Typhoid Fever: Symptoms, Causes and Salmonella Typhi

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  • 0:05 The First Bioterrorist
  • 2:18 Salmonella Enterica…
  • 3:40 Typhoid Fever
  • 6:09 Diagnosis and Treatment
  • 7:14 Prevention
  • 8:08 Lesson Summary
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Lesson Transcript
Instructor: Angela Hartsock

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

Have you ever heard of the infamous Typhoid Mary, a cook responsible for spreading disease to over a thousand unlucky diners? In this lesson, we will learn about typhoid fever and the causative organism Salmonella enterica serovar Typhi.

The First Bioterrorist

The Northeastern United States was a dangerous place to live in the early 1900s if you were in the market for a live-in cook. Eerily similar to the plot from a medical thriller, a bioterrorist was moving around the region, taking brief jobs as a cook and infecting her employers and their families with a deadly disease before changing her name and starting all over again somewhere new.

This bioterrorist not only knew she was infecting people, but she stubbornly, and often violently, refused to stop. She was eventually caught and thrown in jail, but her stay was short-lived. After three years in isolation, she was able to gain enough sympathy from the public that officials agreed to release her in exchange for the assurance she would no longer serve as a cook.

The terrorist swore she had learned her lesson and would not only stop cooking, she would check in with the authorities frequently and regularly. Upon her release, she immediately disappeared, only to be found several years later up to her old tricks: cooking, infecting and killing. This time, the authorities were less lenient. The terror was thrown in jail for the next 25 years, until her death. All told, she infected around 1,300 people in her lifetime, but officially, only three deaths were conclusively linked to her, though some estimates put that number above 50.

This is the story of Typhoid Mary, and it is 100% true. Mary Mallon was a cook that was a confirmed carrier of typhoid fever. She knew she was infecting people, she violently resisted arrest and refused a cure, and she belligerently kept cooking despite the warnings and deaths. Mary Mallon wasn't necessarily a bad person, she just didn't fully understand the consequences of her actions and refused to give up her livelihood.

What is most startling is that Mary wasn't unique; any person could find themselves a serial carrier and distributor of infection, even today. So it is better to educate yourself now, so the next typhoid fill-in-the-blank doesn't include your name.

Salmonella Enterica Serotype Typhi

Typhoid Mary was infected by Salmonella enterica, a Gram-negative, motile, facultative aerobic, rod-shaped bacteria. The species Salmonella enterica is split into many subspecies, also called serotypes. S. enterica serovar Typhi is the serotype that causes typhoid fever.

'Gram-negative' refers to Salmonella having a cell wall with a thin peptidoglycan layer and an outer membrane, making these cells appear red in the classic Gram stain. Being a facultative aerobe, Salmonella can survive with or without oxygen. Humans are the only host for S. enterica serovar Typhi, which lives in the anaerobic human small intestine, blood and gall bladder. Outside of the host, the bacteria are able to survive in the oxygen-rich environment and are very resistant to environmental stresses. These bacteria are most often found in water, sewage and foods.

People are exposed to S. enterica serovar Typhi by the fecal-oral route. Typhoid Mary was infecting her victims by serving them food she had touched with her hands contaminated by her own fecal material. In areas of the world with poor sanitation, this is still a frequent source of infection. Drinking and cooking water contaminated with sewage is the other major source.

Typhoid Fever

Typhoid fever is a potentially fatal foodborne infection caused by Salmonella enterica serovar Typhi. Remember, a foodborne infection is a disease that results from ingesting actively growing bacteria. The symptoms are a direct result of the growth and metabolism of the bacteria in the body.

Typhoid Mary was serving Salmonella to her employers. After they consumed the bacteria, the microbes passed through the stomach, where they are protected from the stomach acid by the food bulk and began to invade the lining of the small intestine.

In a process not fully understood, the bacteria are able to pass through the intestinal cells and enter the lymphatic vessels without triggering any host immune response. Once in the lymphatic system, the bacteria invade the blood, spreading throughout the body. While in the bloodstream, the lipopolysaccharides on the bacterial cell wall, also called endotoxins, induce a massive host immune response, leading to the development of symptoms.

Symptoms of typhoid fever include intestinal ulcers, bloody stools and abdominal pain from the initial intestinal invasion. This is followed by a high fever, often up to 104 degrees Fahrenheit, lethargy and delirium. These symptoms represent the massive immune response to endotoxin. About 30% of patients will develop a faint rash on their chest, called 'rose spots.' These symptoms can last for three to four weeks. Without treatment, most people will recover, but between 15 and 20% will die.

About 5% of those people that recover become a chronic carrier of S. enterica serovar Typhi, with the bacteria hiding in the gallbladder. These people shed the bacteria for years without showing any symptoms themselves. In the case of Typhoid Mary, there is no evidence that she ever developed any symptoms with her initial exposure, which might help explain why she was so resistant to changing her lifestyle.

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