4.3.1. Co-infected Ticks on Birds
During spring and fall migrations, ground-foraging migrants make stopovers at select meadows and sylvatic areas to consume seeds, berries, and invertebrates. These energy-laden morsels include spent gravid
I. scapularis females that have laid eggs, and have died. These tick habitats are also commonly inhabited with small mammals (i.e., deer mice, meadow voles, eastern chipmunk, shrews) that act as hosts for immature life stages of blacklegged ticks and
I. muris ticks [
14,
48,
61,
77]. Several researchers indicate that
I. scapularis are directly connected to
B. odocoilei [
39,
40,
41,
78], and denote that
B. odocoilei overlaps with the distribution range of
I. scapularis and white-tailed deer. Meadows and wooded areas are community-centered foci where deer, small mammals, ground-dwelling songbirds congregate, and form enzootic hubs for the enzootic transmission cycle of Bbsl and
B. odocoilei. Within these tick-conducive habitats,
I. scapularis ticks and white-tailed deer play a pivotal role in perpetuating
B. odocoilei.
A heavily infested songbird can initiate an established population of blacklegged ticks [
32]. Whenever juvenile songbirds are infested with
I. scapularis ticks, these tick collections clearly indicate that an established population is present. For example, ground-frequenting songbirds, such as the Rose-breasted Grosbeak, provide short-distance dispersal of ticks during the nesting and fledgling period (
Figure 7).
4.3.2. Co-infected Ticks on Terrestrial Mammals
The co-infection of
B. microti and Bbsl in an
I. cookei nymph collected from a cat at Site 3 is a first-time event. Not only is
B. microti reported for the first time in
I. cookei, it is the initial documentation of
B. microti in Western Ontario. Of note, these two zoonotic pathogens are typically reported in blacklegged ticks [
79], but not in
I. cookei. Importantly,
I. cookei bites humans [
22,
73,
80,
81,
82], and this present study signifies that this cat-derived
I. cookei could have simultaneously transmit these two tick-borne, zoonotic pathogens (e.g.,
B. microti and Bbsl) to companion animals or people [
2,
4,
69,
83]. Often domestic cats will have a subclinical Bbsl infection; however, they may have various symptoms including lethargy, lameness, irregular gait, pain on manipulation of hips and tail (hip and/or tail pain). They may also be subdued, depressed, and have inappetence (lack of desire or appetite), and/or have severe ataxia of hind legs [
83].
The
B. microti sequence detected in a cat-derived
I. cookei nymph matches closely with a
B. microti amplicon (GenBank accession number AF5446902) from a skunk in Massachusetts. Based on phylogenetic analysis, this strain is a carnivore-associated
B. microti, and not a rodent-associated
B. microti strain [
84]. Even though Barrie, Ontario is 690 km from Massachusetts, the two related
B. microti strains are congruent with each other. Not only are there carnivore- and rodent-associate strains, there are several raccoon-associated strains [
84]. Although
B. microti is widely reported in blacklegged ticks in the USA, it was previously not reported in
I. cookei in Canada. Most notably,
B. microti is reported in
I. cookei which suggests that this piroplasm is cycling enzootically with groundhogs (woodchucks),
Marmota monax. Ecologically,
B. microti has been isolated from white-footed mice (
Peromyscus leucopus) captured in Connecticut [
85]. All three motile life stages of
I. cookei feed on groundhogs, and are likely a reservoir host of
B. microti. After the nymph–adult molt, this female could have transmitted Bbsl and
B. microti to a human. Not only do
I. cookei ticks carry and transmit deer tick virus (Powassan group virus) [
86], they also harbour
Babesia microti and Bbsl. Since
I. cookei is a human-biting tick, it can act as an ecological bridge for
B. microti between reservoir hosts (i.e., groundhogs, coyotes, skunks, raccoons) to humans and, therefore, this tick species is of epidemiological significance [
80,
82].
In North America,
B. odocoilei is commonly associated with
I. scapularis ticks [
57] and, also, white-tailed deer [
57,
78]. White-tailed deer are hosts of all three motile life stages (larvae, nymphs, adults) of
I. scapularis, and support the reproduction of
I. scapularis. In contrast to Bbsl spirochetes,
I. scapularis and cervine hosts both facilitate the enzootic transmission cycle of
B. odocoilei. White-tailed deer are reservoir hosts of
B. odocoilei; however, they are refractory to Lyme disease spirochetes [
87].
In southern Manitoba, we report a
H. leporispalustris tick infected with both a
B. divergens-like piroplasm and, also, a
Borrelia lanei-like spirochete (
Table 2 and
Table 3). This discovery marks the first report of a
Babesia divergens-like piroplasm in Canada. Although
H. leporispalustris ticks rarely bite humans [
88], this tick species can transmit this piroplasm to lagomorphs and domestic animals, such as cats and dogs. Banerjee et al. documented Bbsl in
H. leporispalustris ticks that were collected from a snowshoe hare (
Lepus americanus) in northern Alberta [
89]. In addition, Scott et al. reported Bbsl in
H. leporispalustris collected from songbirds [
22]. Reports of human cases with high levels of parasitemia caused by
B. divergens-like microorganisms include residents of Missouri, Kentucky, Washington, Arkansas, Massachusetts, and Michigan [
90]. In the latter case, Herc et al. reported an asplenic Michigan patient infected with a
B. divergens-like/MO-1 piroplasm, and this 60-year-old lady experienced fatigue, nausea, and hemolytic febrile symptoms [
90]. Not only have
B. divergens-like infections been identified in the blood and spleen of eastern cottontail rabbits, they have also been detected in rabbit-associated ticks,
I. dentatus, on Nantucket Island, Massachusetts, USA [
91]. Both immature stages of
I. dentatus and
H. leporispalustris feed on migratory birds, and facilitate the wide dispersal of infected ticks across North America. Based on DNA sequence assessment,
B. odocoilei and
B. divergens-like piroplasms are closely related to
B. divergens in the
Babesia sensu stricto clade. In Europe,
B. divergens is noted as the most common cause of human babesiosis, and can be fatal [
6,
57].
Both
B. divergens-like species and
B. lanei-like strains have a direct connection to lagomorphs. In fact,
B. lanei (formerly
Borrelia genomospecies 2) was detected in
Ixodes spinipalpis and
Ixodes pacificus (western blacklegged tick) ticks collected from eastern cottontails (
Sylvilagus floridanus) and snowshoe hares, respectively, in southwestern British Columbia [
92]. Since
H. leporispalustris larvae and nymphs parasitize migratory songbirds,
B. lanei-like spirochetes and
B. divergens-like piroplasms could have been transported by songbird-transported ticks across the US-Canada border during northbound migratory flights. Biogeographically, the
B. lanei-like spirochete is documented for the first time in Canada east of the Rocky Mountains.