Impact of previous infestation on dynamics of circulating hypodermin C in cattle artificially infested with Hypoderma lineatum (Diptera: Oestridae)

Four groups of cattle were artificially infested with 50 first instar Hypoderma lineatum after either a primary natural infestation or in the absence of a primary infestation. In two groups the primary infestation had been terminated by the application of either an organophosphate insecticide or a macrocyclic lactone parasiticide. Circulating hypodermin C and specific antibodies were measured for 40 weeks after the artificial infestation. Stage specific mortality of the larvae was also monitored. Previously uninfested cattle exhibited typical antibody and antigen profiles during the infestations. Antibodies were first detected on Week 7 p.i., they rose to maximum values between Weeks 24 and 25, then declined as larvae reached the back. A second peak occurred at Week 32 and antibody remained more less constant thereafter. Previously infested groups exhibited a dramatic anamnestic response by Week 3 p.i. with antibody levels peaking at Week 8. A second peak was noted between Weeks 24 and 26 p.i. after which antibody levels declined and then remained relatively stable. The dynamics of circulating hypodermin C in the previously infested cattle resembled those in the previously uninfested cattle. Mortality of first instars did not differ among the four groups. Similarly mortality of second and third instars, in the warble, did not differ although there was a tendency for higher mortality in the previously infested, untreated group. These results reinforce previous work demonstrating the development of a significant immune response during the primary infestation that is reflected in the rapid and substantial production of antibodies upon re-infestation. It is significant that a challenge model using subcutaneous injection of newly hatched first instars avoids host immune responses in the skin that result in substantial larval mortality. The current data also support the concept that migrating first instars induce significant reduction in host immune response. There is a peak of antibody production as antigen levels peak during first instar migration to the back. As larvae molt to the second instar and antigen production ceases there is a persistence of antibody which suggests release of the immune response from the suppression induced by the first instar secretory antigens.     

Relationship between the resistance of crossbred cattle to ticks, Boophilus microplus (Canestrini, 1887) and Hyalomma anatolicum anatolicum (Koch, 1844)

Studies were undertaken to determine the effect of repeated pure infestations with Boophilus microplus on susceptibility to subsequent pure infestations with Hyalomma anatolicum anatolicum, and the effects of pure infestations with both species of tick on susceptibility to a series of mixed infestations. Crossbred (Bos indicus X Bos taurus) calves were infested with Boophilus microplus (17 times), H. a. anatolicum (four times), followed by five mixed infestations of B. microplus and H. a. anatolicum. The decline in B. microplus engorgement from a mean yield of 274.4 +/- 60.3 ticks per host after the first exposure, to a mean yield of 9 +/- 4.6 per animal after the seventeenth exposure, was observed in animals exposed to only B. microplus. This might be due to acquired resistance. However, these animals were found to be as susceptible to H. a. anatolicum as animals which had never been exposed to ticks of either species. A decline in the yield of H. a. anatolicum from a mean yield of 92.1 +/- 10.7 after the first exposure to 54.7 +/- 11.3 after the fourth exposure, indicated that the cattle could also acquire resistance to repeated pure infestations with this species. After repeated pure infestations with both tick species, cattle reacted to five mixed infestations showing a high degree of resistance to B. microplus and low resistance to H. a. anatolicum (mean yield for B. microplus was only 10 +/- 8.1 ticks per host after the first mixed exposure and declined to 1.3 +/- 1.7 after the fifth, whereas the mean yield for H. a. anatolicum was 71.4 +/- 11.3 ticks per host following the first exposure and declined to 37.3 +/- 7.8 after the fifth). Host responses elicited to one species do not provide cross-resistance to the second species used in this study.     

Histology of bovine skin reactions to Ixodes holocyclus Neumann.

The histology of skin responses to infestations with female Ixodes holocyclus ticks was investigated in naive and previously infested cattle. In the latter hosts, infiltration of the skin site with basophil leucocytes was an early event. Concurrent spongiosis and vesiculation occurred in the epidermis adjacent to the tick mouthparts. This was followed by infiltration of the upper dermis by eosinophils and other leukocytes. Such reactions were evident one hour after attachment of ticks in hosts which had received two prior infestations. Pronounced epidermal vesiculation and bulla formation with eventual serous exudation followed in previously infested cattle, leading to entrapment of ticks.     

The effects of warble fly dressing using an organophosphorus compound on bovine pediculosis

The added benefit of the national campaign in the Republic of Ireland to eradicate bovine warble flies using pour-on organophosphorus compounds annually, has been a significant reduction in the degree of pediculosis there compared to that in Northern Ireland. In Northern Ireland, only warbled cattle are dressed and the level of pediculosis was 72.8% compared to 56.2% in the Republic, 30.4% of 250 cattle examined in the former country had moderate to heavy infestation compared to 8.6% of 185 cattle examined in the latter. Four species of cattle lice were found and reported for the first time in both countries; these were Haematopinus eurysternus, Solenoptes capillatus, Linognathus vituli, and Bovicola bovis. The first named was far more common in Northern Ireland. Following the withdrawal of the national eradication scheme in the Republic in 1975, there are indications that pediculosis has increased in cattle. Of 100 adult cattle examined in the Republic in February, 1976, 19 had heavy infestations, whilst 78 were infested.     

Effect of treatment on the dynamics of circulating hypodermin C in cattle naturally infested with Hypoderma lineatum (Diptera: Oestridae)

An antigen capture ELISA, using a murine monoclonal antibody recognising recombinant hypodermin C (rHyC), was used to evaluate the influence of early treatment with eprinomectin (Eprinex) or fenthion (Spotton) on the kinetics of circulating hypodermin C in calves naturally infested with Hypoderma lineatum. No viable larvae were collected from treated animals, whereas a variable number of warbles were found in control animals. Treatment provoked a decrease in circulating HyC levels that was significant 9 days post-treatment (p.t.). Circulating antigen levels in the treated cattle remained detectable for approximately 99 days p.t. In contrast, control animals had no detectable antigen at 64 days p.t., 42 days earlier than in the treated animals. These results suggest that larvae were either gradually killed, resulting in slow release of antigen or they were encapsulated, leading to the slow liberation of antigen. Kinetics of circulating HyC did not differ among the two insecticide treatments. Antibodies persisted, in all groups, throughout the 120-day study. These results suggest that the antigen capture ELISA will be useful as a technique for detecting successful treatment of cattle grub infestations and for the detection of new infestations in previously infested cattle.     

Ectoparasites of free-ranging pumas and jaguars in the Paraguayan Chaco

Ectoparasites were collected from seven puma (Puma concolor) and seven jaguar (Panthera onca) live-captures (each representing six different animals) in the Paraguayan Chaco from 2002 to 2004. The same five species of ectoparasites were recovered from both host species: the flea, Pulex simulans (total on both hosts combined=30 male, 49 female), and the ticks, Amblyomma cajennense (1 male, 4 female, 46 nymphs, 241 larvae), Amblyomma parvum (42 male, 25 female), Amblyomma tigrinum (1 male, 7 female, 34 larvae) and Amblyomma triste (4 male). There were no statistical differences between the prevalences (percent of hosts infested) for any of these ectoparasite species between the two host species, and only P. simulans showed a significantly higher mean intensity (mean no. of each ectoparasite species per infested host) on one of the host species (jaguar). Clearly, these two large carnivores share similar ectoparasite faunas in the Paraguayan Chaco. However, both carnivores occupy large geographical distributions in the New World and this study, combined with the few previous studies, suggests that their ectoparasite faunas differ slightly in different parts of their respective ranges.     

Efficacy of a pour-on formulation of doramectin against lice, mites, and grubs of cattle

OBJECTIVE: To determine effectiveness of a pour-on formulation of doramectin against Damalinia bovis, Haematopinus eurysternus, Linognathus vituli, Solenopotes capillatus, Chorioptes bovis, Sarcoptes scabiei, Hypoderma bovis, and Hypoderma lineatum. ANIMALS: Cattle of various ages with naturally acquired or artificial infestations with 1 or more species of lice, mites, or grubs. PROCEDURE: In 10 louse and 6 mite studies, cattle were treated with doramectin (500 microg/kg, topically) on day 0, and parasite counts were performed approximately weekly from days 0 to 35. In 6 grub studies, cattle expected to harbor Hypoderma spp were treated before emergence of warbles. After warbles began to emerge, they were counted every 2 weeks, and grubs were collected and identified by species. RESULTS: Burdens of D bovis, H eurystemus, L vituli, and S capillatus on doramectin-treated cattle were 0 by 28 days after treatment. Burdens of C bovis and S scabiei decreased to 0 in naturally infested cattle and approximately 0 in artificially infested cattle by day 14 to 15. In grub studies, 107 of 136 control cattle had warbles, whereas 2 of 136 doramectin-treated cattle had 1 warble each, which represented a cure rate of 98.5%. CONCLUSION AND CLINICAL RELEVANCE: One topical application of doramectin was highly efficacious against common species of lice, mites, and grubs known to affect performance, health, and appearance of cattle.     

Detection of immune response in rabbits infested with Rhipicephalus appendiculatus and Rhipicephalus evertsi evertsi

Two groups of rabbits infested repeatedly with Rhipicephalus evertsi evertsi and R appendiculatus acquired resistance as evidenced by reduced ectoparasite engorged weights and development of anti-tick antibodies in the hosts. The enzyme-linked immunosorbent assay (ELISA) using salivary gland antigens of R appendiculatus was able to detect antibody responses to both the homologous and heterologous tick challenges. It was concluded that the immune response in hosts infested by these two tick species stimulates the production of antibodies which show cross reactions.     

A ten-year review of commercial vaccine performance for control of tick infestations on cattle

Ticks are important ectoparasites of domestic and wild animals, and tick infestations economically impact cattle production worldwide. Control of cattle tick infestations has been primarily by application of acaricides which has resulted in selection of resistant ticks and environmental pollution. Herein we discuss data from tick vaccine application in Australia, Cuba, Mexico and other Latin American countries. Commercial tick vaccines for cattle based on the Boophilus microplus Bm86 gut antigen have proven to be a feasible tick control method that offers a cost-effective, environmentally friendly alternative to the use of acaricides. Commercial tick vaccines reduced tick infestations on cattle and the intensity of acaricide usage, as well as increasing animal production and reducing transmission of some tick-borne pathogens. Although commercialization of tick vaccines has been difficult owing to previous constraints of antigen discovery, the expense of testing vaccines in cattle, and company restructuring, the success of these vaccines over the past decade has clearly demonstrated their potential as an improved method of tick control for cattle. Development of improved vaccines in the future will be greatly enhanced by new and efficient molecular technologies for antigen discovery and the urgent need for a tick control method to reduce or replace the use of acaricides, especially in regions where extensive tick resistance has occurred.     

A review on the treatment and control of ectoparasite infestations in equids

Ectoparasites infestations are a growing concern to horse owners and equine veterinarians alike. Ectoparasites cause significant health and welfare issues and can potentially can serve as vectors for a variety of pathogens. The prevalence of ectoparasites increases around the world, and especially in horses information on the successful prevention and treatment of ectoparasite infestations in scarce and in many instances anecdotal. This poses a challenge to the equine veterinarian and off-label use of drugs can lead to detrimental effects in horses. In this review we describe the current available evidence for the prevention and treatment of ectoparasite infestations in horses. Only a very limited number of products is approved for the use in horses and fortunately many of the other products that are used in an off-label manner appear to be safe in horses. Future research in this area should aim at providing PK/PD modelling data to assure appropriate and safe dose regimen to prevent and treat ectoparasite infestations in horses.     

Studies on naturally acquired immunity to African ticks. II. Observations on cattle exposed to Rhipicephalus appendiculatus under varying periods of repeated infestations.

Groups of Friesian cattle were infested repeatedly with Rhipicephalus appendiculatus at weekly intervals (eight infestations) and at intervals of 3 weeks (seven infestations) and 6 weeks (seven infestations). The engorgement weight of adults, nymphs and larvae decreased significantly initially, from the second infestation, but rose significantly at later infestations. This rise was more dramatic with larval instars than with any other. A new method for quantifying the resistance status of animals was introduced; this method showed that the resistance acquired by cattle during 6-weekly reinfestations was more stable than that acquired by cattle during weekly and 3-weekly reinfestations. The criteria for assessing natural resistance to ticks was reappraised. These are classified into those serving long- and short-term purposes, and those which have direct and indirect effects. Criteria which could serve long- and short-term purposes include a reduced number of engorged ticks, an increased number of dead male and female ticks, a decreased number of ticks which fed above the critical engorgement weight and an increased number which fed within the pre-mating weight and decreased the number of copulations. The criterion of reduced engorgement weight can serve the short-term purpose only. A new manifestation of resistance to ticks, i.e. decreased moulting weights of nymphs and adults, together with the criterion of decreased egg hatchability, were classified as indirect effects because they were manifested after the ticks had dropped off the resistant cattle.     

Chemical control of Haematobia irritans with 0.5% topical ivermectin solution in cattle.

A field trial was conducted to evaluate the efficacy of a topical formulation of ivermectin administered at the dose of 500 micrograms/kg against horn flies (Haematobia irritans) in cattle. Eighty-eight cattle in four herds naturally exposed to horn flies were used in the trial. Replicates were formed of two herds. Within replicates, one herd was randomly allocated to the untreated control and the other to the ivermectin treatment group. Horn fly counts were taken on the treatment day (Day 0) and on Days 7, 14, 21, 28, and 35 post-treatment. There were no horn flies on any cattle in the treatment group, whereas all the control cattle were continuously infested by horn flies on each examination day.     

The Prevalence of Bovine Hypodermosis in Kars Province,Turkey

A total of 1276 cattle from 76 farms in 8 villages were examined by palpation of the skin for evidence of hypodermosis. The effects of age, sex, breed, and colour of cattle on hypodermosis were investigated. The overall prevalence was 31.9%. The mean number of warble fly larvae on infested animals was 8.46. Hypodermosis infestations were encountered in all the villages visited. Within a herd, the intensity of infestion decreased with the age of cattle. Infestation rates of warble fly larvae were lower in native cattle, in females, and in piebald animals.     

Detection of Theileria and Babesia species in ticks collected from cattle

The present study was carried out to detect tick species that infest cattle, and Theileria and Babesia species transmitted by these ticks in Kayseri province (Turkey). A total of 300 cattle were examined for tick infestations. Of the 300 cattle, 117 (39%) were infested with ticks. A total of 1160 ticks belonging to 11 Ixodid genera were collected from the infested animals and their shelters. The most prevalent tick species was Boophilus annulatus 26.37% (306/1160) followed by Hyalomma marginatum marginatum 21.12% (245/1160) and Rhipicephalus turanicus 18.7% (217/1160). The collected ticks were separated into 43 tick pools, according to their species. These pools were examined for bovine Theileria and Babesia species (Theileria sp., Babesia sp., Theileria annulata, T. buffeli/orientalis, Babesia bigemina, B. bovis and B. divergens) by using the reverse line blotting method (RLB). Of the 43 tick pools examined, 6 (14%) were infected with B. bigemina, 4 (9.3%) with T. annulata, and 1 (2.3%) with Babesia sp., whereas 1 (2.3%) displayed mixed infection with T. annulata + B. bigemina. The sequence and phylogenetic analyses of Babesia sp., which could not be identified to the species level by RLB, were performed. In the phylogenetic tree, Babesia sp. (Kayseri 1) grouped with Babesia sp. (Kashi 2), Babesia sp. (Kashi 1), Babesia sp. (Xinjiang) and B. orientalis with 96.8-100% identity.     

The effect of the bont tick (Amblyomma hebraeum) on the weight gain of Africander steers

The effects of the bont tick Amblyomma hebraeum on the productivity of cattle need to be quantified in order to design economically optimal control programs. Liveweight gains (LWGs) of three groups of Africander steers, maintained in the same pasture and exposed to zero, medium or high numbers of larvae, nymphs and adults of the tick, were measured. Larvae and nymphs had no significant effect on LWG but adults had a large, statistically significant effect (P less than 0.05). The tick-free group had an average LWG of 20 kg more than the heavily infested group after 3.5 months. No mortality was recorded from ticks or tick-borne diseases during the experiment. There was no relationship between the number of engorging adult female ticks counted and loss of LWG of individual animals. The latter suggests that exposure to ticks as well as engorgement by female ticks causes losses. The loss per adult female that completed engorgement was estimated, by relating the LWGs of individual animals to their tick infestations, to be 4 +/- 2 g per adult female tick. An alternative estimate, made by comparing the average LWG and tick infestations of each treatment group, was equal to 10 +/- 4 g. This latter estimate includes the effect of challenge (and rejection) as well as tick feeding and so was accepted as giving the best estimate. Screw-worm fly (Chrysomya bezziana) struck an average of 7.5% of the cattle infested with ticks in any week but the effects on the productivity of the cattle were minimized by immediate treatment. There was a significant, positive correlation between the incidence of screw-worm fly strike and the numbers of adult ticks counted on the experimental animals. The results provide data for calculating losses caused by A. hebraeum in different parts of its geographical range.     

Impact of the duration of control of cattle lice with eprinomectin on leather quality

The relationship between lice infestation in calves during their first winter and damage to the leather produced was investigated in a trial involving 500 calves, 100 of which were treated with a pour-on endectocide during the first winter. All the calves received routine lice treatment in the second winter and were reared to slaughter weight. The hides were removed at the abattoir, tanned, inspected for lice-related damage, and graded according to their suitability for the production of high quality leather. The untreated group developed natural infestations of the chewing louse (Bovicola bovis) during the first winter but none was observed in the second winter. Hides from cattle infested with lice in their first winter had higher levels of lice damage than hides from those treated with eprinomectin, at both the chrome-tanned and dried dyed-crust stages of leather production.     

An outbreak of dictyocaulosis in lactating cows on a dairy farm

CASE DESCRIPTION: The owner of a herd of 74 Holstein-Friesian cattle reported decreased milk production, weight loss, and coughing among lactating cows. Owner-initiated antimicrobial treatment was unsuccessful; 1 lactating cow died, and 50% of the lactating cows had clinical signs of respiratory distress, such as tachypnea and coughing. CLINICAL FINDINGS: On the basis of history, physical examination findings, and fecal examination results, affected animals were determined to have Dictyocaulus viviparus (lungworm) infestation. The disease history suggested that the herd contained cows with subclinical patent lungworm infestations; after introduction of susceptible heifers, the pastures had become heavily infested with D viviparus and clinical problems subsequently developed in both newly introduced and resident cows. TREATMENT AND OUTCOME: Affected and unaffected heifers and adult cows were treated with a pour-on formulation of eprinomectin (0.5 mg/kg [0.23 mg/lb]). One animal died, but 2 weeks after treatment, clinical signs among affected cattle were markedly improved. Ten weeks after treatment, milk production improved from 23 kg/cow/d (51 lb/cow/d) to 28 kg/cow/d (62 lb/cow/d). CLINICAL RELEVANCE: The outbreak provides additional evidence that dictyocaulosis is becoming more common among adult dairy cattle, rather than almost exclusively affecting young stock. This may be attributable to anthelmintic use and management practices on dairy farms. Combined with anecdotal reports of an increase in the incidence of dictyocaulosis among adult cattle in North America, D viviparus infestation should be included as a differential diagnosis for decreased milk production, weight loss, and coughing among adult dairy cattle.     

The persistent efficacy of doramectin pour-on against biting and sucking louse infestations of cattle

A repeated-exposure challenge model was used to evaluate the pour-on formulation of doramectin in preventing the establishment of louse infestations in cattle. Twenty calves cleared of preexisting biting and sucking louse infestations were randomly and equally allocated to either a doramectin-treated or untreated control group, with five replicates per group. Doramectin pour-on was administered topically at a dose rate of 500 microg/kg body weight. Every 14 days, from a pool of seeder calves with infestations of at least 50 biting and 50 sucking lice each, 10 calves were selected and 1 was placed in each replicate pen. Every week during the 112-day study, 9 predilection sites on the doramectin-treated and untreated calves were examined to estimate the louse population density. A calf met the infestation criterion for a louse species when two or more live lice were counted on two or more body regions for two consecutive count days. Because only 4 of 10 untreated calves acquired Solenopotes capillatus infestations, the persistent efficacy of doramectin against S. capillatus was not evaluated. Bovicola bovis and Linognathus vituli infestations in the untreated calves developed shortly after exposure to infested seeder calves. The acquisition of B. bovis and L. vituli infestations in the doramectin-treated group was delayed for 77 days and 105 days, respectively.     

Systemic alterations of bovine hemostasis due to Rhipicephalus (Boophilus) microplus infestation

The tick Rhipicephalus (Boophilus) microplus is a hematophagous ectoparasite that causes considerable economic losses to cattle breeding. Although R. microplus saliva contains several molecules that interfere with the blood coagulation process, so far the systemic alterations in the host hemostatic system have not been described. This study aims to determine if R. microplus infestation induces any disturbance to the host’s hemostatic system. To address these questions, six calves were experimentally infested with 20,000 R. microplus larvae and their blood was collected before and 7, 14 and 21 days post-infestation. Collagen and ADP-induced platelet aggregation as well as coagulation (activated partial thromboplastin time and prothrombin time) decreased in infested bovines. Platelet blood count and fibrinogen increased during the course of infestation, probably as a compensatory response. These alterations may play a role in host health status, and show that the host cannot fully counteract the tick anti-hemostatic mechanisms.     

Variation in population density of horn flies (Haematobia irritans irritans) (L.) (Diptera: Muscidae) in Nellore cattle (Bos indicus)

The population density of horn flies was evaluated in the year 1998 in the municipality of Ara?atuba, S?o Paulo Brazil, in relation to temperature and rainfall conditions. Two lots of 30 Nellore steers (Bos indicus) were used which had no insecticidal treatment and were naturally infested with horn flies. The infestations were assessed by two counting methods, i.e., the traditional estimate method and the filming method. The highest fly frequencies were recorded in spring, summer, autumn and the lowest frequencies were recorded in winter. The increase in fly number was positively correlated (P<0.05) with rainfall.