Listeriosis

The disease is caused by Listeria monocytogenes - Gram positive small non spore- forming bacilli seen in soil, silage, sewage and feces of animals and birds. These bacteria can survive outside the host for several years but are susceptible to pasteurization and certain antimicrobials. The clinical symptoms are not specific. There is depression, ataxia and torticollis. The gross lesions observed are focal hepatic necrosis, spleenomegaly with military necrosis, nephritis, enteritis, myocarditis and conjunctivitis. In acute cases the only lesion seen are congestion of the viscera and petechial haemorrhages on several organs.

Definite diagnosis is based on isolation and identification of the bacteria from blood, liver, spleen or brain. Isolation may require pre-incubation of the macerated materials at 4oC for several days or weeks. Isolation of the organism can also be attempted in chicken embryos.  Potential source of infection should be avoided with biosecurity measures.