Tuberculosis In Livestock

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Here's What's Causing TB

There are several strains of TB, caused by a bacteria of the genus Mycobacterium tuberculosis, the human form. The most common strains in barnyard animals are M bovis and Mavium, which are found in cattle and birds, respectively. The human strain and the bovine strain are the most closely related. Literature often refers to the organism as being "acid fast," which means that when the material containing the organism is stained with a red dye and washed with a bleaching acid, the organism retains the red color. This makes it more visible under a microscope.

Many of us think of tuberculosis in the human as being a slow, debilitating condition. However, stress from poor nutrition, exposure to cold and wet, or other diseases can all cause it to be a rapid killer. The human form is seldom found in animals other than non-human primates, but the bovine form readily affects most warm-blooded vertebrates. Birds seldom have any form except the avian, but this form has been found in most barnyard animals, as well as dogs and cats. Exotic pets, in particular, may be carriers of the disease in any one of its three main forms.

Look for These Symptoms

Symptoms of TB may go completely unnoticed in your animal until some form of stress—poor nutrition, old age, missing teeth, or some other disease—takes over. I have seen cattle that were generalized cases at postmortem that had been fat, slick, and producing well just prior to slaughter.

The autopsy lesions of cattle with early cases of TB may only be swollen mandibular lymph glands. Later, a caseous solid pneumonia is apt to be found. In so-called generalized cases, many organs are involved. Regardless of the lesion's size, there will be a scraping sound (as if the lesion contained sand) when a vet cuts into it with a knife.

In humans, the bovine form of the disease often settles in the bones, or the glands of the throat and neck. Literature describes large numbers of human cases that became hunch-backed because the disease causes collapsed vertebrae. I can remember as a boy seeing people with scars on their neck and throat where infected glands had been removed.

The History of Tuberculosis

Early in this century—prior to the pasteurization of milk—there were so many cattle infected with TB that many humans contracted the bovine form of the disease from drinking milk. Tuberculin testing of cattle began in the 1920s as a public health measure. State and federal indemnities were paid to the owners who had reactor cattle removed from their herds.

Since tuberculosis first affects the lungs of the victim, whether human or animal, it is spread most often by saliva and nasal discharge.

These reactor cattle were branded with a "T" on their right cheek, and a special reactor tag was placed in their left ear. They were then shipped to slaughter houses, where veterinarians of the Bureau of Animal Industry did postmortem inspection as they were slaughtered. Generalized cases, in which more than one organ was involved, were "tanked." That is, the whole carcass was destroyed by heat and chemicals in order to keep it out of the food chain.

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