Tuberculosis

Cause
Diagnosis
Treatment and Control
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Introduction

Tuberculosis(TB) is a disease of great importance in both animal agriculture and human health. In animals and humans its most important impact is as a chronic wasting diesease. The disease is endemic/enzootic throughout large regions of the world. It is estimated that one out of three people in the world are infected with TB and this disease remains the most common infectious cause of death among adults (2-3 million people each year). Tuberculosis was once the most prevalent infectious disease of cattle and swine in the US. State animal health agencies and US livestock producers have almost eradicated TB from the livestock population since the 1917 Cooperative Sate-Federal Tuberculosis Eradication Program went into effect. However, M bovis is being detected more frequently in wild cervids. Infected deer populations have been implicated as the source of infection for WI and MI herds since1995.

TB has been reduced in the human population due to advances in sanitation and hygiene, pasteurization of milk and discovery of effective drugs to treat TB. Currently, however there is an increase in the incidence of human TB because of drug resistance and the occurrence of nontraditional strain TB in AIDS patients.

Cause

Tuberculosis is caused by a mycobacterium that are strictly aerobic, Gram-positive, non-spore-forming curved or straight rods with zoonotic properties. There are three major strains of Mycobacterium with there own primary reservoir species but can cause disease in other species.Disease causing mycobacterium can live outside the host for only a few weeks but do not multiply outside a host. Because the bacteria have a slow rate of growth, the disease may take months or years to develop. The bacteria can be dormant in the host’s body for its lifetime without causing disease.

The major mode of transmission of myobacterium is by inhalation of the organisms in aerosolized droplets leading to localization of the bacteria in the lungs. Wherever the organisms localize, tumor like masses called tubercles are formed. Lesions are most frequently seen in lymph nodes, lungs, liver, spleen, and the surfaces of the body cavity, In females, this disease infects the uterus and oviducts producing tubercles and adhesions between the uterus, oviduct, ovary and surrounding tissue. 1-2% of cows develop mycobacterial mastitis with shedding of the organism in the milk. Infection of humans by contaminated milk causes the organism to localize in the GI tract and related lymph nodes. Bovine TB is a chronic disease that is hard to diagnose because there are no symptoms until it has reached an advanced stage or after slaughter.

Mycobacterium tuberculosis Humans cattl

Strain	Primary Reservoir	Accidental Host
M. tuberculosis	Humans	Cattle
M. bovis	Cattle	Humans, goats, pigs, wild animals
M. avium complex	Birds, environment	Humans, domestic and wild animals

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Diagnosis

TB lesions may be found in any organ or body cavity. Carcuses are examined after slaughter for any suspicious lesions and the tissue tested. Positive results lead to identification of the originating herd and quarantine and testing of the herd. A tuberculin skin test can be used in animals and humans to detect an immune response to TB bacteria. Swelling indicates exposure to one of the mycobacterium.Further diagnostic tests are needed to determine the strain. In humans, chest x-rays and sputum cultures can be used to further diagnosis the mycobacterium.

Treatment and Control

The control of TB in cattle is based on an eradication program begun in 1917. Slaughtered cattle with suspicious lesions that are confirmed to be M. bovis,are traced back to the farm of origin. The herd is tested and if positive then it is depopulated or quarantined.

Humans are treated with a 6-9 month regimen of antibiotics. If the bacterium is not antibiotic resistant then treatment is 95% effective.