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PubMed1991

Effectiveness of host-targeted permethrin in the control of Ixodes dammini (Acari: Ixodidae)

Tubes of commercially available permethrin-treated cotton balls were distributed twice each year in 1989 and 1990 at five sites in a Lyme disease endemic area in Connecticut. Five additional sites were not treated. At each application, 48 tubes, sufficient to treat 0.4 ha, were dispersed at 10-m intervals through woodlands, around ornamental plantings, and along rockwalls. The cotton was collected by white-footed mice (Peromyscus leucopus) from the majority of the tubes, which resulted in a decrease (37.2% in 1989 and 91.5% in 1990) in the number of subadult Ixodes dammini Spielman, Clifford, Piesman, and Corwin on the mice in the treated areas. There were no significant decreases in the number of host-seeking nymphs or adults of I. dammini in 1989 or 1990 between the treated and untreated sites. The rates of infection in the host-seeking nymphs with Borrelia burgdorferi, the etiological agent of Lyme disease, at the treated sites (13.0 and 14.6% for 1989 and 1990, respectively) were comparable to those at the untreated sites (16.9 and 13.2% for 1989 and 1990, respectively). The distribution of permethrin-treated cotton around individual residences significantly reduced the number of ticks on P. leucopus but was not sufficient to reduce the risk of exposure to infected host-seeking nymphs and adults of I. dammini after two seasons of treatment.

Animals↗

PubMed1992

Experimental transmission of African swine fever virus by the soft tick Ornithodoros (Pavlovskyella) marocanus (Acari: Ixodoidea: Argasidae).

A total of 1,600 Ornithodoros (Pavlovskyella) marcocanus larvae were fed on a pig with a viremia of 10(7.4) HAd50/ml of African swine fever virus (ASFV). Infected larvae were sampled daily for 15 d, and nymphs were sampled at least once per instar until they became adults. Initial titers of 10(4.48) HAd50 per larva declined to 10(4.04) within 2 d. Larval titers reached a maximum of 10(6.0) HAd50 per larva 10 d after the infective blood meal. Nymphs of each instar were fed on a susceptible pig and in each case transmitted ASFV by bite. Virus titers for first to fourth instars ranged from 10(4.61) to 10(3.34) HAd50 per nymph. Transstadial survival occurred in subsequent first, second, third, and fourth instars with an 89% survival rate over 250 d. Approximately 30% of adult ticks that were infected as larvae remained infected and transmitted ASFV to susceptible pigs 588 d later. In addition, ASFV was recovered from the same adult ticks 655 d after the infective blood meal.

African Swine Fever↗

PubMed1992

Third-year evaluation of host-targeted permethrin for the control of Ixodes dammini (Acari: Ixodidae) in southeastern Connecticut.

The impact of commercially available permethrin-treated cotton balls targeted at Ixodes dammini Spielman, Clifford, Piesman & Corwin on white-footed mice, Peromyscus leucopus, was evaluated for a third year at five residential sites in south-central Connecticut. Each site had been treated twice each year from 1989 through 1991 with sufficient product to treat 0.4 ha of mouse habitat, and results were compared with five untreated sites. There were no significant differences in the number of host-seeking nymphs or adults of I. dammini, the vector of the Lyme disease spirochete, Borrelia burgdorferi, in 1991 between the treated and untreated sites. The rate of infection in host-seeking nymphs by B. burgdorferi at the treated sites (15.3% of 600) was comparable with that at the untreated sites (16.5% of 454). Only 16.3% of 86 P. leucopus captured at the treated sites were infested with I. dammini subadults compared with 66.9% of 118 from the mice at the untreated sites. The impact of permethrin-treated cotton during the third year of treatment was similar to that observed for the first 2 yr and did not reduce the risk of exposure to spirochete-infected, host-seeking nymphs and adults of I. dammini.

Animals↗

PubMed1992

Comparative infections of epizootic and enzootic strains of Venezuelan equine encephalomyelitis virus in Amblyomma cajennense (Acari: Ixodidae).

To compare the potential for an enzootic or an epizootic strain of Venezuelan equine encephalomyelitis (VEE) virus to infect Amblyomma cajennense (F.), larval ticks were fed on guinea pigs (strain 13) inoculated with an enzootic viral strain of variant I-E (68U201) or on guinea pigs inoculated with an epizootic strain of variant I-A (Trinidad donkey). Peak viremias were 10(5.2) plaque-forming units (PFU)/ml and 10(7.3) PFU/ml in guinea pigs infected with enzootic and epizootic viral strains, respectively. Ticks feeding on enzootic- and epizootic-infected hosts had viral titers of 10(2.5) and 10(3.9) PFU per tick, respectively, at drop-off. Although epizootic virus was recovered from 98% (127 of 130) of larval ticks up to 16 d after drop-off, enzootic virus was recovered from 95% (19 of 20) at drop-off (mean titer, 10(2.5) PFU per tick), with recovery rates declining rapidly to 2 of 10 (mean titer, 10(1.4) PFU per tick) by 16 d after drop-off. Transstadially transmitted epizootic virus was found in 0.4% (12 of 2,950) of unfed nymphs (mean titer, 10(2.8) PFU per tick) 63 d after drop-off, 1% (5 of 521) fed nymphs 69 d after drop-off, and 1% (4 of 400) of unfed adults (mean titer, 10(3.6) PFU per tick) 106 d after drop-off. No enzootic virus was recovered from 4,600 unfed nymphs tested 63 d after drop-off.

Animals↗

PubMed1992

Cotton rats and other small mammals as hosts for immature Dermacentor variabilis (Acari: Ixodidae) in central Oklahoma.

Eight species of small mammals were evaluated as potential hosts for American dog ticks, Dermacentor variabilis (Say), in an upland, tallgrass prairie study site in central Oklahoma. Only hispid cotton rats, Sigmodon hispidus, and deer mice, Peromyscus maniculatus, were found to be important hosts for immature D. variabilis. Although D. varibilis larvae and nymphs frequently infested both cotton rats and deer mice, cotton rats were the most important host species for both immature stages in the study area. Cotton rats constituted 63.2% of the total 530 small mammals captured and were hosts to 85.2% of all larvae and 88.7% of all nymphs. Deer mice accounted for 19.8% of all small mammals captured and were hosts for 14.5% of the larvae and 10.8% of the nymphs recovered. The remaining small mammal species were hosts for less than 1% of the immature ticks collected. Larval infestations peaked during summer, whereas summer and spring peaks were noted for the nymphal infestations. The relative importance of cotton rats and deer mice as hosts for immature ticks could be largely, but not completely, explained by cotton rats being more than three times as abundant as deer mice. Attachment site data indicated that differences in grooming behavior also might be partially responsible for the larger infestations observed on cotton rats. Other possible ecological and behavioral explanations of the heavy infestations observed on cotton rats are discussed.

Animals↗

PubMed1992

African swine fever virus infection in the Iberian soft tick, Ornithodoros (Pavlovskyella) marocanus (Acari: Argasidae).

One thousand six hundred Ornithodoros (Pavlovskyella) marocanus Velu larvae were fed on a pig infected with African swine fever virus (titer: 10(7.4) HAd50/ml), and 1,600 larvae were fed on an uninfected pig. Ticks in each group were compared for mortality rates, mean time to death for ticks that died, mean time from feeding to either molting or eclosion, percentage of ticks that eclosed or molted, and the number of blood meals per nymph or instar. Cumulative virus-induced mortality for all immature stages (larvae to adult) of O. marocanus that had been fed as larvae on a pig infected with African swine fever was ca. 73% over a 390-d period. In contrast, less than 9% mortality was observed among ticks fed on uninfected pigs. Mean time to death for infected ticks was 15-87 d versus 10-17 d for uninfected ticks. Differences in the premolt period (number of days from blood meal to molt) between infected and control ticks were not observed. Mean premolt periods for larvae and first-, second-, third-, fourth-, and fifth-instar nymphs fed on pigs were 7, 9, 15, 11, 15, and 15 d, respectively. The majority of infected and all uninfected ticks required only one blood meal from pigs to molt. Mean weights for unfed second-, third-, and fourth-instar nymphs and males and females were 0.50, 0.67, 3.07, 3.63, and 5.91 mg, respectively.

African Swine Fever↗

PubMed1993

Detection of Anaplasma marginale (Rickettsiales: Anaplasmataceae) in hemolymph of Dermacentor andersoni (Acari: Ixodidae) with the polymerase chain reaction.

The polymerase chain reaction (PCR) was used to detect Anaplasma marginale in hemolymph collected from live Dermacentor andersoni Stiles ticks. Hemolymph was collected from severed legs of male and female ticks exposed to A. marginale as either nymphs or adults. Heat treatment was found to be the optimum method of hemolymph preparation for PCR. Hemolymph samples were collected and pooled from adult ticks exposed as nymphs on days 0-10 of feeding on a susceptible calf. For male and female ticks exposed as adults, samples were collected as ticks fed 7 d on an infected calf, while being held 9 d between feedings, and during a second feeding of 10 d (or to repletion) when they transmitted the parasite. Hemolymph samples were collected from uninfected ticks at the same times to serve as controls. Anaplasma marginale DNA was amplified with primers BAP-2 (5'-GTATGGCACGTAGTCTTGGGATCA-3') and AL34S (5'-CAGCAGCAGCAAGACCTTCA-3'), which flank a 409-bp fragment of the A. marginale Florida isolate msp1 beta gene. Infected tick hemolymph was PCR-positive for A. marginale at all collection times, including unfed adults infected as nymphs and previously unexposed adults that fed on infected calves for only 1 d. The PCR-based assay of tick hemolymph proved to be a sensitive method for identification of infected ticks, potentially without killing them; it would be well suited for identification of laboratory- or field-infected ticks that could then be used for further studies. The primers used in this assay were also found specific when tested with species of 18 different genera, and universal for 7 A. marginale isolates from diverse geographical areas of the United States.

Anaplasma↗

PubMed1993

Detection of Anaplasma marginale (Rickettsiales: Anaplasmataceae) in secretagogue-induced oral secretions of Dermacentor andersoni (Acari: Ixodidae) with the polymerase chain reaction.

The polymerase chain reaction (PCR) was used to detect Anaplasma marginale in secretagogue-induced oral secretions of male and female Dermacentor andersoni Stiles exposed as nymphs or adults by feeding on infected calves. A 409-bp DNA fragment derived from the A. marginale (Florida isolate) msp1 beta gene was amplified with oligonucleotide primers BAP-2 (5'-GTATGGCACGTAGTCTTGGGATCA-3') and AL34S (5'-CAGCAGCAGCAAGACCTTCA-3'). The target DNA was amplified in oral secretions of female ticks exposed to A. marginale as adults and stimulated to secrete by injection of dopamine. Conversely, A. marginale was detected in saliva from prefed female ticks exposed as nymphs only after stimulation with a combination of dopamine, gamma-aminobutyric acid, pilocarpine, and theophylline. Saliva from ticks exposed as nymphs and stimulated with ergot alkaloids did not contain the A. marginale target DNA. Saliva collected after 11 d of feeding from dopamine-stimulated male ticks contained A. marginale DNA. The results indicate that A. marginale is present in tick saliva and suggest that the parasite can be transmitted to cattle via saliva of feeding ixodid ticks. The variable appearance of A. marginale in saliva, regardless of the method used to induce salivation, suggests that transmission of A. marginale may be affected by the physiological state of the tick.

Anaplasma↗

PubMed1994

Seasonal and annual abundance of Amblyomma americanum (Acari: Ixodidae) in central Georgia.

Seasonal and annual changes in the abundance of Amblyomma americanum (L.) larvae, nymphs, and adults were monitored over a 5-yr period in the Piedmont physiographic region of Georgia. Tick abundance was monitored with cloth drags (all life stages) and CO2-baited cloth panels (nymphs and adults) monthly during March through September from 1987 through 1991. Larvae appeared in substantial numbers in July and were most numerous in August and September. Small numbers of unfed larvae apparently overwintered each year based on their presence during March, April, or May. Nymphs were most numerous from April through June and declined to much lower numbers by August and September. Adults were most numerous from March through May and virtually disappeared by August. These seasonal patterns were similar to those reported for A. americanum at other southeastern locations. Each life stage exhibited similar trends of annual abundance with an increase in 1988 followed by a relatively steady decline to levels equivalent to or below initial 1987 values by 1991. Major environmental variables that potentially could have influenced annual abundance were identified from Haile & Mount's (1987) computerized model of A. americanum population dynamics. Habitat type, host density, and day length were constants and rationally could be excluded as causes of annual variations in abundance; weather and host-finding rate were presumed to have been primarily responsible for these annual differences.

Animals↗

PubMed1994

Influence of annual and biennial prescribed burning during March on the abundance of Amblyomma americanum (Acari: Ixodidae) in central Georgia.

A 5-yr study to evaluate the influence of annual and biennial prescribed burning in March on the abundance of Amblyomma americanum (L.) was conducted on Oconee Wildlife Management Area in the Piedmont physiographic region of Georgia. Tick abundance on plots embedded in larger burned and unburned areas were monitored with cloth drags and CO2-baited cloth panels monthly during March through September from 1987 through 1991. Annual and biennial prescribed burning from 1988 to 1991 significantly reduced the abundance of larvae, nymphs, and adults but did not alter their seasonal trends of abundance. Annual burning more consistently suppressed all life stages than biennial burning. The magnitude of tick suppression tended to increase with successive burns, especially with the annual burning regime. The order of vulnerability to direct incineration appeared to be overwintered larvae > adults > nymphs; however, only overwintered larvae were highly vulnerable. Consistent reductions in larvae during June-September following burning were associated with reduced litter depths and presumably lowered habitat suitability. During years of fire omission, the abundance of larvae on biennially burned plots increased to levels equal to or exceeding those on unburned plots. Based on cloth drag sampling, mean percentage control during 1988-1991 for larvae, nymphs, and adults, respectively, was 80, 75, and 70% on annually burned plots and 48, 73, and 65% on biennially burned plots. Frequent late-winter prescribed burning, which is commonly used to achieve wildlife habitat management objectives, could be an effective and economical component of an integrated A. americanum control program in habitats ecologically suited to regimes of frequent fire.

Animals↗

PubMed1994

Rearing improvements for the German cockroach (Dictyoptera: Blattellidae).

Known-age cohorts of three strains of German cockroach, Blattella germanica (L.), were mass-reared by establishing one rearing container each week (so that cockroaches within a container would be of known age). An average of 330-443 females was placed in oviposition units within these rearing containers. Percentage hatch of oothecae was 77.49-84.63%, resulting in an average of 12,258-16,359 nymphs per rearing container. Development of nymphs was similar for the three strains. Survivorship of nymphs to the adult stage was 19.95-29.56%; survivorship was significantly higher for the strain most recently colonized from the field. Adult emergence occurred at 6-7 wk, and average production per container was 2,834-3,971 cockroaches.

Animals↗

PubMed1996

Efficient transmission of Borrelia burgdorferi between cofeeding Ixodes ricinus ticks (Acari: Ixodidae).

Feeding ticks are generally spatially distributed in clusters on vertebrate hosts. To test the effect of clustering on transmission of a tick-borne pathogen, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner-infected Ixodes ricinus L. nymphs and uninfected I. ricinus larvae were allowed to feed together in retaining chambers on uninfected AKR/N mice. Engorged infective nymphs dropped off at days 5, 6, and 7, and the 1st infected larvae that fed in the chambers together with the infected nymphs dropped off at day 5. In contrast, ear biopsies and xenodiagnostic larvae placed on the head remained negative during that period. These results suggest that a cofeeding transmission occurred between B. burgdorferi-infected ticks and noninfected ones in the absence of a disseminated infection. Further investigations are being undertaken to determine whether the mechanism responsible for this cofeeding transmission is similar to that described previously with virus-infected ticks.

Animals↗

PubMed1996

Spring migratory birds (Aves) extend the northern occurrence of blacklegged tick (Acari:Ixodidae).

Birds that had migrated northward across Lake Superior were captured upon reaching landfall at Thunder Cape (48 degrees 18' N, 88 degrees 56' W) at the southwestern tip of the Sibley Peninsula, northwestern Ontario, from 9 May to 9 June 1995. Twenty-one of 530 birds examined (6 of 55 species) had a total of 34 ticks; 1 blue jay, Cyanocitta cristata, had a northern fowl mite, Ornithonyssus sylviarum (Canestrini & Fanzago). Four blacklegged tick, Ixodes scapularis Say, larvae were found on an American robin, Turdus migratorius, and 2 on a chipping sparrow, Spizella passerina. This tick was not found on small mammals at Thunder Cape. Twenty-six larvae and a nymph of the rabbit tick, Haemaphysalis leporispalustris (Packard) were found on 1 American robin, 2 Swainson's thrushes, Catharus ustulatus, 1 white-throated sparrow, Zonotrichia albicollis, 1 common yellowthroat, Geothlypis trichas, 1 blue jay, and 12 chipping sparrows. A nymph of H. chordeilis (Packard) occurred on 1 chipping sparrow. Results demonstrate that northward migrating birds transport larvae of I. scapularis to areas of Ontario where the tick does not appear to have become established in small mammal populations. Spring migrants may be more involved in the dispersal of I. scapularis larvae than previously thought. Cooler temperatures and shorter seasons experienced in the more northerly, continental parts of the established distribution of this tick may extend the life cycle, resulting in a predominance of larvae rather than nymphs being acquired by northward-bound birds in early spring. Consequently, the role of spring migrating birds in the northward spread of I. scapularis and of borreliosis should be reevaluated.

Animals↗

PubMed1996

Silt fencing as a barrier to the dispersal of Ixodes scapularis (Acari:Ixodidae) into pastures.

Silt fence barriers were set along pasture fencelines and evaluated as a method of restricting the dispersal of blacklegged tick, Ixodes scapularis Say, adults and nymphs from woodlands into adjacent horse pastures. The barriers received no acaricidal treatment for the 1st cohort of adults. Thereafter the woods side of the barriers was sprayed with cyfluthrin at the onset of each season of host seeking activity of nymphs and adults. When high densities of adults were present, the barriers significantly limited the numbers of ticks in pastures. Nymphs, however, were not significantly fewer in numbers in pasture areas associated with the barriers compared with control areas. Marked adult ticks released in woodlands and ecotones were recaptured on mowed verges and pastures, but there was little dispersal from the woods edge into the woods.

Animals↗

PubMed1998

Effects of the feeding process of Ixodes scapularis (Acari: Ixodidae) on embryonic development of its parasitoid, Ixodiphagus hookeri (Hymenoptera: Encyrtidae).

The chalcid wasp Ixodiphagus hookeri (Howard) is a parasitoid of several ixodid ticks including the blacklegged tick, Ixodes scapularis Say. We evaluated effects of the feeding process of nymphal I. scapularis on the embryonic development of I. hookeri. Potentially wasp-parasitized nymphal I. scapularis were collected on Prudence Island, RI. Subsamples of the questing nymph cohort were allowed to feed on laboratory white mice. Both the body length and the scutal length of ticks were measured individually for questing nymphs and for feeding nymphs that were removed from hosts at time intervals of 12, 24, 36, 48, and 72 h after attachment. The diameters of wasp eggs they contained were also measured for each designated time interval. There was a positive relationship between the mean scutal index (ratio between body length and scutal length) of ticks and the mean diameter of wasp eggs during 72 h of tick feeding (P < 0.05). Moreover, it appeared that within 24 h of tick attachment, the scutal index of ticks remained unchanged. However, after that period, the scutal index increased significantly (P < 0.05). Diameters of wasp eggs increased continuously during tick feeding and at 72 h after attachment, enclosed eggs and completely formed larvae were found in several ticks. We conclude that factors related to the feeding process of nymphal I. scapularis are necessary to initiate the embryonic development of wasps.

Animals↗

PubMed1999

Impact of microclimate on immature tick-rodent host interactions (Acari: Ixodidae): implications for parasite transmission.

Rodents play a significant role in enzootic cycles of tick-borne pathogens, notably, in the northern hemisphere, tick-borne encephalitis virus and Lyme borreliosis spirochaetes. The relative numbers of nymphal and larval ticks feeding on rodents are crucial variables in determining the probability of rodent infection and the degree of amplification of infection prevalence in the tick population. Manipulation of the microclimate within quasinatural experimental arenas revealed that under increasingly dry conditions the numbers of unfed nymphal Ixodes ricinus L. questing in upper layers of the herbage decreased, whereas the rate of fat use and the numbers of nymphs feeding on small rodents, both increased. This is consistent with nymphs descending to the moist lower vegetation layers for water replenishment, where they would come into contact with small hosts. Very few larvae quested or fed on rodents under the dry conditions, but many more did so once the humidity increased, suggesting that larvae escape desiccation by becoming quiescent. The ratio of larvae to nymphs feeding on rodents thus increases with increasing humidity, contributing to the seasonal and geographical variation in disease transmission dynamics.

Animals↗

PubMed2005

Relative encounter frequencies and prevalence of selected Borrelia, Ehrlichia, and Anaplasma infections in Amblyomma americanum and Ixodes scapularis (Acari: Ixodidae) ticks from central New Jersey.

To evaluate their relative importance in tick-borne disease transmission in New Jersey, host-seeking Amblyomma americanum (L.) and Ixodes scapularis Say adults and nymphs were collected during spring activity periods in 2003 and 2004 to determine relative frequencies at which these ticks were encountered from an area known to be hyperendemic for Lyme disease. Although similar numbers of the two species were encountered during early spring of both years, A. americanum were encountered more often later in the season and exhibited a longer activity period than I. scapularis. A. americanum nymphs were collected at frequencies between 2.6 and 7.3 times higher than I. scapularis nymphs. Polymerase chain reaction (PCR) analysis of 121 A. americanum adults yielded infection prevalences of 9.1% for Borrelia lonestari, 12.3% for Ehrlichia chaffeenensis, and 8.2% for E. ewingii, and coinfection prevalences of 4.1% for E. chaffeensis/E. ewingii and 0.8% for E. chaffeensis/B. lonestari. Infection prevalences in 147 I. scapularis adults were 50.3% for B. burgdorferi, 6.1% for Anaplasma (Ehrlichia) phagocytophilum, and 1.4% for a recently described novel Borrelia species, whereas the coinfection prevalences were 2.7% for B. burgdorferi/A. phagocytophilum, 0.7% for B. burgdorferi/novel Borrelia, and 0.7% for A. phagocytophilum/novel Borrelia. The B. burgdorferi infection prevalence in I. scapularis was considerably higher than that in A. americanum. However, the higher A. americanum encounter frequencies compared with I. scapularis may result in increased risk of acquiring exposure to A. americanum-transmitted pathogens. The potential public health implications of these results are discussed.

Anaplasma↗

PubMed1996

Duration of tick bites in a Lyme disease-endemic area.

Regression equations, based on scutal index (body length/scutal width), were developed to determine the duration of attachment for nymphal and adult female lxodes scapularis ticks. Feeding times were calculated for 444 nymphal and 300 female ticks submitted by bite victims between 1985 and 1989 in Westchester County, New York, an area where Lyme disease is highly endemic. Nymphs were attached for a mean of 34.7 hours, with 26.8% removed after 48 hours, the critical time for transmission of Borrelia burgdorferi. Attachment times increased with victim age class (Kruskal-Wallis test, p < 0.05). Mean duration of attachment for female ticks (28.7 hours) was significantly less (Kruskal-Wallis test, p < 0.05) than that for nymphs, with 23.3% attached for more than 48 hours. The 0- to 9-year age class had the highest proportion (37.1%) of females attached for more than 48 hours. Nymphs remain attached to adult tick-bite victims longer than they remain attached to children. However, children have a high risk of acquiring Lyme disease because they receive more nymphal bites and also because they are less likely to have female ticks removed in time to prevent transmission.

Adolescent↗