A few days ago, I wrote about tuberculosis (TB) exposure in several people who performed a necropsy on an infected dog. As part of that investigation, a cat in the household was tested and was also positive for TB. It was euthanized because of the public health concerns. A logical question from a reader was "Is there no treatment for animals, as there is with humans?"

Diagnosis of tuberculosis in an animal often results in prompt euthanasia, and some individuals and groups have euthanasia as a standard recommendation.

Why?

• We have no data about how to properly treat an infected animal.
• We have no data about how effective (or ineffective) treatment may be.
• It’s not easy to test animals before or during treatment to see if they are shedding the TB bacterium (Mycobacterium tuberculosis).
• It’s such a concerning disease in people that the inclination is to err on the side of caution when it comes to public health.

Is it an appropriate response?

In some circumstances, it probably is. In other circumstances, treatment shouldn’t necessarily be dismissed. A major problem is the knowledge gap.

• We don’t know whether infected animals pose any risk to people. Human-animal transmission can occur, but it’s unclear whether animals can transmit the infection back to people.
• If transmission between pets and people occurs, we don’t know what circumstances are involved. TB is not readily transmitted even between people. Short term exposure is not a major concern. It’s likely that close and prolonged contact is required for transmission from pets, but we don’t know for sure.
• We don’t know if certain infected animals are higher risk than others, although there probably are differences. A dog with respiratory TB and active disease is probably a much higher risk than a dog with a localized TB abscess.
• We don’t have easy and accurate ways to test pets for TB exposure and shedding. In people, sputum cultures are tested by having people spit in a cup. Getting a sample like that is obviously difficult in dogs. Collecting a good sample for testing is much more involved in pets and not amenable to routine testing (for research or monitoring).
• We don’t know for how long to treat a pet with TB, or which drugs are optimal for use.

Treatment might be reasonable when there is an animal with mild disease (or no signs of disease), when the animal was infected from a household contact (meaning that some degree of TB exposure has already occurred in the household and the dog would probably only be a secondary source of exposure), when there are committed owners who are willing to embark on time consuming and expensive treatment, when owners are able to keep the dog away from other animals and people during the treatment period, and when there is an understanding that treatment may not work.

When might treatment not be a good idea?

• When the animal is shedding the TB bacterium in respiratory secretions.
• When the owners cannot afford prolonged and expensive treatment and monitoring.
• When the owners cannot be relied on the administer every dose of medication and make every required follow-up appointment.
• When owners cannot be relied on to keep the dog away from other dogs and animals (and people) during the treatment period (or at least during the initial period).
• When there are high-risk people in the household, such as people with HIV.
• When serious disease is present, such that the chances of recovery are low.