3. Listeriosis

What is the aetiology of Listeriosis?

Family. Listeriacae; g. Listeria

* *Listeria monocytogenes, Listeria ivanovii*. 
* *L. innocua, L. gray, L. murrayi*

Gram positive, non-sporulated, facultative anaerobic, resistant to environmental changes.

Describe the characteristics of Listeria monocytogenes

L. monocyogenes produces **hemolytic toxin – listeriolysin O (LLO**) which causes the pathogenicity.

L. monocytogenes is a facultative intracellular bacterium, surviving in phagocytic cells, especially in liver and spleen. Replication is stopped at temperature under -2C and above 45C.

How are Listeria spp. cultivated?

They grow well on blood agar or trypose agar.

How is Listeria inactivated?

**Pasteurization** is the only way to inactivate the bacteria: temperature 72C for 10 min inside the food. Refrigerator temp, frozen food – favourable for Listeria.

What is the epizootiology of Listeria?

Occurrence is in soil, plants, animals, faeces, water, and silage. Important **food-borne disease of humans**! In faeces and water survives 1-2 years. At 5C in soil for 5 years. In **silage 12-16 months; this is the main source of infection for ruminants**, and can be contaminated by rodents.

Viral excretion is through **faeces (main), urine**, **milk, genital tract**. Saprophytes outside the organisms. In farm animals can be a source as often in a carrier state. They have seasonal incidence – sporadic or enzootic, winter-spring. Predisposing factors – hygiene, nutrition, infectious or non-infectious diseases.  

What are the hosts of Listeria?

Susceptible hosts are **– sheep, cattle, pigs, horse, dogs, cats, rabbits, poultry, fish, and insects. Reservoirs of the most virulent strains are rodents.**

Describe the transmission of Listeria

Oral route after **ingestion** of contaminated food products. In humans, those at risk of severe illness include the elderly, unborn babies, new-borns, and immunosuppressed individuals.

**Two cycles of transmission**: human source often vegetables fertilised with animal manure, and animal infection from rodent faeces; these communicate

What is the pathogenesis of listeriosis?

Alimentary entry; conjunctiva or urogenital system; **latent infection** reactivated

→ blood & lymph → enters phagocytic cells (escape immune system) →

* internal organs (espec. liver & spleen), 
* CNS: migration along peripheral nerves 
* genital organs: in pregnancy, through placenta, foetal fluids, foetus aspiration, generalized infection

What are the general clinical signs of listeriosis?

***Septicaemic form*** – weakness, anorexia, serous eye and nose discharge, fever, lung oedema, diarrhoea, death. Occurs mainly in lambs, calves, piglets, kids. **Young** die in 24-48 hours. 

***Encephalitic form*** – stiff gait, twisting, **circling disease**, facial nerve and throat paralysis, opisthotonos. Occur mainly in **adult** animals. Paralysis of limbs, swimming movements, coma, death after 3-10 days. 

***Abortion*** – intrauterine fatal death, retention of placenta, long-lasting secretion of listeria in milk a long time after abortion. Happens mainly during last months of gestation and generally the only symptom of genital infection. May see retained placenta and metritis.

Which animals are most susceptible to Listeria?

sheep

How long is the incubation period in listeriosis?

10-18 days (rapid course; death up to 24-48 hours later)

What are the clinical signs of Listeria in sheep?

Depression, disorientation, circling, facial paralysis and excess salivation, drooping of ears and torticollis, protrusion of tongue, abortion at 12 weeks or later, encephalitis, retained placenta.

What are the clinical signs of Listeria in birds?

**septic form in young**: weak, apathy, unable to move, weight loss, diarrhoea, death

**encephalitic form in adult**: lack of appetite, weakness changes of CNS

What are the clinical syndromes caused by Listeria in man?

* **infection in pregnancy**: proliferate in vagina or uterus, symptomatic in 3rd trimester (fever, myalgia, headache), miscarriage and stillbirth are complications
* **neonatal infection**: early onset sepsis or late onset meningitis from vaginal transmission
* **CNS**: predilection for brain parenchyma (brain stem, meninges) 🡪 nerve palsies, meningoencephalitis, abscesses, seizures in 25% patients
* **Gastroenteritis**: food-borne diarrhoeal disease, typically non-invasive, IP\~21days, lasts 1-3 days, also fever, confusion, loss of balance, aches

**Cutaneous** is rare but after direct skin exposure to intact skin

What are the pathologies caused by Listeria?

Septicaemic form – haemorrhages in pleura, epicardium. Necrotic lesions in liver and spleen. Degenerative changes in myocardium and pericardium, plus oedema of lungs and air sacs (poultry) 

Encephalitic form – oedema of brain, suppurative meningoencephalitis

Abortion – chorioplacental changes, aborted foetus is oedematous, mummified, enlarged spleen and necrotic changes in liver

What is the diagnosis for Listeria?

Clinical signs, necropsy, agent isolation, **serology, PCR..** Samples from heart, liver, kidney, spleen, brain, blood. Microbiological exam is definitive for diagnosis 

Examination of CSF, blood, urine, **paired serum samples**

What are the differential diagnoses for Listeria?

Mammals – pasteurellosis, dysentery, rabies, encephalitis, Septicaemia, abortion

Poultry – paratyphoid, paramyxovirus, E. coli

What is the treatment for listeriosis?

ATBs – ampicillin, gentamicin. For bacteremia 2 weeks, for meningitis 3-6 weeks. High mortality (26%) in children, elder and immunocompromised. 

What is the prevention for listeriosis?

Optimum conditions of breeding and nutrition, correct process of silage and hay fermentation, hygienic standard, disinfection, and rodent control, remove source

**Vaccine in sheep in endemic outbreak areas**