HERD HEALTH PIH-44
PURDUE UNIVERSITY. COOPERATIVE EXTENSION SERVICE.
WEST LAFAYETTE, INDIANA
Internal Parasites
Authors
LeRoy G. Biehl, University of Illinois
R.F. Behlow, North Carolina State University
E. Batte, North Carolina State University
Reviewers
Ralph F. Hall, University of Tennessee
Gerald M. Sandidge, Marshall, Missouri
Even though excellent deworming programs are available, it
is estimated that internal parasites cost the pork industry an
astonishing 250 million dollars or $3.00 per pig produced annu-
ally. Forty-three million pounds of liver were condemned by USDA
inspections from 90 million hogs slaughtered in 1980. Nearly all
of these livers were condemned because of ``white spots'' which
are tissue wound scars left from the migration of immature worms
(larvae).
Worm infections reduce growth rate and feed efficiency
directly by competition for food and damage from larval migration
through various organs. In addition, the tissue injury enhances
the deleterious effects of other disease-producing microorganisms
such as Mycoplasma hyopneumoniae or Treponema hyodysenteriae.
Some degree of worm infection occurs on most swine farms.
Studies indicate that 80-90% of U.S. swine herds are infected
with one or more species of worms. Efficacious swine dewormers
are available and a magazine survey indicated that 74% of the
producers deworm their hogs an average of 1.8 times during a pro-
duction cycle. If such deworming practices really exist, it is
difficult to ascertain why worm prevalence is so high in U.S.
swine. To effectively lower the worm population in a swine herd,
several management practices must be used. Proper selection of
dewormers and proper timing of the deworming are important.
Additional management tools include manure removal and good sani-
tation practices during the production cycle. A knowledge of the
life cycle and the tremendous reproductive capabilities of the
various swine worms will aid one in understanding how best to
break the life cycles of different parasites.
Characteristics of the Common Worms
Roundworms
The large roundworm (Ascaris suum) is the most common and
largest worm that infects young swine. The roundworm (Fig. 1) may
be 10-15 in. long and is often observed in feces or hanging from
the rectum of a pig. The large roundworm normally lies in the
anterior small intestine, but will occasionally migrate into the
stomach. When this happens, the pig may vomit material containing
the worms. The female adult roundworm can produce up to 1,000,000
eggs per day. Roundworm eggs are remarkably resistant to adverse
climate conditions and disinfectants.
Worm eggs must embryonate before they become infective.
Under optimal conditions of high humidity and warm temperature,
eggs embryonate and become infective about 10-14 days after they
are passed. Therefore, fresh manure is not infective and, if ing-
ested by pigs, the eggs will pass on through undigested and
unhatched. Cold exposure delays or completely halts embryonation.
Once the embryonated infective eggs are swallowed, they
hatch and the larvae penetrate through the intestine wall into
the bloodstream and are taken to the liver. The larvae migrate
through the liver back into the bloodstream and end up in the
lungs. They migrate from the lung tissue into the airways, travel
up the trachea to the mouth, are swallowed, and develop into
egg-laying adults in the small intestine. Since the entire life
cycle from ingestion of the egg to egg laying requires about nine
weeks, 8-week-old pigs may harbor immature worms but test nega-
tive on fecal examination.
When the roundworm (ascarid) larvae migrate through the
liver, the body's defense mechanism produces an inflammatory
reaction. A white spot is formed that can be readily seen. If
several are present at slaughter, condemnation of the liver
results (Fig. 2).
White spots reach maximum size 10-14 days following infec-
tion, but will regress with complete tissue repair 35-42 days
following infection. Therefore, white spots observed at slaughter
are the results of an infection within the last six weeks. Evi-
dence indicates that an acquired resistance develops following
the initial roundworm infection. Succeeding exposures to
roundworm eggs result in most of the larvae being trapped and
destroyed in the liver. Larvae from secondary exposures that
escape the liver entrapment will be engulfed and destroyed during
larval migration through lung tissue. But a very few will escape
both liver and lung engulfment and end up in the intestine as
egg-laying adults. These few that survive the attack of the liver
and lungs remain as the perpetuators of the species and keep the
swine facilities contaminated with eggs.
Following the initial infection, the migration of larvae
through the lungs may cause a nonproductive cough. During this
migration phase, the pig also will be more susceptible to
respiratory infections such as influenza and mycoplasma pneu-
monia.
Whipworms
Whipworms (Trichuris suis) are common throughout the United
States and are more common in hogs raised on pasture. The adult
whipworm (Fig. 3) is 2 to 3 in. long and resembles a buggy whip.
The life cycle of the whipworm is direct in which larvae
penetrate only the inside lining of the large intestine and cecum
where they develop into adults. A large infestation of worms can
cause sufficient damage to the intestine, resulting in diarrhea
and death. Diarrhea often occurs two to three weeks after pigs
have been moved from a nursery to an old pasture or contaminated
area. It may resemble bloody dysentery and be unresponsive to
antibiotic therapy.
Nodular worms
Nodular worms (Oesophagostomum spp.) are the most common
worms found in adult swine, although they also often infect young
pigs. The adult worm (Fig. 4) is 1 in. long and thick. It lies
in the large intestine and probably causes little harm, but dur-
ing the life cycle, the larvae encyst in the intestinal wall and
cause a nodule about the size of a pea. Mild infections produce
few clinical signs, but severe infections can result in excessive
weight loss and contribute to the ``thin sow syndrome'' during
lactation.
Threadworms
Intestinal threadworms (Strongyloides ransomi) are small
worms that may infect the sow. She can transmit the living larvae
through her colostrum to nursing pigs. Pigs nursing the infected
milk develop a severe diarrhea at about 10-14 days of age with
mortality occasionally reaching 75% of the infected animals. Sur-
viving pigs may be stunted and feed efficiency will be poor.
Threadworms are more prevalent on southern and southeastern
United States swine farms and are seldom diagnosed in swine
raised in the north central states.
Stomach worms
Red stomach worms (Hyostrongylus rubidus) are distributed
throughout the United States and are more prevalent in pasture-
raised swine. The increase in confinement nationwide has lowered
the incidence of the red stomach worm. Clinically, this worm
usually has little effect on the pig.
Kidney worms
The kidney worm (Stephanurus dentatus) is approximately 1 to
1 1/2 in. long and is located in or around the kidney or along
the tubes leading from the kidney to the bladder. The adult
females produce eggs that are passed into the ureters and
excreted in the urine. Swine are infected either through inges-
tion of the infective egg or by penetration of the skin or mucous
membrane by the infective larvae. Fetuses may become infected via
the blood supply to the uterus.
Oral infections reach the liver in 10 to 32 days. Then they
may migrate in the liver for two to nine months. This prolonged
migration period is responsible for a large percentage of the
liver condemnations, especially in the southeastern states where
the parasite is most commonly found.
Eventually, the larvae break through the liver capsule and
reach the kidney area and develop into egg-laying adults some 9
to 16 months after initial ingestion. During the wandering migra-
tion, ``lost'' larvae that reach the spinal column have been
blamed for posterior paralysis in sows.
Lungworms
Lungworms (Metastrongylus spp.) are found in the central and
Atlantic states when swine are partially or totally raised on
pasture. Since the life cycle of the lungworm requires contact
with the common earthworm, hogs raised in total confinement are
not infected with lungworms.
Mild lungworm infections will magnify the symptoms of
respiratory disease, mycoplasma, influenza, and bacterial pneu-
monia. More severe infestations of the parasite can cause
respiratory signs of coughing and labored breathing on their own.
Diagnosis of Internal Parasites
Internal parasites can be diagnosed by clinical signs,
necropsy, and examination of feces for eggs. Clinical signs
include poor feed efficiency, unthrifty appearance, coughing,
pneumonia, diarrhea, and death. However, many hogs may be heavily
worm-infected that appear normal.
Depending on the worm species, adult worms can be observed
in the intestinal tract, lungs, or kidney at postmortem. Migrat-
ing larvae of roundworms (ascarids) and kidney worms cause scars
or white spots on the liver. These can be observed during
necropsy of young pigs or at the time market hogs are
slaughtered.
The white spots from ascarid larvae disappear approximately
six weeks after formation. Therefore, spots at slaughter associ-
ated with ascarid larvae indicate the finishing hogs have been
infected or reinfected during the last six weeks of feeding.
Scars incurred at weaning will clear up by slaughter age.
To determine the parasite status of a farm, fecal samples
should be obtained from at least five pigs that are more than 9
weeks old. At the same time, five samples should be collected
from 4 to 5-month-old pigs and from the breeding herd.
Mix each set of five samples together so that a composite
sample representing each group is available. These three compo-
site samples should be taken to a veterinarian for a fecal test
for worm eggs.
The species of eggs observed at microscopic examination will
determine treatment and control methods. Occasionally, no eggs
will be observed and treatment is unnecessary. Pigs from dewormed
sows that have been farrowed on clean slotted or mesh floors and
placed in slotted floor nurseries commonly are worm free.
Nevertheless, severe worm infections have been observed in con-
finement operations that allowed a break in sanitation. Annual or
twice-a- year fecal examination to monitor the effectiveness of
the parasite control program is important.
Table 1.Percent removal of common swine parasites by recom-
mended drugs.*
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Pyrantel
Parasite PiperazineTartrateThiabendazoleHygromycin
_______________________________________________________________
Roundworms 75-100% 96-100% -- 95-100%
Nodular worms 50% 88-100% -- 95-100%
Whipworms 0 0 -- 85-100%
Lungworms 0 0 -- 0
Small stomach worms -- -- -- --
Strongyloides
(Threadworms) 0 0 99-100% --
Mature kidney worms 0 0 0 0
Immature kidney worms 0 0 0 0
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Table 1. (Continue ... )
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Parasite BDichlorvosLevamisoleFenbendazole
______________________________________________________
Roundworms 99-100% 99-100% 92-100%
Nodular worms 95-100% 80-100% 100%
Whipworms 90-100% 70-80 % 94-100%
Lungworms 0 90-100% 97-100%
Small stomach worms -- -- 99-100%
Strongyloides
(Threadworms) 60-80 % 80-95 % --
Mature kidney worms 0 83 % 100%
Immature kidney worms 0 0 100%
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Trade name Banminth--Pfizer, Inc.
Trade name Thibenzole--Merck and Co., Inc.
Trade name Hygromix--Elanco Products Company
Trade name Atgard--SDS Biotech Corporation
Trade name Tramisol--American Cyanamid Company
Trade name Safe-Guard--American Hoechst Corporation
*North Carolina Agricultural Extension Service Bulletin
Dewormers
No individual dewormer is effective against all species of
worms (Table 1). Piperazine, administered properly, is fairly
effective against the adult roundworm. But all too often, when
producers administer piperazine via drinking water, an adequate
dosage is not consumed in a 24-hour period because of the drug's
bitter taste.
Dichlorvos (Atgard) has broad deworming activity and is
given as a one- or two-day dewormer in the feed. Dichlorvos is
usually considered a drug of choice against whipworms when the
two-day type treatment is administered.
Levamisole (Tramisol, Ripercol) is also effective against
several species of worms and can be mixed with feed or in the
drinking water.
Pyrantel tartrate (Banminth) is effective against roundworms
and nodular worms. Pyrantel tartrate is administered in the feed
and can be given as a one-day dewormer or fed continuously. Con-
tinuous feeding of pyrantel tartrate prevents the migration of
the hatched larva through the intestinal wall into the liver.
Thus, pigs fed pyrantel tartrate from weaning to 12 weeks will
not have white scars on the liver at the end of drug feeding
period. If, at this time, pigs are placed on clean pastures or on
clean floors, no ascarid liver scars will be present at
slaughter. However, if they are placed on an egg- contaminated
lot, liver spots will form quickly.
Fenbendazole (Safe-Guard) is effective against roundworms,
nodular worms, stomach worms, whipworms, kidney worms (immature
and mature forms), and lungworms. This broad spectrum dewormer is
mixed with the feed and fed for three consecutive days. Fenbenda-
zole is a drug of choice against kidney worms, lungworms, and
whipworms.
Hygromycin B (Hygromix) is a continuously fed dewormer that
is effective against roundworms, nodular worms, and whipworms.
When Hygromycin B is fed for longer than six weeks, a hearing
impairment may develop. Therefore, its use is not recommended in
animals that may be saved for breeding stock.
Thiabendazole paste is used to treat 5 and 10-day-old pigs
for intestinal threadworms.
Parasite Control Program
Parasite control programs vary with the individual farm, but
in general farms are separated into confinement or pasture opera-
tions. Pigs raised on pasture or in dirt lots where reinfection
is inevitable will need a more rigorous control program than pigs
raised on slotted floors. Confinement systems with dirty solid
concrete floors are no different from a pasture lot and should be
considered contaminated with worm eggs.
Before initiating a worm treatment and control program, an
accurate diagnosis of the species of worm present should be made.
At this point, choose the drug most effective against the worms
diagnosed. Deworm sows one week before breeding and again one
week before farrowing with either dichlorvos, levamisole, pyran-
tel tartrate, or fenbendazole. Wash the sows with soap and water,
especially along the udder, to remove worm eggs before sows are
placed in a clean farrowing crate or pen.
Pigs should be dewormed at 6 to 8 weeks and again 30 days
later, or treatment with continuous pyrantel tartrate or Hygromy-
cin B can be initiated at weaning. If threadworms are a problem,
treat baby pigs with thiabendazole paste at 5 and 10 days of age.
Levamisole or fenbendazole treatment is recommended if kidney
worms or lungworms have been diagnosed.
Since the kidney worm requires one year to reach maturity,
the use of a gilts-only program for farrowing for four years is
reported to eliminate kidney worms from the herd.
For economic reasons, the four-times-a-year deworming of
sows and twice-a- year deworming of pigs is often not advisable
in complete confinement systems with clean slotted or mesh
floors. Although deworming may be unnecessary, twice-a-year moni-
toring of feces for worm eggs should still be continued.
Modern dewormers and husbandry practices make it possible to
raise swine practically worm free. Proper diagnosis and timing of
the worm treatment can alleviate this costly menace of the swine
producer.
Reference to products in this publication is not intended to be
an endorsement to the exclusion of others which may be similar.
Persons using such products assume responsibility for their use
in accordance with current directions of the manufacturer.
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REV 6/84 (5M)
Figure 1. Roundworm Ascaris suum).
Figure 2. Damaged liver.
Figure 3. Adult whipworm (Trichuris suis).
Figure 4. Nodular worm (Oesophagostomum sp.).
% Figures are available in hard copy.
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