an epidemiological study of listeriosis in dairy cattle

1. 8. Clinical signs and pathology
Although Listeriosis is manifested by three major clinical signs;
meningoencephalitis, abortion and septicaemia, only one clinical form of the disease
usually occurs in a group of animals or an individual animal. However an overlap of
clinical forms of disease have been reported (Gitter and Terlecki 1965, Gitter 1986,
Low and Renton 1985, Ohshima and others 1974). In addition to these three major signs
of disease, mastitis (Gitter and others 1980), myelitis (Gates and others 1967, Seamen
and others 1990), iritis and/or keratoconjunctivitis (Kummeneje and Mikkelsen 1975,
Morgan 1977, Bee 1993, Walker and Morgen 1993) have also been associated with L.
monocytogenes .
a) Meningo - encephalitis: This is the most commonly recognised form of Listeriosis in
adult ruminants and is the most common bacterial infection of the Central Nervous
System of adult cattle (Rebhun 1987). Although the clinical picture is similar in all
adult ruminants the course of the disease (1-2 weeks) is longer in cattle (Gitter 1989).
The basic clinical picture combines signs of the "dummy syndrome" with
pressing against fixed objects and unilateral paralysis (reviewed by Radostits and others
1994). In the early stages, animals are depressed, disoriented, febrile, indifferent to their
surroundings and usually separate themselves from the rest of the herd (Dennis 1993).
As a consequence of the destruction in the trigeminal nerve there is usually a
facial paralysis with a drooping ear, dilated nostril, and lowered eyelid on the affected
side. This is more common in cattle than in sheep (Gitter 1989). As a result of facial
paralysis animals become dehydrated and fluid-electrolyte balance deviates from
normal (reviewed by Radostits and others 1994).
28