Flu is a disease of birds caused by influenza virus type A, which may be low or high pathogenicity. Spread throughout the world, avian influenza can infect virtually all species of birds, albeit with very different manifestations, from the lightest to the highly pathogenic forms that produce epidemics and contagious acute. If caused by a highly pathogenic form, the disease appears suddenly, followed by rapid death in almost 100% of cases. The fear of a new pandemic, arising from a passage of avian viruses to humans, has sparked a series of extraordinary measures of prevention throughout the world.
A virus unstable
Nature reserves of different subtypes of avian influenza viruses are wild ducks, identified as a source of infection for poultry farming (chickens and turkeys), are particularly susceptible to the disease. In Asian countries, a prominent role in the spread of the virus been identified in the sale of live poultry markets. Moreover, viruses can be transmitted from farm to farm by mechanical means, tools and contaminated instruments, machinery, feed, cages, clothing or even operators.
Viruses of low pathogenicity can, after circulation for short periods in a poultry population, mutate into highly pathogenic viruses. For example, as reported by WHO during the 1983-1984 epidemic in the United States, H5N2 virus initially caused low mortality but became, within six months, highly pathogenic, with a mortality close to 90%. To control the epidemic, in that case, it was necessary to demolish more than 17 million birds, at a total cost of nearly $65 million. (more…)