Morphometric, molecular and histopathologic description of hepatic infection by Orthosplanchnus arcticus (Trematoda: Digenea: Brachycladiidae) in ringed seals (Pusa hispida) from Northwest Greenland

A Review of Circumpolar Arctic Marine Mammal Health-A Call to Action in a Time of Rapid Environmental Change

The impacts of climate change on the health of marine mammals are increasingly being recognised. Given the rapid rate of environmental change in the Arctic, the potential ramifications on the health of marine mammals in this region are a particular concern. There are eleven endemic Arctic marine mammal species (AMMs) comprising three cetaceans, seven pinnipeds, and the polar bear (Ursus maritimus). All of these species are dependent on sea ice for survival, particularly those requiring ice for breeding. As air and water temperatures increase, additional species previously non-resident in Arctic waters are extending their ranges northward, leading to greater species overlaps and a concomitant increased risk of disease transmission. In this study, we review the literature documenting disease presence in Arctic marine mammals to understand the current causes of morbidity and mortality in these species and forecast future disease issues. Our review highlights potential pathogen occurrence in a changing Arctic environment, discussing surveillance methods for 35 specific pathogens, identifying risk factors associated with these diseases, as well as making recommendations for future monitoring for emerging pathogens. Several of the pathogens discussed have the potential to cause unusual mortality events in AMMs. Brucella, morbillivirus, influenza A virus, and Toxoplasma gondii are all of concern, particularly with the relative naivety of the immune systems of endemic Arctic species. There is a clear need for increased surveillance to understand baseline disease levels and address the gravity of the predicted impacts of climate change on marine mammal species.

First elucidation of the life cycle in the family Brachycladiidae (Digenea), parasites of marine mammals

Digeneans of the family Brachycladiidae are cosmopolitan parasites restricted to marine mammals. Their life cycles are unknown. Phylogenetically, Brachycladiidae are closely related to Acanthocolpidae, parasites of marine teleost fishes. Acanthocolpida typically possess three-host life cycles with gastropods of the superfamily Buccinoidea acting as the first intermediate hosts for most species, and either fishes or bivalves acting as the second intermediate hosts. A few species previously identified as Neophasis differ from other Acanthocolpidae in having naticid gastropods as first intermediate hosts, and both fishes and bivalves as second ones. We assumed that this may indicate an incorrect life cycle description and revised previous data on rediae and cercariae of Neophasis spp. from Cryptonatica affinis (Naticidae) and metacercariae from cardiid bivalves at the White Sea using molecular and morphological approaches. Sequence comparison showed that rediae and cercariae from C. affinis resembling some representatives of the genus Neophasis and metacercariae from bivalves resembling Neophasis oculata belong to the brachycladiid species Orthosplanchnus arcticus. Thus, the life cycle of O. arcticus proceeds as follows: seals serve as the definitive host, C. affinis as the first intermediate host and cardiid bivalves as the second. We found one more type of redia and cercaria in C. affinis which, by molecular evidence, also belongs to Brachycladiidae and is closely related to O. arcticus. Here we refer to them as Brachycladiidae gen. sp. 1 WS. We suggest that Brachycladiidae gen. sp. 1 WS may belong to either Orthosplanchnus or Odhneriella, with beluga whales possibly being the definitive host. Morphological features of O. arcticus and Brachycladiidae gen. sp. 1 WS cercariae are summarised and matched with published data on putatively brachycladiid cercariae. We compare and discuss the diversity of life cycle patterns among Brachycladiidae and Acanthocolpidae, and show that they differ not only in the type of definitive host, but also in both intermediate hosts.