TeachableMedicalNews article 10222020

Teachable moment in classrooms:

  1. cellular basis of life chapter – cytosol
  2. nervous system chapter – location of meninges
  3. immune system chapter – vasodilation during inflammation
  4. immune system chapter – emigration by white blood cells
  5. microbiology – Listeria monocytogenes biology

The news item:  Recently a Listeria outbreak was reported to have started from contaminated mushrooms:

Enoki mushrooms tied to listeria outbreak that killed four people and hospitalized 31, CDC says | CNN

Enoki mushrooms are linked to four deaths and 31 hospitalizations in what the US Centers for Disease Control and Prevention says was a multistate listeria outbreak that is now presumed to be over.

The article stated that Listeria outbreak is caused by a bacterium, and that the symptoms of infection are stiff neck, loss of balance, miscarriage, confusion and fever.

So, Why Do I Care??

Infection by Listeria bacterium is the third leading cause of food borne illness, and it is the most lethal food borne illness by killing about 15 – 20% of the infected individuals.  In the US each year about 1600 people get infected, and 260 die. The victims are the most vulnerable of society: elderly, pregnant women, and immunosuppressed people.

Plain English, Please!!!

First, let’s talk about what Listeria is. Listeria is a type of bacterium that infects human beings when they consume Listeria-contaminated food. The bacterium lives inside our cells (in the cytosol), just like worms live inside an apple. When Listeria attacks the cells of our intestines, that causes inflammation, gastroenteritis. In most people the immune system of the small intestines fights back against the invaders, and within a few days or weeks kills the bacteria.

Second, let’s talk about why Listeria can cause death. In some individuals with weakened immune system (pregnant women, the elderly, people taking immunosuppressing drugs, people treated with chemotherapy) the Listeria bacteria overpower the immune system, and worm their way into white blood cells, avoiding being seen by the immune system. Those infected cells travel with the blood, and where they exit the blood vessels the bacteria can worm themselves into cells of the membrane (meninges) around the brain, and the brain itself. Such infections cause meningitis and encephalitis. The inflamed blood vessels leak fluid which collects on the brain causes the malfunction of the nervous system. Infected blood vessels cause clotting and microscopic scarring. Those are the main causes of death.

Third, let’s talk about why Listeria causes miscarriage in pregnant women. While Listeria infection is not normally life threatening for pregnant women; however, if the bacteria manage to spread into the bloodstream inside white blood cells, next they will worm their way into cells of the blood vessels of the placenta where they cause clotting and microscopic scarring, and inflammation of the placenta. The outcome is miscarriage and loss of the developing fetus.  Listeria that spread into the body of fetus (that has very limited immune protection) may cause fetal death by widespread inflammation and damage to the fetal blood vessels and meninges.

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