Summary
- In July 2023, a significant die-off of northern fur seals and Steller sea lions was apparent on Tyuleniy Island, Russia, and this was associated with H5N1 highly pathogenic avian influenza virus.
- H5N1 infection produced severe disease with fever, lethargy and neurological signs in infected animals prior to death; clinical illness was confirmed by histopathology following the finding of viral antigen within lesions.
- Phylogenetic studies have confirmed that virus belongs to clade 2.3.4.4.b strains from aquatic mammals in Japan and eastern Russia. Original transmissions probably occurred to seals during the bird migration.Birds and marine mammals are close together in the area of the island, which probably facilitated quick spread of virus infection; highlighting that further surveillance is required to study viral adaptation and transmission.
- The research highlights the need for knowledge of inter-host transmission in an influenza system and using genetic data to predict and control outbreaks within high-risk animal populations.
A significant event occurred in the Russian Federation on Tyuleniy Island in July 2023, where many northern fur seals and Steller sea lions unfortunately met their end. The Island is a vital habitat for many marine animals such as various species of seals, sea lions and seabirds. Researchers and scientists were concerned by the deaths of these animals.
Subsequent analysis confirmed that a highly pathogenic H5N1 avian influenza virus was responsible for the die-offs in seals and sea lions. The virus induced fever and lethargy in some animals and confusion moving on to cause seizures and death of others. Deceased seals had clinical signs associated with influenza A virus based on the analysis of tissue samples from the lungs, small intestine and liver.
Subsequent sequencing and phylogenetic studies further characterized the H5N1 virus as clade 2.3.4.4.b. The genetic properties of the virus from seals on Tyuleniy Island corresponded to those found in marine mammals living off the coast of Japan and the eastern part of Russia. These results propose a transmission route from avian to seal population during bird´s migration season.
The close proximity of birds with marine mammals on the island may explain the pattern of spread like ‘wildfire’ into these animals. There is a need for long-term surveillance of this virus both in birds and seals to assess viral adaptation over time as well as its potential transmission across populations.
Importantly, these viruses can spread easily and one stronger possibility is that they could be theoretically lethal for many different animal species so its important to keep a close watch on it, so as not more outbreaks occur.
The study highlights the need for studying cross-species transmissions of influenza viruses between animals. Researchers plan to use the genetic features and patterns of genetic characteristics for these viruses to help their prevention and control in high-risk animal populations.
Infectious Diseases, Public Health & Prevention, Emergency Medicine