Co-circulation of viruses between apes and humans in Africa
Posted on April 8, 2014 by Microbiology Society
On 21 July 1969, Neil Armstrong made mankind’s most famous leap, when he opened the Eagle’s hatch and stepped down onto the lunar surface. Hundreds of thousands of miles away in Ghana, something else happened in 1969 that you may not have heard of, yet it happens every year.
Contemporary reports detail an epidemic of a highly contagious disease sweeping across the country. Within hours of being infected, people showed signs of eye inflammation and subconjunctival haemorrhage – bloodshot eyes to you and I.
The disease is known as acute haemorrhagic conjunctivitis (AHC), which although painful, is usually short-lived and results in no long-term damage. The Department of Ophthalmology at the Ghana Medical School reported seeing a total of 13,644 cases between June and October of 19691, with the disease spreading to Asia in 1970 and, ultimately, worldwide. Outbreaks of the disease continue to happen annually in Ghana, where it is called ‘Apollo’, in reference to 1969’s Apollo 11 moon mission and the year the disease first occurred.
The causative agent of Apollo is an Enterovirus (EV) known as EV-D70, a member of the genus Enterovirus. There are four distinct species of EV that infect humans (A to D); new strains of each species arise frequently, particularly in Africa and Bangladesh. New research, published in the Journal of General Virology, has looked how these viruses circulate between humans and non-human primates, which represent a potential reservoir for new strains of EVs. Understanding where new strains of EVs may come from is important, as aside from being responsible for Apollo, EVs are the most common cause of viral meningitis. Other symptoms of EV infection include hand, foot and mouth disease, and myocarditis – inflammation of the heart muscle.
The researchers behind the work, led by Dr Heli Harvala from the Royal Infirmary of Edinburgh, focused on wild chimpanzees, gorillas and bonobos living in remote parts of Cameroon and Democratic Republic of the Congo. The team screened 139 stool samples from the animals, looking for EVs using probes designed to detect human EV infections.
The results showed that 10 per cent of the samples were EV-positive and that most of the positive samples came from South East Cameroon, near the border with the Central African Republic2. Three of the viruses isolated from chimps appeared closely related to the human strain EV-A89, previously isolated from stool specimens of children with acute flaccid paralysis in Bangladesh.
Another of the strains – EV-A119 – has only recently been discovered, having been isolated from children in Cameroon3. While there is no suggestion that this virus has any detrimental effects to humans, there is direct evidence that it has jumped between species, although it doesn’t appear to have spread very far.
The final strains isolated appear to be exclusively found in non-human primates: EV-D120 is a previously undiscovered new strain, while MA5709 – isolated from a single bonobo sample – is vastly different from the others and potentially represents a new species of enterovirus.
While the sample numbers in this study are small, they do show that the non-human primate population of Africa represents a reservoir for enteroviruses and that these viruses can move between species, despite the remote location within which the apes live and the limited contact they have with humans.
A big question in EV research is how related enteroviral strains can be isolated in both a remote corner of an African jungle and in humans in Bangladesh. How have they got from one to the other? It seems that monkeys are an important vector. Humans and monkeys live in close proximity in Bangladesh; researchers have compared human and monkey stools from the country and found a large range of viruses common to both, including 20 distinct enterovirus types4. Dr Harvala is currently studying monkey species to look for new enteroviruses and to learn more about the species barrier between monkeys and humans.
Current research is unable to ascertain the direction that the EVs are being spread – rather than being ape to monkey to human, it can just as easily be the other way round. Either way, increased levels of contact between humans and non-human primates in Central Africa, whether it is as a result of hunting or deforestation, means there is more potential for these viruses to circulate5.
While most media coverage of potential pandemics focuses (perhaps correctly) on the threat of a highly infectious new flu strain, it is important that we continue to monitor the non-human primate reservoir if we’re to understand the roots of emerging viral diseases, which can be pathogenically unpredictable. For example, research in 1999 showed that the closest relatives of HIV-1 – the major causative agent of HIV – are simian immunodeficiency viruses (SIVs) that infect chimps and gorillas6. Unlike the human form, SIVs in non-human primates appear to be non-pathogenic.
While not light on hyperbole, Roger Ebert’s review of the 1995 film Outbreak – which sees of a deadly virus escapes the African jungles via an infected monkey to cause scores of deaths in Small Town, USA – perhaps sums up the doomsday scenario for this field:
“It is one of the great scare stories of our time, the notion that deep in the uncharted rain forests, deadly diseases are lurking, and if they ever escape their jungle homes and enter the human bloodstream, there will be a new plague the likes of which we have never seen.”
I wrote this story earlier in the year, but this research seems especially prescient right now. Over the past few weeks, there has been a significant outbreak of the Ebola virus in Guinea, West Africa. Guinea’s Ministry of Health has reported 151 suspected cases and 95 deaths. The disease has been confirmed in Conakry, the country’s capital, and has been identified in neighbouring Liberia and, potentially, Sierra Leone.
Chatterjee S, Quarcoopome CO, & Apenteng A (1970). Unusual type of epidemic conjunctivitis in Ghana. The British Journal of Ophthalmology, 54 (9), 628-30 PMID: 5458256
Harvala H, Van Nguyen D, McIntyre C, Ahuka-Mundeke S, Ngole EM, Delaporte E, Peeters M, & Simmonds P (2014). Co-circulation of enteroviruses between apes and humans. The Journal of General Virology, 95 (Pt 2), 403-7 PMID: 24189620
Ayukekbong J, Kabayiza JC, Lindh M, Nkuo-Akenji T, Tah F, Bergström T, & Norder H (2013). Shift of Enterovirus species among children in Cameroon–identification of a new enterovirus, EV-A119. Journal of Clinical Virology, 58 (1), 227-32 PMID: 23895932
Oberste MS, Feeroz MM, Maher K, Nix WA, Engel GA, Hasan KM, Begum S, Oh G, Chowdhury AH, Pallansch MA, & Jones-Engel L (2013). Characterizing the picornavirus landscape among synanthropic nonhuman primates in Bangladesh, 2007 to 2008. Journal of Virology, 87 (1), 558-71 PMID: 23097448
Wolfe ND, Daszak P, Kilpatrick AM, & Burke DS (2005). Bushmeat hunting, deforestation, and prediction of zoonoses emergence. Emerging Infectious Diseases, 11 (12), 1822-7 PMID: 16485465
Gao F, Bailes E, Robertson DL, Chen Y, Rodenburg CM, Michael SF, Cummins LB, Arthur LO, Peeters M, Shaw GM, Sharp PM, & Hahn BH (1999). Origin of HIV-1 in the chimpanzee Pan troglodytes troglodytes. Nature, 397 (6718), 436-41 PMID: 9989410