Swine Influenza

Question 1

What are the characteristics of viruses of the family Orthomyxoviridae?

Answer 1

• Orthomyxo - stright mucus
• Single-stranded
• negative-sense
• RNA virus
• Enveloped

Question 2

What are the Genera of Orthomyxoviridae?

Answer 2

• 4 primary genera:
  
  • Influenza A virus (human, birds, mammals)
  • Influenza B virus (almost exclusively humans)
  • Influenza C virus (humans, pigs, dogs
  • Influenza D virus (cattle, pigs

Question 3

What is the genome of a influenza virus like?

Answer 3

• Segmented genome
  
  • 8 segments
  • ssRNA: 14 kb

Question 4

How are influenza viruses classified?

Answer 4

• Based on hemagglutinin and neuraminidase:
  
  • spike-like proteins that project from the surface, important in pathogenesis

Question 5

How are Influenza viruses named?

Answer 5

• Standardized:
  
  • Type/ animal of origin/ geographic origin/ strain number/ year of isolation/ subtype in parentheses
  • No animal species given in Human viruses
  • Ex:
    
    • A/swine/Kansas/B4553/2010 (H1N1)
• Clade system:
  
  • Clade - group of viruses with common ancestor
  • Based on genomic sequences

Question 6

What is hemagglutinin (HA or H)?

Answer 6

• Binds to sialic acid receptors on host cells
• Virus entry into cells
• 18 subtypes (H1 - H18)
• High rates of mutation
• Target of vaccination
• Dominant Antigen recognized by immune system
  
  • Antibodies to hemagglutinin will neutralize the virus

Question 6

What is Neuraminidase (NA or N)?

Answer 6

• Cleaves sialic acid on host cells
• Virus release from host cells and penetration of mucus
  
  • virus is released from parent cell and surrounding mucous layer
  • Repenetrates mucous layer and attaches to new respiratory epithelial cell
• 11 subtypes (N1 - N11)
• Oseltamivir (Tamiflu): neuraminidase inhibitor (limits viral spread)

Question 7

What happens when 2 different strains infect a cell simultaneously?

Answer 7

• Genetic reassortment can occur
  
  • can generate viruses containing a new HA, new NA, or both

Question 8

How is Genetic reassortment different from antigenic drift?

Answer 8

• Genetic Reassortment (antigenic shift)
  
  • Allows rapid major changes in the genetic make-up of influenza viruses
  • Exchange of gene segments ⇢ Subtype change
    
    • Can cause pandemics
• Antigenic drift:
  
  • Subtle point mutations & small changes that occur gradually over time
  • Driven by host immune system
  • Affects antigenic sites in HA and NA
  • Ab no longer fully protective
    
    • Reason for seasonal flu changes
  • Does NOT result in pandemics

Question 9

What is Swine influenza virus (SIV)?

Answer 9

• Caused by influenza type A virus
• Classified by 2 proteins::
  
  • Hemagglutinin (HA)
  • Neuraminidase (NA)
• Different combinations of H and N proteins create subtypes
• Little or no cross-protection between subtypes
• Worldwide distribution
• One of the most important causes of Acute respiratory disease in pigs
  
  • 2009 Pandemic strain of H1N1

Question 10

Is SIV zoonotic?

Answer 10

• Yes, but relatively rare
• human to human transmission inefficient

Question 11

What is the Avian-human species barrier?

Answer 11

• For Influenza A viruses
• Avian influenza virus prefers a2-3 sialic acid receptors
  
  • in the respiratory and GI cells of birds
• Human influenza virus prefers a2-6 sialic acid receptors
  
  • in the respiratory cells of humans

Question 12

How do pigs affect the Avian-human species barrier?

Answer 12

• Considered intermediate “mixing-vessel” host
  
  • Can be infected with both avian and human influenza viruses
  • Potential for genetic shift and Evolution of pandemic viruses

Question 13

What are the key Concepts for SIV?

Answer 13

• Acute, highly contagious, respiratory disease of swine
• Common and widespread in US swine
  
  • nearly all herd in Midwest seropositive
• Effective vaccination becoming difficult due to increased viral diversity
• Primary subtypes circulating in swine:
  
  • H1N1, H1N2, H3N2

Question 14

What is the epidemiologic information for SIV?

Answer 14

• Outbreaks historically common in fall and winter but can occur year-round
• Sudden onset, Rapid spread
  
  • Clinical signs 1-3 dpi
  • Shedding 1-2dpi can continues for 5-8dpi
  • Asymptomatic long-term carrier pigs are rare

Question 15

How do Ab+ swine herds fair in new SIV outbreaks?

Answer 15

• Ab mitigate severity of disease and spread throughout herd
• Outbreaks occur when immunity wanes

Question 16

What is the virulence of SIV?

Answer 16

• Field isolates vary
  
  • Infection ranges from subclinical to acute severe disease
  • May depend on co-factors, co-pathogens (secondary bacterial infections are common)
    
    • Haemophilus parasuis, Actinobacillus pleuropneumoniae, Mycoplasma hyopneumoniae, PRRSV

Question 17

How is SIV transmitted

Answer 17

By aerosolization and pig-to-pig contact (primarily nasal secretions)

Question 18

How does SIV infect an animal?

Answer 18

• Gains access by nasopharyngeal route
• Replicates in the epithelial cells of the nasal mucosa, tonsils, trachea, and lungs
• Epithelium of the bronchi, bronchioles and alveoli can be severely compromised
• Influx of neutrophils and other inflammatory cells leads to epithelial cell necrosis of cells lining the bronchi and bronchioles
• Inflammatory exudate can block smaller airways, leading to atelectasis, emphysema, and bronchointerstitial pneumonia
• Epithelium usually heals within 5-7 days

Question 19

What does the Clinical Disease of SIV look like?

Answer 19

• Sudden onset, rapid spread within 1-3 days
• Clinical signs: pyrexia, deep hacking cough, depression, etc
• Morbidity high: up to 100%
• Mortality low 1-4%
• Duration: 3-7 days
• Economic loss: reduced growth rates and increased time to market weight
• Potential for abortions in late pregnancy

Question 20

What are the clinical signs of SIV?

Answer 20

• Depression
• Pyrexia
• Decreased appetite
• Deep hacking cough
• Sneezing
• weight loss
• huddling
• dyspnea
• tachypnea
• weakness
• conjunctivitis
• mucoid oculonasal discharge

Question 21

What are the common gross lesions of SIV?

Answer 21

• Usually confined to thorax
• Lung:
  
  • Cranioventral bronchointerstitial pneumonia
    
    • lobular distribution of congestion, firmness, atelectasis, emphysema
    • Lesions typically well-demarcated, consolidated and purple/red
    • Lesions tend to be more extensive in apical and cardiac lobes
• Airways:
  
  • Necrotizing bronchitis/bronchiolitis
    
    • may contain mucopurulent or blood-tinged exudate
• Lymph Nodes:
  
  • variably enlarged and congested

Question 22

When should SIV be suspected in a herd?

Answer 22

• History of sudden onset of severe respiratory illness affecting most animals, along with typical signs and lesions

Question 23

How is SIV diagnosed?

Answer 23

• Samples should be collected within 24-72 hours of clinical onset
• Nucleic acid or Ag detection
  
  • Acute phase: nasal swabs, lung tissue
  • Virus isolation, PCR, sequencing, FA, IHC, ELISA
• Antibody
  
  • ELISA
  • Hemagglutination inhibition (HI)
    
    • paired acute and convalescent titers
    • H1 and H3 subtype antigen

Question 24

What is the treatment for SIV?

Answer 24

• No effective treatment
• Supportive care:
  
  • Antimicrobials for secondary bacterial infections
  • NSAIDs for severely affected pigs

Question 25

Is there a vaccine for SIV?

Answer 25

• Commercial killed viruses in US
  
  • Combinations of H1N1, H1N2, H3N2
  • Vaccination of sow/gilts, boars, and piglets
  • Reduce clinical signs but do not always prevent infection
• Autogenous killed vaccines - commercial RNA vaccine, commercial intranasal live attenuated influenza vaccine

Question 26

Are there maternal Abs for SIV?

Answer 26

• Decrease severity of illness in piglets but can also impair the development of immunity
  
  • Colostral Ab may protect piglets for 5-14 weeks
  • Potential interference with vaccine efficacy
  • Vaccines typically given in 2 doses 3 weeks apart

Question 27

What is VAERD?

Answer 27

• Vaccine-associated enhanced respiratory disease
• Combinations SIV vaccine and poorly matched challenge viruses may exacerbate disease in pigs

Question 28

How can SIV be controlled?

Answer 28

• Virus unlikely to survive in environment >2weeks (unless cold conditions/protected from sun)
  
  • Readily inactivated by heat/disinfectants
  • All in/all out with cleaning and disinfecting facilities
• Strict import controls and biosecurity
  
  • Maintain closed herd to avoid introducing infected pigs
  • Stabilizing breeding herd by acclimatization or vaccination
  • Isolating clinical animals may reduce transmission among herd
• management practices and reducing stress
  
  • Overcrowding, air quality, reducing dust
  • People with influenza-like illness should avoid contact with pigs
• Determine sequence/subtype of circulating SIV