1974 ford PREY-PREDATOR TRANSMISSION IN THE EPIZOOTIOLOGY OF OVINE SARCOSPORIDIOSIS Ciclo, transmision

PREY-PREDATOR TRANSMISSION I N THE EP‘IZOOTIOLOGY OF OVINE SARCOSPORIDIOSIS
The ubiquitous nature of Sarcocystis spp infections
in many host animals is well recognlsed (Levine 1961).
It is usual to find microscopic cysts in histological
sections of striated muscle from sheep in Australia.
Detection of macroscopic muscle cysts in aged animals
at the abattoirs leads to condemnation of the tissue and
in severe cases to rejection of the carcass. Information
on rejection at slaughter collected by officers of the
Australian Department of Primary Industries and of
the South Australian Department of Agriculture during
the last six years has led to recognition of the parasite
as a problem in this state. Although the incidence of
reported macroscopic cysts in animals from the lowrainfall pastoral zone is at a low level, around 1 % .
the level of rejection in some lines of sheep from elsewhere, such as from Kangaroo Island, approaches
100%.
Initial histological studies in this laboratory, with
naturally infected grazing lambs from a local experimental field station, have shown Sarcosporidia cysts
about 10 p in diameter in the muscles by four months
of age. Of the three possible modes of infection for
sheep - oral (by grazing), parenteral (via biting arthropods), or trans placental (maternal) -the hypothesis
of transmission by ingestion was considered as most
likely. It was considered probable that Sarcocystis had
a similar mode of spread to the other common muscle
parasite of sheep, Toenia ovis, that is a dog-sheep
cycle, and this was first investigated.
In R pilot trial in this laboratory, dogs which were fed
macroscopic Surcocystis cysts from the oesophagus of
sheep produced a high level of small sporozoan-type
cysts in their faeces from 14 days after infection. Control dogs failed to do so.
More critical work was then undertaken.
Laboratory Beagle bitches at the colony held at this
Institute were kept in a manner to preclude sporozoa
infection and maintained on pyrimethamine” 50 mg/ 100
kg by mouth twice weekly and sulphaquinoxalinef
0.05% in drinking water for three days weekly to control any possible maternal transmission. All food was
processed (heat sterilised). Specific pathogen free (SPF)
puppies bred from these bitches were reared under
quarantine conditions without drugs. Faeces from the
SPF pups were examined at least weekly for several
months to ensure there was no contamination or passage
of a coccidian-like sporoza infection.
The SPE pups were infected with Sarcocystis by feeding fresh meat from Merino lambs containing microscopic muscle cysts. These Iambs had been dosed 5
months previously with the small faecal cysts from other
dogs fed muscle cysts in meat in anticipation of the
above hypothesis. Faeces from the infected SPF dogs
were examined daily between 5 and 50 days after feeding, and otherwise three times each week until they had
been negative for two weeks. A qualitative technique
sensitive to approximately one cyst in five grams and a
modified McMaster counting technique, with saturated
magnesium sulphatc as the flotation liquid, were used
a t each collection.
DOG 0 1 A
....._..__
I
4
a
0
0
10
20
30
40
I 0
60
Figure 2. Sarocystis sporocyst from dog faeces.
x
W
LL
0
ln
r
ln
>
u
0
a
0
n
ln
0
10
20
30
DAVS
SINCE
INFECTIVE
40
50
60
FED
MEAT
Figure 1. The excretion of Sarcocystis sporocysts by dogs fed
muscle cysts from sheep.
33
Small cysts were detected in the faeces of the dogs
fed meat after 15 days, reaching a peak of the order
of 50,000 to 70,000 per gram of faeces around 21 t o
24 days after feeding, as shown for two replicates in
Figure 1. After 60 days only low numbers were detected,
and no cysts were seen after 90 days. The cysts (Figure
2) were very uniform in size, 15 p long x 10 /I wide.
They were considered as coccidian type sporocysts, and
contained four spcrozoites and a residual body when
excreted. Rarely a pair of cybts surrounded by a thin
envelope was detected.
There is thus little doubt that Srircocystis sp, at least
from the sheep, is a sporozoan parasite with a preypredator transmission. These results confirm a similar
relationship found by transmission from sheep t o cats
in Germany (Rommel et a1 1972) and in Australia
(Durie, 1973, personal communication) However, Rom*“Darapr,im” (Burroughs Wellcome).
t“Embaz1n” ( M a y and Baker).
Australian Veterinary Journal, Vol. 50, January, 1974
me1 e f a1 (1972) failed to transmit the organism from
sheep to dogs, from which it could be implied that it
may be normally spread by cats in a similar way to
that shown for Toxoplasma (Hutchison et a1 1971).
This is unlikely to be of primary importance for Sarcocystis from sheep as the known epizootiological features
of the two organisms are different. Further, Dubey
(1973) recovered what appeared to be Sarcocysfis
sporocysts from only one of 516 cats. He designated
these lsospora cati, the larger form of 1. bigemina, as
discussed by Wenyon (1926).
The close association of working dogs with sheep in
Australia. and the potential spread of the small faecal
cyst in dust is sufficient to explain the spread of the
organism and there is no need to assume an alternative
significant source of spread to sheep such as by feral
cats, although this must still be assessed. Dogs have
ample opportunity to become infected with Sarcocysfis,
as with Taenia ovis, due to the management practlces
of sheep farmers who feed sheep meat and allow
sufficient freedom of dogs to eat from fresh carcasses.
If sheep dogs can pass ninety million sporocysts within
two months of eating sheep meat as did each dog in this
experiment, sheep may be highly exposed to infection
when being yarded. Further, our studies of faeces from
other dogs submitted for diagnostic examination indicate
a continuing excretion of low numbers of Sarcocystis
sporocysts from many dogs. Levine and Ivens (1965)
also detected similar faecal cysts from four of 139 dogs,
but at the time speculated that they may be sporocysts
frced from the oocysts of Isospora rivolta.
Further studies are in progress to characterise the
stages of the Sarcocysfis involved in this prey-predator
transmission, and to examine the development in sheep
reared Sarcosporidia free.
I am grateful for the skill applied by Susanne Bleuler
in detecting and counting the sporocysts. Financial
support was provided by the Australian Meat Research
Committee.
G. E. FORD, M.V.Q., Ph.D.
Veterinary Pathology Division,
Institute of Medical and Veterinary Science,
Frome Road,
Adelaide, South Australia, 5000.
15 October 1973.
References
Dubey, J. P. (19731-4. Am. vet. med. Assoc. 162: 873.
Hutchison, W. M., Dunachie, J. F., Work, D., and Siim,
J. Chr. (1971)--Trans. R. SOC. frop. Med. H y g . 65:
380.
Levine, N. D. (1961 )-“Protozoan Parasites of Domestic Animals and of Man”. Burgess; Minneapolis.
Levine, N. D. and Ivens, V. (1965)-J.
Purasit. 51:
859.
Rommel, M., Heydorn, A. 0. and Gruber, F. (1972)Bed. Munch. tierarztl. Wschr. 85: 101.
Wenyon, C. M. ( 1926 )-“Protozoology”.
Bailliere,
Tindall and Cox; London.
Whiting, R. H. (1972)-Ausr.
vet. J . 48: 449.
DETACHED HEADS IN THE EJACULATE OF A HEREFORD BULL
The proportion of detached (loose) heads in the
ejaculate of normal bulls is less than 1 2 % (Lagerlof
1934; Herman and Swanson 1941; Haq 1949; Blom
1950a; Campbell ef a1 1960). The percentage of detached heads in the ejaculates of a series of 85 normal
bulls studied at our laboratory was 5.1 +- 0.74. Increased
proportions of detached heads are associated with
te‘iticular degeneration and with testicular hypoplasia
(Lagerlof 1934; Haq 1949; Blom 1950a, b; Rollinson
1951) and are found in cases of seminal vesiculitis,
ampullitis and epididymitis (Blom 1950a; Galloway
1964).
A specific condition characterised by a high proportion of detached heads has been described in Guernsey
bulls. Cases have been reported in Britain (Hancock
and Rollinson 1949; Haq 1949; Hancock 1955) in the
island of Guernsey (Alun-Jones 1962) and in South
Africa van Rensburg et a1 1966). In the examination
of semen the main features were the generally high
proportion of detached heads, a high proportion of
abnormal tails and low proportion of head abnormalities. Motility was poor to good. Affected bulls were
sterile or of very low fertility.
Eight Hereford bulls of low fertility with a high proportion of loose heads were described by Williams
(1965). Ejaculate volume and concentration were
normal. Motility was poor. In four of the bulls there
was a high percentage of other abnormal forms.
In August 1972 a two year old unmated Hereford bull
was examined for routine breeding soundness, which
included a detailed study of spermatozoan morphology.
The bull was in good health and condition. Physical
examination of the reproductive tract revealed no abnormality. The bull had good libido and his serving
behaviour was normal.
Australian Veteritiary Journal, Vol 50, January, 1974
Semen was collected using an artificial vagina on I 1
August 1972 and 14 August 1972. The bull was run
with 30 cows for 10 weeks from September to mid
November. Further ejaculates were collected for study
on 29 March 1973. Semen was examined as described
by Galloway (1965). The results were presented in
Table 1. Twenty-eight of the 30 cows became pregnant
as judged by rectal examination ten weeks after the
completion of mating.
The only abnormal feature of the semen examination
was the consistently high proportion of detached heads.
The cause of this abnormality is not known. The low
proportion of other morphological abnormalities indicated there was no testicular degeneration or testicular
hypoplasia, and that the condition was dissimilar from
that described in Guernsey bulls. In contrast with the
semen of the Hereford bulls described by Williams
(1965) motility was good. The lack of leucocytes in
the semen and the findings at physical examination indicated an absence of inflammatory lesions.
The results suggest that fertility in the natural mating
situation need not necessarily be impaired by a proportion of detached heads greatly outside normal limits.
Caution should be exercised at reproductive soundness
examinations in interpreting such findings in otherwise
normal animals. The expert technical assistance of Miss
Jill Norman in semen assessment is gratefully acknowledged.
P. J. WRIGHT, B.V.Sc., M.V.Sc.
Department of Veterinary Clinical Studies,
University of Melbourne,
Werribee, Victoria, 3030.
28 June 1973.
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