Tick Parasitism Research Articles

Buffalo-associated Theileria parva: the risk to cattle of buffalo translocation into the Highveld of Zimbabwe.

There has been an increase in the introduction of game animals, including African buffaloes, into the Highveld of Zimbabwe to establish private game reserves on condition that they are confined in separate and secured paddocks. Owing to shortages of pastures cattle were grazed in buffalo-grazed paddocks resulting in outbreaks of buffalo-derived theileriosis. This paper reports the results of epidemiological observations carried out on two game reserves to assess the risk of buffalo translocation. The infection rate with Theileria parasites in ticks collected from buffalo-grazed pastures was high and produced fatal theileriosis in susceptible cattle. Similarly, adult R. appendiculatus ticks artificially fed as nymphs on the buffaloes produced fatal infections in susceptible cattle. Theileria parva (Boleni), the vaccine used to immunize cattle against theileriosis, and a buffalo-derived T. parva stabilate (BV-1) were inoculated in naïve buffaloes to study the Theileria carrier-state in these animals. The two buffaloes that had received the Boleni stabilate showed no clinical theileriosis reaction; however, the ticks derived from them produced a subclinical reaction in one susceptible calf. The buffalo which had received stabilate BV-1 developed fever, high schizont parasitosis for 10 days and 15% piroplasms parasitemia. R. appendiculatus ticks fed as nymphs on this buffalo produced fatal theileriosis reaction in a susceptible calf.

Ticks parasitizing dogs in northwestern Georgia.

From January 1998 through September 1999, 324 dogs in three northwestern Georgia counties were examined for ticks. Six species of ticks were recovered. The three most commonly collected ticks were the American dog tick, Dermacentor variabilis (Say) (310 male male, 352 female female; prevalence, 97%; mean intensity 2.1); the brown dog tick, Rhipicephalus sanguineus (Latreille) (118 male male, 119 female female, 38 nymphs; prevalence, 22%; mean intensity, 3.8); and the lone star tick, Amblyomma americanum (L.) (8 male male 26 female female, 2 nymphs; prevalence, 5%; mean intensity, 2.4). Other ticks recovered were Ixodes cookei Packard (3 female female); the Gulf Coast tick, Amblyomma maculatum Koch (2 female female); and the blacklegged tick, Ixodes scapularis Say (1 female). Another adult female specimen of I scapularis was recovered from a cat, further reinforcing that this medically important tick is present in northwestern Georgia.

Host Associations of Ticks Parasitizing Rodents at Borrelia burgdorferi Enzootic Sites in South Carolina

Host Associations of Ticks Parasitizing Rodents at Borrelia burgdorferi Enzootic Sites in South Carolina

Predation of the cattle tick, Boophilus microplus (Canestrini) (Acarina: Ixodidae), in three Australian pastures

AbstractPredation of engorged females of the cattle tick Boophilus microplus (Canestrini) in pasture was recorded in central and southern Queensland for different periods during 1969–1973 and again in central Queensland in 1984. Patterns of damage and removal of ticks were consistent with direct observations that indicated that ants and the house mouse (Mus musculus L.) were the only significant predators, so these species were assumed to account for all the observed predation. At Amberley, southern Queensland, ticks sealed in nylon gauze cylinders to protect them from ants suffered less predation than ticks in unsealed cylinders that suffered predation by ants as well as mice. Predation rates were higher in long grass than in medium or short grass, probably because the long grass provided greater protection for predators. Predation rates at Jimboomba in southern Queensland were similar at a hill‐top site and on a flat adjacent to a dam with higher soil moisture and denser cover, but there were major differences between years. In central Queensland, ants were consistent predators while the house mouse was responsible for high levels of predation when in plague numbers for a period of time during the study. Losses of ticks attributed to mice were related to coarse estimates of mouse abundance. In 1984, most affected ticks were attacked within 48 h of placement in the pasture. In central Queensland, mouse predation was higher in winter, while ant predation was more frequent in summer. A simulation model of tick populations indicated that a less than proportional reduction can be expected in numbers of parasitic ticks with increases in the predation rate. Those effects will be more evident in less favourable habitats for the ticks.

The impact of tick parasites on the behaviour of the lizard Tiliqua rugosa

Populations of the Australian sleepy lizard, Tiliqua rugosa, near Mt. Mary, South Australia carry natural infestations of two tick species Aponomma hydrosauri and Amblyomma limbatum. In field experiments at two sites, 18 km apart, lizards with experimentally increased tick loads had smaller home ranges, moved shorter distances in a day, and were found basking more but moving less often than lizards from which ticks were experimentally removed. The results were consistent for adult lizards in two years, and for sub-adults in a third year. Laboratory trials showed that juvenile lizards that had tick infestations had lower sprint speeds than uninfested siblings, and that adults with tick infestations had less endurance than those that were uninfested. The results contrast with those of a previous survey that showed that lizards with high tick loads had greater body size and remained longer at a site, but indicate that there may be a balance, for lizards, between the fitness advantages in occupying habitats with high-quality resources, and the costs from parasites that also prefer those habitats.

Persistence of Tick-borne Virus in the Presence of Multiple Host Species: Tick Reservoirs and Parasite Mediated Competition

Tick-borne viruses in tropical and temperate parts of the world have a significant impact on human, livestock and wildlife hosts both directly, through mortality/morbidity, and economically. Since the ticks have multiple life stages and can utilize a large range of host species our understanding of the dynamics of these infections is often not clear. In this paper we consider the impact of a population which is a tick host but non-viraemic on one which is both a tick host and viraemic. We present two simple deterministic models and use joint threshold density curves to illustrate the basic reproductive ratios of both the ticks and the virus. We find that the non-viraemic hosts can have considerable impact on the viraemic host. Either they amplify the tick population and cause the virus to persist, or they dilute the infection and cause it to die out. A general model framework is presented here but a special case of this model describes the red grouse–hare–Louping-ill system.

NovelEhrlichiaOrganism (Rickettsiales: Ehrlichieae) in White-Tailed Deer Associated with Lone Star Tick (Acari: Ixodidae) Parasitism

Polymerase chain reaction (PCR) evidence of a novel Ehrlichia organism was found recently in wild white-tailed deer, Odocoileus virginianus Zimmermann, and lone star ticks, Amblyomma americanum L., from the southeastern United States. To evaluate whether lone star tick parasitism was associated with the presence of this novel Ehrlichia organism in deer, 2 retrospective studies were conducted using specific nested PCR to test archived deer serum samples. The 1st study of 150 serum samples collected from a single deer population over a 15-yr period examined the temporal association between the presence of the Ehrlichia organism in deer and parasitism by lone star ticks. The deer Ehrlichia was not detected in serum samples collected before 1986, when lone star ticks were absent or rare, but was detected in samples collected in 1986 and every year thereafter, when lone star ticks became increasingly abundant. In the 2nd study, serum samples from 120 deer from 24 sites in 14 southeastern states were tested to evaluate if a site-specific, spatial association existed between the presence of the deer Ehrlichia and lone star ticks. All 60 serum samples from the 12 deer populations without evidence of lone star tick infestation were negative for the deer Ehrlichia, whereas 83% of the 12 populations infested by lone star ticks had PCR evidence of infection. These data suggest that lone star ticks may be a vector of the deer Ehrlichia; however, they do not preclude the involvement of other arthropods in maintaining infection with this organism in deer populations.

Seasonal variation of ticks on cattle in Burkina Faso.

Cattle of the Sahel Zebu peuhl breed from traditionally managed livestock herds in a representative area of north soudanese savana (with 400-900 mm of rainfall/year from May to September) located in the central land of Burkina Faso, were monitored over 12 months for tick and blood parasite. Two species of ticks were found: Amblyomma variegatum and Hyalomma marginatum rufipes. H. m. rufipes was found on cattle all year round with a highest infestation rate in June characterized by means of 10 +/- 4.72 male and 3 +/- 2.43 female ticks per animal. A variegatum appeared on cattle at the beginning of the rainy season in May and quickly reached its highest infestation rate in June with means of 36 +/- 3.67 male and 16 +/- 1.54 female ticks per animal. Thereafter, the infestation rate progressively decreased to reach almost zero in October at the end of the rainy season. There were three preferred body sites for attachment: the axilla area, the area of the scrotum or the udder and the teats depending on the sex of the animal, and the anal area. No blood parasites were found in blood smears. However, a higher prevalence rate of dermatophilosis was noticed on highly infested animals during the rainy season as well as wounds on teats leading to decreased milk production and feeding of calves. Effort should be done to fight against ticks of Amblyomma genus at the period of the year where they are most numerous. Manual removal of ticks could be practiced, making certain to completely detach all mouthparts of the ticks. Complete removal of ticks will avoid wounds and secondary bacterial infections as well as myiasis. During the period of highest prevalence, the rainy season, acaricides could be applied on animal either by dipping the animals or spraying on the predilection sites of the ticks which are the axilla, the scrotum or the udder and the teats, depending on the gender of the animal, and around the anus.

Ecology of Hunterellus hookeri (Hymenoptera: Encyrtidae) and Evaluation of Its Impact on Ixodes scapularis (Acari: Ixodidae) on Nonamesset Island in Massachusetts

The impact of Hunterellus hookeri Howard on Ixodes scapularis Say was examined in 1990–1992 at a site in coastal Massachusetts where the parasitoid was released in 1926. Rates of nymphal parasitism were estimated from regression as 25, 21, and 26% for the 3 yr of observation. Analysis of the rates of decline in percentage parasitism values from samples of field-collected nymphs that were dissected immediately compared with subsamples held in the laboratory for 0–4 mo suggests that parasitized nymphs experience enhanced mortality (before parasitoid emergence) compared with unparasitized nymphs. Voltinism and host preferences of H. hookeri also were examined. Analysis of developmental times and seasonality of hosts suggests that >1 generation per year of H. hookeri is unlikely in southeastern Massachusetts. Significantly more I. scapularis nymphs than larvae became parasitized when these stages were exposed together to H. hookeri while feeding on a laboratory mouse. H. hookeri also parasitized 9% of fed, detached I. scapularis larvae that were exposed in a petri dish. Parasitism rates of fed I. scapularis larvae collected from Peromyscus leucopus (Rafinesque) in the field and larvae exposed to H. hookeri while feeding on P. leucopus in a laboratory arena were low (1% and 6%, respectively). These rates are too low to account for the level of parasitism seen in the field in unfed, questing nymphs (21–26%). This finding implies that while some parasitism may occur on mice under field conditions, larger mammals or detached larval ticks must be the principal site where H. hookeri encounters and oviposits in ticks. Further field studies of parasitism of larval ticks on larger mammals would be needed to clarify this issue.

Integrative ecology and the dynamics of species in oak forests

Lyme disease and gypsy moth outbreaks plague many temperate oak forests. Over the past decade, we have developed models and hypotheses designed to allow us to predict irruptions of both gypsy moths and the tick vector of Lyme disease. We have documented a web of connections involving mast production by oak trees, population responses by white-footed mice, habitat selection by white-tailed deer, and population dynamics of both tick parasites and defoliating insects. In patchy landscapes typical of the northeastern U.S., dispersal by mice, deer, and attached ticks between oak and nonoak forests creates dynamics that would not be predictable by focusing on a single patch type. We would not have uncovered these interactions without adopting a research approach that comprised: (1) the inclusion of diverse taxa of animals, plants, and microbes; (2) the integration of individual, population, community, and ecosystem levels of organization; (3) the incorporation of more than one patch type in a heterogeneous landscape; and (4) a combination of long-term monitoring and manipulative field experiments.

Ticks Parasitizing Humans in Georgia and South Carolina

From 1990 through 1995, 913 ticks removed from 460 human patients in Georgia or South Carolina were identified and recorded. The majority of these specimens (758, 83.0%) were lone star ticks, Amblyomma americanum. One hundred and four (11.4%) American dog ticks Dermacentor variabilis, 36 (3.9%) blacklegged ticks Ixodes scapularis, 9 (1.0%) Gulf coast ticks Amblyomma maculatum, and 6 (0.7%) brown dog ticks Rhipicephalus sanguineus were also recovered. All active stages (larvae, nymphs, and adults) of A. americanum were represented, whereas nymphs and adults of D. variabilis and I. scapularis and only adults of A. maculatum and R. sanguineus were recorded. Compared with data published for other regions in the U.S.A., A. americanum was a much more prevalent parasite of humans in the current survey. Only 1 (3%) of the I. scapularis collected was a nymph. Because these tick species are vectors of zoonotic pathogens or cause tick paralysis in humans, the data have epidemiological significance.

Alteration of arachidonate levels in tick salivary glands by dietary modification of host blood lipids.

Tick saliva contains prostaglandins of the 2-series, believed to facilitate bloodmeal acquisition. Because ticks cannot synthesize the prostaglandin precursor, arachidonic acid, investigations were undertaken to study the uptake, incorporation, and distribution of arachidonic acid in the salivary glands of the lone star tick in vitro and in vivo. Uptake of [3H]arachidonate by isolated salivary glands was reduced in the presence of low concentrations of arachidonic or eicosapentaenoic acids, but much higher, non-physiological concentrations of oleic and linoleic acids were required to inhibit [3H]arachidonate uptake. The incorporation of [3H]arachidonate into triglycerides increased at high concentrations of arachidonic or eicosapentaenoic acid, but not at any concentration of oleic or linoleic acid. Eicosatetraynoic acid greatly inhibited [3H]arachidonic acid. Guinea pigs fed hydrogenated coconut oil, safflower/primrose oil, or fish oil exhibited altered blood lipids; notably increased levels of eicosapentaenoic acid when fed fish oil. Salivary gland lipids in ticks fed on these hosts were also altered. Ticks parasitizing fish oil-fed guinea pigs contained high levels of eicosapentaenoic acid with a 30% reduction in arachidonate levels. The results demonstrated that eicosapentaenoic acid in the host diet had profound effects on arachidonate assimilation by tick salivary glands, which could lead to altered prostaglandin content in tick saliva.

The effect of severe drought on the abundance of ticks on vegetation and on scrub hares in the Kruger National Park

Free-living ixodid ticks were collected monthly from August 1988 to July 1993 from the vegetation of landscape zones 17 (Sclerocarya caffra/Acacia nigrescens Savanna) and 4 (Thickets of the Sabie and Crocodile Rivers) in the south-east and south-west of the Kruger National Park respectively, and parasitic ticks from scrub hares in the latter landscape zone. Total tick collections from the vegetation of both landscape zones were lowest in the year following the drought year of August 1991 to July 1992, while the tick burdens of the scrub hares were lowest during the drought year itself.

Human tick bite records in a United States Air Force population, 1989–1992: implications for tick-borne disease risk

Reports of tick parasitism were recorded for US Air Force personnel ( n = 410) from 30 states and the District of Columbia. Of 462 ticks involved in attacks on people, the lone star tick, Amblyomma americanum, and the American dog tick, Dermacentor variabilis, were the most common species represented (34.2% and 34.0%, respectively). Two vectors of Lyme disease, Ixodes pacificus and Ixodes scapularis (including the former Ixodes dammini) also parasitized people but were less common (1.7% and 9.1%, respectively). In addition, 34 (7.3%) brown dog ticks, Rhipicephalus sanguineus, were identified from human hosts. Most ticks submitted for identification were adults (66.5%) and nymphs (29.1%). Larvae were submitted infrequently (<5%). Of those specimens examined for feeding status, 50.0% had blood-fed to some degree. Patients from which ticks were removed were predominantly male (56.8%) and ranged in age from 1 to 76 years with 55.3% (n = 152) being under 20 years. The head and neck area and the lower extremities were the most common sites of attachment by ticks (37.7% and 24.3%, respectively), but ticks were found attached on other areas of the body also, including the trunk, upper extremities, buttocks, and groin. Most ticks (65.5%) bit their victims during May, June, or July, but parasitism occurred during all months of the year. Our data suggest that people from all age groups and from across the United States are vulnerable to parasitism by ticks and, potentially, tick-borne diseases.

Integrated management strategies for Amblyomma americanum (Acari: Ixodidae) on pastured beef cattle.

Data on tick control and knowledge of the damage caused to beef cattle by tick feeding were incorporated into a computerized dynamic life table model (LSTSIM) for Amblyomma americanum (L.). Simulations were made to determine economically feasible, 5-yr integrated pest management (IPM) strategies for A. americanum in forage areas utilized by Bos taurus, Bos indicus, and crossbred cattle (B. taurus x B. indicus). The effects of host resistance, pasture rotation, habitat conversion, topical acaricides, systemic acaricides, and the area-wide application of acaricides to pastures on populations of parasitic female ticks were simulated as individual control technologies and as components of multiple-factor IPM strategies. The most effective, single-factor control strategy for A. americanum in beef cattle forage areas is the use of tick-resistant B. indicus cattle. Pasture rotation combined with area-wide acaricide applications was the only economically feasible IPM strategy for B. indicus cattle and reduced tick densities by 89% after 5 yr. Thirteen economically feasible IPM strategies were identified for use with B. taurus cattle. Of these, the most efficacious was pasture rotation in May combined with systemic or topical acaricide applications. Other strategies included systemic acaricides with area-wide acaricide applications to pastures, topical acaricides with area-wide acaricide applications, pasture rotation with habitat conversion and topical acaricides, and pasture rotation with habitat conversion, topical acaricides, and area-wide acaricide applications. Each technology reduced tick densities on B. taurus cattle by > 80% over a 5-yr period. Nine IPM strategies were economically feasible for use with crossbred cattle. Of these, pasture rotation combined with systemic or topical acaricide applications reduced the number of female ticks on cattle by > 84%; pasture rotation combined with habitat conversion reduced tick numbers by 77%. The most effective nonacaricide-based IPM strategy for B. taurus and crossbred cattle was pasture rotation combined with habitat conversion. No acaricide-free IPM strategy was economically feasible for use with B. indicus cattle.

Detection of the protozoan parasite Theileria annulata in Hyalomma ticks by the polymerase chain reaction

Adult Hyalomma ticks were examined for the presence of Theileria annulata infection using the Polymerase Chain Reaction (PCR). A 372 bp DNA fragment derived from the small ribosomal RNA gene of T. annulata was amplified from 45 out of 50 (90%) H. dromedarii ticks and from 36 out of 50 (72%) H. marginatum marginatum ticks. No product was amplified from non-infected control ticks. Restriction enzyme digestion with Sac II confirmed that the product was derived from the targeted T. annulata gene. As a further confirmation it was shown that both species of Hyalomma ticks were able to transmit T. annulata to experimental calves. PCR detection of Theileria parasites in ticks was compared with conventional staining of dissected salivary glands using methyl green pyronin and its comparative advantages are discussed.

Relative Importance of Bird Species as Hosts for Immature Ixodes dammini (Acari: Ixodidae) in a Suburban Residential Landscape of Southern New York State

Abundance of birds and their tick parasites were estimated in a residential community located in Westchester County, NY, where Lyme disease is endemic. In total, 36 bird species (416 captures) were collected, of which 25 species (69%) were parasitized by ticks. Ixodes dammini Spielman, Clifford, Piesman & Corwin composed 96.4% of the 1,067 ticks found on birds. The bird species most heavily parasitized was house wren, Troglodytes aedon Vieillot (11.1 Ixodes dammini per bird). Relative density estimates of birds, using fixed circle radius counts, revealed dominance by the American robin, Turdus migratorius L. (29.3%), followed by the common grackle, Quiscalus quiscula (L.) (9.3%). Bird density estimates were combined with tick abundance data to calculate an importance value for each bird species as a host for immature I. dammini. The American robin was most important, accounting for 72.7% of all larval I dammini found on birds, followed by the common grackle (8.2%) and the house wren (5.9%). Both the American robin and house wren are reservoir competent for the Lyme disease spirochete Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner and therefore may contribute to the risk of Lyme disease for humans. During August when larvae were most prevalent, 39% of the American robins and 70% of the common grackles were observed on lawns. These species are probable contributors to nymphal I. dammini populations found on lawns.

The incidence of the tick parasite Ixodes uriae in Kittiwake Rissa tridactyla colonies in relation to the age of the colony, and a mechanism of infecting new colonies

Kittiwakes Rissa tridactyla (683 chicks and 64 adults) were examined for ectoparasites in three breeding areas: Isle of May (Firth of Forth, Scotland; eight colonies of approximately known age of occupation on natural sites), North Shields and Gateshead (Tyne and Wear, England; well established colonies of known age on buildings). All the 208 ticks collected were Ixodes uriae. On the Isle of May, a colony which had only been established for 7 years was already infested by ticks. Tick incidence increased significantly with the length of colonization of the area during the first 30 years. Age of colonization did not have an effect after 30 years. In Gateshead only a single adult among the 127 birds examined had a tick. No ticks were found on the 106 chicks born at North Shields checked in 1987 or in 1988. However, among nine visiting newly‐fledged chicks from neighbouring colonies caught at the North Shields colony, six had either ticks or scars of previous infestation. Some visiting chicks remained for several days in the host colony and were even fed by the owners of visited nests. Ixodes uriae may thus spread from one colony to another during visits of newly‐fledged infested chicks to neighbouring colonies. The absence of any infestation in old colonies (38 years in North Shields and 17 years in Gateshead) on buildings that are regularly visited by newly fledged infested chicks, suggests that buildings may lack the rock refuges necessary for tick survival from one year to the next. In this respect Kittiwake colonies on buildings are rather atypical.

Population growth rates forAmblyomma americanum (Acari: Ixodidae) onBos indicus, B. taurus andB. indicus x B. taurus cattle

Densities of Amblyomma americanum (L.) on Bos indicus, B. taurus and B. indicus X B. taurus cattle are compared over a 3-year period, and the growth rate (rate of increase or decrease) of parasitic tick populations on each cattle genotype is estimated. Average log10 densities of parasitic A. americanum larvae are significantly (P = 0.05) lower on B. indicus cattle than on B. taurus and B. indicus XB. taurus cattle. Average log densities of nymphal and adult ticks on B. taurus cattle are significantly higher than on B. indicus cattle but neither cattle genotype differs in this regard from B. indicus X B. taurus cattle. Estimated annual tick population growth rates (log10) for parasitic A. americanum are positive on B. taurus cattle (+0.84 larvae, +0.09 nymphs, +0.22 adults calf-1 year-1), but are negative on B. indicus (-0.18 nymphs, -0.14 adults calf-1 year-1) and B. indicus X B. taurus cattle (-0.45 larvae, -0.24 nymphs, -0.14 adults calf-1 year-1). Populations of parasitic larvae were not detected on B. indicus cattle.

Tick parasitism and antibodies to Borrelia burgdorferi in cats

Summary Ticks were removed from naturally infested cats, and serum samples from these cats were tested for antibodies to Borrelia burgdorferi. Twenty-two of 93 cats (23.7%) had one or more motile stages of Ixodes dammini attached. Of 2 larvae and 20 nymphs removed from cats, 1 larva and 2 nymphs were infected with B burgdorferi. Spirochetes were not found in tissues of 13 female and 4 male ticks. Ten of 71 serum samples analyzed by indirect fluorescent antibody staining or elisa contained antibodies to this spirochete. Maximal antibody titers were 1:256 and 1:2,560, respectively. At titers ≥1:160 in elisa, seropositivity ranged from 8.8% (n = 34 sera tested from 34 cats) in May through July to 33.3% (n = l2 cats tested) during February through April. In clinical studies of 30 cats, there were nearly equal percentages of seropositive cats with limb or joint disorders not accompanied by fever, anorexia, or fatigue (5 of 21 cats) and cats with these signs of illness but lacking lameness (2 of 9 cats.)