Respiratory Viruses

What are the main viruses involved in respiratory disease?

-Orthomyxoviridae: Influenza A-C, Isavirus

-Coronaviruses: SARS, HEV, Infectious bronchitis, CRCV

-Calicivirus: Feline calicivirus

-Herpesvirus: Feline Herpesvirus, Infectious bovine rhinotracheitis

How do new types of viruses emerge?

-Point mutation and genetic reassortment

-Mutations = antigenic (genetic) drift

-Reassortment = antigenic (genetic) shift: Two or more viruses infect the same cell and develop new sub-types

What is the significance of reassortment (antigenic shift) on viral diseases?

-Can lead to novel viruses being created an is a common cause of species hopping

-Can lead to pandemic-causing viruses developing

-Occurs very quickly and frequently

What is the relevance of the influenza virus in the world today?

-Often species jumps

-Causes respiratory disease in animals and humans

-Causes typical flu-like symptoms

Give an example of when the influenza virus species jumped and how this might have happened

-Equine influenza (H3N8) mutated to form canine influenza (H3HA) and infected dogs causing respiratory disease

-Jumped from Horses to Dogs

-Thought to be associated with the close interaction of the environment of racing horses and dogs

--Also could have been that uncooked horse meat was fed to dogs which lead to its transmission

---Mutation of equine influenza to canine influenza then lead to dog-to-dog transmission

List the significant influenza viruses and what species they effect

-HPAI (H5N1): Birds, Cats, humans

-H1N1: Pigs, humans

-H3N8: Horses, dogs

What differentiates low pathogenic avian influenza to high pathogenic avian influenza?

-HPAI has ubiquitous proteases where as LPAI has proteases that are localised in respiratory and intestinal organs

-The ubiquity of proteases determines the severity of diseases caused

-High ubiquity = severe disease

Describe the general characteristics of infectious bronchitis virus

-Acute, highly contagious disease of chickens

-High mortality rate in chicks

-Strains vary in their pathogenicity and tissue tropism

-Can show tissue tropism for urogenital tract (and hence can cause reproductive loses)

-Chicks are vaccinated with an attenuated vaccine by aerosol or in drinking water

--However outbreaks can still occur in vaccinated flocks

Why can outbreaks of infectious bronchitis still occur in vaccinated flocks?

-Emergence of new genotypes in the flock

--By substitution, insertion, deletion or recombination

What are the causes of "Cat Flu"

-Feline Calicivirus (FCV)

-Feline Herpesvirus (FHV)

What proportion of cats in the UK have cat flu?

1/10.

What is the main difference between FCV and FHV?

-FCV is an RNA virus where as FHV is a DNA virus

-Cause differing symptoms

What are the carrier states for FCV and FHV?

FCV:

-30 days

-Most self-cure

-Most continually

shed virus

-75 day 1/2 life

-Dont present with clinical disease

FHV:

-Life-long

-Have intermittent reactivation (shedding but clinically normal)

-Typical latent infection

-Recrudescence (shedding but clinically unwell)

What is a latent infection?

The residence in the body of a specific infectious agent without any manifest symptoms.

What stressors may reactivate FHV in a cat?

-Having kittens

-Being given steroidal drugs

What is a big challenge for vaccinating against RNA viruses?

They mutate often so they vary a lot over time.

How can we control respiratory viruses?

-Husbandry

--Ventilation

--Stocking density

-Biosecurity

-Vaccination