Infectious Disease, Parasites and Toxins

Hawaiian monk seal researcher administers topical dewormer medication to a juvenile monk seal at Laysan Island.
Hawaiian monk seal researcher administers topical dewormer medication to a juvenile monk seal at Laysan Island.

The prevalence and exposure to disease, parasites, and toxins is a major focus of research and recovery efforts for the Hawaiian monk seal. Given that monk seals are endangered, have very low genetic diversity, and have not been exposed to many diseases due to the isolation of the Hawaiian Archipelago, the potential impact of infectious disease on the monk seal population could be severe and have devastating population-level impacts. Thus, vigilant infectious disease surveillance is constantly maintained. Additionally, a Hawaiian Monk Seal Vaccination Research and Response Plan (1.4 MB PDF) was developed to proactively address this threat, particularly for morbillivirus and West Nile virus infections.

In the main Hawaiian Islands (MHI), monk seals forage, travel and rest in close proximity to areas of human activity, domestic and feral animals, and agricultural areas. This increases exposure to contaminated waters from sewage and land based surface run-off, increasing the probability of infectious disease transmission. Monk seal movements throughout the MHI and Northwestern Hawaiian Islands (NWHI) suggest any diseased seal could quickly infect healthy seals with the potential of causing debilitating impacts to the monk seal population, including mass mortality.

Multiple pathogens which are a known risk for other pinnipeds (seals and sea lions) and cetaceans (whales and dolphins) are monitored. Some of the infectious diseases that pose a risk to the Hawaiian monk seal population include distemper viruses, West Nile Virus, Leptospira spp., and Toxoplasma gondii.

In addition to infectious disease, parasites can impart strain on an individual seal's immune function and health. The prevalence of gastrointestinal parasitic infection throughout the monk seal population is significant and the effects on monk seal morbidity and mortality are not fully known. The high rate of infection, concurrent with prey limitation in the NWHI, may be a significant factor affecting the growth and survivorship of juvenile Hawaiian monk seals in this region. Using deworming treatments to reduce parasite burdens in individual seals may be a valuable intervention strategy with the potential to increase growth and survivorship of the monk seal population.

Another concern for Hawaiian monk seals is the presence of human originated and naturally occuring toxins. These toxins are found in seal prey, resulting in the slow bioaccumulation of toxins in the seal's tissues. High concentrations of toxins in tissue and blood may lead to reproductive failure and immunosuppression, as well as other effects, with the potential of having a significant negative influence on monk seal survival.

Recent research measuring the levels of toxic pesticides, PCBs, and other contaminant compounds in monk seals in the NWHI and MHI found that the average concentrations in seal tissues likely do not represent deleterious toxin levels. However, some individual seals were found to have potentially dangerous levels of these compounds.

A study on the potential threat from ciguatoxins, neurotoxins produced by microalgae that accumulate in coral reef associated fish, has shown that some monk seals have significant levels of ciguatoxins in their tissues. However, it is unclear what impacts ciguatoxins have on the health of monk seals.

Efforts are ongoing and in collaboration with other researchers to understand the role of contaminants, both human introduced and naturally occurring, in monk seal vitality.

Further Reading:

Infectious Disease:

Hawaiian Monk Seal Vaccination Research and Response Plan
Aguirre AA, Keefe TJ, Reif JS, Kashinsky L, Yochem PK, Saliki JT, Stott JL, Goldstein T, Dubey JP, Braun R, Antonelis G
2007. Infectious disease monitoring of the endangered Hawaiian monk seal. Journal of Wildlife Diseases 43(2): 229-241. DOI: 10.7589/0090-3558-43.2.229
Baker JD, Harting AL, Barbieri MM, Johanos TC, Robinson SJ, Littnan CL
2016. Estimating contact rates of Hawaiian monk seals (Neomonachus schauinslandi) using social network analysis Journal of Wildlife Diseases 52(3):533-543. doi:10.7589/2015-10-286
Barbieri MM, Kashinsky L, Rotstein DS, Colegrove KM, Haman KH, Magargal SL, Sweeny AR, Kaufman AC, Grigg ME, Littnan CL
2016. Protozoal-related mortalities in endangered Hawaiian monk seals Neomonachus schauinslandi Diseases of Aquatic Organisms. 121(2):85-95. doi:10.3354/dao03047
Hanson MT, Aguirre AA, Braun RC
2009. Clinical observations of ocular disease in Hawaiian monk seals (Monachus schauinslandi). U.S. Dept. of Commer., NOAA Tech. Memo. NOAA-TM-NMFS-PIFSC-18, 9 p.
Honnold, SP, Braun R, Scott DP, Sreekumar C, Dubey JP
2005. Toxoplasmosis in a Hawaiian monk seal (Monachus schauinslandi). Journal of Parasitology 91: 695–697. DOI: 10.1645/ge-469r
Littnan CL, Stewart BS, Yochem PK, Braun R
2006. Survey for selected pathogens and evaluation of disease risk factors for endangered Hawaiian monk seals in the main Hawaiian Islands. EcoHealth 3(4): 232-244. DOI: 10.7589/0090-3558-43.2.229
Nielsen O, Nielsen K, Braun R, Kelly L
2005. A comparison of four serologic assays in screening for Brucella exposure in Hawaiian monk seals. Journal of Wildlife Diseases 41:126–133. DOI: 10.7589/0090-3558-41.1.126
West KL, Sanchez S, Rotstein D, Robertson KM, Dennison S, Levine G, Davis N, Schofield D, Potter CW, Jensen B
2013. A Longman's beaked whale (Indopacetus pacificus) strands in Maui, Hawaii, with first case of morbillivirus in the central Pacific. Marine Mammal Science, 29: 767–776. DOI: 10.1111/j.1748-7692.2012.00616.x
Yantis D, Moeller R, Braun R, Gardiner C, Aguirre A, Dubey JP
2003. Hepatitis associated with a Sarcocystis canis-like protozoan in a Hawaiian monk seal (Monachus schauinslandi). Journal of Parasitology. 89:1258-1260. DOI: 10.1645/ge-3265rn

Parasites:

Baker JD
2008. Variation in the relationship between offspring size and survival provides insight into causes of mortality in Hawaiian monk seals. Endangered Species Research 5:55-64. DOI: 10.3354/esr00122
DeLong RL, Orr AJ, Jenkinson RS, Lyons T
2009. Treatment of northern fur seal (Callorhinus ursinus) pups with ivermectin reduces hookworm-induced mortality. Marine Mammal Science 25(4):944-948. DOI: 10.1111/j.1748-7692.2008.00274.x
Gobush KS, Baker JD, and Gulland FMD
2011. Effectiveness of an Antihelminthic Treatment in Improving the Body Condition and Survival of Hawaiian Monk Seals. Endangered Species Research 15:29-37. DOI: 10.3354/esr00364
Reif JS, Kliks MM, Aguire AA, Borjesson DL, Kashinsky L, Braun RC, Antonelis GA
2006. Gastrointestinal helminths in the Hawaiian monk seal (Monachus schauinslandi): associations with body size, hematology, and serum chemistry. Aquatic Mammals 32(2): 157-167. DOI: 10.1578/am.32.2.2006.157

Toxins:

Bottein MY, Kashinsky L, Wang Z, Littnan C, Ramsdell JS
2011. Identification of Ciguatoxins in Hawaiian Monk Seals Monachus schauinslandi from the Northwestern and Main Hawaiian Islands. Environmental Science & Technology. Environ. Sci. Technol., 2011, 45 (12), pp 5403–5409. DOI: 10.1021/es2002887
Littnan CL, Stewart BS, Yochem PK, Braun R
2006. Survey for selected pathogens and evaluation of disease risk factors for endangered Hawaiian monk seals in the main Hawaiian Islands. EcoHealth 3(4): 232-244. DOI: 10.1007/s10393-006-0059-z
Lopez J, Boyd D, Ylitalo GM, Littnan C, Pearce R
2012 Persistent organic pollutants in the endangered Hawaiian monk seal (Monachus schauinslandi) from the main Hawaiian Islands. Marine Pollution Bulletin. DOI: 10.1016/j.marpolbul.2012.07.012
Lopez J, Hyrenbach KD, Littnan C, Ylitalo GM
2014. Geographic variation of persistent organic pollutants in Hawaiian monk seals Monachus schauinslandi in the main Hawaiian Islands. Endangered Species Research 24: 249-262. DOI: 10.3354/esr00602
Ylitalo GM, Myers M, Stewart BS, Yochem PK, Braun R, Kashinsky L, Boyd D, Antonelis GA, Atkinson S, Aguirre AA, Krahn MM
2008. Organochlorine contaminants in endangered Hawaiian monk seals from four subpopulations in the Northwestern Hawaiian Islands. Mar. Poll. Bull. 56(2): 231-244. DOI: 10.1016/j.marpolbul.2007.09.034