Simian T-lymphotropic virus type 1 (STLV-1) infection in wild yellow baboons (Papio hamadryas cynocephalus) from Mikumi National Park, Tanzania

STLV-1 as a model for studying HTLV-1 infection

Few years after HTLV-1 identification and isolation in humans, STLV-1, its simian counterpart, was discovered. It then became clear that STLV-1 is present almost in all simian species. Subsequent molecular epidemiology studies demonstrated that, apart from HTLV-1 subtype A, all human subtypes have a simian homolog. As HTLV-1, STLV-1 is the etiological agent of ATL, while no case of TSP/HAM has been described. Given its similarities with HTLV-1, STLV-1 represents a unique tool used for performing clinical studies, vaccine studies as well as basic science.

Baboon CD8 T cells suppress SIVmac infection in CD4 T cells through contact-dependent production of MIP-1α, MIP-1β, and RANTES

Simian immunodeficiency virus (SIV) infection in rhesus macaques is often characterized by high viremia and CD4 T cell depletion. By contrast, SIV infection in African nonhuman primate natural hosts is typically nonpathogenic despite active viral replication. Baboons are abundant in Africa and have a geographical distribution that overlaps with natural hosts, but they do not harbor SIVs. Previous work has demonstrated baboons are resistant to chronic SIV infection and/or disease in vivo but the underlying mechanisms remain unknown. Using in vitro SIVmac infections, we sought to identify SIV restriction factors in baboons by comparing observations to the pathogenic rhesus macaque model. SIVmac replicated in baboon PBMC but had delayed kinetics compared to rhesus PBMC. However, SIVmac replication in baboon and rhesus isolated CD4 cells were similar to the kinetics seen for rhesus PBMC, demonstrating intracellular restriction factors do not play a strong role in baboon inhibition of SIVmac replication. Here, we show CD8 T cells contribute to the innate SIV-suppressive activity seen in naïve baboon PBMC. As one mechanism of restriction, we identified higher production of MIP-1α, MIP-1β, and RANTES by baboon PBMC. Contact between CD4 and CD8 T cells resulted in maximum production of these chemokines and suppression of viral replication, whereas neutralization of CCR5-binding chemokines in baboon PBMC increased viral loads. Our studies indicate baboon natural restriction of SIVmac replication is largely dependent on CD4-extrinsinc mechanisms mediated, in part, by CD8 T cells.

Bushmeat and Emerging Infectious Diseases: Lessons from Africa

Zoonotic diseases are the main contributor to emerging infectious diseases (EIDs) and present a major threat to global public health. Bushmeat is an important source of protein and income for many African people, but bushmeat-related activities have been linked to numerous EID outbreaks, such as Ebola, HIV, and SARS. Importantly, increasing demand and commercialization of bushmeat is exposing more people to pathogens and facilitating the geographic spread of diseases. To date, these linkages have not been systematically assessed. Here we review the literature on bushmeat and EIDs for sub-Saharan Africa, summarizing pathogens (viruses, fungi, bacteria, helminths, protozoan, and prions) by bushmeat taxonomic group to provide for the first time a comprehensive overview of the current state of knowledge concerning zoonotic disease transmission from bushmeat into humans. We conclude by drawing lessons that we believe are applicable to other developing and developed regions and highlight areas requiring further research to mitigate disease risk.

Human T-cell lymphotropic virus type 1 subtype C molecular variants among indigenous australians: new insights into the molecular epidemiology of HTLV-1 in Australo-Melanesia

Background

HTLV-1 infection is endemic among people of Melanesian descent in Papua New Guinea, the Solomon Islands and Vanuatu. Molecular studies reveal that these Melanesian strains belong to the highly divergent HTLV-1c subtype. In Australia, HTLV-1 is also endemic among the Indigenous people of central Australia; however, the molecular epidemiology of HTLV-1 infection in this population remains poorly documented.

Findings

Studying a series of 23 HTLV-1 strains from Indigenous residents of central Australia, we analyzed coding (gag, pol, env, tax) and non-coding (LTR) genomic proviral regions. Four complete HTLV-1 proviral sequences were also characterized. Phylogenetic analyses implemented with both Neighbor-Joining and Maximum Likelihood methods revealed that all proviral strains belong to the HTLV-1c subtype with a high genetic diversity, which varied with the geographic origin of the infected individuals. Two distinct Australians clades were found, the first including strains derived from most patients whose origins are in the North, and the second comprising a majority of those from the South of central Australia. Time divergence estimation suggests that the speciation of these two Australian clades probably occurred 9,120 years ago (38,000–4,500).

Conclusions

The HTLV-1c subtype is endemic to central Australia where the Indigenous population is infected with diverse subtype c variants. At least two Australian clades exist, which cluster according to the geographic origin of the human hosts. These molecular variants are probably of very ancient origin. Further studies could provide new insights into the evolution and modes of dissemination of these retrovirus variants and the associated ancient migration events through which early human settlement of Australia and Melanesia was achieved.

The Human T-lymphotropic virus type 1 (HTLV-1) infects at least 5–10 million persons worldwide. In Oceania, previous studies have shown that HTLV-1 is present in a few ancient populations from remote areas of Papua New Guinea, the Solomon Islands, the Vanuatu archipelago and central Australia. The latter comprise one of the most socio-economically disadvantaged groups within any developed country. Characterization of the few available HTLV-1 viruses from Oceania indicates that these belong to a specific HTLV-1 genotype, the Australo-Melanesian c-subtype. In this study, we provide details for 23 HTLV-1 viruses derived from the Indigenous population of central Australia, a vast remote area of 1,000,000 km². We reveal considerable genetic diversity of HTLV-1c subtype viruses and the existence of two HTLV-1c clades within which a high degree of genetic diversity was also apparent. These newly described HTLV-1c clades clustered according to the geographic origin of their human hosts. Indigenous Australians from the North of central Australia harbor HTLV-1c subtype viruses that are distinct from those of individuals from regions to the South. These data suggest that HTLV-1 was probably introduced to Australia during ancient migration events and was then confined to isolated Indigenous communities in central Australia.

Divergent simian T-cell lymphotropic virus type 3 (STLV-3) in wild-caught Papio hamadryas papio from Senegal: widespread distribution of STLV-3 in Africa

Among eight samples obtained from a French primatology research center, six adult guinea baboons (Papio hamadryas papio), caught in the wild in Senegal, had a peculiar human T-cell leukemia virus type 2 (HTLV-2)-like Western blot seroreactivity (p24(+), GD21(+), K55(+/-)). Partial sequence analyses of the tax genes (433 bp) indicated that these baboons were infected by a novel divergent simian T-cell lymphotropic virus (STLV). Analyses of the complete proviral sequence (8,892 bp) for one of these strains (STLV-3/PPA-F3) indicate that this STLV was highly divergent from the HTLV-1 (61.6% of nucleotide similarity), HTLV-2 (61.2%), or STLV-2 (60.6%) prototype. It was, however, much more closely related to the few other known STLV-3 strains, exhibiting 87 and 89% of nucleotide similarity with STLV-3/PHA-PH969 (formerly PTLV-L/PH969) and STLV-3/CTO-604, respectively. The STLV-3/PPA-F3 sequence possesses the major HTLV or STLV open reading frames corresponding to the structural, enzymatic, and regulatory proteins. However, its long terminal repeat comprises only two 21-bp repeats. In all phylogenetic analyses, STLV-3/PPA-F3 clustered together in a highly supported single clade with the other known strains of STLV-3, indicating an independent evolution from primate T-cell lymphotropic virus type 1 (PTLV-1) and PTLV-2. The finding of a new strain of STLV-3 in a West African monkey (Guinea baboon) greatly enlarges the geographical distribution and the host range of species infected by this PTLV type in the African continent. The recent discovery of several different STLV-3 strains in many different African monkey species, often in contact with humans, strongly suggests potential interspecies transmission events, as it was described for STLV-1, between nonhuman primates but also to humans.

Molecular epidemiology of simian T-lymphotropic virus (STLV) in wild-caught monkeys and apes from Cameroon: a new STLV-1, related to human T-lymphotropic virus subtype F, in a Cercocebus agilis

A serological survey for human T-lymphotropic virus (HTLV)/simian T-lymphotropic virus (STLV) antibodies was performed in 102 wild-caught monkeys and apes from 15 (sub)species originating from Cameroon. Two animals (a Mandrillus sphinx and a Cercocebus agilis) exhibited a complete HTLV-1 seroreactivity pattern while two others lacked either the p24 (a Mandrillus sphinx) or the MTA-1/gp46 bands (a Pan troglodytes). Sequence comparison and phylogenetic analyses, using a 522 bp env gene fragment and the complete LTR, indicated that the two mandrill STLV strains belonged to the HTLV/STLV subtype D clade while the chimpanzee strain clustered in the HTLV/STLV subtype B clade. The Cercocebus agilis STLV strain, the first one found in this species, was closely related to the two HTLV/STLV subtype F strains. Such data indicate that the African biodiversity of STLV-1 in the wild is far from being known and reinforces the hypothesis of interspecies transmission of STLV-1 from monkeys and apes to humans leading to the present day distribution of HTLV-1 in African inhabitants.

Molecular and phylogenetic analyses of 16 novel simian T cell leukemia virus type 1 from Africa: close relationship of STLV-1 from Allenopithecus nigroviridis to HTLV-1 subtype B strains

A serological survey searching for antibodies reacting with human T-cell leukemia virus type 1 (HTLV-1) antigens was performed on a series of 263 sera/plasma obtained from 34 monkey species or subspecies, originating from different parts of Africa. Among them, 34 samples exhibited a typical HTLV-1 Western blot pattern. Polymerase chain reaction was performed with three primer sets specific either to HTLV-1/STLV-1 or HTLV-2 and encompassing gag, pol, and tax sequences, on genomic DNA from peripheral blood mononuclear cells of 31 animals. The presence of HTLV-1/simian T-cell leukemia virus type 1 (STLV-1) related viruses was determined in the 21 HTLV-1 seropositive animals tested but not in the 10 HTLV-1 seronegative individuals. Proviral DNA sequences from the complete LTR (750 bp) and a portion of the env gene (522 bp) were determined for 16 new STLV-1 strains; some of them originating from species for which no STLV-1 molecular data were available as Allenopithecus nigroviridis and Cercopithecus nictitans. Comparative and phylogenetic analyses revealed that these 16 new sequences belong to five different molecular groups. The A. nigroviridis STLV-1 strains exhibited a very strong nucleotide similarity with HTLV-1 of the subtype B. Furthermore, four novel STLV-1, found in Cercocebus torquatus, C. m. mona, C. nictitans, and Chlorocebus aethipos, were identical to each other and to a previously described Papio anubis STLV-1 strain (PAN 503) originating from the same primate center in Cameroon. Our data extend the range of the African primates who could be permissive and/or harbor naturally STLV-1 and provide new evidences of cross-transmission of African STLV-1 between different monkey species living in the same environment and also of STLV-1 transmissions from some monkeys to humans in Central Africa.

The risk of using baboons as transplant donors. Exogenous and endogenous viruses

African nonhuman primates harbor several exogenous and endogenous retroviruses which deserve further consideration in the transplant setting. In particular, simian foamy viruses (SFV), simian T-cell lymphotropic virus (STLV), baboon endogenous virus (BaEV), and simian endogenous retrovirus (SERV) are all carried by baboons and may be transmitted to humans by transplantation. We have found baboons to have high seroprevalence rates to both SFV and STLV, and molecular and serologic methods have been developed to detect such agents. In addition, current nonhuman primate breeding programs have thus far not focused on eliminating these viruses. In summary, the close genetic relationship with humans and number of persistent viral infections in baboons translates into a much greater infectious disease risk when compared to that of other domesticated species.

Evolutionary inferences of novel simian T lymphotropic virus type 1 from wild-caught chacma (Papio ursinus) and olive baboons (Papio anubis)

A serological survey of 22 wild-caught South African (Transvaal) chacma baboons (Papio ursinus) and eight olive baboons (Papio anubis) from Kenya indicates that 13 P. ursinus and one P. anubis have antibodies reacting with human T cell leukemia/lymphoma virus type 1 (HTLV-1) antigens, whereas three P. ursinus had a indeterminate reactivity on Western blot analysis. With six primer sets specific to either HTLV-1-Simian T-cell leukemia virus type 1 (STLV-1) or HTLV-2 and encompassing long terminal repeat (LTR), gag, pol, env, and tax sequences, polymerase chain reaction was performed on genomic DNA from peripheral blood mononuclear cells of 18 animals, and the presence of HTLV-1-STLV-1-related viruses was determined in 13 seropositive and three seroindeterminate animals but not in the two HTLV seronegative individuals. Proviral DNA sequences from env (522 bp), pol (120 bp), and complete (755 bp) or partial (514 bp) LTR were determined for three STLV-1-infected P. ursinus and one P. anubis. Comparative and phylogenetic analyses revealed that P. anubis (Pan-486) sequence clusters with one (Pan-1621) of two previously described P. anubis STLV-1. Likewise, P. ursinus viruses (Pur-529, Pur-539, and Pur-543) form a distinct group, different from all known HTLV-1 but closely affiliated with two STLV-1 strains from South African vervets (Cercopithecus aethiops pygerythrus). This study, reporting the first STLV-1 sequences from wild-caught P. ursinus and P. anubis, corroborates the hypothesis of cross-species transmissions of STLV-1 in the wild. Further, phylogenetic analyses indicate that the known HTLV-1 strains do not share a common origin with nonhuman primates STLV in South Africa.

Phylogenetic analysis of simian T-lymphotropic virus Type I (STLV-I) in common chimpanzees (Pan troglodytes): evidence for interspecies transmission of the virus between chimpanzees and humans in Central Africa

Serum and peripheral blood leukocytes from the chimpanzees (Pan troglodytes) of the colony of the Laboratory of Central Nervous System Studies, National Institute of Neurological Disorders and Stroke, NIH, were tested for the presence of STLV-I-specific antibodies and proviral DNA. Antibodies were determined by gelatin particle agglutination and Western blot (WB) assays utilizing HTLV-I antigens. Proviral DNA was detected by four PCR assays targeting three different regions of STLV-I genome: the fragments of the env and pol genes and LTR. Twenty of twenty-two DNA samples from WB-positive animals were PCR positive. None of the DNA samples from WB-negative (n = 5) and WB-indeterminate (n = 4) animals was PCR positive. The results of the nested and double nested env PCR tests were fully concordant; the seminested LTR PCR test was much less sensitive. The DNA sequences from the env (483 bp) and the pol (200 bp) genes and LTR (705 bp) were determined for six, two, and two chimpanzee STLV-I isolates, respectively. Phylogenetic analysis revealed that chimpanzee STLV-I isolates can be attributed to three clades. The first of these clades (SS-PTR1/CSA) included STLV-I isolates from the chimpanzees and West African subspecies of African green monkeys (Cercopithecus a. sabaeus). The other clades (S-PTR2 and S-PTR3) included STLV-I isolates only from chimpanzees. However, both S-PTR2 and S-PTR3 clustered together with Central African HTLV-I comprising the human/simian clade (HS-HSA/PTR). This pattern of phylogenetic clustering suggests that interspecies transmission of STLV-I occurred between chimpanzees and African green monkey subspecies as well between chimpanzees and human populations in Central Africa.