SEATTLE — According to the World Health Organization (WHO), more than 10 million people contracted tuberculosis in 2015. Medical News Today notes that the majority of these cases — 86 percent — occur in Africa, Southeast Asia and the Western Pacific region. In the absence of adequate medical treatment, two-thirds of these patients die.
A paper recently published in The Lancet reports that a significant number of tuberculosis cases are actually misdiagnosed. The bacteria M. tuberculosis causes most human cases of the disease, but a significant number are caused by the M. Bovis bacteria, which is of animal origin.
Human-originating tuberculosis and tuberculosis of animal origin — also called zootonic tuberculosis — present with the same symptoms, and diagnostic tests do not typically distinguish between the two strains. Most of the time, tuberculosis is an airborne disease, spread by coughing and sneezing, laughing and talking. The disease affects the lungs, kidneys and heart. However, zootonic tuberculosis is more often spread through consuming animal products from affected animals.
The distinction between human and animal tuberculosis is significant because the M. Bovis bacteria is naturally resistant to pyrazinamide, one of the four first-line tuberculosis treatments. It can be difficult to ensure that the treatment is effectively combatting the disease especially in light of the lengthy treatment time. It takes a six-month regimen to treat human tuberculosis, and as long as nine months for zootonic tuberculosis. If zootonic tuberculosis is misdiagnosed and then treated with pyrazinamide, it will take that much longer to cure the patient of the infection.
A shorter treatment time is especially desirable because of the unpleasant side-effects associated with drugs used to treat tuberculosis, and because of an additional cost of longer treatment time, both of which could mean lower patient compliance.
Since the 1990s, the death rate in tuberculosis patients has been decreasing. In 2013, patients newly diagnosed with tuberculosis were successfully treated 86 percent of the time. Additionally, between 2000 and 2014, prevention and treatment endeavors saved the lives of 43 million patients who otherwise might have died as a result of tuberculosis.
Even so, many patients are infected with M. Bovis rather than M. tuberculosis. There is not yet an accurate estimate of the prevalence of animal tuberculosis, although there are some regional estimates based on small samples — for example, around 28 percent of tuberculosis cases in Mexico may be due to M. Bovis rather than M. tuberculosis.
For these patients and for others who live or work in close proximity to animals, tuberculosis diagnoses must improve to determine the causative bacteria, additional treatment options must be developed and the prevention of animal-to-human disease transmission must be addressed.
– Madeline Reding