The Chinese agriculture ministry reported on Friday that more than 1,000 wild birds in Qinghai have died from a form of avian influenza. The government had already taken emergency measures after learning last weekend that the disease had killed 178 geese in the region. We've all heard about the potential dangers that bird flu poses to humans. But what effect is avian influenza having on the world's birds?
It's already been devastating. The Food and Agriculture Organization, a branch of the United Nations, estimates that between 120 million and 140 million domesticated birds like chicken and turkey have died from the H5N1 strain since the outbreak began last year. Large numbers of these birds were destroyed by government order to slow down the spread of the disease. It's not clear how many would have died from the illness, though available data suggest that H5N1 kills between 80 percent and 100 percent of the birds it infects. (It's impossible to say what percentage of the world's birds have died from avian influenza. Ornithologists say there's no good way to estimate the worldwide bird population.)
Birds spread the disease through droppings and other secretions, which often contaminate shared feed and water. Domesticated birds show a sudden decline in egg production a few days after they contract the illness; other symptoms include nasal discharge, swollen combs and wattles, severe internal bleeding, organ damage, and sudden death.
Waterfowl are thought to be the primary reservoirs of avian influenza—they can carry multiple strains for long periods of time without becoming seriously ill. Outbreaks occur when chickens and turkeys come into contact with these wild carriers and then spread the disease rapidly in the close conditions of a factory farm. The virus can even jump to humans in close proximity.
An outbreak of "Fowl Plague" in Italy in 1878 was probably an early example of dangerous (or "highly pathogenic") bird flu. The H5N1 virus wasn't identified until an episode in Scotland in 1959. Since then there have been about two dozen outbreaks of highly pathogenic avian influenza, some of which have affected only a single flock. The current outbreak is the largest on record. Dozens of humans and millions of domesticated birds have died in at least eight Asian countries so far, and now China has said the disease is killing wild bar-headed geese, cormorants, and shelducks.
It's not the first time wild birds have fallen victim to avian influenza: Common terns in South Africa began to die from the H5N3 strain in 1961, and wild geese were found to have succumbed to H5N1 in 1996. But the virulence of the disease and the numbers of deaths seen now are cause for concern. Migratory, colonial birds heading north for breeding could spread the disease under the right conditions. There's not much that wildlife health officials can do to prevent this, but they could try to decontaminate high-risk areas or dissuade wild birds from visiting them—for example, by draining lakes.
Explainer thanks Juan Lubroth of the United Nations Food and Agriculture Organization, Christopher Brand of the USGS-National Wildlife Health Center, and Brundaban Panigrahy of the National Veterinary Services Laboratories.