New test detects early stage of wasting disease in cattle.

Researchers at the National Institute for Mathematical and Biological Synthesis (NIMBioS) at the University of Tennessee, Knoxville, have identified a more sensitive test for detecting the early stages of paratuberculosis, a fatal disease that plagues dairy herds and causes an estimated annual loss of up to $250 million to the US dairy industry. Current methods of testing for the presence of the bacteria that cause the disease often misdiagnose animals in the early stages of the disease, which has no cure. Infected animals produce less milk, have fertility problems, and must be culled. Transmission occurs by ingestion of manure-contaminated food and pastures or by colostrum passed from an infected dam to a calf. The disease usually manifests two to three years after the initial infection, but in some cases, can take up to 10 years before it becomes apparent. During this time, infected animals shed the bacteria, putting the health of the entire herd at risk. The research, published in Nature's Scientific Reports, found that the fecal test could not reliably predict persistent infections or early stages.Shedding and potential transmission could occur well before a fecal test yields positive results, so what's needed are other disease predictors. Using a suite of mathematical models and statistical simulations, the researchers determined that a test based on a type of immune cells called macrophages produces more reliable diagnoses.The macrophage based assay could be a better marker in the diagnoses of paratuberculosis infections, especially in slow or non-progressing infections and also in cases that progress to advance diseases rapidly.