exists and is an alternate of . The sperm that reach the egg swim into it and attempt to penetrate the zona pelluca, which is the semi permeable outer membrane of the egg. Some sperm have a shape which makes this relatively easy, and others which are poorly formed are likely to have more difficulty.
1 Shigellosis is an infectious disease caused by a group of bacteria called Shigella. 2  Symptoms of Shigella infection include diarrhea (often bloody), fever, and stomach cramps starting a day or two after exposure to the bacteria. 3  Shigellosis usually resolves in 5 to 7 days.
INFECTIOUS AGENT. Shigellosis is an acute infection of the intestine caused by bacteria in the genus Shigella. There are 4 species of Shigella: Shigella dysenteriae, S. flexneri, S. boydii, and S. sonnei (also referred to as group A, B, C, and D, respectively).Several distinct serotypes are recognized within the first 3 species.he symptoms of shigellosis range from mild to severe and typically last 4â7 days. Disease severity varies according to species; serotype S. dysenteriae serotype 1 (Sd1) is the agent of epidemic dysentery, while S. sonnei commonly causes milder diarrheal illness.