**Tuberculosis and HIV — Doubling the Fatality**

Tatina T. Todorova, Gabriela Tsankova, Neli Lodozova and Tcvetelina Kostadinova

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/61138

#### **Abstract**

Tuberculosis (TB) and HIV/AIDS infection are one of the most ubiquitous and deadli‐ est communicable diseases in the world. They cause millions of deaths each year and are recognized as major threats for public health worldwide. The corresponding pathogens (*Mycobacterium tuberculosis* and HIV) share overlapping epidemiology they affect low-income countries and place an immense burden on their feeble health care systems. Over the last decades, the natural history of both diseases has changed; in addition to devastating single HIV and TB infections, the coinfection with both pathogens has emerged and has spread in pandemic scale. When present as dual in‐ fection in an individual, *Mycobacterium tuberculosis* and HIV potentiate each other and kill in cooperation the host. TB is the leading cause of death in HIV-positive patients and in turn HIV infection is the strongest risk factor for the development of new or reactivation of dormant TB disease. Both pathogens (as single or dual infection) pro‐ voke a robust immune response in the infected host but the immune system does not achieve to eliminate the infectious agent(s). The failure of immune defense results in vulnerable immune balance between the micro- and the macroorganism and often ends up in a fatal outcome.

**Keywords:** Tuberculosis, HIV, immunity, co-infection

#### **1. Introduction**

Human immunodeficiency virus (HIV) and tuberculosis (TB) represent, respectively, the first and the second leading cause of death from infectious disease in the world. Both are responsible for approximately 3 million deaths annually [1].

Either HIV or TB, when present as a single infection, irreversibly affects and exhausts the immune system of the infected person. Moreover, if they simultaneously coexist in an

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individual (coinfection), they act in synergy to deteriorate the defense mechanisms of the host's immunity and to accelerate the fatal scenario.

In this chapter, we will review current knowledge of innate and adaptive immune responses against TB and HIV infections. We will discuss in detail the immunological basis behind the dual threat of TB/HIV coinfection.
