Four spe cies have been identified. Although rare in this country, Shigella dysenteriae type 1 is widespread in rural Africa and India, and causes deadly epidemics in developing countries. Shigella boydii is uncommon in the United States. The diarrhea can contain blood, mucus or pus, and bacteria are shed in the stool. Shigellosis usually resolves in five to seven days but can last for weeks.
Shigellosis is transmitted strictly by human feces.
Unlike several other gastrointestinal agents, no animal reservoir is known. Shigellosis is extremely infectious, as only 10-100 organisms are necessary to cause infection. Other routes of transmission include ingestion of contaminated food or water, homosexual activity, and contact with a contaminated, inanimate object. Houseflies are also vectors, physically transporting infected feces. Infection can be transmitted during the acute illness until bacteria are no longer shed, usually within four weeks after onset.