Lecture 15: Equine Viruses Flashcards
(43 cards)
What are the viral features of equine influenza
Equine Influenza
Orthomyxoviridae:
* Influenza
* 8 segments
* ssRNA
* 11 proteins
- Influenza A: Equine-1 H7N7, Equine-2 H3N8
What are 2 ways that influenza virus evolves
- Evolution via mutation or genetic reassortment
What is the predominant equine influenza subtype
- Influenza A:
o A-1 H7N7 (rare)
o A-2 H3N8 (most)
Hosts of equine influenza
Hosts: Equids (horse, donkey, mule) also dogs
Does equine influenza cross the placental membrane
no
How is equine influenza transmitted
Transmit: contagious via aerosols
* Viral excretion during incubation periods (1-3d) and 5 days after clinical signs start
* Vaccinated and infected viruses can shed
* Virus excretion 7-10d (important for dx)
What are the target cells and mechanism of damage of equine influenza virus
Pathogenesis:
* Target: ciliated epithelial cells and alveolar macrophages
* Viral replication: upper and lower respiratory tract epithelium
* Damage: Destroy ciliated epithelium
What are the clinical signs of equine influenza virus
Clinically: return to athletic activity in 50-100d (resolve in 2-3wk) – morbidity 90%, mortality 20%
* High fever
* Depression (4-5d)
* Anorexia
* Red nasal mucosa/conjunctivitis/serous mucopurulent discharge
* Harsh dry paroxysmal cough
* Laryngitis
* Bronchitis
* Bronchointersitial pneumonia (acute fibrinopurulent pneumonia)
* Pulmonary congestion and edema
* Secondary bacterial infection (if signs persist for 10d)
* Fatal in <2wk foal: premature placental separation and dystocia (fetal hypoxia)
What is the importance of pox virus in vet med
Vector for vaccine (equine influenza and rabies recombinant vaccines)
Cause infections: cowpox
How to diagnose equine influenza
Dx: clinical signs (fast spreading respiratory infection/high fever/cough/depression)
- Virus isolation: inoculate (into amniotic or allantoic space) and incubate 9-11d embryo for 3-4d
o Collect amniotic or allantoic fluid
o Use hemagglutination inhibition test assay add virus and RBC
Positive: agglutination
Negative: RBC form pellet in the bottom (no agglutination)
The last inhibition indicates the titre strength (1:64 vs 1:8 – different serial dilution strengths0 - RT-PCR: separate sub-lineages and identify clades
o H3N8 lineages: American (sub-lineage: Kentucky, South American, Florida – clade 1 and 2) and Eurasian
What samples do you need to diagnose equine influenza
- Sample via nasopharyngeal swab/blood
How to control equine influenza
- Vaccine:
o Killed: from European and American lineage of H3N8
Any killed vaccine not very effective
o modified live: Intranasal, cold adapted
effective
o recombinant: recombinant canary pox vector based equine influenza vaccine - Pregnant mare – vaccinate 2-6wk before parturition (give maternal Ig to foal)
- Foal: vaccination before 6wk old can interfere with maternal antibodies
How does the modified live equine influenza vaccine work
o modified live: Intranasal, cold adapted (replicate in the upper but not lower respiratory tract due to temperature difference = induce mucosal immunity in upper resp)
effective
Can have marker: delete gE glycoprotein + use 2 ELISAs to identify infected vs vaccinated
How does the recombinant equine influenza vaccine work
o recombinant: recombinant canary pox vector based equine influenza vaccine
insert HA gene into Pox genome – Pox virus replicated and induced antibody against HA
When infected – immune response against both HA and NP
Act as a DIVA vaccine and result in immunity to HA proteins
* When using non DIVA vaccine = immunity to some of each HA and NP
DIVA vaccination strategy: vaccinated animals only immune to HA
* Vaccinated and infected animals immune to both HA and NP
What is a vaccination buffer
- Vaccination buffer zone: vaccinate the population to insulate naïve animals from virus
o Infected animals will shed but will induce lower shedding in other vaccinated animals – reduce likelihood of transmission
What are a few non-vaccine methods to prevent equine influenza
- Biosecurity
o Isolate and vaccinate new animals
o Isolate infected animals 50m away from other horses
How to treat equine influenza
- Treatment: amantadine, rimantadine – not effective, drug resistance
causes CNS effect
What are the viral features and taxonomy of equine viral arteritis
Taxonomy: (+)ssRNA, enveloped
* Order: Nidovirales
* Family: Arteriviridae
* Genus: Arterivirus
What are the hosts of equine viral arteritis
Host: Equids +/- SA Camelids
Where is equine viral arteritis found
Geography: Worldwide except Iceland and Japan
How is equine viral arteritis transmitted
Transmit: mainly in breeding facilities (semen collection/fomites) – contaminated frozen semen
* 30-60% infected stallions become persistently infected (carrier without clinical signs)
* Can cross placenta
* Some horizontal transmission (fomite/personal/aerosol) – minor
* Can shed in urine
What is the incubation period for equine viral arteritis
- Incubation: 1-14d
What is the pathogenesis of equine viral arteritis
Pathogenesis:
* Infect alveolar macrophages, type 2 pneumocytes, pulmonary endothelial cells
* Circulate in monocytes to LN
* Infect endothelial cells and myocytes = damage blood vessels
* Distribute to body systems
What is the pathogenesis of abortion in equine viral arteritis
Clinically: no carrier state in mare
* Abortion (rare if venereal infection)
o Infection of uterine blood vessels and myometrium =
vasculitis/myometritis + ischemia and chorionic detachment = abortion of uninfected fetus
infect trophoblast, chorionic mesenchymal = infected fetus aborted
* Congenital infection if mare infected when late term
o Interstitial pneumonia in newborn
