Tuberculosis

Tuberculosis (TB) continues to be a worldwide infectious problem for humans. While human-to-human infection is of greatest concern, one infected dairy herd can infect hundreds, if not thousands, of people.

Potentially, tuberculosis can infect any mammal, although production cattle, especially dairy cattle, are at greatest risk. Complicating efforts to combat the disease is the fact that deer, badgers, elk and other wild species have been found to harbor the mycobacterium. In England, badgers were found to be spreading the infection to herds of cattle. Also, in England and Ireland, herds of sheep were found to be infected. In New Zealand, wild brush tail possums (Trichosurus vulpécula) were discovered to be the main source of infection in livestock, including deer herds. In Tanzania, tuberculosis-infected herds were found more often in small, pastoral farms that have little veterinary monitoring, as opposed to the large, commercial enterprises (19-22).

In a Los Angeles zoo, TB was found in two Asian elephants, three Rocky Mountain goats, and one black rhinoceros. An investigation found no active cases of tuberculosis in humans; however, tuberculin skin-test conversions in humans were associated with training the elephants and attending an elephant necropsy (23).

Human-to-animal transmission of TB has been documented. In an exotic animal farm in Illinois, three elephants died of Mycobacterium tuberculosis and a fourth tested culture-positive. Twenty-two handlers were screened for TB; eleven had positive reactions to intradermal injection with purified protein derivative. One had a smear-negative, culture-positive active TB. DNA comparisons by IS6110 and TBN12 typing showed that the isolates from the four elephants and the handler with active TB were the same strain, thus documenting that the infection of the elephants came from the handler (24).

Mycobacterium (tuberculosis) can infect agricultural workers in a number of ways:

1. Human-to-human contact with co-workers through the inhalation of respiratory droplets

2. Drinking contaminated, unpasteurized milk

3. Direct contact with infected animals

4. Direct contact with the secretions of infected animals such as respiratory droplets, milk, manure, urine, semen, and vaginal secretions

5. Direct contact or inhalations of respiratory droplets during necropsy, slaughter, or processing of meat or dairy products (20-24).

The clinical presentation is that of weight-loss, night sweats, a chronic cough, and hemoptysis. Asymptomatic workers are typically discovered through public health surveys. Diagnosis is through the purified protein derivative (PPD) skin test, smears of respiratory secretions demonstrating acid-fast bodies, cultures of respiratory secretions and other body fluids, radiographs demonstrating caseating granulomas, and other typical findings. Treatment is by multidrug therapy, complicated by regional drug resistance patterns (20-24).

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