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Do the winged visitors harbour bird flu virus?

— Photo: K. Pichumani

A flock of flamingoes over the Pulicat Lake in Andhra Pradesh.

One day in December last year, Niranjan M., a 29-year-old engineer and avid bird-watcher living in Bangalore, drove some 125 km to a lake near Somnathpur in Karnataka. The lake was awash with a couple of hundred migratory birds, mostly bar-headed geese and, in the warm glow of the evening sun, he took over two dozen photographs.

The bar-headed goose, distinguished by two dark bands on the back of its head, is a remarkable bird. If the Arctic tern is the natural world’s champion long-distance migrator, each year travelling from high northern latitudes to as far south as the Antarctic and then back again, the bar-headed goose is the high-altitude expert. This goose is able to fly right across the Himalayas and over some of the world’s tallest mountains. Mountaineers have spoken of seeing bar-headed geese flying over the summit of Mount Everest. In order to do so, the bird’s biology has adapted to efficiently extract and utilise what oxygen is available in the thin air at such altitudes.

In early 2000, scientists fitted a small satellite transmitter to a bar-headed goose at the Keoladeo National Park in Bharatpur, Rajasthan. They were then able to track it as it stopped along the banks of the Ganges before proceeding to cross the Himalayas in less than 24 hours to reach the Tibetan plateau.

It was only when Mr. Niranjan looked closely at the digital photographs he had shot that he noticed that in one a single bar-headed goose had a yellow band around its neck with the letters ‘E6’ inscribed prominently on it. After he put the photograph on the India Nature Watch website, it was identified as the goose that had been tagged in July 2007 at the Darkhad Valley in northern Mongolia, some 4,700 km away, by a team from the New York-based Wildlife Conservation Society and the Mongolian State Central Veterinary Laboratory.

Migrating birds have for decades been tracked by fitting light metal rings to their legs. If the bird was later caught or killed, information inscribed on the ring would tell the person which organisation had tagged the bird. Hopefully, the person would then return the ring to that organisation or else at least inform it of having recovered the ring. The advantage of fitting coloured bands around a bird’s neck or fixing small coloured ‘flags’ to its legs is that, as happened with the bar-headed goose photographed by Mr. Niranjan, the bird can be identified without capturing or harming it in any way.

Yellow was chosen as the colour for the neck-bands because it had not been used in other countries, Martin Gilbert, a field veterinarian with the Wildlife Conservation Society told this correspondent. Coloured neck-bands had been fitted on 50 bar-headed geese and 30 whooper swans in Mongolia. After Mr. Niranjan’s report came in, two more of the colour-banded bar-headed geese were spotted in Maharashtra. Some 18 of the whooper swans were sighted in China.

Ornithologists have long sought to trace the routes that flocks of migrating birds take and the places where they congregate along the way. Birds that migrate from the same geographic region often follow broadly similar routes known as migratory flyways. The East Asian-Australian flyway, for instance, extends from eastern Siberia down to eastern Asia and Australia. The Central Asian flyway spans some 30 countries from the Arctic to the Indian Ocean. But these flyways are just generalisations and bird populations have been known not to strictly follow it.

The drive to understand these patterns of bird migration has received a new impetus and some much-needed funding for an unexpected reason — the spread of the bird flu virus known as H5N1.

In mid-2005, thousands of wild birds that had gathered at Qinghai Lake in western China, a major breeding site for migratory birds, were found to have died after being infected with the H5N1 virus. Shortly thereafter, the virus appeared in Mongolia, Siberia, and Kazakhstan, and then spread to countries in eastern and western Europe as well as to west Asia.

Fingers began to be pointed at migratory birds and a furore soon broke out in the scientific community. Virologists and molecular biologists argued that the genetic similarity of H5N1 viruses found in outbreaks across countries and the timing of those outbreaks suggested that migrating wild birds that became infected could have carried the virus. Naturalists and ornithologists pointed out indignantly that alternate routes for spread of the virus, such as movements of poultry as well as the legal and illegal trade in wildlife (including of birds), were being overlooked.

Wild water birds such as ducks, geese, and swans as well as gulls, terns, and waders are the major natural reservoir of low-virulence bird flu viruses. But only after such low-virulence strains infect poultry do they normally mutate and become highly virulent. The question has been whether the highly virulent H5N1 strain was flowing in the reverse direction from poultry to wild birds and if infected wild birds would then be well enough to continue with their migration.

The hypothesis that migratory birds could transport highly pathogenic H5N1 viruses over long distances rested on the assumption that some infected, virus-shedding birds show no or only mild symptoms and continue their journey unhampered, Thomas Weber and Nikolaos Stillanakis of the European Commission’s Joint Research Centre in Ispra, Italy, observed in a commentary the journal Emerging Infectious Diseases last year.

But long-distance migration was one of the most demanding physiological activities in the animal world, they pointed out. Mounting an immune response was energetically and nutritionally costly to a bird. Studies had shown that activating the immune system could have severe negative consequences for birds. “No convincing evidence has yet shown that infected, asymptomatic wild birds can or do carry influenza virus along established, seasonal long-distance migration routes,” they added.

Global wildlife surveillance carried out between 2005 and 2007 when samples were taken from 300,000 to 350,000 healthy wild birds found no trace of the virus, Scott Newman, international wildlife coordinator for avian influenza at the U.N. Food and Agriculture Organisation (FAO), was quoted as saying in September 2007.

At a recent bird flu conference in Bangkok, he said there was no proof that wild birds were a reservoir for the H5N1 virus. “We know that some wild birds have probably moved short distances carrying viruses and then they died, but we have not been able to identify carriage of H5N1 across large scale spatial distances and then resulting in spread to other birds and mortality in poultry flocks,” he told the Reuters news agency.

Nevertheless, concern over the possibility that wild birds might transport the bird flu virus has led to greater interest in studying bird migration.

The “profile of bird migration and related marking studies have increased following the emergence of the current highly pathogenic strain of avian influenza,” said Dr. Gilbert in an email. “A great deal of funding has become available through donor agencies from the health sector to support studies in migration that have traditionally been more difficult to support through ornithological or conservation directed sources. This has of course been beneficial to both sectors, both in increasing our ability to interpret the nature of any role that wild birds could play in avian influenza dissemination, but also in promoting conservation. Successful conservation of migratory species requires that the needs and movements of migrants are understood across their ranges.”

It has led, among other things, to a Global Avian Influenza Network for Surveillance (GAINS) being set up. “Much of the research being funded by GAINS and other parties concerned about avian flu is contributing much to our knowledge of migratory birds,” remarked Simon Mahood of BirdLife International in an email.

Through the GAINS programme, the Wildlife Conservation Society was currently supporting a bird migration studies in a number of Asian countries, including Mongolia, Cambodia, Vietnam, Indonesia and South Korea, according to Dr. Gilbert. In Mongolia last year, when birds were fitted with coloured neck-bands, samples were taken from a little over 500 birds and turned out to be negative for all H5 flu viruses.

In India, the 120-year-old Bombay Natural History Society (BNHS) has been tagging migratory birds with metal rings since 1959. Interestingly, the bird ringing programme began as a result of a viral disease, the Kyasanur forest disease, that occurred in Karnataka and it was thought that ticks carrying the disease-causing virus might be hitching a ride on migratory birds. A 2002 BNHS report estimated that more than 400,000 birds have been ringed in various parts of the country.

Now, the Society’s bird ringing has become part of the global avian flu surveillance efforts and is receiving support from the GAINS programme.

Last year, some 2,200 birds were ringed at Point Calimere in Tamil Nadu and at Chilka Lake in Orissa, according to S. Balachandran of BNHS. Blood samples and swabs were taken from the birds when they were captured in order to be ringed.

The recovery rate for the rings was typically only about one per cent and nowadays even that was not happening, he admitted. BNHS hoped to carry out satellite tracking of a couple of birds, Dr. Balachandran told The Hindu.

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