Veterinary Epidemiology and Zoonosis

LISTERIOSIS

Synonyms

• In animals: Silage sickness, Circling disease 

Type of zoonosis

• Direct anthropozoonosis

Definition

• Listeriosis is an infectious bacterial infection in ruminants, pigs, dogs, and cats, some wild animals and humans, causing abortions or nervous system disorders in animals. In humans, it is clinically characterized by fever, headache, nausea, vomiting, endocarditis, granulomatous lesions in multiple organs, cutaneous involvement, coryza, conjunctivitis, metritis with abortion, sepsis and meningitis.   

Etiology

• Listeria monocytogenes. Gram positive, facultatively anaerobic bacilli, pleomorphic rod, motile at temperature between 20°C and 25°C and intracellular pathogens of reticuloendothelial system.
• Serovars 4b, 1/2b and 1/2a causes infection in animals, and 4d and 4b in humans.
• It is ubiquitous nature.
• This bacterium can live almost anywhere in soil, manure piles and grass. Listeria thrives in aerobic conditions where the pH is 5.4 or higher. It doesn't do well in very acid conditions. Therefore, the top layers of silage or improperly preserved silage may harbour large numbers of organisms. The increased use of trench silos has been correlated with increased numbers of listeriosis cases among cattle. Because of this, it is important to make sure that silage is tightly packed to ensure proper fermentation. 

Reservoir and incidence

• Refrigeration of foods may provide selective growth of Listeria.
• Environmental contamination (soil, pasture, water bodies, streams) with faeces of animals and birds.
• Stools of pregnant women and female genital tract discharges are the sources of infection.
• Isolated from fish, birds, swine, horses, ruminants, guinea pigs, ferrets, gerbils, rabbits and chinchillas.
• The principle reservoir of the organism is in forage, water, mud and silage.
• The seasonal use of silage as fodder is frequently followed by an increased incidence of listeriosis in animals.
• Healthy animals are not usually affected by Listeria. Cattle with lowered resistance to disease on a high silage diet are prime candidates for listeriosis.
• Sheep and goats are even more susceptible to this disease. 
• Pregnant women are susceptible and at great risk of aborting if they are not properly protected from infection.
• The young, the elderly and the immuno-compromised people are most susceptible to infection.

Transmission

• Ingestion of unpasteurized milk and cheese and contaminated vegetables (food borne transmission).
• Direct contact with infectious material or soil contaminated with infected animal faeces.
• Vertical (transplacental) transmission (mother to fetus in-utero or during passage through the infected birth canal).
• Person-to-person transmission through sexual contact (coitus transmission).
• Inhalation of the organism.
• In animals, poor quality silage feeding (silage sickness).

Disease in animals

• There are two forms: meningoencephalitic and visceral form.
• Meningoencephalitic form
  • Neurological signs with dullness.
  • Lateral deviation of the head with a tendency to circle (circling disease).
  • Paralysis sets in with recumbency and death due to respiratory failure.
• Visceral form
  • Abortion with retained placenta (within the last third of pregnancy in cattle and abortion storms are more common in sheep and most abortions occur after the 12^th week of pregnancy).
  • Microabscesses in the brain.
  • Multiple foci of necrosis in the liver, spleen and heart.
  • Placental lesions are characteristic with yellow necrotic foci and in foetus (multiple granulomas / small yellow foci of necrosis in the foetal liver, shallow abomasal erosions and a yellow-orange meconium).
  • Mastitis is rare manifestation, but affects only a single quarter and not responsive to antibiotics.
  • Abscess formation in the eye can lead to blindness.
  • Fatality is very high, ranges from 3-30% during outbreaks.

Figure: Abscess formation in the eye

Disease in man

• It is clinically characterized by fever, headache, nausea, vomiting, endocarditis, granulomatous lesions in multiple organs, cutaneous involvement, coryza, conjunctivitis, metritis with abortion, sepsis and meningitis.
• Meningoencephalitis
• Acute septicaemia with pharyngitis
• Newborns are mostly affected and also above 50 years of age. It is rare between 1 month and 18 years of age.
• Abortion in second half of pregnancy.
• Miscarriage or birth by a few days or weeks with symptoms of chills, fever, cephalalgia, dizziness and gastrointestinal symptoms.
• Perinatal mortality.
• Symptomless faecal carriage is common.
• Granulomatous lesions and abscesses occur in the liver and other organs and beneath the skin and it is called as listeriomas. 
• Focal necrosis in the placenta with mononuclear infiltration.
• Fatality rates may exceed 20%.

Diagnosis

• Culture and isolation of the causal agent from blood, CSF, amniotic fluid and septicemic foetuses.
• Anton's eye test
• Modified CAMP test
• Intracerebral inoculation into mice
• Serology for the detection of IgM antibodies by FAT, CFT andELISA.
• PCR technique 

Treatment

• For maternal-foetal infection ampicillin alone or combination with aminoglycoside may be useful.
• Antibiotics trimethoprim-sulfamethoxazole can be used.
• Tetracycline (not for children) and chloramphenicol can be used.

Prevention and control

• In areas where neonatal mortality is more, Gram's staining of meconium of a newborn is important, so antibiotic treatment can be started earlier and this can also be applied for the pregnant women.
• Pregnant women and immunocompromised individuals should avoid contact with potentially infective materials such as aborted animal foetuses and known infected persons.
• Pasteurization of milk.
• Rodent control.
• Personal hygiene.
• Safety food production.
• Cooking of foods of animal origin.
• Vegetables and cooking vessels should be washed before use.
• Avoid drinking raw milk, eating raw meat and food products.
• Avoid eating soft cheese by pregnant women.
• In animals:
  • When an outbreak occurs in animals, the affected animals should be immediately treated and isolated and those that have died should be destroyed or removed from the premises.
  • Buildings should be thoroughly disinfected and cleaned and all bedding and feed should be burned.
  • Silage feeding should be reduced and if spoiled, should be avoided.