Diagnosis of Liver Fluke Infection in Cattle

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Diagnosis of Liver Fluke Infection in Cattle
Donald W. Briskey DVM
A Diagnostic Review
Economic Impact
of Fluke
Infestation in
Kansas Feedlots
J. R. Brown
Merial Veterinary
Bulletin
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Economic
Importance of
Liver Flukes and
Fluke Control in
Cattle From the
Gulf Coast
Region
D. Gerdon
Merial Veterinary
Bulletin
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The Parasite
Fasciola hepatica, the common liver fluke, is the most likely cause of liver
fluke disease in domestic ruminants in the United States. The fluke life
cycle requires a snail intermediate host to complete transmission to a new
ruminant host. The parasite is most often found in Florida, along the Gulf
Coast, in the Pacific Northwest, in portions of the Rocky Mountains, and
Hawaii. Other areas, such as Oklahoma, Nebraska and Kansas, have
reported local cattle with fluke disease. This suggests liver flukes are
expanding their range.
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Diagnosis - Examination of the Liver
Diagnosis of liver flukes in cattle is a challenge. The most direct technique
is liver examination at slaughter or necropsy. While this method can
provide information about the status of liver flukes on a particular property,
it does not evaluate annual variations of infection level or lend itself to use
with arriving feedlot cattle from unknown origins.
Diagnosis
Fecal Exam
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Diagnosis - Fecal Exam
Another diagnostic procedure is fecal examination for F. hepatica eggs.
Two points need to be kept in mind when interpreting fecal exam results for
F. hepatica:
a) The prepatent period for F. hepatica is 2-3 months. As a
result, fluke eggs cannot be demonstrated early in the infection.
A group of cattle could be carrying a high burden of young
flukes, but no fluke eggs would show up in their manure.
b) The quantitative value of fluke egg counts is questionable.
Fluke eggs pool in the gallbladder and intermittently pass into
the feces.(1) The fluke egg count on any given day often has
little relationship to the number of flukes in the liver. An
animal with a negative fecal could be parasitized, whereas a
high fecal fluke egg count could just be a high number of eggs
leaving the gallbladder that day, rather than a large fluke
burden.
Fecal Examination Techniques
Fecal examination for fluke eggs requires use of fecal sedimentation,
formalin-ether, or FLUKEFINDER® techniques. Commonly used flotation
procedures open the operculum and sink the fluke egg rather than floating it
for surface detection.(2,3) The FLUKEFINDER screen system has the
advantages of being faster and simpler than other techniques and it requires
no chemicals. The FLUKEFINDER may also be used in the field for
evaluation of arriving cattle.(4) In monitoring liver fluke infections, it is
critical to remember that the fecal exam techniques most frequently used
for nematodes will not demonstrate fluke eggs.
Fluke Egg Seasonality
Seasonality of new liver fluke infections also affects the time of year that
fecal exams can be expected to show fluke eggs. In an Idaho study, calves
picked up an increasing number of flukes as the pasture season progressed.
Transmission peaked in November.(5) With the 2-3 month prepatent
period, the majority of fecals wouldn't be positive until December or later.
Fecal exams for flukes at the typical processing time of October would miss
immature fluke infections in Northwest calves.
In Louisiana, the Gulf Coast transmission pattern for flukes has been
demonstrated to be primarily February-July.(6) Allowing for the prepatent
period, fecals start to show positive for fluke eggs 2-3 months after the peak
transmission times.
Disease Signs
The signs caused by liver flukes in cattle range over the following
syndromes:
a) chronic disease with anemia, bottle jaw and overall
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Diagnosis of Liver Fluke Infection in Cattle Page 3 of 4
unthriftiness.
b) subacute disease with anemia, hemorrhage and death in 7-10
weeks.
c) acute death.
d) subclinical disease with no clinical signs.
Treatment Considerations
The economic impact of F. hepatica has been documented in several
publications.(7-10) The financial losses are stimulation for accurate
evaluation of a herd or group of cattle. Consideration of the cow's role as a
source of fluke infection for their calves is also necessary. In a study of beef
cows from the western United States, 19.2% of the cows showed evidence
of liver fluke infection at slaughter.(11) Cows infected with liver flukes are
a prime source of pasture contamination. Flukicide use in cows may help
control pasture contamination with liver fluke eggs.
In farm and ranch situations, a veterinarian can evaluate past years'
experience, fecal exams, and liver checks from cattle slaughtered or
necropsied on the farm, in order to decide on flukicide use. A feedlot
veterinarian would seldom have this much information to base flukicide use
on. Current livestock transportation services easily move cattle from fluke
endemic areas to feedlots in any part of the United States. If the origin of
incoming feedlot cattle is known, liver fluke prevalence in the area of
origin can be researched. If cattle are purchased from the same source over
a period of years, past liver condemnation rates for fluke infection can be
examined. The FLUKEFINDER system can also be used to check fecals of
arriving cattle for fluke eggs.
Accurate data regarding the fluke status of acquired cattle are often lacking.
In this case, timing of treatments should follow this rationale:
! Cows can be treated at any time of year, since they have had several
seasons to acquire liver flukes.(11)
! Northern calves should be treated for flukes as late in the fall as
possible. Late fall treatment allows the maximum number of flukes in
the calves to mature into adult flukes, which are most easily killed.(5)
! Southeastern calves should ideally be treated for flukes beginning in
September. This allows the last fluke picked up in June or early July
to mature and be easily killed.(7)
! Feedlot animals should be treated at entry. This provides the best
insurance against losses from flukes when the fluke status of arriving
cattle is unknown.(10)
Flukicides
Two formulations of cattle flukicides are marketed by Merial in the United
States. CURATREM® (clorsulon) drench is available to treat both mature
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Diagnosis of Liver Fluke Infection in Cattle Page 4 of 4
and immature flukes. IVOMEC® Plus (ivermectin and clorsulon) Injection
treats sucking lice, mange mites, grubs, and nematode parasites plus mature
liver flukes. These products provide the outstanding parasite control of
ivermectin plus the added insurance of fluke control.
References
1. Zimmerman G. Personal communication. Oregon State University.
2. Sloss MW, Kemp RL, Zajac AM. Veterinary Clinical Parasitology,
6th edition; Iowa State University Press, 1994; 10.
3. Faler K, Faler K. Improved detection of intestinal parasites. Modern
Vet. Practice, April 1984; 273-276.
4. Georgi JR. Parasitology for Veterinarians, 4th edition. W.B.
Saunders, Co., 1986; 228, 248.
5. Hoover RC, Lincoln SD, Hall RF, Wescott R. Seasonal transmission
of Fasciola hepatica to cattle in northwestern United States. JAVMA,
1984. 184: 695-698.
6. Malone JB, Loyacano AR, Hugh-Jones ME, Corkum KC. A threeyear
study on seasonal transmission and control of Fasciola hepatica
in cattle in Louisiana. Prev Vet Med, 1984; 3:131-141.
7. Ross J G. Economics of Fasciola hepatica infections in Cattle.
British Vet J; 1970; 126: xiii-xv.
8. Simpson JR, Kunkle W, Courtney CH, Shearer JK. Economic
analysis of controlling liver flukes. Agri-Practice, 1985; 6.
9. Hope-Cawdrey MJ, Strickland KL, Convey A, Crowe PJ. Production
effects of liver fluke in cattle. British Vet J, 1977; 133: 145-159.
10. Johnson EG. Effects of liver flukes on feedlot performance. Agri-
Practice, 1991; 12:33-35.
11. Briskey DW, Scroggs MG, Hurtig FS. A prevalence survey of liver
flukes (Distoma) in beef cows at slaughter in the western United
States. Agri-Practice, 1994; 15: 8-11.
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