Fecal–oral route ‘major path for paratuberculosis transmission’
MedWire News: The major route for transmission of paratuberculosis among cattle is the contact of calves with adult cow feces, a systematic review indicates.
The report, which synthesized data from multiple sources, identified five interlinked risk factors for transmission, each of which involved the fecal-oral route.
"Paratuberculosis has a worldwide distribution and many countries have implemented control programs to prevent transmission among and within herds," write Elizabeth Doré (University of Montreal, Quebec, Canada) and fellow researchers in the Journal of Veterinary Internal Medicine.
"For these programs to be efficient, knowledge of the risk factors involved in transmission is essential."
To address this need, Doré's team searched the literature for research into risk factors associated with Mycobacterium avium subsp. paratuberculosis (MAP) transmission to dairy calves.
They identified a total of 23 studies that were suitable for inclusion, 16 of which were cross-sectional. Evidence from these studies pointed to five major risk factors for MAP transmission, says the team.
The first related to characteristics of the immediate neonatal environment. For example, factors such as contamination of udders with manure, group housing of periparturient cows, and presence of more than one cow in the maternity pen each significantly increased the risk for MAP transmission.
The type of colostrum fed to calves was another risk factor, with colostrum from serology-positive cows and the use of pooled colostrum from multiple dams both increasing the risk for MAP transmission.
Similarly, the type of milk fed to calves influenced MAP transmission risk, such that milk from enzyme-linked immunosorbent assay (ELISA)-positive cows, calves suckling from foster cows, and the use of waste milk each increased the risk.
The fourth risk factor was group housing of calves, whereas calves raised in individual pens had a decreased odds for a positive MAP culture and those raised in group pens had an increased risk.
Finally, MAP transmission was more likely when calves came into contact with adult cow feces. Indeed, one study found a positive dose-response relationship between the frequency of grazing calves in a paddock and the odds of being a high incidence herd. Additionally, herds where calves were housed with adults before 6 months of age were more likely to be infected by MAP.
"Based on the present systematic review, contact with adult cow feces appears to be the most important risk factor for MAP transmission," Doré and co-authors conclude.
They add: "Most of the risk factors were closely related to fecal contamination (hygiene), for example, cleanliness of the calving area, and udder washed before collection of colostrum."
By Joanna Lyford