Johne's disease in Irish dairy herds: considerations for an effective national control programme

Abstract

The Irish dairy industry has established a reputation for the production of safe and healthy dairy products and is seeking to further expand its export market for high value dairy products. To support its reputation, stakeholders aim to control Johne's disease. To assist decision-makers determine the most appropriate design for an Irish programme, a narrative review of the scientific literature on the epidemiology of Johne's disease, and selected control programmes throughout the world was undertaken. Two modelling studies specifically commissioned by Animal Health Ireland to assess testing methods used to demonstrate confidence of freedom in herds and to evaluate a range of possible surveillance strategies provided additional information. The majority of control programmes tend to be voluntary, because of the unique epidemiology of Johne's disease and limited support for traditional regulatory approaches. While acknowledging that test performance and sub-clinical sero-negative shedders contributes to the spread of infection, a range of socio-political issues also exist that influence programme activities. The paper provides a rationale for the inclusion of a Veterinary Risk Assessment and Management Plan (VRAMP), including voluntary whole herd testing to identify infected herds and to support assurance-based trading through repeated rounds of negative testing, national surveillance for herd-level case-detection, and improved understanding of biosecurity management practices. Identification and promotion of drivers for industry and producer engagement in Ireland is likely to guide the future evolution of the Irish Johne's Control Programme (IJCP) and further enhance its success. The provision of training, education and extension activities may encourage farmers to adopt relevant farm management practices and help them recognize that they are ultimately responsible for their herd's health and biosecurity.

Keywords: Ireland; Johne’s disease; control programme; dairy industry.

Fig. 1

Probability of MAP introduction into an Irish dairy herd via new cattle introductions when herd-level prevalence = 0.28 and overall animal-level prevalence = 0.032 (prevalence estimates from McAloon et al. [37]). Random animal refers to introduction of an animal chosen at random from the national herd given the aforementioned prevalence values. Random herd refers to all introduced animals being from a single randomly chosen herd where herd-level prevalence = 0.28 and within-herd prevalence (WHP) = 0.114

Fig. 2

Factors that enhance the probability of a Johne’s disease control programme successfully controlling spread within and between herds