How humans get Bird Flu

Migratory water fowl and ducks in particular carry the viruses that cause bird flu. Often unaffected themselves, the host birds can spread the infection to susceptible species, especially domesticated chickens, turkeys and geese, resulting in severe epidemics that sicken and kill large number of birds sometimes in a single day.

How humans get Bird Flu

Avian viruses generally don’t affect humans but in 1997 an outbreak of bird flu in Hong Kong infected 18 people, six of whom died. Since then, human cases of bird flu have been reported in the Netherlands, Canada and through out Asia. Most were traced to contact with infected poultry or surface contaminated by sick kids.

The genetic scrambling that occurs in antigenic shift explains how a disease that normally affects a bird or animal can suddenly turn up in humans, often, flu viruses that cross the species barrier originate in areas where people live in close proximity to chickens and pigs. That is because pigs are susceptible to infection with both avian and human viruses and so are an ideal “ mixing bowl” for genes. 

But at least some bird flu viruses don’t need a third party. Instead they shuffle and rearrange their genetic material directly in humans. That seems to be the case in most instances of human acquired bird flu: people become sick after direct contact with infected birds or bird-contaminated surfaces, not from contact with other animals.