Modes of transmission and genetic diversity of foamy viruses in a Macaca tonkeana colony

Abstract

Background: Foamy viruses are exogenous complex retroviruses that are highly endemic in several animal species, including monkeys and apes, where they cause persistent infection. Simian foamy viral (SFV) infection has been reported in few persons occupationally exposed to non-human primates (NHP) in zoos, primate centers and laboratories, and recently in few hunters from central Africa. Most of the epidemiological works performed among NHP populations concern cross-sectional studies without long-term follow-up. Therefore, the exact timing and the modes of transmission of SFVs remain not well known, although sexual and oral transmissions have been suspected. We have conducted a longitudinal study in a free-breeding colony of Macaca tonkeana in order (1) to determine the prevalence of the infection by foamy viruses, (2) to characterize molecularly the viruses infecting such animals, (3) to study their genetic variability overtime by long-term follow-up of several DNA samples in a series of specific animals, and (4) to get new insights concerning the timing and the modes of SFVs primary infection in these monkeys by combining serology and molecular means, as well as studies of familial structures and long-term behavioral observations.

Results/conclusion: We first demonstrated that this colony was highly endemic for SFVs, with a clear increase of seroprevalence with age. Only 4.7% of immatures, and 43,7% of sub-adults were found seropositive, while 89.5% of adults exhibited antibodies directed against SFV. We further showed that 6 different strains of foamy viruses (exhibiting a very low intra-strain and overtime genetic variability in the integrase gene) are circulating within this group. This suggests a possible infection by different strains within an animal. Lastly, we provide strong evidence that foamy viruses are mostly acquired through severe bites, mainly in sub-adults or young adults. Most cases of seroconversion occur after 7 years of age; from this age individuals competed for access to sexual partners, thus increasing the likelihood of being wounded. Furthermore, all the serological and molecular data, obtained in this free-breeding colony, argue against a significant transmission of SFVs from mother or father to infants as well as between siblings.

Figures

Figure 1

Comparative seroprevalence rates for foamy virus and HTLV-1/STLV-1 in the 56 animals of the colony. According to age at the last sampling, animals were classified in three groups corresponding to immatures (0–4 years old), subadults (5–8 years old) and adults (more than 8 years old).

Figure 2

Immunofluorescence and electron microscopy of SFV infected cells. A. Typical multinucleated giant cells with a clear seroreactivity of MtoT1 antigens, using an immunofluorescence assay with a positive anti-foamy serum, on BHK-21 infected cells. B. Electron microscopy of ultra-thin sections from cells infected by MtoTF2. The typical foamy viral particles showed a spherical central core and several envelope spikes. The budding observed here is from the cellular membrane

Figure 3

Semiquantitative PCR for SFV a) Study of integrase and the Beta globin genes in MtoT2 DNA. Lane 1–7 and 10–16: serial dilutions of the DNA from 500 ng to 0,5 pg. Lanes 8 and 17: negative controls. Lanes 9 and 18: positive controls. M: 100 bp ladder b) Study of LTR and Beta globin genes in MtoT4 DNA. Lane 1–7 and 10–16: serial dilutions of the DNA from 500 ng to 0,5 pg. Lanes 8 and 17: negative controls. Lanes 9 and 18: positive controls. M: 100 bp ladder

Figure 4

Phylogenetic tree generated on a 425 bp fragment of the integrase FV gene. The tree includes all of the 17 new macaca tonkeana FV described in this study and other FV sequences from African and Asian apes and monkeys available in GenBank. The phylogeny was generated with the Neighbor-joining method, performed in the PAUP program (v4.0b10). The sequence alignment was submitted to the Modeltest program (version 3.6) to select the best model to apply to phylogenetic analyses. The selected model was the GTR+G+I one. The reliability of the inferred tree was evaluated by bootstrap analysis on 1000 replicates. Numbers at each node indicate the percentage of bootstrap samples in which the cluster to the right is supported and only values greater than 60% are shown. The branch lengths are drawn to scale with the bar indicating 0.1 nucleotide replacement per site. The tree was rooted by using the New World spider monkey Asp(SFV8spm) sequence. *= SFVpfr: (Presbytis Francoisi): despite the Asian origin of this monkey, its sequence clusters within the large African Monkey clade.