A resurgence of outbreaks of avian influenza (A/H5N1) has been reported recently in poultry in Vietnam, South Korea, Japan and Thailand and Hungary, as well as cases of human infection in Indonesia and China, following a period of relatively low activity. This is not unexpected, as similar trends were observed at this time of the year in 2004, 2005 and 2006 [1,2,3]. However, the continuing presence of the influenza A/H5N1-virus is of concern because of the risk of its recombination with human influenza strains and/or its adaptation to humans by continuous mutation which could create a pandemic strain.
Outbreaks in birds worldwide
In Vietnam, 52 outbreaks of avian influenza in wild birds and poultry were notified, between 6 December 2006 and 17 January 2007, affecting 41 communes in 19 districts of seven provinces in the southern part of the country (Ca Mau, Bac Lieu, Hau Giang, Kien Giang, Vin Long, Soc Trang, Tra Vinh). The outbreaks in December and January occurred in provinces where immunisation should have been carried out, although a number of them occurred on farms that were unregistered and therefore had been missed by vaccination teams. Infections also occurred on some registered farms, either because of incomplete immunisation coverage or vaccine failure. Vaccination of domestic poultry is continuing. So far, around 2.1 million birds have been vaccinated (including approximately 0.3 million chickens and 1.8 million ducks) but full coverage has not been achieved yet.
Single outbreaks of avian influenza in domestic poultry have recently also been reported in Japan -on a chicken farm on the island of Kyushu, and Thailand on a duck farm in Phitsanulok province, where there had been no cases of H5N1 infection since 2004 and July 2006 respectively. Outbreaks have also been reported in South Korea .
Situation in Europe
This week, authorities in Hungary reported confirmed H5N1 infections in geese in the east of the country. This is the first confirmed outbreak in birds, wild or domestic, in the European Union (EU) in 2007 and the first outbreak in Hungary since summer 2006. This low number of outbreaks in Europe so far this winter may be related to the mild weather conditions in Europe and Asia. Some ornithologists believe that the severe winter of 2005-6 forced wildfowl (the natural hosts of H5N1) to gather and huddle in groups on their over-wintering grounds in parts of northern Asia, where the epizootics of A/H5N1 in wild birds spread easily. The same severe weather then forced the birds to fly west and south to better conditions in Europe. European veterinary preparedness at that time meant that, despite a considerable threat from infected wild birds, the infection was mostly kept out of poultry and there were no human infections in the EU.
Worldwide situation in humans
As of 22 January 2007, according to the WHO, 269 laboratory-confirmed human cases of A/H5N1 infection have been reported since 2003. Of these, 163 (61%) patients are known to have died.
Infections in humans continue to be reported from Indonesia. So far in 2007, five confirmed human cases of A/H5N1 infection, including 4 deaths, have been reported in Indonesia. Those affected were: a 14 year old boy from west Jakarta, a 22 year old woman from south Jakarta and two women aged 22 years and 37 years, both from Banten Province. The latter’s 18 year old son is also infected; he remains in hospital in a critical condition.
A single human case in a 37 year old farmer who became ill in December, has also been recently reported in China (Anhui Province). There is very little information on any exposure to poultry, infected or otherwise, for this case. Indeed there is very little information about infections in poultry in China, although one academic study found evidence of extensive infection in healthy birds in live birds markets in southern China .
In Egypt, two human cases in two members of one family were reported in December 2006 . Both patients died in the same month. On 18 January 2007, a report by the WHO revealed that samples from these two patients had genetic markers previously observed to be associated with some reduced susceptibility of influenza viruses to oseltamivir. Both patients had been on treatment with oseltamivir, but only for two days before the samples that yielded the viruses were taken. This genetic marker of resistance had previously been identified in Vietnam in one patient in 2005. These markers are not associated with any known change in the transmissibility of the virus between humans, and antiviral resistance is uncommon in Egypt, therefore the public health implications at this time are limited. Monitoring of the levels and type of antiviral resistance is important and is being carried out.
Currently, there is still no indication of any change in the way the virus affects humans, specifically, no increase in cluster size or transmissibility. To date, transmissions have nearly always occurred after close contact between humans and infected birds. However, the situation in birds remains a cause for concern. Despite integrated efforts in the veterinary sector in some countries (vaccination, surveillance, increased biosecurity), outbreaks of H5N1 are still occurring regularly or intermittently in poultry in China, Egypt, Indonesia, Thailand and Vietnam, where humans live in close contact with domestic animals. Furthermore, cases of H5N1 infection have been suspected or reported in birds in countries where people have close contact with poultry but the lack of effective surveillance means it is impossible to determine whether or not H5N1 is present in poultry.
The fact that H5N1 virus has been spreading since 2003 without causing the emergence of a pandemic strain does not necessarily mean it will not do so. It is believed that the avian strain that contributed to the influenza pandemic in 1918-1919 was around in birds for a number of years before the pandemic emerged . That is why the elimination of the H5N1 in domestic poultry remains crucial.