Signalment:  

8-day-old female Aberdeen Angus (Bos taurus), bovine.This calf was from a cow-calf herd with 55 suckler cows. The herd had suffered from increased morbidity and mortality of suckling calves aged 1-9 days old. Clinical signs of this calf included diarrhea, petechiae on the conjunctival and buccal membranes, fever and generalized weakness.

Gross Description:  

Weight 39 kg, moderate post mortem changes, moderate fat stores, and severely dehydrated. All visible lymph nodes were swollen. The umbilical arteries were swollen and deep red. The spleen was moderately enlarged. The liver contained multiple disseminated 2-3 mm pale yellow spots all over the parenchyma. The abomasum contained 1 liter of coagulated milk, mucosa was moderately red and swollen. The distal parts of the jejunal and the ileal serosa and mucosa were red, and ileal lymph nodes were severely swollen and reddish gray. Pale purulent exudate covered the meninges of the brain stem. Fibrinous pale exudate was detected in the joint cavities of the legs.

Histopathologic Description:

Liver: Multifocal, disseminated, random, variable sized foci of deeply eosinophilic (coagulation necrosis) hepatocytes, infiltrated with variable, usually moderate, numbers of degenerating neutrophils and a few macrophages. Brown-Benn staining showed multiple gram-positive short rod shape bacteria in these foci. In other tissues (samples not submitted), a suppurative synovitis and meningitis, and a necrotizing lymphadenitis and enteritis were detected.

Morphologic Diagnosis:  

Liver: Multifocal moderate subacute necrotizing hepatitis.

Lab Results:  

: Listeria monocytogenes was isolated in pure growth from the spleen, liver, lung, ileal lymph node and brain. Salmonella was not detected.

Condition:  

Listeria monocytogenes

Contributor Comment:  

The genus Listeria includes 6 species, of which two, L. monocytogenes and L. ivanovii, are known to cause disease in animals. L. ivanovii has been detected causing abortions in ruminants. L. monocytogenes is ubiquitous in the environment, in the soil, plants and feces of animals. It is a gram-positive short non-spore forming rod capable of growing from 1° C to 45° C and pH 4.5-9.6. L. monocytogenes is an opportunistic pathogen and causes disease in several animal species including mammals, birds and fish. Of the domestic species, most commonly ruminants are affected, rarely also foals or pigs.(2,6) Feeding of poorly fermented silage with pH over 5 has commonly been associated with occurrence of the disease in ruminants. Listeriosis is a zoonosis. 

The three main types of disease caused by Listeria are meningoencephalitis, abortions and septicemia. Meningoencephalitis is the most common form of the disease and occurs mainly in adult ruminants. Abortions in the last third of the pregnancy or stillbirths are most often detected in sheep, goats and cattle. Septicemia occurs in young ruminants and neonate monogastric animals. Less common forms of the disease are conjunctivitis, keratitis or uveitis in ruminants and horses(1); mastitis, endocarditis, meningitis in young animals; spinal myelitis in sheep; and enteritis in adult sheep. Recently, a fatal mesenteric lymphadenitis was described in adult cattle.(5) Also, skin infections have been described in veterinarians. L. monocytogenes septicemia occurs also in rabbits, chinchillas, hares, and has been described in semi-domesticated reindeer calves associated with silage feeding.(3) The disease is often sporadic but small epidemics occur.

Infection occurs via ingestion, from the contaminated feed or udder, via milk or umbilical cord, or in the uterus. The bacteria penetrate the intestinal mucosa and cause a subclinical bacteremia. Encephalitis in ruminants has a different pathogenesis and is probably acquired via cranial nerves from oral mucosal abrasions or an infected tooth cavity. In these cases the bacteria reach the brain stem by using axonal transport. This is supported by the special distribution of the lesions in the brain stem. The incubation period varies from 2 days to several weeks. Only a small proportion of infected animals develop clinical disease. The predisposing factors include stress, pregnancy, parturition, poor nutritional state, large dose and failure of passive transfer. In humans the infection is usually foodborne and pregnant women, elderly and immunocompromised individuals are predisposed.

Listeria is a facultative intracellular parasite and invades cells, macrophages, monocytes, neutrophils and epithelial cells by using a special surface protein, internal in.(2) In the cell, bacteria escape from the phagosomes by producing a haemolysin called listeriolysin O and phospholipases. The bacteria are motile and have a special cell to cell movement system. Cell-mediated immunity has a role in causing tissue damage. Gross pathological findings in septicemic forms of the disease consist of multiple random pale necrotic foci or microabscesses, most commonly in the liver and spleen. 

Histologically, in the septicemic form, multiple necrotic foci or microabscesses with variable numbers of neutrophils and macrophages are seen in the liver, and are often also in the spleen or other tissues. 

The differential diagnoses for necrotic hepatitis include Salmonella, Bacillus piliformis (Tyzzers disease), Yersinia pseudotuberculosis, and in rodents also Toxoplasma gondii.

JPC Diagnosis:  

Liver: Hepatitis, necrotizing, multifocal and random, moderate.

Conference Comment:  

Glycogen vacuoles present in the liver suggest this is a young animal. Because infection occurs following ingestion, Listeria causes individual abortions rather than an abortion storm. It also causes placentitis with cotyledonary necrosis and vasculitis of the chorioallantois but not the amnion. Necrotizing hepatitis and enteritis may also be prominent features in the aborted bovine fetus. With early third trimester infection and following abortion, the placenta is often retained due to mild metritis; however, the dam usually does not suffer severe illness. Conversely, if infected near term, the dam often suffers from dystocia, severe metritis and septicemia.(4) Neutrophils are the primary inflammatory cell in listeriosis, due in part to Listeria infected endothelial cells expressing P- and E-selectin, intracellular adhesion molecule-1 (ICAM-1), and vascular cell-adhesion molecule-1 (VCAM-1), which activate the neutrophil adhesion cascade and neutrophil binding.(7)

References:

1. Evans K, Smith M, McDonough P, et al. Eye infections due to Listeria monocytogenes in three cows and one horse. J Vet Diagn Invest. 2004;16:464-9.
2. Maxie MG, Youssef S. Nervous system. In: Maxie MG, ed. Jubb, Kennedy and Palmers Pathology of Domestic Animals. 5th ed. Vol 1. Philadelphia, PA: Saunders Elsevier; 2007:405-8.
3. Nyyss+�-�nen T, Hirvel+�-�-Koski V, Norberg H, et al. Septicaemic listeriosis in reindeer calves- a case report. Rangifer. 2006;26:25-28.
4. Schlafer DH, Miller RB. Female genital system. In: Maxie MG, ed. Jubb, Kennedy, and Palmers Pathology of Domestic Animals. 5th ed. Vol 3. Philadelphia, PA: Saunders Elsevier; 2007:492-3.
5. Thompson H, Taylor DJ, Philbey AW. Fatal mesenteric lymphadenitis in cattle caused by Listeria monocytogenes. Vet Rec. 2009;164:17-18. 
6. Wilkins PA, Marsh PS, Acland H, et al. Listeria monocytogenes septicaemia in a thoroughbred foal. J Vet Diagn Invest. 2000;12:173-176.
7. Zachary JF. Mechanisms of microbial infection. In: Zachary JF, McGavin MD, eds. Pathologic Basis for Veterinary Disease. 5th ed. St. Louis, MO: Elsevier Mosby; 2011:195.

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4-1. Liver

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