Prevalence of the zoonotic diseases Leptospirosis and Borreliosis in the Maritimes of Canada

Abstract

Leptospirosis and Lyme borreliosis are two globally important infectious diseases caused by the transmission of either the Leptospira spirochaete or the Borrelia spirochaete, respectively. Although the spirochaetes have similarities in their shape, size, and movement, their transmission to animals is quite different. Infection of pathogenic leptospires requires environmental exposure to infected water or soil. The main route of exposure is through mucous membranes, such as drinking from infected water sources. Once infected, some of the leptospires remain in the host’s body and replicate, whereas others pass through the renal tubules to be shed back into the environment through the individual’s urine, continuing the infectious cycle. Borrelia infection, on the other hand, is a tick-borne disease in which an individual becomes infected through the bite of an infected tick. The risk of contracting leptospirosis in Canada has been increasing over the last 30 years, with New Brunswick reporting an increase in infected dogs, an important sentinel species for the infection, with fatal outcomes. To determine the prevalence of Leptospira spp. in the province, multiple methodologies and areas of interest were examined. Three methodologies (centrifugation, filtration, and growth in media) were attempted to detect leptospires in stagnant water sources around areas of recent flooding events. Unfortunately, all three methods returned negative results, although it is unclear if they were unsuccessful in finding the leptospires or if the leptospires were not present in these samples. Molecular testing of local wildlife necropsies, including suspected maintenance hosts as well as accidental hosts, and ticks was carried out. Testing small mammals showed 3.2% specimens were positive for Leptospira borgpetersenii. Testing large mammals showed 1.8% positive for L. borgpetersenii. Infected animals included moose (Alces alces), snowshoe hare (Lepus americanus), meadow vole (Microtus pennsylvanicus), jumping mouse (Napaeozapus insignis), deer mouse (Peromyscus maniculatus), maritime shrew (Sorex maritimensis), and black bear (Ursus americanus). Testing of ticks (Dermacentor variabilis, Ixodes cookei, and Ixodes scapularis) showed 3.6% were positive for L. borgpetersenii. Finally, dog serum was collected from 14 veterinary hospitals across the province with 19.3% testing positive for the presence of antibodies against Leptospira spp. Together, these results elucidate a widespread rate of infection in the wildlife species, sentinel species, and tick species of New Brunswick. The risk of contracting Lyme borreliosis in New Brunswick has also been increasing over the last few years due to expanding tick populations. The risk of transmission of Borrelia species, such B. bissettiae, through the bite of an infected tick within New Brunswick began with the identification of the bacteria in local tick species, yet transmission of B. bissettiae to local wildlife species was still unknown. Of the small wildlife species tested in this study, one meadow vole (M. pennsylvanicus) and one deer mouse (P. maniculatus) were sequence positive for B. bissettiae. Of the large mammals tested, none were positive for the presence of B. bissettiae. This evidence suggests that the bacteria has established maintenance hosts, but evidence for the ability to infect accidental hosts has not yet been found in New Brunswick. Understanding the risk of infection by Borrelia spp. of our local wildlife species becomes directly relevant to human health, as it can cause Lyme disease in humans. In its disseminated form, it can affect organs such as the heart, causing what is known as Lyme carditis, a rare but potentially fatal outcome when diagnoses are missed. This thesis presents a case of fatal severe heart disease following suspected untreated Lyme carditis of a 17-year-old female from Nova Scotia, Canada. Formalin fixed paraffin embedded sections of the heart, lung, kidney, adrenals, and pancreas showed florescent structures through immunohistochemistry staining in similar size and shape of Borrelia bacteria. Due to the nature of these samples, however, these findings could not be confirmed through polymerase chain reaction followed by Sanger sequencing and therefore cannot be confirmed as Borrelia.