The accurate diagnosis of parasitic nematode infections in livestock (including sheep and goats) is central to their effective control and the detection of the anthelmintic resistance. Traditionally, the faecal egg count reduction test (FECRT), combined with the technique of larval culture (LC), has been used widely to assess drug-susceptibility/resistance in strongylid nematodes. However, this approach suffers from a lack of specificity, sensitivity and reliability, and is time-consuming and costly to conduct. Here, we critically assessed a specific PCR assay to support FECRT, in a well-controlled experiment on sheep with naturally acquired strongylid infections known to be resistant to benzimidazoles. We showed that the PCR results were in close agreement with those of total worm count (TWC), but not of LC. Importantly, albendazole resistance detected by PCR-coupled FECRT was unequivocally linked to Teladorsagia circumcincta and, to lesser extent, Trichostrongylus colubriformis, a result that was not achievable by LC. The key findings from this study demonstrate that our PCR-coupled FECRT approach has major merit for supporting anthelmintic resistance in nematode populations. The findings also show clearly that our PCR assay can be used as an alternative to LC, and is more time-efficient and less laborious, which has important practical implications for the effective management and control strongylid nematodes of sheep.

A study on 3 farms, each having a preventive strategy for the control of nematode infections, determined the risk factors associated with diarrhoea among Merino ewes in winter. Comparisons were made among groups of mated and unmated ewes with and without treatment with controlled-release capsules containing albendazole. Diarrhoea was assessed from the accumulations of faeces around the breech (dag score) and related to worm egg counts, total worm counts and histopathological findings. The overall prevalence of severe dag in ewes not treated with a capsule was 26% (221/844). In comparison, only 2.7% of treated ewes had severe dag. The adjusted odds ratio on each farm indicated that untreated ewes were between 12 and 16 times more likely to be affected with severe dag than ewes treated with a capsule. The effect of lactation was significant on only one farm whereas initial body weight had no significant effect. There was no significant association between worm egg counts and the occurrence of severe dag. There were significantly more eosinophils in the small intestine of ewes affected with severe dag compared with unaffected ewes. There were no significant differences in mast cell and globule leucocyte numbers between affected and unaffected ewes. This study provides strong evidence that the main cause of diarrhoea among Merino ewes grazing winter and early spring pastures is the ingestion of trichostrongylid larvae even by sheep that have a well-developed protective immune response to these parasites. New strategies for the control of nematode infections are needed to prevent diarrhoea and dag formation in adult sheep.

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1A multi-species model to assess the impact of refugia on worm control and anthelmintic resistance in sheep grazing systems. RJ ObjectiveDevelop a computer simulation model that uses daily meteorological data and farm management practices to predict populations of Trichostrongylus colubriformis, Haemonchus contortus and Teladorsagia (Ostertagia) circumcincta and the evolution of anthelmintic resistance within a sheep flock. Use the model to explore if increased refugia, provided by leaving some adult sheep untreated, would delay development of anthelmintic resistance without compromising nematode control. ProceduresCompare model predictions with field observations from a breeding flock in Armidale, NSW. Simulate the impact of leaving 1-10% of adult sheep untreated in diverse sheep grazing systems. ResultsPredicted populations of T. colubriformis and T. circumcincta were less than those observed in the field. Attributed to nutritional stress experienced by sheep during drought, and not accounted for by the model. Observed variation in faecal egg count explained by the model (R 2 ) for these species was 40-50%. H. contortus populations and R 2 were both low.Leaving some sheep untreated worked best in situations where animals were already grazing or were moved on to pastures with low populations of infective larvae. In these cases anthelmintic resistance was delayed and nematode control was maintained when 1-4% of adult stock remained untreated. ConclusionsIn general, the model predicted that leaving more than 4% of adults untreated did not sufficiently delay the development of anthelmintic resistance to justify the increased 2 production risk from such a strategy. The choice of a drug rotation strategy had an equal or larger impact on nematode control, and selection for resistance, than leaving 1-10% of adults untreated. The multi-species model described here allows for these phenomena and estimates host mortalities and inappetence based on the total worm populations. To determine the utility of the model, worm populations were monitored in flocks of breeding ewes and weaners that were managed under typical grazing systems in north-eastern Australia. Daily meteorological and management records were kept so that worm populations could be predicted using the multispecies model. Keywords 3In this simulation study, the model was used to: a) estimate the consequences of leaving a proportion of adult stock untreated (as a source of refugia) on the development of anthelmintic resistance and effectiveness of parasite control; b) determine how best to use a new anthelmintic class (amino-acetonitrile derivatives (AAD), represented by monepantel; Zolvix ® , Novartis Animal Health Inc., Switzerland) to control gastro-intestinal nematodes while minimising selection for drug resistance; and c) examine these issues in four environments to determine if there are common principles that can be applied and/or how they need to be modified to suit local environments. The aim was to fully explore the interaction between the fundamen...

Johne's disease was diagnosed in 10 alpacas (Lama pacos) in Australia between February 1993 and May 1994. Eight of the animals were between 12 and 24 months of age, one was a 6-year-old female, and one was a 4-year-old male. Five, including the 6-year-old and the 4-year-old alpacas, showed weight loss and diarrhoea before death or slaughter. The other cases showed no clinical signs of Johne's disease but 4 gave a positive result on faecal culture and one gave a positive result on testing with the caprine AGID assay and had acid-fast organisms in its faeces. At necropsy, all cases had grossly enlarged mesenteric lymph nodes. Johne's disease was diagnosed after histological examination of the lymph nodes with conventional culture and polymerase chain reaction testing of tissue samples. This report outlines the clinical, epidemiological, and pathological findings in these cases.