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The idea that a
microscopic creature on a blade of grass can end up as a large parasite
in the liver of cattle or llamas sounds like science fiction.
But that’s just what happens on a continual basis in cattle in
most of California according to John Maas, University of California,
Davis, Cooperative Extension veterinarian.
“Very few beef cattle
slaughtered in California are free of liver flukes,” Maas said. “The common liver fluke of cattle (and llamas), Fasciola
hepatica, has this bizarre life cycle.
“The animals ingest grass with an encysted stage of the fluke
present. After the animals
eat this contaminated grass, the juvenile flukes “burrow” through
the lining of the intestine, escape into the peritoneal cavity (the
inside of the abdomen) and migrate to the liver.
“Then during a period of about six weeks the parasites make
their way to the interior of the liver and finally arrive in the bile
ducts where they begin to lay eggs.
The fluke eggs are shed into the manure.
These eggs hatch and make their way to fresh water snails, which
they infect and undergo additional development.
They eventually emerge from the snail as young flukes and encyst
(form a resistant coating) on blades of grass.
When cattle and llamas ingest them, the life cycle can be
completed.”
According to Murray Fowler, DVM, “The affected llama will
become anorectic. Mucous
membranes may be pale, and pendant edema (swelling) may be seen.
The fiber becomes dry and brittle, with “breaks” associated
with intense periods of the disease.
Depression and emaciation will follow anorexia.
Either diarrhea or constipation may be seen.”
Fowler indicates some snail hosts are capable of maintaining the
infection for as long as 13 months when buried in dried mud during an
extended drought. The
flukes can persist for a few days to a few weeks while encysted on the
grass. Some of the cysts
may fall to the bottom of the water and be stirred up and ingested when
an animal walks into the water to graze or drink.
The cyst may survive for as long as 8 months on moist hay, but
the usual drying process will shorten life to a few weeks.
If flukes are a problem in local cattle and sheep, and llamas
inhabit similar swampy, poorly drained pastures, it is reasonable to
assume that the llamas will have a fluke problem also.
What damage
do flukes cause?
Maas said, “This is a common question, since such a high
percentage of our cattle in California have liver flukes.
The young flukes can cause quite a lot of damage as they migrate
through the liver. But, if
only a few flukes are migrating through the liver at one time, the
damage to the cattle can be minimal.
“With large numbers of migrating flukes, the damage to the
liver can be extensive. In
these cases, diarrhea, weight loss and jaundice (yellow mucous
membranes) can be observed.” In addition to direct damage to the liver, there are
secondary bacterial infection problems liver flukes can precipitate.
Redwater and Blacks disease are two that livestock owners are
concerned about.
Migrating flukes damage local areas in the liver causing low
oxygen tension, which the clostridial bacteria prefer, allowing rapid
growth in these damaged areas. Vaccination
with a multiple-antigen clostridial toxiod may prevent complications
from these diseases.
Another problem liver flukes seem to be associated with is
decreased fertility in cattle. Studies
show decreased pregnancy rates in replacement heifers and increased age
to puberty in heifers infected with liver flukes.
Nothing in the existing literature suggests similar problems in
llamas, but your neighboring cattle operations will be concerned.
Thus liver flukes can
cause losses in a number of ways: direct damage to the liver, with
weight loss and diarrhea; death loss due to secondary infections
precipitated by liver damage from migrating flukes; and decreased cattle
reproductive performance.
Can liver
flukes be eliminated or controlled?
“Because of our
relatively mild winter conditions, the abundance of snails (the
intermediate host) and wildlife reservoirs, it’s doubtful we’ll be
able to eliminate flukes on our ranches,” Maas said.
“We don’t have liver flukes as a problem in our feedlots or
dairies because of the absence of these sources or infection.
“Our best option is the use of drugs to kill the flukes during
strategic times of the year. Unfortunately,
the timing depends on individual ranch operation.
Killing the adult flukes in the liver of animals before turning
them into clean pastures seems to be the most cost-effective
strategy.”
Maas said this not only kills the flukes, but it prevents further
shedding of eggs in the pastures. Maximum
transmission of flukes occurs in spring and summer in the warmer regions
and late summer to fall in cooler areas.
Depending on pasture rotation schedules, the use of drugs to kill
flukes in the fall or late winter/spring should be the minimum
management strategy.
Which drugs
are effective against liver flukes?
“Currently there are only two drugs available that are
effective against liver flukes in cattle”, Maas said.
“Both work best against the adult flukes, but there is some
effect on the migrating juvenile flukes.
Clorsulon is effective only against liver flukes and it is sold
alone as Curatrem or in combination with ivermectin as Ivomec
Plus. Fowler
recommends clorsulon at a dose of 7-mg/kg-body weight.
This is given twice at 45-60 day intervals.
C. Norman Evans, DVM recommends Curatrem
at 3.5mg/lb orally, repeated 60 days later.
Curatrem can be
used to kill the flukes alone or Ivomec
Plus can be used to kill the flukes plus internal parasites
(worms) and external parasites (including sucking lice).
Additionally, albendazole (Valbazen)
has activity against flukes and internal parasites.
All of the drugs and combinations of drugs have advantages and
disadvantages in terms of costs, ease of administration, withdrawal
times, and effectiveness. Maas
recommends consulting your veterinarian to be certain which product will
work best for a particular operation.
He also suggests that
ranchers review with their veterinarians the time of year that will be
most cost-effective for administration of drugs to kill liver flukes.
Evans suggests some control strategies that include; avoiding
pastures in swampy areas (high snail populations); deworm strategically
at the end of the grazing season and repeat within 8-weeks; on farm
quarantine and fecal check all imported ruminants from infected areas
(much of California according to Maas).
A neighboring commercial
operation raising sheep or cattle for meat production can be very
concerned about the livestock population surrounding their ranches.
In addition to consulting with your veterinarian, discussing
timing of administration of fluke killing drugs with your neighboring
ranchers will enhance the drugs performance and ally some of the
concerns of the “other guy’s” operations.
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Raising
Mystical Llamas in Magical Napa
