Africa – Avian Influenza
19 Mar 2009
CIDRAP News [edited] [Promed]
Scientists who analyzed 67 H5N1 avian influenza viruses from across Africa report that the viruses fall into 3 distinct sublineages, or families, and that some have mutations that make them resistant to antiviral drugs.
The scientists also found that some of the African viruses have genetic markers that are characteristic of human flu viruses rather than avian strains, according to their report, published yesterday [18 Mar 2009] in the online journal PLoS One.
Lethal H5N1 viruses made their African debut on Nigerian poultry farms in January 2006, the report notes. Soon afterward, the virus cropped up in Egypt, Niger,*****, and Cameroon, and in April 2006, it was found in Sudan, Burkina Faso, Djibouti, and Ivory Coast. The virus surfaced in Ghana and Togo in mid-2007 and in Benin in December 2007.
All but 2 human cases of H5N1 disease in Africa have occurred in Egypt, whose official case count is 58, with 23 deaths. Nigeria and Djibouti have each had one human case.
The researchers determined that all the African viruses belong to clade 2.2 and are related to the H5N1 viruses that have been circulating throughout Europe, Russia, and the Middle East since late 2005. Clade 2.2 traces back to the outbreak of avian flu in thousands of migratory birds at China's Qinghai Lake in the spring of 2005, the article notes.
In searching signs of antiviral resistance, the team found 4 bird isolates from Egypt carrying a mutation linked with resistance to the older class of flu drugs, the adamantanes (amantadine and rimantadine). They also found viruses from 2 human cases in Egypt that had a mutation (known as N294S) that confers resistance to oseltamivir (Tamiflu) and slightly reduced sensitivity to zanamivir (Relenza). However, no mutations conferring resistance to oseltamivir or zanamivir were found in any of the African viruses from birds.
In other findings, the report says that 2 different reassortant viruses representing combinations of 2 of the 3 sublineages were found in Nigeria in 2006 and 2007. One of these became the predominant strain in Nigeria's poultry in 2007. "The continued circulation of A/H5N1 viruses in the African continent not only affects the local economy but also impacts on animal and human health," the report states. It concludes with a call for constant efforts to monitor and control avian flu across Africa.
David A. Halvorson, DVM, an avian flu expert at the University of Minnesota in St. Paul, said the report appears to confirm that there were 3 separate introductions of H5N1 into Africa and that those strains continue to circulate. Further, he said the study shows that genetic sequencing "shows evidence for international spread within Africa as well as evidence for local spread and that there have been no additional introductions since the 1st ones." Halvorson also commented that the findings regarding antiviral resistance are not surprising: "These mutations are typical of viruses as they circulate in a host. It seems they can mutate to resistance without any antiviral compound present."




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