Avian flu: ever-changing threat to poultry health

Recent studies suggest that two families of avian influenza virus pose more of a threat than previously thought. While three countries report they have resolved the disease situation, new outbreaks of highly pathogenic avian influenza (HPAI) have been confirmed in poultry and other commercial birds in the Philippines, South Africa, and Vietnam. Following contact with domestic poultry, two Chinese children have tested positive for the H7N9 influenza virus.

(Andrea Gantz)
(Andrea Gantz)

Recent studies suggest that two variants of avian influenza virus pose more of a threat than previously thought. While three countries report they have resolved the disease situation, new outbreaks of highly pathogenic avian influenza (HPAI) have been confirmed in poultry and other commercial birds in the Philippines, South Africa, and Vietnam. Following contact with domestic poultry, two Chinese children have tested positive for the H7N9 influenza virus.

Among the features of viruses that make disease control more challenging is their constant mutation. Recent changes in one virus variant have increased the threat it poses to poultry, according to a new study.

Recent mutations in the H7N9 virus have led to faster replication and greater stability in avian cells, according to The Pirbright Institute in the United Kingdom. As a result, researchers say, these strains represent an increasing threat to poultry, through their improved transmission ability.

Results from the institute show that H7N9 viruses isolated from the field in 2019 demonstrate similar mutations to those shown previously by lab samples. These changes have allowed the virus to overcome more easily the immunity generated by vaccination.

The approach taken by the Institute facilitates the prediction of avian flu virus mutations, according to the head of avian flu research at Pirbright, Professor Munir Iqbal. Not only can this information indicate how the mutations affect the disease risk they pose to people and poultry, but it also supports surveillance efforts by providing early earning of potentially dangerous new strains.

By contrast, the latest mutations in this virus lower the risk it poses to humans.

H3N1 virus: Non-notifiable but a threat to poultry health

Generally, low-pathogenic avian influenza (LPAI) viruses of the H3 family are not seen as important pathogens in poultry. Because they are classified as “non-notifiable,” international agencies do not require outbreaks to be officially reported. However, a new study from Belgium reveals that they can lead to significant reproductive problems as well as substantial mortality in commercial flocks.

In a paper published recently in the journal Emerging Infectious Diseases, scientists at Sciensano in Brussels, Belgium, report their latest work on H3N1 avian flu virus that was linked to a series of outbreaks in that country last year. Genome analysis revealed that the virus originated in wild birds, rather than poultry.

While LPAI viruses often circulate in flocks without causing symptoms, this virus was found to be more pathogenic. This was demonstrated by its systemic distribution in the body, clinical signs, and increased transmissibility in poultry — especially laying hens — under both field and experimental conditions.

According to the researchers, the H3N1 virus was detected at 82 locations in north-western Belgium over about 4 months of 2019, as well as one in the south of the country, and three in France.

First clinical signs observed were discolored eggs. Subsequently, mortality rose up to 100% in a few outbreaks, and generally to 60% in breeding hens, and 40% in shell egg flocks. Even after the birds apparently recovered, laying performance was not fully restored. In some cases, subsequent waves of mortality resulted from secondary infections.

Philippines, South Africa, Vietnam report return of HPAI

After a brief absence, the H5N6 HPAI virus has been detected again in Vietnam. The country’s veterinary authority reports that the disease has hit two large village poultry flocks in the central province of Quang Ngai. Of the total of 8,100 birds affected, almost 4,000 died, according to the official report to the World Organisation for Animal Health (OIE).

For more than 3 years, South Africa’s commercial ostrich sector has been battling the H5N8 HPAI. Two recently reported outbreaks take the country’s total to 218.

Following a three-month hiatus since January, 27 cases were detected among 600 of the birds in Eastern Cape Province in April of this year, according to the OIE report. Two months later, the agriculture department reports, there was a further outbreak. This time, there were around 800 cases among 1,200 ostriches at a farm in Northern Cape Province.

Among other birds, the department reports no new recent HPAI cases. The most recent were detected among a small group of geese at a Northern Cape farm one year ago.

After an absence of several months, HPAI has returned to the Philippines. The H5N6 HPAI virus has been detected at an egg farm in the central Luzon province of Pampanga, reports Philippine News Agency. Around 38,700 hens have been culled and destroyed. Source of the infection is unknown, but migratory wild birds have been seen in the area.

In recent weeks, OIE had received a report from the agriculture department of the Philippines that HPAI had been “resolved.” This followed a single outbreak of the disease (H5N6 HPAI) in a quail flock in the province of Nueva Ecija on Luzon in March of this year.

On the Mediterranean island of Malta, a group of wild ducks at a nature reserve tested positive for an H6 avian flu virus earlier this month, reported Malta Today.

HPAI 'resolved' in Hungary

The HPAI situation in Hungary has been “resolved” in poultry in all three previously affected counties, according to the agriculture ministry.

Between March and May of this year, a total of 270 confirmed outbreaks linked to the H5N8 virus variant were reported to the OIE. With incomplete details for many of these outbreaks, the number of poultry directly affected is likely to be well in excess of the 2.8 million recorded with the agency.

U.S, Dominican Republic: LPAI situation closed

During the month of March 2020, LPAI of the H7N3 subtype was detected among 12 commercial turkey farms in North Carolina and South Carolina, affecting a total of more than 305,000 birds.

According to the latest report to the OIE from the USDA Animal and Plant Health Inspection Service, all recent samples taken from the affected premises have been negative for the virus. As a result, quarantine has been released at all affected premises. As part of avian influenza control programs, routine passive and active surveillance will continue in both states.

In the Dominican Republic, the H5N2 LPAI virus was detected at a total of 26 poultry farms between November of 2018 and August of last year. Involving a total of almost 807,000 birds, the outbreaks were confirmed in Espaillat and seven other provinces in the Caribbean state.

Declaring the situation “resolved” to the OIE, the agriculture ministry reports that the pathogenicity of the virus has reduced to zero. It adds that all affected poultry completed their production cycles, and have been slaughtered, without any new cases being detected.

New human cases of avian influenza

In its latest update on influenza cases in people linked to poultry, the World Health Organization (WHO) outlines two new cases reported since mid-May.

Both were laboratory-confirmed infections with avian influenza A(H9N2) viruses in China, and were linked to contact with domestic poultry. The patients — a 6-year-old boy from Shandong province, and a 10-month-old baby from Fujian — have recovered.

According to the WHO, avian influenza A(H9N2) viruses are enzootic in poultry in Asia.

View our continuing coverage of the global avian influenza situation.

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