Causes of Dysentery

Dysentery reaches you through one route: germs from an infected person's stool getting into your mouth. Everything about prevention - and most of the explanation for why it spreads - hangs on that single fecal-oral chain.

The germs:

• Shigella bacteria (bacillary dysentery). Extremely contagious - it takes as few as a few hundred bacteria to cause illness, which is why it races through households, hostels and schools. Abrupt fever and bloody-mucoid stools are its signature.
• Entamoeba histolytica (amoebic dysentery). A parasite whose cysts survive in contaminated water and food. Slower, colicky illness; its special danger is spreading to the liver.
• Less commonly, other bacteria (Campylobacter, certain E. coli strains) and parasites like Giardia or Balantidium produce a similar picture.

How the chain runs in real life:

• Contaminated water - untreated sources, leaking pipes, monsoon flooding that mixes sewage with supply lines.
• Contaminated food - street food washed in unsafe water, raw salads and cut fruit, food kept warm-not-hot for hours.
• Hands. The infected person who doesn't wash hands after the toilet, and then cooks, serves or touches shared surfaces, completes the chain. Flies do the same job mechanically, ferrying germs from filth to food.
• Poor sanitation - open defecation, overflowing drains, shared toilets without soap - keeps the whole cycle running, which is why monsoon season spikes every year.

Who is most at risk: young children (and the malnourished, who suffer worse illness), people in crowded or low-sanitation settings, and anyone whose stomach acid protection is reduced. Travelers and hostel-dwellers know this illness well.