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This article was published in 1956
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
LISTERIOSIS IN SHEEP
Case Reports
J. H. IRVINE, B.V.Sc., Inspector of Stock, Bathurst.
The small number of outbreaks of Listeriosis in sheep reported in New South Wales over past years indicates that the incidence of this disease is quite low. However, in the past two years, four (4) outbreaks have occurred in the Bathurst District, and in 1952 one occurred in a flock within a short radius of Carcoar.
In addition, two (2) appreciable mortalities from which Listeria monocytogenes was isolated as the probable cause were investigated by the District Veterinary Officer at Orange; one in March, 1955, and the second in May, 1956. The implication well may be that Listeriosis is not nearly so uncommon as has been assumed in the past, and that in the absence of fairly keen differential diagnosis other outbreaks of this disease may have been ascribed to Enterotoxaemia, Mineral Imbalance, Plant Poisoning or Black Disease.
Of the three outbreaks investigated by the writer, two were atypical as to history and symptoms and consequently it is thought well worthwhile to record them in some detail:
CASE 1
This particular outbreak occurred in a mob of 1400 full-mouth Corriedale wethers. The owner possesses two properties, situated about twelve miles apart, and moves his stock frequently between these two holdings. For several years he had noticed when this particular line of wethers was moved, such movement on nearly every occasion resulted in a type of staggers syndrome being exhibited by odd sheep. Sheep affected, after travelling a few miles or perhaps further, would lag behind and, if forced along, go down; usually if left alone regaining their feet only to go down again if the journey continued. Recovery or death might follow. There appeared to be no relationship between the condition of the sheep and the course of the disease. The owner discussed this problem with various veterinarians, including the writer, but no satisfactory answer could be found, and unfortunately opportunity to investigate the condition did not arise for a long time.
On 24/4/52, the owner reported that over a period of about three weeks, sixteen of the subject wethers had become sick whilst in the paddock. Of these, seven had died, two were still sick and the rest apparently had recovered. An examination was made of the two sick animals (it was not known exactly how long they had been sick), and the following is a description of symptoms exhibited by them: Tail twitching, stiffness in hindquarters, shivering and inco-ordination of gait, a tendency to walk in circles (this latter symptom had not been a constant feature in all cases), refusal to drive; finally lying down, with death taking place about five (5) hours later. Affected sheep, after going down, would struggle and kick until death intervened.
Post-mortem: One of the two sheep was selected for most-mortem and killed. This examination revealed the following:
A carcase, in fairly good condition, an apparently normal liver with a gall bladder greatly distended by a thick viscid bile and showing a marked thickening and some ulceration on its wall; which was about one-tenth to one-eighth of an inch thick. Patchy congestion of the mucosa of the small intestine.
Specimens were submitted to the Director of Veterinary Research for his examination, and he advised that cultural examination of pipettes from the liver and kidney revealed a growth of a gram-positive rod from both organs. This organism was identified as Listeria monocytogenes.
This disease continued to cause losses in the subject flock until about 7/6/52, when the mortality ceased. In all, thirty-five (35) deaths were recorded.
On 3/7/52, eleven hundred and eighty-six (1186) of the Corriedale wethers were moved between the two properties, for the first time since the outbreak of Listeriosis. All the sheep in this mob were in excellent condition, the "tail" having been drafted off and left behind. They showed no signs of internal parasitism. Although moved along quietly, they had travelled only two or three miles when two dropped back, and by the time the flock reached its destination, thirteen sheep had been left behind and required to be transported by lorry.
The owner had been requested to report anything of this nature, and this he did sufficiently early to permit investigation.
SYMPTOMS: Symptoms were most unusual. A strong robust animal would drop back from the mob and refuse to move, taking no interest in its surroundings. The pulse and respiratory rate were much increased; with respiration forced but pulse strong. Temperature 102.6F. Conjunctiva and skin colouration normal. If the sheep were forced along at this point, the gait would become stilted and short and then after about fifty or one hundred yards its tail would be seen to twitch; this being followed quickly by muscular tremors all over the body, particularly affecting the fore and hindquarters. Twitching of the muzzle and turning up of the upper lip and muzzle were common. A few seconds after the muscular tremors were evidenced the affected animal, with a hurried movement, would lie down in a normal position. If left alone, it would regain its feet after a time with a recurrence of the foregoing syndrome if forced along.
By the following day, all sheep which had developed symptoms appeared normal and very active, so that difficulty was experienced in mustering them into a yard. One which had shown symptoms the previous day was killed and its carcase examined post-mortem.
Post-mortem: Its condition was fat and there were no marked pathological changes. The liver was normal except for the presence of a few fluke and some miliary abscesses. The wall of the gall bladder was somewhat thickened. There was slight congestion of the renal cortex and the lower part of the small intestine. The colon showed slight to moderate patchy congestion of the mucosa. The mesenteric lymph nodes were much enlarged and juicy. That portion of the meninges covering the frontal lobes of the cerebral hemispheres was noticeably congested.
Specimens were forwarded to the Director of Veterinary Research for examination and he advised that in this case he was not able to isolate Listeria monocytogenes from culture of pipettes. However, he stated that a subacute glomerulo-nephritis was present; and that sections through the brain revealed a considerable degree of neuronal degeneration with neuronophagia. Sections through the gall bladder wall revealed large aggregations of lymphocytes lying beneath the mucous membrane; while the areolar tissue outside the muscle coats was oedematous.
He was of the opinion that this sheep had been infected with Listeriosis although the pathological picture in the brain was unusual in that no perivascular cuffing was evident. Typical brain lesions in this condition are perivascular cuffing with focal necrosis and phagocytic infiltration. Overseas writers have described glomerulo-nephritis as a most important feature of Listeriosis.
No further cases occurred up to the end of June, 1953, and shortly afterwards the owner sold the entire flock of Corriedale wethers.
CASE 2
On 19th July, 1955, the writer had cause to investigate a mortality in a line of twelve hundred (1200) Merino ewes, aged one to seven years, in good store condition and with lambs at foot. They had been running on an improved pasture comprising mainly sub. clover, which could be described as only fair.
The owner advised that sixty (60) deaths had occurred since the 1st May, 1955. Lambing had commenced about the end of that month. Affected animals were seldom seen sick; death being sudden with no previous warning. Carcases decomposed rapidly. On close questioning, the owner recalled that ewes had shown a reddish brown vaginal discharge prior to death. A ewe, dead some six hours, was submitted for post-mortem examination.
Post-mortem: In spite of the extremely low temperatures pervailing at the time, putrefactive changes were advanced. A large quantity of bloodstained fluid was present in the pericardial sac and peritoneal cavity. Both small and large intestines were distended with gas and the small intestine showed quite severe patchy congestion. The kidneys were flabby, with a congested cortex. Examination of the uterus revealed a retained, decomposing placenta with metritis. This ewe had a six weeks' old lamb at foot.
Disregarding the metritis, the post-mortem changes were consistent with those commonly seen in Entero-toxaemia.
At Glenfield Research Station, culture of a pipette from the uterus of the dead animal produced a pure growth of Listeria monocytogenes.
It is interesting to note that there has not been any history of abortion, still-births or circling in this flock, but there has been quite a high percentage of early post-natal deaths. The foregoing together with retained placentae, with metritis and reddish brown vaginal disease, are consistent with the clinical picture of Listeriosis in sheep.
A few losses occurred following this and then the condition seemed to clear up spontaneously.
However, some time ago the owner advised that he had noticed when moving a large number of his sheep, that a few, although in good condition and not at all anaemic, would refuse to drive; stopping, trembling, shivering and later going down. Although none of these died, it was necessary to transport them to their destination.
CASE 3
Towards the end of August, 1955, a sheep owner presented for examination a Merino ewe which had been sick for about twenty-four (24) hours. This ewe was one of three hundred and six (306) mixed sheep, running on good and fairly well improved pasture. About the middle of July, a ewe (not in lamb) became sick; dying within a few days. From then onwards losses occurred at the rate of about one per week. Deaths occurred in weaners, as well as in ewes and wethers. The owner stated that the ewe submitted for examination showed symptoms typical of those exhibited by other sheep which had died.
SYMPTOMS: Early in the course of the disease, the sheep was seen standing apart from the mob; listless and dopey. In a day or two there was a tendency for the animal to hold its head to one side and to move in that direction; more or less in a large circle. As the disease progressed, the head was held in a position which became progressively lower and the circle in which it moved became progressively smaller; the sheep falling over on to the side towards which its head was held, and then being unable to rise unless assisted to its feet. A serous nasal discharge was common; while in two cases, conjunctivitis and keratitis were present.
Post-mortem: The carcase was in good condition. There was a slight discharge from the nostrils and a severe conjunctivitis in one eye. A healthy foetus was present and the ewe appeared to be about six to eight weeks off lambing. The liver was pale and showed some fluke damage. There were a number of Oestrus ovis larvae present in the nasal passages and frontal sinus. Otherwise the carcase appeared normal. A diagnosis of Listeriosis was made but Listeria monocytogenes was not recovered from pipettes at Glenfield Research Station. However, histological examination of the brain tissue revealed evidence of meningo-encephalitis with foci of inflammation in the mid-brain and the medulla. Such findings may be expected in Listeriosis.
On 1/9/55, a visit was paid to this owner's holding in an effort to pursue investigations relating to the suspected Listeriosis. The majority of the sheep on the property appeared to be in quite reasonable condition and there was ample feed available to them. The owner reported that a further two deaths had occurred since the previous investigation and that a Merino wether weaner had on the previous day shown the first symptoms of the condition. This weaner could not be found in the flock, but a search of the paddock discovered it with its horns caught in some wire netting. It was standing quietly, but when released showed evidence of motor excitability. The eyes were dilated and staring and there was muscular twitching and trembling; particularly affecting the facial muscles. Without any warning, the weaner then rushed wildly over the large, open paddock in which the flock was running. It was watched for some time and during this period there was a distinct tendency for it to circle, but the circle in which it moved was very large indeed. There was no attempt to join the rest of the flock, although at times its movements would carry the weaner in close proximity to other sheep.
The weaner was brought back to headquarters, where it was held under observation in a small yard. For the first two days it showed no inclination to feed; either standing with its head pressed against a fence or sitting or laying in a secluded spot. It made no attempt to move when any person approached and appeared quite disinterested in its surroundings. By 3/9/55, it was showing a serous discharge from the nostrils, and when forced to walk would move in a circle. By 6/9/55, it was unable to stand unless assisted to its feet; and on that being done, would turn round on its axis, then falling on its side. The head was flexed strongly to the left side and it was to the left that it circled. On 7/9/55, the animal, then in extremis, was killed and a postmortem examination carried out.
Post-mortem: The carcase was very low in condition and obviously the sheep had not eaten for quite some time. The liver and kidneys showed a slight patchy congestion, but otherwise appeared normal. The mucus membrane of the frontal sinus was thickened and a number of degenerated Oestrus ovis larvae were present. The meninges appeared congested, but no other macroscopic changes were evident.
At Glenfield Research Station, Listeria monocytogenes was recovered from the cerebellum and medulla.
About the middle of December, the owner reported that another sheep was showing symptoms of "Circling". This animal, according to the owner, after showing such symptoms for some days appeared to improve slightly, but later fell into a gully and drowned. Lambing on this property was uneventful and no abortions occurred.
(We are indebted to D. G. Christie, B.V. Sc., District Veterinary Officer, Orange, for particulars of the following two outbreaks in the Orange section of the Bathurst district. Permission to use these notes in this article is appreciated).
CASE 1A
HISTORY: Over two wees, some five (5) deaths occurred in 800 first cross Border Leicester ewes which had been on the holding for three years; the property comprising really first-class pasture-improved country. Losses occurred on ideal feed. The first death was noted in a mob of hoggets; not in the main flock of ewes. This animal showed "Circling", but post-mortem examination did not reveal any significant changes. No other cases occurred in this mob of 260 hoggets; running on self-sown oats, sorrel and clover.
The first case in the ewe group was noted the following day; the affected sheep showing proppiness; and appearing to be blind, with the head held high. The ears twitched noticeably and were "lopped". Examination showed that the animal was able to see. One day later the owner treated this ewe with Calcium borogluconate and from that point she appeared to improve; but relapsed and died eight days after the treatment. On that day the second case appeared in the ewes; this animal being dull, with a staggering gait, dilated pupils and showing some shivering. Apparently completely blind. No response to Calcium injections. The third case occurred within the next six days; and also showed shivering. A fourth ewe was affected about 14 days after the first; symptoms consisting of lopped ears, dilated pupils and apparent blindness. The head was carried to one side; there was excess salivation and the animal was extremely dull.
Post-mortem: The fourth ewe case was examined. This animal was in fat condition and carried a single foetus at about 8-10 weeks. Liver slightly enlarged and the capsule bluish. Liver substance rather light in colour with a few areas of congestion on the diaphragmatic surface. Kidneys showed patchy congestion of the cortex. Small intestines empty.
SPECIMENS: Pipettes of medulla oblongata, cerebellum and liver, portions of same organs in 10% formol saline; blood and serum for calcium and magnesium estimation.
D.V.R. REPORT: Cultural examination of the pipettes resulted in the isolation of an organism considered to be Listeria monocytogenes from the medulla. Cerebellum and liver produced only coliform growth. Calcium and magnesium values were found to be within the normal range.
CASE 2A
HISTORY: Some 1,300 sheep on approximately 450 acres of basalt country carrying a good cover of natural grass on half the area; the remainder being top-dressed with superphosphate, with 80 acres sown to red clover, sub. clover and rye. Owner stated that about 30 sheep had died during a period of 12 months; in each case symptoms not being observed until the animals were down; lying on the side with the head thrown back. Any movement while on the ground took place in one direction only.
EXAMINATION: A 2-tooth ewe. Apparently blind; with the pupils dilated. Lying on the right side and showing marked opisthotonus. No attempt at circling was noted, but the owner stated that earlier this sheep tended to move only in one direction.
Post-mortem: Petechiation noted in lungs and heart. Liver showed fatty degeneration and one small area (shilling size) on the diaphragmatic surface suggested an early Black Disease lesion. Excess pericardial fluid. No macroscopic changes noted in the brain.
SPECIMENS: Pipettes of liver, heart blood, cerebrum, cerebellum and medulla; liver, kidney, cerebellum, cerebrum and medulla in 10% formol saline; ruminal contents.
D.V.R. REPORT: Listeria monocytogenes was recovered from the pipette of the medulla; confirming the diagnosis of Listeriosis.
(NOTE: Although in the cases of Listeriosis reported here there apparently was not any association with Abortion in any of the ewes involved, such an association with the recovery of Listeria monocytogenes was recorded by G. Charles, B.V.Sc., in our publication in 1950.-EDITOR).