Viral latency in blood and saliva of simian foamy virus-infected humans

Abstract

Simian foamy viruses (SFV) are widespread retroviruses among non-human primates (NHP). SFV actively replicate in the oral cavity and can be transmitted to humans through NHP bites, giving rise to a persistent infection. We aimed at studying the natural history of SFV infection in human. We have analyzed viral load and gene expression in 14 hunters from Cameroon previously shown to be infected with a gorilla SFV strain. Viral DNA could be detected by quantitative polymerase chain reaction (q-PCR) targeting the pol-in region, in most samples of peripheral blood mononuclear cells (PBMCs) (7.1 ± 6.0 SFV DNA copies/105 PBMCs) and saliva (2.4 ± 4.3 SFV DNA copies/105 cells) derived from the hunters. However, quantitative real-time reverse-transcription polymerase chain reaction (RT)-qPCR revealed the absence of SFV viral gene expression in both PBMCs and saliva, suggesting that SFV was latent in the human samples. Our study demonstrates that a latent infection can occur in humans and persist for years, both in PBMCs and saliva. Such a scenario may contribute to the putative lack of secondary human-to-human transmissions of SFV.

Figure 1. Detection and quantification of Simian Foamy Virus (SFV) DNA in samples of PBMCs and saliva derived from 14 humans infected by a gorilla strain of SFV.

Detection of SFV DNA: Presence (+) or absence (-) of SFV DNA in PBMCs and saliva samples of each individual are indicated, based on nested-PCR results. Quantification of SFV DNA: Blue and red bars represent mean SFV DNA levels from at least two independent assays run in duplicate in PBMCs and saliva samples, for each individual respectively. Viral loads were normalized to cell equivalents by q-PCR for albumin. Error bars represent the standard deviations from an individual participant. Mean of SFV DNA copies in PBMCs (blue) and saliva (red) of the 14 individuals are shown by the dotted lines.

Figure 2. Phylogenetic tree generated with sequences of 425 bp fragments of the SFV pol-in from blood and saliva of SFV-infected hunters BAK132, BAK177, BAD456 and LOBAK2 and different gorillas

Sequences from hunters BAK132 (A), BAK177 (B), BAD456 (C) and LOBAK2 (D) are indicated in red (saliva clones, "S") and blue (PBMC clones, "P"). Sequences are compared to 8 sequences available in Genbank from different central African NHP gorillas (green). Alignment was performed with the Dambe version 4.5.68 and Clustal W. Phylogenetic analysis was performed with PAUP, version 4.0b10 (Sinauer Associates, Sunderland, MA, USA) based on the Neighbor joining method applying the best model calculated by AIC: HKY (BAK132, BAK177), GTR (BAD456) or TrN (LOBAK2). Bootstrap analysis of 1000 replicates is shown as percentage at nodes. Only values greater than 50% are shown. The scale of the tree is 0.01 nucleotides replacement per site. Of note, phylogenetic tree for BAK132 is representative of trees obtained for the other following hunters (BAK33, BAK74, BAK132, BAD447). Sequences accession numbers for BAK132 SFV clones are KF515432-KF515469. Phylogenetic tree for BAK177 indicates the presence of two distinct groups of SFV clones, suggesting a co-infection with two SFV strains. Sequences accession numbers for BAK177 SFV clones are KC602165 to KC602200. For BAD456 and LOBAK2, some clones displayed G to A mutations (G->A) present in a GG dinucleotide context and absent in the 8 NHP gorillas strains. Sequences accession numbers of SFV clones are KC602201 to KC602238 (BAD456) and KC602129 to KC602164 (LOBAK2). Due to very low viral loads, a single cluster of SFV clones within one compartment (PBMCs or saliva) might derive from PCR amplification of a single SFV copy.