Friday, 12 September 2014

Ebola: Gorillas and other wild animals

Female gorilla in the Jupiter Group
Ngaga Camp,
Republic of Congo, May 2014
Her toddler was clambering in the trees
above her
The conversation at the funeral of a former colleague with another former colleague, a microbiologist with wide interests who I had not seen for some years, turned to the outbreak of ebola virus (EBOV) in West Africa and how it may spread between wild, domesticated and human mammals, and the characteristics needed for one or more reservoir species, in other words, those that carry but do not suffer to the point of rapid mortality the infectious agent.

In May we were at the site of the 2003 outbreak in the Republic of Congo and heard of the devastating effect ebola had on the Western Lowland Gorilla population. Since returning I have had the chance of catching up with the literature on that outbreak and how it was established that ebola has such a devastating effect on the survival of gorillas, with a mortality rate of 90-95% and the estimated loss of 5000 gorillas from a relatively small area.

Magda Bermejo who lives at the camp in the Republic of Congo we visited (see post of 18 August 2014) after the effective loss of her study groups at Lossi to the ebola outbreak, established the death of gorillas and chimpanzees during human outbreaks, found ebola virus in a number of the carcasses and showed an apparent passage from group to group of gorillas rather than independent transmission form a putative reservoir species. But then, and apart from the enormous potential effect on survival of the great apes in Africa, all sorts of question arise as to who or what becomes infected first and how does the infection (not that easily transmitted according to the evidence with contact through body fluids being needed) pass between groups.

Bushmeat has been implicated as the initial source of human infection while bats, particularly, but also duikers, pigs and domestic dogs are suspected as possible reservoir species. Recently, I see those sequencing the virus collected during the current outbreak have found rapid changes and are reaching different conclusions on the origins of EBOV. The article by Gretchen Vogel in Science (29 August 2014) reads:

Some researchers theorized, based on early sequencing data, that EBOV had circulated for decades, undetected, in animals in the region. But the new analysis, strengthened by the unprecedented number of genomes, supports another theory: that the virus spread, via animal hosts, from Central Africa within the last decade. Researchers aren’t sure which animal to blame, but fruit bats are their leading suspects (Science, 11 April, p. 140). At least one fruit bat species known to carry ebolavirus has a population range that stretches from Central Africa across to Guinea.

That more research on ebola and much more money to fund that research are necessary are truisms. The dangers to those working in a human outbreak to collect samples in areas where facilities for the safe care of patients and basic hygiene are poor also cannot be overestimated. Five of those who collected samples for sequencing  in the current human outbreak have died. Until really hard evidence is obtained from extensive surveys in wild (and domestic) animals over meaningful periods of time and over a wide geographical area, speculation and soft epidemiological evidence may have to suffice in the meantime. But, in that meantime and beyond, alongside local outbreaks that devastate human populations, the great apes of Africa are at risk.

Tom, our former colleague, would I am sure have been delighted that his funeral was the occasion for several coffee-room type discussions on science and science politics; Scottish politicians were not rated highly in the latter.

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Useful starting points for further reading:

Bermejo M et al. Ebola outbreak killed 5000 gorillas. Science 314, 1564
Vogel G. 2014. Are Bats Spreading Ebola Across Sub-Saharan Africa? Science 344, 140
Vogel G. 2014. Genomes reveal start of ebola outbreak. Science 345, 989-990
Walsh PD et al. 2003. Catastrophic ape decline in western equatorial Africa. Nature 422, 611-614
Wittmann TJ et al. 2007. Isolates of Zaire ebolavirus from wild apes reveal genetic lineage and recombinants. Proceedings of the National Academy of Sciences of the USA 104, 17123-17127