Causative agent
- PRRS virus, positive-stranded virus, family
  Arteriviridae
- Two distinct antigenic types : American and
  European isolates


Differential diagnosis
- Aujeszky's disease
- Classical swine fever
- Swine influenza
- Porcine respiratory coronavirus infection
- Encephalomyocarditis
- Porcine parvovirus infection
- Porcine cytomegalovirus infection
- Porcine circovirus


1. Epidemiology
- Worldwide except in Australia and New Zealand
- Airborne spread, direct contact with infected or
  carrier pigs
- Virus infection by oronasal route


2. Clinical examination
Reproductive syndrome:
- Late term abortion, increased stillbirth, weak born
  piglets and preweaning mortality
Respiratory syndrome:
- Pneumonia in piglets and fattening pigs


3. Necropsy
- Grayish-pink and firm lung


4. Histophathological observation
Piglets and growing/finishing pigs
- Proliferative interstitial pneumonia, multifocal to
  diffused interstitial pneumonitis characterizing by
  thickening of alveolar septa
- Mild encephalitis
- Lymphoid depletion in lymphoid organs

Fetuses and stillborn pigs
- No specific gross or microscopic lesions
- Late-term abortion and premature farrowing
  containing weakborn, stillborn, and partially
  mummified fetus of approximately the same size
  are typically seen in the early stage of PRRS
  outbreak


5. Antigen detection
Specimens : tonsil, lung, spleen, lymph nodes
Method      : FA test or immunohistochemistry
staining


6. Nucleic acid detection and typing : PCR


7. Serological test
Specimens : - sera, body fluid of fetuses or                       stillborn piglets
                    - paired sera (2-3 weeks apart)
Method      : - ELISA
                    - lPMA


8. Virus isolation
Specimens : serum, plasma, white blood cells, lung,
tonsil, lymphoid organs, thoracic or
ascitic fluid of stillborn or neonatal
fetuses
Method      : primary porcine alveolar macrophages
culture inoculation and CPE
observation


9. Virus identification
- FA test
- Immunohistochemistry staining


Control
- Sanitation and management
- Control secondary infection
- Prevention of introduction new strains of virus into
  the farms
- Vaccination?