Swine flu, is this the big one?

Health officials want to take every step to prevent an outbreak from spiraling into mass casualties. Predicting influenza is a dicey endeavor, with the U.S. government famously guessing wrong in 1976 about a swine flu pandemic that never materialized.

The epicenter was Mexico, where the virus is blamed for 86 deaths and an estimated 1,400 cases in the country since April 13. Schools were closed, church services canceled and Mexican President Felipe Calderon assumed new powers to isolate people infected with the swine flu virus.

International concern magnified as health officials across the world on Sunday said they were investigating suspected cases in people who traveled to Mexico and come back with flu-like illnesses. Among the nations reporting confirmed cases or investigations were Canada, France, Israel and New Zealand.

Meanwhile, in the United States, there were no deaths and all patients had either recovered or were recovering. But the confirmed cases around the nation rose from eight on Saturday morning to 20 by Sunday afternoon, including eight high school kids in New York City — a national media center.

U.S. Centers for Disease Control and Prevention officials say that so far swine flu cases in this country have been mild. But they also say more cases are likely to be reported, at least partly because doctors and health officials across the country are looking intensively for suspicious cases. And, troublingly, more severe cases are also likely, said Dr. Richard Besser, the CDC's acting director, in a Sunday news conference.

"As we continue to look for cases, we are going to see a broader spectrum of disease," he predicted. "We're going to see more severe disease in this country."

Flu pandemics have been occurring with some regularity since at least the 1500s, but the frame of reference for health officials is the catastrophe of 1918-19. That one killed an estimated 20 to 50 million people worldwide.

Disease testing and tracking were far less sophisticated then, but the virus appeared in humans and pigs at about the same time and it was known as both Spanish flu and swine flu. Experts since then have said the deadly germ actually originated in birds.

But pigs may have made it worse. That pandemic began with a wave of mild illness that hit in the spring of 1918, followed by a far deadlier wave in the fall which was most lethal to young, healthy adults. Scientists have speculated that something happened to the virus after the first wave — one theory held that it infected pigs or other animals and mutated there — before revisiting humans in a deadlier form.

Pigs are considered particularly susceptible to both bird and human viruses and a likely place where the kind of genetic reassortment can take place that might lead to a new form of deadly, easily spread flu, scientists believe

Federal officials vaccinated 40 million Americans. The pandemic never materialized, but thousands who got the shots filed injury claims, saying they suffered a paralyzing condition and other side effects from the vaccinations.

To this day, health officials don't know why the 1976 virus petered out.

Flu shots have been offered in the United States since the 1940s, but new types of flu viruses have remained a threat. Global outbreaks occurred again in 1957 and 1968, though the main victims were the elderly and chronically ill.

In the last several years, experts have been focused on a form of bird flu that was first reported in Asia. It's a highly deadly strain that has killed more than 250 people worldwide since 2003. Health officials around the world have taken steps to prepare for the possibility of that becoming a global outbreak, but to date that virus has not gained the ability to spread easily from person to person.

This news is according to Yahoo News pubished in April 27, 2009.