The Mittelhäusern site is the Swiss reference laboratory for highly contagious animal diseases such as foot-and-mouth disease and classical swine fever, as well as other diseases listed in the Swiss Epizootic Diseases Ordinance (TSV). These include bluetongue and porcine reproductive and respiratory syndrome. The reference laboratory functions include the diagnosis of highly contagious animal diseases and confirmation testing of non highly contagious diseases on behalf of external laboratories.
Highly pathogenic avian influenza virus confirmed in Switzerland
On 22 February 2022, a grey heron, found dead in the pelican enclosure of the Bern wildlife park, and a pelican, also dead, were confirmed positive for avian influenza virus. Samples taken were sent to the National Reference Laboratory for Poultry and Rabbit Diseases (NRGK) on suspicion of infection with avian influenza virus (AIV). Investigations at the NRGK revealed an infection with avian influenza virus subtype H5N1. Samples were then sent to the Institute of Virology and Immunology (IVI), the national reference centre for highly contagious animal diseases. Sequencing at the IVI identified the virus as a highly pathogenic H5N1 AIV. In November 2021, an H5N1 virus had been detected in chickens in a hobby farm in the canton of Zurich.
Avian influenza viruses have their natural reservoir in wild birds. Waterfowl in particular harbour a variety of influenza virus subtypes, which differ in their surface structures HA (haemagglutinin) and NA (neuraminidase). Avian influenza viruses are perfectly adapted to their natural hosts and do not cause severe disease in these birds. The viruses replicate mainly in the host’s intestinal epithelium and are excreted into the environment along with the faeces. Transmission of avian influenza viruses to chickens or turkeys kept near resting areas used by migratory birds is therefore a regular occurrence.
If an H5 or H7 subtype of the virus is detected, pathotyping is carried out by sequencing at the IVI.This allows us to distinguish between low pathogenic and highly pathogenic viruses. Avian influenza viruses of subtypes H5 and H7 receive special attention, as these can mutate into highly pathogenic influenza viruses due to changes in the HA protein. Highly pathogenic influenza viruses can cause up to 100% mortality in chickens and turkeys. However, the description “highly pathogenic” (disease-causing) refers only to the infection in poultry! Avian influenza viruses do have zoonotic potential, i.e. they can also be transmitted to humans, but the barrier to such infections is relatively high.
Newcastle disease in a laying hen farm
16.03.2022 - Serum samples from several laying hens were sent to the National Reference Laboratory (NRGK) in Zurich from a poultry farm in Develier near Delémont with suspected Newcastle disease (NCD). Positive serological results suggest an infection with the Newcastle disease virus (NDV), the pathogen responsible for Newcastle disease. The IVI is currently analysing further samples from the farm for NDV virus genome and positive samples will subsequently be pathotyped.
The Newcastle disease virus (NDV) is an avulavirus belonging to the paramyxovirus family. NDV can infect many different species of birds and has three main pathotype groups. Lentogenic (non-virulent) NDV strains cause no or only mild symptoms. Mesogenic strains (medium virulence) have a significant effect on egg quality and production and are associated with increased mortality. Velogenic (highly virulent) strains can produce severe neurological and respiratory symptoms, spread very rapidly and are usually associated with high mortality, which can be as high as 100%.
Transmission and symptoms
As the symptoms are very similar to those of classical avian influenza caused by highly pathogenic avian influenza A viruses, the disease caused by velogenic strains is also described as “atypical avian influenza”. It is a notifiable animal disease. Velogenic NDV strains are highly infectious and can be transmitted through the air as well as through direct contact with faeces and body fluids such as nasal, throat and eye secretions. There is an increased risk to poultry kept outdoors, which can become infected through contact with the droppings of wild birds. Contaminated barn dust, cages, feed, drinking water, footwear, clothing and examination instruments are other potential sources of infection.
The most recent case of Newcastle disease occurred in January 2022 in the canton of Zurich. Switzerland is officially free of Newcastle disease. Vaccination against NCD is prohibited for chickens in Switzerland. Special rules for pigeons are laid down in Article 124 of the Epizootic Diseases Ordinance.
News about the outbreak – FSVO (in German)