Service Communautaire d'Information sur la Recherche et le Développement - CORDIS

Identification of key epidemiological parameters to enhance predictive power of the model

The models were used to identify key epidemiological parameters by exploring changing scenarios with respect to wildlife infection and characteristics of the farming systems. In the quantitative models and with respect to the level of wildlife infection, three scenarios were considered
- Absence of wildlife host (prevalence of Map shedding in wildlife host = 0%),
- Prevalence of 17% and
- Prevalence of 50%.

To illustrate the impact of control measures aimed at removing infectious cows, in the dairy herd model two options were considered for time between becoming infectious and culling, 13 and 15 months. In the beef-cattle herd model scenarios with 1, 2, 4 and 6 months between development of clinical signs and culling were considered. To illustrate the impact of the range of indoor/outdoor farming systems that are used across Europe three scenarios or combinations of indoor/outdoor calving were used for the beef-cattle herd model, 100% outdoor calving, 50% outdoor calving and 100% indoor calving. Several simulations were run investigating the impact of different combinations of the above on the within-herd prevalence of Map-infection.

Given our set of assumptions, the results suggested that the potential impact of the contamination of the environment by wildlife was very limited when compared to the impact of factors such as calving management and hygiene, calving indoors vs. outdoors or time during which a cow remains infectious in the herd. These 3 factors emerged as key predictors of the within-herd prevalence of Map-infection. The impact of Map contamination of the environment by wildlife species was higher for larger farms. The highest impact was observed for a hypothetical farm with 100 cows, 100% outdoor calving in which the estimated prevalence after 30 years was 8% without contamination by wildlife and 12% when the highest level of wildlife infection (50%) was considered.

This quantitative assessment and the qualitative assessment of the risk of a replacement animal infected from wildlife being introduced into the production group on a dairy farm, a beef suckler herd and a sheep breeding flock, agreed that further investigation of the potential impact of wildlife on the within-farm dynamics of Map should target specific production systems in which this component was less likely to be negligible, namely, relatively large farms with a relatively low within-herd prevalence of Map infection and where cows were kept outdoors.

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