Bird Flu To Swine Flu

Almost all human diseases originate from other animals and then adapt to human hosts, says University of Guelph agriculture professor David Waltner-Toews, according to the author of The Chickens Fight Back: Pandemic Panics and Deadly Diseases that Jump from Animals to People.

People, birds and pigs are easily affected with different strains of virus or influenza. The easiest to transmit by human to human virus is human influenza. It is very possible that humans can also get bird influenza and pig influenza, but it typically requires very close contact with the animals, according to Waltner-Toews.

Bird or avian influenza is particularly hard to get, but humans who do get it experience very severe symptoms. That is why people were worried about a deadly pandemic if avian influenza were to mutate in such a way as to become easily transmissible between humans. Swine influenza is somewhat easier to transmit to humans but its symptoms tend to be milder than bird influenza.

Most flus contracted by humans are made up of predominately human influenza, but contain small pieces of avian or swine influenza. Swine flu is unusual because it is made up mostly of swine influenza but contains small amounts of avian and human influenza.

The movement of a virus between species opens up more opportunities for mutations in the virus, said Dr. Ruben Donis, head of the molecular genetics branch of the influenza division at the U.S. Centers for Disease Control.

The mutations would not necessarily make the virus cause more severe disease, but it cannot be ruled out, Donis said.

Mutations could also perhaps make the virus stronger at beating the immune system or resistant to drugs, said Stephen Drews, a clinical microbiologist at Ontario's Public Health Laboratories.