|From The State Vet's Office|
|Taking Another Look at Bovine Tuberculosis|
by Dr. Tony Frazier
It was interesting to notice a headline on a recent evening’s newscast: TB Scare! The brief report went on to tell about a passenger on two international flights that may have exposed every passenger on the planes to Multi-Drug Resistant Tuberculosis. That report just serves to remind us that the battle against TB rages on.
In most industrialized countries of the world, the incidence of human tuberculosis runs from 2 to 10 cases per 100,000 people. A report from the Center for Disease Control stated that in the United States in 2006, there were 13,767 cases of human tuberculosis nationwide, which equals about 4.6 cases per 100,000 people. That was the lowest rate recorded since reporting began in 1953.
After an upsurge from 1985 to 1992, there has been a steady decline in cases, but the decrease is slowing. There are a number of factors that have contributed to the increase in human cases of tuberculosis world-wide. Included in these factors are the increase world-wide of HIV (human immunodeficiency virus), an increasing number of patients on immunosuppressive drugs and the movement of people from countries where tuberculosis is a problem.
In the United States, over the past four decades, there have been 55 documented cases of humans that were infected with the bovine tuberculosis organism. While that number is extremely low, surveillance and eradication of bovine tuberculosis is important both economically and because of the public health concerns.
In many countries around the world, bovine tuberculosis is a problem in livestock as well as a very real public health concern. In those countries, people who drink unpasteurized milk from infected cows are at considerable risk for developing tuberculosis. It is not completely understood where bovine tuberculosis fits into the present surge of human tuberculosis world-wide. However, an upsurge in bovine tuberculosis in cattle and in deer in the United States compels us to take another look at a disease that has not been found in Alabama since 1981.
Mycobacterium bovis is the common cause of tuberculosis in cattle and goats, which are quite susceptible. The signs of tuberculosis in animals are not very specific. In fact, most infected animals may appear to be completely healthy, while exposing other animals as well as humans to the disease. As the disease develops, the animal may experience weight loss, variable appetite and fluctuating fevers. Depending on the route of invasion, other signs may be present. There may be a chronic cough if the route of invasion was respiratory. If the route was by ingesting contaminated feed, the signs may range from diarrhea to constipation and bloat. Those are signs that are shared by numerous diseases. Therefore, without performing an intradermal TB test (skin test) or performing a necropsy, a diagnosis of tuberculosis would not likely be made.
For years, here in Alabama, we have not required any tuberculosis testing on cattle coming in from other bovine tuberculosis-free states. However, we, along with other states are considering some changes that would require testing of certain types of cattle from other states—even though they ship from tuberculosis-free states. Because of the transient nature of rodeo cattle and dairy heifers (before they reach production), it may be difficult to truly know where these animals originate. Presently, the most comprehensive surveillance nationally for bovine tuberculosis is that each carcass is examined at harvest in slaughter facilities. Recently a rodeo bull from Colorado was found to be positive at slaughter. This bull was found to have been in rodeos in several states. Possibly, import regulations that required the bull to have been TB tested prior to entry into other states would have detected that this bull was positive before possibly exposing other livestock.
Another concern in the livestock industry in states where tuberculosis exists is the possibility of the disease spreading into wildlife. There is an old saying that says when a livestock disease gets into wildlife, you’re up a creek without a paddle (paraphrased). Just ask the folks with the Michigan Department of Agriculture. Since 1994, over 500 deer in a 13 county area have been found to be positive for Mycobacterium bovis. The problem in the whitetail deer has been passed back and forth with cattle. The results have included Michigan’s loss of tuberculosis free status, the testing of over 18,000 cattle herds, millions of dollars paid in indemnity claims and mandatory identification for cattle that move within or out of the infected zone.
Minnesota has the same problem. After a cow tested positive in 2005, surveillance on deer has found at least one deer with the exact same strain as the cow had. They have also found other cattle herds to be positive. Thus far, it has cost them over 3 million dollars in indemnity. Additionally, when deer are infected there is the possibility of hunters becoming exposed while field-dressing the carcass or even eating undercooked meat.
As you can see, bovine tuberculosis is a complicated problem with no easy solution. We have kept the door closed to this disease in Alabama for a long time and we intend to do everything we can to keep it that way. As I said before, we are looking at ways to make sure we are doing enough. You know what they say about an ounce of prevention.