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Dysentery and the Bacteria Shigella: Symptoms & Causes

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  • 0:06 Foodborne Infection Example
  • 1:59 Shigella Species
  • 3:40 Shigellosis and Dysentery
  • 5:54 Diagnosis and Treatment
  • 7:00 Prevention
  • 7:56 Lesson Summary
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Lesson Transcript
Instructor: Angela Hartsock

Angela has taught college Microbiology and has a doctoral degree in Microbiology.

You can catch all sorts of diseases from fecal-oral contamination. Shigella is a human fecal bacteria that can cause a potentially fatal dysentery by consuming as few as 10 cells, an amount far too small to ever notice.

Foodborne Infection at the Festival

In August 1988, almost 6,500 women gathered in Michigan for a five-day outdoor music festival. The annual festival, informally known as Women's Woodstock, is staffed, entertained and attended by only women, a celebration of the sex. Except for a brief bout of diarrhea that affected a few staff members leading up to the start of the festival, the event went off without a hitch - until about two days after the festival ended.

Attendees, now back home, spread across the United States, started getting sick. All across the country, the women were experiencing fevers, abdominal pain and diarrhea, similar to the staffers who had been sick. All told, about 3,200 of the 6,500 attendees developed some variation of the same symptoms; 117 had to be hospitalized. Another 182 people who didn't attend the festival caught the illness from someone who did.

During the investigation into the outbreak, officials determined that the sick staffers contaminated the food served during the large, communal meals. Specifically, a tofu salad, served uncooked, was transmitting the disease. Alone, this foodborne source would have been bad enough, but it was compounded by the lack of access to soap and running water needed for appropriate sanitation and personal hygiene. Not only were people exposed to the disease by the tofu, they were also directly passing it from person to person.

The causative organism responsible for making the festival women sick was Shigella sonnei, one of the more virulent, yet rarely life-threatening, bacterial pathogens. In this lesson, we will examine Shigella and see what, if anything, these women could have done to reduce their chances of infection.

Shigella Species

Shigella is a genus of Gram-negative, rod-shaped bacteria that only infects humans and other primates. 'Gram-negative' refers to Shigella having a cell wall with a thin peptidoglycan layer and an outer membrane, making these cells appear red in the classic Gram stain.

There are several species of Shigella that cause disease in humans, but there are two that are of particular importance in the United States. The first is Shigella sonnei. This is the species responsible for the festival outbreak. Infections from S. sonnei are not generally considered life-threatening and are responsible for the majority of cases in the United States. S. dysenteriae is the deadliest species, responsible for causing more severe illness. Fortunately, infections by S. dysenteriae are not very common in the United States, but more frequent outbreaks occur in the developing world and can be deadly.

People catch Shigella by the fecal-oral route. Anywhere that is crowded and difficult to keep clean can be a source of infection. Not surprisingly, cases of Shigella pop up most frequently in daycare centers. Young children are not the easiest to keep clean, and they're too young to be good at maintaining appropriate personal hygiene themselves.

Adults come into contact with Shigella through water contaminated with feces or through food contaminated by infected preparers or handlers. The festival attendees ran into a little of both. The food preparers initially infected some people, but then these people, by not having the ability to thoroughly and frequently wash after using the bathroom, exposed even more people through direct contact.

Shigellosis and Dysentery

Regardless of how it happens, consuming Shigella usually leads to the development of illness. Shigellosis is a food infection caused by bacteria of the genus Shigella. Remember, in a food infection, the symptoms are a result of actively growing bacteria in the host's body. Shigella is noteworthy here because a person only needs to consume a few cells, as few as 10 to 200, for the infection to develop. As a comparison, E. coli and Salmonella, two other common causes of foodborne illness, require several thousand to tens of thousands of cells for symptoms to develop. This allows Shigella to spread very rapidly and infect many people.

So, once infected, what can you expect? The bacteria attack the cells that line the large intestine, triggering the cells to engulf the bacteria. For the next two to four days, the bacteria reproduce inside the cells and release an exotoxin, called a Shiga toxin. The toxin damages the blood vessels and intestinal lining, causing inflammation. Eventually, the reproducing bacteria lyse the intestinal cells, spill out into the large intestine, and reinfect neighboring cells. The lysis and toxin release cause the symptoms of the disease.

Some healthy adults will not show any symptoms, as the immune system quickly handles the infection. Others will only experience mild, watery diarrhea from the intestinal damage and inflammation. But most patients who develop shigellosis will have a fever, abdominal pain and diarrhea containing blood and mucus. Shigellosis usually clears up on its own in about a week.

People infected with S. dysenteriae can develop a more severe illness. Bacterial dysentery is a disease characterized by severe inflammation of the large intestine caused by bacterial pathogen. Dysentery sufferers can expect profuse, prolonged diarrhea with large amounts of blood and mucus as well as fever and abdominal pain. The rapid fluid loss can quickly become life-threatening, and treatment is required. Children who get dysentery can also develop convulsions as a result of the high fever.

Diagnosis and Treatment

Many foodborne illnesses cause diarrhea, so how do you know you have Shigella? Usually, the presence of fresh, bright red blood in the feces, combined with a probable source of infection, is enough for a positive diagnosis. Your doctor can also culture the bacteria from a sample of your feces. There are several different growth media that are used that will differentiate Shigella from the other potential causes.

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