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A molecular epidemiological analysis of the incursion of the raccoon strain of rabies virus into Canada - PubMed

A molecular epidemiological analysis of the incursion of the raccoon strain of rabies virus into Canada

S A Nadin-Davis et al. Epidemiol Infect. 2006 Jun.

Abstract

Three physically separate incursions of the raccoon strain of rabies have entered Canada, two into eastern Ontario in 1999 and one into New Brunswick in 2000. The course of these epizootics is described. Phylogenetic analysis of the index cases from these two provinces with raccoon rabies viruses representative of this strain in the United States supported the independence of these incursions into Canada via cross-border transmission from the United States. Genetic characterization of 190 isolates from these two Canadian provinces over a 550-bp region of the variable central portion of the viral P gene distinguished 14 variants in Ontario and five in New Brunswick although in both regions the variant represented by the initial case was most commonly encountered. The quasi-species nature of the Ontario virus was analysed using isolates taken at different times during the main outbreak to examine whether viral variation was increasing with time as well as changing in nature. These data provide a framework for study of future incursions of this rabies strain into Canada.

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Figures

Fig. 1
Fig. 1

Map of the Ontario raccoon rabies epizootic area showing density of cases reported over the study period. The inset map of the province of Ontario identifies the region of eastern Ontario affected by raccoon rabies. The density of raccoon rabies cases is illustrated in the main map as a grey scale using the density scale at bottom right. Locations of communities mentioned in the text are also shown.

Fig. 2
Fig. 2

Map of the New Brunswick raccoon rabies epizootic area showing density of cases reported over the study period as for Figure 1. The inset map of New Brunswick province identifies the affected region shown in the main map.

Fig. 3
Fig. 3

Quarterly number of raccoon strain rabies cases in Ontario (▪) and New Brunswick (□).

Fig. 4
Fig. 4

Phylogeny of 19 rabies viruses, and an Australian bat lyssavirus isolate used as an outgroup, using a NJ algorithm applied to complete P gene coding sequences. The two raccoon rabies isolates first recovered in the provinces of Ontario and New Brunswick were compared to 17 other rabies viruses representative of the main variants circulating in the United States and Canada. Apart from the sequence of an isolate recovered from a big brown bat in Connecticut (CTV569.BBB), the P gene sequences of these additional isolates have been described previously [21]. Bootstrap values out of 1000 replicates are indicated for major branches and the distance scale is indicated at bottom left.

Fig. 5
Fig. 5

Phylogeny of 11 raccoon rabies viruses as determined using their complete P gene coding sequences with a NJ algorithm and the

dnadist

program. Bootstrap values out of 1000 replicates are indicated for most branches. An isolate of the arctic fox strain was used as an outgroup and its distance with respect to the raccoon viruses has been reduced (dashed line) to better illustrate the branching patterns of the raccoon isolates.

Fig. 6
Fig. 6

Alignment of the predicted P proteins of 11 raccoon rabies viruses using the sequence of the Ontario index case as reference. Dots represent identity with the reference sequence.

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