Critically Endangered Hawaiian Monk Seals Are Dying Due To A Feline Parasite

Fewer than 1,200 Hawaiian monk seals remain in the wild, making them the most endangered marine mammals in the world. Andrea Izotti/Shutterstock

The Hawaiian monk seal – a charismatic species found only in the subtropical waters of its namesake Pacific archipelago – was hunted to the brink of extinction during the 19th century for its luxurious coat and has struggled to recover ever since. It is now estimated that fewer than 1,200 individuals remain, and despite decades of conservation efforts, their numbers continue to decline.

The latest threat to the endangered marine mammal? A parasitic microorganism that evolved to target wild and domestic cats. According to scientists at the National Oceanic and Atmospheric Administration (NOAA) Fisheries department, infection with Toxoplasma gondii is now the leading disease-related cause of death for Hawaiian monk seals after tests confirmed that three females – two adults and one unborn pup – found washed up on O?ahu in May had perished as a result of toxoplasmosis.


NOAA’s report adds that the single-celled organism’s total documented mortality count is 11 since 2001, but many more seals are likely dying from the massive internal damage and organ failure it induces; their carcasses are simply never found.

Female RK60, one of the adults found dead from toxoplasmosis in May. NOAA

Found across the world, T. gondii is an obligate parasite of felines, meaning that it can only complete its life cycle within a cat host. However, the protozoan can infect any mammal that ingests its cysts – the dormant egg form of the next generation that is excreted in the feces of cats. T. gondii cysts are incredibly hardy, surviving outside a host in soil or water for up to a year.

If these cysts do enter a warm body that is not a cat, the parasite within has shockingly sophisticated methods for getting itself inside the desired host’s intestines. Recent studies have established that the organism makes its way into the brains of rodents and, by unknown mechanisms, turns off the ingrained neurochemical switches that cause the prey animals to display caution and run away from signs of cats; thus, they are more likely to get eaten, and in doing so, deliver the T. gondii like a suicidal chauffeur.  

A wave of recent research in humans implies these mechanisms have an insidious effect on our brains as well. Toxoplasmosis has been linked to numerous long-term psychiatric disorders, including schizophrenia, bipolar disorder, and explosive rage. Considering anywhere from 7 to 98 percent of human populations are exposed to the parasite, further study on this topic has become a high priority.


Even when the microorganism does not enter the brain, it can fatally damage the body by burrowing into muscle and cardiac tissue, as the monk seals tragically demonstrate.

To prevent the spread of toxoplasmosis to more marine mammals, officials are lobbying for stricter control of the islands’ feral cat populations.

“Since cats are the only animal that transmit the disease, it only makes sense that reducing the number of feral cats will reduce the risk of infection and serious illness or death,” Dr Bruce Anderson, health director of the Hawaii State Department of Health, said in a statement.

To do your part in keeping the dastardly protozoan in check, always properly dispose of cat litter to keep contaminated waste from entering the land and ecosystems.



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