CALF_News_April_May_2018

16 CALF News • April | May 2018 • www.calfnews.net CALF ANIMAL HEALTH Chuteside Manner EXPLORING THE FRONTIER OF ANIMAL HEALTH Tuberculosis By Patti Wilson Contributing Editor C onsidering the outbreaks of tuberculosis (TB) in two South Dakota beef cattle herds in the past year and a half, it is best for all of us to be aware of some facts about this inconvenient disease. The first step is, of course, to drop any denial on our own part and acknowledge that this does happen. Thanks go to Nebraska State Vet- erinarian Dr. Dennis Hughes and the Nebraska Department of Agriculture for significant input in this article via the Nebraska Cattlemen’s Convention. In February 2017, Dr. Hughes got an unwelcome phone call from his coun- terpart in South Dakota. They had just discovered a new TB-infected herd in Harding County. The 580-head herd had a significant infection rate of 9 percent. The opera- tion they were from had been involved in cow-calf production, and had sold feeder calves to feedlots and heifers for breed- ing. In addition, the family was involved in rodeo and possessed roping steers. Whole-genome sequencing revealed a Mexican strain of TB M. bovis. To make matters worse, some of the heifers sold for feeding had been resold and diverted into breeding programs, to the great consternation of the afore- mentioned veterinarians. Preliminary research revealed that Nebraska has received many traces from the infected herd. A second discovery of TB-positive stock in Tripp County, S.D., broke in December 2017, doubling the efforts of state veterinarians to corral the disease. It quickly spilled traces into Wheeler County, Neb. Resolution of the outbreaks is progressing well, but incidences of the disease continue. What is it? Bovine TB is a chronic bacterial disease that will occasionally affect other species of mammals. It can be spread to humans, making it a zoonotic illness. Infection to humans is generally done by inhalation of airborne disease particles or ingestion of unpasteurized milk. Reservoirs of infection may be found in wildlife, making TB eradication extremely difficult. Spread of TB from cattle to humans is most likely to occur on large dairies where cows are confined and human contact is close and constant. Like- wise, cows can contract TB from dairy employees, as well. It has been suggested that undocumented immigrants who have not undergone standard health screening have likely brought the disease into California dairy herds. The consumption of unpasteurized (raw) milk by humans is also more likely in heavily populated dairy states; it is seen as an option by some fringe con- sumers as the ultimate health food. This practice is a bad idea, namely because the purpose of pasteurization is to kill multiple, potentially deadly pathogens found in raw milk. Reservoirs Saying that wildlife serve as reservoirs of infection is painting with an extra- wide brush. Each country has specific mammal populations that make it nearly impossible to completely eliminate TB. To no one’s surprise, white-tailed deer are the most notorious TB carriers in the U.S. It’s easy to see why they are a probable reservoir for beef cattle. Cana- dians deal with infected bison and elk, and New Zealanders with brush-tailed opossums. African, Asian and Middle Eastern nations suffer the largest and wildest group of TB carriers, making it nearly impossible to manage the disease. The most interesting pool if infection is in the British Isles. England and Ire- land are home to, it seems, a large popu- lation of badgers, who are notoriously elusive and dangerously infected. Over 40 percent carry the bacterium, suffering little or no effects of TB while spreading it through contamination of cattle feed. Efforts to “cull” a large portion of these government-protected pests are being thwarted by animal rights activists. Due to effective control programs, TB has nearly disappeared from domes- ticated animals in several countries.