HepiAI41006

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Avian Influenza is a serious disease for humans, who get the infection after exposure to infected domestic birds, predominantly chickens and ducks. Avian influenza H5N1 appeared first in Hong Kong in 1997, then in the Netherlands and South-Korea in 2003.

Studies have showed that Avian influenza is able to mutate easily and turn to be virulent to other species. Data showed that the virus mutated aggressively since the last outbreak in China and Europe. Genetic material exclusively from avian influenza was found in specimens from the 1918 worldwide outbreak of influenza. Findings from the 2004 outbreak in Vietnam revealed that the H5N1 serotype became virulent for other species such as cats.

Vietnam confronted the epidemic applying control measures rapidly, such as the killing of several hundred thousands of chickens, disinfections, quarantine, control of animal movements and general surveys. Despite these measures, other human cases of Avian flu were confirmed in the region.

The virus reservoir is the bird wildlife. Currently, there is no method available to destroy the virus in its environment. The disease causes considerable economic impact in the community, due to:

· Bird mortality

· Mass killing of livelihood owned by producers.

· High virulence to human produced by new avian influenza strains.

· Massive measures necessary to control outbreaks in the community

Outbreak Facts

· It is caused by various H5N1 strains,

· It was reported in parts of Asia since mid-December 2003. Millions of domestic poultry have either died or been destroyed as a result.

· The disease affected thousands of workers have been involved in the culling operations.

· It causes serious concern for human health as well as for agriculture and the poultry industry.

· It can be controlled by the rapid elimination of the virus from bird populations.

. Human beings should have direct respiratory exposure to infected birds to get the disease.

. The mortality is high and varies.

.Although there is not evidence to date of human-to-human transmission, probability of a new virus strain emerging from an exchange between human influenza and Avian flu genomes needs to be carefully examined.

Transmission

· Most of the avian influenza viruses cause infection in birds and pigs.

· The H5N1 strain may have a unique capacity to cause severe disease, with high mortality in humans.

· The multi-country simultaneous occurrence of epidemics of highly pathogenic H5N1 influenza in domestic poultry has not been documented historically.

· In bird populations, the disease is highly contagious and rapidly fatal, and spreads easily from farm to farm.

· Outbreak situation may grow worse due the nature of the dissemination and high infectivity.

· Wild migratory waterfowl can spread infection to domestic flocks, initiating the potential for further spread of ongoing poultry epidemics.

· Most of the deaths have been attributed to direct exposure to infected fowl, like a boy who was at the scene when his grandfather killed chickens.

· Avian flu H5N1 strain prevalence should be widely established in:

o bird populations

o environment

Environmental Aspects

· Infected birds can shed large amounts of the virus in their feces.

· The virus can survive for long periods in the tissues and feces of diseased birds and in water, especially when temperatures are low. In water, the virus can survive for up to four days at 22oC and more than 30 days at 0oC. The virus survives in frozen material indefinitely.

· The large epidemics of highly pathogenic avian influenza currently seen in poultry could produce a widespread presence of the virus in the environment, increasing opportunities for human infection.

· The epidemics also increase opportunities to exchange genes between human and avian influenza viruses when humans are simultaneously infected by both influenza viruses.

· A completely new influenza virus subtype might emerge, carrying sufficient human genes to allow efficient and sustainable person-to-person transmission due to co-infections between human and avian influenza virus.

· H5N1 infection from birds to humans is greatest in persons having close contact with live infected poultry.

· Contact with poultry kept in live markets is considered the source of infection for 17 of the 18 human cases of H5N1 infection that occurred in Hong Kong in 1997. The additional case – the first in the outbreak – has been linked to contact with poultry at farms experiencing epidemics of highly pathogenic avian H5N1 influenza. Six of the 18 cases were fatal.

· Occupational exposure can occur also among workers involved in culling operations.

· Rapid elimination of the H5N1 virus in animal populations is an essential measure to prevent the emergence of a new influenza virus subtype with pandemic potential.

· Rapid elimination of the H5N1 virus in animal populations not only helps prevent further spread in bird populations, but also reduces opportunities for human infection.

· The large number of “back yard” farms complicate the problem of controlling all human exposures in rural areas.

Laboratory characterization of the H5N1 2004 variant

Laboratories in the WHO Global Influenza Surveillance Network are investigating the antigenic characterization and sequencing of latest H5N1 strains isolated from humans and poultry. The results have showed significant differences between these viruses and strains obtained during previous outbreaks of H5N1 avian influenza ( Hong Kong, in 1997 and 2003). These findings indicate that the virus has mutated.

WHO is updating diagnostic kits for the rapid detection of H5N1 infection in humans with new findings.

There are advances on the development of a prototype virus for use in vaccine manufacturing.

Control and prevention aspects

To eradicate the disease,

Eliminate all infected animals.
Disinfect areas
Quarantine all exposed people
Ban on the movement of all domestic birds during the outbreak
People working on farms and in culling of sick birds, should

1. wear protective clothing

2. avoid close contacts with the animals

Organize long term prevention activities:

1. veterinary and human health surveillance

2. early warning

3. rapid response.

Conform an expert team involving international organizations which objectives should set to

· investigate the origin of the problem

· set up necessary control and rehabilitation measures.

f. Implement Culling operations (high priority). China destroyed its all poultry population in three days in 1997.

g. Provide protection for workers doing culling operations. This, place large numbers of workers at risk of brief but intensive exposure to the virus.

h. Train. Culling operations should be performed by trained government workers, wearing protective masks, gloves, and gowns.

i. Around 3% of persons involved in the culling of infected poultry became infected (investigation detected H5 antibodies in China in 1997). However, no case of severe respiratory disease was detected as a result of culling exposure in China in 1997.

j. 30 million poultry were culled within a week in the Netherlands in 2003 because the outbreak of highly pathogenic H7N7 avian influenza in poultry. 83 persons the virus caused mild illness. One fatal illness was in a veterinarian.

k. Information on safety precautions during culling operations will be issued by the WHO Regional Office for the affected region.

The investigation of the Thailand 9-year-old girl who died of severe respiratory disease' identified exposure to diseased chickens can cause of infection. She assisted in preparation of the birds for cooking, including the plucking of feathers.

For more information, please contact:

· www.who.int

· FAO web site

· OIE web site