Shigella is regarded as one of the oldest human-specific pathogens that evolved approximately 35000 to 170000 years ago. This period is significantly important as the only hosts of this bacteria, i.e. the homo sapiens also originated and expanded during this time. It belongs to the Enterobacteriaceae family. The genus Shigella comprises four species which cause millions of cases of shigellosis every year.
Shigellae is a gram-negative, non-motile bacterium. These are rod-shaped and their genetic structure is closer to that of an E. coli. Shigella are facultatively anaerobic and are non-spore-forming. The Shigella cells are approximately 0.4 to 0.6 micrometers across and 1 to 3 micrometres in length.
Modes of Transmission
Shigella spreads easily and is transmitted through contaminated food and water. Coming in contact with surfaces that are contaminated by the Shigella bacteria can cause an infection. These may include bathroom fixtures, toys, etc. It also spreads through untreated water such as that of swimming pools. Eating food prepared by an infected person, and drinking water that is contaminated with flood water or sewage may also transmit the bacteria.
The virulence factor of the Shigella species is quite high. This allows it to easily adhere to the epithelium of the intestine. Moreover, it survives stomach acidity and attacks the host cells. It escapes the response of the human immune system thereby introducing toxins in the body. Numerous effector proteins allow it to invade the host cell wall. It utilizes a Type III Secretion System to transport this effector protein into the cytoplasm of the human host cells. This secretion is controlled by environmental conditions especially oxygen levels.
Prevention and Treatment
Shigella infection can be prevented through good hygiene practices. Shigellosis is treated with the use of antibiotic treatment of 5 to 7 days (Mumy, 2014).
Mumy, K. L. (2014). Shigella. Encyclopedia of Toxicology, 254-255.