an epidemiological study of listeriosis in dairy cattle

Listeralla hepatolytica. In the same year Nyfeldt made the first confirmed isolation of
Listeria from man. The organism was recovered from an outbreak of an infectious
mononucleosis-like disease (cited by Gray and Killinger 1966). The first report of the
disease in ruminants was in 1929 when Gill reported a disease of sheep (locally called
"circling disease") in New Zealand and two years later isolated the same organism from
sick sheep and designated it Listeralla ovis (Gill 1937). The first report of listeriosis in
cattle was by Jones and Little in 1934 where it was implicated in what is now known as
“typical Listeriosis”, namely meningoencephalitis. The literature on Listeria and
listeriosis has grown rapidly since that time.
Almost every researcher who isolated this newly discovered bacteria named it
differently which resulted in a list of names all referring to the same organism. In 1940
Pirie proposed the name Listeria monocytogenes for this new bacterium after the
British surgeon and medical pioneer Lord Lister. The adoption of this name concluded
the conflict about the name of this new bacteria. By the 1960s Listeria monocytogenes
had been reported from over 50 species of diseased and healthy animals including dog,
cat, horse, pig, fowl and many domesticated and wild animals (Gray and Killinger
1966).
1. 3. Morphology and culture characteristics:
a) Morphology: Listeria are gram positive, non-sporeforming, non-capsular, short,
regular rods. They are, 0.4-0.5μm in diameter and 0.5-2μm in length with rounded ends.
They are motile with a characteristic tumbling movement, best seen at room
temperature. Fresh mature cultures of Listeria show a typical diphtheroid palisade
formation with V and/or Y shapes either singly or in short chains whereas in very young
or old cultures they may be seen in coccoid forms. In fresh cultures they are always
2