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

Area of Science:

• Veterinary Neurology
• Marine Mammal Medicine
• Arbovirology

Background:

• Eastern equine encephalitis virus (EEEV) is a mosquito-borne alphavirus known to cause severe neurologic disease in humans and equids.
• While EEEV primarily affects terrestrial animals, its potential impact on marine wildlife, particularly in coastal regions, remains less understood.

Observation:

• A captive harbor seal (Phoca vitulina) presented with acute anorexia and seizures, unresponsive to treatment.
• Necropsy revealed no gross lesions, but diagnostic testing confirmed EEEV infection in the brain and adrenal glands.
• Histopathology showed severe, multifocal encephalitis and leptomeningitis, with viral antigen present in affected neural and glial cells.

Findings:

• RT-PCR and antibody testing confirmed EEEV infection in the affected harbor seal.
• Histopathology revealed characteristic lesions of severe encephalitis and leptomeningitis.
• Sequencing identified the EEEV strain as a typical North American isolate.

Implications:

• EEEV should be considered in the differential diagnosis for marine mammals exhibiting neurological signs in endemic areas.
• This case underscores the potential for cross-species transmission of EEEV and its impact on marine ecosystems.
• Further surveillance and research are warranted to assess the prevalence and significance of EEEV in marine mammal populations.