Reports this week that clade 2.3.2 of the H5N1 virus has shown up in Indonesia (where previously clade 2.1 has reigned) have also included stories of large, sudden die offs of ducks (see Report: Clade 2.3.2 H5N1 Detected In Indonesia).
Although mortality from H5N1 in ducks isn’t unheard of, ducks - along with other waterfowl - are often able to carry the H5N1 virus without serious ill effect.
Oct 26, 2007 (CIDRAP News) – Apparently healthy domestic geese and ducks in Europe may be harboring the H5N1 avian influenza virus, posing a risk to other poultry and to humans who have contact with them, the United Nations Food and Agriculture Organization (FAO) warned in a statement yesterday.
Most types of ducks are not sickened by the virus and in most countries in Asia, they mingle freely with chickens, providing ample opportunity for the virus to jump between species.
'The problem is in the ducks in Asia, there is no visible disease in these birds,' said Webster of the St Jude Children's Research Hospital in the United States.
The absence of visible infection in poultry makes it harder to track the disease and take preventive measures.
All of which makes the sudden death of 300,000 ducks in central Java a bit surprising. First, a report from VOA NEWS, and then I’ll be back with more.
December 12, 2012
In recent weeks, more than 300,000 ducks have died on the densely populated island of Java.
The government has since confirmed the deaths were caused by a new and highly pathogenic strain of H5N1, or bird flu.
Dr. Rita M. Ridwan, the director of disease control at the Indonesian Health Ministry, says the government is working closely with relevant ministries to investigate further.
“So we are in close contact by sharing information, sharing the virus lab and even working together in the field to do field investigations," Ridwan explained. "I know there are very alarming deaths in the duck population, mostly in the center of duck production by the traditional farming as well as in central Java and East Java.”
While it may seem counterintuitive that a species of waterfowl that normally can carry the H5N1 virus without harm is dying in droves, research has shown that even minor variations in the bird flu virus can greatly affect its pathogenicity.
Last April, in Differences In Virulence Between Closely Related H5N1 Strains, we looked at experiments done on mice and ducks with two variants of the same H5N1 clade (126.96.36.199), and the different mortality rates they produced.
And among known human H5N1 cases reported to the World Health Organization, in Bangladesh, of the 6 known cases, none have died, while in Cambodia 19 of 21 have succumbed to the virus. In Egypt, the CFR is running about 35%, while in Indonesia, it is nearly 83%.
Although there are likely many factors involved in causing this disparity in CFR – including quality of, and delays in seeking medical care – it suggests that the H5N1 virus is more virulent in some regions of the world than in others.
Whatever is driving this higher mortality in ducks is currently a mystery, but is hopefully one that can be solved with a closer analysis of the virus.