Phocine Distemper Virus
Introduction
Phocine distemper virus (PDV) is a paramyxovirus that primarily affects pinniped populations, particularly the harbor seal (Phoca vitulina). It is a highly infectious and often lethal pathogen, causing mass mortality events in seal populations worldwide.
Virology
PDV is a member of the Morbillivirus genus, which also includes the viruses responsible for measles in humans and canine distemper in dogs. The virus is enveloped, with a single-stranded, negative-sense RNA genome. The genome encodes six structural proteins: nucleocapsid (N), phosphoprotein (P), matrix (M), fusion (F), hemagglutinin (H), and large polymerase (L).
Epidemiology
PDV was first identified in 1988 during a mass mortality event among harbor seals in the North Sea, in which approximately 18,000 seals died. A second outbreak in 2002 resulted in the deaths of an estimated 30,000 seals. The virus is believed to be transmitted through direct contact or aerosol droplets, and can also be spread indirectly through contaminated environments.
Pathogenesis and Clinical Signs
Infection with PDV leads to a severe systemic disease, with clinical signs including fever, coughing, nasal discharge, and neurological symptoms such as seizures and disorientation. The virus primarily targets the respiratory and lymphatic systems, causing pneumonia and lymphoid depletion.
Diagnosis and Treatment
Diagnosis of PDV is typically based on clinical signs and confirmed through laboratory testing, including PCR and serology. There is currently no specific antiviral treatment for PDV; management of infected animals focuses on supportive care, including hydration and treatment of secondary bacterial infections.
Impact on Seal Populations
Outbreaks of PDV can have devastating effects on seal populations, causing high mortality rates and significant population declines. The long-term impacts of these outbreaks on seal population dynamics and conservation status are still not fully understood.
Prevention and Control
Efforts to prevent and control PDV outbreaks focus on surveillance and monitoring of seal populations, as well as public education to reduce human-seal interactions that could facilitate the spread of the virus.