The Shigellae bacterium produces four species that cause varying degrees of dysentry and enteritis. S. sonnei produces the mildest disease, and is responsible for the majority of diarrheal cases worldwide. It can also ferment lactose, but only after a long period of time. S. dysenteriae causes the most severe form of diarrhea, known as bacillary dysentery. This bacterium releases a toxin known as the “Shiga toxin,” which is a very powerful exotoxin (neurotoxin) responsible for a deadly type of bloody diarrhea. S. dysenteriae is found mostly in Africa and the Indian subcontinent. Two other strains, S. flexneri and S. boydi cause a disease of intermediate severity.
The Shigella bacteria is found in human feces which often contaminates the soil and water resulting in the ingestion of the bacteria by others. For most other infections, it takes thousands of organisms before an illness becomes apparent but it only takes 10 shigella organisms to cause disease. Flies can also carry the bacteria after landing on fecal matter and then on food or a person’s eyes or mouth. A full two thirds of all the cases worldwide occur in children under 10 and the death rate is high among young children in underdeveloped countries. Dysentery and typhoid killed almost as many soldiers during the Civil War as was in direct combat.
Following ingestion, the bacteria spend the next one to three days of incubation multiplying in the small intestine. As they are carried into the large intestine, they attach to and penetrate epithelial cells, where they continue to multiply. Following the incubation period, the patient will experience a sudden onset of symptoms, consisting of abdominal cramps, fever, and diarrhea, with the stools frequently having mucus and blood. It is the significant loss of water and salts that is the most dangerous, and, if not replenished immediately, this dehydration and loss of electrolytes can cause death. If recovery is uneventful, the duration of the illness will last three to seven days. After recovery, however, a person can remain a carrier for an indefinite period of time, passing the organism onto others through the handling of food or beverages.
By 1959, it was already apparent that Sigella dysenteriae was resistant to four classes of antibiotics – tetracycline, sulphonamide, streptomycin, and chloramphenicol. About the same time, Japanese scientists discovered that E. coli had an identical range of resistance. Travellers are more susceptible to this type of diarrheal disease, but there are various treatments available. The most essential one is replenishing the fluids immediately.