Modeling Paratuberculosis Transmission in a Small Dairy Herd Typical of Slovenia Suggests That Different Models Should Be Used to Study Disease Spread in Herds of Different Sizes.

Abstract

Simple SummaryParatuberculosis is widespread in cattle throughout the world and is an economically important disease, especially in dairy cattle. It is caused by Mycobacterium avium subsp. paratuberculosis and is problematic due to complex transmission and unreliable diagnostic tests. The disease is present in Slovenia, where milk production is one of the most important sectors of agriculture. Our aim was to understand the disease spread in a typical Slovenian dairy herd of about 17 cows. To our knowledge, this is the first study specifically looking at the dynamics of disease spread in a small dairy herd. We relied on real data from the competent authorities on herd structure and data from the literature on disease spread, as well as expert opinion. The results showed that herd size has an influence on disease spread and that the prevalence in a small herd is probably lower than in larger herds because farmers tend to sell and buy animals frequently, which allows for the elimination of diseased animals from small herds. However, this can also reintroduce the disease into the herd. The results suggest that different assessments should be used to study the spread and control of this disease in herds of different sizes.This study aimed to investigate the possible dynamics of paratuberculosis or Johne’s disease in a typical Slovenian dairy herd of about 17 cows. Paratuberculosis is a worldwide endemic disease of cattle caused by Mycobacterium avium subsp. paratuberculosis (MAP) and is associated with significant economic losses. We developed a stochastic compartmental model with two pathways of disease progression, infections of adult cows and infections of young animals through horizontal and vertical transmission, and transmission through animal movements. The average proportions of subclinically and clinically infected cows were 4% and 0.47%, respectively. The prevalence within the herd, which included latently infected animals, averaged 7.13% and ranged from 0% to 70.59%. Under the given circumstances, the results showed a relatively high rate of spontaneous elimination (0.22 per herd per year) of the disease and a high rate of reinfection (0.18 per herd per year) facilitated by active animal trade. To our knowledge, this stochastic compartmental model is the first to be developed specifically to represent a small dairy herd and could apply to other countries with a similar structure of dairy farms. The results suggest that different models should be used to study MAP spread in herds of various sizes.