Active and Passive Surveillance – Analysis of Borrelia in Canada

Article:

Background: Northward expansion of the tick vector Ixodes
scapularis is driving Lyme disease (LD) emergence in Canada.
Information on mechanisms involved is needed to enhance
surveillance here, and identify where LD risk is emerging.
Objectives: Passive and active surveillance, and phylogeographic
analysis of Borrelia burgdorferi were used to investigate LD risk
emergence in Quebec.
Methods: In active surveillance, ticks were collected from the
environment and captured rodents. B. burgdorferi transmission was
detected by serological analysis of rodents and 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, I.
scapularis were found at 55% of sites, and were more likely to be
found 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 at this time. MLST
analysis suggested recent introduction of B. burgdorferi from
northeastern USA.
Conclusions: These data are consistent with I. scapularis ticks
dispersed from the USA, by migratory birds, founding populations
where the climate is warmest, then establishment of B.
burgdorferi from the USA several years after I.
scapularis have established. These observations provide vital
information for public health to minimize the impact of LD in
Canada.