Is our strategy in controlling H5N1 in chicken effective? It was nearly 10 years ago when Malaysia last detected the highly pathogenic avian influenza (HPAI) H5N1 in chickens.

In the past few weeks, cases of H5N1 have been reported in village chickens and game birds in a few districts in Kelantan.

This resembles the first case of H5N1 reported in the country in 2004.

However, not much is known about this elusive virus.

A study is underway to determine the origin of the virus and whether the isolated viruses from the chickens, express receptors that are important for human infection.

Based on what we know of previously characterised H5N1 cases in Malaysia and other countries, the virus is highly contagious and fatal to chickens.

It has a limited capability of causing human infection unless they are in close contact with the infected animals.

Furthermore, there is no clear evidence that the virus can cause human-to-human transmission, as what was reported in the 2009 flu pandemic or swine flu H1N1 influenza.

However, the public should not take things lightly, especially poultry farmers and personnel who handle live and dead chickens from the infected areas.

They should exercise extreme caution as H5N1 can cause fatal infection in humans.

A World Health Organisation (WHO) report confirmed 856 cases of H5N1 infection in humans have been reported from 2003 to this year, with a case fatality rate of 53 per cent, the highest number of cases being in Egypt, Indonesia and Vietnam.

It is important to note that these are among the few other countries in the world that vaccinate against H5N1 in chickens.

Malaysia has vast experience
in controlling outbreaks of zoonotic diseases — such as the Nipah virus, Japanese encephalitis, rabies and HPAI — effectively.

The best strategy to control the disease is strict biosecurity and stamping out of infected chickens within a 10km radius of infected areas.

Immediate banning of the movement of poultry from the infected areas to other places and continuous surveillance of the occurrence of new cases of H5N1 should be implemented.

Although the use of antiviral drugs to control the virus in chicken is uncommon, sequence analysis of the recently isolated H5N1 infected chickens will let us know whether the virus has developed resistance antiviral drugs, such as amantadine
and oseltamivir, that are being used to treat influenza in humans.

Unlike other viral diseases, such as the Newcastle disease and infectious bronchitis, where vaccination is part of routine measures, vaccination against H5N1 is an optional measure, which should only be considered when there is a clear threat of the virus spreading and affecting major commercial poultry farms.

Even in this situation, vaccinations should be prioritised on expensive birds, such as rare exotic birds, purebred, grandparent stocks and long-lived chickens.

The implementation of a vaccination policy may restrict animal movement, marketing and trade of poultry and poultry products due to the difficulty in differentiating between infected and vaccinated birds (Diva). The inability to implement Diva and use of poor quality vaccines will complicate detection of H5N1, increasing the chance of the virus circulating silently and causing public health concerns.

Prof Dr Abdul Rahman Omar is a professor of immunology and infectious diseases, and Bioscience Institute director of Universiti Putra Malaysia

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