Emergence of simian foamy viruses in humans: facts and unanswered questions

A Systematized Overview of Published Reviews on Biological Hazards, Occupational Health, and Safety

Introduction

The COVID-19 pandemic turned biological hazards in the working environment into a global concern. This systematized review of published reviews aimed to provide a comprehensive overview of the specific jobs and categories of workers exposed to biological hazards with the related prevention.

Methods

We extracted reviews published in English and French in PubMed, Embase, and Web of Science. Two authors, working independently, subsequently screened the potentially relevant titles and abstracts recovered (step 1) and then examined relevant full texts (step 2). Disagreements were resolved by consensus. We built tables summarizing populations of exposed workers, types of hazards, types of outcomes (types of health issues, means of prevention), and routes of transmission.

Results

Of 1426 studies initially identified, 79 studies by authors from every continent were selected, mostly published after 2010 (n = 63, 79.7%). About half of the reviews dealt with infectious hazards alone (n = 38, 48.1%). The industrial sectors identified involved healthcare alone (n = 16), laboratories (n = 10), agriculture (including the animal, vegetable, and grain sectors, n = 32), waste (n = 10), in addition of 11 studies without specific sectors. The results also highlighted a range of hazards (infectious and non-infectious agents, endotoxins, bioaerosols, organic dust, and emerging agents).

Conclusion

This systematized overview allowed to list the populations of workers exposed to biological hazards and underlined how prevention measures in the healthcare and laboratory sectors were usually well defined and controlled, although this was not the case in the agriculture and waste sectors. Further studies are necessary to quantify these risks and implement prevention measures that can be applied in every country.

Efficient liver gene transfer with foamy virus vectors

Background

Liver gene transfer offers hope for the correction of genetic and acquired disorders. Efficient gene transfer in large animals can be obtained with hydrodynamic gene transfer (HGT), a method that can achieve sufficient levels of gene delivery.

Material/Methods

To test the relative efficiency between plasmid versus foamy virus (FV) vector-based liver gene transfer efficiency, we applied HGT in 4 juvenile pigs, using the same plasmid backbone, either naked or coated as a FV vector particle. Gene transfer efficiency and persistence of expression was assayed by PCR and real-time PCR, respectively, at 1 week and at 1 month after the infusions.

Results

HGT was tolerated well and no adverse reactions were observed. Plasmid injections resulted in no detectable DNA sequences at 1 week. At the 1 month time point, 2/15 liver sections analyzed were positive for the presence of plasmid DNA. When FV vectors were infused under identical conditions, 18/28 (64.3%) of the liver samples were positive for the presence of vector sequences, and the expression levels reached 29.7 and 15.6% of the endogenous GAPDH levels in the injected and the adjacent liver lobes.

Conclusions

Our results indicate that medium-term therapeutic levels of gene expression can be obtained with FV vectors, an effect that can be attributed to the potential of the HGT procedure and to the natural affinity of FV vectors for hepatocytes.

Identification and characterization of highly divergent simian foamy viruses in a wide range of new world primates from Brazil

Foamy viruses naturally infect a wide range of mammals, including Old World (OWP) and New World primates (NWP), which are collectively called simian foamy viruses (SFV). While NWP species in Central and South America are highly diverse, only SFV from captive marmoset, spider monkey, and squirrel monkey have been genetically characterized and the molecular epidemiology of SFV infection in NWPs remains unknown. We tested a large collection of genomic DNA (n = 332) comprising 14 genera of NWP species for the presence of SFV polymerase (pol) sequences using generic PCR primers. Further molecular characterization of positive samples was carried out by LTR-gag and larger pol sequence analysis. We identified novel SFVs infecting nine NWP genera. Prevalence rates varied between 14-30% in different species for which at least 10 specimens were tested. High SFV genetic diversity among NWP up to 50% in LTR-gag and 40% in pol was revealed by intragenus and intrafamilial comparisons. Two different SFV strains infecting two captive yellow-breasted capuchins did not group in species-specific lineages but rather clustered with SFVs from marmoset and spider monkeys, indicating independent cross-species transmission events. We describe the first SFV epidemiology study of NWP, and the first evidence of SFV infection in wild NWPs. We also document a wide distribution of distinct SFVs in 14 NWP genera, including two novel co-speciating SFVs in capuchins and howler monkeys, suggestive of an ancient evolutionary history in NWPs for at least 28 million years. A high SFV genetic diversity was seen among NWP, yet these viruses seem able to jump between NWP species and even genera. Our results raise concerns for the risk of zoonotic transmission of NWP SFV to humans as these primates are regularly hunted for food or kept as pets in forest regions of South America.

Simian foamy virus in non-human primates and cross-species transmission to humans in Gabon: an emerging zoonotic disease in central Africa?

It is now known that all human retroviruses have a non-human primate counterpart. It has been reported that the presence of these retroviruses in humans is the result of interspecies transmission. Several authors have described the passage of a simian retrovirus, simian foamy virus (SFV), from primates to humans. To better understand this retroviral “zoonosis” in natural settings, we evaluated the presence of SFV in both captive and wild non-human primates and in humans at high risk, such as hunters and people bitten by a non-human primate, in Gabon, central Africa. A high prevalence of SFV was found in blood samples from non-human primates and in bush meat collected across the country. Mandrills were found to be highly infected with two distinct strains of SFV, depending on their geographical location. Furthermore, samples collected from hunters and non-human primate laboratory workers showed clear, extensive cross-species transmission of SFV. People who had been bitten by mandrills, gorillas and chimpanzees had persistent SFV infection with low genetic drift. Thus, SFV is presumed to be transmitted from non-human primates mainly through severe bites, involving contact between infected saliva and blood. In this review, we summarize and discuss our five-year observations on the prevalence and dissemination of SFV in humans and non-human primates in Gabon.

Innate sensing of foamy viruses by human hematopoietic cells

Foamy viruses (FV) are nonpathogenic retroviruses that have cospeciated with primates for millions of years. FV can be transmitted through severe bites from monkeys to humans. Viral loads remain generally low in infected humans, and no secondary transmission has been reported. Very little is known about the ability of FV to trigger an innate immune response in human cells. A few previous reports suggested that FV do not induce type I interferon (IFN) in nonhematopoietic cells. Here, we examined how human hematopoietic cells sense FV particles and FV-infected cells. We show that peripheral blood mononuclear cells (PBMCs), plasmacytoid dendritic cells (pDCs), and the pDC-like cell line Gen2.2 detect FV, produce high levels of type I IFN, and express the IFN-stimulated gene MxA. Fewer than 20 FV-infected cells are sufficient to trigger an IFN response. Both prototypic and primary viruses stimulated IFN release. Donor cells expressing a replication-defective virus, carrying a mutated reverse transcriptase, induced IFN production by target cells as potently as wild-type virus. In contrast, an FV strain with env deleted, which does not produce viral particles, was inactive. IFN production was blocked by an inhibitor of endosomal acidification (bafilomycin A1) and by an endosomal Toll-like receptor (TLR) antagonist (A151). Silencing experiments in Gen2.2 further demonstrated that TLR7 is involved in FV recognition. Therefore, FV are potent inducers of type I IFN by pDCs and by PBMCs. This previously underestimated activation of the innate immune response may be involved in the control of viral replication in humans.

Cross-species transmission of simian foamy virus to humans in rural Gabon, Central Africa

In order to characterize simian foamy retroviruses (SFVs) in wild-born nonhuman primates (NHPs) in Gabon and to investigate cross-species transmission to humans, we obtained 497 NHP samples, composed of 286 blood and 211 tissue (bush meat) samples. Anti-SFV antibodies were found in 31 of 286 plasma samples (10.5%). The integrase gene sequence was found in 38/497 samples, including both blood and tissue samples, with novel SFVs in several Cercopithecus species. Of the 78 humans, mostly hunters, who had been bitten or scratched by NHPs, 19 were SFV seropositive, with 15 cases confirmed by PCR. All but one were infected with ape SFV. We thus found novel SFV strains in NHPs in Gabon and high cross-species transmission of SFVs from gorilla bites.

Frequent and recent human acquisition of simian foamy viruses through apes' bites in central Africa

Human infection by simian foamy viruses (SFV) can be acquired by persons occupationally exposed to non-human primates (NHP) or in natural settings. This study aimed at getting better knowledge on SFV transmission dynamics, risk factors for such a zoonotic infection and, searching for intra-familial dissemination and the level of peripheral blood (pro)viral loads in infected individuals. We studied 1,321 people from the general adult population (mean age 49 yrs, 640 women and 681 men) and 198 individuals, mostly men, all of whom had encountered a NHP with a resulting bite or scratch. All of these, either Pygmies (436) or Bantus (1085) live in villages in South Cameroon. A specific SFV Western blot was used and two nested PCRs (polymerase, and LTR) were done on all the positive/borderline samples by serology. In the general population, 2/1,321 (0.2%) persons were found to be infected. In the second group, 37/198 (18.6%) persons were SFV positive. They were mostly infected by apes (37/39) FV (mainly gorilla). Infection by monkey FV was less frequent (2/39). The viral origin of the amplified sequences matched with the history reported by the hunters, most of which (83%) are aged 20 to 40 years and acquired the infection during the last twenty years. The (pro)viral load in 33 individuals infected by a gorilla FV was quite low (<1 to 145 copies per 10⁵ cells) in the peripheral blood leucocytes. Of the 30 wives and 12 children from families of FV infected persons, only one woman was seropositive in WB without subsequent viral DNA amplification. We demonstrate a high level of recent transmission of SFVs to humans in natural settings specifically following severe gorilla bites during hunting activities. The virus was found to persist over several years, with low SFV loads in infected persons. Secondary transmission remains an open question.

Most of the viral pathogens that have emerged in humans during the last decades have a zoonotic origin. After the initial interspecies transmission, these viruses have followed different evolutionary routes and have spread among humans through distinct mechanisms. The understanding of the initial steps of the emergence of several viruses and associated diseases often remains quite poor. Human infection by simian foamy viruses (SFV) can be acquired by persons occupationally exposed to non-human primates (NHP) or in natural settings. Epidemiological and microbiological studies in specific high-risk populations are necessary to gain new insights into the early events of the emergence process, and the potential to spread or cause disease among humans. The present study found that hunting is still a very common and risky activity for SFV infection in forest areas of South Cameroon. Indeed, recent interspecies transmission of SFVs to young adults is still very frequent, as 1 person out of 5 among the hunters who have reported a bite or scratch by a non-human primate and 2 persons out of a thousand in the general population are persistently infected by a SFV, mostly from an ape. Secondary transmission to other family members and presence of a disease in infected persons are still open questions that are being investigated.

Two distinct variants of simian foamy virus in naturally infected mandrills (Mandrillus sphinx) and cross-species transmission to humans

Background

Each of the pathogenic human retroviruses (HIV-1/2 and HTLV-1) has a nonhuman primate counterpart, and the presence of these retroviruses in humans results from interspecies transmission. The passage of another simian retrovirus, simian foamy virus (SFV), from apes or monkeys to humans has been reported. Mandrillus sphinx, a monkey species living in central Africa, is naturally infected with SFV. We evaluated the natural history of the virus in a free-ranging colony of mandrills and investigated possible transmission of mandrill SFV to humans.

Results

We studied 84 semi-free-ranging captive mandrills at the Primate Centre of the Centre International de Recherches Médicales de Franceville (Gabon) and 15 wild mandrills caught in various areas of the country. The presence of SFV was also evaluated in 20 people who worked closely with mandrills and other nonhuman primates. SFV infection was determined by specific serological (Western blot) and molecular (nested PCR of the integrase region in the polymerase gene) assays. Seropositivity for SFV was found in 70/84 (83%) captive and 9/15 (60%) wild-caught mandrills and in 2/20 (10%) humans. The 425-bp SFV integrase fragment was detected in peripheral blood DNA from 53 captive and 8 wild-caught mandrills and in two personnel. Sequence and phylogenetic studies demonstrated the presence of two distinct strains of mandrill SFV, one clade including SFVs from mandrills living in the northern part of Gabon and the second consisting of SFV from animals living in the south. One man who had been bitten 10 years earlier by a mandrill and another bitten 22 years earlier by a macaque were found to be SFV infected, both at the Primate Centre. The second man had a sequence close to SFVmac sequences. Comparative sequence analysis of the virus from the first man and from the mandrill showed nearly identical sequences, indicating genetic stability of SFV over time.

Conclusion

Our results show a high prevalence of SFV infection in a semi-free-ranging colony of mandrills, with the presence of two different strains. We also showed transmission of SFV from a mandrill and a macaque to humans.

Simian foamy virus infection in humans: prevalence and management

Simian foamy viruses (SFVs) are highly prevalent in all nonhuman primate species and can infect humans following occupational and non-occupational exposure to infected animals and their tissues, blood or body fluids. Virus transmission results in a stable, persistent infection that seems to be latent. SFV infections are thus far nonpathogenic, with no evidence of adverse clinical outcome in their natural nonhuman primate hosts or by experimental injection in animals and upon cross-species transmission in humans. Since the emergence of pathogenic viruses from nonpathogenic viruses upon cross-species infection is well-documented for several retroviruses, it is prudent to take necessary precautions to deter SFV infections in humans. These steps will help prevent the emergence of a novel pathogen and reduce the risk of transmission of another potential pathogenic human retrovirus.

Frequent foamy virus infection in free-living chimpanzees of the Taï National Park (Côte d'Ivoire)

Foamy viruses are frequently found in non-human primates and apes in captivity. However, data on simian foamy virus (SFV) infection in apes from the wild are limited. Necropsy specimens were collected from 14 West African chimpanzees (Pan troglodytes verus) from three communities in the Taï National Park, Côte d'Ivoire. PCR analysis revealed SFV-related int- and env-specific sequences in 12/14 chimpanzees. Two young chimpanzees were not infected. Plasma from 'PCR-positive' chimpanzees reacted against Pr71/74(gag) in Western blot analysis. Phylogenetic analysis demonstrated clustering of all analysed sequences with SFVcpz previously identified from the other P. troglodytes verus, although interestingly the sequences were diverse and no grouping according to a particular animal community was observed. The body compartments of two infected animals were examined and found to contain SFV sequences. Frequent SFV infections in chimpanzees from this area significantly increase the potential risk of zoonotic transmission to rural populations through direct contact, hunting and consumption of bush meat.