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Why can genes affect a person’s susceptibility to tuberculosis even though tuberculosis is caused by bacteria?

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Four kittens with different fur patterns-three tabby and one black-and-white-lying together in a box, illustrating genetic variation among offspring. — heredity Each offspring is a combination of its two parents, receiving some dominant traits from its mother and others from its father.

While tuberculosis is a bacterial infection of environmental origin, a person's susceptibility to the disease is influenced by their genetic makeup. Genes do not cause the infection itself, but they can provide the chemical or physiological basis that makes an individual more or less susceptible to the bacteria when exposure occurs.1

Evidence for this genetic component is observed in studies of identical twins, who show a significantly higher concordance for tuberculosis than fraternal twins when raised in similar environments. This suggests that while the germ is not inherited, the genotype can influence how effectively an individual's body responds to the pathogen. Furthermore, susceptibility is complex and can be affected by polygenes with small individual effects, as well as by environmental factors like nutrition and economic well-being, which often interact with an individual's biological predisposition. Ultimately, whether a person develops the disease depends on the interplay between their unique genetic endowment, the environment, and the virulence of the specific bacterial strain.12