HERD HEALTH                                       PIH-44


                   Internal Parasites

LeRoy G. Biehl, University of Illinois
R.F. Behlow, North Carolina State University
E. Batte, North Carolina State University

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

     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


     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-


     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


     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 (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

     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.*
      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      --       --        --           --     
(Threadworms)              0        0     99-100%        --     
Mature kidney worms        0        0          0           0    
Immature kidney worms      0        0          0           0    

Table 1. (Continue ... )
      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%    
(Threadworms)           60-80 %   80-95 %      --      
Mature kidney worms         0        83 %      100%    
Immature kidney worms       0         0        100%    

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


     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

     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
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.


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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