The Agriculture Ministry of South Korea confirmed on Saturday 24th November that the latest outbreak of bird flu among farmed ducks was of the non-deadly H7 strain, and not the deadly H5N1 strain that is fatal to humans. There is no evidence that H7 affects humans.
The outbreak occurred in a farm about 200 miles south west of the capital, Seoul. The Korean authorities ordered the slaughter of 17,000 ducks on the farm as a containment measure.
Today, the Japanese Ministry of Agriculture said in a statement relayed by the Associated Press that it was temporarily stopping poultry imports from South Korea because of the outbreak. This is only a few months after lifting an earlier ban on poultry imports from South Korea following a bird flu outbreak last year.
South Korean officials said this most recent outbreak does not affect its status as a bird flu free country, since it is the H7 strain that has caused the latest outbreak and not a return of the H5N1, of which there has been no sign since March this year.
According to the World Health Organization (WHO) information on bird flu outbreaks worldwide, there have been no confirmed cases in South Korea of humans with H5N1 to date. However, the Washington Post on 11th February 2007, relayed a report from South Korean health officials that a farm worker was infected with H5N1 but did not develop symptoms of the disease because of “natural immunity”. This was following reports of a sixth outbreak of the deadly virus among farm birds in South Korea in the 12 months preceding that incident, resulting in the slaughter of over 2 million birds.
The deadly H5N1 strain of bird flu can spread to humans if they handle sick or dead birds infected with the disease, and even so it is not easily spread from bird to human. Millions of wild and domestic birds worldwide have been killed or culled as a result of H5N1 outbreaks in recent years.
However, although the current rate of human infection is low, there are two reasons to be concerned about the spread of H5N1. The first is, that even though it does not spread easily to humans, when it does, it is highly dangerous. 206 of the 335 H5N1 worldwide confirmed human cases since 2003 have been fatal, according to the WHO.
The second reason to be concerned about the spread of H5N1 is that many experts now agree that it is only a matter of time before it mutates into a form that does spread easily among humans. And the more opportunities the virus has to infect a large bird population, the more chances it has of mutating into such a form. So containment of H5N1 is important not just for animal health but for human public health too.
But more recently, concern has emerged that it is not just H5N1 that needs to be contained and monitored for reasons of human public as well as animal health.
A recent article by avian flu experts Timm Harder and Ortrud Werner, of the Friedrich-Loeffler-Institute Institute of Diagnostic Virology, Greifswald, Insel Riems, in Germany, writing in the Influenza Report 2006, suggested that even when low pathogenic strains of bird flu, known as LPAI strains, such as H7 and other H5 types, are transmitted from wild birds to susceptible farmed birds such as chickens and turkeys, and have the chance to go through several infection cycles, they can mutate several times over and adapt to their new hosts.
The possibility then arises, wrote Harder and Werner, that not only can the less pathogenic forms of these viruses adapt to their new hosts, but they may have the capability to insert mutations and become strains of a:
“Highly pathogenic form (highly pathogenic avian influenza viruses, HPAIV) inducing overwhelming systemic and rapidly fatal disease. Such HPAI viruses may arise unpredictably de novo in poultry infected with LPAI progenitors of H5 and H7 subtypes.”
Click here for Influenza Report 2006 article by Harder and Werner.
Written by: Catharine Paddock