Porcine Reproductive and Respiratory Syndrome Virus

Question 1

How long is the gestation of a pig?

Answer 1

115 days

Question 2

What are the two paths for piglets when they are born?

Answer 2

Piglets are either selected to be used as meat or for further breeding

Question 3

How long does growing and finishing take between weaning and slaughter?

Answer 3

20-24 weeks

Question 4

After weaning how long it is until a sow will commence heat?

Answer 4

Around 6 months

Question 5

Describe the characteristic replication of Arteriviruses

Answer 5

Arteriviruses replicate in the perinuclear cytoplasm of their host cells.
New virions are released by exocytosis from the surface of the cell.

Question 6

Which cells are the primary targets for the virus?

Answer 6

Alveolar macrophages

Question 7

How is PRRSV transmitted?

Answer 7

Inhalation
Ingestion
Coitus
Skin damage 
Contaminated needles

Question 8

Where does replication of PRRSV take place?

Answer 8

Replication in mucosal, pulmonary, or regional macrophages

Question 9

Describe how the clinical signs/disease differ in the following:

• Sow
• Neonatal pig
• Nursey or grower pig
• Finishing pig
• Boar

Answer 9

• Sow: abortion of premature farrowing, still born pigs, weak live born pigs
• Neonatal pig: dyspnoea, CNS signs, high mortality
• Nursery or grower pig: increased mortality, secondary infections, failure to thrive
• Finishing pig: fever and less fed consumption
• Boar: Fever, semen changes

Question 10

Describe the reproductive damage caused by PRRSV

Answer 10

• Premature farrowings
• Stillborn or mummified piglets
• Weak PRRSV-positive piglets
  (50% die soon after birth)
• Delayed return to service
• Mixture of clinical signs in piglets from the same farrowing

Question 11

What other non-reproductive signs may sows and gilts with PRRSV show?

Answer 11

• Anorexia
• Fever
• Lethargy
• Pneumonia
• Agalactica
  Red/blue discolouration of the ears and vulva
• Subcutaneous and hind limb oedema
• Delayed return to oestrus after weaning

Question 12

In which pigs is PRRSV usually subclinical?

Answer 12

Growers and finishers

Question 13

Describe the subclinical PRRSV infection

Answer 13

• Destruction of macrophages
• Thickening of the alveolar septa
• Occasional lesions in blood and lymphatic vessels
• Minor heart lesions

Question 14

Describe the respiratory clinical signs of clinical PRRSV

Answer 14

Fever
Sneezing
Hyperpnea
Dyspnoea
Coughing
Pneumonia
Lethargy
Periocular oedema
Oculonasal discharge.

Question 15

Describe PRRSV in the first 6-12 hours of infection

Answer 15

Following oronasal exposure, PRRSV replicates in macrophages and dendritic cells in tonsils, upper respiratory tract, and lungs resulting in viremia by 6 to 12 h post-infection

Question 16

How does PRRSV damage cells?

Answer 16

• Induces cell lysis of pulmonary alveolar macrophages and pulmonary intravascular macrophages which are the primary sites of replication of the virus in the lung.
• PRRSV appears to induce apoptosis in bystander cells, thus damaging more macrophages than just those infected with the virus.

Question 17

How is the lung grossly affected by PRRSV?

Answer 17

Interstitial pneumonia pathology

• purple/grey discoloration
• firm consistency

Question 18

Describe the histological changes of interstitial pneumonia

Answer 18

The alveolar wall was enlarged by hyperaemia and inflammatory cell infiltration (lymphocyte and macrophage are abundant)

• Loss of airspaces
• Inflammatory cells

Question 19

Describe the effects of PRRSV being a primary pathogen

Answer 19

Areas and defence mechanisms are affected by primary pathogens of the pig, allowing them and opportunistic pathogens to establish infection, leading to co-infections
PRRSV interacts with other pathogens to cause severe respiratory symptoms in finishing pigs

Question 20

Describe the mechanism by which PRRSV interacts with other pathogens?

Answer 20

It is still under investigation but it has been demonstrated experimentally that:

• Mycoplasma enhances the pathological effects of PRRSV
• PRRSV enhances the pathological effects of Porcine Influenza virus
• PRRSV predisposes pigs to infection and disease caused by Streptococcus suis
• PRRSV can cause a loss of the bactericidal function of pulmonary intravascular macrophages

Question 21

What are the 3 methods of laboratory diagnosis of PRRSV?

Answer 21

• Serology
• ELISA
• Immune fluorescence

Question 22

What serological testing used for?

Answer 22

Serological testing can be used to determine the status of a herd: infected or free. Paired samples are required to confirm the involvement of PRRSV in the clinical problem seen in the herd at a particular point in time

Question 23

What is oral fluid?

Answer 23

Oral fluid is a mixture of saliva and “oral mucosal transudate”
Contains both pathogens and antibodies

Question 24

How should oral fluid samples be handled?

Answer 24

Freeze samples promptly to optimize quality.Oral fluid samples for same day submission may be chilled and submitted on wet ice. Maintain the cold chain to preserve sample integrity.

Question 25

Prognostic profiling relies on testing oral fluid samples how often?

Answer 25

At 2 week intervals

Question 26

Where are PRRSV vaccine targetting?

Answer 26

The surface glycoproteins

Question 27

What are the effects of PRRSV vaccines?

Answer 27

These vaccines are effective in reducing clinical signs and the duration of viral shedding, but they are not likely to completely prevent infection. Also, the vaccine efficacy tended to drop significantly upon heterologous challenge.