Endemic Infection of Central Chimpanzees (Pan troglodytes troglodytes) by Simian Immunodeficiency Virus
Brandon Keele*1, F Heuverswyn2, Y Li1, E Bailes3, S Loul4, J Brookfield3, G Shaw1, P Sharp3, M Peeters2, and B Hahn1
1Univ of Alabama at Birmingham, US; 2Inst Res and Devt, Univ of Montpellier, France; 3Univ of Nottingham, UK; and 4Project Presica, Yaounde, Cameroon
immunodeficiency virus (SIV)cpz,
infects chimpanzees in west central Africa
(Pan troglodytes troglodytes), are the closest
relatives of all groups of HIV-1 (M, N, and O) and have thus been implicated as
the source of the human infection. However, despite testing of more than 2000
apes in captivity, a natural SIVcpz reservoir has never been
identified. Here, we report the first molecular epidemiological study of wild
chimpanzees in southern Cameroon using non-invasive (fecal-based) virus-specific
antibody and virion RNA detection methods as well as
host genetic (microsatellite) analyses.
Ape fecal samples (n = 615) were collected at forest sites (n = 11) throughout southern Cameroon and preserved in RNA later. Fecal
immunoglobulin was isolated and tested for the presence of HIV-1 cross-reactive
antibodies by enhanced chemiluminescence Western blot analysis. Partial (pol and gp41) and
full length SIVcpz sequences were amplified from fecal RNA by real-time
polymerase chain reaction (RT-PCR). Mitochondrial (D loop) and microsatellite
loci (D18S536, D4S243, D10S676. and D9S922) were amplified from fecal DNA for
subspecies and individual identification.
Of 429 P. t. troglodytes samples, 36 were SIVcpz
antibody or virion RNA positive, but none of 32 P. t. vellerosus samples were. Virus-positive
samples were identified at 5 collection sites, indicating a range of SIVcpz
prevalences from 0% to 35%. Phylogenetic
analysis of newly derived partial (pol and env, n = 33) and
full-length SIVcpz sequences (n = 4) confirmed infection with
divergent SIVcpzPtt, but
also revealed strict geographic clustering of locally circulating strains. From
southeastern and south Cameroon, respectively, 2 lineages comprising SIVcpz
formed sister clades immediately proximal to HIV-1
groups M and N.
is widely, but unevenly distributed among wild P. t. troglodytes (but not P.
t. vellerosus) apes in southern Cameroon, indicating an existing chimpanzee
reservoir. Circulating SIVcpz strains
exhibit extensive genetic diversity, but form geographically defined lineages,
likely reflecting P. t. troglodytes populations with non-overlapping habitats.
Two of these endemically infected populations gave rise HIV-1 groups M and N,
and may still serve as a source of human infection. The geographic origin of
group O remains to be identified.