Which phenotypic traits of resistance should be improved in cattle to control paratuberculosis dynamics in a dairy herd: a modelling approach

Abstract

Paratuberculosis is a worldwide disease causing production losses in dairy cattle herds. Variability of cattle response to exposure to Mycobacterium avium subsp. paratuberculosis (Map) has been highlighted. Such individual variability could influence Map spread at larger scale. Cattle resistance to paratuberculosis has been shown to be heritable, suggesting genetic selection could enhance disease control. Our objective was to identify which phenotypic traits characterising the individual course of infection influence Map spread in a dairy cattle herd. We used a stochastic mechanistic model. Resistance consisted in the ability to prevent infection and the ability to cope with infection. We assessed the effect of varying (alone and combined) fourteen phenotypic traits characterising the infection course. We calculated four model outputs 25 years after Map introduction in a naïve herd: cumulative incidence, infection persistence, and prevalence of infected and affected animals. A cluster analysis identified influential phenotypes of cattle resistance. An ANOVA quantified the contribution of traits to model output variance. Four phenotypic traits strongly influenced Map spread: the decay in susceptibility with age (the most effective), the quantity of Map shed in faeces by high shedders, the incubation period duration, and the required infectious dose. Interactions contributed up to 12% of output variance, highlighting the expected added-value of improving several traits simultaneously. Combinations of the four most influential traits decreased incidence to less than one newly infected animal per year in most scenarios. Future genetic selection should aim at improving simultaneously the most influential traits to reduce Map spread in cattle populations.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-017-0468-8) contains supplementary material, which is available to authorized users.

Paratuberculosis: The Hidden Killer of Small Ruminants

“…Domestic ruminants (cattle, sheep and goat) are the commonly affected animals with MAP [ 29 ]. Susceptibility to MAP infection decreases with age; thus age together with the infecting dose and some other factors contribute to limiting the spread of MAP [ 30 ]. It is now known that not all animals exposed to MAP develop JD and some appear to clear the infection spontaneously.…”

A review of paratuberculosis in dairy herds — Part 1: Epidemiology

“…However, the low dose used in this study, 5 x 10 7 given over two consecutive days, was higher than the minimal doses of 1.5 x 10 6 used in other studies, (Sweeney et al, 2006). Nevertheless, this observation could have considerable consequences for control programmes: a recent French modelling study reported that the rate of decay in susceptibility with age had a dramatic effect on within-herd transmission (Ben Romdhane et al, 2017).…”

“…This work demonstrated that the association between shedding levels and infectiousness is not linear; in fact, a 1000-fold increase in bacterial shedding results in only a 2-3 fold increase in infectiousness (Slater et al, 2016). However, other research groups have found that the level of MAP shedding from individual animals is one of the most important control phenotypic traits that can impact on the spread of infection (Ben Romdhane et al, 2017). In addition, field and research observations do support clusters of infection occurring in time and space (Zare et al, 2013).…”