Male C57BL/6J mice have higher presence and abundance of Borrelia burgdorferi in their ventral skin compared to female mice.

Borrelia burgdorferi is a tick-borne spirochete that causes Lyme disease in humans. The host immune system controls the abundance of the spirochete in the host tissues. Recent work with immunocompetent Mus musculus mice strain C3H/HeJ found that males had a higher tissue infection prevalence and spirochete load compared to females. The purpose of this study was to determine whether host sex and acquired immunity interact to influence the prevalence and abundance of spirochetes in the tissues of the commonly used mouse strain C57BL/6. Wildtype (WT) mice and their SCID counterparts (C57BL/6) were experimentally infected with B. burgdorferi via tick bite. Ear biopsies were sampled at weeks 4, 8, and 12 post-infection (PI) and five tissues (left ear, ventral skin, heart, tibiotarsal joint of left hind leg, and liver) were collected at necropsy (16 weeks PI). The mean spirochete load in the tissues of the SCID mice was 260.4x higher compared to the WT mice. In WT mice, the infection prevalence in the ventral skin was significantly higher in males (40.0 %) compared to females (0.0 %), and the spirochete load in the rear tibiotarsal joint was significantly higher (4.3x) in males compared to females. In SCID mice, the spirochete load in the ventral skin was 200.0x higher in males compared to females, but there were no significant sex-specific difference in spirochete load in the other tissues (left ear, heart, tibiotarsal joint, or liver). Thus, the absence of acquired immunity greatly amplified the spirochete load in the ventral skin of male mice. It is important to note that the observed sex-specific differences in laboratory mice cannot be extrapolated to humans. Future studies should investigate the mechanisms underlying the male bias in the abundance of B. burgdorferi in the mouse skin.

Clobetasol increases the abundance of Borrelia burgdorferi in the skin 70 times more in male mice compared to female mice.

Lyme borreliosis is caused by the spirochete Borrelia burgdorferi and is transmitted among vertebrate hosts by Ixodes scapularis ticks in eastern North America. Treatment with topical corticosteroids increases the abundance of B. burgdorferi in the skin of lab mice that have been experimentally infected via needle inoculation. In the present study, female and male C3H/HeJ mice were infected with B. burgdorferi via nymphal tick bite. Infected mice were treated with clobetasol on the skin of the right hindleg on days 35 and 36 post-infection and euthanized at days -2, 1, 3, 5, and 7 post-treatment; a group of control mice was infected but not treated with clobetasol. The spirochete abundance was quantified in 8 mouse tissues including bladder, heart, left hindleg skin, right hindleg skin, dorsal skin, ventral skin, left ear and right ear. Averaged across the 8 mouse tissues, the abundance of B. burgdorferi on days 3 and 5 were 21.4x and 14.4x higher in mice treated with clobetasol compared to the untreated control mice, but there were large differences among tissues. There was a dramatic sex-specific effect of the clobetasol treatment; the peak abundance of B. burgdorferi in the skin (left hindleg, right hindleg, dorsal, ventral) was 72.6x higher in male mice compared to female mice. In contrast, there was little difference between the sexes in the tissue spirochete load in the ears, bladder, and heart. Topical application of clobetasol could increase the sensitivity of direct diagnostic methods (e.g., culture, PCR) to detect B. burgdorferi in host skin biopsies.

Monitoring Risk: Tick and Borrelia burgdorferi Public Participatory Surveillance in the Canadian Maritimes, 2012-2020.

Ticks are vectors of many diseases, including Lyme disease (Ld). Lyme disease is an emerging disease in Canada caused by infection with the Lyme borreliosis (Lb) members of the Borrelia genus of spirochaete bacteria, of which Borrelia burgdorferi is regionally the most prevalent. The primary tick vector in central and eastern Canada, Ixodes scapularis, is increasing in numbers and in the geographical extent of established populations. This study documents the distribution of ticks recovered by passive surveillance, and their B. burgdorferi infection prevalence, in three Canadian Maritime provinces from 2012-2020. These regions represent areas in which tick populations are widely established, establishing, and considered non-established. Using a community science approach by partnering with veterinarians and members of the public, we collected over 7000 ticks from the 3 provinces. The three species found most often on companion animals and humans were I. scapularis (76.9%), Ixodes cookei (10.4%) and Dermacentor variabilis (8.9%). The most common hosts were dogs (60.5%), cats (16.8%) and humans (17.6%). As is typical of passive surveillance tick collections, the majority of ticks recovered were adult females; for I. scapularis 90.2%, 5.3%, 3.9% and 0.6% of the total of 5630 ticks recovered for this species were adult females, adult males, nymphs and larvae, respectively. The majority of B. burgdorferi-infected ticks were I. scapularis, as expected. Borrelia infection prevalence in I scapularis was higher in Nova Scotia (20.9%), the province with the most endemic regions, than New Brunswick (14.1%) and Prince Edward Island (9.1%), provinces thought to have established and non-established tick populations, respectively. The province-wide Borrelia infection prevalence generally increased in these latter tow provinces over the course of the study. The host did not have a significant effect on B. burgdorferi infection prevalence; I. scapularis ticks from dogs, cats, humans was, 13.3% (n = 3622), 15.6% (n = 817), 17.9% (n = 730), respectively. No I. scapularis larvae were found infected (n = 33) but B. burgdorferi was detected in 14.8% of both adults (n = 5140) and nymphs (n = 215). The incidence of B. burgdorferi infection also did not differ by engorgement status 15.0% (n = 367), 15.1% (n = 3101) and 14.4% (n = 1958) of non-engorged, engorged and highly engorged ticks, respectively, were infected. In New Brunswick, at the advancing front of tick population establishment, the province-wide infection percentages generally increased over the nine-year study period and all health district regions showed increased tick recoveries and a trend of increased percentages of Borrelia-infected ticks over the course of the study. Within New Brunswick, tick recoveries but not Borrelia infection prevalence were significantly different from endemic and non-endemic regions, suggesting cryptic endemic regions existed prior to their designation as a risk area. Over the 9 years of the study, tick recoveries increased in New Brunswick, the primary study region, and I. scapularis recoveries spread northwards and along the coast, most but not all new sites of recoveries were predicted by climate-based models, indicating that ongoing tick surveillance is necessary to accurately detect all areas of risk. Comparison of tick recoveries and public health risk areas indicates a lag in identification of risk areas. Accurate and timely information on tick distribution and the incidence of Borrelia and other infections are essential for keeping the public informed of risk and to support disease prevention behaviors.

Ixodes scapularis ticks and Borrelia burgdorferi on Prince Edward Island: Passive tick surveillance and canine seroprevalence.

Ticks and canine sera were submitted by veterinarians from Prince Edward Island over a 15-month period spanning 3 tick seasons. The objective of the study was to determine the infection prevalence of Borrelia burgdorferi, a causative agent of Lyme disease, in the province's ticks and the seroprevalence in its dogs. It was found that 97.8% (n = 368) of ticks submitted were Ixodes scapularis, a species capable of transmitting Borrelia burgdorferi; 10.3% of these ticks [95% confidence interval (CI): 3.6% to 17.0%] were infected. Provincial canine seroprevalence for the 199 submitted samples was estimated at 3.0% (95% CI: 1.0% to 5.1%).

Ixodes scapularis et Borrelia burgdorferi sur l'Île-du-Prince-Édouard : Surveillance passive des tiques et séroprévalence canine. Des tiques et du sérum canin furent soumis par des vétérinaires de l'Île-du-Prince-Édouard durant une période de 15 mois couvrant trois saisons de tiques. L'objectif de l'étude était de déterminer la prévalence d'infection à Borrelia burgdorferi, un agent causal de la maladie de Lyme, dans les tiques de la province et la séroprévalence chez les chiens. Il fut trouvé que 97,8 % (n = 368) des tiques soumises étaient Ixodes scapularis, une espèce capable de transmettre B. burgdorferi; et que 10,3 % de ces tiques [intervalle de confiance de 95 % (CI) : 3,6 % à 17,0 %)] étaient infectées. La séroprévalence canine provinciale pour les 199 échantillons soumis était estimée à 3,0 % (CI 95 % : 1,0 % à 5,1 %).(Traduit par Dr Serge Messier).