There can be little doubt that, in the past, pathogenic effects due to coccidial infection in young sheep have been mistaken for effects due to trichostrongyles. Effects have been due also to combined infections and the whole aetiology attributed to Trichostrongyles and nutritional deficiency.
In recent years, since phenothiazine has been used widely as an anthelmintic and improved pastures have removed major nutritional stresses, it has become increasingly evident that an additional factor was causing far more loss than had previously been realised. Investigation of outbreaks of diarrhoea in young sheep during 1955-1958 has indicated that the factor is Coccidiosis.
DETAILS OF OUTBREAKS
Holding No. 1. One-hundred and thirty (130) Merino lambs, bred on heavy basaltic country at Guyra, and three-hundred and seventy (370) lambs of similar age and breeding, bred on lighter-carrying country some ten miles away, were combined as one mob in mid-May, 1955, when they were weaned, drenched with 1 oz. of phenothiazine and placed in an improved pasture paddock on heavy basaltic soil, at a stocking rate of two sheep per acre.
A month after weaning, a proportion of the mob was showing evidence of diarrhoea which was interpreted by the owner, perhaps correctly, as evidence of Trichostrongylosis. They were drenched immediately with phenothiazine. Diarrhoea became more intense, with bleating during tenesmus. Bodyweight was lost rapidly and they were very tucked up. Characteristic of the more intense stages of diarrhoea was a rapid in and out movement of the upper flanks after and during straining. Faeces were not bloodstained. Less than 5 per cent of the lambs bred on the heavier country showed evidence of diarrhoea. 25 per cent.-30 per cent. of those from lighter country showed evidence of marked diarrhoea. Few deaths occurred. Loss of body weight and set-back to growth were the major loss.
Post-mortem findings. In the small intestine of one lamb diffuse white superficial patches, about a quarter of an inch in diameter, were found. These were attributed to Coccidiosis. Large numbers of white cyst-like structures, less than 0.5 m.m. in size were found also in the mucosa. Counts showed 2,000 Trichostrongyles and 1,500 Nematodirus spp., and 1,000 strongyloid ova per gram, together with a fair number of coccidial oocysts.
In mid-May of 1957 trouble occurred again. History, symptoms and lesions were much the same as in 1955, including invariable observation of the white cyst-like lesions. Eight of nine affected with diarrhoea had egg counts between 200-600 per gramme of faeces; the ninth, scoured profusely, had 4,800 per gm. Oocyst counts ranged from 750 to 163,000 per gm., with an average of 42,000.
Bacteriological examination of tissues revealed no abnormality. Intestinal contents contained toxins too weak to identify by toxin neutralisation tests. Smears from the small intestine revealed no evidence suggestive of enterotoxaemia.
Because of persistent reports that drenching with phenothiazine made the condition worse, four groups of sheep, each of eighteen head, were taken. Two groups were of sheep affected with diarrhoea. One was treated with 2 oz. of phenothiazine. Two groups were not affected with diarrhoea; one of these was drenched with 2 oz. of phenothiazine. After three days and again two days later, it appeared that, on a comparative basis, the sheep which were affected with diarrhoea and were treated with phenothiazine had become worse. There was no appreciable change in the other three groups.
Ten (10) ml. of enterotoxaemia type "D" antiserum was administered subcutaneously to ten affected sheep. An equivalent control group was taken. Seven days later, though groups were incomplete, there was no indication that the treatment had any effect.
Morbidity was regarded as high at about 60-70 per cent. affected with diarrhoea in some degree. Mortality reached approximately 3 per cent. The owner considered the set-back to growth at the beginning of winter to be more costly than losses by death.
Holding No. 2. In mid-November, 1957, six-hundred (600) Merino lambs, 2-2½ months old, running on native and improved pasture combined, and watered by running gullies, had little trouble. About 1 per cent. were affected with diarrhoea.
In a mob of one-hundred (100) lambs of similar age and breeding, running separately, a 12 per cent. mortality from a diarrhoeic condition occurred over a period of three and a half weeks. The morbidity was 75-80 per cent. Tenesmus and bleating in some were noted; but not anaemia. The rate of stocking was two ewes with their lambs per acre of improved pasture. Pastoral conditions at the time were near drought and watering was from a dam. Up to the beginnnig of the outbreak, growth of the lambs was considerably better than average.
Post-mortem features were similar to those reported on Holding No. 1. However, in both abomasum and intestines the cyst-like structures were noted to be smaller than similar bodies observed in autumn in older lambs on Holding No. 1. Faecal examination showed oocysts to be very numerous.
Holding No. 3. Commencing in early 1955, observations were made on four hundred (400) spring-drop Merino lambs on this holding. Half of these 400 died between February and October in spite of reasonably adequate nutrition and frequent drenching; which may have been applied at inappropriate times. There is little doubt that internal parasitism was the predominant factor as the cause of deaths. This included hacmonchosis of the ewes, resulting in cessation of milk flow.
However, in the light of all observations made and of post-mortem examination upon numbers of these lambs, it is now considered that coccidial infection was a significant contributing factor, though the conventional evidence of heavy oocyst production was not demonstrated.
Holding No. 4. About forty (40) of two-hundred and sixty-six (266) September-October drop Merino weaners showed evidence, at the beginning of March, 1958 of having been affected severely with diarrhoea. Three were affected with tenesmus and a quick bellow-like movement of the flanks whilst attempting defaecation. Some faeces lying in the yards was slightly blood marked but anaemia was not noted in affected sheep. Possibly as a result of pain there was an impulse among the sheep to bite at bark on yard rails.
The owner stated that trouble had started in November and repeated episodes, not necessarily involving the same sheep, had been noted during the summer, which was unusually dry. Watering was from a dam.
Post-mortem examination of a severely affected animal revealed a situation much as described for the first holding. However, free blood was present in the anal end of the rectum, though no erosion, ulceration or inflammatory change could be found which would indicate its source.
Careful examination was made for small intestinal worms, of which few were found. A laboratory finding of 400 ova per gram of very fluid faces was in line with a light haemonchus infestation observed. No coccidial oocysts were seen.
Diagnosis of Coccidiosis was based solely on field clinical evidence.
Holding No. 5. An outbreak of diarrhoea occurred in two hundred (200) Merino weaners during the last week in July, 1957. About two months prior to inspection the mob was drenched with phenothiazine and placed on turnips. Three weeks prior to inspection all were drenched with copper sulphate-nicotine because some sheep in the mob were affected with diarrhoea. A week later phenothiazine was administered to the whole mob (a double dose for good measure to any showing evidence of diarrhoea). Four days later, i.e. ten days before inspection, those showing evidence of diarrhoea, possibly still the same sheep, received a further double dose of phenothiazine.
Near drought conditions prevailed at the time, and for a fortnight immediately prior to inspection the mob had been fed good quality lucerne hay, which was not eaten freely. Twice a week, the weather being cool, the sheep were driven to water. In the paddock where the sheep were located was a "soak" or surface spring about 20 yards square. A hole had been scooped out in this to provide a water supply, a few days prior to inspection.
Three had died and three were in extremis. At post-mortem a diffuse catarrhal inflammation of the caecum, for about six inches from its tip, was observed. In the coiled colon particularly were appreciable quantities of dark, tarry, partly digested blood. The kidneys were dark, purplish pink in colour.
White cysts, less than 0.5 m.m. in size, as already described, were numerous in both abomasum and small intestine. In the mucosa of the small intestine were many ulcerations; all such as might be expected to result from rupture of the tiny cysts. These ulcerations were visible as greenish spots, stained either by phenothiazine or intestinal contents. It is not improbable that toxicity from over-dosage with phenothiazine was present in this outbreak.
Treatment. Sulphamezathine has been adopted by sheepowners as a method of treatment. Dose rates vary widely. Five to ten ml. 33⅔% solution per head for one to three days is used on affected animals. Those who have used this treatment are generally happy with results. It is known that owner-diagnosis and treatment has restricted opportunity for observations. No observations are known to have been made with a suitable control group maintained.
Discussion. Throughout these investigations a major difficulty has been to demonstrate to laboratory personnel the slight macroscopic lesions which the writer now believes to be so significant. In preserved tissues the small cysts lose their identity.
It has been found now that unpreserved small intestine can be carried for some hours in the car at summer temperature and then, using a standard specimen box lined with half-inch "Cane-ite," half a pound of dry-ice and newspaper packing, the material could be received by train forty-eight (48) hours after collection, in sound condition for macroscopic examination.
One of the earliest references in Australian literature to the minute, white cyst-like structures was by Johnston (1924), who was emphatic that Moussu & Marotel in their original account of a causal parasite of coccidiosis were in error in their belief that, to quote Johnston (1924), "numerous light-coloured tiny spots, just visible to the naked eye, each a more or less globular parasite, whose cytoplasm eventually divided into a very great number of minute fusiform spores" were stages of coccidia; additional to those they had described in greater detail.
He preferred to consider the minute cysts to be Gastrocystis gilruthi (Globidiron gilruthi).
Boughton (1942), working with calves, produced the following experimental evidence that the cysts, apparently similar to those seen here in sheep, were in fact schizonts:
(1) These bodies are found in large numbers only in calves known to be undergoing coccidial infections.
(2) In experimental infections, involving especially E. bovis, they appear in the greatest numbers toward the end of the prepatent period.
(3) No other type of merozoite-producing form is found in sufficient numbers to account for the enormous oocyst production characteristic of such infections, if allowed to run a full course.
(4) The bodies are never numerous following the massive oocyst production of such infections.
(5) The inocula used to produce the infections in question contained no recognisable sporozoa other than the sporulated oocysts of bovine coccidia.
(6) In one attempt out of two, a discharge of E. bovis oocysts was obtained in a week old, coccidia-free calf, five days after it had been fed material containing numerous schizonts and motile merozoites obtained from an experimental E. bovis infection.
Careful examination of the ileum of adult fat cattle at a local slaughteryard revealed an odd structure macroscopically similar to those described by Boughton (1942). In the absence of the evidence which he produced these would doubtless be considered Globidium besnoiti.
Variable numbers of structures, as illustrated by the plates published by Boughton (1942), in both macroscopic and microscopic studies, are to be found in the small intestine of young sheep. If normally careful search is made, it is unusual to be unable to find at least an odd one in sheep of any age. He also refers to the possible relationship of globidia of sheep to ovine coccidia, referring to the observations of a number of workers, including Marsh & Tunnicliff (1941), who described what, from clinical description and pathology, well could be considered to be Coccidiosis in the light of Boughton's findings. It is to be noted that, on occasion, numerous oocysts were present in faecal samples of some of Marsh & Tunnicliff's cases.
In one's own observations and the literature, there is a substantial body of circumstantial evidence that globidial infection in sheep is in fact infection with Eimeria spp.; the globidia being schizonts.
1. In cases of clinical and confirmed Coccidiosis substantial macroscopic infestation with globidia was found.
2. In no case has a heavy infestation with globidia been found in the abomasum. Where globidia have been observed in both abomasum and small intestine concurrently, the general impression from the scanty infection in the former is that it is aberrant.
3. Descriptive plates in Boughton's (1942) article on coccidial infection in cattle correspond well with what has been seen here in sheep. Motility of the merozoites has not been observed.
4. Light coloured spots, corresponding with schizonts, also have been described by Gaiger and Davies (1932), for the intestinal Coccidiosis of rabbits. Hart (1939) described colonies of schizonts, appearing like fig seeds in the small intestines of poultry.
Reports of exacerbation of symptoms following drenching with phenothiazine have been frequent. It is considered likely that dehydration resulting from prolonged diarrhoea predisposed to susceptibility to toxic effects.
Consideration of the life cycles of Eimeria spp. make it clear that oocyst production may not have commenced when acute symptoms are present. Consequently, low oocyst counts are not necessarily significant. For example, Wilson (1931) fed 8,000 sporulated oocysts of E. auburniensis to a calf which developed diarrhoea from 9th-13th day. Oocysts were not found till the twenty-fourth day.
Detailed descriptions of life cycles of the various ovine coccidial species not being available, or even the species of Eimeria present in Australia, interpretation of laboratory findings presents difficulties. However, demonstration of large numbers of oocysts, in the presence of diarrhoea, is regarded as significant; though the species involved and its relative pathogenicity may not be known.
Field diagnosis on a flock basis has been made on the following features:
A. Profuse diarrhoea with tenesmus and exaggerated movement of the flanks in at least some of the sick sheep. B.
A blueish "bloom" on faecal accumulation on the hocks of sheep in which diarrhoea has ceased. This has been assumed to be due to partly digested blood.
C. At autopsy the finding of schizonts in the mucosa is regarded as diagnostic of coccidial infection, though not necessarily of Coccidiosis. Minute ulcerations at the assumed site of ruptured schizonts may be found. These are regarded as indicative of damage in process; schizonts of damage to come and oocysts of past damage.
Economic Importance. Belschner (1953) stated that Coccidiosis is not of much importance in sheep in Australia, which may be very true of the sheep-raising areas of the Continent as a whole. However, Seddon (1952) expressed the opinion that its incidence is probably higher than is generally realised; due to confusion with Trichostrongylosis.
Investigation of local outbreaks of severe diarrhoea during the period 1955-58 supports Seddon's view. Use of phenothiazine as an anthelmintic and removal of some of the major nutritional stresses have compelled a more critical examination of cases of continuing diarrhoea in young sheep. Increased sheep breeding, and higher rates of stocking co-incident to pasture improvement, doubtless have promoted the incidence of Coccidiosis in the Armidale district.
Insufficient evidence has been secured to prove conclusively that ovine globidia are in fact schizonts of coccidia; and also that the white, minute cyst-like structures often seen, particularly in the lower small intestine of sheep, are in fact schizonts of coccidia. Such is the hypothesis which probably can be tested finally only by planned and controlled experiment.
(a) Details are given of some outbreaks of diarrhoea attributed to Coccidiosis in lambs and weaners during the years 1955-58.
(b) Evidence is set out that minute, white cyst-like structures in the intestinal mucosa of sheep affected with Coccidiosis are schizonts. Evidence is given also to support the contention that Globidia spp. are schizonts at autopsy.
(c) Field diagnosis is based on diarrhoea with tenesmus and exaggerated movements in the flanks, a blueish bloom on dried faeces, and the finding of numbers of schizonts at autopsy.
(d) The economic importance of ovine Coccidiosis in the Armidale district is probably greater than is generally realised.
It is a pleasure to acknowledge the generous assistance of colleagues at Armidale; Mr. Southcott, Senior Research Officer of C.S.I.R.O. Regional Pastoral Laboratory, Armidale; Mr. I. L. Johnstone, Veterinary Practitioner of Armidale, who carried out some observations prior to those reported and collaborated in some reported.
In particular, thanks are due to Mr. I. R. Littlejohns, Veterinary Research Officer of Glenfield Research Station, who has been responsible for laboratory examination of specimens and also has been most helpful with critical suggestions at all stages of the investigation.
Thanks are due also to the Director of Veterinary Research; for permission to publish this article.
Belschner, H. G. (1953)-"Sheep Management and Diseases": Angus & Robertson, Sydney.
Boughton, D. C. (1942)-N. Amer. Ver. 23:173.
Gaiger and Davies (1932)—"Veterinary Pathology and Bacteriology", Bailliere, Tindall & Cox: London.
Hart, L. (1939)-Aust. vet. J., 15:30.
Johnston, T. H. (1924)-Repr. Aust. Assoc. Adv. Sc., 17:712.
Marsh, H. & Tunnicliff, E. A. (1941)-Amer. J. Vet. Res., 2:174.
Seddon, H. R. (1952)—"Diseases of Domestic Animals in Australia. Part 4". Service Publication (Division of Veterinary Hygiene) Number 8. Dept. of Health.
Wilson-Virginia Polytech. Inst. Tech. Bull. 42 (1931) cited by Hagan & Bruner (1952)—"The Infectious Diseases of Domestic Animals". Cornell University Press: New York.