Clustering of host-seeking nymphal deer ticks (Ixodes dammini) infected by Lyme disease spirochetes (Borrelia burgdorferi).

In areas where the agent of Lyme disease is intensely enzootic, the mouse reservoirs may be universally infected. Because a large proportion of the vector tick population appears to feed upon these hosts, the prevalence of infection in the vectors should approach 100%. However, infection in host-seeking nymphal ticks in nature rarely exceeds 40%. To help reconcile this apparent paradox, we examined whether estimates of prevalence might differ if we did not assume that infected ticks are randomly or uniformly distributed within a site. Nymphal Ixodes dammini were collected by dragging a series of 10-meter replicates within an intensely enzootic site. Estimates of the prevalence of spirochetal infection, based upon the monthly means of individual 10-meter collections, were then compared with estimates derived by pooling all samples. Host-seeking ticks tended to cluster. The Lyme disease spirochete was present in 15.6% of 469 pooled ticks. When the prevalence estimate was based solely on ticks in clusters that contained one or more infected ticks, however, at least 50% of the ticks were infected. We conclude that nymphal deer ticks infected by Lyme disease spirochetes tend to aggregate spatially in nature, and that prevalence estimates based upon a mean value for pools may be misleading.

Quantitative evaluation of sampling methods for Ixodes dammini and Amblyomma americanum (Acari: Ixodidae).

Three tick-sampling methods (dry ice-baited tick traps, cloth drags, and ambulatory human host) were evaluated to determine which technique yielded the greatest capture of host-seeking stages of Ixodes dammini Spielman, Clifford, Piesman & Corwin and Amblyomma americanum (L.). The most reliable method, catching more stages and significantly more numbers of I. dammini and A. americanum; was dry ice-baited tick traps. There were no significant differences between the drag and human-host methods for any stage of ticks (I. dammini and A. americanum) collected. The numbers of ticks caught during the study were 5,052 by dry ice-baited tick traps, 199 by cloth drags, and 89 by ambulatory human host.

A comparison of methods for sampling the deer tick, Ixodes dammini, in a Lyme disease endemic area.

The purpose of this study was to compare the trapping and examining of mice, drag sampling, and CO2-baited traps for their ability to detect the presence and abundance of immature deer ticks, Ixodes dammini, in a Lyme disease endemic area in southern New York State. Eight study sites were sampled 14 times between 28 May and 31 August by setting 49 live-traps, four CO2-baited traps, and drag sampling 500 m2. A total of 1540 nymphs and 3079 larvae was collected during the study. Drag sampling collected the most nymphs (705), while more larvae were recovered from CO2-baited traps (1105). Comparisons among the methods showed a significant difference in the numbers of both larval and nymphal ticks collected (P less than 0.01). There was a positive correlation between the numbers of nymphs collected by drag sampling and CO2-baited tick traps (rs = 0.83, P less than 0.05), and between the numbers of larvae collected by drag sampling and mouse trapping (rs = 0.75, P less than 0.05). These results suggest that drag sampling would be the single most reliable method for quantitatively sampling immature I. dammini populations in a Lyme disease endemic area.

Tick sweep: modification of the tick drag-flag method for sampling nymphs of the deer tick (Acari: Ixodidae).

We describe a version of the standard tick drag-flag modified for use in close-growing and tangled vegetation, as well as under ornamental shrubbery and fallen branches. Two major features of the sweep are: (1) it allows the user to remain upright with the flag parallel to the ground, thus sampling effectively beneath low and fallen branches and around shrubs, as well as capturing host-seeking ticks in advance of the operator; and (2) the use of a flannel rubberized-laminate fabric (crib sheet) for the flag that is snag-proof and highly durable in dense and thorny vegetation. In simultaneous 100-m samples, the sweep was as effective as the 1-m standard tick drag for capturing nymphs of the deer tick, Ixodes dammini Spielman, Clifford, Piesman & Corwin, where understory vegetation was sparse, but was twice as effective in dense vegetation, capturing significantly more I. dammini nymphs. The sweep also captured nymphs of the American dog tick, Dermacentor variabilis (Say); rabbit tick, Haemaphysalis leporispalustris (Packard); and lone star tick, Amblyomma americanum (L.).

Tick infestations of white-tailed deer in Alabama.

Four species of ticks were collected from 537 white-tailed deer (Odocoileus virginianus), examined during the hunting seasons (November to January) of 1988-89 and 1989-90 at selected locations in Alabama (USA). Ixodes scapularis was the most common tick recovered (2,060 specimens) and infested 54% of the deer. Dermacentor albipictus was the second most frequent tick (1,253 specimens) and infested 15% of the deer. Amblyomma americanum was the third most frequent tick (315 specimens) and infested 24% of the deer; this was the only species of tick collected from deer at all sampling locations. Amblyomma maculatum was an infrequent parasite (five specimens) and infested only 1% of the deer; this tick species was only recorded during the 1989-90 season. Year-to-year and geographical differences in tick infestation parameters were noted. The data are compared with those reported for previous surveys of ticks infesting white-tailed deer in Alabama and adjacent states.

Parasitization of humans in West Virginia by Ixodes cookei (Acari: Ixodidae), a potential vector of Lyme borreliosis.

In 32 collections, two larvae, 33 nymphs, and one adult female Ixodes cookei Packard were collected from humans in West Virginia from August 1987 to May 1990. Most were attached. The ticks were found in 14 counties and were the most abundant Ixodes found biting humans. One nymphal I. cookei was removed from the left axilla of a 39-yr-old woman who lives and works in Monongalia and Marion counties, W. Va. The bite was the center of an expanding erythematous lesion reaching 4 cm in diameter, clearing centrally, and typical of erythema migrans. This association and the near absence of Ixodes dammini Spielman, Clifford, Piesman & Corwin from the state suggests the possibility that I. cookei may be an important vector of Lyme borreliosis in West Virginia. In five separate collections, five nymphal Ixodes dentatus Marx were removed from humans in four counties, implicating this species as a potential minor vector of Lyme borreliosis in West Virginia.

Trombiculid mites (Acari: Trombiculidae) and Rickettsia tsutsugamushi isolated from wild rodents in a new endemic area of Japan.

Investigations of trombiculid mites and Rickettsia tsutsugamushi in wild rodents were made in southern Gifu Prefecture where patients infected with tsutsugamushi disease recently have been found. A total of 16,396 trombiculid mites, consisting of 10 species from three genera, was collected from 170 Apodemus speciosus in two locations. Kani-Sakahogi and Kuze. Leptotrombidium scutellare (Nagayo et al.) (44.0%) was most predominant, followed by L. pallidum (Nagayo et al.) (26.9%); L. fuji (Kuwata et al.) (13.6%); and Gahrliepia saduski Womersley (14.2%). These four species constituted the bulk of the chigger mite fauna. L. scutellare was present from October to February with a remarkably high peak in November, whereas pallidum occurred from November to March with the highest peak in December. L. fuji and G. saduski showed their highest peaks in December and moderate peaks in early summer (April and May). Positive identification of Rickettsia tsutsugamushi in wild rodents from Kani-Sakahogi were found to be 50 and 58.3% in November 1985 and 1986, respectively, and 38.5% in November 1986 from Kuze. R. tsutsugamushi was isolated from chigger mites of an L. pallidum-rich group, displaying the highest titer to Karp strain. Serological investigation of rodents to R. tsutsugamushi antibodies were calculated as 41.6 and 50% positive in November 1985 and 1986 in Kani-Sakahogi, respectively, and 50% in November 1986 in Kuze. The Karp strain was dominant in specificity to antibodies. These results indicate that the surveyed areas have a high probability of occurrence of tsutsugamushi disease, and L. scutellare and L. pallidum may serve as the vectors in these areas. Particularly, we suggest that L. scutellare is the most important vector which has caused a recent outbreak of this disease in southern Gifu Prefecture.

White-footed mice: tick burdens and role in the epizootiology of Potomac horse fever in Maryland.

One hundred ten white-footed mice (Peromyscus leucopus) were captured on horse farms in south-central Maryland, examined for ticks, and tested for specific antibodies to Ehrlichia risticii, the causative agent of Potomac horse fever. Peromyscus leucopus were consistently infested with immature American dog ticks (Dermacentor variabilis), with monthly prevalences as high as 80%. Sera from all 97 P. leucopus tested for antibodies to E. risticii were negative. This indicates that P. leucopus is not a reservoir of E. risticii, and suggests that immature D. variabilis do not acquire E. risticii in feeding upon white-footed mice.

Myocardial infarction in Queensland provincial cities, 1975.

A survey was made of patients admitted to hospitals with a diagnosis of acute myocardial infarction in seven Queensland provincial cities between January 1, and December 31, 1975. Estimates of the incidence of, and mortality from, myocardial infarction are made, and details of the type of care offered, patient characteristics, and length of stay in hospital and intensive care units are presented.

Transmission of Rickettsia orientalis to man by Leptotrombidium akamushi at a scrub typhus endemic area in Akita Prefecture, Japan.

During the summer seasons of 1956 through 1970, 93 larval trombiculid mites were removed from 386 individuals who had been bitten by chiggers in Jumonji, Akita Prefecture. All 87 larvae that were available for examination were identified as Leptotrombidium akamushi. Infestation of man occurred predominantly during July and August, but the period extended from June to November. The duration of attachment was approximately 1 to 3 days. Usually only 1 chigger was found on a victim but on occasion as many as 7 were removed at one time. Scrub typhus developed in 45 (11.7%) of the 386 farmers bitten by chiggers. Although patients with scrub typhus may have sustained multiple bites, only one eschar was found. However, 76% of the patients did not recognize a bite either at the site where an eschar subsequently appeared or elsewhere prior to the onset of disease. If it is assumed that workers who did not subsequently become ill were equally unaware of chigger bites, then the probable incidence of disease in chigger victims was 3.1%. The minimum infectivity rate of L. akamushi larvae in Akita Prefecture was estimated to be 2.3%. Based upon the assumption that infection was transmitted as the result of a single bite, the infective rate of chiggers attacking man was calculated to be 2.5%.