Viral Diseases of Swine Flashcards
Swine virology is constantly evolving and rapidly changing with new emerging disease
Evolving Fields
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
Evolving Field:
Swine Influenza Virus
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
Evolving Field:
Porcine Reproductive and Respiratory Syndrome Virus (PRRSV)
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
Evolving Field:
African Swine Fever Virus
2007: Introduced into eastern europe, caucus and russia
2018-2020: Introduced into China, Belgium, +12 asian countries
2020: Introduced into Germany
Gilt
female that has not produced a litter of piglets
Sow
female taht has produced a litter of piglets
Boar
intact male
Barrow
castrated male
farrow
to give birth to a litter of piglets
Swine Production:
- Breeding and Gestation
3 months, 3 weeks, 3 days (114d)
Swine Production:
- Farrowing
Birth to weaning
3 week weaning common
Swine production:
- nursery
weaking to 40-50 lbs
Swine Production:
4 Grower - Finisher
until market 250-300lbs
~6 months
Swine Production:
Changes in pig production over time
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
Betaarterivirus
Porcine reproductive and respiratory syndrome virus
Arteriviridae
- Arteri:
- artery
- Single-stranded, positive-sense, RNA virus, enveloped
- Ability to establish prolonged or persistent infections
PRRSV:
Commercial Assay
measure anti-N antibodies
PRRSV:
- FIrst emerged in late 1980s-early 1990s
- Two genotypes
- Genotype 1:
- European
- Genotype 2:
- North American
- Genotype 1:
- Both Genotypes now present worldwide
- High genetic diversity within genotype
- Highest mutation rate for any RNA viruse
- Quasispecies within farm and individual
PRRS is a population disease
-
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
PRRSV:
Kansas Outbreak
2006 Kansas Outbreak
5,500 sow farm
>400 abortions in the first week
Mortality in nursing pigs >50%
Estimate after 1st month: cost >$4millio
PRRSV:
Transmission
- 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
-
Direct: horizontal and vertical transmission
Key Concepts for PRRSV
- Disease occurs in:
- Pregnant gilts and sows :
- Reproductive Failure
- Nursery and Grow-finish pigs:
- Respiratory
- Pregnant gilts and sows :
- Primary site of virus replication:
- MACROPHAGES
PRRSV Infection:
Phase 1
Initial virus replication occurs in the macrophages and dendritic cells of the lungs and upper respiratory tract
PRRSV Infection:
Phase 2
Viremia results within 6-12 hours of infection
Viremia may last for several weeks
Replication in macrophages throughout the body
PRRSV Infection:
Phase 3: Persistent Infection
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”)
PRRSV: Pathogenesis
PRRSV:
Pathogenesis:
Innate Immunity
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
PRRSV:
Pathogenesis:
Adaptive Immunity
Early Production of non-neutralizing antibodies
Delayed production of neutralizing antibodies
Delayed IFN-y producing cells
Pathogenesis, with susceptibility
PRRSV:
Pathogenesis:
Effect on other pathogens
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
PRRSV:
Pathogenesis:
Seasonal
incidence rate high during fall and winter
Incidence rate low during spring and summer
PRRS:
Disease Syndromes:
1, Reproductive Failure
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
- increased stillborm piglets, mummified fetuses, premature farrowings, weak-born pigs, embryonic death, Late-term abortions
- Outbreaks typically last 1-4 months
PRRS:
Gross Lesions
PRRS:
Disease:
- Respiratory Disease
- 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
PRRS:
Respiratory disease:
Gross lesions
Interstitial pneumonia
Lungs wet, heavy
Can be difficult to differentiate form normal
enlarged lymph nodes
PRRS:
Microscopic lesions
- Interstitial pneumonia
- characterisc lesion
- severe and necrotizing
- Macrophages and necrotic cells in alveoli
- Lymphoid hyperplasia
- polyclonal B-cell activation
- Typically no lesion in fetuses
PRRS:
Clinical Manifestations:
Epidemic
Naive herd or new virus strain
All ages affected
Reproductive failure
Acute respiratory disease
Increased bacterial infections
PRRS:
Clinical manifestations:
Endemic - breeding herd immune
Only affects nursery / grower pigs
Respiratory disease
Increased bacterial infections
PRRSV: Diagnosis
Serology
- ELISA: IgG antibody
- detectable within 7-10 days post-infection
- Serum neutralization antibody
- delayed - may not appear until 28 dpi
PRRSV: Diagnosis
Virus Detection
- PCR
- Virus Isolation
- IHC
- Sequencing to determine isolate
PRRSV: Diagnosis
Oral Fluids
- Antibody and or virus detection
- population level sample
PRRSV:
Control
- No effective treatment for PRRS
- NSAIDs:
- reduce pyrexia / inflammation
- Antibiotics:
- reduce secondary bacterial infectins
- NSAIDs:
- 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
- primary means of control
PRRS:
Vaccination
- 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
PRRSV:
Elimination
- 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
- segregated early weaning
PRRSV:
Farm Biosecurity
- 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
