Flipping the Switch: COVID-19 & Latent TB

By Naomi Michelson

Every 2.85 seconds, someone dies of tuberculosis (TB). In 2020, 10 million people contracted the disease. TB is the second leading cause of death by an infectious disease, surpassed only by COVID-19. This respiratory killing agent has been circulating through human populations for thousands of years, leaving trails of devastation in its wake.

Due to the highly virulent nature of the disease, one-quarter of the global population is infected with TB. However, not everyone who has the bacteria living in their body is ill with active TB. Most healthy immune systems are able to fight off the disease itself, while 5-10% of those exposed to TB bacteria contract the disease. The remaining 85-90% are left living with latent, or inactive, TB. Thus, millions of people around the world have latent TB silently taking up residence in their bodies.

So, how does a case of latent TB become active? The answer lies in our immune systems. TB is an opportunistic pathogen, meaning it lies dormant and waits for its host’s immune system to weaken before attacking. Oftentimes, this means an illness that decreases immunity can be the catalyst for a case of active TB. This is most prevalent in HIV-TB coinfections, in which HIV drastically reduces immune function, allowing a once-latent case of TB to reactivate. This phenomenon is so prevalent that those infected with HIV have a TB risk that is 18 times higher than that of the general population.

The COVID-19 pandemic has had a largely deleterious effect on the global fight against TB, as it has limited patient access to resources, diverted financial focuses, and worsened chronic health outcomes. However, as the disease can weaken the immune system and impair lung function, COVID-19 has also served as the catalyst to reactivate latent cases of TB. A recent study on mice populations found evidence of the MHV-1 strain of COVID-19 reactivating dormant Mycobacterium tuberculosis. Researchers showed that within the COVID-19-infected mice populations, decreased immunity allowed TB cells to hijack altruistic stem cells and replicate in the lungs, thus allowing for reinfected cases of pulmonary TB.

One such case was noted in the United States. A 70-year-old woman arrived in the emergency room with signs and symptoms of COVID-19. Upon testing, doctors determined she had COVID-19 pneumonia. However, after her symptoms continued to worsen with treatment, an infectious disease team was called in and discovered she had a reactivated case of TB. After receiving treatment for the correct disease, her condition improved dramatically, and she was released from the hospital. Evidently, this double burden of disease requires a higher level of complex care, one that may not be attainable for systemically underfunded and underserved populations. Lead investigator of the mice study, Dr. Bikul Das, states, “there is an urgent need to study the association of COVID-19 with dormant TB reactivation to avoid a potential global TB pandemic.”

COVID-19 has left a trail of coinfections in its wake, often acting as a syndemic rather than just a pandemic. As cases continue to rise, what does this mean for the future of the fight against TB? While COVID-19 funding remains separate from pre-existing global health efforts and pandemic preparedness, the lines must be drawn between diseases to recognize their complex relationships. There is no single solution, nor is there a single cause to take up. Rather, a collective multi-lateral and multidisciplinary effort is necessary to ensure that no more people die of a curable disease.

Naomi Michelson is a former intern at Friends of the Global Fight.

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