Canine distemper virus (CDV), Leptospira interrogans, and Toxoplasma gondii are potentially lethal pathogens associated with decline in marine mammal populations. The Caspian Sea is home for the endangered Caspian seal (Pusa caspica). In the late 1990s and early 2000s, CDV caused a series of mortality events involving at least several thousand Caspian seals. To assess current infection status in Caspian seals, we surveyed for antibodies to three pathogens with potential to cause mortality in marine mammals. During 2015–2017, we tested serum samples from 36, apparently healthy, Caspian seals, accidentally caught in fishing nets in the Caspian Sea off Northern Iran, for antibodies to CDV, L. interrogans, and T. gondii, by virus neutralization, microscopic agglutination, and modified agglutination, respectively. Twelve (33%), 6 (17%), and 30 (83%) samples were positive for CDV, L. interrogans and T. gondii antibodies, respectively. The highest titers of CDV, L. interrogans, and T. gondii antibodies were 16, 400, and 50, respectively. Frequencies of antibody to these pathogens were higher in seals >1 year old compared to seals <1 year old. Two serovars of L. interrogans (Pomona and Canicola) were detected. Our results suggest a need for additional studies to clarify the impact of these pathogens on Caspian seal population decline and the improvement of management programs, including systematic screening to detect and protect the remaining population from disease outbreaks.
The endemic Caspian seal Pusa caspica breeds on land-fast ice or stable drift ice in the northern Caspian Sea. Breeding has rarely been reported in the ice-free south-eastern Caspian Sea. Five carcases of white-coat Caspian seal pups were recovered from the southern Caspian Sea, Iran, during 2019–2022. From survey interviews, two white-coat Caspian seal pups were also observed in Amirabad and between Ghorogh and Rudsar. These records represent very late pupping dates compared to normal pupping periods. Coastal Iran should be surveyed annually for Caspian seal pups to determine frequency of breeding and areas of importance identified in the Iran Caspian Seal Action Plan.
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