Viral Neurological Diseases Flashcards
what viruses cause encephalitis viruses? describe
2 families
togaviridae: western hemisphere
1. western: western canada, US states west of Mississippi river, Mexico and South africa
2. eastern: eastern Canada, US states east of Mississippi River, Caribbean island
3. venezuelan: mexico; central and south america
flaviviridae:
4. west nile: worldwide
5. japanese encephalitis virus
both families contain:
positive sense, single-stranded, enveloped (doesn’t survive in environment very well; if dried out, not infectious anymore) RNA virus
define enzootic and epizootic life cycles
enzootic: stays in the wetlands between birds and mosquitoes
epizootic: virus escapes to affect other species; transmitted by other mosquitoes
describe how arthropod vectors transmit disease
- mosquito takes blood meal from viremic bird
- carries virus to horse (dead end host)
- transmits while taking blood meal
- transmission peak when temps between 73-79 degrees F (when mosquitoes are out and biting)
give 4 commonalities among viral encephalitis diseases
- fever
- alterations in mentation
- cranial nerve deficits
- spinal ataxia
how do you differentiate between viral encephalitises?
diagnostics!
- serum/CSF titers:
-west nile virus: IgM capture ELISA (positive = ACUTE infection; IgM 1st antibody sent out) - cerebrospinal fluid analysis:
-EEE: neutrophilic pleocytosis (non-degenerate) and increased protein concentration
-WNV: normal or mononuclear pleocytosis and increased protein - necropsy:
-histopathological findings
-PCR: detect virus in nervous tissue
how do we prevent viral encephalitises?
- vaccination is key!!
-vaccines are very effective and often combo vaccines are available
-many viral encephalitis vaccines are core vaccines for horses - mosquito control may help reduce exposure
describe herpesviruses
- enveloped double stranded DNA virus
-not persist in environment for a long time, can disinfect from - restricted host range!
-you can’t get herpes from your cat
how do herpes viruses often cause upper respiratory disease?
- erosions into URT epithelial cells
- spread to LP
- infect other cells
describe feline herpes virus-1
- feline viral rhinotracheitis (FVR)
- transmission: saliva, ocular/nasal secretions
- clinical signs:
- respiratory
- conjunctivitis
how do horses get infected with herpesviruses?
- respiratory secretions!!
- placenta!!
what is a KEY feature of herpesvirus?
latency!!
can cause an acute infection and some of virus will undergo latency and some will go on to replicate and lyse cells
the latent virus will then get reactivated later (recrudescence) and cause replication and lysis
from slide:
viral DNA translocates to nucleus but NO transcription/translation; the viral genome exists as multiple copies in a circular episomal form in the nucleus
what 2 cells house latent herpesvirus?
- CD8+ lymphocytes
-lymphocytes can be infected and cause viremia (CNA detect in blood!!! buffy coat!)
-some host lymphocytes will be latently affects
-these cells have shorter life spans - neuronal cells
-can be infected and latency can result, especially in trigeminal ganglion
-longer life span of these cells
describe reactivation triggers for herpesvirus
- stressors:
-transport
-handling
-rehousing
-weaning - corticosteroids (unreliably)
describe neurologic manifestation of equine herpes myeloencephalopathy
- caused by EHV 1!!! (and also sometimes by EHV 4)
- clinical signs:
-fever preceding neuro signs
-+/- nasal/ocular discharge
-+/- altered mentation
-ataxia (hindlimbs most affected)
-urine dribbling
-loss of tail tone - pathophysiology:
-direct damage not common
-endothelial cells infected: vasculitis, thrombi and ischemic tissue death
-lymphocytic perivascular cuffing in the caudal thoracic spinal cord!! - diagnosis:
-PCR to detect viral DNA
-samples include: blood (buffy coat), nasal swabs/nasopharyngeal swabs, aborted fetus, placenta
-CSF analysis: xanthochromia - prevention: vaccination!!
-safe and effective for respiratory disease cause by EHV 1 and 4
-pregnant mares should be vaccinated using killed vaccine at 5,7,9 months of preg to prevent abortions
-NOT labeled for protection against EHM
-at this time vx not recommended in face of an outbreak
describe rabies
clinical signs:
-neurologic: ANY THING: choking, weakness, staggering, unprovoked excitement
-2-6 weeks or longer to show symptoms
diagnosis: brain RT-PCR, IFA, IHC
treatment: NONE
vaccine: annual vx required in GA only for interstate movement; suggested for horses with public contact
exposure:
-bite: any penetration of skin by teeth
-non-bite: contamination of open wounds, abrasions, mucous membranes, or scratches with saliva or other potentially infectious materal
