Understanding the deadly flu virus

Scientists are scrambling to figure out just how alarmed we should be over the swine flu outbreak from Mexico.

Published April 30, 2009 10:48AM (EDT)

Health officials confirmed Wednesday that the swine flu has claimed its first victim in the United States. A Mexican toddler who had visited relatives in Brownsville, Texas, succumbed to the flu April 27 at Texas Children's Hospital in Houston, making him the first person to die from the virus outside Mexico. The 22-month-old boy developed a fever and other flulike symptoms on April 8, according to the Texas Department of State Health Services.

As the toddler's death was made public, the World Health Organization raised the global threat level for swine flu to Phase 5, indicating that a pandemic is imminent. "Countries should remain on high alert for unusual outbreaks of influenza-like illness and severe pneumonia," said Dr. Margaret Chan, director-general of the organization. But, she added, the "world is better prepared for an influenza pandemic than at any time in history."

Around the world, public health experts and virologists are scrambling to unravel the virus. They are determined to discover whether it contains a new strain to which humans are dangerously susceptible, because our immune systems are less prepared to fight off a novel virus. Understanding its chemical makeup will help identify the proper vaccines and antiviral drugs.

So far the results have been murky, but some clarity is beginning to emerge. The U.S. Centers for Disease Control and Prevention and other health agencies have been posting online the chemical sequences of the viral strains uncovered in the U.S., allowing scientists to analyze them.

One of those scientists is Dr. Vincent Racaniello, professor of microbiology at Columbia University Medical Center, who writes the Virology Blog. "This is a unique combination of pig genes that has not been found before, based on all the sequences that have been released," he said. While this virus appears related to other known piggy ones, Racaniello added, there are enough differences to account for its ability to spread to humans.

It may be somewhat comforting to learn that symptoms of the recent outbreak are not much different from those we've all experienced. In fact, if you're wondering what it's like to have the swine flu, you already have a pretty good idea. The symptoms are similar to the seasonal flu: fever, cough, sore throat, body aches, headache, chills and fatigue.

"The illness that we are seeing is genuinely consistent with seasonal influenza infection," said Dr. Keiji Fukuda, assistant director-general for Health, Security and the Environment at the World Health Organization, at a media briefing in Geneva on Wednesday. He noted evidence that patients suffering from swine flu are more likely to experience diarrhea, too. "This infection can result in anything from very mild illness, where people do not need to be hospitalized and generally recover without any complications after several days, to fatal illness."

What remains unknown is why this flu can develop into severe or fatal illness, and which groups of people are most vulnerable to it. Why, for instance, are more cases being reported in Mexico? "We don't know right now," Fukuda said. "This is one of the main focuses of the current investigation." Yet WHO does know that the virus is still on the move. "It's clear that the virus is spreading, and we don't see any evidence of this slowing down at this point," Fukuda said.

As is often the case in reporting on epidemics, conflicting numbers are circulating in the press, as different countries weigh in with their counts of both laboratory-confirmed cases, and much larger numbers of suspected cases. For instance, as of Wednesday, WHO reported 148 cases of the swine flu virus in Mexico, the United States, Canada, New Zealand, Germany, Canada, the United Kingdom, Israel, Spain and other countries. Yet according to authorities in Mexico, more than 150 people are suspected to have died from the virus there, and at least 2,400 people are suspected to have become infected by it.

In the United States, there have been 91 confirmed cases of swine flu so far, according to CDC, including cases in Arizona, California, Indiana, Kansas, Massachusetts, Michigan, Nevada, New York City, Ohio and Texas.

Despite speculation that industrial pig farms in Perote, Mexico, might be to blame, it's still unknown when and where this virus made the leap from pigs to humans. But such a contagious leap is hardly novel. More than 60 percent of the more than 1,415 infectious diseases known to modern medicine are capable of infecting both humans and animals, explains Dr. Robert Cook, a vice president and veterinarian with the Wildlife Conservation Society. Most of those diseases, including such bugaboos as bubonic plague and Lyme disease, are "zoonotic," meaning they crossed the species barrier to infect people.

Before this global outbreak of swine flu, the U.S. had a few recent cases of infection. From December 2005 to February 2009, the U.S. had 12 cases of human infection with swine influenza, according to the medical journal Lancet. Yet in those cases, the swine flu spread from pig to Homo sapiens, but did not make the subsequent leap from human to human. Yet that's how this swine flu is spreading.

"This was originally a new swine influenza virus, but it is now behaving more or less like a human influenza virus, with transmission going from person to person," explained Fukuda. "At this point, we do not see any evidence that people are getting infected from pigs. We do not have any evidence to suggest that pork meat and those sorts of products pose a risk to people. This appears to be a virus that is moving from person to person."

Some evidence from the virus itself undercuts the fear arising from Mexico. Racaniello hasn't seen the viral strains from Mexico to determine whether they are in fact so unknown as to create genuine alarm. But he has analyzed the ones from the U.S., which may have come from Mexico, as U.S. travelers returned home. He hasn't seen anything to substantiate that the Mexican strain is uniquely lethal.

Despite such words of caution, Egypt, which has had no cases of infection, took the extraordinary step of attempting to slaughter the country's 300,000 pigs. But so far that kind of panic has been kept under control in the U.S.

"Our preparations are for a situation in which this does become a full-fledged pandemic," Secretary of Homeland Security Janet Napolitano said Wednesday. "We are preparing for the worst, hoping for the best." But rejecting calls from U.S. lawmakers to close the nation's borders, she added that "panicking" is unhelpful, noting that the regular flu season claims about 36,000 American lives every year.

By Katharine Mieszkowski

Katharine Mieszkowski is a senior writer for Salon.

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