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Salmonella

“Mary has died of Typhoid Fever”. Ah, yes. If you are of a certain generation, you remember being met with these abrupt notifications while playing Oregon Trail. While this game taught generations of young people about Western migration in 19th-century America, it also made them familiar with various diseases, and how to avoid getting run over by wagon wheels. In this article, we’re exploring the root of the cause – diving into species and subspecies of Salmonella.

The origin of Salmonella thypi

In case you’re not current on your New York City history, or your only reference for Typhoid fever was that Oregon Trail game back in the late 80’s, Typhoid Mary was the name eventually given to a woman named Mary Mallon who lived in New York City in the early 1900’s. She became notorious as a healthy carrier of Salmonella thypi, the bacterium that causes Typhoid fever. She was an immigrant, not necessarily well off, and was employed as a cook for wealthy families. Now, this was before a vaccine was available and before antibiotics. An investigation had started because there were many people getting sick with a fever, and the investigator trying to track down the source noticed there were pockets of families employing the same cook. Mary was leaving after the infection had occurred to move onto a new family to cook for them. In the end, there were a total of 122 people infected and five dead. In 1907 over 3,000 people in New York City had become infected, and Mary was supposedly the source.

What’s interesting is that there was no tracking mechanism in place, so investigations had to be done solely by a small group or single person. There was an assumption that a microorganism was suspected of being responsible, but nobody knew why. The investigation really corroborated that hypothesis which eventually came from a team of veterinary scientists. So, in 1880, Daniel Elmer Salmon ended up naming Salmonella typhi because of this investigation.

The initial outbreak investigation resulted in the naming of Salmonella typhi and now we have Salmonella enterica. It’s important to remember that science naming conventions are like kaleidoscopes, the contents remain the same, but the picture and how it’s described changes depending on who’s holding the instrument. Such has been the reshuffling with Salmonella. Most of the scientific community now break Salmonella into two species: Salmonella bongori and Salmonella enterica. However, it essentially comes down to two groups: Salmonella that causes gastroenteritis and those that cause enteric fevers.

Patient risk of Salmonella

The Centers for Disease Control (CDC) estimated that Salmonella causes 1.2 million illnesses and 450 deaths annually in the US.1 Anybody can become infected with the bacteria, with fecal-oral and food and water being the most common routes. The populations at greatest risk are those under the age of five, over the age of 65, and those with weakened immune systems. The gastrointestinal infection that results when you ingest the bacteria is Salmonellosis. It presents with fever, abdominal cramps, and diarrhea. Symptoms manifest within about 12-72 hours and typically last about a week. You can take antibiotics, but most people will be able to recover without pharmaceutical intervention.

Unique descriptions associated with Salmonella are gram-negative rods, motile with flagella, and about 0.4- 0.7 micron in size. Both varieties of Salmonella do not transmit the same. The variety that causes Typhoid fever are spread from human-to-human only and the variety that result in gastroenteritis are transmitted in food or water.

Typhoid fever is slightly different. Patients become symptomatic gradually, and once a fever presents, it is accompanied by extreme fatigue, skin rash or skin discoloration, headaches, abdominal pain, and constipation. Without medical intervention the fever can be fatal. You can treat it with antibiotics like azithromycin. Typhoid fever should not be confused with typhus as the two are totally different pathologies. Typhus is caused by Rickettsia, a different gram-negative bacterium that spreads around via lice and fleas.

1 Centers for Disease Control and Prevention. (2022, February 2). Salmonella. https://www.cdc.gov/Salmonella/index.html

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