Listeriosis is currently in the Canadian news, having caused a number of deaths following contamination of meat and meat products. But what is listeriosis? It’s a disease caused by species of the bacterium Listeria. There are 6 species of Listeria widely distributed in nature. Listeria monocytogenesis the causative agent of listeriosis, however other species are also pathogenic. For example, Listeria ivanovii is an animal pathogen and in rare cases cause human infection. Even though, human infection is rare, the fatality is high, about 25-30% of cases would die.

Sources of Infection

The sources of infection are food and water contaminated with soil, sewage or any other material containing Listeria. Most outbreaks are caused by eating foods from animal origin e.g. hot dogs, deli meats, cooked poultry, raw milk, cheeses, raw and smoked fish.  Unlike many other bacteria, Listeria can survive and multiply on foods being stored in the refrigerator.

Symptoms of Listeriosis in human

Listeriosis in humans is characterised by a long incubation period of up to 70 days after exposure. However, many people can be asymptomatic carriers of Listeria but few of them develop listeriosis. The symptoms of listeriosis in humans include vomiting, nausea, abdominal pain, severe headache, diarrhea or sometimes constipation with persistent fever. Pregnant women, children and old people are more likely to get listeriosis than other healthy adults. It is probable that Listeria can be transferred to unborn babies through placenta of infected pregnant women and also to newborn babies through milk.

Listeriosis “Circling disease” in animals

Listeriosis affects a wide range of animals and birds. Persistent fever, abortion and circling due to encephalitis are the common symptoms. The disease is highly sever and fatal in small ruminants. Listeria monocytogenes  can be excreted in the milk of either aborting or apparently healthy cows, ewes, and goats. Listeriosis in dogs and cats are mainly visceral and septicaemic “gastroenteritis and fever”.

How to reduce the risk of infection

To reduce the risk of infection, the following practices are recommended:

• Thoroughly cleaning and sanitizing all surfaces used for food preparation
• Thoroughly cleaning fruits and vegetables before eating them
• Defrosting food in cold water or in the microwave, but never at room temperature
• Keeping the temperature inside refrigerator under 4°C to avoid multiplication of Listeriain foods if they are already contaminated with Listeria.

Therapeutic treatment

Listeria monocytogenesis sensitive to penicillin (the drug of choice), cefotaxime, azithromycin and trimethoprim/sulphonamide. It is recommended to test the antimicrobial sensitivity of the isolated Listeria.

Article by: Dr. Zakaria Saleh, PhD 

References:
Health Canada, http://www.hc-sc.gc.ca/hl-vs/iyh-vsv/food-aliment/listeria-eng.php
Wikipedia, http://en.wikipedia.org/wiki/Listeriosis
The Merck Veterinary Manual, 50th Anniversary Edition