Seal Dies of Bird Flu in Sweden: No Increased Risk to Public

A harbor seal in Gothenburg, Sweden, has tested positive for highly pathogenic avian influenza (HPAI), commonly known as bird flu, according to a press release from the Swedish Veterinary Institute (SVA). The seal, which died in late January, was confirmed to have succumbed to the virus following an autopsy.

This case occurs amidst a period of increased bird flu activity throughout Sweden and globally. While concerning, health officials emphasize that this particular finding does not alter the overall infection risk. “The detection of avian influenza in a seal does not change the general infection situation and does not increase the risk for other mammals or birds,” stated Karl Ståhl, the state epidemiologist at SVA.

The emergence of avian influenza in mammals, particularly seals, is a relatively recent development. Historically, the virus primarily affected birds. However, outbreaks in seals were first reported in the United Kingdom, Germany, and Denmark in March 2021, as documented by the Centers for Disease Control and Prevention (CDC). More recently, significant mortality events have been observed in seal populations in South America, beginning in late 2022, with hundreds of thousands of birds also affected in Peru and Chile. Scientists are still investigating the precise mechanisms of transmission to seals, but contact with infected seabirds is considered the most likely route.

The current outbreak is driven by the H5N1 strain of the virus. Since December 2021, HPAI H5N1 has been the dominant strain affecting wild birds in Sweden, as well as in other European countries and the Americas. This strain has demonstrated the ability to jump species, leading to infections in a wider range of animals.

The risk to humans remains very low, according to the Public Health Agency of Sweden. The virus primarily spreads through bird droppings, but can also affect mammals. However, the CDC notes that human infections with avian influenza are rare, and typically occur after close contact with infected birds.

In Gothenburg, officials report that none of the staff at Slottsskogen, the park where the seal resided, have exhibited any symptoms of illness. The remaining five seals in the park are also reported to be healthy. Nevertheless, the SVA is urging the public to report any sick or dead birds they encounter. Owners of domestic poultry are also advised to strengthen biosecurity measures, particularly by minimizing contact between their birds and wild bird populations.

The situation highlights the evolving nature of avian influenza and the potential for spillover events into new animal populations. While the virus continues to primarily circulate among birds, the detection in mammals like seals raises concerns about the potential for further spread and adaptation. The CDC timeline of avian influenza outbreaks shows a pattern of reassortment – gene swapping – between poultry and wild bird viruses, leading to the emergence of new strains with altered characteristics.

The ongoing outbreaks also underscore the importance of surveillance and monitoring of both wild bird and mammal populations. Early detection and rapid response are crucial for controlling the spread of the virus and mitigating its impact on both animal and human health. The Swedish Veterinary Institute (SVA) plays a key role in this effort, conducting autopsies and analyzing samples to track the virus’s evolution and distribution.

The recent detection in a harbor seal serves as a reminder of the interconnectedness of animal and human health. Zoonotic diseases – those that can spread between animals and humans – pose a significant public health challenge, and require a One Health approach that integrates expertise from multiple disciplines, including veterinary medicine, public health, and wildlife biology. The International Fund for Animal Welfare (IFAW) emphasizes the importance of understanding how these illnesses spread to protect both animal and human populations.

While the current situation does not present a significant risk to the general public, continued vigilance and adherence to public health recommendations are essential. The SVA’s call for reporting sick or dead birds is a critical component of this effort, allowing for timely investigation and response. Further research is needed to fully understand the dynamics of avian influenza transmission and to develop effective strategies for preventing and controlling future outbreaks.