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HIV Co-Infection Does Not Directly Drive Spread of Multidrug-resistant Tuberculosis

Researchers have found that although HIV makes individuals more susceptible to acquire tuberculosis, it is not the cause of the spread of multidrug-resistant tuberculosis.

Researchers have long known that the HIV pandemic has fueled the tuberculosis (TB) epidemic, but a new study published in eLife shows that despite what was previously hypothesized, HIV is not a driver in the development of multidrug resistance in TB patients, nor does it account for transmission of drug resistance in those with TB. In addition, the study also found that HIV-positive patients are not more likely to develop drug resistance in comparison to those who are HIV-negative.

Caused by a bacterium called Mycobacterium tuberculosis (Mtb), TB is one of the deadliest infectious diseases, answering for more deaths worldwide than any other infection, according to the study. The World Health Organization (WHO) reports that 9.6 million people were diagnosed with TB in 2014 and about 1.5 million people died from the disease in the same year.

According to a press release, Vegard Eldholm, PhD, a researcher at the Norwegian Institute of Public Health noted that of the 1.5 million deaths, “about 200,000 cases involved multidrug-resistant TB and 400,000 were HIV co-infected.”

It’s widely acknowledged by experts in the field as well as by the CDC, that HIV-infected individuals are particularly at risk for acquiring TB, mostly due to the fact that HIV weakens the body’s immune system, which makes it harder for the body to fight off disease. According to the CDC, “The HIV, or the AIDS virus, helps TB germs make you sick because it weakens your immune system. If you are infected with HIV and with TB germs, you have a very big chance of getting TB disease. The TB germs are much more likely to become active and attack your lungs and other parts of the body.”

Despite this known parallel between HIV and TB, the effect of HIV on drug resistance in TB patients has not yet been made clear, until now.

Norwegian, British, and Argentinian scientists partnered up to study how HIV co-infection influences Mtb drug resistance. Eldholm and colleagues analyzed the genomes, or the complete set of genetic content, of samples collected from 252 patients who had been infected with TB during the 1990s outbreak in South America, the largest multi-drug resistant TB epidemic to date, according to the press release. The isolates were taken from patients that had tested positive for HIV between the mid-1990s and 2009. The researchers then used those genomes to create a phylogenic tree, or evolutionary tree, that aided in the process of identifying the genetic mutations within the sampled patients that assisted bacteria in developing drug resistance.

Furthermore, the scientists were able to reconstruct how TB had spread among individuals during the outbreak through the implementation of a new mathematical model that also allowed them to identify which patients had transmitted TB, and to whom, according to the study. The data yielded from both analysis methods allowed the researchers to identify the patients whose strains of TB had developed mutations that were drug-resistant.

According to the study, “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.” The study did confirm that individuals with HIV were at a higher risk for acquiring tuberculosis and a person infected with HIV will also quicken the rate of TB-related symptoms.