Cryptosporidium is an apicomplexan parasite that is increasingly recognised among immunocompetent hosts as a leading cause of childhood diarrhea in low-resource settings and of waterborne diarrheal outbreaks in high-income countries.[1, 2] C. hominis, for which humans are the only natural host, and C. parvum, which infects bovines, wild animals and humans, account for the majority of human infections.[3] Cryptosporidium oocysts are transmitted via the fecal-oral route, including by person-to-person spread, from contaminated food or water, or from contact with infected animals. The relative contribution of each mode of transmission to the epidemiology of human disease is incompletely understood, due in part to the fact that traditional diagnostic tools do not differentiate species of Cryptosporidium. Symptomatic cases present most often with diarrhea, usually subsiding within 30 days in immunocompetent hosts. However, Cryptosporidium infection (with or without diarrhea) disproportionately affects young children at critical stages of growth and brain development, and has been repeatedly associated with reduced linear growth, impaired cognitive development, poor performance at school, less economic productivity, and lower adult height.[2, 4–6] Worryingly, these effects are exacerbated by food scarcity, which is reported by 24–46% of households surveyed in the Canadian Arctic.[7]

In May 2013, the Parasitology Laboratory of the McGill University Health Centre (MUHC) observed the presence of Cryptosporidium oocysts in stool specimens from Inuit communities in the Canadian Arctic region of Nunavik, Quebec. Human cryptosporidiosis transmission was previously unknown in this region, and very few previous studies have reported it elsewhere in the Arctic.[8, 9] We report clinical, molecular, and epidemiologic details of a multi-village Cryptosporidium outbreak in the Canadian Arctic region of Nunavik, Quebec, starting in 2013.

The present report details the occurrence of human cryptosporidiosis in the Arctic, in a region where this disease was not previously known. After the study period, the outbreak persisted in Nunavik until the end of 2014, where an additional 18 cases were reported; the annual IR for 2013 and 2014 were respectively 322.5 and 246.4 / 100,000 persons. The annual IR for the rest of the province of Quebec, excluding Nunavik, were respectively 0.5 and 0.8 / 100,000 persons in 2013 and 2014. Cryptosporidiosis is nationally notifiable since 2000; 830 cases were reported in Canada in 2013, the most recent year for which data are available, yielding an IR of 2.4 / 100,000 persons (personal communication; Pushpa Narayanan, Public Health Agency of Canada [2015-07-30]). Thus, the IR of cryptosporidiosis in Nunavik was much higher than for the rest of Quebec and Canada as a whole in 2013 and 2014.

In Nunavik, Cryptosporidium spp. has been previously detected in ringed seals, bearded seals and blue mussels, making food-borne transmission through the consumption of marine animals a possible route of infection.[14, 15] Elsewhere in Arctic North America, dogs and caribou have been found to carry Cryptosporidium and may be another source of zoonotic infection.[16, 17] However, in this first observed outbreak of human disease in the region, the identification by molecular typing of C. hominis subtype Id in all 14 specimens tested rules-out zoonotic transmission for these specimens, though the possibility remains that other Cryptosporidium subtypes could have been present in specimens that were not characterised. Further analysis demonstrated single isolates of the subtypes IdA13, IdA14G1 IdA14G2R1 and IdA16, and five isolates each of subtypes IdA14 and IdA15. The latter two subtypes, being the most prevalent in the present study, suggest common anthroponotic sources of infection in these patients. It is interesting to note that, globally, C. hominis subtype Id is found less frequently compared to C. hominis subtype Ib.[3] Human infections with subtype Id have previously been reported in Ontario[18] and British Columbia[19], but not in Arctic ecosystems. No animal-derived subtype Id strains have been described. To the best of our knowledge, the C. hominis “Id subtypes” identified in this study have not been reported previously in Canada. In contrast to the current report, the only other study involving the molecular characterization of Cryptosporidium infections in humans in the Arctic, reported only C. parvum IIa in diarrhoeic patients in Nunavut.[9]

The temporal and geographic distribution of cases we observed (Fig 2) further support predominant person-to-person transmission. A common food vehicle or water source would not explain the observed global epidemiologic profile of this outbreak. Finally, microbiological testing of the water supply chain in Village 1 did not detect any parasites or unacceptable coliform counts, though this assessment was limited by the fact that we were only able to test a single village, at a time when no cases were recorded.

In this study, a higher IR was observed in children younger than 5 years of age. This is in keeping with what is known about cryptosporidiosis in low-income countries where Cryptosporidium is a leading cause of infectious diarrhea in young children but not in older age groups.[2] Secondary cases among family members are well documented.[20] Multiple factors likely contribute to these observations, including less frequent use of appropriate hand hygiene and immature cellular immunity in this age group.[21]

Protocols in our laboratory did not call for routine acid-fast staining of diarrheal specimens from Arctic communities prior to the current outbreak, raising the possibility that human cryptosporidiosis occurred in Nunavik before 2013. The initial cases were detected because they were of sufficiently heavy burden to be visible to experienced technologists on iodine and iron-hematoxylin stained-specimens. The requirement for special laboratory procedures, lack of local diagnostic capacity in affected communities (up to 1,900 km north of Montreal, Qc), and low sensitivity of microscopy, likely result in underestimated disease burden in this region. Moreover, the public health significance of human cryptosporidiosis may go under-recognised because of a combination of prolonged shedding of oocysts from asymptomatic hosts and the fact that long-term developmental impacts in children are not limited to those with diarrhea.[5]

There are a number of limitations to this study. First, the original source of the Cryptosporidium oocysts that caused the outbreak remains unknown. It is possible that seasonal outbreaks have gone unrecognised in the past because of health-seeking behaviours and barriers to appropriate diagnostic testing. Secondly, only laboratory-confirmed cases were included, leading to a likely underestimation of the scope of the outbreak. Thirdly, logistic and geographic obstacles prevented a formal case-control study and the collection of detailed information about possible disease exposures. Available data was limited to questions about contact with a suspected case (before or after disease onset) and travel outside the village of residence, and it proved very difficult to obtain the necessary information from all the respondents. Finally, we were able to perform molecular characterisation of only a subset of outbreak stools because it proved difficult to encourage clinicians and patients to provide additional unpreserved stool specimens for PCR. The latter point proved a key limitation for rapid characterisation of this outbreak and illustrates the need for innovation in point-of-care specimen collection techniques for enteric infections.

In summary, we describe an outbreak of cryptosporidiosis in a region where no Cryptosporidium transmission was reported before. In addition, we identified an anthroponotic genospecies of Cryptosporidium in the Arctic, with epidemiologic features that suggest sustained person-to-person transmission as is more typically seen in low-income countries than elsewhere in North-America. Finally, the heavy burden of neglected parasitic diseases affecting Inuit communities has been well described [22], and this work adds Cryptosporidium to their ranks. The high IR of the Nunavik outbreak and the recent recognition of widespread human cryptosporidiosis in neighbouring Nunavut [23] are cause for considerable concern about the possible long-term effects on growth and development of children in Inuit communities facing myriad other challenges. Though repeated enteric infections are thought to be prevalent in these regions [24], little data currently inform our understanding of their clinical burden and etiologic spectrum. Such data are needed for the development of preventive strategies that take into account human practices and environmental changes that disproportionately affect the Arctic.