Tuberculosis And Polluted Water: Is There A Link?

Tuberculosis (TB) is a respiratory infectious disease caused by Mycobacterium tuberculosis, which spreads when people who are sick with TB expel bacteria into the air, for example, by coughing. While TB is typically transmitted through airborne transmission, there is evidence to suggest that it can also be transmitted through the ingestion of contaminated water and food. The presence of Mycobacterium tuberculosis in water supplies has been observed in several studies, indicating a potential risk of transmission to humans and animals through this route. This raises the question of whether polluted water is a significant cause of tuberculosis and what the implications are for public health.

Tuberculosis is primarily a respiratory disease

Tuberculosis (TB) is a respiratory disease caused by a bacterium called Mycobacterium tuberculosis. The primary site of TB is the lungs, from which it can spread to other parts of the body. This spread from the lungs to other parts of the body is known as extrapulmonary tuberculosis.

TB germs can get into the air when someone with active TB of the lungs or throat coughs, speaks, sings, laughs, or sneezes. People nearby may then breathe in these germs and become infected. The disease is more likely to spread when people spend a lot of time together in indoor spaces with poor air circulation.

The occurrence of Mycobacterium tuberculosis in wastewater has been reported. The bacteria have been detected in raw wastewater, treated wastewater, activated sludge, soil, and water. However, the literature on this topic has largely focused on molecular-based detection, with little to no quantification data presented. This could be due to the challenges associated with quantification methods.

While the presence of Mycobacterium tuberculosis in wastewater has been observed, the focus of this review is on respiratory tuberculosis. The disease primarily affects the lungs and spreads through the air from one person to another. Therefore, while Mycobacterium tuberculosis may be present in wastewater, the primary route of transmission for TB is respiratory, not through polluted water.

Mycobacterium tuberculosis is found in wastewater

Tuberculosis (TB) is a communicable disease and one of the top ten causes of death globally, ranking above HIV/AIDS. It is caused by a group of closely related, slow-growing mycobacteria, collectively named the Mycobacterium tuberculosis complex (MTBC). The MTBC consists of causative agents of both human and animal tuberculosis and is responsible for over 10 million annual infections globally.

Infections occur mainly through airborne transmission, however, there are possible indirect transmissions through a faecal-oral route which is poorly reported. This faecal-oral transmission could be through the occurrence of the microbe in environments such as wastewater. The detection of viable MTBC cells in either treated or untreated wastewater highlights the potential risks of infection for wastewater workers and communities close to these wastewater treatment plants. The generation of aerosols during wastewater treatment could be the main route of transmission.

The occurrence of MTBC in wastewater has been reported over the years. These studies detected the presence of MTBC in different matrices, such as wastewater or sewage and surface water impacted by wastewater. The prevalence of M. tuberculosis in untreated wastewater was between 75%-100%, while M. africanum ranged from 25%-50%. The highest median concentration detected in untreated wastewater was up to 4.9 (±0.2) Log10 copies/ml for total mycobacteria, 4.0 (±0.85) Log10 copies/ml for MTBC, 3.9 (±0.54) Log10 copies/ml for M. tuberculosis, 2.7 (±0.42) Log10 copies/ml for M. africanum, 4.0 (±0.29) Log10 copies/ml for M. bovis and 4.5 (±0.52) Log10 copies/ml for M. caprae.

The study of M. tuberculosis in wastewater could potentially address limitations in our understanding of transmission, which is currently achieved almost exclusively through studying clinical samples. Wastewater-based epidemiology can be used to monitor tuberculosis infections.

Drinking polluted water can cause GITB

Tuberculosis (TB) is a respiratory infectious disease caused by Mycobacterium tuberculosis, which spreads when people who are sick with TB expel bacteria into the air, for example, by coughing. It typically affects the lungs (pulmonary TB) but can also affect other parts of the body (extrapulmonary TB).

While TB is most commonly transmitted through airborne transmission, there is evidence to suggest that it can also be transmitted indirectly through the faecal-oral route. This occurs when Mycobacterium tuberculosis complex (MTBC) is present in the environment, such as in wastewater, and is ingested through contaminated water or food.

Several studies have detected the presence of MTBC in wastewater, sewage, and surface water impacted by wastewater. The occurrence of MTBC in wastewater could be due to the shedding of the bacteria in the faeces and urine of patients with pulmonary TB. The ingestion of contaminated water and food is, therefore, a possible route of transmission for TB, specifically the extrapulmonary form known as GITB.

It is estimated that close to 20% of patients with pulmonary TB may have extra-pulmonary manifestations such as GITB. GITB is usually caused primarily through the ingestion of pathogenic MTBC in water and food. Animals can also ingest contaminated vegetable feed or have their surfaces contaminated with soil containing MTBC, which can then be transmitted to humans.

The survival of MTBC in different environmental matrices, such as water, can be influenced by factors such as temperature, moisture, pH, inhibitors, and protection against solar radiation. MTBC cells can withstand harsh conditions due to their dense external cell wall, composed of a large number of fatty acids. For example, M. tuberculosis has been found to remain viable even after exposure to high temperatures for several months.

Air pollution increases the risk of pulmonary tuberculosis

Tuberculosis (TB) is an infectious disease caused by the bacillus Mycobacterium tuberculosis, which typically affects the lungs (pulmonary TB) but can also impact other sites (extrapulmonary TB). It is one of the leading causes of mortality and morbidity worldwide, with approximately 10 million new cases and 1.4 million deaths globally in 2019. While indoor air pollution is a well-known risk factor for TB, recent studies have also explored the impact of outdoor air pollution on the development of TB.

Air pollution, particularly in urban areas, has been linked to an increased risk of pulmonary TB. Poor air quality, including high concentrations of particulate matter (PM), nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), and carbon monoxide (CO), can have detrimental effects on respiratory health and increase susceptibility to TB infection. For example, a study in the Beijing-Tianjin-Hebei region of China examined the impact of three main air pollutants: PM2.5, O3, and NO2. The results showed a total of 653,373 cases of PTB during the study period.

Several mechanisms have been proposed to explain the link between air pollution and pulmonary TB. One theory suggests that air pollutants impair the immune system, making it less effective at fighting off the Mycobacterium tuberculosis bacteria. For instance, studies have shown that exposure to diesel exhaust particles can reduce the function of immune cells, increasing susceptibility to TB infection. Additionally, air pollutants may directly or indirectly affect the immune process that inhibits TB in humans.

Furthermore, air pollution can increase the risk of drug-resistant TB (DR-TB). Epidemiological studies have found a correlation between exposure to ambient air pollutants and increased mono-drug, poly-drug, and multi-drug resistance in TB cases. Specifically, high exposure to PM2.5, PM10, and CO was significantly associated with increased incidence of multi-drug resistance.

The impact of air pollution on the development of pulmonary TB varies across different regions and populations. For instance, the risk of developing TB is five times higher in people living in urban slums compared to other areas. This may be due to a combination of factors, including impoverished living conditions, crowded spaces, and exposure to indoor and outdoor air pollution from sources such as firewood, charcoal, and vehicular traffic.

Mycobacterium tuberculosis can survive in soil and water

Tuberculosis (TB) is a disease that is transmitted mainly through airborne transmission. However, there is a possibility that Mycobacterium tuberculosis (MTBC) can be transmitted through indirect means, such as through the ingestion of contaminated water and food.

MTBC has been detected in different matrices, including wastewater, sewage, and surface water impacted by wastewater. The occurrence of MTBC in these water sources has been documented over the years, with the most commonly reported bacteria being M. tuberculosis and M. bovis. This could be due to the high number of human infections caused by these pathogens.

The ability of M. tuberculosis to survive in water for extended periods has been confirmed, with 11% of water samples from raceway systems yielding M. tuberculosis. The slow flow of water in these channels may encourage the growth of microorganisms, including M. tuberculosis.

M. tuberculosis has also been found to survive in soil outside its hosts for extended periods. In one study, mice were fed with food that contained M. tuberculosis-contaminated soil, and the bacteria were found to grow in the stomach, intestine, spleen, and lung. This provides clear evidence that M. tuberculosis can survive in soil and highlights the potential risk of transmission through this route.

The presence of circulating genotypes of M. tuberculosis in soil and water underscores the risk of transmission from the environment. While the dominant M. tuberculosis superfamilies in soil and water do not always correspond to the dominant family in patients, the possibility of infection from these sources cannot be ruled out.

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