The term listeriosis refers to an infectious disease caused by a type of bacteria called listeria. The main reservoir of listeria is found in soil, water, mud. In addition, vegetables can be contaminated from the soil or from the manure used as fertilizer. Among the animal, reservoirs are some infected domestic and wild animals, poultry and people.
Being these asymptomatic carriers, they can contaminate foods of animal origin. It is also possible to contaminate processed foods in their transformation, before packing. Listeria monocytogenes is one of the species that most frequently affects animals, but it can also affect humans. Therefore, listeriosis belongs to the so-called zoonoses (diseases of animals transmissible to humans).
The listeries responsible for listeriosis show a great distribution throughout the world, they are practically everywhere, and infection by these bacteria has a high incidence, although it goes unnoticed because, normally, the patients do not develop symptoms. In addition, it is very rare that the pathology affects people with a healthy immune system, who often only show a mild febrile reaction. In most cases, the infection is not detected.
The majority of listeria patients are people older than 60 years. It is also frequent in neonates and children under 4 years of age.
Listeriosis has its causes in an infection by listerias, bacteria that are scattered all over the world. The main pathogen of listeriosis in humans is Listeria monocytogenes, a bacterium with an elongated shape. Listeria monocytogenes is found in wastewater, in food, in animal feces, and even in the feces of healthy people. The listeries can be reproduced at low temperatures and even at low temperatures that means, also in the refrigerator.
Can Listeria be Transmitted From Person to Person?
There are different ways of transmission of listeriosis. The transmission of the infectious disease occurs, mainly, through the consumption of foods contaminated by listerias. The listeries are found, above all, in milk and dairy products (especially in cheese), in raw meat (carpaccio) and meat products (sausages such as salami or ham), in poultry, in fish smoked or marinated (herring or mackerel) and seafood. The pathogens of listeriosis are also found in foods of vegetable origin that have not been handled in a hygienic manner. Bacteria penetrate the body by ingesting the infected food.
On the other hand, the transmission of listeriosis may be due to contact with infected animals or contaminated soil. This can happen in agriculture or when working in a garden. A direct transmission of listeriosis from human to human is also possible in people who have been infected by listeria. Bacteria can be found in your stool for several weeks. Once they stop removing listerias through depositions, the risk of infection disappears.
The transmission of listeriosis from person to person can also occur in different ways. If the urogenital tract is colonized by the bacteria, the listeriosis infection can be transmitted during sexual intercourse. A listeriosis during pregnancy can cause the transmission of the infection from the mother to her child. On the one hand, the baby can become infected during pregnancy through the placenta (transplacental) or through the vaginal canal during delivery. On the other hand, transmission of listeriosis can occur after birth by close contact between mother and child. Listeria infection through breast milk is not possible, so affected women can breastfeed their baby peacefully.
Rarely, listeriosis presents as a hospital infection (nosocomial infection). This infection affects, mainly, people with a weak immune system. This is the case of premature babies admitted to the neonatal unit or people with a serious illness admitted to the ICU (intensive care unit). Possible sources of infection are other patients, hospital staff who do not strictly respect the rules of hygiene, as well as the intake of contaminated food.
As aforementioned, this listeria bacterium can be transmitted through different routes (being the most common the consumption of contaminated food), but it can be passed among people sexually if the microorganism reaches the urogenital tract, it has also been observed that a listeria mother can infect her child either in pregnancy or through the vaginal canal during delivery.
- Centers for Disease Control and Prevention (CDC). (2022). Listeria (Listeriosis). Retrieved from https://www.cdc.gov/listeria/index.html
- European Food Safety Authority (EFSA). (2019). The European Union One Health 2018 zoonoses report. EFSA Journal, 17(12), e05926. https://doi.org/10.2903/j.efsa.2019.5926
- Scallan, E., Hoekstra, R. M., Angulo, F. J., Tauxe, R. V., Widdowson, M. A., Roy, S. L., … & Griffin, P. M. (2011). Foodborne illness acquired in the United States—major pathogens. Emerging infectious diseases, 17(1), 7-15.
- Public Health Agency of Canada. (2021). Listeriosis (Listeria infection). Retrieved from https://www.canada.ca/en/public-health/services/diseases/listeriosis.html
- Murray, E. G. (1990). The normal flora of the mouth. Bacterial infection of the mouth, 1-29.