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Researchers Seek Out Origin Of Swine Flu Virus

Posted on: Thursday, 21 May 2009, 11:35 CDT

Scientists are working on determining exactly when and how the swine flu first jumped from a pig and began infecting people, The Associated Press reported.

Mexico's earliest confirmed case of swine flu was identified in La Gloria, a pig-farming village in the Veracruz Mountains. Scientists plan to take fresh blood samples from villagers and pigs in order to look for antibodies that could suggest exposure to previous swine flu infections.

Reports show that weeks before the new virus was identified, over half of La Gloria's 3,000 residents fell ill with flu symptoms, where acute respiratory infections were diagnosed in about 450 of the sickest residents.

However, Mexican health officials argued the villagers suffered from regular flu symptoms, since the only confirmed swine flu case among 43 villagers whose mucous samples were taken in early April belonged to a 5-year-old boy.

Many disease experts still suspect swine flu was circulating more widely throughout the town.

Dr. Carlos Arias, who lead a group of flu detectives from the Biotechnology Institute and the veterinary school of the National Autonomous University of Mexico, told The Associated Press he could almost bet that there were more infections related to this virus in La Gloria.

Pigs are known to get the flu over the winter months, just like humans, but how this flu managed to become a full-blown human flu is still unknown.

While villagers are pointing the finger at commercial pig farms in the areas, the pork industry suspects pigs raised in the villagers' backyards may not have been vaccinated or cared for with swine flu-prevention in mind.

The investigation will examine environmental and sanitary conditions in homes where pigs are raised, and make recommendations to the Veracruz government aimed at reducing the potential for human infections, Arias said.

He said they plan to look at the evolution of the virus and where or how easily it originates, reassorts and reassociates genes in an environment like La Gloria.

"But also maybe that would mean that we would have to change the conditions of farming animals," he added.

At least 72 farms in the surrounding La Gloria area are jointly owned by Virginia-based Smithfield Foods, Inc., which said it carefully vaccinates its herd, and has found no signs or symptoms of any kind of swine flu in its Mexican operations.

No sign of the new strain was found in mucous samples taken April 30 from pigs at Smithfield's Granjas Carroll subsidiary, according to Enrique Sanchez, a top official in Mexico's Agriculture Department.

However, those samples were taken weeks after most villagers had recovered from their infections. But experts say even after a person or pig recovers, antibodies remain in their blood providing evidence of the body's immune response to the infection.

Arias said that if swine flu antibodies were teased out of pigs in La Gloria, it would suggest that the virus might have jumped from swine to humans there.

But the new strain could possibly have been circulating in humans long before it reached La Gloria, as the strain’s ancestry has ties to a pig farm in North Carolina where in 1998, scientists discovered that pig, bird and human viruses had combined in pigs to form a new strain of swine flu that also infected several people.

CDC officials have said that a majority of the current strain can be traced to that combination. And somehow it combined with other flu strains and jumped back into humans, but it is still unclear when and how it happened.

Dr. Sylvie Briand of the World Health Organization's global influenza program in Geneva believes that learning the source at this point won't change how the world must respond to this epidemic.

Christophe Fraser, the co-author of the WHO Rapid Pandemic Assessment Collaboration, concedes his team has no evidence that La Gloria was ground zero for the virus, but added he was skeptical of Mexico's assertion that seasonal influenza was solely to blame.

He said the attack rate in the outbreak in La Gloria is inconsistent with seasonal influenza. “It is not impossible, though, that multiple viruses were co-circulating.”

Alfredo Torres, an assistant professor at the University of Texas Medical Branch, said enough time had passed that if people or pigs have been infected by similar flu strains in the past, their antibodies could lead to false positives.

"There may not be any footprints to look at," said Tom Ksiazek, director of the university's National Biodefense Training Center.

Arias said the Mexican government has not provided details about its tests on humans and pigs.

"The information has not been distributed freely. We cannot work with only assumptions and rumors. We need solid data," he said.

Source: redOrbit Staff & Wire Reports

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