High Rate of Simian Immunodeficiency Virus (SIV) Infections in Wild Chimpanzees in Northeastern Gabon

The emergence of HIV-1 groups M, N, O, and P is the result of four independent cross-species transmissions between chimpanzees (cpz) and gorillas (gor) from central/south Cameroon and humans respectively. Although the first two SIVcpz were identified in wild-born captive chimpanzees in Gabon in 1989, no study has been conducted so far in wild chimpanzees in Gabon. To document the SIVcpz infection rate, genetic diversity, and routes of virus transmission, we analyzed 1458 faecal samples collected in 16 different locations across the country, and we conducted follow-up missions in two of them. We found 380 SIV antibody positive samples in 6 different locations in the north and northeast. We determined the number of individuals collected by microsatellite analysis and obtained an adjusted SIV prevalence of 39.45%. We performed parental analysis to investigate viral spread between and within communities and found that SIVs were epidemiologically linked and were transmitted by both horizontal and vertical routes. We amplified pol and gp41 fragments and obtained 57 new SIVcpzPtt strains from three sites. All strains, but one, clustered together within a specific phylogeographic clade. Given that these SIV positive samples have been collected nearby villages and that humans continue to encroach in ape's territories, the emergence of a new HIV in this area needs to be considered.

Simian immunodeficiency virus types 1 and 2 (SIV mnd 1 and 2) have different pathogenic potentials in rhesus macaques upon experimental cross-species transmission

The mandrill (Mandrillus sphinx) is naturally infected by two types of simian immunodeficiency virus (SIV): SIVmnd types 1 and 2. Both of these viruses cause long-term, non-progressive infections in their natural host despite high plasma viral loads. This study assessed the susceptibility of rhesus macaques to infection by these two types of SIVmnd and compared the virological and basic immunological characteristics of the resulting infections with those observed in natural infection in mandrills. Whilst both SIVmnd types induced similar levels of virus replication during acute infection in both mandrills and macaques, they produced a more pronounced CD4(+) T-cell depletion in rhesus macaques that persisted longer during the initial stage of infection. Pro-inflammatory cytokine responses were also induced at higher levels in rhesus macaques early in the infection. During the chronic phase of infection in mandrills, which in this case was followed for up to 2 years after infection, high levels of chronic virus replication did not induce significant changes in CD4(+) or CD8(+) T-cell counts. In rhesus macaques, the overall chronic virus replication level was lower than in mandrills. At the end of the follow-up period, although the viral loads of SIVmnd-1 and SIVmnd-2 were relatively similar in rhesus macaques, only SIVmnd-1-infected rhesus macaques showed significant CD4(+) T-cell depletion, in the context of higher levels of CD4(+) and CD8(+) T-cell activation, compared with SIVmnd-infected mandrills. The demonstration of the ability of both SIVmnd types to induce persistent infections in rhesus macaques calls for a careful assessment of the potential of these two viruses to emerge as new human pathogens.

High levels of SIVmnd-1 replication in chronically infected Mandrillus sphinx

Viral loads were investigated in SIVmnd-1 chronically infected mandrills and the results were compared with those previously observed in other nonpathogenic natural SIV infections. Four naturally and 11 experimentally SIVmnd-1-infected mandrills from a semi-free-ranging colony were studied during the chronic phase of infection. Four SIVmnd-1-infected wild mandrills were also included for comparison. Twelve uninfected mandrills were used as controls. Viral loads in all chronically infected mandrills ranged from 10(5) to 9 x 10(5) copies/ml and antibody titers ranged from 200 to 14,400 and 200 to 12,800 for anti-V3 and anti-gp36, respectively. There were no differences between groups of wild and captive mandrills. Both parameters were stable during the follow-up, and no clinical signs of immune suppression were observed. Chronic SIVmnd-1-infected mandrills presented slight increases in CD20+ and CD28+/CD8+ cell counts, and a slight decrease in CD4+/CD3+ cell counts. A slight CD4+/CD3+ cell depletion was also observed in old uninfected controls. Similar to other nonpathogenic models of lentiviral infection, these results show a persistent high level of SIVmnd-1 replication during chronic infection of mandrills, with minimal effects on T cell subpopulations.

Analysis of partial pol and env sequences indicates a high prevalence of HIV type 1 recombinant strains circulating in Gabon

Forty-one HIV-1 strains from Gabonese patients were studied according to the following strategy: nested polymerase chain reaction were performed to obtain an approximately 1,100-bp fragment containing the protease gene and the 5' half of the reverse transcriptase gene. Additional amplifications were carried out to obtain an approximately 700-bp fragment encompassing the C2V3 env gene. Fragments of 600 to 1,200 bp in the gag gene overlapping the pol sequences were used for the study of recombination patterns. Phylogenetic analyses of the different fragments were used to investigate HIV-1 diversity in Gabon. Thirty-one strains were sequenced in the env and pol genes and phylogenetic analyses classified them as subtype A (n = 2), D (n = 4), G (n = 1), H (n = 1), CRF02 (n = 8), and CRF MAL-like (n = 6); in addition, there were 6 unique recombinant forms and 1 unclassified strain, and in 2 cases pol/env sequences classified strains as subtype D whereas gag phylogeny classified them as subtype A. In 10 cases only 1 fragment was available: 4 env (2 subtype D, 1 subtype H, and 1 subtype U) and 6 pol (1 subtype A, 1 subtype C, 2 subtype G, and 2 subtype U). Minor mutations associated with viral resistance to antiretroviral drugs were observed in more than 80% of analyzed strains. Our study confirms the extensive HIV-1 diversity found in Central Africa, with more than 70% of strains from Gabon exhibiting discordant clustering in pol and env genomic regions and less than 60% concordance between sequencing and heteroduplex mobility assay genotyping. These findings highlight the fact that Central Africa represents the epicenter for the origin of HIV-1. The strategy of sequencing pol in association with env has proved to be useful for analysis of the recombinant strains. The main advantage of this approach is that it also allows for evaluation of genotypic susceptibility to antiretroviral drugs without the need for supplementary analyses.

Evaluation of Onchocerca volvulus-specific IgG4 subclass serology as an index of onchocerciasis transmission potential of three Gabonese villages

The major objective of this study was to evaluate the usefulness of IgG4 ELISA and Western blot analysis, using a crude extract of Onchocerca volvulus adult worms as antigens, for diagnosing onchocerciasis in a Gabonese paediatric population with mixed filarial infections. The subjects had loaisis, streptocercosis or mansonellosis in addition to onchocerciasis. Control sera from loaisis or mansonellosis subjects residing outside the endemic zone were used to provide the cut-off point for positive results. The IgG4 ELISA had a specificity of 96% but a lower sensitivity of 78.7%. It detected 25 onchocerciasis cases out of 65 individuals who were negative on parasitological examination. Furthermore, the ELISA provided a more accurate picture of onchocerciasis transmission in a village with very low skin microfilarial load. A 27.5-kD antigen was identified on Western blots as a marker of onchocerciasis. The paediatric population provided a reliable window for assessing the parasitologic and serologic parameters in the three villages with disparate levels of onchocerciasis transmission.

Tolerance and efficacy of single high-dose ivermectin for the treatment of loiasis

A study was carried out in southeastern Gabon to evaluate the tolerance and efficacy of single high doses of ivermectin in 31 Loa loa-infected subjects with low-to-moderate parasitemia (7-7,700 microfilaria/ml). The first group of 16 subjects received 300 micrograms/kg of ivermectin and, seven days later, a second group of 15 received 400 micrograms/kg. Complete clinical and biological monitoring was carried out during the first 10 days post-treatment and again after one and three months. All subjects continued with their usual activities during the study. The clinical tolerance of treatment was very good, and except in one case, only mild adverse reactions were observed, with pruritus being the most common symptom. There were no significant changes in blood or urine function test results or in hematologic results, except for a pronounced eosinophil reaction. The 400 micrograms/kg dose of ivermectin equaled or surpassed in tolerance that of 300 micrograms/kg dose. After treatment, L. loa microfilaremia decreased rapidly to less than 9% of the pretreatment value by day 10. This decrease was enhanced with the 400 micrograms/kg dose, although differences between the two groups diminished slightly with time. At 100 days post-treatment, the microfilaremia was still at less than 10% of the initial values in the two groups, which may indicate an effect of ivermectin on the adult worms.