Viral Diseases of Swine

Question 1

Swine virology is constantly evolving and rapidly changing with new emerging disease

Answer 1

Question 2

Evolving Fields

Answer 2

Pseudorabies virus

1983: 18.8% of U.S. breeding herds seropositive
2004: PRV eradicated from U.S. commercial swine
2022: PRV still present in U.S. feral swine

Question 3

Evolving Field:

Swine Influenza Virus

Answer 3

1918: Human Pandemic Strain
1998: New Strains with genes from human and avian viruses appeared in U.S. swine
2009: Pandemic H1N1 derived from pig virus

Question 4

Evolving Field:

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV)

Answer 4

1987: first recognition of disease
2022: considered most costly swine disease in U.S.

Porcine Epidemic diarrhea virus

2013: Emerged in U.S. 7 million pigs died in 1st year

Question 5

Evolving Field:

African Swine Fever Virus

Answer 5

2007: Introduced into eastern europe, caucus and russia

2018-2020: Introduced into China, Belgium, +12 asian countries

2020: Introduced into Germany

Question 6

Gilt

Answer 6

female that has not produced a litter of piglets

Question 7

Sow

Answer 7

female taht has produced a litter of piglets

Question 8

Boar

Answer 8

intact male

Question 9

Barrow

Answer 9

castrated male

Question 10

farrow

Answer 10

to give birth to a litter of piglets

Question 11

Swine Production:

1. Breeding and Gestation

Answer 11

3 months, 3 weeks, 3 days (114d)

Question 12

Swine Production:

2. Farrowing

Answer 12

Birth to weaning

3 week weaning common

Question 13

Swine production:

3. nursery

Answer 13

weaking to 40-50 lbs

Question 14

Swine Production:

4 Grower - Finisher

Answer 14

until market 250-300lbs

~6 months

Question 15

Swine Production:

Changes in pig production over time

Answer 15

Change over time = changes in disease susceptibility

Large Farms – nearly continuous farrowing

Continuous supply of naive pigs, source of viral shedding

Specialized swine finishing facilities

Shipping pigs after weaning

Question 16

Betaarterivirus

Answer 16

Porcine reproductive and respiratory syndrome virus

Question 17

Arteriviridae

Answer 17

• Arteri:
  
  • artery
• Single-stranded, positive-sense, RNA virus, enveloped
• Ability to establish prolonged or persistent infections

Question 18

PRRSV:

Commercial Assay

Answer 18

measure anti-N antibodies

Question 19

PRRSV:

Answer 19

• FIrst emerged in late 1980s-early 1990s
• Two genotypes
  
  • Genotype 1:
    
    • European
  • Genotype 2:
    
    • North American
• Both Genotypes now present worldwide
  
  • High genetic diversity within genotype
  • Highest mutation rate for any RNA viruse
  • Quasispecies within farm and individual

Question 20

PRRS is a population disease

Answer 20

• Most costly disease of swine in US
  
  • seroprevalence estimated at 71.1% of sites in U.S
  • Costs $664 million / year
    
    • production of herd decreased by 15%
    • Increased pre-weaning mortality 10-40%
    • Animal health costs increased 4x

Question 21

PRRSV:

Kansas Outbreak

Answer 21

2006 Kansas Outbreak

5,500 sow farm

>400 abortions in the first week

Mortality in nursing pigs >50%

Estimate after 1st month: cost >$4millio

Question 22

PRRSV:

Transmission

Answer 22

• Routes of Transmission (EFFICIENT transmisstion)
  
  • Direct: horizontal and vertical transmission
    
    • primary vector; Infected pig
    • PRRSV can cross the placenta in 3rd trimester
  • Indirect: contact with contaminated Fomites +/- aerosol
    
    • needles, boots, coveralls, transport vehicles
    • Importance of aerosol transmission controversial

Question 23

Key Concepts for PRRSV

Answer 23

• Disease occurs in:
  
  • Pregnant gilts and sows :
    
    • Reproductive Failure
  • Nursery and Grow-finish pigs:
    
    • Respiratory
• Primary site of virus replication:
  
  • MACROPHAGES

Question 24

PRRSV Infection:

Phase 1

Answer 24

Initial virus replication occurs in the macrophages and dendritic cells of the lungs and upper respiratory tract

Question 25

PRRSV Infection: Phase 2

Answer 25

Viremia results within 6-12 hours of infection Viremia may last for several weeks Replication in macrophages throughout the body

Question 26

PRRSV Infection: Phase 3: Persistent Infection

Answer 26

Virus replication localized to lymphoid tisses, including Tonsils and Lymph Nodes Virus is no longer detectable in blood and lungs No clinical signs of disease Most pigs clear virus by 3-4 months, but replication can be maintained for 250 days ("life-long")

Question 27

PRRSV: Pathogenesis

Answer 27

Question 28

PRRSV: Pathogenesis: Innate Immunity

Answer 28

inhibits IFN-a Modulates TNF-a and IL-1B production Induces regulatory cytokines, such as IL-10 Inhibits Toll-Like receptors Inhibits NK cells Modulates antigen Presentation and T cell activation

Question 29

PRRSV: Pathogenesis: Adaptive Immunity

Answer 29

Early Production of non-neutralizing antibodies Delayed production of neutralizing antibodies Delayed IFN-y producing cells

Question 30

Answer 30

Pathogenesis, with susceptibility

Question 31

PRRSV: Pathogenesis: Effect on other pathogens

Answer 31

PRRSV infections increases severity of disease caused by other pathogens Porcine circovirus Type 2 Mycoplasma hyopneumoniae Bordetella bronchiseptica PRRSV is the most common virus isolated in clinical cases of porcine respiratory disease complex

Question 32

PRRSV: Pathogenesis: Seasonal

Answer 32

incidence rate high during fall and winter Incidence rate low during spring and summer

Question 33

PRRS: Disease Syndromes: 1, Reproductive Failure

Answer 33

All Parties: pregnant sows and gilts * Clinical Sings: * increased stillborm piglets, mummified fetuses, premature farrowings, weak-born pigs, embryonic death, Late-term abortions * Stillbirths and mummies may increase 25-35% * Abortions may be \>10% * Lethargy, reduced appetite and fever * May see cyanosis of ears and skin * Agalactia in lactating sows * Increase in preweaning mortality * Outbreaks typically last 1-4 months

Question 34

PRRS: Gross Lesions

Answer 34

Question 35

PRRS: Disease: 2. Respiratory Disease

Answer 35

* Newborn, nursery \>\>\>\> Grow-finish pigs * Clinical sings: * dyspnea, tachypnea, open-mouth breathing * lethargy, depression, increased mortality * Reduced appetite, and poor growth * Diarrhea, nasal discharge, coughing, sneezing, fever, aural cyanosis or “Blue ear” * reduced daily weight gain of pigs by 85% * Increase in postweaning mortalitiy * Increased bacterial infections

Question 36

PRRS: Respiratory disease: Gross lesions

Answer 36

Interstitial pneumonia Lungs wet, heavy Can be difficult to differentiate form normal enlarged lymph nodes

Question 37

PRRS: Microscopic lesions

Answer 37

* Interstitial pneumonia * characterisc lesion * severe and necrotizing * Macrophages and necrotic cells in alveoli * Lymphoid hyperplasia * polyclonal B-cell activation * Typically no lesion in fetuses

Question 38

PRRS: Clinical Manifestations: Epidemic

Answer 38

Naive herd or new virus strain All ages affected Reproductive failure Acute respiratory disease Increased bacterial infections

Question 39

PRRS: Clinical manifestations: Endemic - breeding herd immune

Answer 39

Only affects nursery / grower pigs Respiratory disease Increased bacterial infections

Question 40

PRRSV: Diagnosis Serology

Answer 40

* ELISA: IgG antibody * detectable within 7-10 days post-infection * Serum neutralization antibody * delayed - may not appear until 28 dpi

Question 41

PRRSV: Diagnosis Virus Detection

Answer 41

* PCR * Virus Isolation * IHC * Sequencing to determine isolate

Question 42

PRRSV: Diagnosis Oral Fluids

Answer 42

* Antibody and or virus detection * population level sample

Question 43

PRRSV: Control

Answer 43

* No effective treatment for PRRS * NSAIDs: * reduce pyrexia / inflammation * Antibiotics: * reduce secondary bacterial infectins * PREVENTING INFECTION: * primary means of control * testing replacement gilts and boars * Isolation / acclimatization of incoming animals * test on arrival to isolation facility and 45-60 days later prior to introduction into the herd

Question 44

PRRS: Vaccination

Answer 44

* killed vaccines considered ineffective when used alone * **Modified live virus vaccines** * commercially available * used over the last 20+ years * Effective in controlling outbreaks, reducing virus replication and clinical disease, decreasing economic losses * _Limitations:_ * does not provide sterilizing immunity * viral sheding and transmission still occurs * reduces weight gain in pigs if NOT exposed to wildtype PRRSV * Potential for reversion ot virulence and persistent infection * Unable to differentiate infected form vaccinated * Should not vaccinate bors with MLV * Challenges in PRRS vaccine development: * antigenic heterogeneity makes broad protection difficult * Sophisticated immune evasion strategies of the virus

Question 45

PRRSV: Elimination

Answer 45

* Strategies to eliminate PRRSV from herd * segregated early weaning * preventing exposure during nursing * Nursery depopulation * successful when no virus transmisstion in sow herd but nursery and grow/dinish pigs still actively infected * Nursery pigs removed * Nurseries disinfected and left empty for 7-14 days * Endemic infections: * whole herd depopulation - repopulaiton, test and removal, herd closure

Question 46

PRRSV: Farm Biosecurity

Answer 46

* Strict quarantine and testing programs * Obtaining PRRv-naive breeding stock and semen * Sanitation of transport vehicles * Strict protocols of fomite and personnel movement between farms * Air filtration +/- aerosol * Disinfection * PRRSV is labile in environment * Inactivated by lipid solvents * Heat sensitive * Narrow pH stability range * Stable when chilled/frozen