Francesca Tomasi received her B.A. from the University of Chicago and is now a microbiologist.
Cryptosporidium is a microscopic parasite that causes a nasty diarrheal disease called cryptosporidiosis (crypto for short). While most species of Cryptosporidium infect animals, some also infect humans by nestling into our intestines. Symptoms of infection can last several weeks and are usually more severe than the average diarrheal illness. For people with weakened immune systems such as young children or AIDS patients, crypto can be fatal. The parasite is readily spread through contaminated water – Cryptosporidium is protected by an outer shell that allows it to withstand standard water treatments such as chlorination. The fecal-oral route is the other main vector for parasite transmission and plays a huge role in human-to-human spread. Cryptosporidium species have been reported in several countries worldwide, the most surprising until this year being an outbreak from contaminated water in Milwaukee, Wisconsin. This 1993 outbreak affected almost half a million people. Nonetheless, the parasite, especially a strain called Cryptosporidium hominis (so named because it spreads from human to human), is most prevalent in low-income tropical countries.
Earlier this month, researchers from the McGill University Health Centre, the Nunavik Department of Public Health, l’Institut National de Santé Publique du Québec (the Québec Institute for Public Health), and Health Canada published a surprising new finding: the tropical parasite has been identified in the Arctic. Cryptosporidium was found in Nunavik, Québec (see map below), where an outbreak between April 2013 and April 2014 spread through 10 local villages. The particular strain was identified to be Cryptosporidium hominis. In Nunavik, children under 5 years old were the most affected, which is a huge matter of concern: crypto infections have been linked to impaired physical and cognitive development. While there is a treatment for crypto, Canada’s healthcare system has had little reason until now to stock up on it, let alone on the standard diagnostic tools for this disease. After all, when you hear of a tropical disease, the last place you would expect to see it is in the frigid, dry Arctic. Current assessments of the size of the crypto outbreak are therefore likely to be underestimates, implying a larger pending effect on Nunavik residents. The long-term effects on growth and development of the affected children are an unwanted addition to a list of challenges faced by Inuit communities such as overcrowding and food-insecurity.
Interestingly, in March a group of researchers in China reported the first identification of Cryptosporidium canis, a canine strain of the parasite, in Chinese Arctic foxes. Other species of Cryptosporidium have also been isolated from seals, mussels, dogs, and caribou in Arctic North America. This could suggest a zoonotic origin (animal to human transmission) for the Nunavik outbreak. However, according to the Canadian study, the temporal and geographic distribution of cases as well as the nature of the strain suggest anthroponotic (originating from humans) rather than zoonotic transmission. The species implicated in Nunavik, C. hominis, furthermore, is specific to humans. C. hominis has multiple subtypes – interestingly, the one that made its way to Nunavik is relatively rare compared to over human-propagated parasites. This subtype, called “Id,” has been found before in other parts of Canada like Ontario and British Columbia, but not in Arctic ecosystems. Deeper genetic analysis, however, found that the subtype’s subtype (parasites, like bacteria, change quickly and can therefore be sequenced to figure out how closely two strains are related) in Nunavik has not been found anywhere else in Canada, implying a different origin than the Great White North. The researchers tested water and food sources, but none came back positive for any Cryptosporidium. Whatever the original source was, the parasite then hopped from human to human, as evidenced by frequent secondary cases arising amongst family members of infected individuals.
Unfortunately, neglected tropical diseases are not new plagues among indigenous people of the Arctic. “Tropical” refers to the origin and areas of endemic spread of these diseases more so than the requirement that they only proliferate in a tropical ecosystem. Tropical diseases in fact tend to occur wherever extreme poverty occurs, and the Arctic Circle is one such place. Tropical parasitic infections such as toxoplasmosis, trichinellosis, and giardiasis have all been previously identified as significant burdens on Arctic populations. Cryptosporidiosis is now a new parasite to add to the growing list, calling for revitalized attention on pathogen surveillance in this region of the world. Ultimately, programs aimed at the prevention of tropical diseases will need to be implemented for all indigenous Arctic populations if we want to see a decline in the global burden of tropical diseases.