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Modification of the food and agriculture organization larval packet test to measure amitraz-susceptibility against ixodidae.

Modifications of exposure time, substrate, and formulation were made to the Food and Agriculture Organization Larval Packet Test (LPT) to determine a combination suitable for measuring the susceptibility of Boophilus microplus (Canestrini) to amitraz. Exposure time influenced the slope of the dose-response when paper was used as a substrate for amitraz. However, time did not influence the dose-response slope when nylon fabric was used as an amitraz substrate. Formulated amitraz produced results with less deviation from the log-probit model than technical amitraz. The combination of formulated amitraz and nylon fabric as a substrate for amitraz produced results that best fit the log-probit model. The modified FAO procedure (formulated amitraz/nylon substrate combination) was used to assay a Brazilian strain of B. microplus and a Panamanian strain of Rhipicephalus sanguineus (Latreille). Resistance ratios (95% CI) of 26.3 (25.7-26.9) and 7.3 (5.5-9.9) were calculated for the B. microplus and R. sanguineus strains, respectively. A discriminating dose of 0.03% amitraz was determined for B. microplus. This technique will help to locate amitraz resistant tick populations, provide data for improved control practices, and aid in the discovery of resistance mechanisms through synergist studies and verification of molecular techniques.

Animals↗

Lyme disease--United States, 2001-2002.

Lyme disease (LD) is caused by the spirochete Borrelia burgdorferi and is transmitted through the bite of Ixodes spp. ticks. CDC began LD surveillance in 1982, and the Council of State and Territorial Epidemiologists designated LD a nationally notifiable disease in 1991. This report summarizes the analysis of 40,792 cases of LD reported to CDC during 2001-2002. The results of that analysis indicate that annual LD incidence increased 40% during this period. The continued emergence of LD underscores the need for persons in areas where LD is endemic to reduce their risk for infection through integrated pest management, landscaping practices, repellent use, and prompt removal of ticks.

Humans↗

Efficacy of attenuated Anaplasma marginale vaccine under laboratory and field conditions in Colombia.

Four-month-old Holstein-Friesian calves were inoculated with 3 different doses (1, 2, and 3 ml) of attenuated Anaplasma marginale vaccine. Vaccinated calves showed mild anaplasma parasitemia, slight decrease in packed cell volume, low serologic conversion, and no clinical illness. An artificial challenge exposure of vaccinated and unvaccinated calves with virulent Colombian A marginale showed that the vaccine provided protection against clinical signs of the disease, including parasitemia and anemia. The volume of the vaccinal dose did not alter the degree of protection provided. A 2nd group of 8- to 9-month-old Holstein-Friesian calves was then inoculated with 3 ml of anaplasma vaccine and premunized with both Babesia bigemina and Babesia argentina while being housed in an area free of these diseases. Calves were moved to an enzootic region heavily infested with various arthropods, including ticks, for natural field challenge exposure. Control calves, which were not given anaplasma vaccine, suffered clinical illness manifested by severe anemia and an average weight loss of 50.6 kg due to anaplasma field challenge exposure. In contrast, vaccinated calves did not show anemia and their weight loss was 3.9 kg.

Anaplasma↗

Economics of theileriosis control in Zambia.

For an economic analysis of theileriosis control, we adopted the total economic cost (TEC) method, which calculates the sum of output losses from tick damage, theileriosis mortality and morbidity, and expenditures for treatment or prevention of the disease. At farm level, the TEC can be minimized by a specific combination of vector control and/or immunization and an acceptable level of losses. Expenditures for vector control include acaricides, construction of dipping or spraying facilities and their maintenance, and variable costs such as those for water and labour. Economics of vector control depend on the herd size and the method of application of the acaricide. Morbidity, mortality and tick damage losses are effectively reduced by correct and intensive vector control programmes. Expenditures for vector control are estimated at US$ 8. 43, 13.62 and 21.09 per animal per year for plunge dipping, hand spraying and pour-on, respectively. Immunization costs comprise production of parasite stabilates, storage and application, delivery and treatment. At US$ 9.5 per animal, immunization limits losses caused by Theileria parva, but ticks still may reduce the productivity of the animals. Expenditures for treatment after natural infection involve drugs, transport, veterinary fees and farm labour costs. Treatment has a moderate success rate, hence both morbidity and mortality remain important factors. Equally, it does not affect the vector, which may continue to reduce overall productivity of cattle. Expenditures for treatment range between US$ 9.04 and US$ 27.31 per animal. To compare different TECs in relation to different control strategies, assumptions have to be made on disease occurrence, case fatality, value and productivity of the cattle, reductions in productivity due to morbidity and number of animals under a specific control regime. Calculations based on data from Southern Province, Zambia show that large-scale immunization reduces the TEC by 90% compared to no intervention. Treatment, which is the second-best option, reduces the TEC by 60%. Appendix 1 Summary of factors influencing total economic cost

Animals↗

Identification of protective antigens for the control of Ixodes scapularis infestations using cDNA expression library immunization.

Identification of antigens that induce an immune response against tick infestations is required for the development of vaccines against these economically important ectoparasites. In order to identify protective antigens, we constructed a cDNA expression library from a continuous Ixodes scapularis cell line (IDE8) that was initially derived from tick embryos. cDNA clones were subjected to several rounds of screening in which mice were immunized with individual pools and then challenge-exposed by allowing I. scapularis larvae to feed on the immunized and control mice. Immunity against tick infestation was determined by the reduction in the ability of the larvae to feed to repletion and molt to the nymphal stage. Individual clones in pools that induced immunity to larval infestations were partially sequenced and grouped according to their putative protein function by comparison with sequence databases. The screening identified several individual antigens that induced a protective immune response against I. scapularis infestations. Our studies demonstrated for the first time that cDNA expression library immunization (ELI) combined with sequence analysis is a powerful and efficient tool for identification of candidate antigens for use in vaccines against ticks.

Animals↗

IgG responses to salivary gland extract of Ixodes ricinus ticks vary inversely with resistance in naturally exposed sheep.

Enzyme-linked immunosorbent assay (ELISA) was used to investigate the antibody responses of control sheep, and sheep naturally exposed to Ixodes ricinus Linné (Acari: Ixodidae) ticks, to salivary gland extract (SGE) proteins of partially fed, adult I. ricinus. Comparisons between responses of control sheep and naturally infested sheep by Western blot analysis suggested that variations in IgG responses of I. ricinus-exposed sheep were mostly associated with specific responses to I. ricinus SGE antigens. Sheep IgG responses were positively related to the numbers of adult ticks feeding per sheep at the time samples were collected, were greater during the spring than the autumn periods of I. ricinus activity and were inversely related to sheep resistance to ticks measured by the weights of nymphal I. ricinus that engorged on the sheep. These findings suggest that sheep lose their resistance to ticks due to polarization of a Th1 type response to some tick antigens towards a Th2 type response when sheep are exposed to high, natural tick infestations, or to seasonal conditions of relative nutritional stress. Potential consequences for the epidemiology of tick-borne diseases are discussed.

Animals↗

[The reaction of taiga ticks to an attractant. III. The use of attractant-acaricidal granules in a field experiment].

On June 15, a total of 300 granules were placed at 1-m intervals on the sides of a concrete-covered road located along the steep slope of a valley. The number of ticks on 300-m plots decreased from 557 (before the experiment) to 55 on June 24 and to 11 on June 27. On the 200-m control plot there were 256, 280 and 168 ticks, respectively, in the same periods of time. Thus, the efficiency of tick eradication was 91 and 97% on days 9 and 12, respectively.

Animals↗

The influence of various factors on fluid secretion by in vitro salivary glands of ixodid Ticks.

1. Salivary glands of the female ixodid tick, Dermacentor andersoni, secrete fluid in vitro when bathed in a slightly modified version of the mammalian tissue culture medium 'TC 199'. 2. Rate of salivation in vitro increases with progression of feeding, but there is no comparable increase in dry weight of the salivary glands during the early phase of engorgement. Engorged ticks secreted at only 25% the rate of 90-250 mg ticks, indicating that salivary gland degeneration has already begun in the very early post-engorgement stage. 3. A salivary gland stimulating factor can be detected in the nervous system but not in other tissues. 4. Male salivary glands secrete at only 1/20th the rate of female glands. Thus males probably do not use their salivary glands as osmoregulatory organs. 5. From the uniform lack of response to ACh and uniform response to DA in 7 ixodid tick species, it is suggested that the control of salivation is similar throughout the ixodid family.

Acetylcholine↗

Seroprevalence of Babesia infections in humans exposed to ticks in midwestern Germany.

Babesiosis is considered to be an emerging tick-borne disease in humans worldwide. However, most studies on the epidemiology of human babesiosis to date have been carried out in North America, and there is little knowledge on the prevalence of infection and frequency of disease in other areas. The aim of this study was to investigate the prevalence of Babesia infections in a human population in Germany. A total of 467 sera collected between May and October 1999 from individuals living in the Rhein-Main area were tested for the presence of immunoglobulin G (IgG) and IgM antibodies to antigens of Babesia microti and Babesia divergens by indirect fluorescent-antibody (IFA) tests. These sera were derived from 84 Lyme borreliosis patients suffering from erythema migrans, 60 asymptomatic individuals with positive borreliosis serology, and 81 individuals with a history of tick bite. Cutoff values for discrimination between seronegative and seropositive results in the IFA tests were determined using sera from 120 healthy blood donors and 122 patients suffering from conditions other than tick-borne diseases (malaria, n = 40; toxoplasmosis, n = 22; syphilis, n = 20; Epstein-Barr virus infection, n = 20; and presence of antinuclear antibodies, n = 20). The overall specificities of the IFA tests for B. microti and B. divergens were estimated to be >or=97.5%. Positive IgG reactivity against B. microti antigen (titer, >or=1:64) or B. divergens antigen (titer, >or=1:128) was detected significantly more often (P < 0.05) in the group of patients exposed to ticks (26 of 225 individuals; 11.5%) than in the group of healthy blood donors (2 of 120 individuals; 1.7%). IgG antibody titers of >or=1:256 against at least one of the babesial antigens were found significantly more often (P < 0.05) in patients exposed to ticks (9 of 225) than in the control groups (1 of 242). In the human population investigated here, the overall seroprevalences for B. microti and B. divergens were 5.4% (25 of 467) and 3.6% (17 of 467), respectively. The results obtained here provide evidence for concurrent infections with Borrelia burgdorferi and Babesia species in humans exposed to ticks in midwestern Germany. They also suggest that infections with Babesia species in the German human population are more frequent than believed previously and should be considered in the differential diagnosis of febrile illness occurring after exposure to ticks or blood transfusions, in particular in immunocompromised patients.

Adult↗

Efficacy of coumaphos applied as a dip for control of an organophosphorus-resistant strain of Boophilus microplus (Acari: Ixodidae) on cattle.

The efficacy of coumaphos, an organophosphorus acaricide, was tested on a strain of Boophilus microplus (Canestrini) that was 9.5 times more resistant to the chemical than a susceptible strain. Cattle infested with larval, nymphal, and adult ticks were dipped into a vat charged at concentrations of 0.031, 0.083, 0.160, and 0.279% (AI). Assessment of efficacy was based on surviving tick numbers, female weight, egg mass weight, egg hatchability, and index of reproduction. At 0.031% (AI), the level of control was lower than the other coumaphos treatments, and the weight, fecundity, and fertility of surviving females was similar to untreated females, indicating only minimal adverse effects on the ticks. At 0.160 and 0.279% (AI), no differences in control, female weight, egg mass weight, or percentage egg hatch were observed, but effects were greater than that of untreated ticks or ticks treated at 0.031% (AI). At 0.083% (AI), most biological parameters were intermediate, but there was no difference in control compared with the 2 higher concentrations. Thus, even with the increase in concentration of more than 3 times between treatments of 0.083 and 0.279% (AI), there was no substantial increase in control. The residual efficacy of all 4 treatments showed that none provided complete protection against larval reinfestation for even 1 wk after treatment. Therefore, the presence of organophosphorus-resistant ticks at U.S. ports-of-entry could jeopardize the success of the Boophilus eradication program.

Animals↗

Immunisation of smallholder dairy cattle against anaplasmosis and babesiosis in Malawi.

A field study was conducted in the Southern Region of Malawi to evaluate the possible benefits of immunisation of improved dairy cattle against Anaplasma marginale, Babesia bigemina and Babesia bovis. Friesian crossbred heifers were immunised when they were being reared on Government farms. They were then issued to smallholder farmers, together with unvaccinated controls, where many of them were exposed to heavy tick infestation. Vaccination was shown to provide a significant degree of protection against babesiosis on the smallholder farms; 15/32 unvaccinated controls developed clinical disease as compared to only 3/28 vaccinates.

Anaplasma↗