Active and passive surveillance and phylogenetic analysis of Borrelia burgdorferi elucidate the process of Lyme disease risk emergence in Canada.
BACKGROUND
Northward expansion of the tick Ixodes scapularis is driving Lyme disease (LD) emergence in Canada. Information on mechanisms involved is needed to enhance surveillance and identify where LD risk is emerging.


OBJECTIVE
We used passive and active surveillance and phylogeographic analysis of Borrelia burgdorferi to investigate LD risk emergence in Quebec.


METHODS
In active surveillance, we collected ticks from the environment and from captured rodents. B. burgdorferi transmission was detected by serological analysis of rodents and by polymerase chain reaction assays of ticks. Spatiotemporal trends in passive surveillance data assisted interpretation of active surveillance. Multilocus sequence typing (MLST) of B. burgdorferi in ticks identified likely source locations of B. burgdorferi.


RESULTS
In active surveillance, we found I. scapularis at 55% of sites, and we were more likely to find them at sites with a warmer climate. B. burgdorferi was identified at 13 I. scapularis-positive sites, but infection prevalence in ticks and animal hosts was low. Low infection prevalence in ticks submitted in passive surveillance after 2004-from the tick-positive regions identified in active surveillance-coincided with an exponential increase in tick submissions during this time. MLST analysis suggested recent introduction of B. burgdorferi from the northeastern United States.


CONCLUSIONS
These data are consistent with I. scapularis ticks dispersed from the United States by migratory birds, founding populations where the climate is warmest, and then establishment of B. burgdorferi from the United States several years after I. scapularis have established. These observations provide vital information for public health to minimize the impact of LD in Canada.
Ogden
Nicholas H
NH
Centre for Food-Borne, Environmental and Zoonotic Infectious Diseases, Public Health Agency of Canada, Saint-Hyacinthe, Québec, Canada. nicholas_ogden@phac-aspc.gc.ca
Bouchard
Catherine
C
Kurtenbach
Klaus
K
Margos
Gabriele
G
Lindsay
L Robbin
LR
Trudel
Louise
L
Nguon
Soulyvane
S
Milord
François
F
D000818:Animals; D025065:Borrelia burgdorferi / Q000145:classification / Q000235:genetics*; D016000:Cluster Analysis; D021821:Communicable Diseases, Emerging / Q000453:epidemiology* / Q000382:microbiology; D003710:Demography; D014644:Genetic Variation; D006801:Humans; D018884:Ixodes / Q000382:microbiology*; D016015:Logistic Models; D008193:Lyme Disease / Q000453:epidemiology* / Q000382:microbiology; D010802:Phylogeny; D011159:Population Surveillance / Q000379:methods; D011792:Quebec / Q000453:epidemiology; D012377:Rodentia / Q000469:parasitology*; D017422:Sequence Analysis, DNA; D013984:Tick Infestations / Q000453:epidemiology / Q000662:veterinary*