Reduced efficacy of ivermectin, abamectin and moxidectin against field isolates of Haemonchus contortus.

OBJECTIVES: To investigate the reduced efficacy of ivermectin, abamectin and moxidectin against two field isolates of Haemonchus contortus. These isolates were identified on separate properties in the New England region of New South Wales. PROCEDURE: Reduced efficacy of macrocyclic lactone anthelmintics against two field isolates of H contortus was suspected. These isolates were obtained from sheep on separate farms and pen trials were performed to investigate the efficacy of macrocyclic lactones. The percentage efficacy was calculated for moxidectin, ivermectin and closantel against the isolate from one farm (VHR23) and for moxidectin, ivermectin and abamectin against the isolate from the second (VHR29). The persistent activity of moxidectin against both isolates was investigated. RESULTS: Ivermectin and closantel were found to have efficacies below 80% against established populations of VHR23. Moxidectin was effective against an established population of VHR23 but the persistent activity was reduced to 7 days. Moxidectin was also found to be effective against established populations of VHR29, however, ivermectin and abamectin were found to have efficacies below 80%. There was no evidence of persistent activity of moxidectin against VHR29. CONCLUSION: A reduction in efficacy of abamectin and/or ivermectin against field isolates of H. contortus was identified from two farms in the New England region of New South Wales. The persistent effect of moxidectin was reduced against both isolates.

The effect of an oil formulation on the systemic availability of oxfendazole.

Pure oxfendazole (OFZ) suspended in peanut oil and the commercial formulation 'Synanthic' were each intraruminally administered to Merino weaners at 5 mg kg-1. Plasma was collected and concentrations of OFZ, fenbendazole (FBZ) and FBZ sulphone (FBZ.SO2) were determined by HPLC. The maximum concentrations and area under the plasma concentration curve (AUC) of OFZ and FBZ were significantly higher (P less than 0.05) when OFZ was suspended in peanut oil than when administered as the commercial formulation.

Effect of feed type on the pharmacokinetic disposition of oxfendazole in sheep.

The plasma concentration profiles of oxfendazole (OFZ), fenbendazole (FBZ) and FBZ sulphone (FBZ.SO2) were measured followed intraruminal administration of OFZ at 5 mg kg-1 to Merino weaners fed either dry forage or grazed on pasture lucerne clover. Plasma concentrations of OFZ and FBZ were significantly lower in sheep given the dry forage.

A preliminary report on the suitability of sheep epidermal squamous cell carcinoma as a solid tumor model in the evaluation of intra-arterial methotrexate administration.

A preliminary study was undertaken to assess the sensitivity of sheep epidermal squamous cell carcinoma, in the head and neck region, to intra-arterial (IA) methotrexate (MTX) infusion. There was an objective tumor response (40-56% regression) in all three IA-infused sheep, whereas tumor progression was observed in all three animals treated intravenously (IV). Regional and systemic side effects were negligible in all cases. Technically, IA drug infusion in the sheep was an improvement on previous small animal models, with no problems related to arterial catheter insertion, blockage, or dislodgement, and tolerable infusion times being of markedly longer duration. The histological differentiation of moderately differentiated stage II lesions improved during therapy irrespective of clinical response, whilst the histology of well-differentiated stage III and IV tumors remained unchanged. Tumor cell cycle stage and ploidy characteristics, as determined by flow cytometric DNA analysis, were little affected by either mode of drug administration. It is concluded that sheep epidermal carcinoma is responsive to IA MTX, and that this animal model is the most appropriate yet utilised to study the comparative effects of IA and IV chemotherapy in the head and neck region.

Ploidy and proliferative characteristics of sheep epidermal squamous cell carcinoma determined by flow cytometric DNA analysis.

Multiple biopsies from each of 22 primary sheep epidermal squamous cell carcinomas were analysed by flow cytometry to determine the G0/G1 modal DNA content ("ploidy") and cell cycle characteristics within each tumour. Ten of 12 tumours where aneuploidy was present demonstrated uniform intra-tumour aneuploid populations regardless of the site of biopsy. Increasing tumour volume (from stage I/II to stage III/IV lesions) was associated with increased histological variability and ultimate heterogeneity of G0/G1 DNA content, whilst the mean numbers of S phase cells decreased. These features were consistent with the effects of variable tissue hypoxia seen with changes in effective vascularity in developing tumours. Decreasing histological differentiation was associated with an increase in numbers of cells synthesising DNA within 44 biopsies with measurable S phase, and, in stage I/II biopsies, correlated with an increased incidence of aneuploidy.

Ischaemic embolic myelopathy in a Labrador crossbred dog.

A case of ischaemic embolic myelopathy in a dog is described. It was demonstrated histologically that these focal ischaemic lesions were associated with emboli, histochemically identified as fibrocartilagenous.

Clinical, pathologic and cytogenetic observations on two intersex dogs.

Two "bitches" presented with histories of non-attainment of puberty were diagnosed as intersexes. Data on gross morphology, histology of the genitalia, and genetic sex using blood, skin and gonads were employed for the classification of the type of intersex in each case. Both cases were classified as true hermaphrodites.

Eumycotic mycetoma due to Drechslera rostrata infection in a cow.

A case of eumycotic mycetoma with lesions in the skin, nasal cavity and lymph nodes of a cow is reported. The case history, clinical course, macroscopic and microscopic appearance of lesions, and fungal isolation are described. Drechslera rostrata was isolated from pathological tissue and Koch's postulates were satisfied on mouse inoculation. This is the first infection of its type recorded in Australia and features contrasting with cases reported in other countries are discussed.