Explained

8226; Symptoms

In poultry, the viruses cause two distinctly different forms of disease 8212; one common and mild, the other rare and highly lethal. In the mild form, signs of illness may be expressed only as ruffled feathers, reduced egg production, or mild effects on the respiratory system. Outbreaks can be so mild they escape detection unless regular testing for viruses is in place. In contrast, the second and far less common highly pathogenic form is difficult to miss.

8226; Other subtypes

All 16 HA haemagluttinin and 9 NA neuraminidase subtypes of influenza viruses are known to infect wild waterfowl, thus providing an extensive reservoir of influenza viruses perpetually circulating in bird populations. In wild birds, routine testing will nearly always find some influenza viruses. The vast majority of these viruses cause no harm. Only four are known to have caused human infections: H5N1, H7N3, H7N7, and H9N2. To date, all outbreaks of the highly pathogenic form of avian influenza have been caused by viruses of the H5 and H7 subtypes. Not all virus strains of the H5 and H7 subtypes are highly pathogenic

8226; Transmission route

According to the World Health Organisation WHO, circumstantial evidence has suggested that wild waterfowl introduced avian influenza viruses to poultry flocks but did not carry or directly spread highly pathogenic viruses. Experts say that the scenario changed recently, as some species of migratory waterfowl are now thought to be carrying the H5N1 virus in its highly pathogenic form and introducing it to new geographical areas located along their flight routes. Apart from being highly contagious among poultry, avian influenza viruses are readily transmitted from farm to farm by the movement of live birds, people especially when shoes and clothing are contaminated, and contaminated vehicles, equipment, feed, and cages. Highly pathogenic viruses can survive for long periods in the environment, especially when temperatures are low. For example, the highly pathogenic H5N1 virus can survive in bird faeces for at least 35 days at low temperature 4oC. At a much higher temperature 37oC, H5N1 viruses have been shown to survive, in faecal samples, for six days.

8226; History

First identified in Italy in 1878, highly pathogenic avian influenza is characterised by sudden onset of severe disease, rapid contagion, and a mortality rate that can approach 100 per cent within 48 hours. In this form of the disease, the virus not only affects the respiratory tract, as in the mild form, but also invades multiple organs and tissues. The outbreaks of highly pathogenic H5N1 avian influenza that began in south-east Asia in mid-2003 and have now spread to a few parts of Europe, are the largest and most severe on record. Till date nine Asian countries have reported outbreaks listed in order of reporting: the Republic of Korea, Vietnam, Japan, Thailand, Cambodia, the Lao People8217;s Democratic Republic, Indonesia, China, and Malaysia. Of these, Japan, the Republic of Korea, and Malaysia have controlled their outbreaks and are now considered free of the disease. Elsewhere in Asia, the virus has become endemic in several of the initially affected countries. In late July 2005, the virus spread geographically beyond its original focus in Asia to affect poultry and wild birds in the Russian Federation and adjacent parts of Kazakhstan. Almost simultaneously, Mongolia reported detection of the highly pathogenic virus in wild birds. In October 2005, the virus was reported in Turkey, Romania, and Croatia. In early December 2005, Ukraine reported its first outbreak in domestic birds. Most of these newer outbreaks were detected and reported quickly.

8226; Countries with human cases

Till date Cambodia, China, Indonesia, Thailand, Turkey, Iraq and Vietnam have reported human cases of bird flu. The first patients in the current outbreak, which was reported from Vietnam, developed symptoms in December 2003 but was not confirmed as H5N1 infection until January 11, 2004. Thailand reported its first cases on January 23, 2004. The first case in Cambodia was reported on February 2, 2005. The next country to report cases was Indonesia, which confirmed its first infection on July 21, 2005. China8217;s first two cases were reported on November 16, 2005. Confirmation of the first cases in Turkey came on January 5, 2006, followed by the first reported case in Iraq on January 30, 2006. All human cases have coincided with outbreaks of H5N1 avian influenza in poultry. Vietnam has been the most severely affected country, with more than 90 cases. WHO reports 271 human deaths in all due to bird flu.

8226; India8217;s case

This is not the first time bird flu has broken out in India. In 2006, the spread of the H5N1 virus was confirmed in Nandurbar district of Maharashtra.About 8 lakh birds were culled then to contain the spread of the virus. Chingmeirong village near Manipur8217;s capital Imphal had witnessed the bird flu outbreak in July 2007. After the culling of a large number of birds and other preventive measures in both cases, the World Health Organisation WHO had last year declared India 8220;free from bird flu8221;.