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Special Topics in Equine Clinical Practice > Infectious Neurological Diseases > Flashcards

Infectious Neurological Diseases Flashcards

1
Q

Equine Herpes Virus (EHV-1) is an alpha herpesvirus that may cause what 3 types of disease?

A
  1. respiratory disease
  2. neurologic disease
  3. abortion
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2
Q

T/F: EHV-1 is a common viral pathogen which is why we vaccinate horses for it yearly.

A

false – not common.

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3
Q

What are the 2 viral genotypes of EHV-1 and what is the difference between them?

A

D752 = neuropathic form

N752 = wild-type

these are single nucleotide polymorphisms on DNA that result in asparginine (N) or aspartate (D).

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4
Q

T/F: both the D752 and the N752 genotypes can cause neurologic disease in horses

A

true
D752 is more likely to cause neurologic disease, but they both can.
N752 is more likely to cause respiratory disease and abortion.

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5
Q

How do horses get infected with EHV-1 and what is the incubation?

A

Direct contact, aerosols, or contaminated equipment/personnel.

The incubation is 2-10 days

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6
Q

which bodily site is the PRIMARY site of infection with EHV-1?

A

the respiratory tract

after, the virus travels to the lymph nodes and into the monocytes.

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7
Q

Viremia that occurs with equine herpesvirus myeloencephalopathy infection results in …

A

Vasculitis and ischemic damage to the brain and spinal cord.

The ischemic damage is caused by virus-induced alterations to the coagulation cascade resulting in thrombosis of small vessels.

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8
Q

Which of the following is NOT a possible clinical sign of EHM?
A. ataxia and dog-sitting posture
B. fecal and urinary incontinence
C. anhidrosis
D. fever
E. obtunded mentation
F. cranial nerve deficits
G. recumbency
H. seizures

A

C. anhidrosis

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9
Q

Which test is the BEST for definitively diagnosing EHV-1?

A

Quantitative PCR using a nasal swab or EDTA blood.
This will tell us viral load and genotype (N vs D)

CSF cytology is another possibility but only tells us xanthochromia, increased protein, and mononuclear pleocytosis.

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10
Q

Which of the following statements is FALSE about EHV-1?
A. morbidity is low for EHV-1 if the horse does not develop EHM
B. horses with high fever are more likely to die
C. horses who become recumbent are more likely to die

A

A. morbidity is low for EHV-1 if the horse does not develop EHM

morbidity for EHV-1 is high (88%)

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11
Q

How do you treat a horse with EHM?

A
  1. valacyclovir (prevents viral replication)
  2. flunixin (banamine) or steroids
  3. heparin (anticoagulant that prevents viral activation of the coagulation cascade to reduce risk of thrombosis formation in the brain and spinal cord)
  4. supportive care (fluids, nursing, sling, ucath + TMS)
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12
Q

T/F: combining valacyclovir and heparin reduces incidence of EHM and improves the survival in EHV-1 outbreaks

A

true

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13
Q

How can you inform owners to prevent EHV-1?

A
  1. Biosecurity – new horses quarantined for 2 weeks, no nose-to-nose contact, do not use public water/feed/wash areas
  2. Vaccination – if high risk, vxnate every 6 months. (vxn does not prev EHM, but decreases viral shedding and dz severity)
  3. +/- immune supplements that contain zinc
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14
Q

Of the 3 equine encephalomyelitis viruses, which has the worst prognosis?

A

Eastern equine encephalitis virus (EEE)

this virus has been reported in south, southeast, and northern states.

VEE has the next highest mortality (40-80%), and WEE is the least (20-50%)

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15
Q

Of the 3 equine encephalomyelitis viruses, which is a reportable foreign animal disease?

A

Venezuelan encephalitis virus (VEE)

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16
Q

how are the equine encephalitis viruses spread?

A

mosquitoes

birds and small mammals are reservoirs

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17
Q

T/F: horses are intermediate hosts for the equine encephalitis viruses

A

false – they are classified as accidental hosts. If they obtain the virus from a mosquito bite, then that mosquito can transmit the virus to another horse.

additionally, with EEE and WEE, horses do NOT amplify enough virus in order to be infective to other horses or humans, but with VEE, they DO amplify enough to spread it human and other horses.

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18
Q

What are the clinical signs associated with the equine encephalitis viruses?

A
  1. high fever (106)
  2. neuro signs: circling, head pressing, hyperesthesia, seizures, obtundation, aggression, somnolence, and proprioceptive deficits.
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19
Q

T/F: there is no treatment for any of the equine encephalitis viruses

A

kinda true
there is no ‘specific’ treatment for the viruses.
you treat with anti-inflammatories and supportive care.

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20
Q

what is the BEST way to diagnose a horse with one of the equine encephalitis viruses?

A

Serology – IgM capture ELISA (make sure it is IgM because this will differentiate true infection versus vaccine)

we can also do CSF cytology, but this will only show mononuclear pleocytosis and increased protein.

21
Q

How can we prevent horses from getting the equine encephalitis viruses?

A
  1. mosquito control
  2. vaccination – in foals give at 3-6 months, then 1 booster in 4-6 weeks, and another booster at 1 yr; if unvaccincated adult give initial vaccine and 1 booster in 4-6 weeks.
    vaccines should be given annually in the SPRING or biannually.
22
Q

West Nile Virus is a zoonotic flavivirus that amplifies in which 2 organisms (reservoir and vector)?

A

birds and mosquitoes

horses and ppl are accidental hosts.

23
Q

What are the clinical signs associated with West Nile Virus in horses?

A
  1. diffuse fine muscle fasciculations
  2. change in mentation and consciousness
  3. cranial nerve abnormalities
  4. spinal ataxia +/- hypermetria
  5. +/- fever

these signs tend to wax and wane too.

24
Q

what is the treatment for WNV?

A
  1. supportive care
  2. anti-inflammatories
  3. WNV hyperimmune plasma (expensive)
25
Q

what is the BEST way to diagnose WNV?

A

IgM capture ELISA

we can also do CSF cytology, but it’ll show either mononuclear pleocytosis, xanthochromia, or be normal.

26
Q

What is the prognosis for WNV?

A

If they do not become recumbent, then the prognosis is good.
But those who do become recumbent (30-40%), fail to survive mostly.

27
Q

how can owners prevent WNV in their horses?

A

Vaccination – initial and then booster in 2-3 weeks. Then, booster annually in the SPRING or biannually if higher risk.

28
Q

What is the incubation period for rabies in the horse?

A

9 days – 1 year

29
Q

where does the rabies virus go once it gains entry into the body via bite by infected animal?

A

It infects and replicates within the monocytes at the bite site.
It then infects the peripheral nerves and ascends to the CNS and rapidly mulitplies (this is why the incubation period is so variable).

30
Q

What are the 3 clinical forms of rabies that can be seen in horses and which is the most common?

A
  1. cerebral/furious – aggression, hyperesthesia, muscle tremors, hydrophobia
  2. brainstem/dumb – obtundation, head tilt, pharyngeal paraylsis (this one is the MOST common)
  3. spinal/paralytic – shifting lameness +/- self-mutilation, ataxia, paralysis
31
Q

What is the BEST way to diagnose rabies in horses?

A

Post-mortem:
send 1/2 brain in formalin (histopath) and other 1/2 shipped on ice (FAT, MAT, mouse inoculation)

32
Q

what finding on histopath is suggestive of rabies?

A

negri bodies (eosinophilic inclusions within neurons or ganglion cells)

33
Q

What is the vaccine protocol for rabies in horses?

A

in foals – give 1st vxn at 3-6 months of age, then booster in 4-6 weeks
in unvxnated adults, give single dose and booster annually

In all horses, booster annually.

if a horse is exposed, give a booster immediately if they were previously vaccinated. if they were not, call the state health official.

34
Q

What are the 3 ways horses can get bacterial meningitis?

A
  1. hematogenous
  2. traumatic
  3. extension of paranasal sinus infection or mass
35
Q

What is a necessary prerequisite for a horse to get hematogenous bacterial meningitis?

A

immune compromise
foals – FPT and sepsis
adults - common variable immunodeficiency, lymphoma, transient IgM deficiency

36
Q

what agents are commonly causing bacterial meningitis?

A

streptococcus ** most common
actinobacillus
actinomyces
e. coli
staphylococcus

37
Q

what are clinical signs associated with bacterial meningitis?

A
  1. fever
  2. multifocal brain signs and seizures, may progress to being comatose
38
Q

what is the best way to diagnose bacterial meningitis?

A

CSF cytology – shows a neutrophilic pleocytosis and elevated protein. the glucose will be <50 mg/dl (because the bacteria and WBCs are consuming it all)

you can also do bloodwork to see an inflammatory leukogram and elevated acute phase proteins.

39
Q

what is the treatment for bacterial meningitis?

A
  1. IV broad spectrum antibiotics at first
    (can do: CRI of time-dep abs like ampicillin, K penicillin, or cephalosporins; oxytetracycline; then transition to enrofloxacin which has a better BBB penetration)

+ NSAIDs, plasma, supportive care, and seizure care.

40
Q

Describe qualities of the causative agent for Lyme disease

A

Agent = borrelia burgdorferi
this is a gram negative spirochete spread by ixodes sapularis tick

41
Q

which tick spreads lyme disease to horses?

A

ixodes scapularis

42
Q

What are clinical signs of lyme disease in horses?

A
  1. neck and back pain, hyperesthesia
  2. cranial nerve signs, ataxia, obtundation
  3. fever
  4. uveitis

+/- ADR, weight loss, shifting leg lameness

43
Q

what is the BEST diagnostic test for lyme disease in horses?

A

Lyme multiplex
(antibody test that gives titers; also gives information about vaccine, versus early/mid infection, versus chronic infection)

The POC ELISA test also has high sensitivity and specificity, but just doesnt tell you acute vs chronic.
You should also perform a CSF cytology – neutrophilic pleocytosis.

Lyme disease is truly a diagnosis of exclusion.

44
Q

T/F: antibody titers for lyme will not change despite treatment or not.

A

true

45
Q

Why is testing for lyme when there are NO clinical signs not a good idea?

A

because there is a high seroprevalence but not all cases are necessarily experiencing clinical disease. And, titers do not change if you treat vs if you dont.

46
Q

what is the treatment for horses with lyme disease?

A

oxytetracycline or minocycline

47
Q

what are clinical signs of otitis media/interna in horses?

A

head shaking
ear rubbing
aural discharge
+/- CN VII and VIII deficits

48
Q

how do you diagnose otitis interna/media in horses?

A

xray or CT*

49
Q

how do you treat otitis interna/media in horses?

A

long term antibiotics
aural endoscopy and lavage

Special Topics in Equine Clinical Practice (18 decks)

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