Veterinary Influenza (Week 1, Mod 9)

What is the difference between an “enzootic” disease and an “epizootic” disease?

Enzootic means a disease is constantly present in an animal population at a low, predictable level

Epizootic is a sudden, widespread outbreak affecting a large proportion of animals, similar to an "epidemic".

• Interspecies infection

Describe the general characteristics of Swine Flu… how long does it last?  Symptoms?

• Seasonal, explosive outbreaks in fall and winter.

• Clinical disease lasts ~7 days

  • high fever

  • runny nose

  • lethargy

  • “goose honk” cough

  • reduced appetite!!!

• Few animals develop pneumonia

• High morbidity (~100%). 

• Low mortality

Describe the general characteristics of Equine Flu… how long does it last?  Symptoms?

• Enzootic in most countries

• Clinical disease lasts ~5-10 days

  • fever

  • dry hacking cough

  • conjunctivitis

  • runny nose

  • muscular soreness 

  • Few animals develop pneumonia

• High morbidity in unvaccinated herds (~100%). 

• Low mortality (except for foals)

Donkeys SEVERELY affected

Describe the general characteristics of Canine Flu… how long does it last?  Symptoms?

• Enzootic in Asia (UK is free of disease)

• Clinical disease variable: hyperacute (severe), 10-14 days (mild)

  • fever

  • runny nose

  • rarely pneumonia

• Could be fatal in adult animals

• Variable morbidity (home dogs vs kennel dogs). 

• Variable mortality

Describe the general characteristics of Bovine Flu… how long does it last?  Symptoms?

Virus affects the MAMMARY GLANDS

Transmission possibly associated with milking equipment and/or human handling while milking

• Recently emerged in USA

• Clinical signs

  • low appetite

  • reduced milk production 

  • abnormal appearance of milk (thickened, discolored). 

  • Lactating cows most affected

  • Abortions?

• No morbidity data available yet. Associated with cattle movement. 

• Low mortality

• High levels of virus in milk (destroyed by pasteurization)

• Diagnosis

  • PCR (milk)

Describe the general characteristics of Avian Flu (poultry)… how long does it last?  Symptoms?

Enzootic in wild birds

Epizootic in poultry; infected BY wild birds

• Clinical signs variable, two different possibilities:

  • Low pathogenicity influenza

    • Subclinical or mild respiratory disease

    • Anorexia 

    • Lethargy 

    • Decreased egg production

    • Ruffled feathers

  • High pathogenicity influenza

    • High mortality (sudden death)

    • Cessation of egg laying

    • Respiratory distress 

    • Diarrhea, cyanosis, edema of the head.

Describe the general characteristics of Avian Flu (wild birds)… how long does it last?  Symptoms?

MAINLY affects the GI tract if its a low pathogenicity infection… virus is then shed through feces

• Low pathogenicity viruses cause mild or no disease. They infect the GI tract and transmit via faecal-oral route. 

• High pathogenicity viruses cause outbreaks and epizootics. They can affect the resp tract too.

• Clinical signs variable (difficult to assess in wild birds)

  • High mortality

  • Swollen heads

  • Respiratory distress 

  • Neurological signs

How does animal influenza impact pig production? (3 things…)

• Weight loss 

• Poor growth 

• Can lose up to 12 pounds of body weight over a three to four-week period.

How does animal influenza impact poultry production? (4 things…)

• Culling and compensation (HPAI)

• Decline in egg production

• Trading restriction

• Infrastructural costs (biosafety)

How does influenza spread in general?

Either:

• Direct contact

• Indirect contact (fomites)

• Aerosol transmission

Describe the structure of the influenza virus particle… what kind of genome do they have?

The influenza viruses are:

• Pleomorphic (spherical and filamentous forms)

  • Are very sensitive to the environment; cannot withstand many chemicals or cleaners

• negative strand RNA viruses

• have a segmented genome (8 segments specifically), encapsidated into ribonucleoprotein complexes (RNPs)

• form enveloped virions

What are the two main surface proteins that can be found on the surface of influenza virions?

Hemagglutinin (HA)

Neuraminidase (NA)

What do we use to classify different influenza A viruses into subtypes? (ex: H1N1, H3N2, etc.)

The surface glycoproteins found on virion envelopes, hemagglutinin (HA) and neuraminidase (NA)

• Classified based on what TYPE of HA or NA there is

  • HA → 1, 2, 3… 19

  • NA → 1, 2, 3… 11

What is the main determinant of whether or not a virus will infect a certain species?

Hemagglutinin (HA)

• Mediates virus attachment and entry based on whether or not that specific HA can bind to specific sialic acids (alpha 2,3 or alpha 2,6) found on the surface of that mammal’s cells

• Determines the virus’ host range

What are the 2 different ways to diagnostically confirm an influenza virus infection?  What are 3 things you need to consider for each method?

Virus detection and antibody detection

Virus detection:

• Sample type: think about virus tropism. 

• What are you detecting to confirm virus presence? Think about virus structure.

• When are you collecting your samples? Think about the duration of infection.

Antibody detection:

• When is serology informative?

  • If virus is exotic.

  • If there is no vaccination with antigenically similar strains.

  • If you could detect a raise in Ab levels.

• What is your antibody target?

  • Conserved proteins

  • Subtype-specific proteins (HA/NA)

• Which animals are you sampling?

Because of the genomic structure of influenza viruses, what exactly do they need to replicate their genome that mammals don’t have?  What does this inevitably lead to?

They need RNA-dependent RNA polymerases to copy their genomes

• The virus itself has these

• BUT these enzymes lack proofreading ability… this means that during replication, mutations are introduced that CANNOT be corrected

  • Means that the virus evolves

What are the 2 ways influenza viruses can evolve?

1) Mutation - discussed previously

2) Reassortment - when two different viruses infect the same cell… replication of both genomes leads to mixed genomic sequences, resulting in different kinds of viruses all together (see image)

• Is usually what leads to pandemics

What animal is the MAIN CARRIER for influenza viruses?

WILD BIRDS