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At least 1,243 records · Page 69Linked to original sources
PubMed2000

Seasonal dynamics of Anocentor nitens on horses in Brazil.

Anocentor nitens is a widespread ectoparasite of horses in Brazil. A study of the seasonal dynamics of the parasitic phase of this tick was made by regular census of engorging females (>/=4mm) on free-ranging horses, fortnightly from July 1995 to July 1997, at Pedro Leopoldo, Minas Gerais. Twenty horses were divided into four groups of five animals per group, each having a similar mix of resistant and less resistant animals, based on initial infestation. Every 2 weeks, one of the groups, in sequence, was treated with an acaricide to prevent excessive infestations, and female ticks were censused 38 days later. The acaricide dips did not interfere with the seasonal dynamics of the tick population, which produced three major peaks of activity over a 12-month period. The first two peaks were in the hot, wet season and the third in the cold dry season. Tick numbers were similar for the two 12-month periods, decreasing from the spring and summer to the autumn and winter. Infestation rates were not equal among different horses. Twenty percent of the horses were responsible for 48% of the total parasite load, while 30% accounted for only 2.5% of the total parasite load. Principal predilection sites were; the ear (61%), mane (21%), and muzzle and face (6%). Measures for the strategic control of A. nitens ticks are discussed.

Animals↗
PubMed2005

Neurologic, neuropsychologic, and electroencephalographic findings after European tick-borne encephalitis in children.

Tick-borne European early summer meningoencephalitis is believed to be a benign disease in childhood. The causative RNA virus is from the same family as the West Nile virus, and the respective clinical presentations have many similarities. We studied 19 German children who had suffered from tick-borne encephalitis virus meningitis or meningoencephalitis in an endemic area and compared them with 19 matched controls. Epidemiologic data were consistent with known features of tick-borne encephalitis infection in southern Germany. None of the children studied had severe neurologic or neuropsychologic sequelae. One child developed significant clinical depression shortly after the illness. Electroencephalograms (EEGs) from children with tick-borne encephalitis were significantly slower on follow-up than control EEGs. After tick-borne encephalitis, children had a higher likelihood of having an impairment of attention and psychomotor speed. Using the Touwen neurologic examination, after tick-borne encephalitis, children had lower scores than control children on 4 of the 10 subsystems. Owing to the small sample size, it was difficult to identify risk factors for and predictors of adverse outcomes.

Adolescent↗
PubMed1990

Haemoparasites of equines: impact on international trade of horses.

The geographical distribution of Babesia equi and Babesia caballi and their tick vectors is discussed. Control of infections with these protozoa is hampered by the lack of a suitable antiprotozoal drug and a reliable serological test. No vaccine is available. Ehrlichia risticii (the causal agent of Potomac horse fever) and E. equi are rickettsial parasites which are difficult to control. Little is known of their geographical distribution and vectors. Early diagnosis is required for tetracycline therapy to be effective and there is a need for a rapid test to provide an early diagnosis.

Animals↗
PubMed2000

Testosterone, ticks and travels: a test of the immunocompetence-handicap hypothesis in free-ranging male sand lizards.

The immunocompetence-handicap hypothesis suggests that androgen-dependent male characters constitute honest signals of mate and/or rival quality because of the imposed costs through immune suppression associated with elevated testosterone levels. We demonstrate in a field experiment that male sand lizards (Lacerta agilis) exposed to elevated testosterone suffered from increased mass loss and tick load compared to control males. Although the first of these two results could be due to an elevated basal metabolic rate from increased plasma testosterone levels, the increased parasite load was statistically independent of the loss in body condition and is likely to be due to compromised immune function. Testosterone-treated males showed greater mobility than control males, and greater mobility resulted in higher mating success. Our experiment thus lends support to the immunocompetence-handicap hypothesis, suggesting that male testosterone levels have been moderated by balancing selection for reproductive success and sustained immune function.

Animals↗
PubMed2002

Transmission of Anaplasma phagocytophila (human granulocytic ehrlichiosis agent) in horses using experimentally infected ticks (Ixodes scapularis).

Most human granulocytic ehrlichiosis (HGE) studies carried out in horses use needle inoculation of infected leucocytes or cell cultures. This route of inoculation does not accurately reflect natural infection of the tick-borne agent. To investigate whether tick transmission influences the course of granulocytic ehrlichiosis in the horse model, experimental transmission through infected laboratory-reared Ixodes scapularis ticks was attempted into two healthy horses. One additional horse served as negative control and was exposed to uninfected ticks. Eleven days after exposure to nymphal or adult ticks infected with Anaplasma phagocytophila (HGE agent) the two horses developed severe clinical and laboratory signs consistent with granulocytic ehrlichiosis. Bacteraemia was determined at various time points in the two horses by observation of morulae within neutrophils and by detection of A. phagocytophila genomic DNA by PCR of peripheral blood leucocytes. Further, both horses seroconverted. In contrast the control horse stayed uninfected. The results demonstrate that A. phagocytophila can be experimentally transmitted by infected nymphal and adult ticks and that the agent is able to produce a severe disease, similar to naturally occurring cases. Therefore, tick transmission is highly reproducible and can be successfully used in the equine animal model in order to study HGE.

Anaplasma phagocytophilum↗
PubMed1998

Impact of controlled burns on the abundance of Ixodes scapularis (Acari: Ixodidae).

Information on the effect of vegetative destruction by controlled burns in reducing the abundance of the blacklegged tick, Ixodes scapularis Say, the vector for the agents of Lyme disease, human babesiosis, and human granulocytic ehrlichiosis, is limited. Therefore, the abundance of nymphal, larval, and adult I. scapularis was monitored by dragging the vegetation at 2 separate 4-ha tracts in Cockaponset State Forest in Connecticut following a single controlled burn on 15 April or 21 May 1992. The burn at the April burn site was rated as light to moderate with a flame height of 0.3 m and consumed approximately 67% of the surface leaf litter. The burn at the May burn site was rated moderate to severe with a flame height of 0.6-0.9 m., which consumed vegetation < 5 cm in diameter and approximately 100% of the surface leaf litter. The impact of the burn was strongly influenced by the intensity and timing of the burn. Burning of the vegetation resulted in a reduction of the abundance of nymphal I. scapularis by 74% at the moderately burned site and 97% at the severely burned site, compared with adjacent unburned woodland. No larvae were recovered later in the summer from the severely burned tract. However, judging by the comparable abundance of adult I. scapularis in the fall at the burned and unburned woodlands, the effect of the burns was temporary. Burning the vegetation for the control of I. scapularis appears limited in effect and could be applied only on a large scale in areas with little or no human habitations.

Animals↗
PubMed1997

[Application of the 3 R]

This report describes the various ways in which animal experiments were replaced, reduced or refined by the manufacturer in the quality control of the tick-borne encephalitis (TBE) vaccine over the past fifteen years. The total number of test animals was reduced from 4.278 to 2.011 per vaccine lot. This involves a reduction of 34.005 test animals per year. If a further planned change submitted to the regulatory authorities is approved, the number of animals used will be further reduced to 961 per vaccine lot. This will result in a total saving of 49.755 animals per year. A newly developed TBE vaccine, which will be submitted to the EC regulatory authorities in 1997, will involve even further reductions in the number of test animals required for quality control. Only 531 test animals will be required per lot for this newly developed vaccine i. e. almost 90% reduction compared to the numbers required for the original vaccine. It has been possible to convince the national regulatory authority that only a minimal amount of animal tests are essential for the quality control of this vaccine. This has been made possible by the intensive search for replacement tests and by the high standard of validation of these tests. It will probably not be possible to totally eliminate animal tests for vaccine quality control in the future. However, the vigorous implementation of the 3R"s will certainly lead to a reduction in the number of animals required and the reduction of animal suffering. The aim of this policy must be seen not only as a reduction in the number of animals used, but primarily a reduction in suffering to the lowest possible levels for the animals still required.

Journal Article↗
PubMed2006

Gluttony and sex in female ixodid ticks: how do they compare to other blood-sucking arthropods?

The central issue dealt with here is the role of copulation in the control of feeding behaviour in ticks and some haematophagous insects. Female ticks of the family Ixodidae normally engorge to approximately 100 x their unfed body weight, and then drop from the host, produce and lay eggs, and die. Virgins, on the other hand, normally do not exceed 5-40% (depending on species) of the normal engorged body weight. But instead of detaching voluntarily at that point most virgins remain fixed to the host for extended periods, waiting for males to find them so they can complete engorgement. Virgin haematophagous insects, and virgin ticks of the family Argasidae display little, if any, reduction in blood meal size compared to mated females, at least not during the first ovarian cycle. During subsequent ovarian cycles, meal size in some virgin insects may be somewhat reduced depending on how many eggs are retained in the reproductive tract, but the reduction is not nearly to the same extent as that observed for virgin ixodid females. The stimulatory effect of copulation on engorgement in the latter is caused by a pair of proteins (voraxin alpha and beta) produced in the testis and transferred to the female with the spermatophore. Here, I propose why it might be adaptive for an ixodid female to remain small until mated. The hypothesis is suggested from the facts that ixodid ticks remain attached to the host for days (rather than minutes), and that virgin ticks, above a certain critical weight, lose all opportunity for producing viable offspring should they be groomed off the host prematurely, or should the host die while ticks are still attached.

Adaptation, Physiological↗
PubMed2000

Simulation of rotational grazing to evaluate integrated pest management strategies for Boophilus microplus (Acari: ixodidae) in Venezuela.

Ranchers in Venezuela historically have controlled the cattle-fever tick, Boophilus microplus (Canestrini), with acaricide treatments of cattle but no technical planning. We developed a simulation model to evaluate cattle-tick population dynamics in systematic pasture rotation systems and Integrated Pest Management (IPM) approaches to managing ticks in the tropical dry-forest ecological zone of Venezuela. Model output showed five generations of cattle-ticks produced each year throughout the dry and rainy seasons that occur in this zone. Sensitivity analyses showed disproportionately large changes in on-host B. microplus populations in response to small changes in larval mortality rates, such as those resulting from differences in the innate resistance of cattle to tick parasitism. Simulation results with 1-6 pasture systems suggest that adjusting the graze:rest sequence with systematic rotation among 4-6 pastures could suppress, but not eradicate, tick populations.

Animal Husbandry↗
PubMed1991

Evaluation of Rhipicephalus sanguineus as a potential biologic vector of Ehrlichia platys.

The brown dog tick, Rhipicephalus sanguineus (Acari: Ixodidae), transmits several diseases among dogs including Ehrlichia canis infection. The role of Rhipicephalus sanguineus as a biologic vector for E platys, the rickettsial agent of infectious canine cyclic thrombocytopenia, was studied in dogs. Laboratory-cultured, pathogen-free nymph ticks were fed to repletion on dogs acutely infected with E platys. Tick engorgement coincided with the development of initial parasitemia and thrombocytopenia in the infected dogs. Following repletion, nymph ticks were allowed to molt under controlled conditions. One-month-old E platys-exposed adult ticks failed to infect naive dogs in animal transmission studies. The presence of E platys was not detected in midguts or salivary glands of similarly exposed adult ticks by use of light and transmission electron microscopy. These studies indicate that R sanguineus may not transmit E platys infection.

Animals↗
PubMed1996

The efficacy of amitraz against cattle ticks in Tanzania.

The efficacy of amitraz on cattle ticks was assessed by susceptibility tests, spraying and dipping trials. Tests on the susceptibility of three tick species, Rhipicephalus appendiculatus, Amblyomma variegatum and Boophilus decoloratus to amitraz (technical grade-purity 98.6% w/w) showed all 15 tick strains tested to be highly susceptible, with LC50 ranging between 0.001% and 0.03%, and LC99, between 0.01% and 0.07%. Spraying trials were carried out on calves infested with R. appendiculatus, A. variegatum and B. decoloratus. Amitraz wettable powder [as Taktic total replacement (TR)] was tested against B. decoloratus, and amitraz emulsifiable concentrate (as Taktic EC) against the other two species. Both formulations showed instant action, with ticks detaching from the calves between 30 min and 8 h after spraying. More than 50% of the detached engorged females failed to lay eggs. The remainder laid few eggs, and these had a low hatching rate of 0-2%, compared with 90-98% in the controls. The detached nymphs failed to moult, and the males and non-engorged females also detached, were immobilized and finally died. In the dipping trials, cattle heavily infested with ticks (mean tick counts of about 800) were dipped once weekly in amitraz (Taktic TR). Weekly tick counts showed that the reinfestation rate was reduced to zero after the ninth dipping. The results of the three trials complement each other, showing that amitraz is at present effective in the control of African tick species on cattle in Tanzania.

Animals↗
PubMed2005

Morphological alterations of Metarhizium anisopliae during penetration of Boophilus microplus ticks.

Chronological histological alterations of Metarhizium anisopliae during interaction with the cattle tick Boophilus microplus were investigated by light and scanning electron microscopy. M. anisopliae invades B. microplus by a process which involves adhesion of conidia to the cuticle, conidia germination, formation of appressoria and penetration through the cuticle. Twenty-four hours post-infection conidia are adhered and germination starts on the surface of the tick. At this time, the conidia differentiate to form appressoria exerting mechanical pressure and trigger hydrolytic enzyme secretion leading to penetration. Massive penetration is observed 72 h post-inoculation, and after 96 h, the hyphae start to emerge from the cuticle surface to form conidia. The intense invasion of adjacent tissues by hyphae was observed by light microscopy, confirming the ability of M. anisopliae to produce significant morphological alterations in the cuticle, and its infective effectiveness in B. microplus.

Animals↗
PubMed1997

The impact of Ixodiphagus hookeri, a tick parasitoid, on Amblyomma variegatum (Acari: Ixodidae) in a field trial in Kenya.

In an experiment to investigate the effect of the tick parasitoid, Ixodiphagus hookeri, on tick numbers on cattle, 150000 parasitoids were released over a period of 1 year in a field where ten cattle infested with multiple tick species were kept. Amblyomma variegatum was reduced from 44 to two ticks per animal while Rhipicephalus appendiculatus increased over the time of parasitoid release. During the time of release 51% of the nymphs of A. variegatum collected from the animals were parasitized. The recovery of the parasitoids after the releases were stopped was only 9%. The total numbers of A. variegatum remained low up to 1 year after the parasitoid release was stopped. This study gives an insight into how I. hookeri could be used strategically for the management of A. variegatum on small-scale farms.

Animals↗
PubMedDate not supplied

Is the detection of anti-Rhipicephalus sanguineus (Rs24p) antibodies a valuable epidemiological tool of tick infestation in dogs?

Antibodies against the 24 kDa Rhipicephalus sanguineus (Rs24p) protein were detected by ELISA to evaluate the relationship between antibodies and tick infestation. The mean titer of 3 dogs that underwent 2 experimental infestations with adult ticks was transiently increased after the second infestation. There was a significant difference in mean titers between positive control dogs naturally infested with ticks and tick-naive dogs. These results suggested that anti-Rs24p antibodies detected by ELISA are a marker of tick exposure. There was no significant difference in mean titers between tick-naive dogs and seropositive dogs to Ehrlichia canis. Some dogs positive for E. canis antibodies showed, however, higher titers than most tick-naive dogs. R. sanguineus may be related to the E. canis infection in Japan.

Animals↗
PubMed2002

Efficacy of macrocyclic lactone endectocides against Boophilus microplus (Acari: Ixodidae) infested cattle using different pour-on application treatment regimes.

The efficacy of pour-on formulations of three macrocyclic lactone endectocides (moxidectin, ivermectin, and eprinomectin) was evaluated on cattle against Boophilus microplus (Canestrini) using two different treatment regimes. A single application treatment regime with each endectocide showed that fewer ticks per calf were recovered from all treated calves than from untreated cattle, but the level of control among the three treatments was similar (range; 78.7-87.7%) against all stages of ticks on the calves at the time of treatment. The engorged female and egg mass weights of all treated ticks were less than that of untreated ticks. Among the treated groups, the ivermectin and eprinomectin-treated females weighed less and produced lower weight egg masses than those from moxidectin-treated cattle. In a double application treatment regime with a 4-d interval between treatments, there were fewer ticks per calf recovered from the treated cattle than from untreated cattle. In addition, all treated females weighed less and produced lower weight egg masses than those from untreated cattle. Control with moxidectin (90.3%) was lower than with either ivermectin (98.9%) or eprinomectin (99.7%). The mean female and egg mass weight of the ivermectin and eprinomectin-treated groups was also less than that of the moxidectin treatment. A single application treatment against either 18- or 20-d-old adult ticks indicated that both moxidectin and ivermectin were less effective against 20-d-old ticks that were nearer to completing their parasitic development on the animal. In contrast, eprinomectin was the only endectocide tested that was equally effective against both 18- and 20-d-old ticks.

Animals↗
PubMed1991

Reduction in egg viability resulting from infestations on cattle of hybridized Boophilus ticks and B. microplus (Acari: Ixodidae) at various ratios.

The competitiveness of hybridized Boophilus males, which are 100% sterile, was compared to B. microplus (Canestrini). Hybrid larvae used in the study were the offspring derived by cross-mating B. annulatus (Say) males with B. microplus females. Cattle were infested with a total of 2,500 larvae at ratios of 5:1 and 10:1 (hybrid to pure strain). The reduction in egg hatch resulting from the hybrid males was 68 and 77.5% at the 5:1 and 10:1 ratios, respectively. Both treatment ratios produced egg sterility that were lower than expected, assuming purely random mating, suggesting that hybrid ticks were not as competitive as B. microplus males. At the 5:1 treatment level, genotypic determinations based on isoenzyme analysis indicated that mate pairings involving hybrid males occurred 20-40% less frequently than expected, whereas matings involving pure-strain B. microplus males occurred twice as frequently as expected. At the 10:1 treatment level, mate pairings involving hybrid males occurred 10-20% less frequently than expected, whereas pairings involving pure strain B. microplus occurred 2-4 times more frequently than expected. The results indicated that in a sterile hybrid male program, it would be necessary to increase the ratios of hybrids by approximately 2-fold over the 5:1 or 10:1 ratios to achieve the 80-90% sterility expected, because of the decreased competitiveness of hybrid males.

Animals↗
PubMed2003

The efficacy of collars impregnated with flumethrin and propoxur against experimental infestations of adult Rhipicephalus sanguineus on dogs.

The efficacy of 2 sets of collars (Kiltix Collar, Bayer AG), containing different plasticisers and impregnated with the acaricides flumethrin (2.25%) and propoxur (10%), was compared against adult Rhipicephalus sanguineus on experimentally infested, kennelled dogs. Thirty individually penned dogs were infested with 25 male and 25 female, unfed R. sanguineus. On the following day they were allocated to 3 groups of 10 dogs each on the magnitude of their tick burdens. Two days after infestation, medicated collars containing 1 of the plasticisers were fitted to 10 of the dogs and similar collars containing the other plasticiser were fitted to 10 others. The remaining 10 dogs were the untreated controls. Seven and 28 days after having fitted the collars, all dogs were re-infested with 50 unfed adult ticks of both sexes, and again at approximately 28-day intervals up to the 5th month, and then at approximately 14-day intervals during the 6th month. Efficacy was determined by comparing the mean number of live, attached ticks on the untreated control group with those on the collared dogs 2 days after each re-infestation. Immediate efficacy of the collars (Day +2) was > 95%, and residual efficacy was > 98% up to and including Day +114, and > 93% up to Day +170 on both groups of collared dogs. The mean tick counts on the 2 groups of collared dogs did not differ significantly (P < 0.0001) for any of the assessment days.

Animals↗