Viral Diseases of Swine - Lectures 15, 16

What swine viruses are important in the USA?

• PRRS

• PCV2

• Swine influenza

• Rotavirus

• PED (also delta coronavirus, TGE)

• Porcine parvovirus

What swine viruses are less important in USA?

• Senecavirus A

• Pseudorabies virus (PRV)

• inclusion body rhinitis

• Porcine picomaviruses (Entero, Teschen, Talfan, Sapelovirus)

• HEV (hemagglutinating encephlomyelitis virus

• Porcine respiratory coronavirus (PRCV)

• Swine pox

• Non-foreign animal disease vesciular diseases (stomatisis exanthema)

• Encephalomyocarditis virus (EMC)

What swine viruses are foreign animal diseases?

• foot and mouth disease

• african swine fever

• classical swine fever (hog cholera)

• swine vesicular disease

• Japanese encephalitis

• Blue eye disease

What swine viruses are emerging in USA?

• Atypical porcine pestivirus

• Procine circovirus type 3

• Porcine sapovirus

• Procine parainfluenza virus type 1

• Torque teno virus

• Hepatitis E virus

• Filioviruses (ebola, Marburg)

• parmyxoviruses (menangle, nipah)

• Pestivirus F (Bungowannah)

• Porcine adenovirus, astrovirus-4, bocavirus

• West nile virus (Kunjin virus)

• Porcine circovirus type 4

Do DNA or RNA viruses have a higher mutation rate?

RNA

Are enveloped or non-enveloped viruses more durable in the environment and resistant to disinfection?

Non-enveloped

Point mutations during replication causes what?

genetic drift

What requires co-infection of two variants in a single host cell?

recombination

Define localized pathogenesis (tissue/cell tropism).

• specific cell type in specific tissue

• specific lesion in infected cell

• apoptosis (bystander cell death)

What is an example of localized pathogenesis?

Swine influenza in respiratory tract

Define systemic pathogenesis (tissue/cell tropism).

• infects immune cells (macrophage, lymphocyte)

• promotes co-infections via cytokines induced which causes prolonged resolution of infection (prolonged shedding)

• prostaglandin release causes luteolysis and maternal abortion

Give an example of a virus with systemic pathogenesis that promots co-infections via cytokines induced.

• PRRS

• PCV2 (circovirus)

Give an example of a virus with systemic pathogenesis and causes maternal abortion due to prostaglandin release.

influenza

Define virulence.

• ability to cause disease in populations

• disease severity in infected animals

• dose dependent

What affects transmissibility of a virus?

• minimum infecting dose

• shedding pattern (amount and duration)

• persistance in environment

Give examples of general clinical signs.

• fever (tachypnea), appetite, behavior (lethargy)

Give examples of specific clinical signs.

• cough, tachypnea, diarrhea, fetal death

True or false: There are no “long term” decision without lab testing in US swine industry.

True

Define pathognomic.

specific sign or symptom that is characteristic and indicative of a particular disease

Are swine viral disease pathognomic?

rarely

Give examples of control strategies.

• vaccination

• biosecurity

• metaphylactic antimicrobials

What sample methods can be used?

• blood

• nasal and fecal swabs

• tissues (necropsy, baby pig tongues)

• oral fluids

• processing fluids

• placental umbilical cord blood

• udder wipes

• environmental wipes

Match the sampling method to the description:

• newer method

• mainly used for pathogen detection via PCR but culture is susceptible to contamination

• more sensitive than oral or nasal swabs for PCR

• antibody assessment in development

oral fluids

Match the sampling method to the description:

• testicles from castration or tails from tail docking

• can use daily aggregate for herd monitoring

• can use litter sample for research with litter as experimental unit

• tails contribute very little blood/fluid

processing fluids

Match the sampling method to the description:

• in utero transmission

• umbilical cord from the “placental” side

• “milk” 3-5 cords per litter into one tube

• “pre-suckle” sample — no maternal antibody

• test “as is” — no centrifugation

PUCS — Placental Umbilical Cord Serum (blood)

Match the laboratory tests to the description:

• demonstrate/localize virus in microscopic (histopath) lesion

• used to detect viral nucleic acid via primer

in situ hybridization (ISH)

Match the laboratory tests to the description:

• demonstrate/localize virus in microscopic (histopath) lesion

• detects viral antigen in lesion via antibody

immunohistochemistry (IHC)

Match the laboratory tests to the description:

• detects viral nucleic acid (analyte)

• very sensitive and specific

• semiquantititative analyte concentration is based on cycle times

• quantitative analyte concentration based on standard curve generated from dilutions of known amount of analyte ont he same microtiter plate

PCR

Match the laboratory tests to the description:

• standard — “Sanger”; known target

• NGS enables identification of. “unknown” viruses in a sample

Sequencing

Match the laboratory tests to the description:

• mainly ELISAs

• IFA for PCV2

• hemagglutination inhibition for flu

• virus/serum neutralization is rare now but still best for surrogate estimating protection

• historical view of exposure

• disease surveillance (PCR used more now)

• vaccination compliance monitoring

serology

What are “platform” vaccines?

• non-replicating, RNA particle or naked DNA

• subunit, vectored — baculovirus system

What type of vaccine is used for all standard vaccine antigens and is adjuvant driven?

killed

What factors can determine vaccination success?

• use of the correct antigen

• vaccination timing (maternal antibody interference needs to be avoided)

• were pigs infected before or during vaccination (unstable sow herd)

• compliance (injection quality/accuracy)

What are the external components of biosecurity?

• incoming animals and semen (PRRS)

• people

What are the internal components of biosecurity?

• evaluate cleaning/disinfection processes (post PED outbreak)

• change nedles to prevent disease spread (PRRS)

Which virus is described by the following:

• RNA virus, enveloped

• segmented genome

• genetics is constantly changing (antigenic drift and shift)

• type A is animals

Swine influenza virus

Which genetic change requires co-infection of a cell, is receptor based, and is caused by gene recombination?

antigenic shift

The pig acts as a mixing vessel for antigenic shift of which virus?

Swine influenza virus

What promotes reassortment of viruses in genetic shift/reassortment?

TRIG cassette

What are the three important antigns of swine influenza virus?

• hemagglutinin (HA)

• neuraminidase (NA)

• nucleoprotein

Which antigen of swine influenza virus is the main antigen for vaccines, is involved in cell entry, and is used for diagnostic assays?

hemagglutinin

Which antigen of swine influenza virus is involved in cell exit and cell to cell spread, and is used as a minor antigen for vaccines (more recent)?

Neuraminidase

Which antigen of swine influenza virus is conserved among type A’s and is the antigen for ELISA antibody test?

nucleoprotein

What is the traditional strain of swine flu in the US?

H1N1

What is the relatively new strain of swine flu to the US in 1998, spread throughout the country in 2-3 years, and has a promiscuous gene group (TRIG cassette)?

H3N2

What is the strain of swine flu first detected in Indiana and is a combination of H1N1 and H3N2?

H1N2

Swine flu is transmitted how?

direct transmission via aerosols

The airborne spread of swine flu has rapid onset in growing pigs, which may result in what and last how long?

• may result in explosive outbreaks (epidmic form)

• may last 7-14 days

The endemic form of swine flu is due to what?

• incomplete immunity

• continuous source of pigs

Where is the replication site for swine flu?

• upper airways

• trachea, bronchi, bronchioles

• respiratory epithelium

Detecatble antibody of swine flu appears in how many days?

6-7 days

What are the clinical signs of swine flu?

• sudden onset after incubation

• “goose honk” cough

• fever >105 degrees, but variable

• nasal/ocular discharge

• anorexia

• lethargy

• dyspnea (labored breathing)

• abortion due to prostaglandin release from lungs

Are the gross lesions of swine flu pathognomic?

No, confirmatory lab testing is required

What causes the cough of swine flu?

degeneration and necrosis of respiratory epithelium

What can be used as presumptive diagnosis for swine flu?

acute respiratory outbreak involving herd

What can be used as definitive detection of swine flu?

• nasal swabs (PCR)

• tissue (IHC, PCR)

• acute stage of disease (within 4 days)

Sequencing is common for strain matching of swine flu, which is important for what?

• autogenous vaccine production

• platform vaccine production (vaccine made from sequence information)

• homologous HI serology testing

Which serology test for swine flu is described by the following:

• nucleprotein antibody (conserved antigen so no subtype differentation)

• exposure or vaccination

• limited use now

ELISA

Which serology test for swine flu is described by the following:

• HA antibody

• must match HA type

• ability to evaluate cross reactivity between HA types (homologous format by using specific variants)

Hemagglutination inhibition

Which molecular technique of swine flu is decribed by the following:

• virus detection

• subtyping using several primers

PCR

Which molecular technique of swine flu is described by the following:

• homology tables

• dendograms

sequencing (standard)

What is the treatment protocol for swine flu?

• no specific therapy

• nursing care, draft-free, warm, dry environment

• antibiotics for secondary bacterial infections (water meds for all pigs in barn, injectable meds for severe pigs)

• anti-inflammatories in water (aspirin no longer allowed due to FDA regulations, use ibuprofen)

What is the prevention protocol for swine flu?

• maintain good biosecurity (proper cleaning and disinfecting, limit people and animal movement, quarantine new arrivals)

• vaccination

• maternal derived antibody (vaccination of sows to protect pigs, may interfere with piglet vaccination)

What should we keep in mind when using the new NA vaccine?

• limit infection in sows with HA vaccine

• low levels of NA MDA means there will be minimal MDA vaccine interference

What virus is the most important disease in pigs worldwide and impacts nearly all production decisions?

PRRS

The following genetic characteristics matches which virus:

• constantly mutating (“quasi-species”, variable expression of disease severity)

• immunity introduced by one “strain” does not protect against another “strain” causes implications for vaccine development

PRRS

What is the pathogenesis of PRRS virus?

• infects dendritic cells (macrophages) primarily in respiratory tract

• cytokine mediated disease

What macrophages attacked by PRRS allow for increased susceptibility to bacteria that circulate in blood like Strep suis and Glaeserella parasuis?

Pulmonary intravascular macrophages

Which macrophages attacked by PRRS cause increased suscpetibility to other respiratory pathogens?

pulmonary alveolar macrophages

How is PRRS transmitted?

oro-nasal spread (body secretions including semen and blood via injections from using the same needle)

PRRS is highly infectious, meaning what?

takes only a few particles to infect a pig and an increasing dose means quicker onset of disease

What affects of PRRS virus can be seen in the gestational stage of reproduction?

• weak born pigs

• stillborn pigs

• mummies

• early embryonic death causing reduced litter size

• return to estrus

• abortion

Since PRRS virus is shed in semen, boars in studs are monitored how?

by PCR testing of blood swabs

What is the clinical outcome of PRRS virus in suckling and nursery pigs?

• severe respiratory disease including interstitial pneumonia

• rapid breathing, especially after stress

• variable death loss

• often takes 30-45 days longer to reach market

• severity of infection diminished greatly after 8 weeks of age unless co-infected with another agent like Porcine circovirus type 2, swine flu, or Mycoplasma hypopneumoniae

What is the appearance of gross lesions of interstitial pneumonia due to PRRS virus?

• can visualize septa — fine pattern

• tan discoloration — mottles or coalescing

• rubbery texture

• fail to collapse

What are the best enlarged lymphnodes to view for PRRS virus? Why?

sub-iliacs because they are least likely to be affected by other pathogens

What lab tests can be used for PRRs virus?

• histopath in cases of interstitial pneumonia

• IHC in tissues

• PCR in tissues, blood, fluids

• serology (ELISA)

• virus characterization

Which lab test can not be used as a measure of protection since PRRS seroconverts by 2 weeks post infection and has some false positive results?

ELISA

What is the purpose of virus characterization of PRRS virus?

• epidemiologic investigations — biosecurity lapses

• not strain matching for vaccine selection

What are the methods of virus characterization for PRRS virus?

• RFLP (restriction fragment length polymorphism)

When seuqencing PRRS virus for virus characterization, what is the part found which codes for a major envelope glycoprotein?

ORF5

What is the treatment protocol for PRRS virus?

• supportive (no more aspirin due to FDA, ibuprofen)

• control secondary bacterial infections

What is the prevention protocol for PRRS virus?

• biosecurity (people, fumigation chamber for supplies, support functions, air filtration of facilities)

• monitoring by PCR of sow herds via offspring and blood swabs of boars

• vaccination

• outbreak management via load (replacements), close (no new animals for 6-8 months), and expose via live virus inoculation

What circovirus type is the cause of post-weaning multi-systemic wasting syndrome (now referred to as PCVAD or PCVD)?

type 2

Which circovirus type is the possible cause of infectious congenital tremors and is a porcine cell line contaminant?

type 1

Which circovirus type is discovered more recently (2016) and has 35-40% genetic homology to PCV2?

type 3

Which circovirus type is the most recently discovered (2019) and has been seen in China, South Korea, and Spain?

Type 4

Which DNA virus evolved from non-pathogenic to pathogenic within the swine population and has a high rate of mutation compared to other DNA viruses (but mutation has not yet caused vaccine failure)?

PCV2

Which subtype of PCV2 is used as antigen in vaccines?

PCV2a

Which subtype of PCV2 is highly pathogenic, has high death loss, and has become the dominant strain since its emergence in 2006?

PCV2b

Which subtype of PCV2 has a chinese origin, and emerged 9-10 years ago?

PCV2d

The following physical characteristics matches which virus:

• physically very durable

• non-enveloped

• very stable in environment which makes controlling exposure dose more problematic

PCV2

Since PCV2 is so stable and persistant in the environment, what is important?

high rate of vaccination success

What is the pathogenesis of PCV2?

• infects lymphocytes which leads to atrophy of lymph nodes and immune suppression

• prolonged infection

• delayed development of neutralizing antibodies

• infection does not always lead to disease but high case mortality rates in affected pigs

How long is PCV2 virus shed?

• at least 70 days via nasal secretions and/or feces

• viremic (virus in blood) for 3-5 months

All PMWS cases are positive for what?

PCV2

Do all PCV2 positive pigs have PMWS?

No, but all PMWS cases are PCV2 positive

What are other contributing factors are strongly associated with PCV2 pathogenesis?

• hard to replicate severe diease under lab conditions

• viral burden

• bacterial burden

• stressors (environment, nutrition, management)

• immune stimulation (vaccination, environemntal endotoxins)

• inherent attributes (genetics, litter origin, dam parity)

What are the three criteria for diagnosing PCVAD (PCV2)?

• wasting

• microscopic lesions (lymphoid depletion —> granulomatous infiltration)

• detection of PCV2 in lesions (nucleic acid by in situ hybridization initially, but now we have antigen by immunochemistry)

Describe wasting of PCV2.

• occurs quickly — cachexia

• water consumption declines causing dehydration

• high case mortality in pigs that exhibit wasting