New research findings show that Avian influenza is able to mutate easily and turn to be virulent to other species. The virus mutated aggressively since the last outbreak in China and Europe. Additionally, genetic material exclusively from avian influenza was found in specimens from the 1918 worldwide outbreak of influenza. Findings from the 2004 outbreak in Vietnam reveals that the H5N1 serotype became virulent for other species such as cats.

  After Vietnam declared an outbreak of Avian Influenza H5N1 during the first week of 2004, the World Health Organization (WHO), the Office International des Epizooties (OIE) in Paris and FAO formed a team to investigate the outbreak. The organizations expressed serious concerns about the spread of Avian flu in East Asia.  The disease seems to have a regional dimension, with South Korea, Vietnam and Japan being affected in a short period of time. Vietnam rapidly has applied appropriate control measures, such as the killing of several hundred thousands of chickens, disinfections, quarantine, control of animal movements and general surveys. The international team will investigate possible links between these outbreaks aiming to elucidate epidemiological causes of the outbreak.

   Despite these measures, the situation continues to be a cause for concern after the human cases of Avian flu have been confirmed. The experts said that possible new outbreaks in the region were expected.

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

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

·       bird mortality,

·       mass killing of domestic birds and other control measures. Outbreaks affect the livelihood of thousands of farmers relying on chicken production.

·       Important virulence to human by new avian influenza strains.

·       Massive measures to control outbreaks in the community

Outbreak Highlights

·       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.

·       It affects 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 H5N1 virus in bird populations and should be given high priority as a matter of international public health importance.

Avian flu in humans

  To be contaminated, human beings should have direct respiratory exposure to infected birds. The mortality is high and varies. The morbidity and mortality during previous outbreaks were:

·       Hong Kong in 1997, 6 deaths out of 18 cases occurred

·       Netherlands in 2003, 83 cases occurred and one person died.

•  Vietnam so far, the authorities have declared 14 cases of severe respiratory disease in Hanoi, and 11 people have died. Three of these cases were confirmed as Avian flu victims.

There is still no evidence to date of human-to-human transmission but this matter has to be treated very seriously, If the number of infected people increases, the probability of a new virus strain evolving 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 only

·       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 Thai 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 Virus highlights 

·       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. T

·       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” chickens 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). This 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 avances on the development of a prototype virus for use in vaccine manufacturing. However, viruses from birds of other currently countries are needed to complete the process. The information generated from these investigations are needed by WHO to recommend and develop a vaccine strain that can protect humans against circulating H5N1 strains.

Control and prevention aspects

Although the import chickens from Asia was already forbidden, USDA mandated a new ban for "plugging any holes that may exist" in shipments from Asia. The poultry products of most concern were feather products that were not already restricted by the ban for exotic Newcastle disease.

To eradicate the disease,

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

1.    should wear protective clothing

2.    avoid close contacts with the animals

6. Organize long term prevention activities:

1.    veterinary and human health surveillance

2.    early warning

3.    rapid response.

7. 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.

Additional information:

·       www.who.int 

·       FAO web site

·       OIE web site

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