The impact of HIV on Drug-Resistant Tuberculosis

Second of five student guest posts by Nai-Chung N. Chang

Tuberculosis (TB) is a major disease burden in many areas of the world. As such, it was declared a global public health emergency in 1993 by the World Health Organization (WHO). It is a bacterial disease that is transmitted through the air when an infected individual coughs, sneezes, speaks, or sings. However, not all individuals who contract the disease will display symptoms. This separates the infected into two categories, latent and active. Latent individuals are non-infectious and will not transmit the disease, whereas active individuals are able to transmit the disease.

TB is a significant concern in patients diagnosed with HIV, since individuals diagnosed with HIV and latent forms of TB infection is more likely to develop the disease, then the HIV negative individuals. In addition, in people living with HIV, TB is one of the leading causes of death. (CDC, 2012) The fact that latent forms of the disease are capable of becoming fully active forms given the right stimulus represents a high risk to individuals living in poor conditions, which is widely present in developing nations. It is of even greater concern to individuals who have immune system diseases, such as HIV. Individuals with latent TB infection depend on robust immune system responses to prevent the infection from going into active form. HIV and similar diseases targets and weakens immune systems so that the response to infections becomes weaker, providing increased risk of TB infections and the activation of latent forms.

TB is a major concern not only because of its status as a global epidemic. While there are many forms of prevention and treatment for the disease, such as antibiotics and vaccine, these treatments are not overly effective in combating and controlling the spread of the disease. TB is widespread and has a high chance of becoming resistant to any treatment that it is exposed to, especially antibiotics and other chemotherapeutic drugs such as isoniazid. Several of these strains already exist and each has varying levels of resistance, including Multidrug-Resistant (MDR) and Extensively Drug-Resistant (XDR). MDR is a strain that is resistant to two of the most often used and potent TB drugs, isoniazid and rifampin; whereas XDR is MDR strains that have developed resistance to any fluoroquinolone and at least one of three second-line drugs such as kanamycin or capreomycin. Also, the vaccine that has been developed for preventing TB is not overly protective, and sometimes fails to protect against infection. (CDC, 2012) The vaccine is not designed to prevent the infection of TB; instead, it is aimed towards boosting and speeding up the immune system response to any new infection so that the infected individual remains in latent forms. (Russell, et al., 2010)

The increasing trends in the resistance of TB to various treatments is a serious concern as it have major impacts in controlling the spread of the disease in many regions. This condition worsens with MDR and XDR TB. With regular, normal strains of TB, latent and early infections could be combated and controlled by a successful chemotherapeutic treatment even in patients with immune system diseases. However, with MDR and XDR TB, the strains are able to fully develop in an individual with weakened immune system, as evident in areas where incidence of TB and HIV is high, such as South Africa. (O'Donnell, et al., 2013) For cases with MDR and XDR strains, the weakened immune systems are not potent enough to prevent infections or keep them in latent form. Additionally, the active forms of these strains are resistant to common, and in some cases, advanced treatments.

With the increasing development of drug-resistant TB, the most effective way to combat TB is not only through vaccines and treatments. Instead, strict public health policy is needed to properly maintain control and combat the spread of TB. With a well-structured public health system, we can ensure that the long treatment of TB is complete, since most of the increase in the resistance to treatment often results from issues during treatment. Events such as patient non-compliance to the treatment and inadequate health-care supervision can all result in the development of new strains of the bacteria that have developed resistance to the treatments that was used. (Russell, et al., 2010) Also, a well-structured public health system can maintain better supply and quality of drugs throughout the treatment process, as well as the prevention and detection of possible new drug resistant strains. More importantly, it can maintain better surveillance and ensure patient compliance during the treatment process, which would help in reducing the development of drug resistant strains. The surveillance systems can also target comorbid diseases such as HIV to reduce risk factors for activating latent forms of the disease in patients with HIV and similar diseases.

References:
CDC, 2012. Tuberculosis (TB). [Online]
Available at: http://www.cdc.gov/tb/topic/basics/default.htm
[Accessed 13 2 2013].
O'Donnell, M. R. et al., 2013. Treatment Outcomes for Extensively Drug-Resistant Tuberculosis and HIV Co-infection. Emerging Infectious Disease [Internet], 19(3).
Russell, D. G., Barry 3rd, C. E. & Flynn, J. L., 2010. Tuberculosis: What We Don’t Know Can, and Does, Hurt Us. Science, 328(5980), pp. 852-856.