Frequency of exposure of endangered Caspian seals to Canine distemper virus, Leptospira interrogans, and Toxoplasma gondii

Abstract

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.

Viral Metagenomic Survey of Caspian Seals

“…In the current work, no morbillivirus contigs were recovered from metagenomic sequencing of samples 2009-2020, and the were no positive detections by RT-PCR for 2019-2020 samples. Together, our two studies and others[90], suggest that CDV has circulated episodically in Caspian seals since 2001, but the trigger mechanisms for mass mortalities are still unknown.…”

Leptospira spp. and Toxoplasma gondii in stranded representatives of wild cetaceans in the Philippines

“…in the sirenian Peruvian Amazon manatees ( Trichechus inunguis ) [18] as well as in pinnipeds including harbor seals ( Phoca vitulina ) [19, 20], Northern elephant seals ( Mirounga angustirostris ) [21], California sea lions ( Zalophus californianus ) [22–26, 17], and Chilean South American sea lions ( Otaria byronia ) [27]. Most recently, two serovars – Pomona and Calicola – of Leptospira interrogans were detected in serum samples of endangered Caspian seals ( Pusa caspica ) in the Caspian Sea off Northern Iran [28]. Information on the prevalence of Leptospira in cetaceans is scarce, with the first isolation of the proposed L. brihuegai sp.…”

Status epilepticus caused by canine distemper virus in a striped hyena (Hyaena hyaena)

“…10 The occurrence of canine distemper is common in different parts of Iran [11][12][13][14] and there is a report of contamination of Caspian seals with CDV. 15 Recently, the prevalence of distemper disease in dogs in Mashhad (the location of this report) has been determined to be 4% (unpublished data). However, the prevalence of it in Iranian wildlife is unknown.…”

“…reported that other wildlife in each area may be the reservoir of CDV other than dogs, and that hyenas may get the virus from other wild animals or transmit it to other wild animals and domestic dogs 10 . The occurrence of canine distemper is common in different parts of Iran 11–14 and there is a report of contamination of Caspian seals with CDV 15 . Recently, the prevalence of distemper disease in dogs in Mashhad (the location of this report) has been determined to be 4% (unpublished data).…”