Effects of Streptococcus dysgalactiae polyarthritis on lamb growth and mortality and risk factors for disease

Molecular detection and genotype characterization of Streptococcus dysgalactiae from sheep flocks with outbreaks of infectious arthritis

Outbreaks of infectious arthritis in young lambs are a growing concern for the Norwegian sheep industry. In other countries, Streptococcus dysgalactiae subspecies dysgalactiae (SDSD) is a frequent cause of such outbreaks. The objectives of this study were to investigate the causes of outbreaks of infections arthritis in Norwegian sheep flocks, and describe the sources, colonization patterns and genetic diversity of SDSD in affected and healthy sheep flocks. Almost 2000 samples from joints, animal body sites and the indoor environment were analysed by qPCR and culturing for SDSD, which was detected in 27 of 30 flocks. The proportion of positive samples was greater in outbreak flocks compared to healthy flocks. Altogether, SDSD was detected in 48 % of the samples from lambs, 27 % of the samples from ewes and 48 % of environmental samples. A relatively high proportion (67 %) of ear tag wounds were SDSD positive. These wounds may provide a port of entry for SDSD. Whole genome sequencing revealed a clonal distribution of SDSD-isolates, and identified four different multi locus sequence types (STs), among which two STs, ST454 and ST531, dominated. These STs were found in geographically distant flocks. ST454 was almost exclusively found in outbreak flocks. The current study points to skin, wounds and mucous membranes of animals as the main reservoir of SDSD in sheep flocks. However, a significantly higher proportion of SDSD-positive environmental samples in outbreak flocks compared to healthy flocks suggests that also indirect transmission may play a role.

Flock-level risk factors for outbreaks of infectious arthritis in lambs, Norway 2018

BACKGROUND

Outbreaks of infectious arthritis in young lambs associated with Streptococcus dysgalactiae subspecies dysgalactiae (SDSD) lead to reduced animal welfare, increased use of antibiotics and economic losses for sheep farmers. Understanding risk factors is essential when developing strategies to prevent such outbreaks. This questionnaire-based cross-sectional study classified sheep flocks of respondents as cases or controls. Flock-level risk factors for outbreaks of infectious arthritis were assessed using a multivariable logistic regression model.

RESULTS

Eighty-four of 1498 respondents (5.6%) experienced an outbreak of infectious arthritis in their flock in 2018, the year of study. Factors associated with a higher risk of outbreak were larger flock size (OR 1.3, 95% CI 1.1-1.4, per 100 lambs), plastic mesh flooring in the lambing pen (OR 3.0, 95% CI 1.7-5.3) and a lambing percentage greater than 200 (OR 2.0, 95% CI 1.1-3.5). Flocks where farmers observed infections around the ear tags of lambs also had an increased risk of outbreak (OR 2.6, 95% CI 1.6-4.3).

CONCLUSIONS

The risk factors identified in this study are characteristic of modern and intensively managed sheep farms in Norway. A distinguishing feature of Norwegian sheep farming is winter housing and indoor lambing. One might expect that this in itself is a risk factor because of high stocking densities during lambing. However, outbreaks of infectious arthritis in young lambs are reported by the industry to be a more recent phenomenon. The current study indicates that intensification of indoor management systems with larger flocks and higher production per ewe may predispose to outbreaks. The results provide a basis for further studies on transmission dynamics of SDSD in sheep flocks with indoor lambing.

Impacts of major health conditions affecting the Australian sheepmeat value chain: a review

Major health conditions in sheep contribute to substantial economic losses throughout the sheepmeat supply chain in Australia. A systematic review was undertaken to explore the measurable impact of six conditions: arthritis, sheep measles, pleurisy, pneumonia, grass seeds and rib fractures, on the production of lamb and mutton across the meat value chain. Peer-reviewed scientific literature from three databases and non-peer-reviewed articles and reports from Australian government and non-government websites were searched between 11 and 17 November 2019. Original articles, including studies conducted in Australia and New Zealand, that had measurable impacts on conditions of interest were included. The search yielded 16 articles and reports and were classified as producer impact and/or processor impact studies. Mortalities were quantified for pneumonia and arthritis, with pneumonia having the highest impact for producers. Grass seed infestation resulted in the highest impact on carcase and liveweight losses compared to arthritis and pneumonia. Arthritis had the highest trim weight losses for both lamb and mutton and the highest rate of carcase condemnation. Grass seed was the only condition where other impacts on the processor (chain speed and staff relocation to the boning room) were quantified. Although quantifiable production and processing losses were available for some conditions, this review has highlighted that limited quantifiable data based on scientifically sound research were not available for other conditions. The evidence for some conditions found in this review can be used to target future research activities and to further assist producers in making informed management decisions on prevention and control.