Discovery Of Ebola In Pigs Raises Concerns

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Main Category: Infectious Diseases / Bacteria / Viruses
Also Included In: Veterinary;  GastroIntestinal / Gastroenterology;  Blood / Hematology
Article Date: 10 Jul 2009 - 7:00 PDT

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Scientists studying a strain of Ebola virus found in domestic pigs in the Philippines last year suggest that although the particular strain is not one linked to disease in humans its emergence in the human food chain is cause for concern.

The investigation was the work of scientists from the US Department of Agriculture at the Plum Island Animal Disease Center in New York, the US Centers for Disease Control and Prevention in Atlanta, and the Department of Agriculture in the Philippines and is published as a paper in the 10 July issue of Science.

Ebola and Marburg viruses belong to the filovirus family, which cause hemorrhagic fever, characterized by bleeding, vomiting and diarrhea, and a 90 per cent death rate.

Outbreaks of infection appear to happen in humans and primates at random, making it very important to locate sources of host organisms that could be acting as potential reservoirs.

Ebola-Reston was found in pigs raised on farms near Manila, the capital of the Philippines after farmers reported high rates of sickness and deaths among their livestock in May 2008. The infected pigs were originally investigated because they were experiencing an unusually severe outbreak of porcine reproductive and respiratory disease syndrome.

Reston is deadly in monkeys but doesn't appear to infect humans: it is the only member of the filovirus family that does not, said the authors, who nevertheless expressed concern that it has emerged in the human food chain.

When they studied isolates of the virus taken from pig samples, the researchers found that they were more divergent from each other than from the original strain isolated in 1989, when Reston was first identified in crab-eating macaques imported to the US from the Philippines (Reston is the place in Virginia where the lab was based that first spotten the new strain).

When you have isolates that are more different from each other than from an original strain, it indicates they have multiple ancestral origins (they did not descend in a neat line from generation to generation). This suggests, said the authors, that the Ebola-Reston isolated from the pigs is a strain that has been around since before 1989 when Reston was first found in the crab-eating macaques.

Although Reston has not been found to cause deadly hemorrhagic fever in humans, when the researchers tested some of the pig farmers they found antibodies to Reston in their blood, suggesting pig-to-human transmission had taken place, even though the farmers showed no symptoms.

The concern is that pig herds could be convenient hosts for Reston to mutate into a form that does cause illness in humans, and also, if pigs can be hosts to Reston, as this outbreak reveals, then perhaps they could also be hosts to other Ebola strains that do cause harm to humans.

There are lots of unknowns, a lot more questions than answers, and this is the worry, said the researchers, because pigs are in the human food chain and there is lots of contact between pig herds and humans.

"Discovery of Swine as a Host for the Reston ebolavirus."
Roger W. Barrette, Samia A. Metwally, Jessica M. Rowland, Lizhe Xu, Sherif R. Zaki, Stuart T. Nichol, Pierre E. Rollin, Jonathan S. Towner, Wun-Ju Shieh, Brigid Batten, Tara K. Sealy, Consuelo Carrillo, Karen E. Moran, Alexa J. Bracht, Gregory A. Mayr, Magdalena Sirios-Cruz, Davinio P. Catbagan, Elizabeth A. Lautner, Thomas G. Ksiazek, William R. White, and Michael T. McIntosh.
Science 10 July 2009 325: 204- 206.
DOI: 10.1126/science.1172705

Sources: CDC, Science.

Written by: Catharine Paddock, PhD
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today