Table Of ContentThe
Common Liver Fluke
Fasciola hepatica L.
BY
E. M. PANTELOURIS
Department of Zoology
The Queen's University of Belfast
PERGAMON PRESS
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Copyright © 1965
Pergamon Press Ltd.
First edition 1965
Library of Congress Catalog Card No. 63-21135
PRINTED IN GREAT BRITAIN BY THE BAY TREE PRESS, STEVENAGE, HERTS.
PREFACE
THE liver fluke, Fasciola hepatica^ causes great damage to stock
throughout the world, and is responsible not only for "liver rot",
the uncomplicated fascioliasis, but also (in association with the
bacterium, Clostridium oedematiens) for the notorious "black
disease". Moreover, numerous cases of human fascioliasis are
reported each year.
To its economic importance should be added the great bio-
logical interest of a Trematode with a succession of free and
parasitic generations, ending up in a physiological relationship
with the mammalian host that presents a variety of important
aspects for study; a Trematode moreover that has so far avoided
radical control by man: drugs fail to kill its younger migratory
stages, vaccines are ineffective, neither ecological measures nor
grazing management eliminate all risk to stock (although they
greatly reduce it), and many wild animals provide a reservoir of
infection.
The liver fluke is therefore the concern of the zoologist as well
as the veterinarian and agriculturalist. It is the aim of this book to
provide: for the research worker, a thorough review of the exten-
sive literature on the subject and a comprehensive bibliography,
as well as practical details of techniques for handling material;
for the veterinarian, biologist and agriculturalist, an account of our
knowledge about this important animal and the disease it causes
and of the way in which this knowledge has been accumulated.
The author is indebted to many for generous help with the
work involved in writing this book. I wish particularly to thank
Dr. J. F. Gracey, Professor R. A. R. Gresson, Dr. D. L. Hughes,
Miss Barbara Knox, Dr. C. B. Ollerenshaw, Mr. T. Ross, Mr.
A. W. Stelfox, Dr. L. T. Threadgold and Dr. J. R. Todd, who
have discussed various aspects with me and have provided data
and information from their work. Dr. Threadgold has taken the
trouble to prepare original drawings illustrating his findings about
the structure of the worm. My sincere thanks are also due to
vii
Vlll PREFACE
those who have helped in the search for the more inaccessible
references or with translations from Hungarian, Japanese, Polish
and Russian. Finally, I thank Miss Barbara E. Knox for checking
the manuscript and Mr. S. Armstrong for expert photographic
work.
E. M. P.
Zoology Department,
Queen's University, Belfast.
ACKNOWLEDGEMENTS
The author would like to acknowledge the helpfulness of
publishers and authors who have given permission for the use of
illustrations from their publications. In each case the source of
the material is indicated by the reference quoted in the caption to
the figure.
Vlll PREFACE
those who have helped in the search for the more inaccessible
references or with translations from Hungarian, Japanese, Polish
and Russian. Finally, I thank Miss Barbara E. Knox for checking
the manuscript and Mr. S. Armstrong for expert photographic
work.
E. M. P.
Zoology Department,
Queen's University, Belfast.
ACKNOWLEDGEMENTS
The author would like to acknowledge the helpfulness of
publishers and authors who have given permission for the use of
illustrations from their publications. In each case the source of
the material is indicated by the reference quoted in the caption to
the figure.
CHAPTER 1
LIFE CYCLE AND SYSTEMATICS
THE common liver fluke, Fasciola hepatica L., is a parasite flatworm
that can be collected in large numbers from the bile ducts of in-
fested cattle, sheep and other mammals. The infestation causes
loss of condition, renders the liver unsuitable for human consump-
tion and reduces the amount and quality of meat and milk pro-
duced. In severe cases the infestation may cause death either
directly, or indirectly by initiating or aggravating bacterial infec-
tions, as in the case of "black disease".
In years when weather conditions favour the parasite, "liver
rot" or fascioliasis (as the liver fluke disease is called) may assume
the proportions of an epidemic and decimate flocks. It is, however,
very difficult to assign a figure to the economic losses caused
throughout the world by fascioliasis; no comprehensive statistics
exist, much of the damage is indirect, taking the form of loss of
condition and productivity of the animals, and the disease may
be caused also by other similar fluke-worms. However, to
indicate the size of the problem, a list is given of some relatively
recent reports from various countries (Table 1).
Outline of the Life Cycle (Fig. 1)
The worms found in the bile ducts of mammals represent the
adult stage of the liver fluke. They are leaf-shaped, about 30 x
10 mm, whitish or tinted. They are hermaphrodite and produce
enormous numbers of eggs; these reach the host gut with the
bile and are shed to the outside with the faeces.
By this time the egg contains an early embryo. Under favour-
able conditions, this develops further whilst still within the egg
to form a conical larva, covered with a ciliated epithelium and
equipped with a pointed tip or rostellum at its anterior end; this
larva is called a miracidium.
3
X w n o o z < w a w
%
m
y froes eaths 12-9 60 18
nlec p D
ASCIOLIASIS. Estimates of incidence, maidetection of eggs in fa Cattle Sheefected % Infected % 38-6 50 46 91 40 15
F n
I
F
O
ON THE INCIDENCE Abattoir statistics (Livers condemned) Sheep Cattle /o /o 63-3 15-3 29 17-7 8-3 20-9 21-5 35-5 19-1 10-3 2 5-7 68 7-5 37-5 2-6
A
T
RECENT DA Period 1958-59 1946-54 1958 1954, June 1951-52 1956 1945 1952 1953 1960 1957-62 1956-61 1951-57 1958 1952
E
M
O a
S m
TABLE 1. Region Anglesey Ireland, Northern Scotland, Central Wales Devon United Kingdom Poland Lithuania Rumania Bavaria, Regensburg Bavaria, Regensburg Sweden, Ostergotland Milan (Italy) Netherlands Rhodesia, Southern South Africa Japan Japan, HigashimatsuyaPuerto Rico U.S.A. Gulf Coast U.S.A.
e
c
eren 1 2 3 4 5 6 7 8 9 10 10 11 12 13 14 15 16 17 18 19 20
f
e
R
£ tfl O ° W ^ ^ ►< J~j K £ n
Data from various regions are not strictly comparable; for example, in most countries only the rather heavily infested livers are condemned, and the thoroughness of the inspection procedure may vary. The data assembled therefore in this Table serve to indicate the widespread incidence of fascioliasis and its substantial economic importance rather than to establish valid comparisons of incidence. Furthermore, incidence varies enormously from year to year depending on weather conditions. Anon. (1959). Figure refers to ewes, 12,000 of which died in the epidemic that winter. Data supplied by the Belfast City Veterinarian, Dr. J. F. Gracey. See also Table 19 and Fig. 62. eta/.;Parnell see Fig. 62. In a survey of "a typical hill sheep farm in the Western Highlands", Wilson 0/07.(195 3) found 50 percent of the ewes and whethers and 24 per cent of the hoggs infected. Anon. (1959). Peck (1957). Data from Hatherleigh knackery. Peters and Clapham (1942). Data from 486 slaughterhouses (73,000 cattle). Stefanski (1959). et a/.Babenskas (1958). Lungu(i959). Keller (1952). Salinas (1954). Carrara and Recalcati (1961). Honer and Vink (1963). Survey of 3 largest abattoirs covering 710,401 lambs under 13 months old, January 1957-June 1962.See Fig. 63. Fasciola gigantica. Condy (1962). Data refer to infection with Purchase (1957). Ono(i958). et a/,Takashino (i960). Rivera-Anaya and De Jesus (1952). Schwartz (1947). Olsen (1949a).
N.B. i 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
6 THE COMMON LIVER FLUKE
On hatching from the egg, the miracidium rotates and moves
in the water by the action of its cilia, but it can survive for only a
few hours, unless it finds and enters a suitable snail host. If a
snail of the species Limnaea truncatula is available, the miracidium
is attracted to it and bores, rostellum first, into its tissues. In the
process it loses the ciliated cover and elongated shape, to become
a sac-like sporocyst.
FIG. 1. Diagrammatic representation of the life history of the
liver fluke.
1. The adult parasite in the bile ducts of a sheep; its eggs are shed
on the pasture. 2. The ciliated miracidia hatching from the eggs enter
a snail host. 3. The larvae have now formed rediae in the digestive
gland of the snail. 4. The rediae have given rise to tailed cercaria.
5. The cercaria become free of the snail, encyst on the grass and the
cysts are picked up by grazing animals. The cyst releases the
metacercarium in the alimentary canal of the final host, and the young
fluke migrates through the viscera to enter the liver.
As the sporocyst grows within the snail, new and different
larvae develop inside it: the rediae. These are mobile and break
free by rupturing the wall of the mother sporocyst. In favourable
cases, the sporocyst finds itself eventually in the pulmonary cavity
LIFE CYCLE AND SYSTEMATICS 7
of the snail, but the redia migrates from there to the digestive
gland or "liver" of the snail host.
Feeding on the substance of the snail liver, a redia gives rise
to several daughter rediae. Each one of these may again repeat
the process, growing and producing a further generation of rediae.
Eventually, however, the rediae give rise to still another type of
larva, the cercarium. This is round with a long unforked tail; it
leaves the snail through the pulmonary cavity and swims free in
water, finally attaching itself on to a blade of grass or other object;
in the meantime it loses its tail and becomes a metacercarium
enclosed in a cyst.
It is these cysts that are infective to grazing mammals who may
pick them up with the grass. In the stomach of the mammal the
metacercarium excysts, bores through the wall of the gut into the
abdominal cavity and reaches the surface of the liver. It then
bores into the liver mass and tunnels its way through it, feeding
and growing, until, as a mature egg-producing adult, it settles in
the bile ducts. In badly infested animals, tens or even hundreds
of flukes can be found blocking the larger bile ducts. Their eggs
reach the host's intestine with the bile, and are shed with the
faeces, to begin another cycle.
To summarize, the life cycle of the liver fluke comprises
several morphologically distinct stages; of these, both sporocysts
and rediae are capable of multiplication, so that up to a few
hundred of cercaria may eventually arise from a single egg. Two
hosts are involved in this life-history, a snail and a mammal.
The free larval stages are produced in large numbers but require
moisture, and are non-feeding and short-lived.
The Discovery of the Life Cycle
The fascinating story of how this complex life cycle was
elucidated has been told by Taylor (1937) and in more detail by
Reinhardt (1957). Some points have been discussed by Jefferies
and Dawes (1960).
The earliest references are listed by Schaper (1890), but the
ideas then current about the liver fluke had little foundation on
facts.
An idea of the prevailing explanations in those times may be
