Patagonia - Assessing the risk of avian influenza in seabirds and wild mammals along the Patagonian coast

Location: Patagonia - a region shared by Argentina and Chile 

Project Leaders: Dr. Marcela Uhart (opens in a new tab) & Dr. Ralph E. T. Vanstreels (opens in a new tab)

Status: Starting 

Duration: 2 years – February 2026 to February 2028 

Partner:

An emerging epizootic in South America  

Highly pathogenic avian influenza (HPAI), particularly caused by H5Nx viruses (H5N1 clade 2.3.4.4b), continues to circulate actively worldwide. 

In October 2022, the H5N1 HPAI virus appeared in South America for the first time. The first waves of the outbreak, concentrated along the Pacific coast of Peru and northern Chile, caused massive mortality among pelicans (genus Pelecanus), boobies (genus Sula), cormorants (family Phalacrocoracidae), gulls (genus Larus), and terns (subfamily Sterninae). In early 2023, a new variant emerged in northern Chile, capable of spreading directly among marine mammals - sea lions and fur seals (family Otariidae), elephant seals (genus Mirounga), dolphins (family Delphinidae), and sea otters (subfamily Lutrinae) - a capability that had previously been rarely documented in wild animals living in the wild. This variant then spread southward across the continent and up the Atlantic coast, crossing Argentina, Uruguay, and Brazil during the second half of 2023. 

The arrival of the virus in Argentine Patagonia led to mortality on an unprecedented scale in a region recognized worldwide for the exceptional density and diversity of its marine fauna.  

• ~95% of elephant seal pups born in 2023 in Argentine Patagonia died as a result of the virus. 
   
• The adult elephant seal population may have declined by 50 to 60%, with an estimated recovery time of 70 to 80 years. 
   
• Fur seal and sea lion colonies have seen declines of 15% and 44%, respectively, in Argentine Patagonia.  (opens in a new tab)
   
• Some tern colonies have experienced mortality rates estimated at between 50 and 60%. 
   
• In total, more than 520,000 wild birds and 60,000 wild mammals are believed to have been found dead in connection with these epizootics in South America (opens in a new tab) - a figure that is likely underestimated, as only a fraction of the dead animals are actually discovered.
   

Despite the scale of these events, many fundamental questions remain unanswered. Certain species that are vulnerable elsewhere (penguins, cormorants, gulls, and skuas) were largely spared in Argentine Patagonia, with no clear explanation to date. The potential role of certain species, such as giant petrels, as asymptomatic carriers (without visible clinical signs) of the virus in this ecosystem is also unknown. Furthermore, while the number of cases declined significantly in 2024, the virus reemerged in Argentina in February 2025 and in Brazil in May 2025, this time involving new reassortant variants: a reminder that viral dynamics remain unpredictable.
 

Virological evolution and epidemiological challenges
 

From a virological perspective, the strains circulating among mammals have acquired adaptive mutations while retaining their ability to infect wild birds, revealing remarkable genomic plasticity.  

Furthermore, the possibility of transplacental or breast milk transmission in pinnipeds also constitutes a concerning epidemiological mechanism that remains poorly documented. 

How can we explain the unpredictable dynamics of HPAI in Patagonia, particularly the differing susceptibility of species and the potential role of asymptomatic reservoirs and the recurrent emergence of new reassortant ? 

What the Project aims to demonstrate 
 

• To continue and expand the study of the ecology of HPAI within Patagonian wildlife populations,  
• To understand how the virus evolves in this unique environment,  
• To understand which species act as reservoirs or vectors,  
• To investigate the conditions under which new outbreaks are likely to occur. 

The project’s success will be measured by the number of samples collected and processed, with the ultimate indicator of success being the publication of the results in a peer-reviewed article  

The project results have not yet been published but will be released shortly. 

Our role in this Project  

• Financial support, 
• Expertise: monitoring and providing scientific expertise.

Ashley E, Vanstreels RET, Barbieri M, Puryear W, Gulland F, Field C, Johnson CK, Uhart M. (2026). High pathogenicity avian influenza in pinniped conservation. Phil. Trans. R. Soc. B 381: 20240320. 

Read more (opens in a new tab)

Uhart, M. M., & Vanstreels, R. E. T. (2025). Overview of highly pathogenic avian influenza H5N1 clade 2.3.4.4b in wildlife from Central and South America, October 2022–September 2025. Canadian Journal of Microbiology, 71, 1–8. 

Read more (opens in a new tab)