Longitudinal data collection of Mycobacterium avium subspecies Paratuberculosis infections in dairy herds: the value of precise field data

Abstract

Longitudinal infection data on Mycobacterium avium subspecies paratuberculosis (MAP) was collected on three dairy farms in Northeastern United States during approximately 10 years. Precise data on animal characteristics and animal location within farm were collected on these farms. Cows were followed over time with regard to MAP status during biannual fecal and serum sampling and quarterly serum sampling. Approximately 13 000 serum samples, 6500 fecal samples and 2000 tissue samples were collected during these years. Prevalence of positive samples was 1.4% for serological samples, 2.2% in fecal samples and 16.7% in tissue samples. Infection dynamics of MAP was studied and resulted in a number of potential changes in our understanding of MAP infection dynamics. First, a high prevalence of MAP infection was observed in these herds due to lifetime follow up of cows, including slaughter. Second, two distinctly different infection patterns were observed, so called non-progressors and progressors. Non-progressors were characterized by intermittent and low shedding of MAP bacteria and a virtual absence of a humoral immune response. Progressors were characterized by continuous and progressive shedding and a clearly detectable and progressive humoral immune response. Strain typing of MAP isolates on the three farms identified on two of three farms a dominant strain type, indicating that some strains are more successful in terms of transmission and infection progression. Continuous high quality longitudinal data collection turned out to be an essential tool in our understanding of pathobiology and epidemiology of MAP infections in dairy herds.

Effects of subclinical Mycobacterium avium ssp. paratuberculosis infection on some physiological parameters, health status and production in dairy cows

“…Animals without clinical signs are not culled and continue to spread the pathogen, thus increasing the infection rate within the herd (Clarke, 1997). Additionally, many MAP-infected animals can show a latent or intermittent shedding stage where no MAP isolated can be found using the current diagnostic methods (Schukken et al, 2015), as it was seen in our study, namely that some MAP-negative animals were rearranged to the MAP+ group at the end of the experimental period.…”

A new compartmental model of Mycobacterium avium subsp. paratuberculosis infection dynamics in cattle

“…New analysis of longitudinal data from endemic herds, however, indicates that adult infections may occur (Espejo et al, 2013), especially when the adult is housed with a supershedder (Pradhan et al, 2011). These data also seem to indicate 2 paths for MAP infection: intermittently low-shedding or non-shedding animals that do not progress to clinical disease, and continuously shedding animals that quickly progress to high shedding and, eventually, clinical disease (Mitchell et al, 2015a, 2015b; Schukken et al, 2015). The cause of these 2 paths is unknown, but may be related to the age at infection (Mitchell et al, 2012), the dose of infection (Weber et al, 2010), the strain of infection (Mitchell et al, 2015b; Stewart et al, 2007), or genetic resistance (Gonda et al, 2006; Hinger et al, 2008).…”

“…Animals that were not defined as high-path were defined as low-path if any FC or tissue culture result was positive. These data have previously been used to identify the two paths, labeled progressors (high-path) and non-progressors (low-path) (Schukken et al, 2015). …”

Economic consequences of paratuberculosis control in dairy cattle: A stochastic modeling study

“…The number of test-positive animals in each category was determined by means of a binomial distribution, in which the probability of a positive result was the sensitivity Se i for the shedding categories and the complement of the specificity, 1-Sp , for uninfected and latent animals. It was assumed, based on observation (Schukken et al, 2015), that non-progressing low-shedders would not test positive more than once. We assumed that test-positive animals were culled after no delay when tests were based on ELISA or polymerase chain reaction (PCR), while we assumed a delay of 3 months when tests were based on fecal culture (FC).…”