Prevalence and severity of anthelmintic resistance in ovine gastrointestinal nematodes in Australia (2009-2012).

OBJECTIVE: This study aimed to provide an indication of the prevalence and severity of anthelmintic resistance (AR) in the Australian sheep industry by compiling the results of faecal worm egg count reduction tests (FECRTs). METHODS: Government and private parasitology laboratories, pharmaceutical companies and veterinarians known to have conducted FECRTs were asked to provide results that conformed to Australian and New Zealand standard diagnostic procedures. RESULTS: Data were available from a total of 390 tests, with larval differentiation conducted in 222 cases. Pooled results from all states for the macrocyclic lactone (ML) class showed a lower prevalence of AR against combined species for moxidectin (54%) compared with abamectin (77%) and ivermectin (87%). Analysis by state revealed higher levels of ML-resistant Teladorsagia sp. in Tasmania and Western Australia than in other states and ML-resistant Haemonchus sp. was more frequently detected in New South Wales. CONCLUSION: This compilation of results of FECRTs conducted by Australian parasitology laboratories in 2009-12 showed widespread AR of the common sheep nematodes (Teladorsagia, Trichostrongylus and Haemonchus) to all broad-spectrum anthelmintics, with the exception of monepantel, whether used singly or in combination.

Effective control of a suspected cyromazine-resistant strain of Lucilia cuprina using commercial spray-on formulations of cyromazine or dicyclanil.

OBJECTIVE: To demonstrate the protection of Merino sheep from flystrike by Lucilia cuprina with cyromazine or dicyclanil in an implant study and in the field. METHODS: In the implant study, sheep were treated with cyromazine or dicyclanil and implanted with 1st-stage larvae from a newly isolated field strain of L. cuprina (CYR-LS) or a reference strain (DZR50), then assessed over 3 days and compared with the implants on untreated control sheep. In the field study, weaner lambs were treated with cyromazine or dicyclanil and monitored weekly for flystrike over 18 weeks of grazing on the same farm from which the L. cuprina were isolated. RESULTS: Implant study: cyromazine (6%) provided effective protection against CYR-LS and DZR50 L. cuprina for a minimum of 13 and 10 weeks, respectively. Dicyclanil (5%) provided at least 18 weeks' protection against both strains. Field study: only 1 of 386 lambs in the cyromazine-treated group was struck in the first 14 weeks of the trial. No strikes occurred in the 198 sheep treated with dicyclanil (5%). Rainfall, temperature and flytrap data indicated consistent fly pressure during the study. CONCLUSIONS: Based on the results of these studies, there was no evidence of reduced susceptibility to cyromazine or dicyclanil and the periods of protection of sheep against L. cuprina were unaffected and consistent with the registered label claims.

Financial effect of bovine Johne's disease in beef cattle herds in Australia.

OBJECTIVE: To assess the financial effect of programs for controlling bovine Johne's disease (BJD) in beef herds. DESIGN: A spreadsheet simulation model of a self-replacing beef herd in south-eastern Australia selling 400-kg steers at 15 months old. METHODS: The model calculated the monthly cash flow, and net present value (NPV) of cumulative cash flow, over 10 years. Four main control options were compared: (1) a base herd (no action to control the disease), (2) test and cull, and (3) partial and (4) total destocking. It was assumed that BJD was eradicated after 3 and 5 years with total and partial destocking, respectively, and not eradicated with a test and cull program. Scenarios were compared for both commercial and stud enterprises. RESULTS: If there was no discount on the sale price of cattle in commercial herds, deaths from BJD had to exceed 5% before the NPV of partial or total destocking was similar to taking no action to control the disease over a 10-year period. When cattle sales incurred a 10% discount, deaths had to exceed 1% before the destocking strategies would break even after 10 years. CONCLUSION: Control options for BJD should be carefully planned on an individual herd basis, as significant production and financial risks accompany destocking programs. Eradication will only be more profitable in the longer term, compared with living with the disease, when discounts on the sale of stock from infected herds are high. This can occur with the selling of store cattle or breeders. In stud herds, BJD will usually cause the total failure of the business.

Epidemiology of bovine Johne's disease (BJD) in beef cattle herds in Australia.

OBJECTIVE: To describe the epidemiology of bovine Johne's disease (BJD) in beef herds in Australia. DESIGN: Retrospective survey of beef herds detected with BJD between 1991 and 2006. METHODS: Information about the management and physical characteristics of affected herds, index and clinical cases, testing and control programs, and attitudes to BJD were collated from existing data and personal interviews of herd owners or managers. Herds were excluded if they contained fewer than 30 breeding cows or operated as a dairy farm. RESULTS: Records from 109 herds demonstrated the first detected ('index') case was 3.4-fold more likely to be a beef rather than dairy breed. However, further analysis revealed association with dairy cattle was an important risk factor for introducing BJD. Index cases were most likely detected by veterinarians investigating clinical cases of scouring or ill-thrifty animals during winter, particularly bulls or aged cows. Most herds with clinical BJD had only a single case, with only one high prevalence herd detected in the survey group. Over the period of observation, test and cull programs did not eradicate BJD unless combined with culling of known high-risk animals, but removal of high-risk cattle by partial or total destocking generally restored the trading status of affected herds. CONCLUSION: Excluding cattle with dairy contact from beef herds, ensuring more effective farm biosecurity, promptly seeking veterinary advice regarding scouring cattle and sourcing replacement cattle from demonstrably low-risk herds, such as CattleMAP and 'Beef Only' herds, are simple strategies that should reduce the risk of introducing BJD infection into beef herds.

Sensitivity and specificity of two serological tests for the detection of ovine paratuberculosis.

OBJECTIVE: To determine the sensitivity and specificity of an absorbed ELISA and an AGID test for the detection of clinical and subclinical paratuberculosis in sheep. DESIGN: By testing a panel of sera from 1257 Australian Merino and crossbred sheep greater than 1 year of age, of which 1137 sheep were not infected with Mycobacterium avium subsp paratuberculosis and 120 sheep had paratuberculosis. PROCEDURE: Sera were collected from 457 sheep in Victoria and 800 sheep in Western Australia. Presence of M a paratuberculosis infection in Victorian sheep was determined by histological examination of intestinal tissues, whereas sheep from Western Australia were presumed to be free of Johne's disease. The ability of an absorbed ELISA to discriminate between infected and uninfected sheep was described by test sensitivity and specificity, the distribution of ELISA OD, and the area under a receiver operating characteristic curve. RESULTS: The absorbed ELISA had a specificity of 98.2 to 99.5% (CI) and a sensitivity of 35 to 54% (CI). In sheep from infected flocks in Victoria, the AGID test had a specificity of 99 to 100% (CI) and a sensitivity of 38 to 56% (CI). The sensitivity of serological tests was higher in sheep with a body condition representative of the lower quintile of their flock of origin. CONCLUSION: The AGID test and absorbed ELISA are useful tests for the detection of ovine paratuberculosis. Although the tests had a similar accuracy, they detected different subpopulations of infected sheep with only moderate overlap. The AGID test had a higher specificity than the absorbed ELISA.

Mycobacteria distenct from Mycobacterium avium subsp. paratuberculosis isolated from the faeces of ruminants possess IS900-like sequences detectable IS900 polymerase chain reaction: implications for diagnosis.

PCR targeting the 5' end of IS 900 has been considered specific for identification of Mycobacterium avium subsp. paratuberculosis and is frequently applied to confirm the presence of this organism in the diagnosis of Johne's disease. IS 900 PCR has also been applied to studies of the aetiology of Crohn's disease. Mycobacterium spp. isolated from the faeces of 3 clinically normal animals in 2 Australian states appeared not to be M. paratuberculosis but were positive by IS 900 PCR. The isolates were characterized using mycobactin dependency, biochemical tests, IS 900 and 16 S rRNA sequencing and restriction fragment length polymorphism (RFLP) using IS 900 as probe. DNA sequencing confirmed that the isolates had between 71% and 79% homology with M. paratuberculosis in the region of IS 900 amplified, were most closely related to Mycobacterium scrofulaceum, and confirmed the usefulness of restriction enzyme analysis of amplified product to identify the false positive results. RFLP analysis with Bst Ell detected three to five copies of the IS 900 -like element in the isolates. These were located in molecular weight fragments that were clearly different to IS 900 in previously characterized strains of M. paratuberculosis. It is likely that these isolates are environmental mycobacteria. Southern blotting with an internal probe is unlikely to provide differentiation of M. paratuberculosis from these organisms. We recommend the adoption of restriction endonuclease analysis of IS 900 PCR product as a routine precaution to prevent the reporting of false positive IS 900 PCR results.