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Biological Health Hazard – New Zoonotic Virus strain (HTLV-4): Gabon


Published Date: 2016-07-16 00:06:06
Subject: PRO> HTLV-4 – Gabon: new strain, gorilla, hunters
Archive Number: 20160716.4347889

Administrative Map of Gabon

Administrative Map based on a UN map. Source: UN Cartographic Section

Wednesday 13 Jul 2016
Source: Science Blog [edited]

New virus strains found in hunters bitten by gorillas
Scientists from the Institut Pasteur and the CNRS [French National Centre for Scientific Research] have identified 2 new strains of the HTLV-4 virus in 2 hunters who were bitten by gorillas in Gabon. These findings, published in the journal Clinical Infectious Diseases, support the notion that gorillas represent a major source of infectious agents that can be passed on to humans.

Many of the viral pathogenic agents that have emerged in humans in recent decades are of animal origin — including SARS coronavirus, avian influenza virus, hantaviruses, Ebola virus, Marburg virus and Nipah virus. After the initial contact between species, some of these viruses used a variety of evolutionary mechanisms to adapt to their new human host. Scientists from the unité d’Epidémiologie et physiopathologie des virus oncogènes (Institut Pasteur/CNRS), directed by Antoine Gessain, are working on a group of RNA viruses known as HTLV retroviruses. In 2 to 8 per cent of cases, HTLV type 1 results in severe forms of leukemia/lymphoma or neuromyelopathy.

There are 4 types of HTLV virus (types 1 to 4). The animal reservoir for all 4 types is non-human primates, especially gorillas and chimpanzees. These viruses can be spread by sexual contact, blood transfusion or breastfeeding. Nearly 20 million people worldwide are thought to be infected by HTLV-1, especially in Japan, the Caribbean, Latin America and tropical Africa. HTLV-2 mainly affects Native American populations, some Pygmy populations and intravenous drug users; approximately a million people are infected worldwide. The HTLV-3 virus has only been observed in a small number of people in Cameroon living in close contact with infected non-human primates. HTLV-4 had previously only been identified in 1 person living in southern Cameroon, and the origin of the infection was unable to be traced.

Scientists from the Institut Pasteur and the CNRS, working in cooperation with the International Center for Medical Research in Franceville, Gabon (the CIRMF) and the Pasteur Center in Cameroon, set about identifying HTLV retroviruses in people at risk of contact with non-human primates. By using molecular screening to examine blood samples from 300 people who had been bitten by monkeys in Central Africa, they were able to identify the HTLV-4 virus — previously only observed in Cameroon — in 2 individuals in Gabon.

These individuals reported having been severely bitten by a gorilla during hunting activities, which seems to confirm the zoonotic origin of the virus. The fact that this virus was only found in 2 people who had been bitten by a gorilla and not in anyone who had been bitten by a chimpanzee or a smaller monkey suggests that the virus is specifically transmitted by gorillas. Moreover, the gorilla bites occurred several years before the blood samples were taken, revealing the chronic persistence of this virus in humans.

The scientists also discovered that one of the 2 new strains is divergent from the previously known strain of HTLV-4, highlighting the genetic diversity of this human virus.

This research supports the idea that gorillas should be seen as key reservoirs for infectious agents that can be passed on to humans. The findings suggest that there are probably several other cases in Cameroon and Gabon, as well as in neighboring countries. Work now needs to be done to identify diseases that may be caused by the HTLV-3 and HTLV-4 retroviruses.

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ProMED-mail from HealthMap Alerts

[“The bites occurred years before blood samples had been collected (17 and 9 years for the 2 hunters) in which infection was shown. Our results thus indicate the chronic persistence of this virus in humans, which is the case for the other human retroviruses HTLV-1 and human immunodeficiency virus type 1 and type 2. Our data also demonstrate HTLV-4 chronic persistence in gorillas with no evident genetic variability during 6 years.” … – more

The full citation for this brief report is L Richard et al. Zoonotic Transmission of Two New Strains of Human T-lymphotropic Virus Type 4 in Hunters Bitten by a Gorilla in Central Africa. Clin Infec Dis 29 June 2016 (

Molecular screening of 300 at-risk people from Central Africa identified 2 human T-lymphotropic virus (HTLV)-4-infected individuals. A zoonotic origin of infection was suggested, as both individuals reported being severely bitten by a gorilla during hunting activities. One strain was highly divergent and was designated as the HTLV-4 subtype-b prototype.

Here, we demonstrated the presence of HTLV-4 infection in 2 hunters of NHPs living in Gabon, Central Africa. The fact that these viruses were found exclusively in 2 persons severely bitten by a gorilla (2/102) and not in persons bitten by a chimpanzee (0/34) or a small monkey (0/164) suggests zoonotic transmission of this retrovirus to humans through a bite from these animals. The presence of an HTLV-1 infection of genotype b (the subtype present in gorillas) in 1 of the 2 HTLV-4-infected hunters (GabL36), as well as an infection by a gorilla SFV (a virus mainly present in saliva and thus nearly exclusively transmitted through severe bites), strongly reinforces the very probable zoonotic origin of HTLV-4 infection in this hunter.” … – more

It is interesting that the bites appeared 17 and 9 years prior to blood collection and testing. It is not clear whether remarkable illness was associated at any time with the bites, but one hunter is currently suffering from insulin-dependent diabetes and pulmonary tuberculosis.

“Human T-cell lymphotropic virus (HTLV) was the 1st human retrovirus discovered. HTLV belongs to the Retroviridae family in the genus Deltaretrovirus. Retroviruses are RNA viruses that use an enzyme called reverse transcriptase to produce DNA from RNA. The DNA is subsequently incorporated into the host’s genome. HTLV predominantly affects T lymphocytes.

Prior to 1979, the isolation of retroviruses was possible only in nonhuman primates; in fact, it was believed that human retroviruses did not exist. In 2005 in Retrovirology, Gallo reflected about earlier concepts that supported this belief. First, if human retroviruses did in fact exist, then why had they not yet been discovered? Second, the virus was easily detected in animals, and therefore should have also been easily detectable in humans. Third, technical difficulties hampered efforts to grow primary human cells in the laboratory. Finally, it was shown that the human complement lyses animal retroviruses in vitro, suggesting erroneously that humans were intrinsically protected from these viruses [1].

In 1979, T-cell lymphotropic virus was isolated in a patient with cutaneous T-cell lymphoma [2]. This led to the discovery of the 1st HTLV and marked the beginning of the human retrovirus era. Two years later, HTLV-2 was documented in a patient who had been diagnosed with hairy cell leukemia [3], although subsequent studies showed no affiliation between the 2 processes.

In 1983, the 3rd and most important retrovirus was discovered. At the time of its discovery, this virus was classified in the HTLV genus. However, upon further research, it was reclassified into the Lentivirus genus and given the name human immunodeficiency virus (HIV). In 2005, 2 novel viruses, HTLV-3 and HTLV-4, were discovered. Little is known about these viruses, as only a few cases have been reported.” … – more

Full text and references available at – Mod.LK

A HealthMap/ProMED-mail map can be accessed at:]

See Also

HTLV-II, brain disorder – Brazil 20000820.1382

A ProMED-mail post
ProMED-mail is a program of the International Society for Infectious Diseases

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