Question

How are the causes of tuberculosis and diphtheria similar? How are they different?

Answer 1

Tuberculosis is caused by Mycobacterium tuberculosis. While diphtheria is caused by Corynebacterium diphtheriae. Both diseases are caused by bacteria. They are highly infectious diseases and are transmitted through aerosol or droplets.

Complete answer:
Similarities between tuberculosis and diphtheria are:
-Both the bacteria are non-motile and non-capsulated.
-Both are aerobic.
-Both have the same mode of transmission that is through the air transmitted by droplets.

Dissimilarities -
Corynebacterium diphtheria infects the upper respiratory tract and remains confined to the site of entry (usually the upper respiratory tract), where they multiply and start producing toxins. It leads to the formation of pseudomembranes, which is a characteristic feature of diphtheritic infection. It also leads to toxemia. This toxin usually affects nerve endings, cardiac muscle, and adrenal glands. Children may usually die due to choking of upper respiratory tract infection.

Mycobacterium tuberculosis is a lower respiratory tract infection. It attacks the cell-mediated immunity of the body by attacking helper T cells. The lesion is divided into two types -
-Primary Tuberculosis - After the inhalation of tubercle bacilli are engulfed by alveolar macrophages in which they replicate and form a lesion called Ghon’s focus. It is usually found in the lower lobe or lower part of the upper lobe. Some bacilli are transported to the hilar lymph nodes. Together the Ghon focus together and enlarged hilar lymph nodes form a unit called the primary complex.
-Secondary (Post-primary) Tuberculosis - It is caused by reactivation of the primary lesion (endogenous) or by exogenous reinfection. Reactivation tuberculosis is likely to occur in immunocompromised individuals. Granulomas of secondary tuberculosis are usually found in the apex part of the lungs.

Note: Both the infections are thought to be causing co-infection in which the effectiveness of tuberculosis at assimilating extracellular iron may lead to increased production of diphtheria toxin, worsening that disease, which may, in turn, exacerbate tuberculosis. Iron-dependent repressor genes connect both diseases.