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Health Officials Are Wary but Hopeful
CDC Says Virus Lacks 'Virulence' Traits; Mexico's Death Toll Tied to Wider Spread

By Joel Achenbach
Washington Post Staff Writer
Monday, May 4, 2009

With four Washington area schools closed over the swine flu outbreak and the region bracing for another tense week of flu news, top health officials here and abroad projected yesterday a cautious optimism that the new virus is not as lethal as initially feared.

Genetic analysis has failed to detect in the influenza virus the "virulence factors" seen in the killer 1918 Spanish flu or the avian flu that surfaced earlier this decade, Richard E. Besser, acting director of the Centers for Disease Control and Prevention (CDC), said yesterday.

Moreover, the new virus may have been more widespread in Mexico than originally reported, which would make the seemingly high mortality rate there a misperception, he added.

"We are starting to see that there was widespread flu in Mexico," Besser said on NBC's "Meet the Press," as he joined two other Obama administration officials in making the rounds of Sunday morning talk shows. "As we learn more about how widespread this is, it may be that the rates of severe disease in Mexico will end up being not different than what we see here."

In Mexico, Health Secretary José Ángel Córdova said that the outbreak is "in its declining phase" there as hospitals report fewer new and serious cases. A shutdown of Mexico City's restaurants, bars and movie theaters is likely to be lifted Wednesday, Córdova added.

Still, Córdova warned, "We can't let down our guard," and the situation remains shot through with unknowns.

It took on a new twist with reports this weekend from the Canadian province of Alberta that a farmworker who recently had returned from Mexico had apparently passed the virus to a herd of pigs. The farmworker and the pigs have recovered, and the World Health Organization said there is no sign that the virus mutated or adapted into a more virulent form.

Health officials took pains to say that there is no danger of infection from eating pork that is properly cooked. A food safety scientist at the World Health Organization, Peter Ben Embarek, said cured pork products are safe because of their long maturation process. "You can continue to safely eat your prosciutto," he said.

U.S. Agriculture Secretary Tom Vilsack said in a statement that there is no evidence of the new virus in American pigs, and he noted that the Canadian herd had been quarantined. He added, "As a precaution, people with flulike symptoms should not interact with swine."

This is a delicate moment for U.S. public health officials, who are dealing with a skittish public, a rapidly moving virus and lingering memories of the Bush administration's botched response to Hurricane Katrina. The officials want to relay the encouraging news of recent days and hours without exposing themselves to ridicule in the event the virus shifts into a different gear and causes a devastating pandemic.

The new virus is one for which most people probably have limited immunity (though the CDC noted that it does not seem to be showing up very often in Americans older than 50, suggesting that they possess some immunity to it).

Across the country, there have been instances of what some have called overreaction. Fort Worth's entire school district closed after a single case of swine flu. Emergency rooms reportedly have been swamped by people complaining of a cough. Administration officials said healthy people should still go to graduation events, ride public transportation and so on. "Common sense: You don't need to wear a mask," Homeland Security Secretary Janet Napolitano said on "Fox News Sunday."

Two schools in Prince George's County and one each in Montgomery and Anne Arundel counties have been closed because of the swine flu. [Story, A5.] Public health officials have advised schools to close for up to 14 days if they have one or more cases of the swine flu, but there has been no similar advice to businesses.

"We don't want to shut down the production capacity of the country for a flu when that's not necessary," Napolitano said on ABC's "This Week."

The Canada pig farm case offered a reminder that influenza is a mobile and opportunistic virus that can evolve as it moves from person to person and from species to species. If two strains of flu infect an organism, they can potentially swap genes -- "reassort" -- and produce an entirely new strain.

"Pigs actually serve as a wonderful mixing vessel for influenza viruses to reassort," said Nancy Cox, head of the flu division at the CDC. "If pigs are infected with this new virus and some swine influenza viruses that are already circulating, there could be additional reassortment."

Viruses can reassort within a human being as well, but transmission from one species to another creates a greater risk of a new strain, said Ellen Silbergeld, a professor of environmental health sciences and epidemiology at Johns Hopkins University's Bloomberg School of Public Health. She said transmission between species is probably common at industrial pig operations.

"It's my opinion that these kinds of events go on all the time because we have so little regulation of industrial agriculture," she said. "It's appropriate to refer to these animal operations as viral mixing bowls."

In Egypt, meanwhile, police tear-gassed irate pig farmers who were protesting the government's order last week to slaughter all 300,000 pigs in the country in a preemptive strike, the Associated Press reported. There has been no detection of the new virus in Egypt, and the World Health Organization has said that such actions are unnecessary.

The AP reported that 14 people were arrested, and seven police officers were among the 12 people injured. Police were sent in after farmers resisted government efforts to haul the pigs away.

Correspondent Joshua Partlow in Mexico City and staff writer Ceci Connolly in Atlanta contributed to this report.

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