HIV is not a super-spreader of drug-resistant tuberculosis
Tuberculosis bacteria don’t evolve drug resistance faster in HIV patients, but HIV does increase risk of contracting tuberculosis.
Tuberculosis is an infectious disease caused by a bacterium called Mycobacterium tuberculosis that causes more deaths worldwide than any other infection. Individuals who are infected with the Human Immunodeficiency Virus (HIV), which weakens the immune system, are particularly vulnerable to tuberculosis. However, treating individuals who are infected with both HIV and tuberculosis is complicated because the drugs currently used to treat one infection can interfere with the effectiveness of the drugs used to treat the other.
Tuberculosis is generally treated with antibiotics. However, some strains of M. tuberculosis are difficult to treat as they have evolved to resist the effects of multiple types of antibiotics. These “multidrug-resistant” bacteria appear to be particularly common in areas where HIV infections are also common. However, it was not known whether HIV directly influences whether M. tuberculosis bacteria evolve into drug-resistant forms.
Vegard Eldholm, Adrien Rieux and colleagues have now analysed the genomes, or total genetic content, of 252 samples of M. tuberculosis taken from the largest outbreak to date of multidrug-resistant tuberculosis in South America. This made it possible to identify the genetic mutations that enable the bacteria to resist antibiotic treatment. Using mathematical models to reconstruct the spread of multidrug resistant M. tuberculosis bacteria during the outbreak also made it possible to assess who transmitted tuberculosis to whom.
The results suggest that M. tuberculosis does not evolve drug resistance any faster in patients with HIV than otherwise. Furthermore, patients infected with both HIV and tuberculosis did not transmit tuberculosis to others more often than patients who did not have HIV. However, being infected with HIV did increase the likelihood that an individual would contract tuberculosis. HIV also increased the rate at which the symptoms of tuberculosis progressed in an individual.
To clarify the effect of HIV on the spread of tuberculosis, similar studies are needed that collect more complete patient data, including their anti-HIV treatment history and their degree of immune weakening.
To find out more
Read the eLife research paper on which this eLife digest is based: “Impact of HIV co-infection on the evolution and transmission of multidrug-resistant tuberculosis”(August 9, 2016).
