MARINE MAMMAL RESEARCH NEWSLETTER     |     Sept. 2014 (Issue 11)

From the Field
Terrestrial Parasites are infecting and causing disease in Hawaiian monk seals

Parasites are a normal, natural part of all ecosystems.  Even people carry their own specific parasites.

Most parasites do not seriously harm their hosts.  However, parasites can sometimes cause disease and death if consumed by species that have not been previously exposed to them.  A classic example of this was the massive mortality of southern sea otters that occurred in 2004 after a coccidian parasite, Sarcocystis neurona appeared in the coastal marine waters of California.


A Hawaiian monk seal doing what comes naturally while on a beach in Hawaii.
NOAA HMSRP, NMFS permit #10137-07

Sarcocystis neurona is a terrestrial parasite carried by the Virginia opossum—its definitive host and North America’s only marsupial.  This parasite is closely related to Toxoplasma gondii (the kitty-box parasite), and is passed in the feces of wild and domestic cats.

Cats and opossums have been expanding their ranges as humans develop more land and travel greater distances.  This in turn has allowed their parasites to also expand their ranges and invade new ecosystems.

People have been bringing pet cats and other companion animals with them to the Hawaiian Islands in the middle of the Pacific Ocean with little thought about the parasites that will be passed through feces into the Hawaiian ecosystem. Some of the parasites that are shed by the cats will complete their natural life cycles on land, but others will ultimately end up in the ocean and may infect and kill species—such as Hawaiian monk seals—that have no resistance to them.


Diagram showing the two-host life cycle of Toxoplasma gondii. Note that though the host species may vary, this two-host life cycle is typical of coccidian parasites.

The Hawaiian monk seal is a highly endangered pinniped that is endemic to the Hawaiian Islands. They inhabit both the Main and Northwestern Hawaiian Islands, and are one of only two remaining species of monk seal (the other is the Mediterranean monk seal).


A Hawaiian monk seal and green sea turtle share a bit of warm sand on a sunny Hawaiian beach.
NOAA HMSRP, NMFS permit #10137-07

Veterinarian and UBC PhD candidate Katie Haman is working with the National Institutes of Health and the National Oceanic and Atmospheric Administration’s Hawaiian Monk Seal Research Program to assess the risk posed by Toxoplasma gondii to monk seals in the waters around the main Hawaiian Islands.  To date, they have found that this parasite is infecting and killing some monk seals, and that most of the detected infections are occurring around the main Hawaiian Islands. This is consistent with the large number of cats living on these Islands.


This diagram represents the potential mechanisms of transmission of Toxoplasma gondii (and other terrestrial-sourced coccidian parasites) into the coastal marine waters of Hawaii. Once these parasites are washed into the marine ecosystem, often by terrestrial freshwater runoff, they may become concentrated in fish and other invertebrates. The Hawaiian monk seal would then become infected with the parasite by ingesting fish or invertebrates.

The segment of the monk seal population that uses the main Hawaiian Islands is small (approximately 200 out of the 1,100 remaining seals live there), but it is also the only portion that is showing positive trends in births and survival. Therefore, understanding the emerging effects of Toxoplasma gondii in this potentially important region is essential for informing population recovery efforts.

Toxoplasma gondii are likely being washed into the coastal waters of Hawaii from areas that have been contaminated with infected cat feces.  However, it is not known how monk seals are becoming infected. In other places of the world, accumulations of the infectious eggs of Toxoplasma gondii have been found in filter-feeding fish and bivalves (molluscs such as clams, oysters and mussels). Monk seals may thus be eating fish that have filtered the parasitic eggs from the water—and these eggs may in turn be hatching once inside the warm-blooded seal.


A Hawaiian monk seal watches a green sea turtle hatchling making its way to the ocean.
NOAA HMSRP, NMFS permit #10137-07


Hawaiian monk seals hauled out on a small patch of sand in the Hawaiian islands.
NOAA HMSRP, NMFS permit #10137-07

Understanding the mechanism and extent of the infections of Toxoplasma gondii is important to ensuring that Hawaiian monk seals remain healthy.  However, this knowledge also has implications for people eating fish in Hawaii because parasites like Toxoplasma gondii are zoonotic (spread between people and animals) and can infect and cause disease in humans.

Katie still has work to do to determine just how prevalent this parasite is in monk seals, and the extent to which it is associated with disease.  Ultimately, Katie hopes that what she is learning about pathogenic threats from terrestrial sources will aid in the conservation and recovery of Hawaiian monk seals.


Katie Haman is a Ph.D. candidate at UBC’s Marine Mammal Research Unit.

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