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Tick-borne diseases are a growing threat to public health in the United States, especially among outdoor workers who experience high occupational exposure to ticks. Long-lasting permethrin-impregnated clothing has demonstrated high initial protection against bites from blacklegged ticks, Ixodes scapularis Say (Acari: Ixodidae), in laboratory settings, and sustained protection against bites from the lone star tick, Amblyomma americanum (L.) (Acari: Ixodidae), in field tests. However, long-lasting permethrin impregnation of clothing has not been field tested among outdoor workers who are frequently exposed to blacklegged ticks. We conducted a 2-yr randomized, placebo-controlled, double-blinded trial among 82 outdoor workers in Rhode Island and southern Massachusetts. Participants in the treatment arm wore factory-impregnated permethrin clothing, and the control group wore sham-treated clothing. Outdoor working hours, tick encounters, and bites were recorded weekly to assess protective effectiveness of long-lasting permethrin-impregnated garments. Factory-impregnated clothing significantly reduced tick bites by 65% in the first study year and by 50% in the second year for a 2-yr protective effect of 58%. No significant difference in other tick bite prevention method utilization occurred between treatment and control groups, and no treatment-related adverse outcomes were reported. Factory permethrin impregnation of clothing is safe and effective for the prevention of tick bites among outdoor workers whose primary exposure is to blacklegged ticks in the northeastern United States., (© The Author(s) 2020. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Several methods of extracting DNA from ticks were examined to improve the efficiency of polymerase chain reaction (PCR) detection of the human granulocytic ehrlichiosis (HGE) agent. DNA was extracted from laboratory-reared uninfected and HGE-infected ticks using 3 separate methods. In one treatment, unfed nymphs and engorged larvae of Ixodes scapularis Say, either individually or in pools of 3, were homogenized in 40 microliters of 1x PCR buffer and boiled for 30 min. A 2nd group of ticks was extracted using the QiaAmp Tissue kit, a silica column separation method. A 3rd group was extracted with DNA-STAT, a guanidinium thiocynate method. Five microliters of each extract was used for PCR amplification. Pathogen-free tick DNA samples did not amplify a product. Laboratory-infected ticks extracted either with the QiaAmp kit or those homogenized and boiled in PCR buffer amplified product in 37.5% and 87.5% of the samples, respectively. Infected ticks extracted with DNA STAT-60 amplified a product in 100% of samples. No differences were observed in detection efficiency between ticks tested singly or in pools.

Zoonotic prevalence of Babesia microti Franca piroplasms infecting white-footed mice, Peromyscus leucopus Rafinesque, was determined at 34 sites in Rhode Island where nymphal blacklegged tick, Ixodes scapularis Say, densities ranged from low to hyperabundant (1.7-525.3 nymphs per hour of flagging). Babesia was only detected at sites where tick abundance was moderate to high (> 20 nymphs per hour of flagging) and appeared to exhibit a clumped distribution. Where B. microti was detected, the mean number of nymphal ticks collected per hour of flagging was 229.2 compared with a mean of 40.1 at sites where Babesia was not detected. By combining the spatial occurrence of Babesia with a tick density database in a geographic information system, it may be possible to predict the pattern of zoonotic and human infection with B. microti.

The duration of tick attachment is one factor associated with risk for human infection caused by several tick-borne pathogens. We measured tick engorgement indices at known time intervals after tick attachment and used these indices to determine the length of time that ticks were attached to tick-bite victims in selected Rhode Island and Pennsylvania communities where the agents of Lyme disease and human babesiosis occur. The total body length and width as well as the length and width of the scutum were measured on nymphal and adult female Ixodes scapularis Say removed from laboratory animals at 0, 12, 24, 36, 48, 60, and 72 h after their attachment. Three engorgement indices were calculated at each time interval. In addition, engorgement indices measurements were recorded for 504 ticks submitted to a commercial laboratory for pathogen detection testing between 1990 and 1992. No detectable change was observed in the average engorgement indices for either nymphal or adult ticks between 0 and 24 h of attachment using any of the engorgement indices. After 24 h of tick attachment, all engorgement indices continuously increased: average indices for nymphs attached 36, 48, and 60 h were significantly different from those attached < or = 24 h and from each other. Similarly, average engorgement indices for adult ticks attached < or = 36 h were significantly different from those attached for 48 h or more. More than 60% of tick-bite victims removed adult ticks by 36 h of attachment, but only 10% found and removed the smaller nymphal ticks within the first 24 h of tick feeding. The duration of tick attachment may serve as a useful predictor of risk for acquiring various infections, such as Lyme disease and babesiosis, transmitted by I. scapularis. Regression equations developed herein correlate tick engorgement indices with duration of feeding. A table containing specific engorgement index prediction intervals calculated for both nymphs and adults will allow the practitioner or clinical laboratory to use easily measured tick engorgement indices to predict transmission risk by determining the duration of feeding by individual ticks.

Seasonal variation in the capacity of bank voles, Clethrionomys glareolus (Schreber), to infect larval Ixodes ricinus (L.) ticks with Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner was examined from May through October 1991 at Bogesund, near Stockholm in south-central Sweden. Although larval infestations of bank voles were greatest in June and July, nearly 70% of all larval ticks infected with spirochetes by bank voles at this site became infected during August and September. Seasonality of infectivity was related to the degree of earlier nymphal infestation on voles as well as to the age composition of the vole population. These factors may influence the infectivity of other rodent reservoirs of B. burgdorferi, both in Europe and North America. Moreover, in determining the reservoir potential of tick hosts, a host population's spirochetal infectivity should be determined for the entire period of larval infestation rather than just during the period of peak larval infestation.

The risk for human infection with Lyme disease appears linked to the abundance of infected vector ticks, principally Ixodes dammini Spielman, Clifford, Piesman & Corwin, in the eastern United States. Habitat destruction by burning, although not well studied, has long been considered as an effective alternative to synthetic insecticides as a means of reducing tick populations. We evaluated the effect of a single spring burning of the woodland understory on the transmission risk of Lyme disease spirochetes (Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner) on Shelter Island, Long Island, NY. Following a burn in early April 1991, the abundance of nymphal I. dammini was 49% lower in the burned portion of a woodlot compared with the unburned portion. However, risk of encountering nymphs infected with B. burgdorferi remained similar in both burned and unburned woods. It is suggested that burning vegetation may disproportionately kill deer-derived rather than rodent-derived nymphs, significantly reducing tick abundance without affecting transmission risk.

The wasp Hunterellus hookeri Howard parasitizes several species of ixodid ticks including Ixodes dammini Spielman, Clifford, Piesman & Corwin, the vector of Lyme disease spirochetes, Borrelia burgdorferi, in the northeastern United States. We detected the occurrence and evaluated the distribution of this wasp parasitoid in populations of I. dammini in Rhode Island. There has been no intentional introduction of a tick parasitoid recorded anywhere in Rhode Island; yet, we found this wasp at one of the six study sites (Prudence Island), where it parasitized 21 (n = 243) and 17% (n = 284) of nymphal I. dammini collected during 1988 and 1989, respectively. The proportion of nymphs parasitized was greatest during May (46%) and was less in June (18%), July (18%), and August (11%). In Rhode Island, the wasp was only found parasitizing ticks at the site with the highest (by a factor of 2) tick population, confirming similar observations in Massachusetts and New York. It is suggested that establishment as well as the distribution of H. hookeri depends upon a super abundant deer tick population. The usefulness of this parasitoid as a biological control agent is yet unknown.

We compared the intrinsic vector competence of Ixodes dammini Spielman et al., Dermacentor variabilis (Say), and Amblyomma americanum (L.) for the Lyme disease spirochete (Borrelia burgdorferi Johnson et al.) on Prudence Island, Rhode Island, a Lyme disease-endemic site where all three ticks occur together. Natural and experimental spirochete infection rates were determined in those ticks and their degree of contact with white-footed mice (Peromyscus leucopus), the principal reservoir host, was compared. Host-seeking nymphal and adult I. dammini and A. americanum, collected by flagging, were nearly equally abundant, as were adult D. variabilis, but only I. dammini were infected with B. burgdorferi. Larvae and nymphs of both I. dammini and D. variabilis were found infesting mice, but A. americanum never were found on this host. Furthermore, although larvae of all three tick species became infected by ingesting spirochetes while feeding on experimentally infected mice, only I. dammini remained infected following the transstadial molt. These findings suggest that of these three tick species, only I. dammini is competent as a vector of the Lyme disease spirochete.