Following a survey of the available literature, one is left with a definite impression that Listeriosis is a disease which is considerably more widespread than the few reports of its occurrence would suggest.
This condition may exhibit one of two manifestations: (a) The Foetal (or Uterine) type, and (b) The Nervous Type.
The first reports of Listeriosis in farm animals came from Gill; who diagnosed a case of the Nervous Type in New Zealand in 1931.
In the following year, Hindmarsh and Blumer recorded an outbreak of abortions in sheep in N.S.W., due to Listeria spp.
Following this, cases of early post-natal deaths in human infants (Burn, 1936), abortions in cattle (Graham et al., 1939) and abortions in sheep (Patterson, 1940) due to Listeria monocytogenes were reported.
As far as Australia is concerned, Listeriosis has been reported from Queensland (Moule, 1953), N.S.W. (Hindmarsh and Blumer, 1932; Charles, 1950: Irvine, 1955 and Diplock, 1957), and suspected in Victoria (Paulsen and Moule, 1953).
(a) Foetal or Uterine Type. Flocks and herds usually are affected sporadically, but epizootics have occurred. The disease is characterized by abortion with out premonitory symptoms. Abortion can occur any time between the twelfth week and full term in the case of sheep.
The proportion of the flock affected usually lies between 3% and 16% as far as sheep are concerned, but there seems to be little data on this point in other species. However, a Scandinavian worker recently reported 14 cases of the Foetal type and 4 of the Nervous type of Listeriosis in 3 herds comprising 91 goats; no mention being made in the abstract cited as to whether the nervous cases occurred in the same herd as the foetal cases.
Metritis, accompanied by a vaginal discharge, is a not uncommon sequel of abortion, but it is not seen invariably. However, retention of the foetal membranes for several days is observed frequently. The foetal membranes at times will also show changes from the normal; un-associated with the cotyledons.
No clinical abnormalities are shown by the rams.
Aborted lambs, or those which die within 2-3 days of birth, frequently show no gross abnormalities but subcutaneous haemorrhages sometimes may be seen.
Nervous symptoms, such as "Circling". are seen very rarely during outbreak of Listerial abortion.
(b) Nervous Type. Affected sheep show signs of depression, weakness, incoordination, walking in circles, pushing into objects and progressive paralysis, leading to death within two to three days.
The symptoms in cattle are similar; but in pigs they are liable to be rather vague, although suggestive of disturbances of consciousness.
Poultry are also susceptible; the main symptoms observed being emaciation and general weakness. Post-mortem lesions consist of oedematous tissues fluid in the body cavity and pericardial sac, and focal necrosis of the liver.
(a) Bacteriology. From pipettes of foetal stomach, brain and heart blood. At present this is the only reliable method.
(b) Serology. A German worker has reported a serological test: the accuracy of which, however, appears to be rather low.
(c) Hematology. In view of the characteristic monocytosis observed in this disease, the possibility of diagnosis on the basis of the hematological picture was considered, but as the normal range for monocytes, particularly in sheep, is extremely wide, and as it is difficult to differentiate monocytes from lymphocytes in ruminants, it seems unlikely that this approach would be feasible.
(a) Foetal Type. Brucellosis; Leptospirosis; Virus Abortion (Ovine).
(b) Nervous Type. Other forms of Encephalitis or meningoencephalitis (e.g. due to Staphylococci).
Treatment in general seems to be of little value. However, Mayer, working in Germany, reports that losses in Chinchillas, where previously 15 out of 72 had died from Listeriosis, ceased after treatment with 10 to 12.5 mg. Chlortetracycline daily for three weeks.
The writer treated four separate cases of "circling" in sheep which occurred over a period of 2 years, with 500,000 units of Procaine Penicillin daily for two days. This was followed by clinical recovery in three cases and death in the fourth case; which was examined subsequently and found to be positive for Listeriosis.
PUBLIC HEALTH ASPECTS
As Listeria monocytogenes appears to show little species specificity cross infection between various animals does occur. Several cases are on record of spread to humans, particularly from infected sheep.
Osebold and his co-workers recently investigated this aspect following an epizootic of Listeriosis in sheep in California. These investigators examined numerous native birds and animals and succeeded in isolating Listeria spp. from a sick skunk in the epizootic area; where an obscure illness had been observed in this native species at the same time as the epizootic in sheep. Workers in Connecticut some years ago, also reported the disease occurring in foxes raised for pelts.
In view of these observations, it seems not unlikely that native animals may play a part in the natural dissemination of this organism, and their role could assist in explaining, at least in part, the sporadic occurrences of this disease.
A comprehensive review of Listeriosis is given by Olsen, C. (1954) in the Proceedings book of the 91st Annual Meeting of the A.V.M.A.