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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. |
