Origins of HIV and the AIDS Epidemic [Discussion Meeting (2000: London, England)]

considered to be one of the oldest ethnic population in Central Africa. Their susceptibility to HIV has been
demonstrated (Gonzalez JP 1987). They have been (and are still) frequently and directly exposed to nonhuman primate blood during hunting, slaughtering and cooking. They are generally isolated from the other
ethnic groups even though contacts with neighboring tribes are not unusual. Surprisingly, HIV/SIV infection
among pygmies has been rather rare or uncommon between the 80's and 90's (Brun-Vezinet F 1986;
Froment A 1986; Ndumbe PM 1993; Zekeng L 1995; Kowo MP 1995; Bikandou B 1996; Ndjomou J 1997).
In recent surveys carried out in selected areas in Cameroon, the HIV prevalence in this population group
seems to be increasing as a result of their contacts with neighboring bantus. The possibility of a more recent
introduction of HIV in this community should not be ruled out. Ongoing studies among highly exposed
individuals to SIVs and wild living primates might provide new information.
AIDS as a Zoonosis: Characterizing the Primate Reservoir
Professor Beatrice H Hahn
University of Alabama at Birmingham, USA
West-central African chimpanzees (Pan troglodytes troglodytes) are known to harbor divergent strains of
SlVcpz that are closely related to all three major variants of HIV-1 (groups M, N and 0), and have thus been
implicated as a primate reservoir for human infection. Whether chimpanzees in west or east Africa are also
infected with SlVcpz is not known, but this is of importance for elucidating the evolutionary origins of the
SlVcpz/HIV-1 group of viruses. We have developed a novel method for non-invasively screening wild
chimpanzees for SlVcpz antibodies and viral nucleic acids (vRNA) by analyzing fecal and urine samples. The
sensitivity of antibody detection was tested in captive chimpanzees of known HIV-1 or SlVcpz infection status
and found to be 100% for urine and 62% for feces. Specificity in each instance was 100%. The sensitivity
of PCR amplification of vRNA from feces of SlVcpz infected chimpanzees was 58%. Using these assays, we
tested 28 chimpanzees from two wild communities in west Africa (P.t.verus), and 30 chimpanzees from two
wild communities in east Africa (P.t.schweinfurthii). All of the west African chimpanzees tested negative for
SlVcpz antibodies and nucleic acids. However, one of 30 east African chimpanzees was strongly positive for
urine SlVcpz antibodies. This infected individual was one of six chimpanzees sampled from a larger
community. These data demonstrate the feasibility of screening wild chimpanzee populations using entirely
non-invasive means and represent the first detection of SlVcpz infection in the wild.
Phylogenetic estimates of the timing of most recent common ancestor in HIV-1 lineages.
Dr Bette Korber
Los Alamos National Laboratory, USA
In earlier work, HIV-1 sequences were analyzed to estimate the timing of the ancestral sequence of the main
group of HIV-1, the viruses that are responsible for the AIDS pandemic (Korber et al., Science 288:1789
2000). That work will be briefly reviewed, outlining how phylogenetic tools were extended to incorporate
improved evolutionary models, how the molecular clock model was adapted to incorporate variable latency,
and how the approach was validated by correctly estimating the timing of two historically documented
dates. The advantages, limitations, and assumptions of the approach will be summarized, with
considerations of the implications of branch length uncertainty and recombination. We have recently
undertaken phylogenetic analyses of an extremely diverse set of HIV sequences, from the former Zaire (now
the Democratic Republic of the Congo), collected by Dr. Martine Peeters and colleagues. Analyses of the
new data set both corroborates and extends the conclusions of our original study; for this data set it was also
appropriate to use coalescent methods for inference of the demographic history (Pybus et al., Genetics
155:1429 2000), and this analysis will also be discussed.