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พุธ, 17 ธันวาคม 2008

Disease Situation in Philippine Swine – An unfolding situation

The situation

December 2008. or the first time, the Ebola-Reston virus has been found in pigs. The virus was discovered in the Philippines after field investigations and sample collections by the Bureau of Animal Industry (BAI), Department of Agriculture of the Philippines, because of suspected outbreaks of Porcine Reproductive and Respiratory Syndrome (PRRS) affecting several swine production areas.


Source FAO

The discovery of the Ebola-Reston virus in pigs requires further medical, veterinary and biological research. Testing animal handlers and wildlife for the presence of the Ebola-Reston virus will be helpful to understand how pigs may have become infected and to learn more about a potential spill over to humans. It will probably take weeks or even months to obtain the first results of this analysis. To date, there are no reports of sick or ailing people among those having had contact with infected pigs according to the Philippine Ministry of Health and the Bureau of Animal Industry. There were incidents of pig illness and deaths on the farms where Ebola-Reston infected swine were bred and raised. However other microorganisms isolated from sick and dying swine may have been the cause of elevated mortality rather than the Ebola-Reston virus.





What is Ebola, what is Ebola-Reston?


Ebola is the common term for a disease caused by a group of viruses belonging to the genus Ebolavirus of the family Filoviridae to which humans and other primates are susceptible. Ebola or Ebola hemorrhagic fever is named after the Ebola River Valley, Democratic Republic of the Congo (before known as Zaïre), where the first outbreak of Ebola haemorrhagic fever in humans was reported in 1976.



In humans, Ebola is characterised by fever, vomiting, diarrhoea, generalized muscle and joint pain, and sometimes internal and external bleeding. Despite treatment, case fatality rates (the proportion of those with the disease that subsequently die from it) are high, ranging from 50–90%. The cause of death usually is organ failure and blood loss. Treatment through intravenous infusion of fluids is supportive and no approved vaccine is available.


Ebola-Reston virus is also a filovirus with genetic characteristics similar to the virus first identified in Zaïre, but of Asian origin. It was discovered in macaques (Macaca fascicularis) at the Hazleton Laboratories in Reston, Virginia (USA) in 1989, where monkeys kept for research purposes became ill and some died. These monkeys had been imported weeks earlier from the Philippines.


Two notable differences between Ebola-Reston and other Ebola viruses are known: Reston-Ebola virus, unlike the African strains of Ebola virus shown to cause disease in humans, is transmitted by air, Also, Reston-Ebola virus does not affect humans and is of low fatality in monkeys. However, in monkeys, co-infection of Reston-Ebola virus with simian haemorrhagic fever virus (SHFV) exacerbates the disease, and its fatality rate.


During the 1989 Ebola-Reston incident in the US, six animal caretakers developed a virus-specific immune response as determined by antibody assays. Similar cases of immune response in humans have been documented in the Philippines.


The Reston-Ebola virus was again introduced through the importation of cynomolgus macaques from the Philippines to the US in 1990 and 1996 and into Europe in 1992. The Philippines is one of the world’s major sources of cynomolgus macaques used for biomedical research.


This is the first time Ebola-Reston virus has been identified in pigs.


Hunting for the Ebola reservoirs


The natural reservoirs of the Ebola viruses are likely to reside in the rain forests in Africa and the Western Pacific. And although antibodies to Ebola virus have been found in free-living rhesus monkeys, African green monkeys, cynomolgus monkeys and baboons, healthy animals with Ebola virus (typical for reservoirs) have not been found. It is known that chimpanzees, gorillas, rhesus monkeys, vervet monkeys, cynomolgus monkeys, newborn mice and guinea pigs can develop clinical illness and fatal infections following infection with Ebola viruses. The natural reservoir of the Ebola viruses likely resides in rain forests in Africa and the Western Pacific.


Can humans become infected with Reston-Ebola and what are the consequences?


To date there is no evidence that Ebola-Reston virus causes disease in humans (antibody responses do provide evidence that infection occurs). A close collaboration between health officials, producers, veterinarians, and market intermediaries is required to assess the risks to humans. The experience of the animal caretakers in Reston, Virginia, in 1989, offers an insight into the human risk and this particular filovirus where with high virus exposure, no clinical disease, and a normal immune response was observed.


Does Reston-Ebola cause disease in pigs?


Pigs can become infected with Ebola-Reston but it is not known if they show signs of disease. It cannot be ruled out that infection with other microbes may have caused illness and fatalities on the farms where the Reston-Ebola infected pigs were bred and raised. FAO expects that specific laboratory tools can be developed to test swine and other animals throughout the Philippines and see how extensive the Ebola-Reston infection is and to undertake studies in previously non-exposed pigs.


Is pork safe?


As a basic principle of food hygiene, sick animals should not enter the food chain. Carcases or scraps from sick or dead animals should not be fed to other animals and should be disposed of properly. Veterinary and public health inspectors should ensure that animals destined for slaughter do not have fever and are clinically healthy.


Meat handling and preparation should be done in a clean environment (table top, utensils, knives, and other food contact surfaced) and by handlers following good personal hygiene practices (e.g. clean hands, clean protective clothing). Meat should be cooked well as thorough cooking destroys any bacteria, parasites or viruses that may be present in food. Cooked food must be kept separate from any potential sources of contamination in order to avoid re-contamination. Producers, marketers, butchers and market stall owners must be informed about the risks and of measures required to avoid contamination with, or exposure to the virus.


As a precautionary measure, pork meat infected with Reston-Ebola virus should not be handled, since the true risk of infection and consequences are unknown.


What about exports and imports?


Countries facing an animal health problem should immediately apply export bans for livestock and livestock products at risk. Without such an export ban, the disease could spread causing a risk to animal and also potentially human health. While the economic impact of such measures for the industry and producers is recognized, the country’s credibility and future trading position remains intact. Furthermore, should the animal health problem be of a zoonotic nature (disease that can be transmitted between animals and humans), it is no longer only an economic issue but also a public health concern.


What other animals are known to be infected?


Antibodies to Ebola virus have been found in rhesus-monkeys, African green monkeys, cynomolgus monkeys and baboons. Chimpanzees, gorillas, rhesus monkeys, vervet monkeys, cynomolgus monkeys, newborn mice and guinea pigs can develop clinical illness.


Experimentally, rabbits, pigeons and various species of mice, bats, frogs, geckos, snakes, tortoises and arthropods have been infected but did not develop clinical signs. Virus multiplication, however, was recorded in bats, snakes, mice and spiders at different levels.

Last Updated ( พุธ, 17 ธันวาคม 2008 )
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