06 Wilfredo Resoso (Phils)

VACCINATION AND OTHER STRATEGIES TO
CONTROL PORCINE REPRODUCTIVE RESPIRATORY SYNDROME
(PRRS)
Wilfredo Resoso
President, Accredited Swine Breeders Association of the Philippines
Email: 1wpr@infarmco.com
ABSTRACT
Porcine Reproductive Respiratory Syndrome (PRRS) is an economically significant disease that affects the
pig industry globally. This presentation will elucidate and cover the most recent strain that has hit the
Philippine swine industry locally and other two major countriesin Asia: China and Vietnam. It was in
2006, when the swine industry suffered a disease problem that was so damaging, challenging and
annoyingly enigmatic that had created a huge vacuumin the supply chain of pork for a persistent long
period of time. With this development, swine veterinarian practitionersand stakeholders became vigilant
and critical in understanding as we embark in one of the most challenging control programs against
Porcine Reproductive Respiratory Syndrome (PRRS).
Case definition was established to differentiate “Typical PRRS virus infection from“Atypical PRRS
virus variant strain infection.” Field observationsindicate a confirmed case of High Pathogenic – PRRS
(HP-PRRS) with mortality observed in all stages but it was more lethal in piglets.High feverof 41*C ++,
reddeningof the skin,gummy eyelidin sows, 30 % mortality in growersif complicatedwith othersecondary
bacterial pathogens. Most of the lesions,(spleen,kidneys, and lungs are similar to that observed in hog
cholera cases.Farmsaffected,may sufferfromotherco – infectionlikePED,PCVAD,Ileitisand HCwhich
were known to have affected farms with previousPRRS vaccination.
With 85% of cases affecting pregnant sows and spread to other production building in a single site
farm, we formulated diagnostic protocol to confirmthe profile of farms affected.
INTRODUCTION
The attacksof swine diseaseshave always beena constant threatespecially with the intensification of swine
production. A change in disease patterns was also observed and new diseases, unheard of in the early days
of animal production are now being reported. As always, these disease outbreaks have seriously affected
farm viability. The outbreak was considered one of the most devastating disease problems that affected the
swine industry. The severity of PRRS and the economic repercussions it has in the swine industry have
influenced producers and veterinarians to progresstowards a betterunderstanding of and a meansto control
this disease. This has moved the disease to the forefront of swine disease research,as explained by the
seeming uncontrolled spread of the disease spanning through countries and continents, mindless of
territorial boundaries. PRRS has become one of the most important disease entities affecting pigs
worldwide. It’san RNAvirus and has the characteristic of mutation even in the same herd. North American
and the European genotypes were recognized and documented to be both stable and most likely to change
genetically and equally capable of changing.
The 2007 Asian episode of the high fever Atypical PRRS in Asia (China, Vietnam and Philippines)
may have evolved PRRS in a mix of pathogens. It was a genetically different isolates of PRRS that differ

in virulence – in terms of their ability to cause the disease. Clinical signs, lesions and severity are also
different from the typical PRRS. In the past ten years, the disease brought plenty of research with good
results, but the puzzle is not solved for still we have the frustration that we cannot effectively and properly
control the disease. We are still confronted with what happened to the pigs in terms of immune response
when the pigs are infected. Gaps in keeping a virus free farm status and maintaining it is very difficult
because risk of re-infection is always a challenge. There is the persistence of the virus especially in an on-
farm situation, that we are dealing with heterologous strains of both genotypes of PRRS virus.
BACKGROUNDER
Porcine reproductive respiratory syndrome unraveled
Most swine farm owners and practicing veterinarians recognized the presence of Porcine Reproductive
Respiratory Syndrome (PRRS). Started in the third quarter of 1993 up to the second quarter of 1994, there
were undisclosed outbreak of the disease affecting swine breeding herd causing reproductive failures and
chronic losses due to viral associated pneumonia. Typical Porcine Reproductive Respiratory Syndrome
virus was confirmed by the virology section of the National Animal Disease Diagnostic Laboratory of the
Bureau of Animal Industry (NADDL-BAI). It was disclosed that 32% of tissue samples submitted were
found to be positive in Fluorescent antibody (FA) test. The PRRS disease outbreak was considered one of
the most devastating disease problems that affected the swine industry.
Typical Porcine Reproductive Respiratory Syndrome (PRRS), was confirmed in 1994 through a
seroprevalence study conducted by vaccine companies selling PRRS vaccine. They collected serum
samples in all swine producing areas except Bacolod and Iloilo to establish the prevalence of PRRS
antibody in Philippine swine farms. On the account of most swine practitioners, symptoms observed are of
“rolling” inappetence in gestating and lactating sows, developing high temperature and often being
lethargic. If this clinical signs are observed in late gestation, these sows will show late abortion. Pre-mature
farrowing is a common sign that increases stillbirths and mummified fetuses to 2–3 % and 5– 6 %
respectively. Two to 3% of the total live born piglets suffer Splayleg and the review of literature suggests
that this clinical signs are related infection due to Porcine Reproductive Respiratory Syndrome. Palpebral
edema is also commonly observed in newly born piglets born from sows affected with PRRS. Documented
pre-weaning mortality is as high as 60 – 80 % in the initial outbreak. Older piglets 10 days or older suffer
from abdominal breathing pattern and same abdominal breathing is observed in the nursery section. They
tend to be affected with secondary bacterial infection and do not respond to individual treatment using
antibiotics. Morbidity and mortality in the nursery affectedpigs is ashigh as 30%. Grower and fattenerpigs
affected with respiratory signs have lung lesions of interstitial pneumonia.
Atypical Porcine Reproductive Respiratory Syndrome (PRRS),as recorded on June 2007, backyard farms
in Bulacan province reported a highly contagious viral disease that spread Northward up to Isabela and
Southward up to Batangas.The episode of the outbreak startedin sowsand affectedall stagesof production.
There is no parity predisposition, losses observed in all stagesbut the disease is more lethal in piglets. Upon
further studies and documentation, cases of this outbreak only occurred in Luzon and confirmed to be of
HP-PRRS. This presentation will elucidate and cover the most recent strain that has hit our swine industry
locally and other two major countries in Asia: China and Vietnam. It was in 2006, when the swine industry
suffered a disease problem that was so damaging, challenging and annoyingly enigmatic that had created a
huge vacuum in the supply chain of pork for a persistent long period of time. With this development, swine
veterinarian practitioners and stakeholders became vigilant and critical in understanding as we embark in
one of the most challenging control programs against Porcine Reproductive Respiratory Syndrome (PRRS).

Field observations indicate a confirmed case of High Pathogenic – PRRS (HP-PRRS) with mortality
observed in all stagesbut it wasmore lethal in piglets. High feverof 41*C ++, reddening of the skin, gummy
eyelids in sows, 30% mortality in growers if complicated with other secondary bacterial pathogens. Most
of the lesions, (spleen, kidneys, and lungs are similar to that observed in hog cholera cases. Farms affected,
may suffer from other co – infection like PED,PCVAD,Ileitis and HC. Known to have affected farms with
previous PRRS vaccination.
With 85% of cases affecting pregnant sows and spread to other production building in a single site
farm, we formulated diagnostic protocol to confirm the profile of farms affected. The diagnostic flow for
PRRS include:
1. Clinical Signs
2. Post – mortem findings:
a. Gross pathology
b. Microscopic pathology
Virologic test/Serology:
Conventional Methods:
a. Enzymes Linked Immunosorbent Assay (ELISA)
b. Virus Isolation – PRRS virus.
c. Immunohistochemistry.
Molecular Diagnostic Methods:
a. Virus Amplification (PCR)
b. Gene sequencing
GUIDELINES ON PRRS CONTROL AND PREVENTION
Control ofPRRS
The fundamental principle of PRRS control understands the pattern of virus transmission within an
infected population. Studies confirmed that the PRRS virus may limit itself to an individual population
within the herd (i.e. nursery). It is therefore imperative to understand the pattern of PRRS virus
transmission with an individual farm, and on an area wide basis to determine which methods of control
have the greatest chance of success. It must be pointed out that in addition to herd area-wide profiling,
submission of tissues or whole animals to the laboratory is needed. This ensures that the components of
the disease process are identified such as the pathology involved and the concurrent infection (bacterial,
viral). Of course, it may also be necessary to characterize the virus through molecular diagnostic methods.
Finally, clinical observations and their effects on production cannot be over emphasized.,
Serological profiling and sample size consideration
To date, serological profiling is most helpful in monitoring and determining the levels of serum anibodies
and therefore the disease pattern. However,it is extremely necessary to decide how many samples to take
and why sampling has to be done. For PRRS,we assume that there are reasons why we need to take a
sample.
a. To determine whether or not a population is infected (detection sampling)
b. To estimate the percent of the population that has been infected (prevalence estimation) and is a
helpful tool in assessing whether to proceed with the intervention already made.

The exact sample sizes can be obtained from epidemiology references or by using computer software.
As a general rule, sampling should include a minimum of 30 breeding age animals, and 10 animals at 4-
weeks of age intervals in the nursery, grower and finisher population.
Moreover, when sampling, population can be tested using either cross-sectional or prospective
testing. Cross-sectional testing is done by randomly selecting a number of pigs from each population and
sampling at one point and time, while prospective testing consists of identifying specific animals and
testing the same periodically over time.
Farm classification
Farm Classification – is based on a system proposed by Scott Dee (1998). Through this classification it is
easier to determine which control strategies could work best in the herd or in the area.
1. Gilt development/Isolation/Acclimatization:
a. Breeder stabilization is critical
b. Gilt developer facility is helpful to successfully prepare gilts for entry into an infected farm.
c. Function under ALL- IN ALL- OUT (AIAO) pig flow.
d. Gilts may be introduced as weaned piglets from 2 – 5 months of age.
2. Period of gilt development:
a. Isolation period
b. Serologic testing day 1 to 2
i. Vaccination shortly upon arrival if decision is made.
3. Acclimatization period:
a. Starts 30 days after gilts’ entry into the developer facility.
4. Recovery period:
a. Sources of field virus are removed from the development facility (eg. nursery pigs, culled
sows)
b. Period of 30 days prior to entry into the gilt pool
5. Partial depopulation:
a. Adjustment in pig flow to interrupt horizontal transmission of PRRS virus.
b. This technique is primarily used in the nursery.
6. All In All Out (AIAO) Pig flow:
a. Basis of strict control over movement of animals to reduce perpetuating and intensifying
effect of the virus by avoiding mixing of older and slower growing poor performance in pigs
with younger animals.
b. Solid division of pens and individual rooms.
Vaccination
1. To reduce immune response which will alter the course of infection and protect against clinical
disease.
2. Vaccination does not stop infection.
A number of controlled studies have demonstrated safety and efficacy of modified live virus
(MLV) PRRS vaccines against homologous and heterologous challenge. Mass vaccination and
unidirectional pig flow have been used effectively. The basis is to stop transmission of PRRS
virus infected finishers by vaccinating all animals twice with an MLV over a 30-day period and
simultaneously stopping the introduction of naïve pigs for a period of 60 days. Following the

emptying of rooms during routine marketing, facilities are washed,disinfected and allowed to dry
for two days.
McREBEL
Management changes to reduce exposure to bacteria to eliminate losses.
1. Cross foster only during the first 24 hours of life.
2. Stop cross-fostering piglets between litters for resizing or for saving sick pigs and runts
3. Cross foster pigs to equalize litter size only up to 24 hours after birth.
4. Only moved pigs within farrowing rooms at birth. Don’t move sows or piglets between
rooms.
5. Stop using nurse sows for weak born, PRRS virus –infected pigs and runts.
6. Minimize handling of piglets, especially for routine antibiotic or extra iron injection.
7. Evaluate the effect on clinical disease levels of each non-essential processing or treatment
procedure for suckling and nursery pigs.
8. Immediately euthanize pigs that get very sick and are unlikely to recover.
9. Don’t move pigs that fall behind or are lightweight into rooms of younger pigs or to nursing
sows.
10. Immediately stop all feedback programs of stillborn or aborted fetuses.
11. Establish strict AIAO nursery pig flow. Provide 2 – 3 days for cleanup and disinfecting room
between groups.
PREVENTION OF PRRS VIRUS INFECTION
The primary source is the infected pig. For this reason,it is critical to routinely isolate and test breeding
stocks intended for PRRS virus –negative herds. Naïve farm owners should purchase replacement stocks
from known negative sources which carry out a regular schedule of monitoring and communication with
veterinary practitioner.
Isolation facilities should be located on another farm site and visited at the end of each working day.
If diagnostic results indicate that incoming stocks are infected, all animals should be removed from the
premise and marketed. The isolation facility should be cleaned using 90 – 92*C water,disinfected using
formaldehyde based products and allowed to sit empty for a minimum of seven days. Biosecurity should
be practiced at all times.
Vaccination*
*Consult your veterinarian for possible biosecurity and vaccination as part of your control and prevention
measures (particularly for naïve clinically and serologically negative farms wherein vaccination may or
may not be an option)
For Positive – Stable/Unstable farms:
 Replacement gilts and junior boards
o 2 shots with MLV PRRS vaccine before breeding 3 – 4 weeks interval and the second dose
should be at least 3 – 4 weeks before breeding (gilts should be isolated withion 60 days).
 Sows
o Initial Program – mass vaccination with MLV – PRRS vaccine 2 shots with 30 days interval.
o Maintenance Program: - 3 Options
 Mass vaccination every 4 months using MLV-PRRS vaccine.

 Mass vaccination every 4 months using killed inactivated PRRS vaccine
 Regular program with MLV-PRRS vaccine 14 days post farrowing.
 Piglets
o Mass vaccination with MLV-PRRS 18 – 21 days old or 21 days old piglet.
 Boars
o Every four months with MLV-PRRS vaccine ( as a precaution boars to be vaccinated may be
batch into two:
 Vaccinate the first batch, then rest for four weeks,after which, vaccinate the second
batch.
REFERENCES
Bell, A. (1966). A Means to Solve the PRRS Mystery. Herd Health Report. Pork. February edition. Pp. 24
– 28.
Dee,S.A.,(1998). A protocol to define breeding herd stability and classify farms according to PRRS status
to identify potential intervention strategies: a summary of 200 farms. Proceedings of the American
Association of Swine practitioners pp. 409 – 411.
Guo, Quan (2008). Efficacy of a modified live PRRS vaccine in a highly pathogenic PRRS infected herd
in China. Proceedings of the 20th
International Pig Veterinary Society Congress, Durban, South Africa.
PO1.153.p 153.
Li. (2006). PRRS MLV Efficacy in High Fever Cases, China Animal Health and Epidemiology Center
(directly under MOA) unpublished.
Livestock Conservation Institute (1992). Pseudorabies Progress Report. December 6; 12.
Prevention, Control and Eradication. PRRS Compendium (1998). 8; 87-95.
Principles of Prevention, Control and Eradication. PRRS Compendium; Producer’s edition (2003) 9; 79-87.
Russnogle, J. (1998). PRRS plan. Hogs Today. June 1998.
Gospadinov, Ivan., Pathogens and Prevention.,”Five Pillars of Control” October., 2015.
R and D, FRAmelco.com.”PRRS Control by Adjusting the sow’s diet.”Best Practices” LAMB Livestock
and Meat Products Magazine., Vol. 3 # 7. 2014 pp. 16.
Waddilove, Jake. (October,2007), PRRS in Focus, Disinfection clears PRRS virus from transporters., Pig
International.,2007., pp 12-13.
Atypical PRRS : Field Primer An Orientation Guide on the PRRS Virus Variant Strain in the
PHILIPPINES. PCSP publication.

06 Wilfredo Resoso (Phils)

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