CHICAGO (Reuters) – Two U.S. children were infected with flu viruses that originated in pigs in the past two months, and an analysis of both viruses showed they had picked up genetic material from the 2009 pandemic influenza A H1N1 virus, government researchers said on Friday.

They issued a warning to health workers to watch out for suspect viruses because those that cross between species can be especially virulent.

In both children, one from Indiana and one from Pennsylvania, an analysis of the viruses showed they contained a gene of the 2009 pandemic flu virus, according to a report released by the U.S. Centers for Disease Control and Prevention.

Flu viruses that jump from one species to another are a concern because they can swap genes and form an entirely new virus, making them harder to protect against.

“Pandemic viruses get started when they reassort and they emerge as a new virus. That is why we have to keep close watch on new influenza viruses as they emerge,” CDC spokesman Tom Skinner said.

“They are constantly changing, and that is why we have to have really good surveillance systems in place to detect them when they do emerge,” he said.

So far, this new virus does not appear to be able to easily pass from human to human, but Skinner said the CDC is still investigating.

Since 2005, there have been about 22 cases of human infection from swine-origin influenza viruses similar to the cases now being reported, Skinner said. All 22 people have recovered.

In one of the two new cases, a young boy from Indiana who had gotten a flu vaccine last September developed fever, cough, shortness of breath, diarrhea and a sore throat in late July. He was taken to the emergency department and a swab of his throat indicated that he had been infected by an influenza A virus.

The boy was sent home untreated but returned to the hospital the next day to be admitted and treated for multiple chronic health conditions, which had gotten worse because of his infection.

The boy recovered and was sent home, but further testing by state officials suggested his virus had originated in pigs, and his sample was sent to the CDC for confirmation.

According to the CDC report, the child had no prior direct contact with pigs, but a child-care worker who looked after the boy did report having contact with pigs before the child’s symptoms appeared.

In the second case, a Pennsylvania girl under age 5 who had received a flu shot the prior year developed a suspected infection with swine-origin influenza A (H3N2) in August.

Later testing by state officials and the CDC confirmed that she, too, had developed a form of flu that originated in pigs, likely from direct contact at an agricultural fair.

The girl was not treated and has completely recovered.

So far, the CDC has not seen any additional cases of people developing a pig form of influenza, but Skinner said the CDC is publishing the report to remind doctors and health workers to be watchful for suspicious cases of flu.

The H1N1 pandemic flu strain was discovered in Mexico and the United States in March 2009 and spread rapidly across the world. The World Health Organization estimates about 18,450 people died from the virus up to August 2010, including many pregnant women and young people.

Seasonal flu vaccines being offered across the world protect against the H1N1 strain. Flu vaccines are made by several drugmakers including Glaxosmithkline, Sanofi and Novartis.

(Editing by Cynthia Osterman)

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Two U.S. Children Contract New Strain of Swine Flu

By By Steven Reinberg
HealthDay Reporter | HealthDay – Fri, Sep 2, 2011

FRIDAY, Sept. 2 (HealthDay News) — Experts at the U.S. Centers for Disease Control and Prevention are investigating two recent cases of swine flu in which the new strain of flu passed directly from pigs to children.

This strain of flu does not appear capable of human-to-human transmission, but further study is needed, because if it were to spread among humans, the implications would be severe, the agency said. The CDC says the new strain contains genetic material from the H1N1 virus that swept the world last year, plus DNA from other pig flu viruses.

“We hope to learn more about the extent of transmission as soon as possible,” said CDC spokesman Tom Skinner. “We see a couple of cases of swine origin influenza every year, and usually it’s in people who have direct contact with swine. Right now there doesn’t appear to be any sustained human-to-human transmission.”

Both cases, revealed Sept. 2 in an early release of the CDC’s Morbidity and Mortality Weekly Report, involved children under 5 years old, one in Indiana and the other in Pennsylvania.

The Indiana boy who came down with the flu had no contact with pigs, but a caregiver had been in direct contact with swine in the weeks before the boy became sick. In the other case, a girl developed flu after having contact with pigs at a fair, according to the report.

Both children recovered, and no other family members got sick, the CDC said.

According to Skinner, these are the first cases of new swine flu seen this year.

“As far as the general population is concerned, here we have a situation where we have a couple of cases in people who have had contact with swine,” Skinner said. “The general public, I don’t think, should be concerned about these cases.”

However, people who have contact with swine and develop an upper-respiratory illness accompanied by fever need to make sure their doctor knows that they had contact with swine, Skinner said.

“This report shows our system of being able to detect new and emerging influenza viruses is working,” he said.

Skinner added that the flu viruses known to go from person-to-person are those seen during the flu season, which usually starts in December.

This year’s seasonal flu vaccine contains the same strains as last year’s, which are the ones seen now in the Southern Hemisphere, he said. Skinner urged people to get a flu shot before the flu season begins in North America this winter.

Flu expert Dr. Marc Siegel, an associate professor of medicine at New York University School of Medicine in New York City, said “there is no concern for the public at this point.”

“You have to remember that swine flu strains and bird flu strains are coming out all the time, and two cases doesn’t mean anything,” Siegel said.

Pigs are mixing vessels for flu, Siegel explained. “We see this every year. The key here is that we don’t see any tendency toward sustained human spread,” he said.

More information

The U.S. Centers for Disease Control and Prevention has more about flu.