Listeriosis Fact Sheet
Synopsis of Listeriosis
Listeriosis, also known as "circling disease" and "silage sickness," is a serious bacterial infection caused by the bacterium Listeria monocytogenes. L monocytogenes is ubiquitous in the environment and has been isolated from raw meat, dairy products, vegetables, and seafood. There are 13 serovars of L monocytogenes; and, although all are considered to be potentially virulent, serovars 4b, 1/2b, and 1/2a cause most animal and human disease. Wild and feral mammals, birds, fish, and crustaceans serve as reservoirs for this infection as well as soil. Infected animals can shed L monocytogenes in their feces, milk and uterine discharges. In the United States, listeriosis is recognized as one of the important public health problems. According to the CDC, there are an estimated 2,500 cases of serious listeriosis each year, approximately 500 of which are fatal. This disease affects primarily pregnant women, newborns, and adults with weakened immune systems.- High risk groups:
- Pregnant women (account for approximately 27% of all cases)
- Newborns
- Persons with weakened immune systems
- Persons with cancer, diabetes, or kidney disease
- Persons with AIDS (300 times more likely to get listeriosis than people with normal immune systems)
- Persons who take glucocorticosteriod medications
- Elderly
- Transmission:
- Ingestion of contaminated food products
- In animals, listeriosis typically occurs after the consumption of contaminated silage or other feed
- In humans, listeriosis typically occurs after consumption of contaminated food sources, particularly the following:
- Raw meat and fish
- Unpasteurized dairy products
- Processed foods that have been contaminated after processing, particularly soft cheeses, deli cold cuts, sliced or grated cheese, and ice cream
- Uncooked vegetables
- Vertical transmission is the usual source of infection for newborn human infants and ruminants
- Transplacentally
- Infected birth canal
- Inhalation
- Direct contact with infected animals or persons
Clinical Signs and Symptoms
Animals:
- Incubation:
- Encephalitis in ruminants: 10 days to 3 weeks
- Septicemia and abortions can appear after one day or more
- Turkeys: 16 hours to 52 days
- Affects a wide variety of domestic and wild mammals, birds, fish, and crustaceans (many of which carry L monocytogenes asymptomatically in their intestines).
- Clinical disease is most often seen in ruminants and occasionally in rabbits, guinea pigs, pigs, dogs, cats, poultry, canaries, and parrots.
Ruminants (Sheep, cattle, and goats):
- Clinical signs and symptoms:
- Encephalitis
- Initial symptoms:
- Depression
- Anorexia
- Neurologic signs:
- Facial paralysis with profuse salivation
- Torticollis
- Strabismus
- Circling
- Incoordination
- Head pressing or turning of the head to one side
- Recumbent during the final stages of disease (involuntary running movements or characteristic chewing motions)
- Death
- Neurological signs are often unilateral
- Initial symptoms:
- Abortions
- Occur mostly during late gestation
- Animal is usually asymptomatic with the exception of a possible fever and anorexia
- Septicemia
- Occurs most often in newborns and young
- Signs and symptoms include the following:
- Fever
- Depression
- Inappetence
- Death
- Encephalitis
- Gross lesions are absent or minimal
- Turbid CSF
- Areas of softening in the medulla oblongata
- Congested meningeal vessels
- Necrotic foci in the internal organs, especially the liver, are typically seen in the septicemic form
- Aborted fetuses:
- May be slightly to significantly autolyzed
- Blood-tinged fluid in the serous cavities
- Shallow erosions in the mucosa of the abomasums
- Foci of necrosis in the liver and possibly the lungs, spleen, or other organs
- Shrunken and gray liver (cattle)
- Areas of necrosis in the placental cotyledons and intercotyledons
Birds:
- Listeriosis is rare in birds, with most cases occurring in the young.
- Clinical signs and symptoms:
- Septicemia (most common syndrome)
- Depression
- Listlessness
- Diarrhea
- Emaciation
- Meningoencephalitis (occasionally reported)
- Torticollis
- Stupor
- Tremors
- Paresis or paralysis
- Septicemia (most common syndrome)
- Peracute deaths can be seen, sometimes without other clinical signs.
- In young geese, both encephalitis and septicemia can be seen concurrently.
Rabbits:
- Abortions
- Most occur during late pregnancy
- Nonspecific clinical signs:
- Anorexia
- Depression
- Weight loss
- Sudden death
Swine:
- Uncommon in swine
- Septicemia (most common syndrome)
- Occurs in young piglets
- Death within 3 to 4 days
- Encephalitis and abortions are seen occasionally
Dogs and cats:
- Encephalitis or septicemia
- Rare cases in cats
- Typical signs and symptoms:
- Depression
- Inappetence
- Abdominal pain
- Vomiting
- Diarrhea
- Septicemia and neurologic signs
- Seen in dogs
- Resembles rabies
Humans:
- Incubation: 3 to 70 days (median is 3 weeks); for newborns infected during birth development: 2 to 14 days; for gastroenteritis in healthy people: 1 to 2 days
- Most healthy people seem to be able to eat Listeria-contaminated foods without developing clinical signs and symptoms.
- Up to 10% of the population may carry L monocytogenes asymptomatically in the intestines.
- Four distinct clinical syndromes:
- Infection during pregnancy - Listeria can be proliferated asymptomatically in the vagina and uterus.
- If the mother becomes symptomatic, it is usually in the third trimester and includes the following symptoms:
- Fever
- Chills
- Slight dizziness
- Myalgias
- Arthralgias
- Headache
- Abortion, stillbirth, and preterm labor are complications of infection
- Click here for more information on listeriosis and pregnancy published by the USDA.
- If the mother becomes symptomatic, it is usually in the third trimester and includes the following symptoms:
- Neonatal infection (granulomatosis infantisepticum)
- Two forms
- Early-onset sepsis
- Late-onset meningitis
- Clinical signs and symptosm:
- Septicemia
- Disseminated granulomatosis
- Respiratory disease
- Meningitis with hydrocephalus
- Death
- Two forms
- CNS infection - Listeria has a predilection for the brain parenchyma, especially the brain stem and the meninges
- Headache
- Stiff neck
- Confusion
- Loss of balance
- Convulsions
- Mental status changes are common
- Seizures (in at least 25% of patients)
- Cranial nerve palsies (can occur)
- Encephalitis (can occur)
- Meningitis (can occur)
- Meningoencephalitis (can occur)
- Abscesses (can occur)
- Gastroenteritis (typically noninvasive)
- Diarrhea for 1 to 3 days
- Fever
- Myalgias
- Nausea
- Abdominal pain
- Infection during pregnancy - Listeria can be proliferated asymptomatically in the vagina and uterus.
- Veterinarians who handle aborted cows or perform necropsies on septicemic animals may develop a cutaneous eruption, characterized by a popular rash or pustules. Fever, chills, or generalized pain may also occur.
- Conjunctivitis has been reported in workers in poultry processing plants.
- Overall mortality rate: 20-30%
- Of all pregnancy-related cases, 22% resulted in fetal loss or neonatal death
Diagnosis and Treatment
Diagnostic Samples:
- In animals:
- Blood
- Cerebral spinal fluid
- Brain tissue
- In humans:
- Blood
- Cerebrospinal fluid
Differential Diagnosis:
- Differential diagnoses include any abortion-causing diseases, meningitis, streptococcus infection, and Escherichia coli infection.
Clinical Diagnosis:
- Clinical diagnosis is difficult due to the absence of pathognomonic signs.
Laboratory Tests:
- Definitive diagnosis:
- Isolation of L monoctyogenes from blood, CSF, the placenta, or aborted fetus, as well as the placenta or uterine discharges following an abortion
- Following necropsy, the liver, kidneys, and spleen can be cultured from septicemic animals or the pons and medulla from animals with encephalitis
- L monoctyogenes can also be isolated from nasal discharges, urine, or milk of affected animals
- Fecal culture is not sensitive or specific
- Commercial rapid identification methods (based on biochemical tests and enzyme reactions):
- ELISA
- Immunofluorescence
- Immunochromatography
- Immunomagnetic separation
- PCR
- Serology is unreliable
Treatment:
- In animals:
- Supportive treatment
- Antibiotics
- Wide variety
- High doses and early treatment are required
- Animals with severe neurologic signs usually die despite treatment.
- Vaccines:
- There is no vaccine for listeriosis
- In humans:
- Treatment can take up to six weeks or more depending on the form of the disease and, due to the intracellular location of some bacteria, may have a low cure rate.
- Supportive care
- Antibiotics
- Ampicillin
- Gentamicin
Economic Consequences and Disease Eradication
Economic Consequences:
- Loss of livestock due to increased abortions
- Costs associated with disease eradication
- Medical costs associated with illness
Disease Eradication:
- Prevention (animals):
- Feeding ruminants good quality silage with a low pH
- Avoid spoiled or moldy silage as well as silage from the superficial few inches exposed to air
- Remove any leftover silage after feeding
- Rodents should be controlled
- New animals should be quarantined prior to being added to the herd
- Animals with clinical listeriosis should be isolated
- The placenta and fetus should be removed after an abortion
- Feeding ruminants good quality silage with a low pH
- Prevention (humans):
- Thoroughly cook raw food from animal sources
- Wash raw vegetables thoroughly before eating
- Keep uncooked meats separate from vegetables and from cooked foods and ready-to-eat foods
- Avoid unpasteurized dairy products or food made from unpasteurized dairy products
- Wash hands, knives, and cutting boards after handling uncooked foods
- Consume perishable and ready-to-eat foods as soon as possible
- Prevention for high risk groups:
- Do not consume hot dogs, luncheon meats, or deli meats, unless they are reheated until steaming hot
- Avoid getting fluid from hot dog packages on other foods, utensils, and food preparation surfaces, and wash hands after handling hot dogs, luncheon meats, and deli meats
- Do not eat soft cheeses such as feta, Brie, and Camembert, blue-veined cheeses, or Mexican-style cheeses such as queso blanco, queso fresco, and Panela, unless they have labels that clearly state they are made from pasteurized milk
- Do not eat refrigerated pates or meat spreads (canned or shelf-stable pates and meat spreads may be eaten)
- Do not eat refrigerated smoked seafood, unless it is contained in a cooked dish
- Click here for more information on listeriosis and food safety published by the USDA.
- Click here for more information on guidelines for controlling listeria contamination in ready-to-eat foods.
- Viability:
- The bacteria can survive for weeks at low temperatures in water, moist soil, hay, straw, or decaying animal carcasses.
- L monocytogenes is relatively resistant to freezing, drying, and heat
- L monocytogenes will grow under the following conditions:
- Temperatures from 1°C to 45°C (can proliferate at refrigeration temperatures on contaminated foods)
- A pH from 3.6 to 9.5 (a pH > 5, that of spoiled silage, favors growth)
- A sodium chloride content of 20%
- Inactivation:
- L monocytogenesis susceptible to the following:
- 1% sodium hypochlorite
- 70% ethanol
- Gluteraldehyde
- Moist heat, 121°C for a minimum of 15 minutes
- Dry heat, 160-170°C for 1 hour
- Cooking or pasteurization
- Ozone
- Chlorine dioxide
- Chlorinated trisodium phosphate
- Peroxyacetic acid
- 1.5% lactic acid plus 1.5% hydrogen peroxide for 15 minutes at 40°C
- Combination of pH 10.5 and 10% NaCl plus monolaurin or lauric acid
- Antibiotics:
- Aminoglycosides (streptomycin, gentamicin)
- Tetracyclines
- Chloramphenicol
- Fluoroquinolones
- Generally resistant to beta-lactam antibiotics
- L monocytogenesis susceptible to the following:
Listeriosis and Bioterrorism:
- Listeriosis presents unique challenges such as the following:
- Long incubation period
- Many potential vehicles, such as ready-to-eat foods
Outbreaks
Human Cases
- 2002: A multi-state outbreak of listeriosis (northeastern United States) as a result of eating deli turkey (46 cases, 7 deaths, and 3 stillbirths)
- 1998: A multi-state outbreak of listeriosis occurred as a result of hot dogs (108 cases, 14 deaths, and 4 miscarriages)
- 1997: An outbreak of listeriosis occurred among attendees of Holstein cow show in Illinois (~45 cases). The outbreak was traced back to contaminated chocolate milk.
- 1981: 100 people in Canada; 34 of the infections occurred in pregnant women (resulting in 9 stillbirths, 23 infants born infected, and 2 live healthy births)
Sources and Related Articles
Sources:
- America Meat Institute, 2002. Fact Sheet: Listeria monocytogenes. Available at http://www.amif.org/FactSheetListeria.pdf.
- CDC Division of Bacterial and Mycotic Diseases, October 12, 2005. Listeriosis. Available at http://www.cdc.gov/ncidod/dbmd/diseaseinfo/listeriosis_g.htm#symptoms.
- CIDRAP, April 14, 2006. Listeriosis. Published on the CIDRAP Website. Available at http://www.cidrap.umn.edu/cidrap/content/fs/food-disease/causes/listerioview.html.
- Anonymous, 1999. Listeriosis and Food Safety Tips. Published by the USDA. Available at http://www.fsis.usda.gov/oa/pubs/lmtips.pdf.
- Anonymous, 2001. Listeriosis and Pregnancy: What is Your Risk? Published by the U.S. Department of Agriculture. Available at http://www.fsis.usda.gov/oa/pubs/lm_tearsheet.pdf.
- Anonymous, 2002. Public Health Dispatch: Outbreak of ListeriosisóNortheastern United States, 2002. MMWR. 51(42):950-951. Available at http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5142a3.htm.
- Graves, L. M., S. B. Hunter, A. R. Ong, D. Schoonmaker-Bopp, K. Hise, et. al., 2005. Microbiological aspects of the investigation that traced the 1998 outbreak of listeriosis in the United States to contaminated hot dogs and establishment of molecular subtyping-based surveillance for Listeria monocytogenes in the PulseNet network. J Clin Microbiol. 43(5):2350-2355.
- Suslow, T. and L. Harris, 2000. Guidelines for Controlling Listeria monocytogenes in Small- to Medium-Scale Packing and Fresh-cut Operations. Published by the University of California Division of Agriculture and Natural Resources. Available at http://anrcatalog.ucdavis.edu/pdf/8015.pdf.