How does the highly pathogenic bird flu virus spread to new countries?

Apr 2 2007

How does the highly pathogenic bird flu virus spread to new countries?

Might the domestic bird trade be responsible? Or is it wildfowl? Since last year, a team from CIRAD has been working on wildfowl. To date, the virus has not been detected in healthy wild birds, but many dead or dying birds have been found near infection foci. Are they victims or reservoirs? In all likelihood the former, but the latter hypothesis cannot be ruled out. Six healthy ducks carrying the virus - out of a total of 4600 tested and in a particularly severely infected zone - were found in China in January 2005.

In 2005 and 2006, migrating birds were often under suspicion. However, their migration corridors and periods did not necessarily correspond to the virus spread patterns seen in recent years. To clarify matters, researchers are now plotting comprehensive, accurate flight plans. To this end, with FAO funding, they are fitting birds with small Argos transmitters. This equipment will provide a large number of data and fill the gaps in information on the subject. Migration has already been studied in detail in Europe and Asia, but this is far from the case in Africa, where monitoring is limited to counting the populations in each country or ringing birds, despite the fact that some five million ducks from Eurasia winter in Subsaharan Africa and there are more than four million African ducks that fly between the different regions of the continent.

In particular, the transmitters will provide information on the number of migration stages and where the birds stop off during migration. In fact, they stop off in humid zones propitious to pathogen transmission, where the different species mix with one another. The study should also provide more general information on migration: travelling times and the ecological and manmade factors that determine the stops.

Three species were chosen for the operation: the blue-winged teal, fulvous whistling duck and comb duck, each of which represents a typical migration route. The teal is a Europe-Asia-Africa intercontinental migrator and winters exclusively in Subsaharan Africa, where it is the most common wintering bird. The comb duck restricts its movements to Africa, but covers several regions, while the fulvous whistling duck, the most common African duck, is a nomadic species on a regional level. The researchers' first step was to test the impact of the transmitters on the birds' behaviour in captivity at Montpellier's Lunaret Zoo. They then travelled to Africa, and captured and equipped 45 birds in February. Captures were made at three sites: northern Nigeria, a very humid zone where there have been bird flu foci for more than a year; the inland delta of the Niger River, in Mali, which is the biggest wintering site for Eurasian ducks in Africa; and Malawi, which had the necessary sites for a study of interregional migration. Now that the birds have been released, they can be monitored, and the results, updated twice weekly, are now available on a CIRAD website: http://wildbirds-ai.cirad.fr.

The study is a first for Africa. Teams from the FAO and the United States Geological Survey, which work with CIRAD, have also equipped swans in China and Mongolia. For the time being, the researchers do not know how long the transmitters will continue to supply data (this depends on the birds' lifespan).

Each transmitter weighs between 12 and 30 grammes. The 12- and 18-gramme ones are used for teals and fulvous whistling ducks, and the 30-gramme ones for comb ducks, which are larger. They are fitted to the body of each bird, like small backpacks, using teflon straps. The location of each bird is determined using the Argos system. The transmitter emits a signal that is picked up by satellites in polar orbit at a height of 850 km. The satellites then send the signal back to terrestrial reception stations. The data received are subsequently processed by centres specializing in the Argos system. Lastly, once processed, the data are passed on to users.

The maps available on the Wild birds and avian influenza in Africa website can be used to monitor bird movements, virtually in real time. At the moment, the teals from Nigeria are moving towards Lake Chad. They should be heading north in the next few days.

http://wildbirds-ai.cirad.fr