Host and Pathogen Factors in Paratuberculosis

13.2.1 Animal risk factors

In cattle, age of the animal at exposure, breed resistance, genetic susceptibility and other dis­eases have been mentioned as risk factors for development of paratuberculosis (Radostits et al., 2007).

2013, 2015; Abraham et al., 2017; Cecchi et al., 2017).

13.2.2 Environmental and management risk factors

Conditions predisposing to MAP infection in­clude poor hygiene that exposes young kids to manure from older animals and contaminated milk. Inadequate feeding and low body condition increase the susceptibility to infection (Radostits et al., 2007). Experiments have shown that in­fected goat kids can excrete the bacteria in their faeces and thereby infect other kids (Stewart et al., 2006). In goats, MAP seroprevalence has been associated with a herd size of over 200 ani­mals, the presence of foreign breeds and a high replacement rate (Mainar-Jaime and Vazquez- Boland, 1998). Recently, Freitas et al. (2015) and Angelidou et al. (2014a) have described fur­ther risk factors, e.g. water sources and the time spent by kids with their mother.

Cross-species infections are suspected to occur between cattle and goats (Holstad et al., 2005).

13.2.3 Pathogen risk factors

MAP isolates have been classified into two main lineages based on culture characteristics and mo­lecular characterization: MAP-S (also called Type S or Type I/Type III) and MAP-C (also called Type C or Type II) (see Chapter 6, this volume). Goats can be infected by both lineages (de Juan et al., 2005), and the isolates of MAP obtained from goats manifest genetic variability by a number of different molecular methods (Pillai et al., 2001; Djonne et al., 2005; Sevilla et al., 2007, 2008). Phenotypic differences between these strains of MAP have been described, with one group sug­gesting that isolates from goats have lower path­ogenicity for cattle (Saxegaard, 1990). This is supported by findings in macrophages in a study by Abendano et al. (2013). The genetic basis for this observation is, however, not known. In con­trast, a study by Gollnick et al. (2007) did not find any differences in the ability of different MAP strains to survive in bovine monocyte-derived macrophages. At present, there does not appear to be a strain of MAP specific to goats, and the importance of strain variability for infection and disease in goats requires further study.

13.3