The development of new acaricides is a long and very expensive process. Worryingly, there is increasing resistance to available acaricides worldwide leading to the real possibility that our dwindling ...supply of effective acaricides will be exhausted unless action is taken to increase the number of new acaricidal products and reduce the rate of resistance development. In 1995, eight major animal health pharmaceutical companies formed the Veterinary Parasite Resistance Group (VPRG) to act as an expert consultative group to guide the FAO in resistance management and collaborate in the prudent use of acaricides. In this paper, members of the VPRG discuss the problems and processes in acaricide development, resistance in the field to commonly used acaricides and the different considerations when targeting the cattle and pet market, and give their view of the future for tick control from the perspective of the animal health industry.
A high rate of phenotypic variation in the lipooligosaccharide (LOS) electrophoretic profile of Haemophilus somnus occurred in most isolates obtained at approximately weekly intervals from three ...calves intrabronchially challenged with a cloned isolate of H. somnus 2336. Daily subculturing for 2 weeks resulted in at least one major alteration in the LOS electrophoretic profiles for strain 2336 and both additional disease isolates examined, but no change occurred in the LOS electrophoretic profiles for any of three commensal isolates examined. None of the LOSs from any of the postchallenge intrabronchial isolates reacted with rabbit antiserum to the challenge strain LOS in immunoblotting, but LOSs from two nasopharyngeal isolates did. Antigenic variation in the extracted LOSs of most of the isolates was supported by the results of an enzyme-linked immunosorbent assay. Preimmune serum from each of the calves did not react with any of the isolates or the challenge strain, whereas sera obtained 35 days after challenge reacted with the challenge strain and zero to five additional isolates and sera obtained 74 days after challenge reacted with two to six additional isolates. Recognition of LOSs from isolates obtained near the end of the 70-day experiment by day-74 sera was related to clearance of the bacteria from the lungs. Isolates demonstrating major electrophoretic changes showed variations in the composition of the oligosaccharide, but not lipid A, moiety of their LOSs. The oligosaccharide of the LOS of each isolate was composed predominantly of glucose but varied substantially in the contents of galactose, arabinose, xylose, mannose, and 3-deoxy-D-manno-octulosonic acid. Therefore, the LOS of H. somnus is capable of undergoing compositional and antigenic variations, which may act as an important virulence mechanism for evading host immune defense mechanisms.
Fungi morphologically consistent with class Oomycetes were recovered on primary culture from 20 of 22 ulcers on 21 fish with epizootic ulcerative syndrome (EUS) collected from 5 sites in the ...Philippines. Eleven primary isolates, and the unifungal cultures derived from them, were identified as Aphanomyces spp.; the remaining 9 primary isolates were lost through contaminant overgrowth. The Aphanomyces isolates were morphologically and culturally indistinguishable from those reported from red spot disease (RSD) in Australia. Comparison of 4 representative Aphanomyces isolates from Australian fish with RSD and 3 representative Aphanomyces isolates from Philippine fish with EUS, using SDS-PAGE (sodium dodecyl sulphate polyacrylamide gel electrophoresis), revealed similar peptide banding profiles, indicative of a single Aphanomyces species. These findings, combined with epizootiological and pathological similarities between EUS and RSD, suggest the 2 syndromes are identical, and that a single Aphanomyces sp. may be the primary infectious cause.
AIM: To quantify and economically evaluate the effect on milk production of peri-parturient treatment of dairy cows with eprinomectin.
METHODS: On 3 farms in separate geographic areas of New Zealand, ...849 first-calf heifers and multiparous cows were ranked and paired within parity, date of calving and expected milk production. Within pairs, cows were randomly allocated to treatment with either a commercial formulation of eprinomectin, applied at a dose rate of 500 ώg/kg liveweight, or an equivalent volume of vehicle containing no antiparasitic agent and administered at the same dose volume, generally within the first week post-calving. On each farm, trial cows shared the same pasture. Over a single lactation, records were maintained of milk quantity and content.
RESULTS: Trichostrongylid eggs were identified in pre-treatment faecal samples from all farms, verifying the presence of gastrointestinal parasites. Overall 25.5% of the cows sampled were positive for nematode eggs, but only 8% had counts ≥50 eggs per gram of faeces (epg). Daily milk volume, milk protein and milksolids (yield of milk fat + milk protein) were higher for eprinomectin-treated multiparous cows than for controls (milk volume: 20.36 l/day vs 19.76 l/day, p=0.005; milk protein: 0.700 kg/day vs 0.685 kg/day, p=0.012; milksolids: 1.613 kg/day vs 1.583 kg/day, p=0.031, respectively). The daily value of the increased production from eprinomectin-treated multiparous cows was estimated to be NZ$0.034 for milk fat (p=0.095) and NZ$0.078 for milk protein (p=0.012), equating to NZ$0.104 for milksolids (p=0.031), averaged over the whole lactation. No significant difference in milk production was detected between treated and control first-calf heifers. Averaged over the whole herd, the peri-parturient treatment of multiparous cows and first-calf heifers with eprinomectin increased daily milk volume and milk protein production of treated vs control cows (19.28 l/day vs 18.86 l/day, p=0.020, and 0.661 kg/day vs 0.650 kg/day, p=0.047, respectively).
CONCLUSION: These data provide evidence that the use of a peri-parturient treatment of eprinomectin on multiparous cows can increase their production of fluid milk and milksolids.
A series of five controlled studies involving 114 cattle were conducted in Australia, North America and the United Kingdom to examine the effect of simulated rain, coat length and exposure to natural ...climatic conditions, on the efficacy of a topical formulation of eprinomectin against nematode parasites of cattle. In all trials infections were induced with a range of bovine nematode species and treatment was applied when the majority of nematodes were mature. In one study, simulated rain was applied to cattle ending one hour before treatment or geginning one, three or six hours after treatment. In a second study cattle had short (1 cm) or long (3–6 cm) haircoats at the time of treatment. Three other studies were conducted usinv cattle housed indoors or exposed to various natural climatic conditions. Nematode counts were determined using standard techniques and the efficacy of treatment was assessed relative to vehicle-treated controls. Regardless of the timing of simulated rain relative to treatment, eprinomectin was at least 99.9% effective (
p < 0.01) against
Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei and
Cooperia spp. There were also no differences (
p > 0.10) in efficacy between treatment administered to dry or wet cattle, or treatment administered before or after simulated rainfall. Efficacies against
O. ostertagi, T. axei, Cooperia oncophora and
Dictyocaulus viviparus were >99.5% (
p < 0.01) regardless of the length of the haircoat at the application site. Exposure of treated cattle to sunshine and precipitation had no effect on anthelmintic efficacy (
p > 0.10) with efficacies of greater than 99.5% being maintained against
H. placei, O. ostertagi (adult and fourth-stage larvae),
T. axei, Cooperia spp.,
Nematodirus helvetianus (adult and inhibited fourth-stage larvae) and
Oesophagostomum radiatum.
These findings indicate that eprinomectin (500 μg/kg) in a topical formulation is a safe and highly effective nematocide for cattle regardless of their coat length and this high level of efficacy is maintained in cattle exposed to a wide variety of climatic conditions.
An immunodominant Haemophilus somnus outer membrane protein with an apparent molecular mass of 40 kDa on Western blots (immunoblots) of gradient sodium dodecyl sulfate-polyacrylamide gel ...electrophoresis gels was characterized because a monospecific antibody against this antigen was protective. This monospecific antibody was used for immunoaffinity purification of the antigen. The immunoaffinity-purified antigen reacted with a polyclonal antibody to the 40-kDa antigen but not with a monoclonal antibody (3G9) which reacted with the 40-kDa antigen in gradient gets. On 8 or 10% gels, the approximately 40-kDa antigen was resolved as two bands, a 40-kDa band which reacted with the protective monospecific polyclonal antibody (p40) and a band of lower molecular mass which reacted with monoclonal antibody 3G9. The latter antigen was designated p39. Both antigens were conserved in all H. somnus isolates tested. The specific antibodies were also used to detect cross-reacting antigens in other gram-negative bacteria. Antibody to p40 reacted with proteins of 55 to 28 kDa, with the greatest intensity shown among proteins from other members of the family Pasteurellaceae. Antibody to p40 was reduced by absorption with live H. somnus or other members of the family Pasteurellaceae, so the antigen appears to be surface exposed. Antibody to p39 only cross-reacted with a broad band (38 to 40 kDa) in Haemophilus agni. Since H. agni is not a bovine pathogen and since convalescent-phase serum from H. somnus-infected animals did recognize p39, the latter may be a good immunodiagnostic antigen, if the lack of cross-reactivity with antigens in other gram-negative bacteria is confirmed with a polyclonal antibody to p39. The cross-reactivity of antiserum to p40 with antigens of members of the family Pasteurellaceae and the ability of this antiserum to protect against H. somnus pneumonia indicate that p40 may be a useful vaccine antigen for H. somnus disease and perhaps even diseases caused by other members of the family Pasteurellaceae
Six studies were conducted to evaluate the persistent efficacy of eprinomectin pour-on against experimental challenges with infective nematode larvae in calves. In each study, calves were randomly ...assigned to one untreated group and up to four test groups, which were treated with eprinomectin at 500 microg/kg body weight at weekly intervals before single bolus challenge. The calves were necropsied approximately 4 weeks after challenge infection for nematode recovery. Eprinomectin pour-on provided > or =90% efficacy against challenge with Haemonchus placei, Trichostrongylus axei and T. colubriformis at 21 days after treatment and against Cooperia oncophora, C. punctata, C. surnabada, Dictyocaulus viviparus, Nematodirus helvetianus, Oesophagostomum radiatum and Ostertagia ostertagi at 28 days after treatment.
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