Listeria Infection

February 2, 2017

Listeria infection (also known as listeriosis) is a rare but potentially severe illness caused by Listeria monocytogenes bacteria. Listeria infection is caused by eating food that contains Listeria monocytogenes bacteria.

Listeria are widespread in nature and can be found in soil, animal and human feces, sewage, silage and water. The bacteria are known to persist in food processing environments, where they may contaminate food products. Particularly dairy products, processed meat and seafood may be infected with Listeria.

All people occasionally ingest Listeria, but it is mainly individuals with weakened immune systems or elderly, pregnant and newborns, who develop symptoms from Listeria infection (listeriosis). Symptoms of Listeria infection vary from diarrhoea and influenza-like conditions to blood poisoning and/or meningitis.

Prevention of Listeria infection is possible through proper handling, cooking, and/or kitchen hygiene. Listeria infection or Listeriosis is a global foodborne disease. Even though listeriosis is not as common as other food related infections, the severity of the individual impact is higher.

Listeria bacteria can survive refrigeration and even freezing. That’s why people who are at higher risk of serious infections should avoid eating the types of food most likely to contain listeria bacteria.

What is Listeria monocytogenes?

  1. monocytogenes is one of the most virulent food-borne pathogens. It can flourish with or without oxygen and, unlike many other bacteria, can thrive and reproduce at temperatures as low as 0°C. L. monocytogenes typically enters the host through the intestines and infects the liver first. In the liver the bacteria multiplies until the host’s immune system tackles it; at this stage, the vast majority of infections end. However, in immunocompromised or other at-risk individuals, the infection may continue and eventually move to the brain.

The Listeria bacterium is able to enter and survive within immune cells such as macrophages. L. monocytogenes is also capable of hijacking cellular machinery and tricking cells into drawing the bacterium inside the safety of its cellular walls.

The range of cell types that Listeria is capable of invading include:

  • Epithelial cells – a common cell type lining cavities
  • Hepatocytes – liver cells
  • Endothelial cells – cells lining the interior of blood vessels.

Within these cells, the bacteria can multiply and spread to neighboring cells, safe from the immune system. This ability to live within human cells makes it unusual, dangerous and very difficult to treat.


Listeriosis is caused by Listeria, a type of bacteria that is commonly found in water, soil and feces. Humans are infected when they consume foods that harbor the bacteria.

The most common foods to cause listeriosis outbreaks are deli meats and unpasteurized dairy products. However, many other foods have also been found to spark outbreaks, including caramel apples, cantaloupe and cabbages fertilized by sheep manure.

Infected stools – It’s thought that listeria can be found in the digestive systems of many animals, such as sheep and cattle, and these animals may pass stools contaminated with listeria. It’s estimated that up to 1 in 20 people may be carriers of listeria, but have no symptoms of listeriosis. Human carriers can also pass stools contaminated with listeria, which can spread if, for example, the carrier doesn’t wash their hands after going to the toilet, then handles food.

Infected Food – Many ready-to-eat foods are considered high risk foods for Listeria infection. This is because these foods are sometimes contaminated with Listeria bacteria during or after the manufacturing process and the bacteria can continue to grow at refrigerator temperatures.

People at risk of Listeria infection should avoid the following foods:

  • paté
  • cold ready-to-eat chicken
  • manufactured ready-to-eat meats, including polony, ham and salami
  • soft cheeses, including brie, camembert, fetta and ricotta
  • pre-packed, pre-prepared or self-serve fruit or vegetable salads
  • freshly squeezed fruit and vegetable juices
  • ready-to-eat cold, smoked or raw seafood, including smoked salmon, oysters, sashimi and cooked prawns
  • sushi
  • soft serve ice cream and thick shakes
  • tofu, both soft and hard types, and tempeh
  • unpasteurised milk and unpasteurized milk products

Risk Factors

Pregnant women and people who have weak immune systems are at highest risk of contracting a listeria infection.

Pregnant women and their babies –

Pregnant women are significantly more susceptible to listeria infections than are other healthy adults. Although a listeria infection may cause only a mild illness in the mother, consequences for the baby may include:

  • Miscarriage
  • Stillbirth
  • Premature birth
  • A potentially fatal infection after birth

People who have weak immune systems

This category includes people who –

  • Are older than 65
  • Have AIDS
  • Are undergoing chemotherapy
  • Have diabetes or kidney disease
  • Take high-dose prednisone or certain rheumatoid arthritis drugs
  • Take medications to block rejection of a transplanted organ


The initial symptoms of listeriosis might not become apparent for some time; the incubation period is variable and can be anything from 11 to 70 days after consuming food with Listeria.

The following symptoms of Listeria infection are likely to last 1-3 days –

  • Muscle aches
  • Fever
  • Flu-like symptoms
  • Nausea
  • Diarrhea

For many people, a Listeria infection will pass unnoticed. However, in some individuals, the infection will spread to the nervous system where symptoms might include –

  • Headache
  • Confusion
  • Stiff neck
  • Tremors and convulsions
  • Loss of balance

In susceptible individuals, listeriosis can lead to a serious blood infection (septicemia) or inflammation of the membranes around the brain (meningitis)

If the listeriosis infection spreads to the brain, the outcomes can be severe and may include –

  • Cranial nerve palsies: paralysis and tremors
  • Encephalitis: inflammation of the brain
  • Meningitis: inflammation of the membranes covering the brain and spinal cord
  • Meningoencephalitis: a combination of meningitis and encephalitis
  • Cerebral abscesses: localized pus build-up within the brain.

Symptoms during pregnancy or for newborn infants

Pregnant women are 20 times more likely to develop listeriosis than the general population. The incidence of listeriosis during pregnancy is 12 per 100,000, compared with 0.7 per 100,000 in the general population.

While a mother with a Listeria infection may not show any outward symptoms, an unborn child might be severely affected.

Listeriosis can result in miscarriage or premature birth. There is a possibility that a newborn might suffer a life-threatening infection in the days and weeks after birth.

The symptoms in a newborn child can be subtle but may include –

  • Irritability
  • Fever
  • Vomiting
  • Loss of interest in feeding


Most listeria infections are so mild they may go unnoticed. However, in some cases, a listeria infection can lead to life-threatening complications — including –

  • A generalized blood infection (septicemia)
  • Inflammation of the membranes and fluid surrounding the brain (meningitis)

Complications of a listeria infection may be most severe for an unborn baby. Early in pregnancy, a listeria infection may lead to miscarriage. Later in pregnancy, a listeria infection may lead to stillbirth, premature birth or a potentially fatal infection in the baby after birth — even if the mother becomes only mildly ill.


Listeriosis is treated with antibiotics. A person in a higher-risk category (pregnant woman, older adults, and people with weakened immune systems) who experiences fever and other non-specific symptoms, such as fatigue and aches, within 2 months of eating contaminated food should seek medical care and tell the physician or health care provider about eating the contaminated food.

If a person has eaten food contaminated with Listeria and does not have any symptoms, most experts believe that no tests or treatment are needed, even for persons at higher risk for listeriosis.

Self Help – Although listeriosis is rare, there are a number of ways to further reduce the chances of becoming infected; these precautions are especially important during pregnancy –

  • Cleanliness – wash hands with warm soapy water before preparing food. Clean utensils and work surfaces in the same manner
  • Raw vegetables – scrub clean under warm water with a brush
  • Cook thoroughly – ensure that meat and egg dishes are heated thoroughly and throughout. A food thermometer can be useful
  • Cheese – avoid soft cheeses including Brie, feta, Camembert, blue-veined cheeses, or Mexican-style cheeses such as queso fresco, panela and queso blanco; unless the label clearly specifies the product was made with pasteurized milk
  • Meat – avoid cold meats, especially deli meats and hot dogs, unless cooked at a high temperature before eating. Be careful to wash anything that comes into contact with raw and cold cooked meat
  • Smoked seafood – avoid refrigerated smoked seafood unless it is cooked thoroughly before consumption.

Alternative Treatment

Alpha-lipoic acid – Several reports indicate that alpha-lipoic acid, an antioxidant commonly found in broccoli, spinach, and beef, may help treat Listeria infection, especially when combined with milk thistle (Silybum marianum).

Vitamin A – Studies on rats show that vitamin A offers some protection against listeria infection.

Other – Drinking sufficient amount of fluids is essential. Activated charcoal is an effective remedy against listeriosis as it has quality to adsorb poisons and toxins. Syrup of Ipecac is taken to induce vomiting in cases of food poisoning.

Other natural treatments include dose of natural antibiotic goldenseal. Milk thistle and red clover help in liver and blood cleansing. Garlic is another excellent natural antibiotic that helps prevent bacterial growth.

Probiotic and fermented foods work well to help stimulate acid production as well as providing the right kind of bacteria for the stomach.

Vitamin D – This vitamin is important for addressing any infectious component.

Reference –

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