Scientists issue caution against mass poultry vaccination

By staff reporter

- Last updated on GMT

With confirmed cases of human-to-human transmission of the avian
influenza virus, scientists are now warning that mass vaccination
of domestic poultry may hinder detection of the deadly H5N1 strain
of the disease.

Mass vaccination is seen as one way of calming consumers' fears about the safety of the bloc's poultry flock. Consumption of poultry and poultry products have plunged by as much as 70 per cent in some countries at the start of this year.

However mass vaccination can also serve to disguise the presence of any H5N1 that manages to survive in innoculated flocks, and thus pose a great danger, others have argued.

So far the EU and its member countries have resisted calls for mass vaccination of the domestic poultry stock. Limited vaccinations have been done in areas where bird flu outbreaks have occurred.

While no human case of the H5N1 virus has occurred in the EU, scientists worldwide have been worried that H5N1, which can pass from poultry to humans, may mutate so that it can be transmitted from human to human and start a influenza pandemic.

Those fears became a reality for the first time last week, when World Health Organisation (WHO) officials confirmed H5N1 had mutated in a family in Indonesia, passing from a son to his father. Seven of the eight family members died as a result.

WHO has not yet published a report into the cases, but the Associated Press said it had obtained a copy.

Human-to-human transmission has been suspected in a number of previous family case clusters but has never been confirmed by lab tests.

Meanwhile the European Centre for Disease Prevention and Control last week warned that vaccination programmes that are widely but imperfectly instituted in poultry, like those in China and Indonesia, may impede detection of human cases.

"Surveillance for human cases may be becoming harder where poultry immunization is widely but inevitably imperfectly practiced as the marker of local poultry deaths for human case detection is being lost,"​ the CDPC stated in a report. "Declines in the number of sporadic human cases in some countries should therefore be interpreted cautiously. It is also unclear as yet if massive immunisation poultry programmes increase or decrease the overall human population exposure to H5N1 viruses.

At least three countries -- China, Indonesia and Viet Nam -- are undertaking large-scale poultry vaccination programmes against H5N1, alongside with the mass culling of millions of birds.

"If poultry immunisation is efficient and well monitored it could reduce the population burden of H5N1 in poultry and hence the risk for humans,"​ the CDPC stated. "Equally however if it leads to the silent circulation of H5N1 in poultry it could actually increase the threat to humans in those countries and the risk of co-infection with other influenzas…Falling numbers of reported human cases in countries practicing large scale poultry immunisation may therefore be misleading."

Indonesia became the focus of international attention last month when the largest cluster of human H5N1 cases was identified. The outbreak involved eight members of a single family in North Sumatra. The outbreak was considered controlled on June 12, three weeks after the death of the last case with no new cases reported.

Of the 51 human cases confirmed to date in Indonesia, 39 have been fatal. Of the 228 human cases worldwide, 130 have been fatal.

Outbreaks of highly pathogenic avian influenza (HPAI) viruses in domestic poultry have been increasing since the late 1990s and have affected poultry in Europe as elsewhere.

The result has been a cutting off of poultry imports from key suppliers outside the EU and a plunge in consumption in some countries.

Last week, the European Commission announced an aid plan to cut down on the bloc's poultry supplies, in a bid to keep prices from plunging much more. Poultry meat and eggs are piling up in storage across the EU.

The glut has led to falling prices for poultry and egg supplies, and additional costs for storage. Cutting back on production could make prices stabilise or even rebound.

The Czech Republic, Germany, Greece, Spain, France, Ireland, Italy, Cyprus, Hungary, the Netherlands, Austria, Poland, Portugal and Slovakia have applied for aid.

Consumption of poultry meat has dropped by more than half in some EU states, with 300,000 tonnes and more in storage across the bloc, according to previous EU estimates.

The continuing fight against the spread of avian influenza throughout Europe has focused on preventing the spread of the disease to domestic flocks from wild birds.

Supplies from other countries have also been restricted. Earlier this month the Commission banned the import of all poultry and poultry products from Romania, for example.

A confirmed outbreak in domestic geese in Hungary was situated in a region where cases of highly pathogenic avian influenza occurred in wild birds earlier this year. It marked the fifth outbreak of high pathogenic H5N1 avian influenza in domestic poultry in an EU member state.

Previous outbreaks have occurred in domestic poultry in France, Sweden, Germany and Denmark. Cases of avian influenza H5N1 have occurred in wild birds in thirteen member states of the EU to date - Greece, Italy, Slovenia, Hungary, Austria, Germany, France, Slovakia, Sweden, Poland, Denmark, Czech Republic and UK.

In March this year the European Commission approved limited vaccination of bird flocks in certain areas of the Netherlands and France.

Vaccination ended 1 April 2006. Sentinel birds, which are unvaccinated control birds, were used as part of the monitoring for avian influenza.

The UN Food and Agriculture Organisation (FAO) reported earlier this year that recent avian influenza outbreaks in Europe, the Middle East and Africa have caused dramatic swings in poultry consumption, increased trade bans and sharp price declines.

The UN agency expects poultry consumption shocks this year in many countries.

According to the FAO report consumption shocks are ranging from a dramatic 70 per cent decline in Italy in mid-February to 20 per cent in France and 10 per cent in northern Europe.

Following the major geographical spread of the H5N1 avian influenza virus from South-East Asia in 2005, the EU intensified its programmes for the surveillance and early detection of avian influenza, both in wild birds and poultry.

A total of 57 countries around the world have so far reported detecting the avian influenza strain, either in wild birds or domestic poultry.

Bird flu has killed 64 percent of those people known to be infected with the virus this year, according to World Health Organization statistics.

There were 217 cases of infection and 123 deaths worldwide. Most of the deaths occurred in Asia. Earlier this year four died in Turkey.

The H5N1 virus is considered firmly entrenched in poultry throughout much of Indonesia, and this widespread presence of the virus has resulted in a significant number of human cases.

This year alone, Indonesia has reported more than 33 cases with 27 deaths. Deaths have also occurred in Azerbaijan, Cambodia, China, Djibouti, Egypt, Iraq, Thailand, and Viet Nam.

Related topics: Food Outbreaks

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