N. Gopal Raj

With the regular movement of people and goods across the border, there is always a chance that the virus might hitch a ride into India.

AS NEIGHBOURING Bangladesh battles to root out the lethal strain of bird flu known as H5N1 that has spread among its poultry flocks, the ability of the virus to thrive could be aided by the millions of ducks in that country. Recently, the Food and Agriculture Organisation declared that the bird flu situation in the country was a matter of serious concern and recommended "vigorously stepping up and extending current H5N1 control campaigns in order to prevent the virus becoming widely entrenched."

As long as the virus continues to circulate among chicken and ducks across the border, there is always the danger that the virus might slip over and infect poultry in India.

In many rice-growing countries in Asia, ducks form an integral part of the cultivation method. Ducks going through rice fields after the harvest eat the leftover grain as well as insects, and the bird droppings fertilize the fields. Bangladeshi agriculture scientists also found that raising ducklings in rice fields reduced cultivation costs and increased productivity. By eating harmful insects, trampling and feeding on weeds, and with their droppings enriching the soil, the ducklings reduced the need for expensive agro-chemicals.

Bangladesh has 37 million ducks as well as 220 million chicken, according to the FAO. It has the third largest population of ducks in Asia, and the largest number in South Asia.

Spread by ducks

When a virulent form of bird flu is around, ducks can help it spread. The problem arises because ducks infected with the H5N1 virus often suffer few ill-effects and can appear to be healthy. But all the while they could be shedding vast quantities of the virus in their respiratory tract secretions and droppings.

Ducks live in a watery environment and the flu virus is able to survive in water for a couple days, points out Marius Gilbert of the Universite Libre de Bruxelles in Brussels, Belgium. In this manner, the virus can be transmitted to other ducks as well as to terrestrial poultry. Ducks are more resistant to the virus than chicken and only a small proportion of ducks that are infected become ill, he told this correspondent.

In a study published last year, Dr. Gilbert and other scientists analysed H5N1 outbreaks among poultry in Thailand during 2004-05. They found that although most of the bird flu outbreaks occurred in chicken, the spatial distribution of the outbreaks did not correspond to areas with high densities of these birds. North-eastern Thailand, for example, had many native birds (chicken) not protected by bio-security measures. Yet in this region, apart from some incidental outbreaks, there was no marked increase of bird flu.

The geographic pattern of bird flu outbreaks in Thailand indicated that the disease was not primarily driven by long-distance transmission between chicken-production units or between villages. Instead, wetlands used for double-crop rice production, where free-grazing ducks could feed year round in rice paddies, appeared to be "a critical factor" in the persistence and spread of the virus, reported the scientists.

Flocks of ducks in Thailand can be moved quite extensively, sometimes by truck over large distances, Dr. Gilbert told this correspondent. One of the measures that the Thai Government took to curb the spread of bird flu was requiring that ducks be tested for the virus before being transported beyond a certain distance.

"One may hypothesise that mixed duck and rice farming predisposed for HPAI [highly pathogenic avian influenza] persistence," observed Dr. Gilbert and his collaborators in a subsequent paper published this year. In both Vietnam and Indonesia, preliminary studies indicated links between highly virulent bird flu and duck concentrations.

In the paper, the scientists showed it was possible to identify areas in Thailand with a high density of free-grazing ducks by using satellite imageries to estimate the intensity of rice cropping. Preliminary results indicated the method would also work in Vietnam but not as well in Indonesia where the association between ducks and rice was slightly different, said Dr. Gilbert in the course of a telephonic interview. Consequently, it was not a technique that could be blindly applied to Bangladesh, he cautioned. "We should know a lot more about how the duck husbandry works in Bangladesh," he added.

The first outbreak of H5N1 in Bangladesh occurred at a poultry farm on February 5 this year, according to information provided by the Government to the World Organisation for Animal Health (OIE). But the OIE was first informed about the outbreaks only on March 30. The presence of the virus among poultry had been confirmed in 39 farms in 11 districts, and more than 1.45 lakh birds were culled up to May 28, according to the website of the Bangladesh Government's Ministry of Fisheries and Livestock.

For India, with the regular movement of people and goods across the border, there is always a chance that the virus might hitch a ride into this country. The tyres of all vehicles entering India from Bangladesh are being disinfected at the border, says S.K. Bandyopadhyay, the Union Government's Animal Husbandry Commissioner.

The border authorities have been asked to be vigilant against any smuggling. Greater surveillance of poultry was also being undertaken in States bordering Bangladesh, he added.