Avian Influenza in our backyard.
We are so lucky to have wonderful environments to enjoy; however, with Avian Influenza now in Australia, you may encounter sick or dead wildlife infected with the virus, especially around the coast.
We will maintain this as a “living” post with updates as we learn more, including links to key information and recommendations on what to do if you encounter impacted species.
It’s quite normal to feel upset and helpless to witness one or even many affected animals, but you can do something to help.
In all cases, it is recommended that you AVOID close contact, RECORD what and where, and REPORT. If an animal is alive and clearly suffering call: 1800 675 888.
The following link takes you to the Victorian Government portal, which provides links for the latest updates and an online form to report sick or injured wildlife, including the location, and to upload photos.
We are concerned that H5N1 has been confirmed in fur seals and a common dolphin in South Australia. This makes it even more important to maintain long-term monitoring of our Victorian populations.
The following section provides some overall context. It suggests that seals are at greater risk because their colonies overlap with bird rookeries, creating crowded, stressful conditions that are ideal for the virus to spread.
The overwhelming message is that susceptibility is certainly due to this virus not having been encountered before. However, susceptibility does not occur in a vacuum and also relates to ecosystem health and stressors, including climate change, which in turn influence species’ immune responses.
The global context – and risks to our marine mammals
(The following was researched using Gemini)
Species Impacted & Evidence (Global vs. Australia)
Globally, H5N1 (Clade 2.3.4.4b) has been isolated in a growing array of cetacean species across Europe, North America, and South America. Confirmed global cases include:
- Common Dolphins (Delphinus delphis) — United States, Europe, South America.
- Bottlenose Dolphins (Tursiops truncatus) — United States (Florida).
- Chilean Dolphins (Cephalorhynchus eutropia) — South America.
- Harbor Porpoises (Phocoena phocoena) — Sweden, Netherlands.
In Australia, the situation was historically non-existent until the recent 2026 mainland outbreak. The first Australian cetacean case was recorded in South Australia (Goolwa on the Fleurieu Peninsula) in a stranded short-beaked common dolphin (Delphinus delphis). Prior to this, Australian H5N1 marine mammal cases were restricted to sub-Antarctic pinnipeds (e.g., mass elephant seal mortality on Heard Island).
Extent of Impacts & Clinical Presentation
Unlike pinnipeds, cetaceans experience sporadic individual spillover events rather than wide-scale colony die-offs.
- Global Extent: Low total numbers relative to birds or seals, but individual cases suffer high mortality. Pathology consistently indicates severe meningoencephalitis (brain inflammation), interstitial pneumonia, and localized pulmonary edema. Affected dolphins exhibit neurological signs including disorientation, loss of equilibrium, swimming in circles, and inability to maintain blowhole control, leading to rapid death or stranding.
- Australian Extent: Single confirmed mainland cases in a common dolphin alongside isolated Pinniped detections (Long-nosed fur seal). However, common dolphins are now nationally rated as “high risk” due to potential population impacts if localized cluster transmissions escalate.
Proposed Transmission Vectors
Cetaceans generally do not feed on seabirds, ruling out direct predation as the primary vector in most cases. Marine mammal epidemiologists propose three key exposure routes:
- Opportunistic / Nipping Behavior: Direct nose-to-beak interactions, play, or curiosity toward infected, dying, or dead seabirds floating on the ocean surface.
- Inhalation of Viral Aerosols: Breathing in viral particles (droplet nuclei) at the air-water interface near dense, actively infected seabird colonies or high-density roosting sites.
- Trophic / Mechanical Ingestion: Ingesting water directly contaminated with high concentrations of shed avian feces (fecal-oral route) or feeding on lower-trophic prey species that act as mechanical transport vectors.
Ecological Health & Compromised Immunity
H5N1 spillover susceptibility in cetaceans does not happen in a vacuum; it directly intersects with cumulative ecosystem stress:
- Infectious Co-factors: Morbillivirus (Cetacean Morbillivirus – DMV) and Toxoplasma gondii infections are widely documented immune-suppressors in dolphins, making individuals significantly more vulnerable to secondary viral neuro-invasion like H5N1.
- Anthropogenic & Chemical Stressors: Bioaccumulation of persistent organic pollutants (POPs, PCBs) and heavy metals causes chronic immunotoxicity in high-trophic predators, dampening innate T-cell immune responses.
- Thermal / Climate Stress: Shifting ocean temperatures alter prey distribution, leading to localized nutritional stress, elevated cortisol levels, and compromised mucosal immunity.
Cetacean Vulnerability vs. Seal (Pinniped) Vulnerability
| Parameter | Dolphins (Cetaceans) | Seals & Sea Lions (Pinnipeds) |
| Social / Spatial Structure | Aquatic pelagic groups; lower physical density per unit surface area. | Dense land/ice haul-outs; thousands breeding shoulder-to-shoulder. |
| Transmission Dynamics | Primary isolated spillover events from birds. | High potential for sustained mammal-to-mammal airborne/contact spread. |
| Impact Scale | Low individual cases, severe neuro-pathology. | Catastrophic mass mortality events (tens of thousands of pup/adult deaths). |
| Seabird Proximity | Occasional surface interaction. | Direct habitat overlap on nesting islands and rocky outcrops. |
