STLV-I antibodies in feral populations of East African vervet monkeys (Cercopithecus aethiops)

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.

Modes of transmission of Simian T-lymphotropic Virus Type 1 in semi-captive mandrills (Mandrillus sphinx)

Non-human primates (NHPs) often live in inaccessible areas, have cryptic behaviors, and are difficult to follow in the wild. Here, we present a study on the spread of the simian T-lymphotropic Virus Type 1 (STLV-1), the simian counterpart of the human T-lymphotropic virus type 1 (HTLV-1) in a semi-captive mandrill colony. This study combines 28 years of longitudinal monitoring, including behavioral data, with a dynamic mathematical model and Bayesian inference. Three transmission modes were suspected: aggressive, sexual and familial. Our results show that among males, STLV-1 transmission occurs preferentially via aggression. Because of their impressive aggressive behavior male mandrills can easily transmit the virus during fights. On the contrary, sexual activity seems to have little effect. Thus transmission appears to occur primarily via male-male and female-female contact. In addition, for young mandrills, familial transmission appears to play an important role in virus spread.

Modes of transmission and genetic diversity of foamy viruses in a Macaca tonkeana colony

BACKGROUND

Foamy viruses are exogenous complex retroviruses that are highly endemic in several animal species, including monkeys and apes, where they cause persistent infection. Simian foamy viral (SFV) infection has been reported in few persons occupationally exposed to non-human primates (NHP) in zoos, primate centers and laboratories, and recently in few hunters from central Africa. Most of the epidemiological works performed among NHP populations concern cross-sectional studies without long-term follow-up. Therefore, the exact timing and the modes of transmission of SFVs remain not well known, although sexual and oral transmissions have been suspected. We have conducted a longitudinal study in a free-breeding colony of Macaca tonkeana in order (1) to determine the prevalence of the infection by foamy viruses, (2) to characterize molecularly the viruses infecting such animals, (3) to study their genetic variability overtime by long-term follow-up of several DNA samples in a series of specific animals, and (4) to get new insights concerning the timing and the modes of SFVs primary infection in these monkeys by combining serology and molecular means, as well as studies of familial structures and long-term behavioral observations.

RESULTS/CONCLUSION

We first demonstrated that this colony was highly endemic for SFVs, with a clear increase of seroprevalence with age. Only 4.7% of immatures, and 43,7% of sub-adults were found seropositive, while 89.5% of adults exhibited antibodies directed against SFV. We further showed that 6 different strains of foamy viruses (exhibiting a very low intra-strain and overtime genetic variability in the integrase gene) are circulating within this group. This suggests a possible infection by different strains within an animal. Lastly, we provide strong evidence that foamy viruses are mostly acquired through severe bites, mainly in sub-adults or young adults. Most cases of seroconversion occur after 7 years of age; from this age individuals competed for access to sexual partners, thus increasing the likelihood of being wounded. Furthermore, all the serological and molecular data, obtained in this free-breeding colony, argue against a significant transmission of SFVs from mother or father to infants as well as between siblings.

Molecular epidemiology of simian T-cell lymphotropic virus type 1 in wild and captive sooty mangabeys

A study was conducted to evaluate the prevalence and diversity of simian T-cell lymphotropic virus (STLV) isolates within the long-established Tulane National Primate Research Center (TNPRC) colony of sooty mangabeys (SMs; Cercocebus atys). Serological analysis determined that 22 of 39 animals (56%) were positive for STLV type 1 (STLV-1). A second group of thirteen SM bush meat samples from Sierra Leone in Africa was also included and tested only by PCR. Twenty-two of 39 captive animals (56%) and 3 of 13 bush meat samples (23%) were positive for STLV-1, as shown by testing with PCR. Nucleotide sequencing and phylogenetic analysis of viral strains obtained demonstrated that STLV-1 strains from SMs (STLV-1sm strains) from the TNPRC colony and Sierra Leone formed a single cluster together with the previously reported STLV-1sm strain from the Yerkes National Primate Research Center. These data confirm that Africa is the origin for TNPRC STLV-1sm and suggest that Sierra Leone is the origin for the SM colonies in the United States. The TNPRC STLV-1sm strains further divided into two subclusters, suggesting STLV-1sm infection of two original founder SMs at the time of their importation into the United States. STLV-1sm diversity in the TNPRC colony matches the high diversity of SIVsm in the already reported colony. The lack of correlation between the lineage of the simian immunodeficiency virus from SMs (SIVsm) and the STLV-1sm subcluster distribution of the TNPRC strains suggests that intracolony transmissions of both viruses were independent events.

High simian T-cell leukemia virus type 1 proviral loads combined with genetic stability as a result of cell-associated provirus replication in naturally infected, asymptomatic monkeys

Simian T-cell leukemia virus type 1 (STLV-1) is a primate T cell leukemia virus of the group of oncogenic delta retroviruses. Sharing a high level of genetic homology with human T cell leukemia virus type 1 (HTLV-1), it is etiologically linked to the development of simian T cell malignancies that closely resemble HTLV-1 associated leukemias and lymphomas and might thus constitute an interesting model of study. The precise nature of STLV-1 replication in vivo remains unknown. The STLV-1 circulating proviral load of 14 naturally infected Celebes macaques (Macaca tonkeana) was measured by real-time quantitative PCR. The mean proportion of infected peripheral mononuclear cells was 7.9%, ranging from <0.4% to 38.9%. Values and distributions were closely reminiscent of those observed in symptomatic and asymptomatic HTLV-1 infected humans. Sequencing more than 32 kb of LTRs deriving from 2 animals with high proviral load showed an extremely low STLV-1 genetic variability (0.113%). This paradoxical combination of elevated proviral load and remarkable genetic stability was finally explained by the demonstration of a cell-associated dissemination of the virus in vivo. Inverse PCR (IPCR) amplification of STLV-1 integration sites evidenced clones of infected cells in all infected animals. The pattern of STLV-1 replication in these asymptomatic monkeys was indistinguishable from that of HTLV-1 in asymptomatic carriers or in patients with inflammatory diseases. We conclude that, as HTLV-1, STLV-1 mainly replicates by the clonal expansion of infected cells; accordingly, STLV-1 natural monkey infection constitutes an appropriate and promising model for the study of HTLV-1 associated leukemogenesis in vivo.

The discovery of two new divergent STLVs has implications for the evolution and epidemiology of HTLVs

We have isolated and characterised two divergent simian T-lymphotropic viruses (STLV), not belonging to the established human and simian T-lymphotropic virus lineages HTLV-1/STLV-1 and HTLV-2. STLV-L, from an Eritrean sacred baboon (Papio hamadryas), has been typed as a third type of simian T-lymphotropic virus, distinct from HTLV-1/STLV-1 and HTLV-2. The other virus, isolated from Congolese bonobos (Pan paniscus), is a distinct member of the HTLV-2 clade and has been designated STLV-2. The isolation of these two simian viruses shows that the spectrum of HTLVs/STLVs is larger than previously expected. Our data indicate that the two lineages STLV-L and HTLV-2/STLV-2 are of African origin, while the HTLV-1/STLV-1 lineage has been shown to be of Asian origin. These data, together with our phylogenetic analyses, suggest an African origin of the HTLV/STLV ancestor, which provides new clues about virus dissemination. Furthermore, the atypical serological profiles exhibited by STLV-L or STLV-2 infected animals in western blot, raise questions about the efficiency of current screening methods to type highly divergent HTLVs/STLVs. Considering the growing interest in xenotransplantations, more epidemiological and biological knowledge of simian and human T-lymphotropic viruses is necessary to estimate the risk of interspecies transmissions.

The origin and evolution of human T-cell lymphotropic virus types I and II

Studies on human T-cell lymphotropic virus types I (HTLV-I) and II (HTLV-II) are briefly reviewed from the viewpoint of molecular evolution, with special reference to the evolutionary rate and evolutionary relationships among these viruses. In particular, it appears that, in contrast to the low level of variability of HTLV-I among different isolates, individual isolates form quasispecies structures. Elucidating the mechanisms connecting these two phenomena will be one of the future problems in the study of the molecular evolution of HTLV-I and HTLV-II.

Detection of simian T cell leukemia virus type I infection in seronegative macaques

Simian species of Asian and African origin are naturally infected with the simian T cell leukemia virus type I (STLV-I). Like the closely related human T cell leukemia virus type I (HTLV-I), STLV-I is primarily cell associated, and typical infections exhibit low viral burdens. Four macaques experimentally inoculated with a new STLV-I strain isolated from a sooty mangabey monkey were examined over extended periods of time for signs of infection by (1) commercial enzyme immunoassay and immunoblot assay for cross-reactive serum antibodies to HTLV-I, (2) commercial HTLV-I p24gag antigen-capture assay on supernatants from cocultures of macaque peripheral blood mononuclear cells (PBMCs) with human PBMCs, and (3) nested PCR amplification of proviral sequences in macaque PBMC DNA. The nested PCR assay was 100% specific and detected a single STLV-I copy in 150,000 PBMCs. In addition, our data show that experimental infection of macaques with STLV-I can be serologically silent for more than 43 months.

Growth, development, and sexual dimorphism in vervet monkeys (Cercopithecus aethiops) at four sites in Kenya

Body weight and ten body segment measurements were collected from 367 wild-trapped vervet monkeys (Cercopithecus aethiops) in central and southern Kenya. The animals represent between 70 and 95% of the animals in each of 30 troops at four geographical locations separated by 80 to 380 km. The capture sites differed in altitude, mean annual rainfall and temperature. Two questions are addressed: (1) what are the differences in male and female growth patterns, and (2) what is the relationship between size, climate, and availability of food? Each animal was assigned to an age class based on dental examination. Means for all variables do not diverge for males and females from birth to age class 4 (15-18 months). After this, male and female growth rates diverge. This sexual dimorphism in growth pattern may reflect timing of entry into the reproductive community. A nested analysis of variance (ANOVA) was employed to compare sites, groups within sites and individuals within groups. Statistically significant differences between sites in body weight and body segment measurements are found for adult females. Except for tail length, these differences do not follow Bergmann's or Allen's Rules correlating size differences and temperature, but rather may reflect proximity to cultivated areas or tourist lodges with greater access to human food.

Occurrence and frequency of transmission of naturally occurring simian retroviral infections (SIV, STLV, and SRV) at the CIRMF Primate Center, Gabon

Among the primates held at the CIRMF Primate Center, Gabon, no serological sign of SIV infection could be demonstrated in 68 cynomolgus monkeys, 60 chimpanzees, nine gorillas, and 12 sun-tailed monkeys, while seven of 102 mandrills and six of 24 vervets were infected with SIV. Six mandrills, seven vervets and ten cynomolgus monkeys exhibited a full HTLV type 1 Western blot profile. The sera of two gorillas and one chimpanzee presented with a positive but not typical HTLV Western blot profile. The sera of the gorillas lacked p24 antibodies, and the chimpanzee had a Western blot profile evocative of HTLV-II. All attempts to amplify viruses from these animals by PCR were unsuccessful. Two other chimpanzees and seven gorillas presented with indeterminate HTLV Western blot profiles. In the mandrill colony, only male animals were STLV seropositive and no sexual transmission to females was observed. SIV infection was also more frequent in male than female mandrills and sexual transmission appeared to be a rare event. No SRV infection was observed in macaques.

Isolation and characterization of a new simian T-cell leukemia virus type 1 from naturally infected celebes macaques (Macaca tonkeana): complete nucleotide sequence and phylogenetic relationship with the Australo-Melanesian human T-cell leukemia virus type 1

A study of simian T-cell leukemia virus type 1 (STLV-1) infection in a captive colony of 23 Macaca tonkeana macaques indicated that 17 animals had high human T-cell leukemia virus type 1 (HTLV-1) antibody titers. Genealogical analysis suggested mainly a mother-to-offspring transmission of this STLV-1. Three long-term T-cell lines, established from peripheral blood mononuclear cell cultures from three STLV-1-seropositive monkeys, produced HTLV-1 Gag and Env antigens and retroviral particles. The first complete nucleotide sequence of an STLV-1 (9,025 bp), obtained for one of these isolates, indicated an overall genetic organization similar to that of HTLV-1 but with a nucleotide variability for the structural genes ranging from 7.8 to 13.1% compared with the HTLV-1 ATK and STLV-1 PTM3 Asian prototypes. The Tax and Rex regulatory proteins were well conserved, while the pX region, known to encode new proteins in HTLV-1 (open reading frames I and II), was more divergent than that in the ATK strain. Furthermore, a fragment of 522 bp of the gp21 env gene from uncultured peripheral blood mononuclear cell DNAs from five of the STLV-1-infected monkeys was sequenced. Phylogenetic trees constructed with the long terminal repeat and env (gp46 and gp21) regions demonstrated that this new STLV-1 occupies a unique position within the Asian STLV-1 and HTLV-1 isolates, being, by most analyses, related more to the Australo-Melanesian HTLV-1 topotype than to any other Asian STLV-1. These data raise new hypotheses on the possible interspecies viral transmission between monkeys carrying STLV-1 and early Australoid settlers, ancestors of the present day Australo-Melanesian inhabitants, during their migrations from the Southeast Asian land mass to the greater Australian continent.

Phylogenetic associations of human and simian T-cell leukemia/lymphotropic virus type I strains: evidence for interspecies transmission

Homologous env sequences from 17 human T-leukemia/lymphotropic virus type I (HTLV-I) strains from throughout the world and from 25 simian T-leukemia/lymphotropic virus type I (STLV-I) strains from 12 simian species in Asia and Africa were analyzed in a phylogenetic context as an approach to resolving the natural history of these related retroviruses. STLV-I exhibited greater overall sequence variation between strains (1 to 18% compared with 0 to 9% for HTLV-I), supporting the simian origin of the modern viruses in all species. Three HTLV-I phylogenetic clusters or clades (cosmopolitan, Zaire, and Melanesia) were resolved with phenetic, parsimony, and likelihood analytical procedures. Seven phylogenetic clusters of STLV-I were resolved with the most primitive (deeply rooted) divergence involving several STLV-I strains from Asian primate species. Combined analysis of HTLV-I and STLV-I revealed that neither STLV-I clusters nor HTLV-I clusters recapitulated host species specificity; rather, multiple clades from the same species were closer to clades from other species than to each other. We interpret these evolutionary associations as support for the occurrence of multiple discrete interspecies transmissions of ancestral viruses between primate species (including human) that led to recognizable phylogenetic clades that persist in modern species. Geographic concordance of divergent host species that harbor closely related viruses reinforces that physical feasibility for hypothesized interspecies virus transmission in the past and in the present.

Sexual transmission of SIVagm in wild grivet monkeys

This study reports the prevalence of simian immunodeficiency virus and the relationship of serostatus to age and sex among a wild population of Ethiopian grivet monkeys (Cercopithecus aethiops aethiops). Seropositivity paralleled patterns of sexual activity, being nearly universal in females of reproductive age, and absent in all males except those that were fully adult. One female seroconverted between two capture seasons at an age consistent with first breeding. Our findings support a predominantly sexual mode of transmission among SIVagm infected grivets.

Serologic confirmation of simian T-lymphotropic virus type I infection by using immunoassays developed for human T-lymphotropic virus antibody detection

Serum specimens from diverse species of Old World monkeys, categorized as seropositive (n = 97) or seronegative (n = 23) for human T-lymphotropic virus (HTLV) infection, were tested by using recombinant env-spiked Western immunoblot assays and synthetic peptide assays for simultaneous detection and discrimination of simian T-lymphotropic virus (STLV) infection. Of the 97 seropositive specimens, 93 reacted with the recombinant transmembrane (r21env) protein and 90 reacted with a recombinant, MTA-1, derived from the central region of the external glycoprotein of HTLV-I (rgp46env), thus yielding test sensitivities of 96 and 93%, respectively. While 1 of the 23 negative monkey specimens reacted with r21env, none reacted with rgp46env, for overall specificities of 96 and 100%, respectively. Analysis of synthetic peptide-based immunoassays demonstrated that while 85 of 97 (88%) seropositive specimens reacted with HTLV-I-specific epitope (p19gag), none of the specimens reacted with HTLV-II-specific epitope (gp52env). These results show that recombinant envelope-spiked Western blots provide a simple means for serologic confirmation of STLV-I infection and that type-specific synthetic peptides can be used to confirm the virus type in seropositive monkey specimens.

Increased peripheral lymphocytes, lymphoid hepatitis and anaemia in African vervet monkeys seropositive to retroviruses

Wild-caught African Vervet monkeys are commonly infected by Simian T-lymphotropic virus I (STLV1) and Simian immunodeficiency virus (SIV), yet the natural histories of these infections are largely unknown. Seropositivity was associated with increased total, T and atypical lymphocytes. In seropositive females there was mild, normocytic, normochromic anaemia. Lymphoid hepatitis was present in seven seropositive cases. African Vervets used in biomedical research, vaccine production and organ transplantation research are often infected by exogenous retroviruses which can be oncogenic and immunosuppressive in captive monkeys. Elimination of these infections may be possible by breeding Vervets in captivity.

Serological survey and virus isolation of simian T-cell leukemia/T-lymphotropic virus type I (STLV-I) in non-human primates in their native countries

Infection with a simian retrovirus (STLV-I) closely related to human T-lymphotropic virus type I (HTLV-I) was investigated in non-human primates living in their native countries in Africa and Asia. Serum antibodies cross-reacting with HTLV-I antigens were detected in 85 of 567 non-human primates of 30 species. Seropositive animals were found among African green monkeys, olive baboons, Sykes' monkeys, mandrills and patas monkeys in several countries in Africa, and cynomolgus monkeys, Celebes macaques and siamangs in Indonesia. The frequency of seropositivity was much higher in adult than in young African green monkeys, cynomolgus monkeys and Celebes macaques. STLV-Is were isolated by establishing II lines of virus-producing lymphoid cells in the presence of interleukin-2 from 5 species of seropositive non-human primates, i.e. the African green monkey, Sykes' monkey, Celebes macaque, cynomolgus monkey and siamang. All these cell lines had T-cell markers and Tac antigen, and the cell lines from the African green monkey and Sykes' monkeys were Leu2a+ while those from other species were Leu3a+. These cell lines expressed viral antigens reacting with human sera from adult T-cell leukemia (ATL) patients and monoclonal antibodies (MAbs) against p19 and p24 of HTLV-I core proteins, and produced virus particles having RNA-dependent DNA polymerase activity. Cellular DNAs from these cell lines contained provirus sequences homologous to HTLV-I, shown by Southern blot hybridization. The restriction patterns of these provirus genomes were different from those of HTLV-I and were also dissimilar in the different species.