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Box 1. H5N1: Into the Americas

From the following article:

Avian flu and the New World

Nature 441, 137-139(11 May 2006)

doi:10.1038/441137a

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Trade

Every day, millions of live poultry are moved around the world by ground, air and sea transport, which potentially could carry H5N1 to fresh areas.

Replenishing flocks at huge industrial farms is now a global business: commercial hatcheries export billions of hatching eggs and one-day-old chicks. Egypt, for instance, exported some 180 million chicks annually before the H5N1 virus was detected there and exports were halted. Many experts see trade as the major cause of the spread of avian flu, through infected bird droppings on shells, crates and other surfaces.

In the United States, imported live birds must undergo a 30-day quarantine and tests for avian flu, says Madelaine Fletcher, a spokeswoman for the US Department of Agriculture. Most day-old chicks reaching the country are from Canada or the United Kingdom, and their crates are either disinfected or destroyed, she says.

Hon Ip, a virologist at the US National Wildlife Health Center in Madison, Wisconsin, says it is hard to assess how well quarantine works, as the United States has so far avoided an outbreak of H5N1. But an outbreak of contagious Newcastle disease in California in 2002 shows that quarantine is not always watertight, he says.

A country is generally banned from exporting poultry when it officially reports an outbreak of H5N1 in commercial flocks. But H5N1 can be present before a report is made. Moreover, although H5N1 has occurred in 13 countries in the European Union (EU), the United States bans imports only from regions involved, not from entire countries.

Most US imports from Europe are pet birds from Belgium and poultry products from France, but the country also imports bird skins and feathers from 16 EU nations. In 2005, the United States imported more than 16.8 million day-old chicks and other live poultry as well as 16.8 million hatching eggs.

Smuggling

On 5 September 2005, customs inspectors at the US Department of Agriculture (USDA) found an illegal shipment of 98,400 chicken eggs at a port in California. During October and November, they intercepted nearly 75 tonnes of poultry smuggled in from Asia.

Last month, a man from Nigeria — a country with H5N1 — was stopped at Miami airport after dogs detected dead birds, ostensibly brought in for a religious rite, in his luggage.

How much smuggling goes undetected is anyone's guess, but the illegal trade in birds and poultry products is thought to be third only to narcotics and arms in value. With trade bans imposed on countries with H5N1, the risk of smuggling has gone up, says Ip. "It has become more likely that illegally imported birds could come from an affected country," he says.

Inspections of markets and restaurants in major US cities regularly turn up illegal imports of poultry from Asia and elsewhere, admits one USDA official.

On the front line, 122 inspectors from the US Fish and Wildlife Service work across 35 ports looking for another target: exotic birds. The risk is real. In October 2004, a Thai man was caught at a Belgian airport as he tried to smuggle in two eagles that were later found to have H5N1.

Most smuggled birds are parrots, macaws and their relatives, or songbirds, says Ip. They come mainly from H5N1-free Australia, South America and Mexico. But traffic is brought in from many other countries. The black-capped lory (Lorius lory) from Indonesia, an H5N1-infected country, is a highly prized bird that is frequently targeted by smugglers, he notes.

"An infected bird in one part of the world can be in North America within 24 hours, whether that bird is fit to fly or not," says Ip.

Migration

Migratory birds could bring H5N1 to the Americas as early as this month — to Alaska, a short hop across the Bering Strait from Russia. Some 6.6 million birds will arrive in the state by the end of May, travelling up a flyway from Siberia, China and southeast Asia. The fear is that these birds could infect American migrants, which would then carry the disease back down the length of the Americas in the autumn.

To prepare for this, US agencies are already catching birds for testing — the start of a procedure that will examine 75,000-100,000 swabs from the birds for avian flu. "It's the largest and most complex migratory bird capture and sampling programme in the history of Alaska," says Dirk Derksen of the Alaska Science Center in Anchorage, one of the project's main coordinators. Birds will also be monitored along the major flyways running down through North America, particularly along the West Coast.

H5N1 could also arrive from the east: birds from West Africa and Europe fly over Greenland into northern Canada. But the smaller number of birds and species, and the longer flight distances, make this a less likely route for H5N1, says Derksen, and so sampling is not taking place there.

Biologists have identified the relative risk of each species of Alaskan migrant. Top of the list is the northern pintail (Anas acuta), which breeds widely across North America and Eurasia. It is among the most highly infected of waterbirds, with one in ten birds carrying some flu virus (B. Olsen et al. Science312, 384–388; 2006).

But whether migratory birds can carry H5N1 over long distances remains controversial. The first outbreak of H5N1 in Africa — in Nigeria — was widely attributed to migratory birds. But many now see the imports of day-old chicks as a more plausible cause.

D.B.

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