Shigellae are Gram-negative rods, closely related to E. coli, that invade the colonic mucosa. There are four main groups: Sh. dysenteriae, flexneri, boydii and sonnei. In the tropics, bacillary dysentery is usually caused by Sh. flexneri, whilst in the UK most cases are caused by Sh. sonnei. Shigellae are often resistant to multiple antibiotics, especially in tropical countries. The organism only infects humans and its spread is facilitated by its low infecting dose of around 10 organisms.

Spread may occur via contaminated food or flies, but transmission by unwashed hands after defecation is by far the most important factor. Outbreaks occur in mental hospitals, residential schools and other closed institutions, and dysentery is a constant accompaniment of wars and natural catastrophes, which bring crowding and poor sanitation in their wake. Shigella infection may spread rapidly amongst men who have sex with men.


Disease severity varies from mild Sh. sonnei infectionsthat may escape detection to more severe Sh. flexneri infections, while those due to Sh. dysenteriae may be fulminating and cause death within 48 hours. In a moderately severe illness, the patient complains of diarrhoea, colicky abdominal pain and tenesmus. Stools are small, and after a few evacuations contain blood and purulent exudate with little faecal material. Fever, dehydration and weakness occur, with tenderness over the colon. Arthritis or iritis may occasionally complicate bacillary dysentery (Reiter’s syndrome, associated with HLA-B27.


Oral rehydration therapy or, if diarrhoea is severe, intravenous replacement of water and electrolyte loss is necessary. Antibiotic therapy with ciprofloxacin (500 mg twice daily for 3 days) is effective in known shigellosis and appropriate in epidemics. The use of antidiarrhoeal medication should be avoided.

The prevention of faecal contamination of food and milk and the isolation of cases may be difficult, except in limited outbreaks. Hand-washing is very important.


The medicines that can be thought of use are:-

  • Arsenic
  • Podophyllum
  • Veratrum
  • Aloe
  • Cinchona