Exam 1 - Equine Neurology - Viral Diseases Flashcards
what is EHVM?
equine herpesvirus myeloencephalopathy
what is equine herpesvirus myeloencephalopathy?
acute viral disease of horses with worldwide distribution that causes a vasculitis in the central nervous system
what are other common names for EHVM?
equine herpes
rhinopneumonitis
rhino
what virus primarily causes EHVM?
equine herpesvirus 1
T/F: EHV-4 is a rare cause of EHVM
true
T/F: EHVM from EHV-4 is a reportable disease in Texas
true
what is the pathogenesis of EHVM?
neuropathogenic strain
vasculitis with thrombotic ischemia following endothelial infection
ischemic necrosis of brain, brainstem, or spinal cord
T/F: not all EHVM is caused by a neuropathogenic strain from a point mutation in DNA polymerase enzyme
true
T/F: EHVM causes direct damage to the neurons by the virus
false - damage comes from vasculitis
T/F: vaccination for EHV-1 does protect against EHVM
false - it doesn’t protect the animal
T/F: Nearly all horses are believed to have a latent infection of EHV by 1 year of age
true
Can the neuropathogenic strain of EHV cause latent infection?
yes
how is it proposed that EHVM develops in terms of a latent or lytic infection?
not clear
either:
new infection from lytic cycle or reactivation of latent infection
what is the signalment of horses affected by EHVM?
any age, breed, or sex
older horses may be more susceptible
what is the typical history of a patient with EHVM?
no premonitory clinical signs
biphasic fevers leading into neuro signs
sporadic or epidemic
when do clinical signs associated with EHVM appear?
1-10 days after infection/onset viremia with peak severity 2-3 days after the onset
what are the common clinical signs associated with EHVM?
highly variable
usually NO SKELETAL MUSCLE ATROPHY
what area of the spinal cord is most often affected with EHVM? what clinical signs are seen with this?
caudal segments of the spinal cord & sacral plexus
usually symmetrical ataxia, paresis, & spasticity that is worse in the hind limbs
sacral nerve involvement - bladder atony (incontinence, urinary retention) & perineal sensory deficits
there may be cranial nerve involvement with EHVM - if there is, what is typically involved?
most commonly head tilt - vestibulocochlear
how is EHVM diagnosed?
history (outbreak) & clinical signs (sacral nerve involvement - loss of anal tone, urine scalding - nature of progression, & cranial nerve involvement)
how is EHVM diagnosed indirectly using hematology?
early leukopenia followed by viral infection, non-specific evidence, not very useful
how is EHVM diagnosed indirectly using CSF analysis?
increase in protein & WBC concentrations
xanthochromia!!! - increase in protein & RBC breakdown
EHV-1 antibodies in CSF indicate exposure but is not confirmatory
how is EHVM diagnosed indirectly using serology with complement fixation?
measures IgM - rises & falls rapidly
rising CF titers separated by 10-14 days is good evidence
single high titer in a clinically affected horse is useful
how is EHVM diagnosed indirectly using serology with virus neutralization?
measures IgG - rises more slowly & persists longer
not clinically useful
how is EHVM diagnosed indirectly using serology with ELISA?
measures IgG - type specific (EHV-1 vs EHV-4)
same limitations as virus neutralization
how is EHVM diagnosed directly using immunofluorescence?
its rapid, reasonably sensitive & specific
used on nasal/nasopharyngeal swabs or post-mortem tissues
how is EHVM diagnosed directly using virus isolization?
gold standard for diagnosis!!!
cytopathic effects in cell culture, can follow with PCR
currently more sensitive than IFA or PCR
what is the gold standard test for diagnosing EHVM?
virus isolation
what is the test commonly used to diagnose EHVM?
PCR for direct demonstration of the virus
how is EHVM diagnosed directly using PCR?
tests for EHV-1 or EHV-1 neuropathic, reasonably sensitive, rapid, quantitative with real time PCR
nasal swabs are better than nasopharyngeal & synthetic swabs are preferable to cotton
why is it hard to diagnose a latent infection of EHVM?
they don’t have any clinical signs, usually test negative, under the radar of the immune system, so they don’t express viral-encoded proteins
what should you do with a horse that is positive for EHVM?
isolate the animal!!! horses with neuro signs can shed the virus & transmit it directly (aerosol) or indirectly (fomites)
what treatment is used for EHVM?
no controlled studies - empiric treatment
anti-inflammatories (flunixin meglumine/glucocorticoids), anti-virals, & supportive care
why are glucocorticoids controversial for treatment use in horses with EHVM?
they may cause viral replication or reactivation - but no strong evidence (reaction only at 1mg/kg)
what is the anti-viral drug of choice for EHVM?
valacyclovir at 30mg/kg, PO, q8-12 hours
better bioavailability than acyclovir - prodrug of acyclovir
what should be included in your supportive care for EHVM?
deep stall bedding for recumbent animals, lubricate eyes, vaseline to perineum, catheterize bladder/evacuate rectum, sling, & IV fluids/other treatments as needed
what is the prognosis for recumbent horses with EHVM?
very poor
how is EHVM prevented using vaccines?
it doesn’t protect the animal from EHVM but it can reduce viral shedding & help with control
how is EHVM prevented using biosecurity?
28 days isolation - don’t move off premises or within premises once isolated
separate gear/tack
disinfect in-contact surfaces
quarantine new arrivals
minimize stress
what does WNVE stand for?
west nile encephalomyelitis
what causes west nile encephalomyelitis?
flavivirus - RNA virus
transmitted by mosquitoes
what is the pathogenesis of west nile encephalomyelitis?
mosquitoes transmit the virus
causes necrosis of nervous tissue especially in the midbrain, brainstem, & lumbosacral spinal cord
polioencephalomyelitis!! gray matter disease!!
T/F: ~90% of WNVE horses show no clinical signs
true
what are the big clinical signs of west nile encephalomyelitis?
muscle fasciculations!!! fine & coarse fasciculations of face/neck, but muzzle & eyelids may be most notable
spinal ataxia - asymmetrical, can progress to recumbency
what is the mentation like of an animal with west nile encephalomyelitis?
altered behavior/depressed attitude, weakness
does west nile encephalomyelitis affect cranial nerves?
sometimes
what is the progression of disease of west nile encephalomyelitis?
improvement in 3-5 days (often) - some may have recrudescence after 7-10 days
most fully recover within 1-6 months
can have residual ataxia, limb paresis, & exercise intolerance
what is the prognosis for west nile encephalomyelitis in a recumbent horse?
poor prognosis
how is west nile encephalomyelitis diagnosed?
clinical signs/history/vaccine status
serology - IgM capture ELISA titer > 1:400, lasts about 6 weeks
post-mortem detection of west nile virus in the brain using IHC, PCR, or virus isolation
what is the treatment for west nile encephalomyelitis?
supportive care, anti-inflammatories, & IV immunoglobulins (WNV hyperimmune plasma)
how is west nile encephalomyelitis prevented?
mosquito control, surveillance, & vaccination
when should you vaccinate for west nile encephalomyelitis?
before mosquito season!! duration of immunity & frequency of the vaccine is unclear
T/F: west nile encephalomyelitis is a reportable disease
true
what is equine encephalomyelitis (EEE/WEE/VEE)?
infectious viral disease of equids characterized by deranged consciousness, motor irritation, ataxia, paralysis, & high case fatality rate
equine encephalomyelitis viruses can affect any part of the CNS - what aspects of the CNS are affected more? (gray matter/white matter)
gray matter
what causes equine encephalomyelitis?
togaviruses - RNA viruses in the alphavirus genus of togaviridae
eastern, western, & venezuelan equine encephalitis viruses
how many subtypes does EEE have?
6
how many antigenic subtypes of WEE are there?
2 antigenic subtypes
what kind of hosts are horses for EEE & WEE?
dead end hosts - they don’t result in sufficient viremia
T/F: EEE/WEE/VEE can cause disease in humans
true
what is the most important source of VEE?
horses
of the viruses that cause equine encephalomyelitis, which carries the highest fatality rate for humans & horses?
EEE
of the viruses that cause equine encephalomyelitis, which carries the lowest fatality rate for humans?
VEE
what are the clinical signs for EEE/WEE/VEE?
fever - usually precedes neuro signs
irritative signs - restlessness, hypersensitive, tremors, may see blindness, circling with ataxia
progression to depressive signs - sleepy, obtunded, head held low, & unnatural posture
what are the terminal clinical signs for EEE/WEE/VEE?
dementia, paralysis, seizures, & coma leading to death
T/F: EEE/WEE/VEE is reportable!!
true
how is EEE/WEE/VEE diagnosed?
clinical signs/history - vaccine status is important
serology - IgM titer > 1:400, CSF is more convincing than serum, or IgG 4 fold increase in acute/convalescent serum
post-mortem detection in brain - IHC, PCR, & virus isolation
what is the treatment for EEE/WEE/VEE?
anti-inflammatories, supportive care - same as WNV
how is EEE/WEE/VEE prevented?
mosquito control, surveillance, & vaccination
of EEE/WEE/VEE, what are we primarily vaccinating for?
EEE/WEE
may need to vaccinate > 1yr
what is rabies?
highly fatal, rapidly progressive viral encephalomyelitis classically manifesting as motor irritation, ascending paralysis, & mania/dummy attitude
what causes rabies?
neurotropic rhabdovirus
how is rabies transmitted?
animal bites primarily - but occasionally by inhalation/ingestion
what is the pathogenesis of rabies?
virus travels from the site of inoculation to the CNS via axons, then peripherally to other organs via the nerves
viremia may occur after infection - can be shed in milk & feces
what are the 3 syndromes of rabies?
prodromal form, furious form, & dumb form
what are the signs associated with the prodromal form of rabies?
early signs mimic other diseases - lameness, colic, spinal ataxia
what are the signs associated with the furious form of rabies?
hyperesthesia, muscle tremors, aggressive behavior, tenesmus, circling, self-mutilation, abnormal sexual activity
what are the signs associated with the dumb form of rabies?
somnolence, stupor, paralysis, depression
what clinical signs should alert you to suspect rabies?
change in behavior, hypersensitivity, choke (in cattle especially), abnormal phonation, self-mutilation, & abnormal aggression
how is rabies diagnosed post-mortem?
fluorescent antibody test of the brain & detection of negri bodies
T/F: rabies is a reportable disease
true
exercise care & follow regulations for submitting tissues as this is a public health risk
what is the treatment for rabies?
supportive care until death or euthanasia
assumed all cases will die
how is rabies prevented in horses?
avoid exposure, vaccination, annual booster recommended, core vaccine in TX
how is rabies prevented in humans?
vaccination, proper PPE for handling neuro cases, keeping good records, & avoiding exposure
what equine viral diseases are reportable that cause neurological disease?
EHVM, WNVE, EEE/WEE/VEE, & rabies
what equine viral diseases that cause neurological diseases are core vaccines as designated by the AAEP?
EEE/WEE/VEE & rabies
T/F: there is a vaccine for EHVM
false, there is none
other than neurological signs, EHV-1 can cause what other clinical signs?
respiratory disease, abortion, & ocular disease
T/F: EHV-4 is a rare cause of EHVM
true
T/F: EHVM can affect horses of any age, but older horses may be more susceptible
true
