Even if poultry are vaccinated against highly pathogenic avian influenza (HPAI), biosecurity is a crucial tool in disease control, according to a new European study that also looked at surveillance strategies.
Even if poultry are vaccinated against HPAI, biosecurity remains an essential element of disease control.
This is one of the key messages in a second paper on the control of avian flu recently published by the European Food Safety Authority (EFSA) and the European Reference Laboratory for Avian Influenza.
“Vaccination is an important tool in the fight against avian influenza, and is recommended as part of an integrated disease control approach,” said Frank Verdonck, head of EFSA’s Biological Hazards and Animal Health and Welfare Unit. “Nonetheless, there is a need to follow up with a strategic surveillance scheme and implement measures to reduce the risk of virus transmission.
“Maintaining a high level of biosecurity remains essential, even when vaccination is used. Raising awareness among farm owners and practitioners can help to ensure that any changes in poultry production or increased mortality are promptly reported and acted upon.”
Furthermore, the authors stress the importance of carrying out post-vaccination surveillance of poultry. This will not only allow the detection of further HPAI outbreaks, but also help to demonstrate freedom from the disease, and facilitate the safe movement of birds and poultry products.
In the paper, the experts examined surveillance strategies for both emergency and preventative vaccination. They went on to identify and recommend the optimum number of animals to be tested, diagnostic method, and sampling period for three poultry types — namely laying hens, turkeys, and ducks.
When the amount of virus in the bird’s blood is low following vaccination, the researchers suggest that more sensitive methods be used.
The group's previous paper on HPAI vaccination of poultry was published in October of 2023.
Wageningen study investigates virus testing methods
Rapid tests carried out on farms can offer support for the diagnosis of avian flu viruses, according to Wageningen Bioveterinary Research (WBVR) — part of Wageningen University Research in The Netherlands. However, these rapid tests are not currently a satisfactory replacement for polymerase chain reaction (PCR) tests carried out in the lab.
This is the main conclusion from a recent study in which WBVR scientists explored the sensitivity and specificity of several rapid tests for avian flu viruses.
Among the drawbacks of some of the tests was the feint line generated by a low virus concentration was difficult to see. However, a PCR test accurately showed the sample was positive for the virus.
The study found that all the three most sensitive tests detected all 16 virus H-subtypes, although they do not allow the type to be identified.
Overall, about 90% of the field samples found to be positive by PCR were also positive using the rapid tests.
New HPAI outbreaks reported in Bulgaria, Hungary
Over the past 10 days, just two European states have confirmed new HPAI outbreaks in commercial poultry.
In Bulgaria, these have involved four premises, according to the Bulgarian Food Safety Agency.
Affected since the end of March have been two laying flocks comprising around 25,000 and 154,000 laying hens in the central province of Haskovo and in Plovdiv in the south, respectively. Also in Haskovo was an outbreak involving 300,000 broilers, while the other outbreak was in an unregistered mixed flock of around 100 poultry in the adjacent province of Kardzhali.
Based on official notifications to the World Organisation for Animal Health (WOAH), 10 outbreaks linked to the H5N1 HPAI virus serotype have occurred in Bulgaria this year, up to the end of March.
Following a brief hiatus, the same HPAI virus variant has been detected again in two counties of Hungary.
In the last 10 days, the national animal health agency has notified WOAH about four outbreaks in Bekes in the southeast of the country, and one in neighboring Jasz-Nagykun-Szolnok. The reports do not include details of flock sizes or bird types.
Ten H5N1 HPAI outbreak series in Hungary between November of 2023 and January this year affected a total of 76 premises with more than 1.6 million poultry across much of the country, based on reports to WOAH.
Overview of the HPAI situation in European poultry, captive birds
Since the start of 2024, 16 European countries have together recorded 138 HPAI outbreaks in commercial poultry flocks (as of April 12).
This is according to the Animal Disease Information System from the European Commission (EC). It monitors the disease situation in European Union (EU) member states and neighboring countries.
Compared with the previous edition dated April 5, the outbreak total rose by three — all in Bulgaria.
The highest national total since the start of the year is 55 outbreaks in Moldova, followed by Poland (with 25). Neither country has added to its total since early March.
During the whole of 2023, the EC System recorded a total of 521 outbreaks in poultry across 24 countries.
In a separate category of “captive birds” the EC System records HPAI outbreaks in non-commercial poultry, zoos, and similar premises.
Seven European countries have registered a total of 46 outbreaks affecting this population in 2024 (as of April 12). No new cases in this category have been reported since mid-March.
For comparison, 15 countries registered a total of 99 HPAI outbreaks among captive birds last year.
Slow rise in cases among wild animals in Europe
There are signs that the peak season for HPAI infections in the region’s wild birds has passed.
So far in 2024, a total of 379 outbreaks have been registered with the EC System in this population by 26 countries (as of April 12).
While a first case of the year has been recorded in Latvia, the overall outbreak total has risen by just six since the previous System edition dated April 5.
Three of these were confirmed in Germany, which also has the highest total to date at 133. Next come Denmark (72) and Romania (23), but neither has added to its total over the previous week.
Further cases in wild birds have been registered with the EC by Norway (two outbreaks) and Poland (one).
Not included in the EC System is the Great Britain, where the veterinary authority has notified WOAH about one additional infection in a wild bird linked to the H5N1 virus variant.
Earlier this month, two red foxes tested positive for the H5N1 HPAI virus near the German city of Hamburg. Based on WOAH reports, Germany has recorded a total of 21 such cases in “unusual hosts” (non-avian species) over the past two years.
View our continuing coverage of the global avian influenza situation.
