Risk factors for HTLV-1 infection in Central Africa: A rural population-based survey in Gabon

There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

Abstract

Background

Human T-Lymphotropic Virus type 1 (HTLV-1) is a human oncoretrovirus that infects at least 5 to 10 million people worldwide and is associated with severe diseases. Africa appears as the largest HTLV-1 endemic area. However, the risk factors for the acquisition of HTLV-1 remain poorly understood in Central Africa.

Methods

We conducted an epidemiological survey between 2013 and 2017, in rural areas of 6 provinces of Gabon, in a rainforest environment. Epidemiological data were obtained and blood samples were collected after informed consent. Plasma were screened for HTLV-1 antibodies by ELISA and the positive samples were then tested by Western blot (WB). Genomic DNA derived from buffy-coat was subjected to two semi-nested PCRs amplifying either HTLV-1 env gene or LTR region fragments.

Results

We recruited 2,060 individuals over 15 years old, including 1,205 men and 855 women (mean age: 49 years). Of these, 299 were found to be ELISA HTLV-1/2 seropositive. According to WB criteria, 136 were HTLV-1 (6.6%), 25 HTLV-1/2 (1.2%) and 9 HTLV seroreactive (0.4%). PCR results showed that 146 individuals were positive for at least one PCR: 104 for the env gene and 131 for the LTR region. Based on both serological and molecular results, 179 individuals were considered infected with HTLV-1, leading to an overall prevalence of 8.7%. The distribution of HTLV-1 infection was heterogeneous across the country. Based on multivariable analyses, female gender, increasing age, ethnicity (Pygmy) and multiple hospitalizations (more than 5 times) were found to be independent risk factors for HTLV-1 infection. Furthermore, a non-human primate bite appeared to be marginally associated with a higher risk of HTLV-1 infection.

Conclusion

Based on state-of-the-art serological and molecular methods, we have demonstrated that rural adult populations in Gabon are highly endemic for HTLV-1. Our results regarding risk factors should lead to public health actions aiming to reduce HTLV-1 transmission.

Author summary

Human T-Lymphotropic Virus type 1 (HTLV-1) infects at least 5 to 10 million people worldwide and is associated with severe diseases. Africa, particularly the sub-Saharan region, is considered as the largest HTLV-1 endemic area. HTLV-1 can be acquired through three main routes: mother-to-child, sexual and through contaminated blood products. In addition, zoonotic transmission from non-human primates still occurs in specific rural African populations. Gabon is considered to be a very high HTLV-1 endemic area. However, risk factors for such a retroviral infection remain poorly known in Central Africa. In this study, using state-of-the-art serological and molecular tests, we aimed to get new insights on risk factors associated with HTLV-1 infection in rural Gabon. We report an overall prevalence of HTLV-1 of 8.7%, demonstrating that HTLV-1 is highly endemic in rural adult Gabonese populations. In the study population, we identified female gender, increasing age, ethnicity (Pygmy) and multiple hospitalizations (more than 5 times) as independent risk factors for HTLV-1 infection. Furthermore, a non-human primate bite appeared to be marginally associated with a higher risk of HTLV-1 infection. Our results regarding the risk factors for such a retroviral infection are important for public health actions aiming to reduce HTLV-1 transmission.

Related collections

Most cited references 33

Record: found
Abstract: found
Article: not found

Detection and isolation of type C retrovirus particles from fresh and cultured lymphocytes of a patient with cutaneous T-cell lymphoma.

B Poiesz, F Ruscetti, A Gazdar … (1980)

Retrovirus particles with type C morphology were found in two T-cell lymphoblastoid cell lines, HUT 102 and CTCL-3, and in fresh peripheral blood lymphocytes obtained from a patient with a cutaneous T-cell lymphoma (mycosis fungoides). The cell lines continuously produce these viruses, which are collectively referred to as HTLV, strain CR(HTLV(CR)). Originally, the production of virus from HUT 102 cells required induction with 5-iodo-2'-deoxyuridine, but the cell line became a constitutive producer of virus at its 56th passage. Cell line CTCL-3 has been a constitutive producer of virus from its second passage in culture. Both mature and immature extracellular virus particles were seen in thin-section electron micrographs of fixed, pelleted cellular material; on occasion, typical type C budding virus particles were seen. No form of intracellular virus particle has been seen. Mature particles were 100-110 nm in diameter, consisted of an electron-dense core surrounded by an outer membrane separated by an electron-lucent region, banded at a density of 1.16 g/ml on a continuous 25-65% sucrose gradient, and contained 70S RNA and a DNA polymerase activity typical of viral reverse transcriptase (RT; RNA-dependent DNA nucleotidyltransferase). Under certain conditions of assay, HTLV(CR) RT showed cation preference for Mg(2+) over Mn(2+), distinct from the characteristics of cellular DNA polymerases purified from human lymphocytes and the RT from most type C viruses. Antibodies to cellular DNA polymerase gamma and anti-bodies against RT purified from several animal retroviruses failed to detectably interact with HTLV(CR) RT under conditions that were positive for the respective homologous DNA polymerase, demonstrating a lack of close relationship of HTLV(CR) RT to cellular DNA polymerases gamma or RT of these viruses. Six major proteins, with sizes of approximately 10,000, 13,000, 19,000, 24,000, 42,000, and 52,000 daltons, were apparent when doubly banded, disrupted HTLV(CR) particles were chromatographed on a NaDodSO(4)/polyacrylamide gel. The number of these particle-associated proteins is consistent with the expected proteins of a retrovirus, but the sizes of some are distinct from those of most known retroviruses of the primate subgroups.

0 comments Cited 385 times – based on 0 reviews      Review now

Bookmark

Record: found
Abstract: found
Article: not found

Cross-species transmission of simian retroviruses: how and why they could lead to the emergence of new diseases in the human population.

Sabrina Locatelli, Martine Peeters (2012)

The HIV-1 group M epidemic illustrates the extraordinary impact and consequences resulting from a single zoonotic transmission. Exposure to blood or other secretions of infected animals, through hunting and butchering of bushmeat, or through bites and scratches inflicted by pet nonhuman primates (NHPs), represent the most plausible source for human infection with simian immunodeficiency virus (SIV), simian T-cell lymphotropic virus (STLV) and simian foamy virus. The chance for cross-species transmissions could increase when frequency of exposure and retrovirus prevalence is high. According to the most recent data, human exposure to SIV or STLV appears heterogeneous across the African countries surveyed. Exposure is not sufficient to trigger disease: viral and host molecular characteristics and compatibility are fundamental factors to establish infection. A successful species jump is achieved when the pathogen becomes transmissible between individuals within the new host population. To spread efficiently, HIV likely required changes in human behavior. Given the increasing exposure to NHP pathogens through hunting and butchering, it is likely that SIV and other simian viruses are still transmitted to the human population. The behavioral and socio-economic context of the twenty-first century provides favorable conditions for the emergence and spread of new epidemics. Therefore, it is important to evaluate which retroviruses the human population is exposed to and to better understand how these viruses enter, infect, adapt and spread to its new host.

0 comments Cited 54 times – based on 0 reviews      Review now

Bookmark

Record: found
Abstract: found
Article: found

Is Open Access

Frequent and Recent Human Acquisition of Simian Foamy Viruses Through Apes' Bites in Central Africa

Edouard Betsem, Réjane Rua, Patricia Tortevoye … (2011)

Introduction Most of the viral pathogens that have emerged in humans during the last decades have originated from various animals, either domestic or living in the wild [1], [2], [3], [4]. After the initial interspecies transmission, these viruses have followed different evolutionary routes and spread into the human population through various distinct mechanisms. Such mechanisms have been well studied, often well understood, thus allowing a certain level of risk control, and a decrease of inter-human dissemination [3], [4], [5]. In contrast, the understanding of the initial steps of the emergence of several viruses and associated diseases often remains quite poor. Epidemiological and microbiological studies in specific high-risk groups and populations are thus necessary to gain new insights into the early events of the emergence process. Nonhuman primates (NHPs) are hosts for several pathogens potentially transmissible to humans. Indeed, people in contact with NHPs are at risk for infection with viruses such as Simian T Lymphotropic Viruses [6], [7], [8], [9], [10], [11], [12] or Simian Immunodeficiency Viruses through interspecies transmission [13], [14], [15], [16], [17]. Simian foamy viruses are exogenous complex retroviruses of the Spumaretrovirinae subfamily [18], [19]. They are highly prevalent in several animal species, in which they cause persistent infection [20], [21], [22], [23]. Switzer et al., suggested that foamy viruses have co-speciated with Old World NHPs for at least 30 million years [24]. Such a long-term co-evolution may explain their apparent lack of pathogenicity observed in vivo, and the persistence of the infection. Indeed, SFVs are considered to be non pathogenic in naturally or experimentally infected animals, even though disease association has not been systematically evaluated in any NHPs species. This strongly contrasts with the in vitro cytopathic effect seen in infected cell cultures, with a characteristic foamy appearance of vacuolized cells [25]. SFV seroprevalence in captive adult NHP populations can reach 75–100% [26], [27], [28], [29], [30]. The situation seems very similar in semi-free ranging colonies [31], [32] and in wild troops [33], [34], [35]. Transmission of SFV among NHPs occurs via infected body fluids, mainly through biting, but also with grooming and possibly to a lesser extent, sexual contacts [32], [34]. SFV appears to be present at high concentration in the saliva of infected animals [36], [37], [38] and viral replication has been shown to occur in a superficial cell niche of the oral mucosa in macaques [38]. The first FV to be isolated in humans was reported by Achong in 1971 [39]. This virus was identified in a cell culture from a Kenyan patient suffering from a nasopharyngeal carcinoma. Further phylogenetic analysis indicated that this virus was from an east African Chimpanzee subspecies and the virus was now renamed “the prototype HFV” [40]. However, the first clear evidence of SFV in humans was demonstrated in 1995 by Schweizer et al., who found antibodies directed against SFV antigens and the presence of FV DNA in the peripheral blood of 3 persons among 41 laboratory and animal house personnel [27]. These initial studies were followed by series of others, mainly by a CDC team led by Dr W. Heneine and W. Switzer who published a series of clear demonstrations of the presence of SFV infection in cohorts of workers occupationally exposed to NHP, including animal caretakers, research scientists, and veterinarians [41], [42], [43], [44]. In most cases, the supposed infecting contacts were bites, from chimpanzees and African monkeys and, to a lesser extent, puncture wounds. In rare cases, no evident risk factors were identified, suggesting that other cutaneomucous contacts can also lead to such zoonotic infection [44], [45]. The next step was to search for such zoonotic infection in a more natural setting. Wolfe el al. pioneered the work by investigating the presence of SFV in villagers of South Cameroon reporting direct contacts with blood and/or body fluid from wild NHPs. This study demonstrated the presence of antibodies directed against SFV in 1% of the 1099 tested individuals and the presence of SFV sequences in the blood of 3 persons [46]. Our team has developed and extended such results in South Cameroon, demonstrating the presence of persistent SFV infection in a series of 13 individuals all, except one, being men bitten during hunting activities in the forest, by an ape or a monkey [47]. Studies in South-east Asia showed transmission of macaque SFVs in a series of 10 people including zoo workers, owner of NHP pets, bush meat-hunters and temple workers [33], [48]. Furthermore, mathematical modeling showed that in Bali, about six of every 1000 visitors to monkey temples will be infected by SFV [49]. In an area of high NHP diversity and ongoing ecologic and socio-demographic changes, the goals of the present study were to gain new insights into the risk factors associated with the presence of SFV infection in human populations neighboring a nature reserve rich in game. In this area, hunting and butchering for subsistence are still very active. A second goal was to characterize SFV strains and viral loads in peripheral blood of infected individuals and finally, we searched for any intra-familial dissemination of SFV from the originally infected index cases. Materials and Methods Clearance and ethics The study received administrative and ethical clearance in Cameroon from the research division of the Ministry of Public Health (reference D30-295/AR/MINSANTE/SG/DROS/CRC/CEA1) and from the National Comity of Ethics (reference 034//CNE/MP/06), and in France, from the “Comité de Protection des Personnes” (reference 2011/01NICB) and the “Commission Nationale de l'Informatique et des Libertés” (reference EGY/FLR/AR111711). Prior to field sampling, community and individual written informed consent was provided by participants after detailed information and explanations of the study were provided. Written consent for children underage was obtained from their parents or recognized guardians. The population This study was carried out in rural areas located in south and east Cameroon (figure 1) in a rainforest region home to a variety of non human primate (NHP) species. The human populations in these areas include numerous Bantu tribes including. Pygmies in this work are from the Baka and the Bakola tribes [50]. A large part of this study was focused on areas and villages surrounding and within the Dja and Campo Maan nature reserves (figure 1). A systematic approach for the enrolment of adults was carried out in the populations (Pygmies and Bantus) in all reachable villages and settlements, scattered alongside roads and tracks across the forest. A standardized questionnaire was used to collect personal epidemiological data and two study population groups were defined. A large group designated “general population”, included all consenting subjects who had been living in the study areas for several years and been exposed to NHPs. A second group, smaller in size, designated the “contact group”, made up of all those individuals who had reported an encounter with a NHP during their lifetime, and which has resulted in physical injury by a scratch, a bite or both, from the animal in question. The classification into the two groups was made on the basis of a simple questionnaire, and an explicit declaration of an injury related to contact with a NHP, no matter what the circumstances. Collected data included the name, age, sex, location, ethnicity and family links, as well as specific questions about date of contacts with NHPs, the location, description of circumstances, the type and site of body lesions if any and the presence of after-effects. 10.1371/journal.ppat.1002306.g001 Figure 1 Geographic distribution of the studied population. Samples were collected systematically in the coloured areas without specific focus on a particular site. Native inhabitants of these areas include a great variety of ethnicities among which are the Banen, Yebekolo and Soo in the Centre (orange areas), the Bakola Pygmies, Mvae and Ngumba in purple colored area and finally the Baka Pygmies, the Bulu, Fang Badjoue and Zime tribes located in the blue coloured areas. The 198 individuals from the “contact group” are indicated by red (SFV-infected) and yellow (SFV non-infected) dots. The 2 SFV infected individuals from the “general population” are represented as black dots. A 5 to 10 ml whole blood sample was collected in EDTA K2 vacuum tubes, from all consenting individuals meeting the inclusion criteria. Plasma and buffy-coat were obtained 48 to 72 hours after sampling and kept frozen at −80°C. A simple clinical examination was performed when requested by participants in the study. Treatment for common local ailments was given if available. A transfer to an appropriate medical facility was advised for severely ill individuals encountered on site. Serologic tests All available plasma was screened with an experimental WB method, using a classical antigen produced in baby hamster kidney cells (BHK-21), infected by the prototype strain HFV [39] at a MOI (Multiplicity of infection) = 1. All samples were screened with a classical cell lysate antigen. Positive and indeterminate samples were tested anew with a concentrated purified antigen obtained from a culture supernatant, for clearer and more conclusive results. This antigen was produced from a cell lysate, filtrated through a 0.45 µm filter followed by 40 minutes of ultracentrifugation at 25000 rpm. The resulting concentrated pellet was suspended in 1× Laemmli buffer and kept frozen at −20°C. Antigenic 70 kDa and 74 kDa Gag proteins were separated by a 4 hour migration on polyacrylamide 10% bis tris gel (INVITROGEN, Aukland, New Zealand) with a direct 130 V filed. Antigens were transferred to a polyvinylidene fluoride (PVDF) membrane. Positivity in serology was considered as the presence of the p70 and p74 Gag doublet (figure 2-A). Samples showing only one of the two Gag proteins were considered indeterminate and absence of doublet was considered a negative result. 10.1371/journal.ppat.1002306.g002 Figure 2 Serological and molecular results patterns for SFV detection. A) Western blot results using purified classical chimpanzee antigen sero-positive samples (lanes 3, 4, 6, 10, 12). Sero-indeterminate (lanes 2, 7, 8, 14). Sero-negative samples (lanes 5, 9, 11, 13). Positive SFV control serum from a gorilla-infected human (lane 15), and a macaque (lane PC). B) Nested PCR detection of 465 bp Integrase sequences of SFV M = molecular weight marker. CN = Negative Control. HFV = Human foamy virus, positive control, H2O = Water. Molecular studies High molecular weight genomic DNA was extracted from the buffy-coat of all individuals whose plasma was WB positive or indeterminate for the Gag doublet with a blood extraction kit (Qiagen, Gmbh, Hilden Germany) and for all subjects in the “contact group”, independently of their WB result. Quantified DNA (Biophotometer RS 232 C; Eppendorf, Hamburg, Germany) was amplified (Mastercycler, epGradient; Eppendorf) for a 229 bp fragment of the β-globin gene with primers PCO4 and GH2O as previously described [51]. Two nested PCRs were carried out for the specific detection of SFV DNA. Amplification of a 465 bp fragment on the pol-In (polymerase gene-Integrase), was done for 35 cycles (30″ denaturation at 95°C, 30″ annealing at 55°C, 1′ extension at 72°C and final 7′ extension step at 72°C) using highly generic primers (POL1outse, POL2outas,POL3inse, POL4inas) as previously described [52]. The second PCR was hemi-nested and amplified a fragment of the LTR for 35 cycles (30″ denaturation at 95°C, 30″ annealing at 55°C, 30″ extension at 72°C and final 7′ extension step at 72°C), using generic primers (PBF1se, PBF2as and PBF3se) [53]. “Classical” criteria for SFV infection were defined as 1) clear positivity to WB and 2) positive PCR for the pol-In and/or the LTR DNA fragments. The few individuals with a positive PCR and a negative or indeterminate WB were defined as “non classical”. Amplified DNA was purified with a gel extraction kit (Qiagen, Gmbh, Hilden Germany), and inserted into a 3.9 pCR 2.1 plasmid vector (Invitrogen) with the Rapid DNA ligation kit (ROCHE). Plasmids were cloned in chemically competent Escherischia coli (Invitrogen). Two to four different bacterial clones were selected for plasmid extraction and purification using the quick plasmid minipreps kit (Invitrogen). EcoRI digested fragments were sequenced using universal forward T7 and reverse M13 primers. Sequence analysis and phylogenetic studies For every selected clone, both forward and reverse amplified nucleotide sequences were aligned using “Clustal X alignment” software included in the DAMBE version 4.5.68 (Xia, X., Xie, Z., 2001). Only one clone was considered when sequences were found identical. A consensus sequence was built when one or more nucleotides variations were found. A final consensus sequence was built for every sample from its different clone's consensus sequences. Final sequences were aligned and compared to different old world NHP prototype sequences. According to Akaike Information Criterion (AIC), different evolutionary models were tested using PAUP software version 4.0b10 (Sinauer associates, Inc. Publishers, Sunderland, Massachussets). Phylogeny was performed with the neighbour joining method and the best tree was selected after a bootstrap analysis of 1000 replicates. (Pro)viral loads Quantitative PCR assays for DNA (qPCR) were performed using the Eppendorf realplex master gradient detection system. We used SYBR Green Quantitect (Qiagen) in a 20 µl volume reaction containing 10 µl of SYBR Green buffer, 150 nM of each primer and a 500 ng DNA sample. Five primer pairs were designed in a region of the Integrase in the polymerase gene, conserved among all our sequenced gorilla foamy virus strains. Primers (GF5qpcr-TAGACCTGAAGGAACCAAAATAATTCC, and GR5qpcr-TCCTTCCTCATATTAGGCCACC) gave the best sensitivity (1 to 10 copies per 500 ng). They were designed to detect a 144 pb nucleic acid region of the gorilla FV polymerase gene. The optimized qPCR conditions used were as follows: 95°C for 15 min, 40 cycles of: 95°C for 15 s, 60°C for 30 s and 72°C for 30 s. To standardize qCPR, a 465-pb region that included the PCR target sequence from one primary isolate was cloned into a PCR cloning vector, TOPO TA cloning kit (Invitrogen). Known amounts of the target gorilla foamy virus sequence (from 1 to 104 copies) were added to 500 ng of human genomic DNA from MS5 cell line (fibroblastic cell line) to generate DNA standard curves. In addition to a standard curve, each PCR run included a buffer-only and foamy virus negative DNA controls. DNA derived from PBMC or buffy-coat was used at 500 ng (75×103 cell equivalents). A cellular albumin qPCR was done on each sample to normalize with cellular DNA content (albF-AAACTCATGGGAGCTGCTGGTT, albR-GCTGTCATCTCTTGTGGGCTGT). Each DNA sample was tested at least in duplicate. We checked in every individual assay the specificity of the primers by using a melting curve. Statistics Statistical analyses were performed on Stata software. A univariate analysis was performed for risk factors, by the double entry Fisher exact method with a significance of p 50years 736 18 2.45 0.98 Sex Woman 647 1 0.15 Man 872 36 4.13 <10−3 Ethnicity Bantus 1084 14 1.29 Pygmies 412 23 5.29 <10−3 Circumstances of contact Hunting 190 35 18.42 <10−5 Pets 8 0 0 No contacts 1321 2 0.15 Type of NHP Monkeys 103 2 1.94 <10−5 Apes 95 33 34.74 No contacts 1321 2 0.15 Type of contact Bites 187 31 16.5 <10−5 Scratches 6 1 16.6 Both 5 3 60 No contacts 1321 2 0.15 Localisation of the Wound* Upper body 114 21 18.3 Lower body 68 14 20.59 <10−3 No contacts 1332 2 0.15 Univariate analysis was performed with stata. χ2 and fisher exact test were realised with a critical p value of 0.05. *missing data in this category (5). Secondary intra-familial transmission A secondary intra-familial transmission was searched for in 12 children aged 9 to 37 years born after the presumed infecting contact and in 30 wives aged 23 to 65 years and who had lived from 1 to more than 30 years with the index case after the presumed infecting contact with the NHP. All these samples were tested serologically. Among the women, only a 51 year-old woman Bad460 (married to Bad447) was clearly sero-positive, while three others, wives of Bobak153, Bak46 and Bak55, were sero-indeterminate. Among the children, a nine year old male child Bak108 (son of Bak40) was sero-indeterminate. Repeated PCR analyses on samples from these five individuals were negative for the pol-In and for the LTR. A second sample was collected 6 months later and still showed similar results. Discussion This study reports the largest series yet published, of humans infected with a simian foamy virus, a retrovirus highly endemic in NHPs. Furthermore, this work provides the first data, to our knowledge, concerning the peripheral blood viral load of such retroviral and zoonotic infection in human, by a quantitative PCR method. We report also the negative search for this viral infection in a large series of spouses and children from infected index cases. Lastly, this study reinforces the findings that such zoonotic infection is mainly but interestingly not exclusively acquired through contacts occurring during bites by NHPs. These observations bring out a greater concern on questions concerning the natural history of SFVs in humans: 1) What is the magnitude of such human infection in areas highly endemic for infected NHPs, especially in Central Africa? Concerning central Africa, the work pioneered by Wolfe et al [46], which was followed by our preliminary study [47] identified 16 persons infected by SFVs, as demonstrated by both serological and molecular means. In the present study, we added a series of 39 persons infected by SFVs of NHP origin. Taken together, these data demonstrate FV infection by a wide diversity of NHPs species, in individuals living in different geographical areas of South Cameroon and originating from different ethnic groups (several Bantu groups and two tribes of Pygmies). As only a small proportion of the inhabitants of this large region has been tested for such viruses, it is, however, possible to estimate conservatively that, at least, several hundreds of adults are infected by SFVs in southern Cameroon [55]. The situation is barely known for other African countries. Indeed, apart from one case of infection in a commercial sex worker (CSW) in the Democratic Republic of Congo (DRC)/ex Zaire) [56], only two recent preliminary reports from ongoing studies, indicate the presence of similar zoonotic infection in Gabon (Mouinga-Ondeme, 2011, Abstract Retrovirology) and the DRC (Switzer, 2011, Abstract Retrovirology). Interestingly, in Central Africa, the number of contacts between humans (mostly hunters and their wives and butchers) and NHPs has very probably greatly increased during the last decades [57]. This is mainly due to increased hunting activities, which results from a combination of urban demand for bush-meat, greater access to NHP habitats provided in part by logging roads, easier accessibility to fire arms, and finally, an increase in populations living in forest areas, and the associated increase in local food needs [58]. The results of our study fully support the role played by such factors. Indeed, most (83%) of the SFV infected individuals were relatively young hunters (up to 40 years old) when the presumed infecting contact occurred, but more surprisingly, 16.7% of these contacts occurred within the last 20 years (1991 to 2011). This clearly indicates that hunting NHPs is still an ongoing activity in villages and settlements of southern Cameroon, especially around areas rich in game, such as nature reserves (figure 1). Such hunting activities represent a high-risk occupation for a wide diversity of retroviral zoonotic infections including not only SFVs, but also other retroviral infections such as SIV [16], [17], [59], [60] and STLV [11], [12], [61]. Indeed, even if most of the 16 cumulative cases of human SFV infection reported previously from Cameroon [46], [47] and most of our current 39 cases, were infected by a FV from gorilla (69%, 38/55), at least seven other species of NHPs can also lead to a SFV zoonotic infection in humans. These include chimpanzee, mandrill, baboon and also the most frequently hunted game, including cercopithecus nictitans, cercopithecus cephus, cercopithecus neglectus and some colobus and cercocebus. Another point concerning the estimation of the prevalence of SFV infection in human relates to the quite frequent finding of a positive WB serology associated with a negative detection of SFV (in the blood cells) by PCR. Such was the case for 32% (17/53) of WB positive individuals in the “contact group” and 80.7% (21/26) of WB positive persons in the “general population” (data not shown). Whether these persons are infected or not remains unclear. They were not considered as infected in the present study. Similar findings have already been reported and discussed in the literature [46], [47] and might be related to low viral loads in the blood or less likely, to the presence of divergent SFV strains, not recognized by the generic primers used. These primers can detect and amplify a large variety of African SFVs, and also Asian macaque strains [26], [29], [32], [54]. Non-specific reactivity with the SFV Gag proteins (or Gag-only responses) can also be considered as a cause for these profiles. In this work, we have reported 2 individuals being either sero-indeterminate (only one band by WB) or even sero-negative (2 cases) but in whom we confirmed presence of SFV DNA in their leucocytes blood. Such findings may be related to several factors including a possible long delay of sero-conversion in some cases, especially the individual having been bitten only few months before the sampling. Another possibility could be an individual lack of sero-reactivity for certain proteins as it has been well described in several HTLV-1 or STLV-1 infection, especially for the p24 or some env proteins or peptide [62], [63]. Lastly, in the few persons infected by a Cercopithecus monkey foamy strain, this could be linked to the fact that we have used in our WB chimpanzee viral antigens. However, such antigens cross-react strongly to most of the African and Asian SFV yet tested as demonstrated in several published studies [29], [32], [46], [47]. 2) Is SFV infection pathogenic in humans? The potential for an SFV infection to cause disease in humans is not yet fully understood. The apparent lack of pathogenicity in infected persons, which is still based on a very limited number of cases [45], [64], contrasts strongly with the massive in-vitro lytic properties of these FVs in monkey and human cells [65]. Furthermore, the selection bias inherent in the enrolment of healthy persons in our study, as well as in all of the few published investigations greatly limits the ability to identity any severe acute or chronic diseases. A current case control, based on the series of infected persons reported here, is ongoing to try to detect any potential clinical chronic disease and/or biological abnormalities in persons chronically infected with SFV. However, we have also to keep in mind that the incidence of a disease in a person chronically infected by a retrovirus might be very low and may follow a very long latency. Such features are well exemplified by HTLV-1 infection, another human primate retrovirus of zoonotic origin [66]. Another important issue concerns the possible co-infection by SFV and HIV in the same individual. This has been reported by Switzer et al., in two persons (one CSW and one blood donor) from DRC and Cameroon respectively [56]. Due to the HIV pandemic, in areas where SFV infected persons live (Central Africa and South-East Asia), such co-infections are surely greatly underestimated. Whether HIV-induced immunosuppression could increase the likelihood of developing a disease due to SFV infection remains unknown [55], [56], [67]. Interestingly, cellular tropism of SFV was shown to be enhanced in SIV-induced immunosuppression in a macaque model [37]. 3) How are SFVs transmitted from apes and monkeys to humans? As seen above, most (37/39 = 95%) of the persons infected by a SFV had been bitten, often severely, with persisting scars, by a NHP. These data are consistent with our preliminary study in another area of Cameroon, with a severe bite reported in 12/13 infected persons [47]. Similarly, 6 of 8 SFV infected persons in Southeast-Asia reported having been bitten by a macaque, at least once [48]. Furthermore, in persons occupationally exposed to NHPs in primate centres, zoos and laboratories in Germany and North America, the majority of the infected individuals reported also a bite from a NHP [41], [44], [68]. This situation is also exemplified by a recently published study performed in the CIRMF in Gabon [31]. The high rate of infection by gorilla and chimpanzee FVs in our study (17%, 34/198) as compared to other monkeys (1.5%, 3/198), may be related to the severity of the wounds during apes bites. Indeed, in such cases, tissue damage is much more serious (with soft tissue crushing, tearing and bleeding) with possibly deeper and longer contact between apes saliva and blood of the human hunter. In infected monkeys, especially in macaques, studies have provided evidence that SFV is present at high concentrations in saliva and oral mucosa, with viral replication [36], [37], [38]. Furthermore, it appears that in a semi-free colony of macaques, SFV is mostly acquired through severe bites usually in young adults when they compete for sexual partners [32]. A paper also strongly suggests that chimpanzees acquire SFV by horizontal routes, most likely by exposure to saliva [69]. Therefore, all these data indicate that blood and/or injured tissue contact with saliva are the key factor for this form of zoonotic transmission. No infection was found in the 8 individuals bitten by pets in our study despite 2 WB indeterminate results (data not shown). Pets are usually small sized orphan monkeys, captured at young age, free of infection and brought in the villages where they are raised, away from contacts with infected adult monkeys. Moreover, bites when they happen are almost always superficial. However, grooming as shown in SFV-infected felines, and possibly to a lesser extent sexual contacts, may also lead to transmission between NHPs [23]. It is thus noteworthy that in our study, as in most of the few other studies reporting SFV infection in humans, some of the infected individuals had not reported severe injuries or bite from a NHP [44], [45], [47], [48]. Furthermore, in some cases, the species that inflicted the injury was not the same as that associated with the infecting SFV strain [45]. Indeed, to our knowledge, a dozen of cases have been reported world-wide among the currently known 85 SFV infected persons, including the 39 from our study. This may suggest that, in some cases, infection occurs through other routes than bites, including from saliva spraying into small open wounds or unprotected muco-cutaneous areas without clear injury. Such a possibility can therefore not be ruled out in the only SFV infected case associated with gorilla scratches in our study (Ako394 table 4). Considering that a majority of people living in West Central Africa frequently butcher, cut or manipulate NHP carcasses or meat [57], [58], other modes of contamination involving external mucosal contacts with infected saliva may be considered. This mode of transmission is likely in this study for the two infected cases in the “general population” series who did not report a NHP bite during their lifetime (Bobak237, Ako254 in table 3). Some transmission routes may be similar to that of transmission for simian herpes B [70]. A better knowledge of such risk factors is important to establish proper protective equipment that should be recommended for worker safety in zoos and primate centres. 4) Are these simian viruses transmissible from human to human? Person to person transmissibility of zoonotic SFV infection remains unclear at present. A major concern of our study was the search for secondary intra-familial transmission from index cases to their close relatives. Indeed, to our knowledge, only 11 spouses of SFV infected persons (6 from workers in North America [45] and 5 in our previous study in Cameroon [47]) and very few of their children that have been tested. They were all found negative for SFV infection. In our current series, one woman was interestingly found repeatedly (two times at 6 months interval) to be SFV seropositive among the 30 tested wives of SFV infected hunters. This 51 year-old woman had lived for 6 years with index case Bad447, after probable infectious contact and they had not had children. In the absence of a positive PCR with a sequenced SFV DNA fragment comparable to that of her husband, we can not formally rule out, a serological reaction secondary to circumstantial exposition to a virus from the husband. This probably coincidental sero-reactivity could be, as said before, either a non specific Gag reactivity, or a low viral load SFV infection acquired through another route. Besides, the infection may probably not be transmitted given the quite low (pro)viral load (9 copies for 105 cells) observed in the husband (Bad447) (Table 3). These data indicate that SFV transmission from man to woman does not occur easily by sexual contact or saliva exposure, as previously suggested in the literature [41], [44], [45], [47]. Disease occurrence and transmissibility are related to in-vivo (pro)viral load levels in an infected person. We provide here, to our knowledge, the first data concerning the level of (pro)viral load, as determined by a quantitative PCR method, in persons chronically infected by SFV of zoonotic origin. Our results, based on a series of 28 individuals, all infected by a gorilla virus, indicate a low viral load (in the DNA of the peripheral blood cells) of most persons, but with a quite large range (<1 to 145 copies per 105 cells). The degree of this viral load may be related to the origin of the virus (apes versus small monkeys for example) but also to genetic factors, including innate restriction, as already shown for other human retroviral infection of zoonotic origin such as HIV-1 and HTLV-1 [71], [72], [73]. In our series, we have found a women (Ako254) infected by a SFV from a Cercopithecus. This is, to our knowledge, the fifth reported case of an infection by a SFV in a woman (as demonstrated by both serological and molecular means) [44], [46], [48]. Moreover, two other reported cases of women living in Southeast Asia and sero-positive for macaque SFV have been reported, without demonstration of viral DNA presence in their blood [48]. All together, these data indicate, as already suggested [44], that SFV might also be spread from mother to child and/or through sexual contacts with infected women. The demonstration of highly frequent and recent SFV infections by this study raises important public health concerns not only about the risk for the acquisition of SFV, but also about the consequences of such a zoonosis with regard to other simian viruses that may cause disease in humans [4], [58], [67], [74]. This emphasizes the need for continued long term monitoring of SFV infected individuals to evaluate any changes in host and viral dynamics. Although evidence of a secondary transmission are still sought, vigilance must be maintained on the possible emergence of human-to-human transmission from infected individuals, since SFV transmission by blood transfusion has been demonstrated in a monkey model [42], [75] demonstrating infected blood as a mode of virus transmission. Dual infections with SFV and HIV-1 have been reported [56], and the outcome of such an infection in an immunosuppressed person is unknown. Strategies for proactive preparedness for SFV strains that may have the potential for human transmission and clinical outcome must be implemented. Efforts to reduce the risk of cross-species infection are necessary to control the potential threat of new simian pathogens, such as SFVs. Therefore, general public education would be necessary in these areas where interaction with NHP, mostly through hunting is part of culture and tradition, as well as related to economic needs. Preventive actions must then be taken, considering supply alternatives to hunting.

0 comments Cited 53 times – based on 0 reviews      Review now

Bookmark

All references

Author and article information

Contributors

Delia Doreen Djuicy: Role: ConceptualizationRole: Formal analysisRole: InvestigationRole: MethodologyRole: SoftwareRole: ValidationRole: Writing – original draftRole: Writing – review & editing

Augustin Mouinga-Ondémé: Role: ConceptualizationRole: InvestigationRole: MethodologyRole: SupervisionRole: Writing – review & editing

Olivier Cassar: Role: Formal analysisRole: MethodologyRole: SupervisionRole: Writing – original draftRole: Writing – review & editing

Jill-Léa Ramassamy: Role: Formal analysisRole: Writing – review & editing

Antony Idam Mamimandjiami: Role: Investigation

Rodrigue Bikangui: Role: Investigation

Arnaud Fontanet: Role: Formal analysisRole: Writing – review & editing

Antoine Gessain: Role: ConceptualizationRole: Funding acquisitionRole: InvestigationRole: MethodologyRole: Project administrationRole: ResourcesRole: SupervisionRole: Writing – original draftRole: Writing – review & editing

Edgar M. Carvalho: Role: Editor

Journal

Journal ID (nlm-ta): PLoS Negl Trop Dis

Journal ID (iso-abbrev): PLoS Negl Trop Dis

Journal ID (publisher-id): plos

Journal ID (pmc): plosntds

Title: PLoS Neglected Tropical Diseases

Publisher: Public Library of Science (San Francisco, CA USA )

ISSN (Print): 1935-2727

ISSN (Electronic): 1935-2735

Publication date (Electronic): 12 October 2018

Publication date Collection: October 2018

Volume: 12

Issue: 10

Electronic Location Identifier: e0006832

Affiliations

[1 ] Institut Pasteur, Unité d’Epidémiologie et Physiopathologie des Virus Oncogènes, Département de Virologie, Paris, France

[2 ] CNRS, UMR 3569, Paris, France

[3 ] Centre International de Recherches Médicales de Franceville, Groupe des Rétrovirus Animaux, BP: Franceville, Gabon

[4 ] Ecole Doctorale Régionale d’Afrique centrale, Infectiologie Tropicale, BP: Franceville, Gabon

[5 ] Institut Pasteur, Unité de Recherche et d’Expertise Epidémiologie des Maladies Emergentes, Département d’Infection et Epidémiologie, Paris, France

[6 ] Conservatoire National des Arts et Métiers, Unité PACRI, Paris, France

Hospital Universitário Professor Edgard Santos, BRAZIL

Author notes

The authors have declared that no competing interests exist.

* E-mail: agessain@ 123456pasteur.fr

Article

Publisher ID: PNTD-D-18-00812

DOI: 10.1371/journal.pntd.0006832

PMC ID: 6200283

PubMed ID: 30312301

SO-VID: 8491bdf3-953c-457d-954c-2a29af0d96ad

License:

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

History

Date received : 22 June 2018

Date accepted : 10 September 2018

Page count

Figures: 3, Tables: 3, Pages: 16

Funding

Funded by: funder-id http://dx.doi.org/10.13039/501100004794, Centre National de la Recherche Scientifique;

Award ID: UMR 3569

Award Recipient : Antoine Gessain

Funded by: funder-id http://dx.doi.org/10.13039/501100002708, Agence Universitaire de la Francophonie;

Award Recipient : Delia Doreen Djuicy

Funded by: funder-id http://dx.doi.org/10.13039/501100001665, Agence Nationale de la Recherche;

Award ID: ANR10-LBX-62IBEID

Award Recipient : Antoine Gessain

Funded by: European Union

Award ID: FOOD/2016/379-660

Award Recipient : Jill-Léa Ramassamy

DDD was supported by the “Agence Universitaire de la Francophonie” (AUF), the Institut Pasteur in Paris and the “Centre international de Recherches Médicales de Franceville” (CIRMF) in Gabon. This study received funding from the CNRS (UMR 3569) (AG); the Institut Pasteur, France (AG), and through the “Investissement d’Avenir” as part of a “Laboratoire d’Excellence” (LabEx) French research program: Integrative Biology of Emerging Infectious Diseases (ANR10-LBX-62 IBEID) (AG). JLR was financially supported by the European Union (FOOD/2016/379-660). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Custom metadata

PLOS Publication Stage vor-update-to-uncorrected-proof

Publication Update 2018-10-24

Data Availability All relevant data are within the paper and its Supporting Information files.

Risk factors for HTLV-1 infection in Central Africa: A rural population-based survey in Gabon

Read this article at

Abstract

Background

Methods

Results

Conclusion

Author summary

Related collections

Quaternary ammonium surfactants as nanoparticles against infection

Most cited references 33

Detection and isolation of type C retrovirus particles from fresh and cultured lymphocytes of a patient with cutaneous T-cell lymphoma.

Cross-species transmission of simian retroviruses: how and why they could lead to the emergence of new diseases in the human population.

Frequent and Recent Human Acquisition of Simian Foamy Viruses Through Apes' Bites in Central Africa

Author and article information

Contributors

Journal

Affiliations

Author notes

Article

History

Page count

Funding

Categories

Custom metadata

Comments

Comment on this article

Similar content 614

Cited by 12

Most referenced authors 821