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Wednesday, October 26, 2005

H5N1 bird flu already in Africa?

An interesting report from last year found that ostriches in South Africa were testing positive for antibodies to H5 virus. However, apparently the virus they had been infected with was H5N2, not the H5N1 virus that we are currently worried about birds carrying to Africa. How many other birds in Africa have already experienced H5N2 infections, and how will that impact their ability to withstand potential future H5N1 infections? Have birds with H5N1 already reached Africa in past years? Unfortunately, we know very little about the extent and distribution of H5 infections in birds. Since the first H5 virus to be detected (H5N3) was from a tern in South Africa in 1961, some forms of H5 virus have apparently been in Africa for as long as we've known about them.

With media speculation about H5N1 being carried to Africa by migratory birds, there has been little discussion of the exact mechanism for this to take place. Mallards, which have been shown in the lab to be able to harbor and transmit some H5N1 genotypes without showing signs of infection, are found in marshlands in North Africa, but are not as common throughout the continent. Most Mallards in Africa are also probably from Western Europe, where the virus is not yet thought to be widespread.

Garganey, a small Asian teal, may be a more likely candidate to carry H5N1 to Africa. While the virus has been found in a Garganey in Russia, it is not known how extensive the virus is in Garganey populations, or how well these birds are able to withstand, carry, and transmit H5N1. If these ducks are able to carry and transmit the virus along their migratory route, they may carry it to Africa, where large flocks spend the day on large lakes and move into rice fields to feed at night. Garganey in Africa reportedly stay well clear of human settlements, so they may not pose an immediate health risk to people, but if they can transmit H5N1 to other local birds, there may be a greater risk of the virus spreading to other birds and even humans.

These are a lot of ifs, but in order to gauge the possibility of H5N1 spreading in Africa, monitoring of Garganey flocks might be a good place to start.

But for real effective virus monitoring, we need a global commitment to widespread surveillance of all wild birds.

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