Prevalence and Geographic Distribution of Borrelia miyamotoi in Host-Seeking Ixodes pacificus (Acari: Ixodidae) Nymphs in Mendocino County, California

Abstract

Borrelia miyamotoi is an increasingly recognized human pathogen transmitted by Ixodes ticks in the Northern Hemisphere. In North America, infection prevalences of B. miyamotoi are characteristically low (<10%) in Ixodes scapularis (Say; Acari: Ixodidae) and Ixodes pacificus (Cooley & Kohls; Acari: Ixodidae), both of which readily bite humans. We tested 3,255 host-seeking I. pacificus nymphs collected in 2004 from 79 sites throughout Mendocino County in north-coastal California for presence of B. miyamotoi. The collection sites represented a variety of forest types ranging from hot, dry oak woodlands in the southeast, to coastal redwoods in the west, and Ponderosa pine and Douglas fir-dominated areas in the northern part of the county. We found that B. miyamotoi was geographically widespread, but infected I. pacificus nymphs infrequently (cumulative prevalence of 1.4%). Infection prevalence was not significantly associated with geographic region or woodland type, and neither density of host-seeking nymphs, nor infection with Borrelia burgdorferi sensu stricto was associated with B. miyamotoi infection status in individual ticks. Because B. burgdorferi prevalence at the same sites was previously associated with woodland type and nymphal density, our results suggest that despite sharing a common vector, the primary modes of enzootic maintenance for the two pathogens are likely different.

Phylogeography of Borrelia spirochetes in Ixodes pacificus and Ixodes spinipalpis ticks highlights differential acarological risk of tick-borne disease transmission in northern versus southern California

“…miyamotoi is found in approximately 1% of I . pacificus nymphs and adults in California [12, 54]. While there is evidence of B .…”

A new Borrelia on the block: Borrelia miyamotoi – a human health risk?

“…Among 20 studies found in this review, from countries reporting clinical cases and B. miyamotoi prevalence in ticks, infectionrates in ticks ranged from 0.02 to 6.4%, although most studies reported a range between 1 and 2% (Table 1) [3,5,15,18,19]. Nevertheless, pockets of higher infection rates have been described.…”

“…Nevertheless, pockets of higher infection rates have been described. In Napa County, California, US, for example, 15.4% of adult ticks (10/65 I. pacificus ) studied were infected with B. miyamotoi [3] compared with a background infection level of 1.4% (44/3,255) of nymphs of this same species [19]. Moreover, in a study in Kurgan, Russia, 16% of ticks (26/162 I. persulcatus ) were found infected [2].…”

“…For example, subsequent to a study finding 264/5,431 (4.9%) B. burgdorferi sensu stricto in nymphal I. pacificus ticks, a subset of 3,255 ticks was retested for B. miyamotoi . A total of 44 (1.4%) ticks were infected B. miyamotoi alone, and only one single individual with B. burgdorferi sensu stricto was also found co-infected with B. miyamotoi [19,47]. On the other hand, among I. scapularis ticks from Midwestern US, Hamer et al report a 2.1 times lower level of co-infection with B. burgdorferi and B. miyamotoi (0.05% co-infection among 1,565 questing adult ticks) than expected by chance [48].…”

“…Remarkably, the prevalence of B. miyamotoi infection in ticks appears indifferent to variations in the habitat type, or to ecological influences that impact upon the prevalence of B. burgdorferi s.l. [19]. As nutritional requirements are likely to overlap, is there antagonism between these species, indifference or a more synergistic relationship?…”