HERD HEALTH                                       PIH-38


              Pseudorabies (Aujeszky's Disease)

David G. Thawley, University of Minnesota
Donald P. Gustafson, Purdue University
Robert R. Ormiston, USDA, Washington, D.C.

John M.  Cunningham, Lincoln, Nebraska
Willard Korsmeyer, Beardstown, Illinois
Gale and Lois Pohlman, Plymouth, Nebraska
Hilman Schroeder, Sauk City, Wisconsin

Introduction and History

     Pseudorabies is an acute, frequently fatal disease affecting
most  species of domestic and wild animals; however, man and cer-
tain apes are resistant to it. The disease is caused  by  a  her-
pesvirus and is characterized by a variety of clinical signs; the
most prominent  involve  the  nervous  and  respiratory  systems.
Severe  itching and self-mutilation are seen in most species, but
rarely in swine.

     Aujeszky first recognized pseudorabies as a disease of  cat-
tle and dogs in Hungary in 1902. It soon became evident, however,
that swine were the natural hosts of the virus,  and  pigs  could
die  as  a result of the disease.  For years in Europe, pseudora-
bies has been recognized as an important cause of death in  swine
of  all  ages  and as a cause of abortion.  Until the late 1960's
and the early 1970's, the disease in the United States  was  con-
sidered important only as a cause of death in baby pigs and occa-
sionally in cattle, sheep, dogs and cats.  However,  pseudorabies
is more prevalent in the U.S. than was formerly believed, and the
present viruses are capable of causing a variety of clinical man-
ifestations, including death in newborn and adult swine and fetal
death with abortion in pregnant swine. The disease is  widespread
and  of  considerable  economic  importance in several midwestern
states. A slaughter serum survey conducted  in  1983  revealed  a
nationwide prevalence of 18.8% in breeding swine with state rates
ranging from 0% to 34.3%.

Clinical Signs

     Pigs less than 3 weeks old. In baby pigs, the disease may be
characterized  by  sudden death with few, if any, clinical signs.
Frequently death is preceded by fever  which  may  exceed  105o F,
dullness,  loss  of  appetite, vomiting, weakness, incoordination
and convulsions. If vomiting and diarrhea occur, the  disease  in
baby  pigs closely resembles transmissible gastroenteritis (TGE).
In pigs less than 2 weeks old, death losses  frequently  approach
100%.  Baby  pigs  may  have become infected before birth and die
within 2 days after birth,  occasionally  after  showing  violent
shaking  and  shivering. Piglets infected immediately after birth
may show clinical signs within the first 2 days of life and  usu-
ally die before they are 5 days old.

     Pigs 3 weeks to 5 months old. After 3  weeks  of  age,  pigs
usually  develop a degree of resistance to the disease, and death
losses may decrease from 50% in pigs exposed when 3 weeks old  to
less than 5% in pigs exposed when 5 months old. Death losses vary
with different strains of the  virus,  and  even  in  grown  pigs
severe death losses occasionally occur.

     Fever is a prominent clinical sign in these growing pigs and
is followed by loss of appetite, listlessness, labored breathing,
excessive salivation, vomiting, trembling and  eventually  marked
incoordination,  especially  of  the hind legs. Normally death is
preceded by convulsions.  Involvement of  the  respiratory  tract
with  sneezing, rubbing of the nose and coughing may occur. Clear
to yellowish nasal discharges may be  seen.  Infected  pigs  that
recover  have  lost  condition  and  will be slow to reach market

     Mature pigs. The disease in adult pigs often is not  severe,
but  with  some  strains of pseudorabies virus, deaths may occur.
The disease in adult pigs is characterized by fever and  respira-
tory  signs  which  may  include nasal discharges, sneezing, nose
rubbing and coughing.  Pseudorabies is often found in  operations
with other respiratory diseases such as Pasteurella and Actinoba-
cillus (Hemophilus) pleuropneumonia.  Nervous signs such as trem-
bling,  incoordination and itching occasionally occur, and blind-
ness may follow pseudorabies infection. Vomiting and diarrhea  or
constipation may be seen. Since 1980, an acute, often fatal pneu-
monia caused by pseudorabies virus has increased  in  prevalence.
This  condition  is  most  often seen in herds having a prolonged
history of pseudorabies infection.   Animals  often  die  from  a
fatal secondary bacterial pneumonia.

     Sows infected in the early stages of pregnancy may return to
heat  because  of  death  and  resorption  of their fetuses. Sows
infected in  middle  pregnancy  may  eventually  abort  mummified
fetuses,  whereas  sows infected late in pregnancy often abort or
give birth to weak, shaker or stillborn pigs.

Postmortem Lesions

     No gross lesions characteristic of pseudorabies are  consis-
tently  found.   Small  greyish-white spots of focal necrosis may
occur in the livers and spleens  of  pseudorabies-infected  young
pigs.  Congested  pneumonic lungs are commonly seen. Virus isola-
tion and fluorescent antibody examination of these and other tis-
sues will reveal if the lesions are related to the disease.


     Recovery by swine from pseudorabies confers some  resistance
for  at  least  12 months. Re-exposure may result in reinfection,
but it is usually asymptomatic.  The passive immunity  passed  on
from  an  immune  sow  to her offspring through the colostrum may
protect the piglets for 5 to 10 weeks, after which they gradually
become  fully  susceptible.  However, the passive immunity may be
too low to protect the piglets so the offspring  of  immune  sows
also may die of pseudorabies.

     Vaccines have been used in Europe  for  years,  and  in  the
United States since 1977. The research consensus is that vaccines
reduce swine losses and spread of the disease but do not  totally
prevent  infection  and  the  establishment of a carrier state in
recovered swine.  Vaccines have been reported to enhance the con-
trol  and  eradication  of pseudorabies. Newer ``differentiable''
vaccines combined with their appropriate serological tests permit
vaccinated  animals  to be distinguished from those infected with
``field'' strains of virus. Differentiable  vaccines  permit  the
monitoring of herd infection status in vaccinated herds.

Spread of Infection

     Pseudorabies is spread  mainly  by  direct  contact  between
swine;  the  nose  and  mouth  are  the main entry points for the
virus. Nasal discharges and saliva contain the virus;  therefore,
drinking  water,  bedding  and other objects such as clothing and
instruments may become contaminated.  The  virus  can  be  spread
without  movement  of  pigs.  When entering swine premises, clean
clothes should be worn, and  boots  should  be  disinfected  upon
entering  and leaving the premises.  Virus also may spread by the
movement of air within buildings and for short distances  outside
depending upon climatic conditions. Air spread in late winter and
early spring is suspected to be over greater distances than  pre-
viously thought.

     Recovered pigs may remain carriers of the  virus  and  later
can  infect  susceptible pigs or cattle with which they come into
contact. Severe cattle losses from pseudorabies have occurred  as
a  result  of  contact  infection  from apparently normal carrier
swine. The disease also has been introduced  to  swine  farms  by
introduction of carrier pigs.

     Dogs and cats are very susceptible to pseudorabies and  usu-
ally  become  infected  through  contact with infected pigs. Wild
animals such as raccoons, skunks and mice are also susceptible to
the disease. Dogs, cats and wild aniimals are potential spreaders
of the disease within an endemic area, but are not  considered  a
factor in the spread outside the area.


     The clinical signs of pseudorabies are variable so  clinical
diagnosis should always be confirmed by laboratory tests. Several
tests-the Serum-Virus Neutralization Test (SN),  Virus  Isolation
(VI), Fluorescent Antibody Tissue Section Test (FATS), the Enzyme
Linked Immuno-Sorbent Assay (ELISA) and the  Latex  Agglutination
Test  (LAT)-have been approved for the diagnosis of pseudorabies.
Other tests are being developed.

     The SN, LAT and ELISA tests detect  pseudorabies  antibodies
in  serum  of  pigs that have been infected with the virus. These
antibodies appear in the serum about day seven of  infection  and
may persist for years. The presence of pseudorabies antibodies is
evidence that the pig has been infected with  the  virus  in  the
past or has been vaccinated. Absence of antibodies indicates that
the animal has probably not been infected or that it  may  be  in
the early stages of the disease. Diagnosis of a pseudorabies out-
break can be made by conducting SN tests on paired serum samples,
one  taken from the pig early in the disease, and the second 3 to
4 weeks later. A significant rise in antibodies between the first
and  second  bleeding indicates active pseudorabies infection has
been present.

     The SN, LAT and ELISA are extremely  reliable  tests.  While
these tests accurately detect antibodies to pseudorabies, they do
not  differentiate  between  antibodies  resulting  from  natural
disease and those resulting from vaccination.  Only the differen-
tial tests will permit such a distinction.

     Serum submitted for SN  examination  must  be  collected  in
clean, sterile tubes (not Brucellosis tubes) and submitted packed
in ice. If serum is badly hemolyzed  or  contaminated  with  bac-
teria, the SN test is unreliable.

Control of Infection

     The chances for introduction of the disease can be minimized
if  the  owner  strictly controls movement of people, animals and
objects into swine premises. Clean clothes and  boots  should  be
decontaminated  with  a  good  disinfectant  before introduction.
Cats, dogs and other animals should be kept away from  pigs.  Add
breeding stock from a herd known to be pseudorabies-free, and all
additions should be tested and found free, isolated for at  least
30  days, and then retested. Untested feeder pigs should never be
brought onto premises where farrowing operations exist.

     When pseudorabies occurs on a farm, quarantine the premises;
all movement of people and animals should be strictly controlled.
If possible, separate healthy pigs from the sick.  Control  move-
ment  between  them.   Dispose  of  dead  pigs  by deep burial or
incineration. Recovered pigs should be sold only for slaughter to
prevent spreading the infection to other farms by carrier swine.

     Many herds which are infected may be freed of  infection  by
using  either ``test and removal'' procedures or offspring segre-
gation.  Vaccinate exposed or offspring segregated gilts  in  the
first  generation  with  differentiable vaccines if random sample
testing is used to  determine  herd  status.  Monitor  until  the
second  generation  turnover.  Results using these procedures are
very encouraging except in herds undergoing an  acute  infection.
In highly concentrated herds, the virus appears to cycle continu-
ously.  In these herds vaccination with a differentiable  vaccine
may  stop  spread  and  permit  effective removal of pseudorabies
virus (PRV) from the herd.  In less concentrated operations,  the
virus  appears  to  cycle  intermittently, and many offspring are
pseudorabies-free. In these herds, a testing program with  isola-
tion  and  removal of infected animals appears to be an effective
herd clean-up strategy, and vaccines may also be used  to  advan-

     State regulations and requirements on PRV control vary among
states.   Consult  the  state veterinarian about individual state
requirements/regulations on PRV testing, control and  eradication
procedures.   More information on eradication can be found in the
publication "Plans for Elimination of  PRV  from  a  Swine  Herd"
available  from Livestock Conservation Institute, 6414 Copps Ave-
nue, Suite 204, Madison, Wisconsin 53716.

U.S. Eradication Plan

     A national eradication program  (with  a  starting  date  of
January 1) was approved by the National Pork Producers Council in
1989. This decision was made after many discussions, meetings and
debates  that  had  been  going  on  for about 15 years since the
disease first began to cause problems in swine herds.  The  plan,
endorsed by several other livestock groups, was written by a task
force created by Livestock Conservation Institute (LCI)  made  up
of representatives of all segments of the pork industry.

     A series of pilot eradication projects in five states over a
three-year  period  were  conducted to answer two questions:  Are
tools available to eradicate the disease?  What would eradication
cost and would it be cost effective?  The technical advisory com-
mittee to the pilot projects  concluded  that  pseudorabies  area
control  is feasible and can be accomplished by methods which are
acceptable to pork producers and to the program coordinators.

     The eradication plan developed and supported by the industry
is flexible.  It calls for establishment of state committees made
up of producers and other segments of the industry  to  determine
program activities and advancement from stage to stage in indivi-
dual states.  The first stage of the program is preparation, dur-
ing  which state committees are formed, prevalence of the disease
is measured and plans are made for future activities,  and  what-
ever  changes  in  state  laws and regulations and/or legislative
authorities needed are determined.

     The second stage is the control stage, during  which  states
will  implement  surveillance  programs  to  find infected herds;
quarantine such herds and if they choose, begin a voluntary  pro-
gram of eliminating the virus from infected herds.

     The third stage is the start  of  mandatory  herd  clean-up,
during which owners of infected herds will be required to develop
and implement individual plans to eliminate the virus from  their

     The fourth stage is for states which have completed the herd
clean-up  phase  and have no known infected herds but continue to
look for infection.  The fifth and final stage  is  pseudorabies-
free status.


     1.   Pseudorabies is a disease of economic  significance  in
          the United States.

     2.   Severe death losses, abortions and reproductive failure
          may occur in pseudorabies-infected swine herds.

     3.   Cattle, sheep, dogs, cats and  wild  animals  also  die
          from the disease.

     4.   Pseudorabies does not cause disease in  humans  and  is
          not related to rabies.

     5.   Recovered animals may be  carriers  of  the  virus  but
          rarely become ill upon re-exposure.

     6.   Many vaccines, both modified and killed, have been  ap-
          proved for use in the United States subject to the con-
          trol of the State Animal Health Official.  Vaccines re-
          duce  the  severity  of the disease, but do not totally
          prevent natural infection or the establishment  of  the
          carrier  state.  When PRV occurs on a farm, vaccination
          should be encouraged immediately- subject, however,  to
          individual state laws and regulations.

     7.   Diagnostic methods are reliable if  adequate  specimens
          are submitted.

     8.   Spread of the disease can  be  reduced  by  quarantine,
          proper disposal of dead pigs, and strict application of
          hygienic measures.

     9.   Additions to breeding herds should be PRV negative  and
          from PRV negative herds. They should be isolated for at
          least 30 days and retested prior to  release  into  the

     10.  Untested feeder pigs  should  not  be  introduced  onto
          premises where farrowing operations exist.

     11.  Infected herds often can be freed of infection by test-
          ing and animal selection procedures.

     12.  ``Differentiable'' vaccines may be used effectively  in
          most herd ``clean-up'' programs.

     13.  The National PRV Eradication Program began  January  1,


     The Epidemiology of Pseudorabies. 1990. Livestock  Conserva-
tion Institute, 6414 Copps Avenue, Suite 204, Madison, WI 53716

     Plans for Elimination of PRV from a Swine Herd. 1990. Lives-
tock  Conservation  Institute,  6414  Copps  Avenue,  Suite  204,
Madison, WI 53716.

     Pseudorabies  Eradication,  State-Federal-Industry   Program
Standards.   USDA,  Animal  and  Plant Health Inspection Service,
Veterinary Services.  U.S.G.P.O.:1989-617-013/04354.

REV 6/91 (7M)


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