Avian influenza in 2015

Avian influenza is a disease in poultry that is caused by Avian Influenza (AI) viruses. In November 2014, four outbreaks of the H5N8 subtype were detected in the Netherlands, which resulted in the culling of all poultry on the affected farms. Thanks to the effective monitoring in the Netherlands and the alertness of poultry farmers, the H5N8 virus did not spread any further.

The recent outbreak of bird flu in the United States shows that an outbreak can have far-reaching consequences. This outbreak began in December 2014 and lasted until 2015. It resulted in the culling of 48 million birds.

Subtypes and symptoms
There are several subtypes (H1 to H16) of the avian influenza virus. Low Pathogenic AI (LPAI) produces mild symptoms in flocks, such as reduced egg laying and less feed intake. Viruses of subtypes H5 or H7 may transform into Highly Pathogenic AI (HPAI) viruses. Infection with HPAI causes the animals to quickly sicken and die.

In accordance with the European legislation, farms infected with a H5 or H7 subtype must be culled and the government imposes transport restrictions. All poultry farms in the Netherlands are tested at least once per year and checked for avian influenza. Besides this surveillance, it is important for the poultry farmers themselves to be alert to symptoms that could indicate avian influenza. This process has gone well in the Netherlands. 

Diagnosis of AI
Samples are sent by a veterinarian or the Netherlands Food and Consumer Product Safety Authority to CVI, where they are tested with PCR in the laboratory for all variants of the AI virus. If this test is positive, then a follow-up test is conducted to determine whether the virus is the H5 or H7 subtype. If this is the case, then it is determined whether it is a low-pathogenic or high-pathogenic virus. To detect infection, AI antibodies can also be tested in the blood, and the N subtype can be determined. In 2015 (January-November) a total of 19 introductions of LPAI were detected in poultry, including 5 introductions of the H5 or H7 subtype. 

Reservoir
Wild (aquatic) birds are considered to be the reservoir of influenza viruses. There are no indications that AI infections among wild birds have increased. Nevertheless, the number of introductions in poultry appears to be higher in recent years. Hygiene measures are important to prevent infection and to limit its spread. For farms with free range poultry, it is important to prevent contact with wild birds as much as possible.

Dr Nancy Beerens,
Senior Researcher, project leader Avian Influenza and Newcastle Disease