Respiratory viruses

Page 1

Respiratory viruses

Canine distemper virus

Cycle

Inhalation

Cross respiratory mucosa

Macrophages?

Lymphoid tissue?

Blood

CNS

Epithelial surfaces

Virus release

Why be pathogenic ?

Conventional wisdom

Parasite host co-evolution is towards commensalism or mutualism

Virulence is a measure of recent associations between pathogen + host

The enlightenment

Some level of virulence required for transmission

Too virulent kills host before transmission

Not virulent enough limits opportunities for transmission

Virulence may increase transmission

Amount of virus shed

Diarrhoea

Amount taken up by vectors

Contact rates with susceptible (behavioural)

Rabies

Main infectious causes of viral respiratory disease

Classification

Genome

Number and sense of strands

Morphology

Genome sequence similarity

Ecology

Orthomyxoviridae

RNA viruses

Family = Orthomyxoviridae

Genus

Influenza A virus

Species = Influenza A virus

Animals + humans

Human vaccinations

Influenza B virus

Species = influenza B virus

Humans

Vaccinations

Influenza C virus

Species = influenza C virus

Humans

Isavirus

Species = infectious salmon anaemia virus

Thogotovirus

Species = Thogoto virus

Tick borne

Influenza A virus particle

Segmented genome

Evolve quickly

New types

Point mutation + genetic reassortment

Mutations = antigenic drift

Variation within a subtype

Reassortment = antigenic shift

Two or viruses infect the same cell

Development new subtypes

Epidemic

Phases 1-3

In animals

Evolves to infect humans

Doesn't pass from human to human

Phase 4

Evolves to pass from human to human

Phase 5

Widespread human infection

Pandemic

Post peak

Possibility of recurrent events

Post pandemic

Influenza species jumps

H3N8 -horses to dogs

Been in horses for 40 yrs

Cough 10-14 days

Fear nasal discharge

Occasional death

Antigenic shift

Vaccine

Periodic updates

Competing horses

Evolved to infect dogs

Dogs

Evolved to spread dog to dog

Via food chain

10% inapparent infection

80% mild kennel cough

Nasal discharge and cough , 10-21 days

5-8% pneumonia and death

High fever, dyspnoea, lung consolidation?

Incubation period 2-5 days

Shedding period 7-10 days

Canine influenza in the UK

Outbreak of respiratory disease in foxhounds

Lung samples tested positive for H3N8

Some dogs are still antibody positive but low levels suggest virus no longer present

AHT did a serosurvey of 300 dog samples - suggests the virus is not prevalent in the UK

Vaccinated in USA

H3N2 spread from dogs in Asia to dogs in USA

H5N1 - avain to people

Highly pathogenic

Highly virulent

Very close contact with animals

Where present in poultry it must be reported

Low pathogenicity avian influenza

Proteases localised in respiratory and intestinal organs

Proteases cleavage can only occur in intestinal tract

Highly pathogenic avian influenza

Ubiquitous proteases

Protease cleavage can occur all over body

Cats

1 of 15 cats ate a chicken carcass on a farm with outbreak

That cat disappeared

14 became weak, started vomiting +coughed up blood

13 died

3 sent for necropsy which confirmed they had H5N1

Tigers

Fed with chickens who'd died from H5N1

Became transmissible tiger to tiger

147 tigers died or euthanised

Unlikely to pass from cats to peopl

Humans form chickens??

Amount excreted by cats much lower that chickens

No evidence

Recommended that cats in infected zones + outbreaks should be kept indoors

When it gets into people it kills

Not yet transmissible person to person

H1N1 pig recombinant to humans

Cat?

Clinical. signs

Depressed

Inappetant

Respiratory signs 4 days

Reluctant to lie in lateral recumbency

Dyspnea

Bilateral lung sounds

Afebrile

Dehydrated

Radiographs showed bilateral caudodorsal alveolar pattern

?

Infectious bronchitis virus

Coronavirus

Affects chickens

Acute

Highly contagious

High mortality in young chickens

Strains vary in pathogenicity / tissue tropism from respiratory ??

Kidney??

Most strains show some tropism for the urogenital tract in adults

Reduction in egg yield

Vaccination

Chicks vaccinated within first week

Attenuated vaccine

Aerosol

In drinking water

Outbreaks can still occur

New genotypes

Substitution/insertion/deletion/recombination

Surveillance strategies need to be in place to allow most appropriate antigens to be incorporated based on geographical context?

Coronaviruses

Ss+ sense RNA

biggest RNA genome

Enveloped

Common cold

Canine respiratory coronavirus

Problem in mild cases in respiratory disease

Likely to be new component of kennel cough

Feline viral respiratory disease

Feline calicivirus

Clinical signs

Oral ulceration

Oculonasal discharge

Conjuctivitis

Lameness

Carriers

30 days most

Most self cure

Evolution

Most continually shed virus

No clinical disease?

Very variable

Must pick one strain for vaccine

Reduce likelihood of clinical signs

Don't prevent them

Feline Herpesvirus

Clinical signs

Lethargy

Oculonasal discharge

Sneezing

Salivation

Keratitis

Carriers

100%

Lifelong

Latency

Intermittent reactivation

Recrudescence

Prevalence

Very common

FCV- whether diseased or not 10% shed disease

Cycles

FHV

Infection

Clinical disease

Shedding

Latently infected

Clinically normal

Not shedding

Variable period of time

Increase in stress

Reactivation of disease

Clinically normal or diseased

Shedding virus

FCV

Infection

clinical disease or not

Shedding disease

Clinically normal

Shedding virus

75 day half life

Immune

Not shedding virus

Naïve-susceptible

Not shedding virus

Vaccination

Immune

May still become infected

Shed disease

No clinical signs

Live vs killed vaccines

Live

Virus weakened - less likely to cause disease

Limited replication stimulates immune response

May under rare conditions cause infection

Not licensed during pregnancy

Killed

No chance of causing infection

Need adjuvants to stimulate immune response

Greater association with sarcomas

Licensed during pregnancy

Control

Husbandry

Ventilation

Stocking density

Biosecurity

Vaccination

Can't overcome bad husbandry

IBR marker vaccine

Delete component of virus

Differentiate injected from vaccinated animals !! (DIVA)

Change the way we control disease outbreaks