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Cetacean morbillivirus (CeMV) is a major natural cause of morbidity and mortality in cetaceans worldwide and results in epidemic and endemic fatalities. The pathogenesis of CeMV has not been fully elucidated, and questions remain regarding tissue tropism and the mechanisms of immunosuppression. We compared the histopathologic and viral immunohistochemical features in molecularly confirmed CeMV-infected Guiana dolphins (Sotalia guianensis) from the Southwestern Atlantic (Brazil) and striped dolphins (Stenella coeruleoalba) and bottlenose dolphins (Tursiops truncatus) from the Northeast-Central Atlantic (Canary Islands, Spain) and the Western Mediterranean Sea (Italy). Major emphasis was placed on the central nervous system (CNS), including neuroanatomical distribution of lesions, and the lymphoid system and lung were also examined. Eleven Guiana dolphins, 13 striped dolphins, and 3 bottlenose dolphins were selected by defined criteria. CeMV infections showed a remarkable neurotropism in striped dolphins and bottlenose dolphins, while this was a rare feature in CeMV-infected Guiana dolphins. Neuroanatomical distribution of lesions in dolphins stranded in the Canary Islands revealed a consistent involvement of the cerebrum, thalamus, and cerebellum, followed by caudal brainstem and spinal cord. In most cases, Guiana dolphins had more severe lung lesions. The lymphoid system was involved in all three species, with consistent lymphoid depletion. Multinucleate giant cells/syncytia and characteristic viral inclusion bodies were variably observed in these organs. Overall, there was widespread lymphohistiocytic, epithelial, and neuronal/neuroglial viral antigen immunolabeling with some individual, host species, and CeMV strain differences. Preexisting and opportunistic infections were common, particularly endoparasitism, followed by bacterial, fungal, and viral infections. These results contribute to understanding CeMV infections in susceptible cetacean hosts in relation to factors such as CeMV strains and geographic locations, thereby establishing the basis for future neuro- and immunopathological comparative investigations.

We sequenced a novel rhabdovirus, Tupavirus delphini (dolphin tupavirus), from the brain of a stranded dead Atlantic white-sided dolphin with severe encephalitis in Canada. In situ hybridization linked presence of the virus to the animal's brain pathology and death. Our findings underscore the importance of monitoring marine mammals for unexpected pathogens.

Since 2010, Guiana dolphin morbillivirus (GDMV; family Paramyxoviridae , genus Morbillivirus , species Morbillivirus ceti , syn. Cetacean morbillivirus ) is recognized as the cause of death of multiple cetacean species along the Brazilian coast, including an unusual mortality event in Rio de Janeiro state. Coronaviruses of the genus Gammacoronavirus (family Coronaviridae ) have been previously detected in cetaceans in the northern hemisphere. After the emergence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), responsible for the COVID-19 pandemic and with the potential to affect several mammal species, there is an increased concern about the risk of infection in aquatic mammals. The goal of this study was to molecularly screen the presence of morbillivirus and coronavirus infections in cetaceans stranded in several regions of the Brazilian coast in order to determine their occurrence rates, pathogenicity, and range of potentially susceptible cetacean species. We molecularly tested tissue samples of 118 cetaceans, belonging to 20 species, found stranded in Brazil, between 2015 and 2022. Overall, 2.5% (3/118) of the analyzed cetaceans were positive for GDMV infection: a Guiana dolphin ( Sotalia guianensis ), an Atlantic spotted dolphin ( Stenella frontalis ), and a humpback whale ( Megaptera novaeangliae ). None of the animals were positive for coronavirus. Our findings indicate that the morbillivirus sequence type identified in Indo-Pacific bottlenose dolphins ( Tursiops aduncus ) of Australia and our GDMV sequences from Brazil belong to the same strain. The systematic monitoring of cetacean morbilliviruses is recommended to properly estimate the occurrence rate, pathogenicity and evolution of these viruses, which may help anticipate novel epizooties and reduce their impact on endangered cetacean populations.

A northern Gulf of Mexico (GoM) cetacean unusual mortality event (UME) involving primarily bottlenose dolphins (Tursiops truncatus) in Louisiana, Mississippi, and Alabama began in February 2010 and continued into 2014. Overlapping in time and space with this UME was the Deepwater Horizon (DWH) oil spill, which was proposed as a contributing cause of adrenal disease, lung disease, and poor health in live dolphins examined during 2011 in Barataria Bay, Louisiana. To assess potential contributing factors and causes of deaths for stranded UME dolphins from June 2010 through December 2012, lung and adrenal gland tissues were histologically evaluated from 46 fresh dead non-perinatal carcasses that stranded in Louisiana (including 22 from Barataria Bay), Mississippi, and Alabama. UME dolphins were tested for evidence of biotoxicosis, morbillivirus infection, and brucellosis. Results were compared to up to 106 fresh dead stranded dolphins from outside the UME area or prior to the DWH spill. UME dolphins were more likely to have primary bacterial pneumonia (22% compared to 2% in non-UME dolphins, P = .003) and thin adrenal cortices (33% compared to 7% in non-UME dolphins, P = .003). In 70% of UME dolphins with primary bacterial pneumonia, the condition either caused or contributed significantly to death. Brucellosis and morbillivirus infections were detected in 7% and 11% of UME dolphins, respectively, and biotoxin levels were low or below the detection limit, indicating that these were not primary causes of the current UME. The rare, life-threatening, and chronic adrenal gland and lung diseases identified in stranded UME dolphins are consistent with exposure to petroleum compounds as seen in other mammals. Exposure of dolphins to elevated petroleum compounds present in coastal GoM waters during and after the DWH oil spill is proposed as a cause of adrenal and lung disease and as a contributor to increased dolphin deaths.

Polyomaviruses (PyVs) are small double-stranded DNA viruses able to infect species across all vertebrate taxa. In cetaceans, PyVs have been reported only in short-beaked common dolphin (Delphinus delphis), common bottlenose dolphin (Tursiops truncatus) and killer whale (Orcinus orca). Herein, we surveyed PyV in 119 cetaceans (29 mysticetes and 90 odontocetes) stranded along the Brazilian coast, from 2002 to 2022, comprising 18 species. DNA extracted from the lungs was tested using a nested PCR targeting the major capsid protein gene of PyV. Polyomavirus was detected in lung samples of 1.7% (2/119) cetaceans: two juvenile female Guiana dolphins (Sotalia guianensis) stranded in Rio de Janeiro (Rio de Janeiro state) and Guriri (Espírito Santo state), in 2018. Both retrieved sequences were identical and presented 93.3% amino acid identity with Zetapolyomavirus delphini, suggesting a novel species. On histopathology, one of the PyV-positive individuals presented basophilic intranuclear inclusion bodies morphologically consistent with polyomavirus in the lungs. Other available tissues from both cases were PyV-PCR-negative; however, both individuals tested positive for Guiana dolphin morbillivirus. To our knowledge, this is the first report of PyV infection in cetaceans of the Southern Hemisphere and the first description of a co-infection with morbillivirus.

Interspecies transmission of viruses poses significant risks to animal and human health. Tembusu virus (TMUV), an emerging flavivirus, is primarily associated with avian diseases. This study reports the first documented natural infection of TMUV in mammals, specifically zoo dolphins in Thailand, offering insights into its evolution, transmission dynamics, and zoonotic potential. In July 2023, three bottlenose dolphins developed neurological symptoms and died. Postmortem analyses, including histopathology, immunohistochemistry, high-throughput sequencing, and transmission electron microscopy, confirmed TMUV infection. Viral loads were high in brain and lung tissues, followed by kidney and spleen whereas the TMUV antigen was identified in only brain tissue. TMUV was localized in neurons and astroglia cells, and immunohistochemistry revealed CD3-positive T lymphocyte perivascular cuffing in the brain. Phylogenetic analysis placed the dolphin TMUV strains within cluster 3, related to strains found in mosquitoes in China. Retrospective analysis of dolphin samples from 2019 confirmed persistent TMUV circulation. Viral isolation on Vero cells showed characteristic cytopathic effects, and transmission electron microscopy revealed enveloped virions. This study highlights the virus’s ability to infect diverse hosts, including mammals. The findings underscore the need for continuous surveillance and a One Health approach to mitigate emerging viral threats.

River dolphins are a highly threatened polyphyletic group comprised of four odontocete families: Iniidae, Pontoporiidae, Lipotidae, and Platanistidae, the first two endemic to South America. To address the knowledge gap regarding infectious agents in this cetacean group, we surveyed the presence of herpesviruses by PCR in skin and/or blood samples of live-captured Amazon ( Inia geoffrensis , n = 25) and Bolivian ( Inia boliviensis , n = 22) river dolphins of the Amazon basin and in selected tissue samples of franciscanas ( Pontoporia blainvillei , n = 27) stranded or bycaught in southeastern Brazil. Additionally, available franciscana tissue samples were examined by histopathology. Herpesvirus DNA was amplified in 13 Bolivian river dolphins (59.1%, 95% CI 38.5–79.6%) and 14 franciscanas (51.9%, 95% CI 33.0–70.7%). All Amazon river dolphins were herpesvirus-negative. Two different herpesviruses were found in Bolivian river dolphins: a previously known gammaherpesvirus detected in blood and/or skin samples of all positive individuals and a novel alphaherpesvirus in the skin of one animal. A new gammaherpesvirus was found in several franciscana samples—the first herpesvirus recorded in Pontoporiidae. Intranuclear inclusion bodies consistent with herpesvirus were observed in the lymph node of one franciscana. The high divergence among the obtained herpesviruses and those previously described can be explained by viral-host coevolution, and by the fact that these populations are fairly isolated.

Cetacean morbillivirus (CeMV) is a major threat to cetaceans worldwide, causing individual deaths and outbreaks of mass mortality. Based on partial sequences of the viral phosphoprotein, CeMV is subclassified into seven strains and two distinct lineages. To date, only CeMV-1 strains, including the dolphin morbillivirus (DMV), have been completely sequenced. The CeMV-2 lineage was first reported in Guiana dolphins (Sotalia guianensis) in Brazil and was associated with an unusual mortality event in 2017–2018. Here we provide the nearly complete Guiana dolphin morbillivirus (GDMV) genome sequence, representing the first within the CeMV-2 lineage. GDMV was isolated using Vero.DogSLAMtag cells, the viral RNA was extracted, and deep sequencing analysis was performed. Gaps in the viral genome were completed by Sanger sequencing. The final genome length was 15,607 nucleotides covering 99.3% of the DMV reference genome, including full sequences of the six structural proteins encoded by morbillivirus. The sequence similarity was 74–77.9% to other CeMV strains, with highest identity to the DMV. The complete L protein amino acid sequence comparison-based taxonomy indicates that GDMV is a distinct morbillivirus species; however, as GDMV and CeMV-1 strains infect a similar host spectrum, our findings support that GDMV represents a new CeMV-2 lineage.

Dolphin morbillivirus (DMV) is considered an emerging threat having caused several epidemics worldwide. Only few DMV genomes are publicly available. Here, we report the use of target enrichment directly from cetacean tissues to obtain novel DMV genome sequences, with sequence comparison and phylodynamic analysis. RNA from 15 tissue samples of cetaceans stranded along the Italian and French coasts (2008–2017) was purified and processed using custom probes (by bait hybridization) for target enrichment and sequenced on Illumina MiSeq. Data were mapped against the reference genome, and the novel sequences were aligned to the available genome sequences. The alignment was then used for phylogenetic and phylogeographic analysis using MrBayes and BEAST. We herein report that target enrichment by specific capture may be a successful strategy for whole-genome sequencing of DMV directly from field samples. By this strategy, 14 complete and one partially complete genomes were obtained, with reads mapping to the virus up to 98% and coverage up to 7800X. The phylogenetic tree well discriminated the Mediterranean and the NE-Atlantic strains, circulating in the Mediterranean Sea and causing two different epidemics (2008–2015 and 2014–2017, respectively), with a limited time overlap of the two strains, sharing a common ancestor approximately in 1998.

Herpesvirus (HV) is widely distributed among cetacean populations, with the highest prevalence reported in the Mediterranean Sea. In this study, a comprehensive analysis was conducted, including epidemiological, phylogenetic, and pathological aspects, with particular emphasis on neuropathology, to better understand the impact of HV in these animals. Our results show a higher presence of HV in males compared to females, with males exhibiting a greater number of positive tissues. Additionally, adults were more frequently affected by HV infection than juveniles, with no infections detected in calves or neonates. The affected species were striped ( Stenella coeruleoalba ) and bottlenose dolphins ( Tursiops truncatus ). The highest positivity rates were observed in the genital system, cerebrum, and skin tissues. Phylogenetic analysis indicated a higher occurrence of Gammaherpesvirus (GHV) sequences but increased genetic diversity within Alphaherpesvirus (AHV). Key neuropathological features included astro-microgliosis (n = 4) and meningitis with minimal to mild perivascular cuffing (n = 2). The presence of concurrent infections with other pathogens, particularly cetacean morbillivirus (CeMV), underscores the complex nature of infectious diseases in cetaceans. However, the presence of lesions at the Central Nervous System (CNS) with molecular positivity for GHV, excluding the involvement of other potential neurotropic agents, would confirm the potential of this HV subfamily to induce neurological damage. Pathological examination identified lesions in other organs that could potentially be associated with HV, characterized by lymphoid depletion and tissue inflammation. These findings enhance our understanding of HV in odontocetes and highlight the need for ongoing research into the factors driving these infections and their broader implications.