Cryptosporidium and Giardia sp. are widespread protozoan parasites that are capable of causing severe enteric disease particularly in immunocompromised hosts. While these organisms have been well studied in many terrestrial vertebrates and freshwater systems, their epidemiology in the marine environment is less well known. Recent studies have shown that both protozoans are present in coastal waters near sewage outflows as well as in a variety of marine mammals and shellfish.1 As part of a health assessment program on endangered North Atlantic right whales (Eubalaena glacialis), we conducted a five-year study to assess the prevalence of Giardia and Cryptosporidium and determine the genotypes of isolates to assess the potential impacts of these organisms on health and fitness. From 2002-2006, 125 fecal samples were examined for the presence of Giardia and Cryptosporidium cysts/oocysts using an immunofluorescent assay procedure.2 The overall prevalence of Giardia was 68% annually (range = 38-77%), which is the highest reported to date for a marine mammal. Cryptosporidium oocysts were detected in 14% of samples (range = 7-38%), and all positive samples were also Giardia positive. Molecular characterization and phylogenetic analysis of the right whale Giardia based on the glutamate dehydrogenase gene suggested that it is a novel isolate within the G. intestinalis species-complex, while molecular studies of the Cryptosporidium isolate were not successful. For comparison, 29 fecal samples were collected from the rapidly recovering population of South Atlantic right whales (Eubalaena australis) off the coast of South Africa in 2004-2005 and examined for Giardia and Cryptosporidium using the same methods. Cysts of Giardia were detected in 24%, while all samples were negative for Cryptosporidium. Phylogenetic analysis showed that Giardia isolates from both right whale species clustered together. While the effects of these organisms on marine mammals are generally unknown, infection of North Atlantic right whales with Cryptosporidium was correlated with a decline in body condition using a visual assessment method.3 Extensive use of near shore habitats by these highly endangered whales may increase exposure to pathogens originating from land, and low genetic diversity in this small population may increase disease susceptibility and heighten the risk of morbidity and mortality from infection with protozoan parasites.
Our thanks to the North Atlantic Right Whale Consortium for access to the North Atlantic Right Whale Catalogue and database, and to Meredith Thornton for collection of samples in South Africa. This work was supported by contracts (to RMR) from NOAA Fisheries and a grant from the National Research Foundation of South Africa (to PBB).
1. Fayer R., J.P. Dubey, and D.S. Lindsay. 2004. Zoonotic protozoa: from land to sea. 20: 531-536.
2. Hughes-Hanks J.M., L.G. Rickard, C. Panuska, J.R. Saucier, T.M. O'Hara, L. Dehn, and R.M. Rolland. 2005. Prevalence of Cryptosporidium spp. and Giardia spp. in five marine mammal species. J Parasitol 91: 1225-1228.
3. Pettis H.M., R.M. Rosalind, P.K. Hamilton, S. Brault, A.R. Knowlton, and S.D. Kraus. 2004. Visual health assessment of North Atlantic right whales (Eubalaena glacialis) using photographs. Can J Zool 82(1): 8-19.