Pilot project to investigate over-wintering of free-living gastrointestinal nematode larvae of sheep in Ontario, Canada.

This study investigated the overwintering survival and infectivity of free-living gastrointestinal nematode (GIN) stages on pasture. The presence of GIN larvae was assessed on 3 sheep farms in Ontario with a reported history of clinical haemonchosis, by collecting monthly pasture samples over the winter months of 2009/2010. The infectivity of GIN larvae on spring pastures was evaluated using 16 tracer lambs. Air and soil temperature and moisture were recorded hourly. Free-living stages of Trichostrongylus spp. and Nematodirus spp. were isolated from herbage samples. Gastrointestinal nematodes were recovered from all tracer lambs on all farms; Teladorsagia sp. was the predominant species. Very low levels of Haemonchus contortus were recovered from 1 animal on 1 farm. The results suggest that Haemonchus larvae do not survive well on pasture, while Teladorsagia sp., Trichostrongylus spp. and Nematodirus spp. are able to overwinter on pasture in Ontario and are still infective for sheep in the spring.

Projet pilote pour faire enquête sur l'hivernage des larves de nématodes gastro-intestinaux libres chez les moutons en Ontario, au Canada. Cette étude a examiné la survie à l'hivernage et le pouvoir infectieux des stades des nématodes gastro-intestinaux (NGI) libres dans les pâturages. La présence de larves de NGI a été évaluée en recueillant des échantillons mensuels dans le pâturage pendant les mois de l'hiver 2009­2010 dans 3 fermes ovines en Ontario avec des antécédents documentés d'hémonchose clinique, tandis que le pouvoir infectieux des larves de NGI sur les pâturages du printemps a été évaluée en utilisant 16 agneaux sentinelles. La température et l'humidité de l'air et du sol ont été notées toutes les heures. Les stades libres de Trichostrongylus spp. et de Nematodirus spp. ont été isolés d'échantillons d'herbage. Les NGI ont été récupérés de tous les agneaux sentinelles dans toutes les fermes et Teladorsagia sp. était l'espèce prédominante. De très faibles taux d'Haemonchus contortus ont été récupérés chez 1 animal dans 1 ferme. Les résultats suggèrent que les larves d'Haemonchus ne survivent pas bien dans le pâturage, tandis que Teladorsagia sp., Trichostrongylus spp. et Nematodirus spp. peuvent survivre l'hiver dans le pâturage de l'Ontario et être toujours infectieux pour les moutons au printemps.(Traduit par Isabelle Vallières).

Development of a Taenia ovis transmission model and an assessment of control strategies.

The metacestode stage of the tapeworm, Taenia ovis, causes cystic lesions in the skeletal and cardiac muscle of sheep, which can result in the condemnation of the entire carcass. In recent years, Canadian farms have seen a marked increase in the number of condemnations due to T. ovis. Mathematical transmission models provide a useful tool for predicting parasite transmission and for evaluating the efficacy of potential control options. To date, no model has been developed exclusively for T. ovis. In the work described here, a compartmental, deterministic transmission model was developed to better understand the transmission dynamics of T. ovis on Canadian sheep farms. The model was intended to be practical, and represent the transmission of infection burdens in lambs that result in carcass condemnation, or transmission to canids. All transmission parameters were obtained from the literature or, when unavailable, expert opinion. The model incorporated each stage of the parasite lifecycle using the most probable transmission route on Canadian sheep farms; including definitive host (guard dogs), intermediate host (pastured lambs), and environment. Based on literature, the model performed as expected, and provided a reasonable estimate of parasite prevalence in lambs. In addition, modeling allowed the efficacy of potential control options to be evaluated and compared. Model simulations suggested that infection risk in market lambs could be eliminated through the regular treatment of guardian dogs every fifth week with an appropriate cestocide, or through eliminating carcass consumption by guardian dogs.

Distribution of, and risk factors associated with, sheep carcass condemnations due to Cysticercus ovis infection on Canadian sheep farms.

Cysticercus ovis, the intermediate stage of a canine tapeworm, Taenia ovis, produces cystic lesions in the skeletal and cardiac muscle of sheep which, if numerous, will result in the condemnation of an entire carcass. In 2007 and 2008, the number of carcass condemnations due to C. ovis rose dramatically across Canada, suggesting that the prevalence of this infection on sheep farms was increasing. Trace-back of 237 carcasses condemned at Ontario provincially inspected abattoirs, between March 2009 and March 2011, revealed they originated from 133 farms across Canada. A case-control study was performed (n=40 cases, 56 controls) to identify farm-level risk factors associated with carcass condemnations due to C. ovis. Participating farms, located in Alberta, Saskatchewan, Manitoba and Ontario, were asked to answer a short questionnaire which collected information about each farm's geographic location and management practices. A multivariable logistic regression model revealed that farm dogs scavenging deadstock (OR=4.04; 95% CI: 1.16-14.04) and failing to dispose of deadstock (OR=11.78; 95% CI: 2.93-47.40) were significantly associated with condemnations (p ≤ 0.05).

The effect of sampling time and sample handling on the detection of Staphylococcus aureus in milk from quarters with subclinical mastitis.

Staphylococcus aureus mastitis is an important cause of economic loss for the dairy industry. Control programs rely on the timely and accurate identification of positive quarters. The effects of sampling time and sample handling were examined in an attempt to improve the accuracy of detection of S. aureus. Premilking and postmilking milk samples were collected from 55 lactating quarters with subclinical S. aureus infection. Each sample was divided into 2 aliquots; one of which was cultured fresh, the other was frozen at -20 degrees C for 14 days before being cultured. Analysis of variance was used to determine the effect of sampling time (premilking vs postmilking) and sample handling (fresh vs frozen) on the detection of S. aureus, as measured by the mean category for colony-forming units per millilitre (cfu/mL). A stratified analysis was required, due to interaction between sampling time and sample handling. Only a fresh postmilking sample was inferior, yielding a lower mean category for cfu/mL (P < 0.05). The ability to detect S. aureus in quarters with subclinical intramammary infection, as measured by the mean category of cfu/mL, was maximized in fresh or frozen premilking samples and in frozen postmilking samples.