Abstract
Simian immunodeficiency virus (SIVgor) causes persistent infection in critically endangered western lowland gorillas (Gorilla gorilla gorilla) from west central Africa. SIVgor is closely related to chimpanzee and human immunodeficiency viruses (SIVcpz and HIV‐1, respectively). We established a noninvasive method that does not interfere with gorillas' natural behaviour to provide wildlife pathogen surveillance and health monitoring for conservation. A total of 1,665 geo‐referenced fecal samples were collected at regular intervals from February 2006 to December 2014 (123 sampling days) in the Campo‐Ma'an National Park (southwest Cameroon). Host genotyping was performed using microsatellite markers, SIVgor infection was identified by serology and genetic amplification was attempted on seropositive individuals. We identified at least 125 distinct gorillas, 50 were resampled (observed 3.5 times in average) and 38 were SIVgor+ (seven individuals were seroconverters). Six groups of gorillas were identified based on the overlapping occurrence of individuals with apparent high rates of gene flow. We obtained SIVgor genetic sequences from 25 of 38 seropositive genotyped gorillas and showed that the virus follows exponential growth dynamics under a strict molecular clock. Different groups shared SIVgor lineages demonstrating intergroup viral spread and recapture of positive individuals illustrated intra‐host viral evolution. Relatedness and relationship genetic analysis of gorillas together with Bayesian phylogenetic inference of SIVgor provided evidence suggestive of vertical transmission. In conclusion, we provided insights into gorilla social dynamics and SIVgor evolution and emphasized the utility of noninvasive sampling to study wildlife health populations. These findings contribute to prospective planning for better monitoring and conservation.
Highlights
All the above instances represented the most suitable options to identify cases of SIVgor vertical transmission and we investigated if the corresponding viral strains matched in the phylogenetic trees
The present study provides new insights into the ecology of unhabituated gorillas from the Campo-Ma’an National Park and into SIVgor evolution
The long-term follow-up allowed us to document an individual over an a span of 10 years and to re-capture several other individuals providing room for further development of noninvasive sampling of free-ranging apes
Summary
Simian immunodeficiency viruses (SIVs) have been isolated from many wild African non-human primates species, each infected with a species-specific SIV (Locatelli & Peeters, 2012; Sharp & Hahn, 2011). We observed that sequences from individuals CPg-004 and CPg-005 (who frequently were observed together within group A) sampled in 2007 were distinct from those collected during 2011–2013 in the env tree This pattern could result from either a mixed infection or an exceptionally high viral substitution rate. In order to assess SIVgor transmission we opted for less stringent constraints—in the interindividual’s relatedness analysis—to include more pairs where both individuals were SIVgor positive and had SIVgor genetic data These constraints were as follows: the pairs that had a Wang estimate over the full siblings threshold (0.43 was the data-inferred relatedness-threshold for full siblings), the pairs that were discriminated as parent–offspring in the ML analysis and where the log likelihood of the individuals being unrelated was at least three times less than the log likelihood of the parent–offspring, and the pairs with a posterior probability below 0.5 in the Bayesian calculations. In these instances the mots likely scenario is the horizontal transmission of SIVgor
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