50 , 59 ). Zoonotic human infections with SFVs are shown in bold italics, with CAM indicating those from Cameroon. The numbers shown at branch nodes represent bootstrap percentages from 1,000 replicates; only values greater than 70% are shown. Branch lengths are proportional to the evolutionary distances (scale bar) between the taxa. The primate taxonomic nomenclature used here is defined elsewhere ( 21 ). NHPs were coded by using the first letter of the genus and the first two letters of the species names, with their house names or codes within parentheses. Asterisks indicate NHPs native to Cameroon. Cmo, Cercopithecus mona (mona monkey); Cal, Cercopithecus albogularis (Sykes monkey); Cce, Cercopithecus cephus (red-eared guenon); Cpy, Chlorocebus pygerythrus (vervet); Clh, Cercopithecus lhoesti (L’Hoest’s monkey); Cne, Cercopithecus neglectus (De Brazza’s guenon); Lal, Lophocebus albigena (grey-cheeked mangabey); Pcy, Papio cynocephalus (yellow baboon); Pan, Papio anubis (olive baboon); Cto, Cercocebus torquatus (red-capped mangabey); Cag, Cercocebus agilis (agile mangabey); Mta, Miopithecus talapoin (talapoin monkey); Mle, Mandrillus leucophaeus (drill); Msp, Mandrillus sphinx (mandrill); Cgu, Colobus guereza (mantled guereza); Mmu, Macaca mullata (rhesus macaque); Mcy, Macaca cyclopsis (Formosan rock macaque); Ppy, Pongo pygmaeus (Bornean orangutan); Hpi, Hylobates pileatus (pileated gibbon); Ggo, Gorilla gorilla (Western lowland gorilla); Ppn, Pan paniscus (bonobo); Psc, Pan troglodytes schweinfurthii (East African chimpanzee); Pvl, Pan troglodytes vellerosus (Nigerian chimpanzee); Ptr, Pan troglodytes troglodytes (Central African chimpanzee); Pvr, Pan troglodytes verus (West African chimpanzee); Asp, Ateles sp. (spider monkey).
Identification of HTLV-3 and HTLV-4, two novel human viruses. Shown are the phylogenetic relationships of HTLV and STLV polymerase (pol) sequences (614 bp) by neighbor-joining analysis as described in detail elsewhere ( 57 ). The sequences of the new HTLV-3 and HTLV-4 viruses are shown in boxes. Support for the branching order was determined by 1,000 bootstrap replicates; only values of 60% or more are shown. Branch lengths are proportional to the evolutionary distances (scale bar) between the taxa.