Virology - Equine Respiratory Viruses

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Most prevalent Equine Respiratory virus

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-adenovirus type 1

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Adenovirus
-morphology

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-DNA
species specific

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Adenovirus
-pathogenesis in equine

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-oronasal
-regional lymphatics
-bronchitis (necrosis --> hyperplasia --> obstruction)

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Most economically important contagious respiratory disease in horses

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0equine influenza virus (type 1 & 2)

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Equine Influenza Virus
-morphology

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-ssRNA
-enveloped
-hemagglutinin
-neuraminadase

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Equine influenza virus
-family

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-orthomyxoviridae

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Neuraminidase
-function

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-break down mucopolysaccharides and glycoproteins

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Hemagglutinin
-function

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-bind to sialic acid

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Neuraminidase inhibitors

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-Relenza
-Tamiflu

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Important fact of equine influenza virus

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-genetic reassortment can occur if multiple viral strains infect the same cell

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Genetic Shift
-definition

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-rapid changes in the make up of influenza viruses

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Genetic Drift
-defintion

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-subtle point mutation and recombination events

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Influenza virus
-antibody to what protein will cause virus neutralization

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-hemagglutinin

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Equine influenza virus
-pathogenesis

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-oronasal
-infects respiratory epithelium
-multifocal areas undergo inflammatory response
-progression of inflammatory process
-macrophage function becomes impaired
-secondary bacterial infection can occur

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Equine Influenza Virus
-diagnostic signs

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-cough
-fever
-hyperemia
-edema
-exudation
-desquamation
-focal erosions

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Equine influenza virus
-presumptive diagnosis

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-rapidly spreading febrile disease with frequent and pronounced coughing in a group of susceptible horses

-virus isolation from nasopharyngeal swabs or tracheal aspirates at time of the fever

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Equine influenza virus
-confirmatory diagnosis

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Paired serum sample
-ELISA
-IFA

Nasopharyngeal swab
-RT-PCR

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Equine influenza virus
-most conserved protein

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-matrix

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Influenza
-gold standard for diagnosis

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-Virus isolation via embryonated chicken eggs

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Influenza virus
-groups that can infect people
-groups that can infect birds and other mammals

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-people: A. B. C
-birds and animals: A

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Mammalian influenza viruses are through to have orginated from:

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-avian source

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Equine influenza virus
-treatment

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symptomatic
-respiratory epithelium takes 3 wks to regenerate
-confinement

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Equine influenza virus
-control

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Control in an outbreak
-eliminate source of infection
-fomite spread (isolation, avoid stress, limit personnel, clean stable, equipment, vehicles)
-vaccinate (partial immunity, decreased severity)

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Equine influenza virus
-prevention

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-implement and enforce health and vaccination requirements on all incoming horses (isolate 2-3 wks)
-routine vaccinations for other viral diseases
-educate personnel (hygiene and sanitation)

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Avian influenza virus
-receptor preference

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-alpha2-3 sialic acid receptors (respiratory and GI cells)

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Mammalian influenza virus
-receptor preference

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-alpha2-6 sialic acid receptors (respiratory cells)

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Influenza Virus Type A
-how many segmented genes in the genome

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-8

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Equine Herpes Virus types with respiratory concern

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-Types 1 & 4

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Equine herpes virus type with abortion storms and neurological problems

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-Type 1

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Equine Herpes Virus
-type

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-DNA virus

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Equine Herpes Virus
-pathogenesis

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-oronasal
-nasopharynx and lymphreticular tissue or the respiratory system
-incubation
-necrosis
-viremia ---> fetal infection or maternal uterine vasculitis --> abortion or infection of the CNS

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Equine herpes virus
-clinical signs

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-none
-fever
-coughing
-nasal discharge
-anorexia

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Equine herpes virus
-abortions occur when

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-infection in late gestation
-wks to months after infection
-sporadic or multiple incidences

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Equine herpes virus
-effect of a fetus being infected but not aborted

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-weak foal at parturition
-death shortly after birth (pneumonia)

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Equine herpes virus Type 1
-aborted fetus gross lesions

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-fresh appearance
-edema and congestion
-grey necrotic foci on liver
-petechial hemorrhage

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Equine herpes virus type 1
-how is the aborted fetus differentiated from equine arteritis virus

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-fetus is partially autolyzed in equine arteritis virus

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Equine herpes virus type 1
-mare after abortion

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-does not need any special treatment
-is susceptible to re-infection but less severe

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Equine herpes virus type 1
-describe neurologic problems

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-sporadic
-all ages susceptible
-associated often with abortion storms or without any EHV syndromes
-acute
-CNS signs associated with spinal cord damage (ischemia)

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Equine Herpes Virus Type 1
-diagnostic signs of neurologic problems

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-altered gait
-weakness in hind limbs
-head tilt
-ataxia
-paraplegia or quadriplegia

-recovery in cases that do not become recumbent

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Equine Herpes Virus Type 1
-reason for occasional neurologic signs

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-single point mutation in DNA polymerase gene

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Equine Herpes virus
- why is diagnosis complicated

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1) lots of differentials
-EIV (respiratory)
-EAV (respiratory and abortions)
-Protozoal myeloencephalopathy (neurological)
-West Nile (neurological)
-EEE (neurological and public health concern)

2) inapparent herpes infections

3) ability to infect horses with high SN Ab titers

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Equine Herpes Virus
-is serum neutralizing antibody effective in clearing the virus?

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-no

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Equine Herpes Virus
-diagnosis

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Respiratory form
-virus isolation
-PCR

Abortions
-virus isolation (mare)
-IFA
-Immunohistochemistry
-PCR
-Histopathology (lung, liver, spleen, thymus)

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EHV
-goal of prevention

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-minimize exposure (quarantines implemented by state vet)
-segregate all horses by age
-maximize immune preparedness through vaccination
-minimize likelihood of reversing latent infections

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EHV
-vaccines

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-EHV-1 and combo EHV-1 & 4
-MLV or inactivated
-antibody titer decreases rapidly so need to frequently revaccinate

Give killed vaccine to mares on 5th, 7th, 9th gestation months