Porcine circovirus type 2 (PCV2) is an endemic pathogen of global relevance, responsible for porcine circovirus-associated diseases (PCVAD). Consequently, vaccination against PCV2 is a standard practice in intensive swine production systems. This study aimed to evaluate the effect of a prototype vaccine on PCV2 viral load and associated lesions. Thirty-nine pigs from a high-health-status farm were randomly assigned to three experimental groups (n = 13 per group), corresponding to a placebo group, a commercial vaccine group and a prototype vaccine group. Viral load was assessed by qPCR from serum samples, while lesions were evaluated through necropsy and histopathological analysis of lymph nodes and lungs tissue. No statistically significant differences in viral loads were observed among the three groups, and most animals did not exhibit detectable viremia. However, the placebo group showed more numerous and severe lesions in lymph nodes and lungs compared to the vaccinated groups, with the commercial vaccine group showing milder lesions than the prototype vaccine group. These findings suggest that the absence of viremia in most animals may reflect the timing of infection or effective containment by host immunity. Both the commercial and prototype vaccines were associated with reduced lesion severity, although the prototype vaccine demonstrated an intermediate performance between the placebo and commercial vaccine groups. Further development and optimization of the prototype formulation are warranted to enhance its protective efficacy.

1. High pathogenicity avian influenza (HPAI) H5N1 clade 2.3.4.4b poses a major global conservation threat, with Antarctic and subantarctic ecosystems at particular risk given the substantial ecosystem services driven by birds and mammals susceptible to HPAI in these regions. Understanding its impacts on threatened species and ecosystems, and the effectiveness of surveillance tools used by conservation managers, is critical. 2. We surveyed seabirds and marine mammals at Dismal and Horseshoe Islands, Marguerite Bay, Western Antarctic Peninsula, in February-March 2025 for signs of HPAI H5N1 infection and mortality at the presumed southern limit of its spread, and sampled seabirds (primarily South Polar Skua Stercorarius maccormicki) using rRT-PCR and rapid antigen kits (VDRG (R) AIV Ag Rapid Kit 2.0). 3. HPAI H5N1 was confirmed by rRT-PCR in 22 South Polar Skuas and one Kelp Gull Larus dominicanus. High skua mortalities were consistent with global trends, though many pairs were still breeding during surveys. No other species showed signs of infection despite observed environmental risk factors, although none were tested. Rapid tests showed 90% agreement with rRT-PCR results across 23 carcasses and seven live bird samples, indicating their potential utility for early detection. 4. Practical implication: Sustained monitoring of Antarctic and subantarctic birds and mammals-integrating long-term monitoring data where possible, and where appropriate, implementing rapid antigen testing to enhance early detection (pending further evaluation and/or used with caution)-should be prioritised to improve our understanding of population-level impacts of HPAI H5N1 and track its ongoing global spread.

H5 clade 2.3.4.4b high pathogenicity avian influenza viruses (HPAIVs) have caused unprecedented mortality in marine wildlife. However, host determinants of susceptibility to influenza A virus (IAV) infection remain poorly understood. IAVs adapted to different hosts show distinct binding preferences for different kinds of sialic acid (Sia) receptors on cell surfaces. Human‑adapted IAVs preferentially bind Sia α2,6-linked glycans, while avian‑adapted viruses prefer Sia α2,3-linked glycans. We characterized the distribution of α2,6- and α2,3-linked Sia, and fucosylated or sulfated Siaα2,3 across respiratory, intestinal, and neural tissues from stranded marine animals, including two South American sea lions (Otaria flavescens), a Burmeister's porpoise (Phocoena spinipinnis), and a Magellanic penguin (Spheniscus magellanicus). We also compared binding patterns of recombinant hemagglutinins (rHAs) derived from a classical H5 clade 1 virus and contemporary clade 2.3.4.4b viruses in the same tissues. We detected widespread expression of Sia receptors and H5 rHA binding in bronchial and alveolar epithelium (including air capillaries of the penguin) of the lung, enterocytes and goblet cells of intestinal villi, and the meninges and vascular endothelium of neural tissues, with species‑ and tissue‑specific patterns. These findings indicate that marine mammals and penguins possess receptor landscapes compatible with infection by both classical and contemporary H5 HPAIVs. Further investigation is necessary to determine how receptor distribution relates to productive replication, respiratory or fecal shedding, and cross-species transmission risk, particularly given the pronounced neurotropism and peracute disease course associated with clade 2.3.4.4b viruses.

Emerging avian avulaviruses (AVVs) have been identified in Antarctic ecosystems; however, their biological properties and current circulation remain poorly understood. This study utilized historical egg-isolated Antarctic penguin avulavirus strains (AVV17, AVV18, and AVV19) and combined molecular characterization with field surveillance during the 2024-2025 Antarctic season. The historical isolates were molecularly confirmed using RT-qPCR targeting the L gene, confirming their classification as AVV17, AVV18, or AVV19. These isolates were tested for replication indicators in REM 134, MDCK cells and embryonated chicken eggs. Only AVV18 showed evidence of productive replication in REM 134 cells, as indicated by decreasing Ct values and the presence of cytopathic effects.AVV17 and AVV19 were detectable by RT-qPCR but did not exhibit cytopathic changes or replication dynamics. None of the viruses replicated efficiently in MDCK cells. Further propagation of AVV18 in embryonated chicken eggs showed viral amplification in some eggs. Concurrent surveillance at five sites in the South Shetland Islands detected low-level circulation of AVV17-19, exclusively in cloacal swabs, with no viral RNA found in environmental samples. These findings link historical isolates to current circulation, highlighting selective replication among Antarctic AVVs and limited ecological spread in penguin hosts.

Background: Human Immunodeficiency Virus type 1 (HIV-1) remains a major global health challenge. Despite advances in antiretroviral therapy, new prevention strategies are needed, particularly topical microbicides capable of blocking the earliest steps of viral entry. HIV-1 attachment relies on interactions with heparan sulfate proteoglycans on host cell surfaces; therefore, sulfated heparan-mimetic polymers have been explored as antiviral agents. In this context, sulfated chitosan microparticles are designed to mimic natural glycosaminoglycan receptors, acting as biomimetic decoys that prevent viral attachment and entry. Methods: Low-molecular-weight sulfated chitosan (LMW Chi-S) microparticles were synthesized and characterized (SEM, EDS, DLS, FTIR) following US Patent No. 11,246,839 B2. Their antiviral activity was evaluated by incubating the microparticles with high-viral-load HIV-1-positive plasma (~3.5 × 106 copies/mL) to enable viral binding and removal by pull-down. The performance of the synthesized Chi-S microparticles was compared with established heparinoid controls, including soluble heparin and heparin microparticles. Results: Chi-S microparticles exhibited stronger virus-binding and neutralizing capacity than all heparinoid comparators, achieving up to 70% reduction in viral load relative to untreated HIV-1 plasma. In comparison, soluble heparin and heparin microparticles reduced viral load by approximately 53% and 60%, respectively. Subsequent evaluation across multiple tested concentrations confirmed a consistent antiviral effect, indicating that the synthesized Chi-S microparticles maintain robust virus–particle interactions throughout the concentration range examined. Conclusions: These findings demonstrate that LMW Chi-S microparticles possess potent antiviral properties and outperform classical heparinoid materials, supporting their potential application as topical microbicides targeting early HIV-1 entry mechanisms.

Maternal behavior in mammals is critical for offspring survival and provides insight into the evolutionary pressures shaping reproductive strategies. Postmortem attentive behavior (PAB) is a rare form of epimeletic behavior in which individuals show attachment, distress, or curiosity toward deceased conspecifics, most often between mothers and offspring. While PAB has been documented in terrestrial mammals and cetaceans, it has been rarely documented in pinnipeds. Here, we describe multiple instances of maternal PAB in the Antarctic apex predator, the leopard seal (Hydrurga leptonyx), at two sites in Patagonia, Chile. We document PAB in two adult females, including repeated observations of one individual across three years. One female displayed PAB for up to 20 days—the longest documented case in pinnipeds and among the longest for any mammal. Behaviors included carrying and mouthing the pup, maintaining close proximity, and displaying territoriality over the carcass. We also conducted a necropsy on one pup, yielding the first detailed anatomical assessment of this species at an early life stage. Our findings suggest death due to emaciation, likely from inadequate nursing. As no pups have been observed surviving to weaning in Chile, potential drivers of high preweaning mortality may include habitat instability, genetic load, or insufficient maternal investment. This study offers novel insight into leopard seal reproductive biology, highlighting the need for continued monitoring of this Antarctic seal.

Bovine tuberculosis (bTB) is mainly caused by Mycobacterium bovis, which affects cattle, leading to significant economic losses. In Chile, the vaccination with the M. bovis Bacillus Calmette-Guérin (BCG) strain has been implemented in dairy herds with high prevalence of bTB. This study evaluated non-specific protection associated with BCG on the detection of pathogen-associated genes (nsp5, stx1, stx2, invA, IS1081) and mortality related to diarrhea and pneumonia in calves. A total of 186 calves from a commercial dairy farm were enrolled and grouped as vaccinated (n = 96) and non-vaccinated (n = 90). The BCG Russia strain (2–5 × 105 UFC) was inoculated subcutaneously within the first 30 days after birth. Animals were monitored through fecal sampling at 3 and 6 months of age for molecular detection of gene sequences. A logistic regression analysis showed differences in detection rates of the stx1 sequence at 3 months, with a higher risk for the non-vaccinated individuals (OR 2.91, CI 1.42–5.94, p = 0.03) and for those born in the cold season (OR 9.55, CI 2.02–45.11, p = 0.004). A Kaplan–Meier survival analysis showed a significant difference in deaths in vaccinated calves compared with non-vaccinated animals (p = 0.018), suggesting that BCG confers non-specific protection during the first 3 months after birth, in field conditions.

In 2024, we sequenced highly pathogenic avian influenza virus A(H5N1) clade 2.3.4.4b genomes isolated from 5 brown skuas from James Ross Island, Antarctica. Phylogenetic analysis suggested the virus reached Antarctica through South America. Continued genetic surveillance will be critical to elucidate H5N1 virus transmission dynamics within Antarctica and surrounding areas.

Influenza A virus (IAV) continuously threatens animal and public health globally, with swine serving as a crucial reservoir for viral reassortment and evolution. In Chile, H1N2 and H3N2 subtypes were introduced in the swine population before the H1N1 2009 pandemic, and the H1N1 was introduced from the H1N1pdm09 by successive reverse zoonotic events. Here, we report two novel introductions of IAV H3N2 human-origin in Chilean swine during 2023. Our study reveals a closer relationship between recent human seasonal H3N2 and novel swine strains. Interestingly, one strain maintains all the genes from the original human virus, but the other strain is already a reassortment of human H3N2 and an H1N2 previously observed on the farm. Observing global IAV sequences, a similar pattern was identified in the USA confirming the reverse zoonotic potential of current seasonal human H3N2 strains. These results highlight the importance of ongoing surveillance and reinforcing biosecurity in swine farms. These findings raise questions about their potential impact on viral dynamics in the swine population and public health, underscoring the need for further investigation into the origin and evolutionary dynamics of this emerging swine H3N2 reassortant virus.

Feline calicivirus (FCV) is a significant pathogen in cats, characterized by high genetic diversity. Understanding the characteristics of local FCV strains is essential for developing optimal therapeutic and preventive measures. This study presents, for the first time, the epidemiology, genotypic variation, and biological characteristics of FCV strains in cats from Santiago, Chile. Oropharyngeal swabs were collected from cats with respiratory disease and one cat suspected of having virulent systemic disease (VSD) in veterinary clinics between 2016 and 2019. The FCV detection rate was 48.8 % by RT-PCR. Among FCV-positive cats, 19.0 % had been vaccinated against FCV, 71.4 % were free-roaming, and 52.4 % were less than one year old. The most frequently observed clinical signs included oral ulcers (61.9 %), stomatitis (57.1 %), and nasal discharge (42.9 %). Phylogenetic analysis revealed a high genetic diversity among Chilean FCV strains (69.45-100 % nucleotide identity) and identified two distinct subgroups within the GI genogroup, with GI.1 being predominant. Comparison of the amino acid sequences of the 5'HVR_E region showed conserved differences between these subgroups, suggesting potential variations in antigenicity, tropism, and infectivity. Moreover, the viruses analyzed in this study lacked the molecular markers previously proposed for FCV pathotypes, and the replicative efficiency of the VSD-suspected strain FCV21 was similar to the URTD-FCV strains of GI.1 and GI.2 subgroups, suggesting that not all the VSD-FCV strains would have a higher replicative efficiency than URTD-FCV strains, indicating substantial regional strain diversity. Future research will be crucial for developing more effective prevention and control strategies.

Highly pathogenic H5N1 avian influenza viruses (HPAIV) belonging to lineage 2.3.4.4b emerged in Chile in December 2022, leading to mass mortality events in wild birds, poultry, and marine mammals and one human case. We detected HPAIV in 7,33% (714/9745) of cases between December 2022-April 2023 and sequenced 177 H5N1 virus genomes from poultry, marine mammals, a human, and wild birds spanning >3800 km of Chilean coastline. Chilean viruses were closely related to Peru's H5N1 outbreak, consistent with north-to-south spread down the Pacific coastline. One human virus and nine marine mammal viruses in Chile had the rare PB2 D701N mammalian-adaptation mutation and clustered phylogenetically despite being sampled 5 weeks and hundreds of kilometers apart. These viruses shared additional genetic signatures, including another mammalian PB2 adaptation (Q591K, n = 6), synonymous mutations, and minor variants. Several mutations were detected months later in sealions in the Atlantic coast, indicating that the pinniped outbreaks on the west and east coasts of South America are genetically linked. These data support sustained mammal-to-mammal transmission of HPAIV in marine mammals over thousands of kilometers of Chile's Pacific coastline, which subsequently continued through the Atlantic coastline.

The potential role of rodents as reservoirs for SARS-CoV-2 has gained global attention due to their proximity to humans and their involvement in zoonotic disease transmission. Rodents were sampled from urban, rural and natural areas across the Metropolitan Region of Chile between June 2023 and June 2024. Molecular testing (RT-qPCR) revealed no active infections among the 421 analysed individuals, while serological assays (ELISA) detected SARS-CoV-2 antibodies in 4 of 459 rodents (0.87%). All seropositive rodents were Rattus rattus captured in rural areas. These findings suggest localised exposure to SARS-CoV-2, possibly influenced by environmental or anthropogenic factors. The results align with global studies reporting sporadic rodent exposure to SARS-CoV-2, emphasising the importance of integrating molecular and serological approaches in zoonotic surveillance. Despite the low prevalence observed, the potential role of rodents in viral spillover and recombination events with other coronaviruses underscores the need for continued monitoring. These results contribute to understanding zoonotic dynamics and inform public health strategies in a One Health framework.

High pathogenicity avian influenza (HPAI) H5N1 2.3.4.4b poses a substantial conservation threat to ecosystems, populations, and species globally, with its continued spread into new regions increasing concern for potential ecological consequences. During surveys in February – March 2025, we confirmed the virus’s presence at the southern extent of its known range along the Western Antarctic Peninsula, with recorded mortalities in South Polar Skuas S tercorarius maccormicki on distinct islands in Marguerite Bay, as well as one confirmed and one suspected case in Kelp Gulls Larus dominicanus . At the time of sampling, no evidence of infection was observed in other seabird or mammal species. Consistent with previous global reports, skuas – here, South Polar Skuas – appear particularly vulnerable, yet broader impacts on the local seabird and mammal community remain unclear. Additionally, our use of rapid antigen tests (VDRG® AIV Ag Rapid kit 2.0 – Median Diagnostics) in the field demonstrated their potential utility for real-time surveillance, though false negatives (10%) highlight limitations in test sensitivity. These findings contribute to a growing understanding of the impacts of HPAI H5N1 2.3.4.4b outbreaks on Antarctic species and populations, and will inform continued monitoring, conservation strategies, and biosecurity measures in response to the virus’s ongoing spread. ### Competing Interest Statement The authors have declared no competing interest.

SARS-CoV-2 infection susceptibility in dogs and cats has been documented, with identified risk factors contributing to transmission dynamics. Understanding viral prevalence and the evolution of emerging variants across pandemic waves can clarify the potential role of pets as reservoirs. This study evaluated 3298 serum samples (1921 dogs, 1377 cats) collected from 2020 to 2024. Samples were analyzed using ELISA and viral neutralization assays, revealing a positivity rate of 2.7%. We assessed neutralizing antibody titers (nAbs) against the Wuhan-Hu-1 and Omicron BA.1 strains, finding higher titers in felines compared to canines. A marked reduction in samples exceeding the detection limit was observed after November 2022. Longitudinal data from up to 30 months in a dog and 15 months in two cats demonstrated sustained antibody responses, with increased nAb titers in 7 of 14 monitored animals. Multivariable logistic regression of 275 samples indicated that a pet’s vaccination status was associated with an increased risk of infection, while spring season, the owner’s number of COVID-19 vaccinations, and the owner’s vaccination status were protective factors. These results emphasize the significance of vaccination strategies for both human and animal health, supporting the One Health approach.

From December 2023 to March 2024, a surveillance program to detect HPAI H5N1 was performed on Antarctica Territory, at Fildes Peninsula (King George Island, Maritime Antarctic), and James Ross Island. At Fildes Peninsula, samples from marine birds and mammals from four sampling locations were collected, based on their accessibility and the presence of animal colonies: Ardley Island, which presents a high concentration of Gentoo penguins ( Pygoscelis papua ); Ardley Cove were small groups of likely non-reproductive Chinstrap penguins ( Pygoscelis antarcticus ); Southern elephant ( Mirounga leonina ) and Weddell ( Leptonycotes wedellii ) seals haul-out sites; and, a nesting site of Southern giant petrels ( Macronectes giganteus ). On February 28th the surveillance group received a request for sample collection, due to the observation of deceased seabirds at James Ross Island in the area neighboring the Lachman lakes (63.7989 S, 57.8105 W). Six samples from five dead South polar skuas ( Stercorarius maccormicki ) were collected on March 3rd, 2024. All samples were collected adhering to the Antarctic Treaty guidelines. After collecting a total of 943 samples from Fildes Peninsula all results tested negative, and no individuals had clinical signs or behaviors compatible with HPAI. However, all samples from South polar skuas from James Ross Island were confirmed positive for HPAI H5N1 clade 2.3.4.4 by specific real-time RT-PCR reactions. These results confirmed the first mortality event registered in Antarctica (south of 60°S) caused by HPAI H5N1, in this case on South polar skuas. Further studies are needed to genetically characterize the virus and to better understand the role of skuas in the dynamics of viral dissemination in Antarctica. ### Competing Interest Statement The authors have declared no competing interest. The data that support the findings of this study are available from the corresponding author, V.N., upon reasonable request.

From December 2023 to March 2024, a surveillance program aiming to detect Highly Pathogenic Avian Influenza (HPAI) H5N1 was conducted on Antarctica territories, specifically at Fildes Peninsula (King George Island, Maritime Antarctic), and James Ross Island. At Fildes Peninsula, samples from marine birds and mammals were collected from four accessible sampling locations with significant animal colonies: Ardley Island, hosting a large concentration of Gentoo penguins (Pygoscelis papua); Ardley Cove, where small groups of likely non-breeding Chinstrap penguins (Pygoscelis antarcticus) were present; seal haul-out sites of Southern elephant (Mirounga leonina) and Weddell (Leptonycotes wedellii); and, a nesting site of Southern giant petrels (Macronectes giganteus). Additionally, six samples were collected from five dead skuas near the Lachman lakes on James Ross Island (63.7989S, 57.8105W) on March 3, 2024. Despite collecting a total of 943 samples from Fildes Peninsula, all results tested negative for HPAI, and no animals displayed clinical signs or behaviors consistent with HPAI infection. However, all skua samples from James Ross Island tested positive for HPAI H5N1 clade 2.3.4.4 by specific real-time RT-PCR reactions, confirming the first recorded HPAI-related mortality event in Antarctica (south of 60°S), specifically in skuas. Further research is necessary to genetically characterize the virus and better understand the role of skuas in viral dissemination in Antarctica.

In January 2023, an active surveillance initiative was undertaken in the South Shetland Islands, Antarctica, with the specific objective of ascertaining evidence for the presence of avian influenza, and specifically the highly pathogenic avian influenza virus subtype H5N1 (HPAIV H5N1). The investigation encompassed diverse locations, including Hanna Point (Livingston Island), Lions Rump (King George Island), and Base Escudero (King George Island), with targeted observations on marine mammals (southern elephant seals), flying birds (the kelp gull, snowy sheathbill and brown skua), and penguins (the chinstrap penguin and gentoo penguin). The study encompassed the examination of these sites for signs of mass mortality events possibly attributable to HPAIV H5N1, as well as sampling for influenza detection by means of real-time RT-PCR. Two hundred and seven (207) samples were collected, including 73 fecal samples obtained from the environment from marine mammals (predominantly feces of southern elephant seals), and 77 cloacal samples from penguins of the genus Pygoscelis (predominantly from the gentoo penguin). No evidence of mass mortality attributable to HPAIV H5N1 was observed, and all the collected samples tested negative for the presence of the virus, strongly suggesting the absence of the virus in the Antarctic territory during the specified period. This empirical evidence holds significant implications for both the ecological integrity of the region and the potential zoonotic threats, underscoring the importance of continued surveillance and monitoring in the Antarctic ecosystem.