With charts, graphs, and diagrams, Dr. Mark Rasnake, infectious disease specialist, explained the development, history and effects of the H1N1 influenza virus on the world, the US, and Knox County at the weekly Science Forum lecture at Thompson-Boling Arena's dining room C Oct. 2.

The H1N1 flu is a global concern because of its contagious nature and new characteristics. Dr. Rasnake compared it to three other viruses: SARS, H5N1 virus, and the virus of the 1918 pandemic.

"Compared to past pandemics and seasonal flues, it [H1N1] is a mild virus. It won't kill a lot of people even though it will infect a lot of people," said Rasnake. One sick person infects 2.5 others.

Compared to past pandemics and seasonal flues, it [H1N1] is a mild virus. It won't kill a lot of people even though it will infect a lot of people. Dr. Mark Rasnake, infectious disease specialist

"Estimates says one-third of the US population will be infected," Rasnake said. "The typical flu hits the very young and those over age 80. But H1N1 has the highest cases in children and young adults."

The highest risk of death is to children who are already ill with other conditions. Dr. Rasnake showed the Center for Disease Control's Web site map of current H1N1 cases.

"Most years, the mortality rate for seasonal influenza is approximately 35,000 in the United States," Rasnake said. "For the cases resulting in death, the influenza makes your other diseases worse (or) the flu virus leads to influenza pneumonia."

The estimates on the H1N1 flu indicate a possible 90,000 to 100,000 mortality rate this year for the United States. Estimates for Knox County are 240 deaths if the pandemic is mild, escalating to 2,395 deaths if the effect is severe.

Most people who catch the flu will recover in 4-5 days while others will progress to a more serious illnesses.

"The big weakness in treating the flu is we have] no intravenous medicine. How do you deliver an oral medicine to an intubated patient?" asked Dr. Rasnake.

Elders are typically susceptible to seasonal flues. But, "we think the majority of those over 65 had exposure to the H1N1 virus as children," he said. "Elders are not vulnerable to this virus - if they are over 65 years old, they may have robust immunity to this H1N1 strain."

Schools are closing when absenteeism reaches 15 percent, to cut the child-to-child transmission rate.

The H1N1 virus developed from a combination of swine, human and avian flu genes.SARS is an unrelated virus that is more related to the common cold. Both develop in humans' respiratory tracts.

The initial outbreak of the SARS virus in 2003 caused fears of a pandemic when people became sick in several countries.

"One individual with SARS infected people in adjacent hotel rooms in the Metropole Hotel in Hong Kong. There was no other specific contact," he said.

The SARS virus then was spread by these travelers to Canada, Bangkok, Vietnam, Singapore, the USA, Ireland, and China. Approximately 8,000 people became sick and 800 died during this outbreak. This demonstrated the potential for respiratory viruses to spread rapidly across the globe by modern air travel.

Scientists have studied the virus responsible for the devastating 1918 flu pandemic which killed an estimated 50 million people. They determined the virus was an avian strain with one gene segment change that converted it to a human flu strain.

"All influenza viruses ultimately come from avian influenza," Dr. Rasnake said.

Researchers have traced the origin of the current H1N1 virus outbreak to swine farmers in Mexico. Human and avian adapted viruses can combine in pigs' respiratory epithelium.

"It is the perfect mixing vessel for influenza viruses," Dr. Rasnake said. The pigs appear to be ill with swine flu. "This year's flu is a reassortment of the 1918 pandemic virus with different gene segments; it is still the H1N1 virus."

The fourth virus of global concern, H5N1, causes respiratory problems with a 50 percent mortality rate from a primary influenza pneumonia. Usually influenza deaths result when the patient, weakened by the flu virus, succumbs to a secondary bacterial pneumonia.

The first cases of H5N1 flu were thought to be dengue fever or typhoid because the symptoms were so extreme. The feared pandemic has not happen because the virus is basically transmitted from birds directly to a human. Human to human transmission happens rarely.

"The H5N1 can kill, but it cannot spread," Dr. Rasnake said.

Scientists compare viral strains to determine their origins and to predict their possible effects on people. But flu viruses are ever-changing. The reason an annual shot is recommended is because at the end of each flu season the current flu strain will have mutated so that the vaccine is no longer effective against it. When the surface proteins of a virus change just enough to make the previous vaccine ineffective, it is called antigenic drift. When a new strain of flu emerges, the surface proteins have undergone a greater change called antigenic shift.