The geographic distribution and genetic variation of Echinococcus multilocularis in Canada
Date
2013-01-29
Authors
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Journal ISSN
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ORCID
Type
Degree Level
Masters
Abstract
Echinococcus multilocularis, Leuckart, 1863, is a small cestode that averages 4mm in length. It utilizes carnivores and rodents as definitive and intermediate hosts, respectively, and is
increasing in distribution and prevalence in people and animals across its circumpolar range. The
inadvertent ingestion of infectious eggs by people results in alveolar hydatid disease. The larval stage grows throughout liver like a metastatic tumour and if left untreated has an extremely high
fatality rate. While early diagnosis is difficult, due to a long latency period, it is paramount to patient survival.
Until recently, E. multilocularis received very little attention outside Europe, Asia and Alaska, primarily due to the number of human infections in those areas. The recent discovery of a European strain in British Columbia and a seemingly increased presence in Canadian urbanbased wildlife, however, has raised alarms, as increased zoonotic potential may be associated with strains of Eurasian origin. Identification of areas of potential risk for infection by Echinococcus species often
involves a survey of wild animals. The recommended method for the extraction of adult cestodes is the sedimentation and scraping technique (SCT), which requires an hour of sedimentation per
sample. A new method of extraction, the scraping, filtration and counting technique (SFCT), was developed to increase the efficiency and decrease the time associated with extraction of cestodes from the small intestines of carnivore hosts. A comparison of SFCT and SCT was performed.
The SFCT took an average of 8.5 minutes less to quantify than the SCT, not including the onehour
sedimentation, which is a significant decrease (p = 0.0001, ! = 0.05). There was no significant difference in adult cestode count between the two methods (p = 0.801, ! = 0.05);
however, SCT had a sensitivity of 91% and a negative predictive value of 97% when compared
to SFCT. Therefore, SFCT is more sensitive and decreases time required for the extraction of adult cestodes from carnivore intestines.
SFCT was used to investigate the potential establishment of E. multilocularis in wild carnivores in Quesnel, BC, Canada as follow-up to the discovery of a European strain in a BC
dog in 2009. SFCT was used to identify infection prevalence in 10 of 33 carnivores collected within 80 km of Quesnel. Analysis of four mitochondrial loci (nad1, nad2, cob and cox1)
indicates that the same strain was infecting the domestic dog and the wild carnivores, implying local transmission of this parasite. This study confirms the establishment of this parasite in local
wildlife and is the first report of E. multilocularis in the Boreal forest habitat previously considered incapable of supporting sufficient rodent densities for life cycle requirements. This is
also the first report of a European-type strain of E. multilocularis in North American wildlife. This finding highlighted the lack of understanding of the current diversity and origins of
E. multilocularis in North America, which has been hampered by early impressions of low genetic diversity within E. multilocularis. The currently documented haplotypes found in North America are based on findings from Alaska and the contiguous United States without sampling from the intervening region in northwestern Canada. In this study, analysis of the mitochondrial
gene nad1 revealed seven previously unrecognized haplotypes, undermining the reasoning that this gene does not hold significant variation. The newly identified haplotypes were found in BC,
SK and Nunavut (NU). All haplotypes (B-H) displayed distinct geographic associations with the exception of haplotype A, which had a broad distribution within North America and was
identical to sequences reported from Europe and Asia. This illustrates the need for large-scale geographic sampling when determining genetic polymorphisms, or mutations, and generates hypotheses about the origins and movements of this parasite and its hosts across the circumpolar
north. A second European strain was recovered from a coyote in Saskatoon, SK, which was remarkably different from published sequences. There were six nucleotide mutations between its
closest European relation (E4) and seven differences between it and the European haplotype found in BC wildlife. In addition, seven samples resulted in six unique haplotypes were detected
in SK deer mice. Four additional mouse samples were identical to the N2 North American strain, present in the northcentral United States.
Identification of areas of endemicity or newly established foci for this parasite may be a step towards mitigating the risk of human disease. In southern Saskatchewan, 8% of 516 adult
and subadult deer mice collected in 2009, and 2% of 252 in 2010, had alveolar hydatid cysts confirmed using both morphological and molecular identification techniques. There was no
difference in infection prevalence between male and female mice. A slightly higher prevalence in
infected mice was found in native and hay field habitat types, compared to active croplands. Flintoft was an area of increased focus, with a site prevalence of 26%. Therefore, areas with higher risk of transmission are present within agriculturally altered landscapes, which may have significance for both animal and human health as this parasite continues to emerge worldwide.
Description
Keywords
zoonoses, cestode, public health
Citation
Degree
Master of Science (M.Sc.)
Department
Veterinary Microbiology
Program
Veterinary Microbiology