Lecture 15: Equine Viruses Flashcards
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
What is the consequence of resp infection of equine viral arteritis
Resp Infection
* Fever/anorexia
* Leukopenia
* Depression
* Lymphopenia
* Nasal discharge
* Edema (limbs)
o Periorbital edema/conjunctivitis
o Scrotal preputial edema
o Mammary glands
* Epiphora (excessive tears)
* Urticarial rash
What is the consequence of equine viral arteritis in stallions
- Stallion: reduced fertility/sperm quality/libido
What are the histologic signs of equine viral arteritis
Histo: perivascular edema, necrosis of artery wall, lymphocytic infiltration
* Intracytoplasmic inclusions
What are the gross lesions of equine viral arteritis in acute infections/foal/aborting mares
Gross Lesions
* Acute: edema, congestion, hemorrhage
* Foal: pulmonary edema, interstitial pneumonia, splenic infarct, enteritis
* Aborting mare: endometrial hemorrhage +/- autolyzed fetus
How to diagnose equine viral arteritis
Dx: Virus isolation (semen + rabbit kidney cells)
* RT-PCR (to detect nucleic acids)
* IHC (to detect antigens)
* ELISA/Virus neutralization for serology
* Can detect carrier stallions by breeding 2 sero(-) mares
How to control equine viral arteritis
Control: annually notifiable to CFIA
* Separate pregnant mares from others and isolate new animals
* Breed carrier stallions to vaccinated or sero(+) mares
* Isolate infected stallions
* Clean/disinfect
* Can’t eliminate chronic infection
* Vaccine: protect uninfected stallion
o Must vaccinate before breeding season
o Modified live
What is the viral features of equine sarcoids
Papillomavirus: dsDNA, non-enveloped
Agent: Bovine papilloma virus 1 and 2: Virus infects the basal epithelial cells and eventually released in cornified cells
* Replicate in nucleus
* Does not complete replication in equines – no full viral particle formation
o No amplification of virus in horses/donkey/zebra/mule
What is the prevalence of equine sarcoids
Prevalence: 20% all equine neoplasia, 36% all skin tumors of horse
How are equine sarcoids transmitted
Transmit: fomites contaminated by cattle
* Cannot transmit between equids because it does not complete viral replication in equids
What are the clinical signs of equine sarcoids
Clinically: nodular and verrucous form
* Groin/sheath/face
* Fibroblastic form: leg/groin/eyelid (previous site of injury) – large ulcerated masses
What is the pathogenesis of equine sarcoids
Pathogenesis: infection and transformation of basal epithelial cells
* Invade dermis
What is the histo features of equine sarcoids
Histo: long rete pegs into the dermal fibroblastic tissue
* Whorled fibrocellular mass (immature fibroblasts + miotic figures0
How to treat equine sarcoids
Tx; none
* +/-cryotherapy/excision/immune modulation
You are a veterinarian in an equine practice in North
America and presented with horses for vaccination
against equine influenza. The subtype you choose for
vaccination is
A H7N7
B H6N1
C H5N1
D H4N6
E H3N8
e
The cold-adapted equine influenza vaccines are
considered safe since
A The vaccine strain is temperature-insensitive
B Vaccine strain replicates only in the lower respiratory
tract
C Vaccine strain does not replicate in the host
D Vaccine strain replicates only in the upper respiratory
mucosa
E It is more efficacious when administered during the
winter
d
Equine Arteritis Virus (EAV) infection
A Is rarely recorded in North America
B Carrier state is common in mares, geldings and foals
C Is not transmitted via artificial insemination
D Reduces fertility in stallion
E Acquired mainly via vector borne transmission
D
Equine Arteritis Virus (EAV) is transmitted
predominantly via
A Biting flies
B Respiratory route
C Venereal route
D Faecal oral route
E Formites
C
Equine sarcoids:
A Transmissible between horses
B Occur due to autonomous growth of vascular
endothelium in the skin
C Associated with the presence of bovine retroviruses
D Can be controlled by vaccination
E Cannot be cured
E
Which virus is the most stable in the
environment?
A Equine influenza virus
B Equine arteritis virus
C Bovine papilloma virus
D Equine herpesvirus
E Poxvirus
C
