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Recent acquisitions on tick and tick-borne disease resistance in N'dama (Bos taurus) and Gobra zebu (Bos indicus) cattle.

The use of disease resistant breeds is recognised as an economically realistic alternative to acaricide application and drug administration in tick and tick-borne disease control schemes. Although resistance is mainly associated with zebu (Bos indicus) breeds, studies carried out in The Gambia show a higher resistance to ticks and tick-borne diseases in N'dama (Bos taurus) than in Gobra (B. indicus) cattle. Tick resistance in N'dama breed appears to be effective against those species with long hypostome, such as Amblyomma variegatum and Hyalomma spp. The possible mechanisms involved are discussed. Further investigations are identified to assess the economic value of tick and tick-borne disease resistance in the N'dama breed.

Africa, Western↗

Theileriosis of sheep and goats in China.

Theileriosis is an important disease of sheep and goats in West China. Its main distribution includes Qinghai, Gansu, Ningxia, Inner Mongolia, Shaanxi and Sichuan. The epidemic period is from late March to July with April-May being the peak months. This is the period of most intensive tick attack by Haemaphysalis qinghaiensis (77.2-99.24%) during the year. It has been proved that the nymphs and adults, which develop from larvae and nymphs engorged on infected sheep or goats can transmit the pathogen. Experimental infections revealed the incubation period, clinical signs and the pathogen's morphological characteristics. The disease was more serious in lambs and exotic adult animals than native adult animals. The sickness rates of lambs, exotic and native adult animals were 78-85%, 41% and 9% respectively; death rates were 81.41%, 62.5% and 65% respectively. Clinical prophylaxis, chemical therapy and destruction of ticks have been carried out with antiparasitic compounds to control the disease since 1982. Experiments demonstrated that the curative rate was up to 76-86%, but no satisfactory prophylactic methods were found.

Animals↗

Status of Borrelia burgdorferi infection after antibiotic treatment and the effects of corticosteroids: An experimental study.

Sixteen specific-pathogen-free beagles were infected with Borrelia burgdorferi. Three groups of 4 dogs were treated with antibiotics for 30 consecutive days starting 120 days after tick exposure; 4 dogs were untreated controls. At day 420 after tick exposure and again before euthanasia, 2 dogs of each group were treated with prednisone for 14 days. All dogs contracted infection and 11 developed acute arthritis 50-120 days after exposure. After day 120, one of 12 antibiotic-treated dogs and 2 of 4 untreated dogs became lame. Antibiotic therapy reduced the frequency of Borrelia-positivity in subsequent skin biopsy samples. After prednisone treatment, both control dogs developed severe polyarthritis. At euthanasia, single tissues of the antibiotic-treated dogs and multiple tissues of all control dogs were Borrelia-positive by polymerase chain reaction. Viable spirochetes were not recovered from antibiotic-treated dogs. Two antibiotic-treated dogs showed histologic evidence of minimal lesions, whereas all control dogs had mild polyarthritis with periarteritis.

Animals↗

Mosquito vector control and biology in Latin America--a 15th symposium. Abstracts.

The 15th Annual Latin American symposium presented by the American Mosquito Control Association (AMCA) was held as part of the 71st Annual Meeting in Vancouver, British Columbia, Canada, in April 2005. The principal objective, as for the previous 14 symposia, was to promote participation in the AMCA by vector control specialists, public health workers, and academicians from Latin America. This publication includes summaries of 40 presentations that were given orally in Spanish or presented as posters by participants from 8 countries in Latin America and the USA. Topics addressed in the symposium included results from chemical and biological control programs and studies; studies of insecticide resistance; and population genetics, molecular, ecological, and behavioral studies of vectors of dengue (Aedes aegypti and Ae. albopictus) and other arboviruses, malaria (Anopheles albimanus, An. aquasalis, An. neomaculipalpus, An. pseudopunctipennis), leishmaniasis (Lutzomyia), and Chagas Disease (Triatoma), as well as a vaccine for control of Boophilus ticks on cattle.

Animals↗

Prevalence and potential risk factors for amitraz resistance in Boophilus microplus ticks in cattle farms in the State of Yucatan, Mexico.

Southern cattle tick, Boophilus microplus, control in the Mexican tropics is based on the application by spray, dip or pour-on of acaricides. In Mexico the first report of ticks resistant to amitraz was reported in 2002. Amitraz resistance affecting the cattle industry of Yucatan State, Mexico, has not been investigated. A cross-sectional study was carried out in order to investigate the possible association between management risk factors and the prevalence of B. microplus ticks resistant to amitraz in Yucatan, Mexico. Ninety-eight cattle farms were randomly selected and a sample of 20-30 engorged B. microplus females was collected from at least 10 cattle from each farm. Collected ticks were taken to the laboratory where the larval progeny were obtained. The modified larval immersion test was used to detect ticks resistant to amitraz. A discriminating dose of 0.0002% amitraz was used. A questionnaire was applied on each collaborating farm. For the statistical analysis a 2x2 contingency table was used to identify potential risk factors. The prevalence of farms with B. microplus resistant to amitraz was 19.40%. However, even though tick resistance to amitraz is a present problem there was no evidence that it was associated with the risk factors analyzed in this survey.

Animal Husbandry↗

Arthropods as predators of ticks (Ixodoidea).

The existing information on arthropods as predators of ticks is based mainly on sporadic observations and their role in reducing tick populations and in most cases is still not clear. Some reports suggest that in certain ecological habitats arthropods play an important role in the control of the tick population. This publication reports on some 100 relevant publications that appeared between 1906 and 1999. Ants, beetles, and spiders seem to be the major arthropods preying on ticks. In general, engorged ticks are more often preyed upon by arthropods than are unfed or feeding ticks.

Animals↗

Regulation of seasonal occurrence in the tick Rhipicephalus appendiculatus Neumann, 1901.

Published data on the seasonal occurrence of Rhipicephalus appendiculatus at 8 localities in east, central and southern Africa has been compared and an analysis of the regulatory roles of different climatic factors has been undertaken. It has been shown that the pattern of seasonal occurrence is largely dependent on the timing of the activity period of the adult stage and this is regulated by the combined influences of humidity, temperatures and daylength. By use of a simple model it is shown how the adult activity period in a given climatic regimen can be predicted on the basis of easily obtainable meteorological data. The value of the model in planning tick and disease control programmes is discussed.

Animals↗

Quality control assessment for the PCR diagnosis of tick-borne encephalitis virus infections.

BACKGROUND: Reverse transcriptase-polymerase chain reaction (RT-PCR) is an efficient method for the early detection of tick-borne encephalitis virus (TBEV) RNA in blood and serum samples taken prior to the appearance of antibodies. Improved diagnostics are critical for optimally detecting and managing TBE infections and quality control measures are therefore essential. OBJECTIVE: To assess the diagnostic quality of laboratories by performing an external quality assurance (EQA) programme for the molecular detection of TBE infections. STUDY DESIGN: A panel of 12 prepared human plasma samples were distributed and tested for the presence of TBEV-specific RNA. The panel comprised eight samples spiked with different TBEV strains of European, Siberian and Far Eastern subtypes, and included a 10-fold dilution series. Two specificity controls consisted of a sample with Louping ill virus (LIV) and a sample with a pool of four other flaviviruses, and two negative control samples were further included. RESULTS: Twenty-three laboratories from 16 European and 2 non-European countries participated in this EQA programme. Only two participants correctly identified all samples. Nine laboratories correctly identified 75.0-91.7% of the samples; seven laboratories correctly identified 54.5-66.7% and five laboratories correctly identified < or =50%. CONCLUSIONS: The EQA programme provides information on the quality of the RT-PCR methods used by the participating laboratories and indicates that most of these need to improve sensitivity and specificity of their molecular assays for TBEV.

Encephalitis Viruses, Tick-Borne↗

Family pesticide use in the home, garden, orchard, and yard.

This study examined family use of pesticides in the home, garden, orchard, and yard. Data were collected from 238 families in Missouri during telephone interviews from June 1989 to March 1990. Nearly all families (97.8%) used pesticides at least one time per year and two thirds used pesticides more than five times per year. More than 80% used pesticides during pregnancy and 70% used pesticides during the first 6 months of a child's life. The most common setting for family pesticide use was in the home, where 80% of families used pesticides at least once per year. This was followed by herbicide use to control yard weeds (57% of families) and insecticide use to control fleas and ticks on pets (50% of families). A substantial number of families also used pesticides in the garden or orchard (33%). Flea collars were the most popular pest control product (50% of families). Carbaryl or Sevin was also popular, with 28.2% of families reporting use. No-pest-strips (dichlorvos) and Kwell shampoo (lindane) were used by almost 10% of participating families. Examination of study data revealed that families limited exposure to pesticides for the mother during pregnancy and for children during the first 6 months of life. Families failed to recognize and reduce pervasive exposures associated with no-pest-strips and flea collars.

Animals↗

Evaluation of four modelling techniques to predict the potential distribution of ticks using indigenous cattle infestations as calibration data.

Efficient tick and tick-borne disease control is a major goal in the efforts to improve the livestock industry in developing countries. To gain a better understanding of the distribution and abundance of livestock ticks under changing environmental conditions, a country-wide field survey of tick infestations on indigenous cattle was recently carried out in Tanzania. This paper evaluates four models to generate tick predictive maps including areas between the localities that were surveyed. Four techniques were compared: (1) linear discriminant analysis, (2) quadratic discriminant analysis, (3) generalised regression analysis, and (4) the weights-of-evidence method. Inter-model comparison was accomplished with a data-set of adult Rhipicephalus appendiculatus ticks and a set of predictor variables covering monthly mean temperature, relative humidity, rainfall, and the normalised difference vegetation index (NDVI). The data-set of tick records was divided into two equal subsets one of which was utilised for model fitting and the other for evaluation, and vice versa, in two independent experiments. For each locality the probability of tick occurrence was predicted and compared with the proportion of infested animals observed in the field; overall predictive success was measured with mean squared difference (MSD). All models exhibited a relatively good performance in configurations with optimised sets of predictors. The linear discriminant model had the least predictive success (MSD>or=0.210), whereas the accuracy increased in the quadratic discriminant (MSD>or=0.197) and generalised regression models (MSD>or=0.173). The best predictions were gained with the weights-of-evidence model (MSD>or=0.141). Theoretical as well as practical aspects of all models were taken into account. In summary, the weights-of-evidence model was considered to be the best option for the purpose of predictive mapping of the risk of infestation of Tanzanian indigenous cattle. A detailed description of the implementation of this model is provided in an annex to this paper.

Animals↗

Assay of fipronil efficacy to prevent canine monocytic ehrlichiosis in endemic areas.

Our objective was to evaluate the efficacy of fipronil for the prevention of Ehrlichia canis transmission to dogs by Rhipicephalus sanguineus in two endemic areas situated in Africa (Dakar and Djibouti). We carried out controlled trials in kennels for 1 year on 248 dogs, mainly police dogs and military working dogs. Eight groups were studied in a multi-centre study. Fifty five fipronil treated dogs were located in two separated kennels (G3, 37 dogs in Djibouti and G8, 18 dogs in Dakar). G1 (66 dogs) and G2 (60 dogs) were untreated control groups located in Djibouti, whereas G4 (32 dogs), G5 (13 dogs), G6 (18 dogs) and G7 (4 dogs) were the control groups located in Dakar. The epidemiological status of each group is known. G1 and G2 dogs were not kept in kennels, whereas G3, G4, G5, G6, G7, G8 dogs were housed in equivalent kennels. Tick infestation, clinical status and Ehrlichia seroprevalence were assessed during 1 year (duration of the study). Dog treated with fipronil showed neither canine monocytic ehrlichiosis (CME) nor tick infestations. In all groups of untreated control animals, R. sanguineus tick infestations were frequent, particularly in kennels (G5, G6 and G7) as well as morbidity and mortality due to CME. E. canis infection rates were low for fipronil treated animals: 2.7% (1/37) for G3 and 5.5% (1/18) for G8 group. Among control animals, seroprevalence was maximum (100%) in dogs kept in kennels (G5, G6 and G7 groups) and high among native dogs in Djibouti (G1 group): 69.7% (46/66) and in Dakar (G4 group): 50% (16/32). Dogs belonging to expatriate citizens (G2 group) were less likely to be infected: 21.7% (13/60). The comparison of serological results among French army dogs and French citizen dogs that were introduced in Djibouti for an average of 10 months shows a statistically significant (P<0.001) difference. Among fipronil treated animals (G3 group), 2 dogs out of 55 seroconverted (3.6%) compared to 13 out of 60 dogs (21.7%) in the control G2 group. The results of our study indicate the preventative efficacy of a fipronil monthly treatment to avoid CME in endemic areas. Epidemiological data concerning animals that live in the same endemic areas are an example of the serious consequences (in terms of mortality and morbidity) that are related to the absence of efficient methods for tick-control. In order to protect dogs that are in transit in endemic areas against tick-transmitted diseases, the use of an adapted acaricide product is recommended.

Africa↗

Isolation of a cDNA for an octopamine-like, G-protein coupled receptor from the cattle tick, Boophilus microplus.

Octopamine is a biogenic amine neurotransmitter of invertebrates that binds to a G-protein coupled receptor that has seven transmembrane domains. Formamidine pesticides like amitraz are highly specific agonists of the octopamine receptor. Amitraz is used extensively to control the cattle tick, Boophilus microplus, and many other ticks but now there are strains of ticks that are resistant to amitraz. We have isolated a cDNA from the cattle tick, B. microplus, that belongs to the biogenic amine family of receptors. The predicted amino acid sequence from this cDNA is most similar to octopamine receptors from insects. The nucleotide sequence of this gene from amitraz-resistant and amitraz-susceptible cattle ticks was identical. Thus, a point mutation/s did not confer resistance to amitraz in the strains we studied. Alternative explanations for resistance to amitraz in B. microplus are discussed.

Amino Acid Sequence↗

Protection of dairy cows immunized with tick tissues against natural Boophilus microplus infestations in Thailand.

Boophilus microplus has a major impact on cattle production, and an antitick vaccine would be a valuable tool for control of this important ectoparasite in Thailand. Previous work has shown that immunization of hosts with different tick tissues has different implications regarding tick feeding and fecundity under experimental conditions. The purpose of this study was to assess the effects of immunization of dairy cattle with B. microplus salivary gland or midgut extracts on natural infestations by this tick species. The different antigen extracts (1 mg total protein) or equivalent amounts of adjuvant alone were injected intradermally every two weeks for a total of three times before allowing cattle to graze in a tick-contaminated pasture. Animals were checked daily, and engorged female ticks collected, counted, weighed, and maintained in tick incubators to observe tick performance parameters, including engorged weight, egg mass weight, nonviable eggs, mortality, oviposition period, egg incubation period, and F1 larval weight. After six months, each group was reimmunized with the same antigen and/or adjuvant, and ticks were again collected and evaluated. Immunization of cattle with salivary gland preparations resulted in reductions in mean tick counts and in engorged female weights. Immunization with midgut antigens reduced tick oviposition and reduced egg mass weights. In addition, more ticks recovered from midgut-immunized cows produce nonviable eggs. This investigation indicates that a vaccine based on these antigen preparations could induce a lasting, protective immune response against B. microplus that would be expected to provide a safe nontoxic means of tick control.

Animals↗

Immunization of mice with recombinant P27/30 protein confers protection against hard tick Haemaphysalis longicornis (Acari: Ixodidae) infestation.

The success of immunological control methods is dependent upon the use of potential key antigens as tick vaccine candidates. Previously, we cloned a gene encoding 27 kDa and 30 kDa proteins (P27/30) of Haemaphysalis longicornis, and identified the P27/30 is a troponin I-like protein. In this study, the recombinant P27/30 (rP27/30) expressed in Escherichia coli was used to immunize mice and the mice were challenge-infested with ticks at different developmental stages of the same species. The rP27/30 protein stimulated a specific protective anti-tick immune response in mice, evidenced by the statistically significant longer pre-feeding periods in adult ticks. Furthermore, significantly longer feeding periods were noted in both larval and adult ticks. On the other hand, only larval ticks exhibited low attachment rates (31.1%). Immunization of mice with rP27/30 protein confers protection against hard tick Haemaphysalis longicornis infestation. These results demonstrated that the rP27/30 protein might be a useful vaccine candidate antigen for biological control of ticks.

Animals↗

Reduction of the Amblyomma americanum (Acari: Ixodidae) population at Fort A.P. Hill, Virginia, by aerial application of diazinon granules: correlation of percentage control with received dose.

Habitat (280 ha) of lone star tick, Amblyomma americanum (L.), was aerially treated with 14% diazinon granules. Concentration of acaricide reaching the forest floor ranged from 0.02 to 1.25 kg (AI)/ha. Greater than 85% control was achieved at study plots receiving the highest dose. A positive correlation was shown between dose received at the forest floor and percentage of control of adults (r = 0.91) and nymphs (r = 0.86).

Animals↗

The control of parasites in antelope in small gama reserves.

The most important parasites of antelope in small game reserves are ixodid ticks, the larvae of oestrid flies and nematodes. Methods of control based on the seasonal prevalence of these parasites are suggested. Adult ticks can be controlled during summer by the introduction of cattle which are dipped or sprayed with an acaricide at 5-day intervals. The larvae of oestrid flies can be controlled by the capture during winter of all alcelaphine antelope and their oral treatment with a larvicide, while the addition of an anthelmintic to feed supplement blocks during winter can be used to control nematodes.

Animal Population Groups↗

Successful and currently ongoing parasite eradication programs.

The eradication of parasitic diseases is not a new concept. The most successful programs of parasite eradication have occurred with species of veterinary importance. The first such program, the eradication of Texas Cattle Fever from the United States, is one of the great success stories of disease eradication. The American screwworm eradication program is ongoing and is serving as a guiding impetus for many of the ongoing or proposed vector eradication schemes around the world. The success of these programs prompted similar successful operations in human health. Although they once led the way, veterinary parasitologists have taken second place in eradication planning. The only three parasitic diseases of veterinary importance that have been targets of recent eradication programs are Hypoderma species in Great Britain and Europe, Cochliomyia hominivorax after its introduction into Libya from the Americas, and Echinococcus granulosus in Tasmania, Australia. There is also work on the eradication of the tick, Amblyomma variegatum, from the Caribbean Islands. Some animal diseases are targeted under the auspices of the human eradication programs, most notably the eradication of the tsetse fly from parts or all of Africa. This paper reviews some of the past or ongoing successful eradication programs and presents a brief summary of the history of the programs, the methods used or planned, and potential controversies surrounding their success and implementation.

Animals↗

Bovine resistance to Amblyomma americanum ticks: an acquired immune response characterized by cutaneous basophil infiltrates.

Purebred Holstein calves acquired resistance to Amblyomma americanum adult ticks after 1 infestation and expressed resistance during a challenge infestation 26 days later. Tick yields from resistant animals were normal, but mean tick weight and egg-mass weight were reduced significantly (31 and 32%, respectively). Cutaneous cellular responses at tick feeding sites in primary (naive) hosts consisted almost exclusively of mononuclear cells, until 24-h post-infestation when granulocytes appeared. At 48 h, basophils were the most abundant granulocyte and comprised 19% of the total cellular response. Secondary and tertiary hosts expressed significant cutaneous basophil responses as early as 6 h post-tick infestation, indicative of an anamnestic response. Cutaneous basophil levels in tertiary hosts (16-34% of the infiltrate) were increased by 2-fold over secondary hosts (12-16% of the infiltrate). Neutrophils and eosinophils were fairly abundant in secondary hosts (22-33%, and 3-13%, respectively), but decreased significantly in tertiary hosts corresponding to increased basophil levels. Mast cells comprised less than 10% of the cells found in primary hosts, and less than 5% in secondary and tertiary hosts representing a consistent, but insignificant component of the total cells. Basophils were not observed in the blood of hosts during any tick infestation, but a peripheral blood basophilia (0.1-1.1%) marked the end of each tick feeding period. A neutropenia was observed in the blood of tertiary hosts corresponding to a decreased tissue neutrophil response. Blood eosinophil, lymphocyte and monocyte levels remained unchanged during each tick infestation compared to controls. In summary, calves acquired immunity to A. americanum ticks, resulting in significant decreases in feeding and ovipositional success associated with a local cutaneous basophil response and peripheral blood basophilia. These findings suggest that basophils are involved in bovine immunity to ticks as has been established in the guinea pig model.

Animals↗