equine viral diseases 2 - Nicole

Question 1

Which subtypes of equine herpesvirus are prevalent?

Answer 1

EHV-1 and EHV-4

EHV-1 has a seroprevalence of 8-30%
EHV-4 has a seroprevalence of 85-100%

Question 2

Which subtype of equine herpesvirus is the most clinically significant?

Answer 2

EHV-1

Causes respiratory signs, abortion storm, and encephalomyelitis.

Question 3

How is EHV transmitted?

Answer 3

Direct or indirect contact or short distance aerosols.

Question 4

What is the incubation period of EHV?

Answer 4

1-10 days

Question 5

Where does EHV develop latency?

Answer 5

Trigeminal ganglia

Question 6

What body systems can be affected by EHV?

Answer 6

• Resp
• Repro
• Neuro

Question 7

What are the clinical signs of EHV?

Answer 7

• Biphasic fever!!!
• Initially respiratory (mostly subclinical/mild)
• Late term abortion storms (7-11 months)
• Neurologic (paralysis, paraplegia, recumbance, head pressing, ataxia, loss of bladder function)

Question 8

Which subtype of EHV causes neurological signs?

Answer 8

EHV-1 only

Question 9

How does EHV cause abortion?

Answer 9

• Viral antigens in placenta (can infect fetus)
• Vasculitis
• Thrombus (cuts off blood to fetus)

Question 10

How is EHV diagnosed?

Answer 10

• Nasopharyngeal swabs for PCR/virus isolaton
• EDTA blood (virus is in buffy coat)
• Aborted fetus tissue for histology or immunostaining

Question 11

What percentage of EHV-1 strains are neurovirulent?

Answer 11

Only 10%

Question 12

What causes certain EHV strains to be neurovirulent?

Answer 12

A point mutation in the viral polymerase genome

Question 13

Describe how EHV vaccines induce immunity.

Answer 13

In susceptible horses, EHV enters through resp epithelium and it is spread to lymph nodes/CNS from there.

In protected/immune horses, immunity is induced at the respiratory tract which inhibits virus entry into repro and CNS.

Question 14

What type of virus causes equine infectious anemia?

Answer 14

Retrovirus = lifelong infection.

Question 15

Which animals are susceptible to EIA?

Answer 15

All members of equidae are affected but donkeys may be without clinical signs. Clinical disease occurs in horses and ponies.

Question 16

How is EIA transmitted?

Answer 16

• Mechanical transmission through fly vectors (mouthparts of biting insects)
• Fomites
• In utero
• Via milk
• Venereal
• Aerosols

Question 17

Describe the pathogenesis of EIA.

Answer 17

• Circulating immune complexes deposit causing vasculitis and glomerulonephritis
• Infection and destruction of macrophages
• Up-regulation of TNF-a, IL1 and IL6 contribute to fever, decreased bone marrow production of platelets and RBCs
• Complement binds to RBCs causing them to undergo phagocytosis

Question 18

What are the three mechanisms for anemia caused by EIA?

Answer 18

1. Decreased erythrocyte lifespan
2. Depressed erythropoiesis
3. Impaired flow of iron from macrophage to plasma

Question 19

What is unique about the fever caused by EIA?

Answer 19

Fever comes in recurrent episodes (peaks then goes away) - it is associated with viral replication.

Question 20

How is EIA diagnosed?

Answer 20

Serology or real time PCR

Serology:
Combine coggins test and ELISA: Coggins has high rate of false -ves, ELISA has high rate of false +ves. Want both tests to agree but if they don’t = immunoblot.

Real time PCR:
Does not detect carriers (no clinical signs)

Question 21

What is required to control EIA?

Answer 21

Adaptive immunity

Question 22

How is EIA controlled?

Answer 22

REPORTABLE DISEASE!

No vaccine available, infected animals are carriers for life (CFIA orders them destroyed or they undergo lifelong quarantine)

Question 23

How can you prevent EIA transmission within a stable?

Answer 23

Prevent transmission between horses
- Fly contol
- Single use needles
- Don’t breed positive ones (in utero, milk, venereal transmission)
- Prevent aerosol transmission

Question 24

What family of virus is west nile virus?

Answer 24

Flavivirus

Enveloped +sense ssRNA

Question 25

In which species is WNV enzootic?

Answer 25

Birds and mosquitoes (culex)

Question 26

Which animals develop high titers to WNV?

Answer 26

Peri-domestic avians (corvids) - american crows, yellow-billed magpies, jays. High mortality in these species.

Question 27

What vectors allow WNV to be transmitted to humans and equines?

Answer 27

Bridge vectors = Aedes spp mosquitoes

Question 28

What are the dead end hosts of WNV?

Answer 28

Humans and equines

Question 29

How does WNV enter the CNS?

Answer 29

Entry via axonal retrograde transport along peripheral neurons into the spinal cord or hematogenous transport across BBB

Question 30

What are some potential mechanisms for WNV passing across the BBB?

Answer 30

* Trojan horse model: intracellular transport within macrophages or neutrophils * Loss of integrity of the BBB: cytokine-mediated (TNF-α) or matrix metalloproteinases disruption of tight junctions and basement membranes

Question 31

What are the clinical signs of WNV?

Answer 31

* Stumbling * In-coordination * Weak limbs * Partial paralysis * Muscle twitching * Death in some cases ## Footnote Fever has occurred in less than one fourth of all confirmed equine cases

Question 32

How is WNV diagnosed?

Answer 32

Viremia induced by WNV is very short - diagnosis should look for neutralizing antibodies instead (serology).

Question 33

What can be done for WNV control?

Answer 33

* Minimize mosquito bites * Vaccination (canarypox vectored vaccine, live-attenuated/inactivated WNV-yellow fever chimera)

Question 34

Equine herpesvirus (EHV)1 and 4 are different since: A. EHV1 induces no clinical signs and EHV4 induces encephalomyelitis B. EHV4 induces no clinical signs and EHV4 induces coital exanthema C. EHV1 establishes lifelong infection whereas EHV4 is cleared in 7-10 days D. EHV1 induces no clinical signs and EHV4 induces keratoconjunctivitis E. Seroprevalence of EHV1 is lower than that of EHV4

Answer 34

E

Question 35

A common outcome of equine herpesvirus (EHV)1 and West Nile virus (WNV) infection is: A. Colic B. Anemia C. Reproductive failure D. Swollen limbs E. Infection of leukocytes

Answer 35

E

Question 36

What is the possible clinical sign of equine infectious anemia virus (EIAV) infection? Please mark the WRONG answer. A. Recurring episodes of disease B. Colic C. Fever D. Depression E. Nasal discharge

Answer 36

B

Question 37

Viremia of EHV1... A. Follows lytic viral replication in trigeminal ganglion B. Occurs after infection with neuropathogenic but not with non-neuropathogenic strains C. Is mostly cell-associated D. Is not involved in viral dissemination in the body E. Is not evident in this infection

Answer 37

C

Question 38

Anemia due to equine infectious anemia (EIA) virus infection is A. Due to increased erythrocyte life-span B. Not related to compromised erythropoiesis C. Due to destruction of erythroblasts D. Non-immune mediated E. Due to impaired flow of iron from macrophage to plasma

Answer 38

E