Swine Flu in U.S., Mexico Lung Illness Heighten Pandemic Risk

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By Jason Gale

April 24 (Bloomberg) -- Disease trackers are trying to determine whether a previously unseen strain of influenza in the U.S. is related to more than 130 cases of severe respiratory illness in Mexico and may spark a pandemic.

A new variant of H1N1 swine influenza has sickened at least seven patients in California and Texas, the Centers for Disease Control and Prevention in Atlanta said yesterday. Mexico’s Health Minister Jose Cordova canceled classes in the capital today and recommended citizens avoid public places after 20 fatalities from an illness possibly caused by an H1N1 flu virus.

“The infection of humans with a novel influenza-A virus infection of animal origins, as has happened here, is of concern because of the risk, albeit small, that this could represent the appearance of viruses with pandemic potential,” the European Centre for Disease Prevention and Control said in a statement.

Scientists in both countries and Canada are studying the cases to determine whether they pose a larger public health threat. A pandemic can start when a novel influenza type-A virus, to which almost no one has natural immunity, emerges and begins spreading. Experts believe the so-called 1918 Spanish Flu pandemic, which may have killed as many as 50 million people, began when an avian flu virus jumped to people.

Authorities in Mexico asked the Public Health Agency of Canada to help identify what’s causing the lung infection that has also spread to five health-care workers, the Ottawa-based agency said in an e-mail yesterday.

Critical Study

Canada’s National Microbiology Lab received 51 specimens from Mexico on April 22 and will be testing them for a range of pathogens, the public health agency said. Tests in Mexico found patients were also infected with the H1N1 and type-B influenza strains and the parainfluenza virus, the agency said.

“It will be critical to determine whether or not the strains of H1N1 isolated from patients in Mexico are also swine flu,” Donald Low, an infectious diseases specialist at Toronto’s Mount Sinai Hospital, told the Canadian Press.

Thirteen fatal cases of severe respiratory illness were reported in Mexico City; four in San Luis Potosi, a city north of the capital; two in the state of Baja California Norte, bordering California; and another in Oaxaca city in the south. Most cases occurred in southern and central Mexico in previously healthy adults aged 25 to 44 years old.

Symptoms include high fever, headache, eye pain, shortness of breath and extreme fatigue with rapid progression of symptoms to severe respiratory distress in about five days, the Canadian agency said. A “high proportion” of cases require mechanical respiration, it said.

Milder Symptoms

In contrast, the four males and three females in San Diego County and Imperial County, California, and in San Antonio diagnosed with swine flu had mild flu-like symptoms. The patients, aged 9 to 54 years, began feeling unwell from March 28 to April 19. All have recovered and only one was hospitalized briefly, according to the CDC.

“We have determined that this virus is contagious and is spreading from human to human,” the CDC said in a statement on its Web site. “We have not determined how easily the virus spreads between people.”

Preliminary analyses of the virus indicate it contains four different gene components representing both North American swine and avian influenza, human flu and a Eurasian swine flu.

“It’s a real mutt,” Walter Dowdle, who in worked in the CDC’s virology unit during a major swine flu outbreak in 1976, told the Center for Infectious Disease Research and Policy’s daily newsletter yesterday. “When you have an evolving RNA mechanism, it’s hard to be surprised by anything,” said Dowdle, who now works with the Task Force for Child Survival and Development, based in Atlanta.

Human Infections

Swine influenza is a respiratory disease of pigs caused by type-A influenza that regularly causes outbreaks among the animals, according to the CDC. Swine flu doesn’t normally infect people, though human infections do occur and cases of human-to- human spread of swine flu viruses have been documented.

In 1976, 13 soldiers in basic training at Fort Dix in New Jersey fell severely ill from swine flu and one died, prompting concern that a pandemic was unfolding. A vaccine developed to prevent the illness was associated with a paralyzing neurologic illness affecting more than 1,000 people.

Infection in pigs is regarded as especially problematic because of the risk of “reassortment” to produce a new virus, the European Centre for Disease Prevention and Control said.

“These mild U.S. cases infected with a novel influenza are not reflecting the emergence of a pandemic strain, but they at least raise the possibility that there has been limited human- to-human transmission,” the health agency said.