Semi-field evaluations of three botanically derived repellents against the blacklegged tick, Ixodes scapularis (Acari: Ixodidae)

Three compounds derived from botanicals sources, ethyl perillyl carbonate, geranyl isovalerate, and citronellyl cyclobutane carboxylate, were tested for repellent activity against Ixodes scapularis Say in a semi-field trial. Tick drags were treated with the compounds or with N, N-diethyl-m-toluamide (DEET) at high (0.25mg/cm2) or low (0.15mg/cm2) concentrations. Negative controls included untreated drags and drags treated with acetone, the carrier for all repellents. Freshly treated drags (within 20 minutes) were used to collect I. scapularis ticks at a county park in Wisconsin. To assess effectiveness, we measured tick encounter rates, detachment rate, and time to detachment. None of the repellent treatments resulted in significantly fewer encounters compared to both control treatments. However, the percentage of ticks that detached within 3 min was significantly higher on drags treated with repellents compared to controls. DEET was the most effective, repelling 69.7 - 87% of ticks by 3 min, but the effectiveness of the three test compounds was still high, ranging from 42% to 87% of ticks detaching by 3 min. For time to detachment, there were no significant differences between DEET and the three test compounds. We conclude that these botanically-derived repellents were effective against I. scapularis in a semi-field trial and could be viable alternatives to DEET.

1198. Lyme Disease Post-Exposure Prophylaxis by Single-Dose Doxycycline in Three Healthcare Systems

Background Lyme disease, the most common tickborne disease in the United States, may be prevented by taking a single 200-mg dose of oral doxycycline after a high-risk bite from a blacklegged tick. Currently, it is not known how Lyme disease post-exposure prophylaxis (PEP) might vary by region and healthcare system. We identified single-dose doxycycline medication orders in three healthcare systems in states with high incidence of Lyme disease and compared associated patient and provider characteristics. Methods Electronic health record data during 2012 – 2016 were obtained from three healthcare systems: Geisinger (Pennsylvania), Marshfield Clinic (Wisconsin), and Mayo Clinic (Minnesota/Wisconsin). Creation of analytic variables and analysis were harmonized across the three sites. Medication orders for single-dose doxycycline ≤200 mg that were accompanied by specific key words or diagnostic codes (e.g., tick bite; Lyme disease prevention) were considered evidence of PEP. Manual chart review was performed from a random subset to evaluate the algorithms used to identify PEP. Results Among 2,937,585 patients with at least one medication order or clinical encounter during the study period, 14,102 single-dose doxycycline orders for Lyme disease PEP for 13,172 unique patients were identified. The typical patient receiving PEP was older (mean age 51 – 58 years), male (56 – 59%), and non-Hispanic White (81 – 98%). The annual seasonality of medication orders was bimodal, with peaks occurring during April – July and October – November. The most common encounter setting was an outpatient clinic or urgent care center (80 – 91%); medication orders after patient phone calls in the absence of an in-person visit occurred frequently (14 – 19%) in two health systems. Chart abstractions (n=600) revealed instances of PEP prescribed inappropriately (e.g., bite from a non-blacklegged tick; patient with symptoms of acute Lyme disease). Conclusion Lyme disease PEP with a single dose of doxycycline was frequently prescribed in healthcare systems where there is a high incidence of Lyme disease. PEP was most commonly prescribed to non-Hispanic Whites over the age of 50 years. Public health initiatives for tickborne disease prevention should include clinician education on the appropriate use of Lyme disease PEP. Disclosures Anna M. Schotthoefer, PhD, HelixBind (Other Financial or Material Support, salary support) John Zeuli, PharmD, INSMED (Other Financial or Material Support, honoraria for educational speaking)

Tick Cell Culture Analysis of Growth Dynamics and Cellular Tropism of Rickettsia buchneri, an Endosymbiont of the Blacklegged Tick, Ixodes scapularis

The blacklegged tick, Ixodes scapularis, a species of significant importance to human and animal health, harbors an endosymbiont Rickettsia buchneri sensu stricto. The symbiont is largely restricted to the ovaries, but all life stages can harbor various quantities or lack R. buchneri entirely. The endosymbiont is cultivable in cell lines isolated from embryos of Ixodes ticks. Rickettsia buchneri most readily grows and is maintained in the cell line IRE11 from the European tick, Ixodes ricinus. The line was characterized by light and electron microscopy and used to analyze the growth dynamics of wildtype and GFPuv-expressing R. buchneri. qPCR indicated that the genome copy doubling time in IRE11 was >7 days. Measurements of fluorescence using a plate reader indicated that the amount of green fluorescent protein doubled every 11 days. Two 23S rRNA probes were tested via RNA FISH on rickettsiae grown in vitro and adapted to evaluate the tissue tropism of R. buchneri in field-collected female I. scapularis. We observed strong positive signals of R. buchneri in the ovaries and surrounding the nucleus of the developing oocytes. Tissue tropism in I. scapularis and in vitro growth dynamics strengthen the contemporary understanding of R. buchneri as a transovarially transmitted, non-pathogenic endosymbiont.

Ehrlichia and Anaplasma

Ehrlichia and Anaplasma are bacteria that cause diseases, known as ehrlichiosis and anaplasmosis, in humans and other animals. Ehrlichia and Anaplasma are primarily transmitted through the bites of infected hard ticks, such as the lone star tick, the blacklegged tick, and the American dog tick. This publication describes the various forms of ehrlichiosis and anaplasmosis and the tick vectors.

Monitoring the patterns of submission and presence of tick-borne pathogens in Ixodes scapularis collected from humans and companion animals in Ontario, Canada (2011–2017)

Background The universal nature of the human–companion animal relationship and their shared ticks and tick-borne pathogens offers an opportunity for improving public and veterinary health surveillance. With this in mind, we describe the spatiotemporal trends for blacklegged tick (Ixodes scapularis) submissions from humans and companion animals in Ontario, along with pathogen prevalence. Methods We tested tick samples submitted through passive surveillance (2011–2017) from humans and companion animals for Borrelia burgdorferi, Borrelia miyamotoi, Anaplasma phagocytophilum and Babesia microti. We describe pathogen prevalence in ticks from humans and from companion animals and constructed univariable Poisson and negative binomial regression models to explore the spatiotemporal relationship between the rates of tick submissions by host type. Results During the study, there were 17,230 blacklegged tick samples submitted from humans and 4375 from companion animals. Tick submission rates from companion animals were higher than expected in several public health units (PHUs) lacking established tick populations, potentially indicating newly emerging populations. Pathogen prevalence in ticks was higher in PHUs where established blacklegged tick populations exist. Borrelia burgdorferi prevalence was higher in ticks collected from humans (maximum likelihood estimate, MLE = 17.5%; 95% confidence interval, CI 16.97–18.09%) than from companion animals (9.9%, 95% CI 9.15–10.78%). There was no difference in pathogen prevalence in ticks by host type for the remaining pathogens, which were found in less than 1% of tested ticks. The most common co-infection B. burgdorferi + B. miyamotoi occurred in 0.11% of blacklegged ticks from humans and animals combined. Borrelia burgdorferi prevalence was higher in unengorged (21.9%, 95% CI 21.12–22.65%) than engorged ticks (10.0%, 95% CI 9.45–10.56%). There were no consistent and significant spatiotemporal relationships detected via regression models between the annual rates of submission of each host type. Conclusions While B. burgdorferi has been present in blacklegged ticks in Ontario for several decades, other tick-borne pathogens are also present at low prevalence. Blacklegged tick and pathogen surveillance data can be used to monitor risk in human and companion animal populations, and efforts are under consideration to unite surveillance efforts for the different target populations. Graphic Abstract

First Report of Ixodes scapularis Ticks Parasitizing a North American Porcupine in Canada

Adult females of the blacklegged tick, Ixodes scapularis (Acari: Ixodidae), were collected from a North American porcupine, Erethizon dorsatum, in eastern Ontario, Canada. This porcupine parasitism indicates that an established population of I. scapularis is present in the local vicinity. This tick species is known to parasitize more than 150 different vertebrate hosts, including the North American porcupine. The presence of I. scapularis ticks parasitizing a North American porcupine constitutes a new tick-host record in Canada.

No Evidence of Competition Between the Blacklegged Tick (Acari: Ixodidae) and American Dog Tick on the Rodent Host White-Footed Deermouse (Rodentia: Cricetidae) in Southwestern Tennessee

Investigations that analyze interspecific associations of vectors on their hosts are important for understanding community structure and implementing ways to comprehend mechanisms of pathogen transmission. We assessed the interspecific association of two tick species (Ixodes scapularis Say (Ixodida: Ixodidae) and Dermacentor variabilis Say (Ixodida: Ixodidae)) on the rodent host Peromyscus leucopus Rafinesque (Rodentia: Cricetidae) at the Hobart Ames Research and Education Center in southwestern Tennessee. Of the rodents captured, 95 (63%) had neither species of tick, 6 (4%) had both tick species, 25 (16%) had I. scapularis only, and 26 (17%) had D. variabilis only. A coefficient of association (C7 = −0.08) was calculated, which suggested there was competition between the two species of ectoparasites, but this value was not significant, indicating that there was a neutral relationship between the tick species on P. leucopus. The co-occurrence of both tick species on their host at the same time suggested that the two tick species can occupy the same host and use the same resources without competing.