Protozoan and Helminth Infections of Marine Mammals: Recognized and Emerging Diseases?
With strong interest in the marine environment, its flora and fauna, and the advent of new diagnostic technologies, studies of diseases of marine mammals have uncovered “new” pathogens of interest to wildlife biologists, wildlife veterinarians, and marine scientists. These “new” pathogens include viruses (e.g., phocine and cetacean morbillivirus), bacteria (e.g., Brucella), fungi (e.g., Coccidioides), protozoa (e.g., Giardia), and helminths (e.g., metastrongylus). Protozoans recently identified from marine mammals include: Giardia, Entamoeba, Sarcocystis, Toxoplasma gondii, Eimeria, Cystoisospora, Neospora, Cryptosporidium, Kyaroikeus, Haematophagus, and additional unidentified flagellates and ciliates. Some of these protozoans may be natural to marine mammals while others may be of anthropogenic origin. Most helminths, which include cestodes, digeneans, acanthocephalans and nematodes, in marine mammals have been known for years; however, some helminth species in “natural” hosts or in recently captured hosts can produce severe pathologies associated with immune status, changing ecologic relationships and, or deteriorating environments. Some of these pathogens are implicated in clinical disease observed in stressed captive animals, animals undergoing rehabilitation or in wild free-ranging animals. Serology, histology, light and electron microscopy, monoclonal antibody techniques, PCR, and other techniques have proven useful in detecting recognized or previously unrecognized pathogens (some of which are zoonotic) or in monitoring emerging diseases. Field and laboratory studies are required to corroborate clinical observations and to determine the significance and role of these “new” pathogens in wild marine mammal populations.