Listeria is known as an “opportunistic pathogen" and that means, it hangs around acting normal within the human body—maybe even in the intestines—until that body loses some of its protection or if the immune system and the ability to fight disease lowers, then listeriosis strikes.
Most healthy adults can be exposed with no risk. The body’s normal defense system against listeria is named cell-mediated immunity because lymphocytes or “T-cells" can fight it off. But even though it has been around for decades in soil and decaying vegetation, now every year it causes about 2,600 instances of severe illness.
Eating contaminated food is the link to illness, and listeriosis infection causes symptoms such as:
- Fever and chills
- Muscle aches
- Nausea or vomiting
Diarrhea or other gastrointestinal—stomach related—symptoms
If it spreads to the less healthy human:
- Stiff neck
- Loss of balance
Few people with normal immune function go on to have the more severe, life-threatening forms of listeriosis; characterized by septic shock (body wide infection), meningitis (inflammation of the protective membranes covering the brain and spinal cord known as the meninges,) and encephalitis (infection of the brain tissue itself).
Early signs of listeriosis can generally be found in stool cultures. Machines like Magnetic-resonance Imaging (MRI) are used to confirm or rule out brain or brain stem involvement.