In 2023, an unprecedented outbreak of highly pathogenic avian influenza (HPAI) H5N1 resulted in the death of thousands of pinnipeds along the Argentinean coast, raising concerns about its ecological and epidemiological impact. Here, we present clinical, pathological, and molecular findings associated with HPAI H5N1 infection in pinnipeds from Chubut, Argentina. Necropsies were conducted on three South American Sea Lions (SASLs) ( Otaria flavescens ) and one Southern Elephant Seal (SES) ( Mirounga leonina ), followed by histopathological, immunohistochemical and RT-sqPCR analyses. Neurological clinical signs were observed in two SASLs, with one also exhibiting respiratory distress. Neuropathological findings included lymphoneutrophilic meningoencephalomyelitis and choroiditis, neuronal necrosis, gliosis, hemorrhages, and perivascular cuffing. Viral antigen was localized in neurons, glial cells, choroid plexus epithelial cells, ependymal cells, and the neuropil. Systemic manifestations included HPAI-related necrotizing myocarditis in the elephant seal and placental necrosis in a sea lion, with fetal tissues testing positive for HPAIV. Pulmonary lesions were minimal, limited to bronchial glands in one individual. RT-sqPCR confirmed HPAI H5 in all tested animals. Our findings highlight the neurotropism of HPAI H5N1 in pinnipeds, and expand the known systemic effects of the virus, revealing new tissue tropism and vertical transmission.

The Atlantic puffin (Fratercula arctica) is a seabird species characterized by great diving capabilities and transoceanic migratory behavior. These movements contribute to the dispersion of the species during migration, and episodes of mortality associated with migration may be a normal event in the dynamic of the Atlantic puffin populations. This study aimed to describe the anatomopathological findings of an unusual mortality event of Atlantic puffins observed during the non-breeding period along the coast of the Canary Islands. The most consistent gross finding during necropsy was generalized muscle atrophy and fat depletion. The main histological findings were centered in the urinary tract, with dilation and inflammation of the primary ureter branch and medullary cones, and intraluminal trematodes identified as Renicola sloanei based on morphology and molecular analysis. Influenza virus infection was ruled out. The postmortem investigations performed in this mortality event of Atlantic puffins indicate that the animals were severely emaciated and suffered from nephropathy. The etiopathological investigation performed in relation to this mortality event of Atlantic puffins indicates starvation associated with bad weather conditions during migratory movement as the most likely cause of the unusual mortality event.

Avian poxvirus was diagnosed in eight wild Stone-curlews (Burhinus oedicnemus) from the Canary Islands, based on a combination of pathological and molecular analysis. Affected birds exhibited lesions consistent with poxvirus infection; three of four with mild lesions (≤2 on pelvic limbs, excluding phalanges) were successfully rehabilitated and released, while four with moderate (≤2 on phalanges) to severe lesions (≥3 on phalanges) potentially faced impaired mobility, increased predation risk, and reduced foraging efficiency. Histopathology of six individuals revealed Bollinger bodies, characteristic of Avipoxvirus infection, and molecular analysis confirmed the presence of viral DNA in six cases. Three genetically distinct viral variants were identified, each associated with different phylogenetic clades and subclades, suggesting substantial viral diversity within this host species. Co-infection with Aspergillus fumigatus was also detected in six of the eight birds, confirmed by molecular analysis in either skin lesions or lung tissue. To our knowledge, this represents the first report of A. fumigatus co-infection in Stone-curlews with Avipoxvirus. Additionally, one individual presented a tumor-like lesion, expanding the known pathological manifestations of the disease. These findings provide new insights into avian pox and highlight the importance of considering fungal co-infections in the differential diagnosis, given their potential to exacerbate disease severity.

Avian haemosporidians are globally distributed protozoan parasites transmitted by hematophagous vectors, yet information on their occurrence in the Stone-curlew (Burhinus oedicnemus), particularly from the Canary Islands, is scarce. Between 2020 and 2024, 47 Stone-curlews were examined for Haemoproteus, Plasmodium, and Leucocytozoon spp. using nested PCR targeting the cytochrome b gene, followed by sequencing and phylogenetic analysis. Histopathological examination was performed on formalin-fixed tissues. Leucocytozoon sp. DNA was detected in one individual (case FS415/23), with identical sequences amplified from multiple organs. Phylogenetic analysis placed this isolate within lineage CIAE02, previously reported in raptors and other avian taxa. Microscopic evaluation revealed megalomeronts in the liver, kidney, and skin, consistent with Leucocytozoon infection. Despite concurrent infection with Avipoxvirus and Aspergillus fumigatus, no prominent inflammatory reaction surrounded the haemosporidian tissue states. The only prior haemosporidian reported in Burhinus is Haemoproteus burhinus, described from B. oedicnemus saharae in Iraq, and no Leucocytozoon infections have previously been recorded in this genus. Therefore, this represents the first evidence of Leucocytozoon infection in the Stone-curlew, extending the known host range of lineage CIAE02. These findings highlight the relevance of integrative diagnostic approaches for detecting latent or cryptic haemosporidian infections in non-passerine avian hosts.

In 2023, high pathogenicity avian influenza (HPAI) H5N1 outbreaks caused mass mortality events affecting pinnipeds throughout South America. Here, we present the clinical, pathological, immunohistochemical, and molecular findings associated with HPAI H5N1 infection in 3 South American sea lions ( Otaria flavescens ) and 1 southern elephant seal ( Mirounga leonina ) stranded during the outbreak in Chubut, Argentina. Neurological signs were observed in 2 sea lions, with 1 also exhibiting respiratory distress. Necropsies were conducted on all 4 animals. Neuropathology revealed mild-to-severe lymphohistiocytic (2/4) to mixed neutrophilic (2/4) meningoencephalitis with neuronal necrosis, neuronophagia, glial cell proliferation, multifocal hemorrhage, and perivascular cuffing in all animals. Novel findings for HPAI H5N1-infected pinnipeds included choroid plexitis (2/4) and myelitis (2/4). Immunohistochemistry for viral nucleoprotein was positive in 3 of 4 animals and involved neurons (3/3), glial cells (3/3), and ependymal cells (2/3). Viral-related systemic findings included multifocal necrotizing myocarditis in the elephant seal and multifocal necrotizing placentitis in a sea lion, with HPAI virus detected within fetal tissues. Pulmonary lesions were minimal and were limited to multifocal necrosis of bronchial glands in 1 sea lion. HPAI H5 clade 2.3.4.4b virus was confirmed by polymerase chain reaction and sequencing in all animals. These findings indicate a predominance of central nervous system involvement in HPAI H5N1-infected pinnipeds and expand the recognized spectrum of virus-associated lesions, identifying novel tissue tropisms and transmission routes.

The mortality of birds resulting from collisions and electrocutions with overhead lines, such as power lines and phone lines, among others, has been implicated in the decline of various avian species globally. Specifically, overhead line collisions pose a significant threat to the conservation of the Canarian houbara bustard (Chlamydotis undulata fuertaventurae), an endangered subspecies endemic to the Canary Islands. This study centers on the postmortem findings of Canarian houbara bustards that have collided with overhead lines, providing insights into the post-collision outcomes for these birds. A complete standardized necropsy of nine Canarian houbara bustards revealed that trauma was the cause of death in all cases. The most notable gross lesions associated with trauma included bone fractures, soft tissue lacerations, hemorrhages, luxations, and hemocoelom. The inguinal area, chest, and wings were the body regions more frequently affected. A histopathology, immunohistochemistry, and entomology analysis confirmed that numerous birds survived the initial trauma. We concluded that when a houbara bustard collides with an overhead line, it frequently survives the initial trauma, with a survival time ranging from minutes to hours. The histopathology, immunohistochemistry, or entomologic analysis may be helpful to approximate the timing interval between trauma and death.