West Nile Flavivirus Polioencephalomyelitis in a Harbor Seal (Phoca vitulina)

[Zoonotic potential of brucellosis in marine mammals]

Introduction

Brucellosis in marine mammals (cetacean and pinnipeds) has emerged in a very significant way during the last two decades. Currently Brucella ceti and Brucella pinnipedialis are the two recognized species in marine mammals, but available information is still limited. Several genotypes have been identified, and studies on the relationship between sequence type (ST) and organ pathogenicity or tropism have indicated differences in pathogenesis between B. ceti sequences in cetaceans. The zoonotic potential of this disease is based on the identification of the main sources of introduction and spread of Brucella spp. in the marine environment as well as on the factors of exposure of marine mammals and humans to the bacteria.

Bibliographic review

This article is a bibliographical review on marine mammal brucellosis, including the features, sources and transmission modes of each Brucella species, as well as their potential pathogenicity in animals and humans.

Conclusion

Different genotypes of marine Brucella spp have been isolated from marine mammal species but without any evidence of pathology induced by these bacteria. Associated lesions are variable and include subcutaneous abscesses, meningo-encephalomyelitis, pneumonia, myocarditis, osteoarthritis, orchitis, endometritis, placentitis and abortion. The isolation of marine B. spp from marine mammal respiratory parasites associated to lung injury has raised the intriguing possibility that they may serve as a vector for the transmission of this bacterium.The severity of marine B. spp remains unknown due to the lack of an estimate of the prevalence of this disease in marine mammals. The number of suspected human cases is still very limited. However, by analogy with other germs of the genus Brucella responsible for abortion in ruminants and for a febrile and painful state in human beings, prevention measures are essential. The significant increase in the number of strandings coupled with a high seroprevalence in certain species of marine mammals must be considered for people in direct or indirect contact with these animals. Ongoing epidemiological monitoring combined with extensive post-mortem examinations (necropsy, bacteriology and sequencing) of all species of stranded marine mammals would deepen knowledge on the zoonotic potential of marine Brucella species.

Alien Crabs as Potential Hosts of Pathogens Impacting Marine Megafauna's Health and Conservation

Climate change, with a special emphasis on global warming, is believed to be a key driver of the accelerated rate of alien species expansion into the Mediterranean Sea basin and, more generally, into all marine and oceanic ecosystems [...].

RETROSPECTIVE REVIEW OF NEUROLOGIC DISEASE IN STRANDED ATLANTIC HARBOR SEALS (PHOCA VITULINA CONCOLOR) ALONG THE NEW ENGLAND COAST

Harbor seals (Phoca vitulina) are a common species admitted to marine mammal rehabilitation facilities. As important indicators of marine ecosystem health, monitoring trends of disease in harbor seal populations is critical. However, few studies have evaluated neurologic disease in this species. The general objective of this study was to retrospectively review and delineate neurologic disease in free-ranging Atlantic harbor seals (P. vitulina concolor) that stranded along the New England (United States) coast and entered a rehabilitation facility between 2006 and 2019. Any Atlantic harbor seal that stranded live along the New England coast during the study period and was diagnosed with neurologic disease on either antemortem or postmortem evaluation was included; medical records and pathologic reports were reviewed. From 211 records, 24 animals met the inclusion criteria. Prevalence of neurologic disease was 11% in the study population and six major categories of neurologic disease were identified including: inflammatory (54%), idiopathic (33%), trauma (4%), congenital (4%), and degenerative (4%). Of the seals diagnosed with neurologic disease, 13 (54%) seals died during rehabilitation, 10 (42%) seals were euthanized, and 1 (4%) seal survived to release. Unique cases seen included a seal with Dandy-Walker-like malformation and another seal with histopathologic findings compatible with neuroaxonal dystrophy, a degenerative process that has not been previously reported in marine mammals. This study contributes to the overall knowledge of the health of free-ranging Atlantic harbor seals and may aid clinicians in characterizing neurologic conditions that may be present in seals undergoing rehabilitation.

Aquatic Flaviviruses

Flaviviruses are positive-sense single-stranded RNA viruses, including some well-known human pathogens such as Zika, dengue, and yellow fever viruses, which are primarily associated with mosquito and tick vectors. The vast majority of flavivirus research has focused on terrestrial environments; however, recent findings indicate that a range of flaviviruses are also present in aquatic environments, both marine and freshwater. These flaviviruses are found in various hosts, including fish, crustaceans, molluscs, and echinoderms. Although the effects of aquatic flaviviruses on the hosts they infect are not all known, some have been detected in farmed species and may have detrimental effects on the aquaculture industry. Exploration of the evolutionary history through the discovery of the Wenzhou shark flavivirus in both a shark and crab host is of particular interest since the potential dual-host nature of this virus may indicate that the invertebrate-vertebrate relationship seen in other flaviviruses may have a more profound evolutionary root than previously expected. Potential endogenous viral elements and the range of novel aquatic flaviviruses discovered thus shed light on virus origins and evolutionary history and may indicate that, like terrestrial life, the origins of flaviviruses may lie in aquatic environments.

Pathogenicity and virulence of West Nile virus revisited eight decades after its first isolation

West Nile virus (WNV) is a flavivirus which transmission cycle is maintained between mosquitoes and birds, although it occasionally causes sporadic outbreaks in horses and humans that can result in serious diseases and even death. Since its first isolation in Africa in 1937, WNV had been considered a neglected pathogen until its recent spread throughout Europe and the colonization of America, regions where it continues to cause outbreaks with severe neurological consequences in humans and horses. Although our knowledge about the characteristics and consequences of the virus has increased enormously lately, many questions remain to be resolved. Here, we thoroughly update our knowledge of different aspects of the WNV life cycle: virology and molecular classification, host cell interactions, transmission dynamics, host range, epidemiology and surveillance, immune response, clinical presentations, pathogenesis, diagnosis, prophylaxis (antivirals and vaccines), and prevention, and we highlight those aspects that are still unknown and that undoubtedly require further investigation.

Interactions between the imperiled West Indian manatee, Trichechus manatus, and mosquitoes (Diptera: Culicidae) in Everglades National Park, Florida, USA

Arthropod-borne viruses (arboviruses), including those vectored by mosquitoes, have recently been cited as potential emerging health threats to marine mammals. Despite the fully aquatic habits of cetaceans, immunologic exposure to arboviruses including West Nile virus and Eastern equine encephalitis virus has been detected in wild Atlantic bottlenose dolphins, and captive orcas have been killed by West Nile virus and St. Louis encephalitis virus. Currently, there is no evidence of direct interactions between mosquitoes and marine mammals in nature, and it remains unknown how wild cetaceans are exposed to mosquito-vectored pathogens. Here, we report the first evidence of direct interactions between an aquatic mammal, the West Indian manatee, a federally threatened species, and mosquitoes in nature. Observations of manatees in Everglades National Park, Florida, USA, indicate that mosquitoes of three genera, Aedes, Anopheles, and Culex are able to locate and land on surface-active manatees, and at minimum, penetrate and probe manatee epidermis with their mouthparts. Whether mosquitoes can successfully take a blood meal is not known; however, an arbovirus-infected mosquito can inoculate extravascular host tissues with virus-infected saliva during probing. These observations suggest that it is possible for marine mammals to be exposed to mosquito-vectored pathogens through direct interactions with mosquitoes.

Comparative Pathology of West Nile Virus in Humans and Non-Human Animals

West Nile virus (WNV) continues to be a major cause of human arboviral neuroinvasive disease. Susceptible non-human vertebrates are particularly diverse, ranging from commonly affected birds and horses to less commonly affected species such as alligators. This review summarizes the pathology caused by West Nile virus during natural infections of humans and non-human animals. While the most well-known findings in human infection involve the central nervous system, WNV can also cause significant lesions in the heart, kidneys and eyes. Time has also revealed chronic neurologic sequelae related to prior human WNV infection. Similarly, neurologic disease is a prominent manifestation of WNV infection in most non-human non-host animals. However, in some avian species, which serve as the vertebrate host for WNV maintenance in nature, severe systemic disease can occur, with neurologic, cardiac, intestinal and renal injury leading to death. The pathology seen in experimental animal models of West Nile virus infection and knowledge gains on viral pathogenesis derived from these animal models are also briefly discussed. A gap in the current literature exists regarding the relationship between the neurotropic nature of WNV in vertebrates, virus propagation and transmission in nature. This and other knowledge gaps, and future directions for research into WNV pathology, are addressed.

Co-infection of Dirofilaria immitis and Japanese encephalitis virus in a spotted seal (Phoca largha) in the Republic of Korea

A 10-year-old male spotted seal presented with loss of appetite and decreased activity. Grossly, the internal organs revealed several filarial nematodes in the right ventricle of the heart and the pulmonary vessels. Histopathological examination of the brain revealed moderate nonsuppurative meningoencephalitis with glial nodules and neuronophagia. Japanese encephalitis virus (JEV) of genotype I was isolated from the brain. All nematodes were identified as Dirofilaria immitis. This is the first clinical case of co-infection with D. immitis and JEV in a seal, suggesting that the seal, may be a dead-end host, like the human and horse, for JEV.

ANTIDOG IgG SECONDARY ANTIBODY SUCCESSFULLY DETECTS IgG IN A VARIETY OF AQUATIC MAMMALS

Serological tests play an important role in the detection of wildlife diseases. However, while there are many commercial assays and reagents available for domestic species, there is a need to develop efficient serological assays for wildlife. In recent years, marine mammals have represented a wildlife group with emerging infectious diseases, such as influenza, brucellosis, and leptospirosis. However, with the exception of disease-agent-specific assays or functional assays, few reports describe the use of antibody detection assays in marine mammals. In an indirect enzyme-linked immunoassay (EIA) or an immunofluorescence assay, antibody is detected using an antitarget species secondary conjugated antibody. The sensitivity of the assay depends on the avidity of the binding reaction between the bound antibody and the detection antibody. A commercial polyclonal antidog IgG conjugated antibody was tested in an EIA for its ability to sensitively detect the IgG of seven marine mammals including sea otter ( Enhydra lutris ), polar bear ( Ursus maritimus ), grey seal ( Halichoerus grypus ), harbor seal ( Phoca vitulina ), northern elephant seal ( Mirounga angustirostris ), California sea lion ( Zalophus californianus ), Pacific walrus ( Odobenus rosmarus ) and one freshwater mammal: Asian small-clawed otter ( Aonyx cinerea ). With the exception of Asian small-clawed sea otters, the detection of IgG in these marine mammals either exceeded or was nearly equal to detection of dog IgG. The use of the tested commercial antidog IgG antibody may be a valid approach to the detection of antibody response to disease in sea mammals.

Retrospective study of etiologic agents associated with nonsuppurative meningoencephalitis in stranded cetaceans in the canary islands

Nineteen natural cases of etiologically undetermined encephalitides in free-ranging cetaceans were studied retrospectively. Histological examination of the brains revealed variable degrees of nonsuppurative encephalitis or meningoencephalitis, characterized predominantly by perivascular lymphohistiocytic infiltrates. A PCR assay was used on brain and other available tissues to detect the presence of morbillivirus, herpesvirus, West Nile virus, Toxoplasma gondii, and Brucella spp. In addition, immunohistochemical (IHC) staining was performed on selected tissues to determine the presence of morbilliviral antigens. Six animals (5 striped dolphins and 1 common dolphin) showed IHC and/or molecular evidence of morbilliviral antigens and/or genomes, mainly in brain tissue. Conventional nested PCR detected herpesviral DNA in brain tissue samples from two striped dolphins. There was no evidence of West Nile virus, T. gondii, or Brucella spp. in any of the brain tissue samples examined. The information presented here increases the number of confirmed morbillivirus-positive cases within the Canarian archipelago from two previously reported cases to eight. Furthermore, a new nested-PCR method for the detection of morbillivirus is described here. Regarding herpesvirus, the phylogenetic analysis performed in the current study provides valuable information about a possible pathogenic branch of cetacean alphaherpesviruses that might be responsible for some fatal cases worldwide.

West Nile virus infection in killer whale, Texas, USA, 2007

In 2007, nonsuppurative encephalitis was identified in a killer whale at a Texas, USA, marine park. Panviral DNA microarray of brain tissue suggested West Nile virus (WNV); WNV was confirmed by reverse transcription PCR and sequencing. Immunohistochemistry demonstrated WNV antigen within neurons. WNV should be considered in cases of encephalitis in cetaceans.

Concurrent occipital bone malformation and atlantoaxial subluxation in a neonatal harbor seal (Phoca vitulina)

A stranded male harbor seal (Phoca vitulina) neonate with progressive clinical signs of ataxia, tremors, and deteriorating consciousness was evaluated using magnetic resonance imaging for suspected cerebellar brain disease prior to euthanasia because of grave prognosis. Magnetic resonance imaging identified occipital bone dysplasia with cerebellar herniation and concurrent atlantoaxial subluxation with spinal cord compression. These imaging findings elucidated the cause of histopathology changes including gliosis of the cerebellum and axonal degeneration and dilation of myelin sheaths of the dorsal funiculus of the spinal cord. Occipital bone dysplasia and/ or atlantoaxial subluxation should be considered as differentials for abnormal neurologic signs in harbor seal neonates. Magnetic resonance imaging is a valuable modality for antemortem diagnosis.

Eastern equine encephalitis in a captive harbor seal (Phoca vitulina)

A 31-yr-old male, captive harbor seal (Phoca vitulina) was evaluated for a 48-hr period of anorexia followed by the onset of seizures. A prolonged seizure failed to respond to anticonvulsant therapy and the animal was euthanized. At necropsy, no significant gross lesions were identified. Reverse transcriptase-polymerase chain reaction testing of brain samples was positive for eastern equine encephalitis virus (EEEV) RNA, and serum was positive for anti-EEEV antibodies by plaque reduction neutralization. Histopathologic evaluation revealed severe and multifocal encephalitis with leptomeningitis, characterized by neutrophilic infiltrates in neuropil, neuronal necrosis, satellitosis, neuronophagia, and perivascular cuffs of lymphocytes, macrophages, and neutrophils. Additionally there was moderate, multifocal, adrenal cortical necrosis. Immunohistochemical staining for EEEV demonstrated viral antigen within necrotic neurons and glial cells. Virus was isolated from frozen brain tissue, sequenced for comparison to other strains, and determined to be a typical North American strain. EEEV should be included as a possible cause of neurologic disease in harbor seals with compatible signs located in geographic regions where vector transmission of EEEV is encountered.

Diagnosis and treatment of Sarcocystis neurona in a captive harbor seal (Phoca vitulina)

A captive harbor seal (Phoca vitulina) presented with partial anorexia, ataxia, and head bobbing, which progressed to complete anorexia, lethargy, and persistent whole-body intention tremors within several days. Response to treatment with ponazuril, serology, and cerebrospinal fluid analysis supported a diagnosis of Sarcocystis neurona. Analysis of serum levels for ponazuril indicated that therapeutic levels could be achieved at a dosage of 5 mg/kg p.o. s.i.d., whereas clinical response was improved at a dosage of 10 mg/kg. Several months after initiation of antiprotozoal therapy, the neurologic signs resolved, although rare intermittent tremors were seen with significant exertion.

Effects of climate change on Arctic marine mammal health

The lack of integrated long-term data on health, diseases, and toxicant effects in Arctic marine mammals severely limits our ability to predict the effects of climate change on marine mammal health. The overall health of an individual animal is the result of complex interactions among immune status, body condition, pathogens and their pathogenicity, toxicant exposure, and the various environmental conditions that interact with these factors. Climate change could affect these interactions in several ways. There may be direct effects of loss of the sea ice habitat, elevations of water and air temperature, and increased occurrence of severe weather. Some of the indirect effects of climate change on animal health will likely include alterations in pathogen transmission due to a variety of factors, effects on body condition due to shifts in the prey base/food web, changes in toxicant exposures, and factors associated with increased human habitation in the Arctic (e.g., chemical and pathogen pollution in the runoff due to human and domestic-animal wastes and chemicals and increased ship traffic with the attendant increased risks of ship strike, oil spills, ballast pollution, and possibly acoustic injury). The extent to which climate change will impact marine mammal health will also vary among species, with some species more sensitive to these factors than others. Baseline data on marine mammal health parameters along with matched data on the population and climate change trends are needed to document these changes.