Wednesday, December 24, 2008

When Viruses Jump Species


# 2592



Viruses generally adapt to a fairly narrow range of species.  Horse viruses generally attack equines, and not say, cats and dogs.   Cat viruses tend to attack felines, and not birds.   Bird viruses usually only infect avian species.


The species that a virus will infect is known as its host range.  And while usually limited, it isn't always the case.  Rabies is a good example of a virus that can infect a wide host of species.


We know that every once in awhile, viruses do jump to a new species.  Canine influenza is caused by a recent species jump from an equine influenza virus , and that is exactly what we are seeing with the H5N1 bird flu virus over the past decade.  


We've  seen H5N1 infections in cats (including tigers), dogsmartens, civets, and of course humans. Researchers have successfully infected cattle with the H5N1 virus, along with ferrets and mice for testing.


So what was once purely an avian virus has now expanded its host range to include a variety of mammals, some of which appear to be able to carry the virus asymptomatically - while others manifest serious, often fatal symptoms.   


If the H5N1 virus had not shown the ability to jump species, we would probably just consider it another fowl plague.  A costly nuisance for the poultry industry, but not a danger to humanity.


In recent weeks we've been hearing about a new species jumping event,  and the implications of this aren't immediately obvious.  In the Philippines, pigs have been found to carry the Ebola Reston virus.





Ebola-Reston virus is a filovirus with genetic characteristics similar to the deadly Ebola Zaïre, but unlike its deadly African cousin, this Asian strain has never been shown to cause disease in humans.  


It can be fatal in simians, however.


This new strain of Ebola  was first discovered in crab-eating macaques, imported from the Philippines, at a research laboratory in Reston, Virginia (USA) in 1989.   This discovery was recounted in the book, The Hot Zone, by Richard Preston.


While humans could apparently be infected, and develop antibodies to the virus (3 researchers in Reston developed high antibody titers to the virus), all have reportedly been asymptomatic.


Of course, the concern is that viruses have a nasty habit of mutating.  What was true yesterday may not be true tomorrow.


Since pigs and humans share many commonalities in their physiology (if that induces discomfiture in you, think how the pig feels) any disease that jumps to swine is of immediate concern to scientists.   Which is why the WHO/FAO and OIE are all vitally interested in the reports coming out of the Philippines of pigs infected with Ebola Reston.


Of course, there are many diseases of swine that  humans are not susceptible to, such as Porcine reproductive and respiratory syndrome (PRRS). 


For now, this is pretty much just a fascinating medical mystery. There doesn't appear to be any immediate biological threat to humans from this outbreak of Ebola Reston in swine.   


But it is a truism in science that you never know where research will lead you.  Anything that expands our knowledge on how viruses jump species, mutate, or spread could prove invaluable later on down the line.



This update from the FAO newsroom.





First detection of Ebola-Reston virus in pigs


FAO/OIE/WHO offer assistance to the Philippines

Manila/Roma, 23 December 2008 - Following the detection of the Ebola-Reston virus in pigs in the Philippines, FAO, the World Organization for Animal Health (OIE) and the World Health Organization (WHO) announced today that the government of the Philippines has requested the three agencies send an expert mission to work with human and animal health experts in the Philippines to further investigate the situation.


An increase in pig mortality on swine farms in the provinces of Nueva Ecija and Bulacan in 2007 and 2008 prompted the Government of the Philippines to initiate laboratory investigations. Samples taken from ill pigs in May, June and September 2008 were sent to international reference laboratories which confirmed in late October that the pigs were infected with a highly virulent strain of Porcine reproductive and respiratory syndrome (PRRS) as well as the Ebola-Reston virus.


Ebola-Reston in swine

Although co-infection in pigs is not unusual, this is the first time globally that an Ebola-Reston virus has been isolated in swine. It is not, however, the first time that the Ebola-Reston virus has been found in the Philippines: it was found in monkeys from the Philippines in outbreaks that occurred in 1989-1990, 1992, and 1996.


The Ebola virus belongs to the Filoviridae family (filovirus) and is comprised of five distinct species: Zaïre, Sudan, Côte d'Ivoire, Bundibugyo and Reston. Zaïre, Sudan and Bundibugyo species have been associated with large Ebola hemorrhagic fever (EHF) outbreaks in Africa with high case fatality ratio (25-90%) while Côte d'Ivoire and Reston have not. Reston species can infect humans but no serious illness or death in humans have been reported to date.


Since being informed of this event in late November, FAO, OIE and WHO have been making every effort to gain a better understanding of the situation and are working closely with the Philippines Government and local animal and human health experts.


The Department of Health of the Philippines has reported that initial laboratory tests on animal handlers and slaughterhouse workers who were thought to have come into contact with infected pigs were negative for Ebola-Reston infection, and that additional testing is ongoing. The Bureau of Animal Industry (BAI) of the Philippines Department of Agriculture has notified the OIE that all infected animals were destroyed and buried or burned, the infected premises and establishments have been disinfected and the affected areas are under strict quarantine and movement control. Vaccination of swine against PRRS is ongoing in the Province of Bucalan. PRRS is not transmissible to humans.


The planned joint FAO/OIE/WHO team will work with country counterparts to address, through field and laboratory investigation, important questions as to the source of the virus, its transmission, its virulence and its natural habitat, in order to provide appropriate guidance for animal and human health protection.


Basic good hygiene


Until these questions can be answered, the FAO and WHO stressed the importance of carrying out basic good hygiene practices and food handling measures.


Ebola viruses are normally transmitted via contact with the blood or other bodily fluids of an infected animal or person. In all situations, even in the absence of identified risks, meat handling and preparation should be done in a clean environment (table top, utensils, knives) and meat handlers should follow good personal hygiene practices (e.g. clean hands, clean protective clothing). In general, hands should be regularly washed while handling raw meat.


Pork from healthy pigs is safe to eat as long as either the fresh meat is cooked properly (i.e. 70°C in all part of the food, so that there is no pink meat and the juices run clear), or, in the case of uncooked processed pork, national safety standards have been met during production, processing and distribution.



Meat from sick pigs or pigs found dead should not be eaten and should not enter the food chain or be given to other animals. Ill animals should be reported to the competent authorities and proper hygiene precautions and protection should be taken when destroying and disposing of sick or dead pigs. The Philippines Department of Agriculture has advised the Philippine public to buy its meat only from National Meat Inspection Services certified sources.


As a general rule, proper hygiene and precautionary measures (wearing gloves, goggles and protective clothing) should also be exercised when slaughtering or butchering pigs. This applies both to industrial and home-slaughtering of pigs. Children and those not involved in the process of slaughtering should be kept away.

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