A tuberculosis reservoir is the primary source from which Mycobacterium tuberculosis bacteria spread. This reservoir harbors the bacteria, allowing them to survive and be transmitted to new individuals. Understanding these sources is fundamental for global disease control efforts, as it enables public health initiatives to target interventions effectively.
Humans as the Main Reservoir
Humans are the predominant reservoir for Mycobacterium tuberculosis, the bacterium responsible for most tuberculosis cases. This occurs in two main forms: active tuberculosis disease and latent tuberculosis infection (LTBI). Individuals with active pulmonary tuberculosis exhibit symptoms like a persistent cough and transmit the bacteria through the air. These cases represent the immediate infectious source in communities.
Many people carry Mycobacterium tuberculosis in a latent state (LTBI). In LTBI, the bacteria are inactive, causing no symptoms and not being contagious to others. Despite being asymptomatic, individuals with LTBI constitute a potential reservoir because the dormant bacteria can reactivate at a later time. Reactivation often occurs when a person’s immune system weakens, such as due to conditions like HIV, malnutrition, or advanced age.
Animal Reservoirs and Zoonotic Transmission
Certain animal species also serve as reservoirs for tuberculosis, primarily involving Mycobacterium bovis (bovine tuberculosis). Cattle are the main hosts for this bacterium, shedding it via respiratory secretions, feces, and milk. Infections are also found in deer, bison, elk, goats, and badgers. These animal populations can act as ongoing sources of infection.
Zoonotic transmission, the spread of disease from animals to humans, most commonly occurs through consuming unpasteurized dairy products. For instance, raw milk or cheeses can contain Mycobacterium bovis. Less frequently, humans can contract the infection through direct contact with infected animal tissues (e.g., during slaughter or hunting) or by inhaling bacteria exhaled by sick animals.
How Tuberculosis Spreads
Tuberculosis primarily spreads through the air when individuals with active lung or throat TB expel tiny infectious particles. These particles, known as droplet nuclei, contain Mycobacterium tuberculosis bacteria. They are released when an infected person coughs, sneezes, speaks, or sings. These minute droplets can remain suspended in the air for several hours, depending on environmental conditions.
People nearby can inhale these airborne bacteria, leading to new infections. Transmission is more likely in enclosed spaces with poor ventilation, where infectious droplets can build up. Not everyone exposed to the bacteria will become infected, and only a fraction of those will develop active disease. The risk of transmission depends on the source person’s infectiousness and the duration of exposure.
Managing Tuberculosis Reservoirs
Controlling tuberculosis reservoirs involves a multi-faceted public health approach targeting both human and animal sources. For the human reservoir, early diagnosis of active cases is important to quickly initiate treatment and eliminate the source. Completing the full course of antibiotics is important to cure the disease and prevent drug-resistant strains. Screening high-risk groups for latent tuberculosis infection and providing preventive treatment can reduce future active cases.
Addressing animal reservoirs primarily focuses on Mycobacterium bovis control in livestock. This includes veterinary surveillance, routine cattle testing, and culling infected animals to prevent further spread. Pasteurization of milk and dairy products effectively destroys Mycobacterium bovis, preventing zoonotic transmission through food. Public health efforts also emphasize improving living conditions, ensuring adequate ventilation, and maintaining robust surveillance for prompt case detection and contact tracing.