Infectious Diseases and Vaccinations Flashcards
what is used to maintain healthy horses?
management and vaccination programs
what 4 things does a vaccination program for horses depend on?
- disease prevalence in the area
- degree of confinement (horse travel?)
- number of horses
- frequency of contact with other horses (closed environment?)
what is meant by a closed environment?
no horses in or out
how long are incoming horses isolated and why?
7-14 days; this covers the incubation period of most infectious diseases
if a horse is coming from a knonw disease area how long is it isolated?
for 30 days
what 2 things must you do when working with a diseased horse?
- change clothes before seeing nondisease horses
- disinfect yourself before handling other horses
what is a fomite?
an object that can carry transmissible diseases from one individual to another
what are pathognomonic symptoms? give an example
symptoms specific/distinctive to only one disease; sawhorse stance in tetanus
what is tetanus also known as and why?
lockjaw due to the masseter muscle being one of the first affected
what causes tetanus?
neurotoxins produced by anaerobic bacteria (clostridium tetani)
where is tetanus particularly common (2 wound types) and why?
- puncture wounds
- lacerations
these are deep and close over, making the anaerobic bacteria very happy
what is another potential cause of tetanus other than wounds?
intestinal infections, as clostridium tetani are normal inhabitants of the gut tract
where are clostridium tetani bacteria found?
they are widely distributed in soil and manure
what animals are affected by tetanus? whicha re particular susceptible?
all animals affected; horses susceptible
describe how the bacteria cause tetanus (3)
- c. tetani gain entry to the tissue and release exotoxins (proteins) that attack the CNS
- the toxins block inhibitory transmitters (GABA and glycine) within descending motor tracks
- abnormal contractions of muscles occur from reflex reactions after normal stimulation
what does GABA stand for?
gamma amino butyric acid
when do tetanus symptoms begin?
1-3 weeks after infection
what are 5 symptoms of tetanus?
- stiffness of legs
- inability to eat due to lockjaw
- prolaps of third eyelid
- horse is rigid and assumes sawhorse posture
- excitement stimulates exaggerated responses such as muscle spasms and convulsions
what are the pathognomic symptoms of tetanus? (2)
- prolapsed third eyelid
- sawhorse stance
why can tetanus be fatal? (3)
- respiratory paralysis
- complications of recumbency
- aspiration pneumonia
what kind of vaccine is available for tetanus?
the toxoid vaccine
describe tetanus vaccination for a foal from a vaccinated mare
3 doses
1st dose at 4-6 months
2nd dose 4-6 weeks after 1st dose
3rd dose at about 10-12 months
describe tetanus vaccination for a foal from an unvaccinated mare
first dose given at 3-4 months, then follow 2nd and 3rd dose like vaccinate mare protocol
when are pregnant mares vaccinated against tetanus?
annually and then 4-6 weeks prior to foaling
when are adult horses vaccinated against tetanus?
annually
describe tetanus antitoxin
provides passive, short-term immunity for immediate protection
when is tetanus antitoxin given? (2)
- to newborn foals whose dams were not vaccinated 4-6 weeks prior to foaling
- also used for treatment of horses with tetanus
what is encephalitis?
inflammation of the brain
what is encephalomyelitis?
inflammation of the brain and spinal cord
what are 2 other names for equine encephalitis?
- sleeping sickness
- blind staggers
what is equine encephalitis caused by?
by 3 antigenically different arbovirus strains: eastern, western, and venezuelan
what serves as reservoirs for the viruses that cause quine encephalitis?
passerine songbirds for sure plus potentiallly other wild animals
how are the equine encephalitis viruses transmitted to horses from the bird reservoirs?
by the blood sucking arthropods (mosquitoes) that serve as vectors or carriers of the virus
when does the equine encephalitis disease occur?
in warm months when mosquitoes are active
which if the 3 equine encephalitis viruses is the only one that can be transmitted horse to horse? describe the other two as well
VEE is the only horse to horse transmission; in WEE and EEE the horse is a dead end host as they cannot be transmitted between horses or people
describe the disease course of equine encephalitis, give percentages for each type
acute onset that is usually fatal; results in inflammation of the brain (and spinal cord)
EEE: 80% fatality rate
WEE: 30%
VEE: 60%
give the general range of incubation period of equine encephalitis, then specifically for EEE and WEE
1-3 weeks; but 5-14 days is common for E and W
what are 10 symptoms of equine encephalitis?
- mild fever that become high fever
- absence of feed intake
- stiffness
- incoordination
- reeling gait
- compulsive walking
- loss of vision
- grinding teeth
- inability to swallow
- head pressing
describe the reeling gait of a horse with equine encephalitis
fast, uncoordinated, stumbling
are any equine encephalitis symptoms pathognomonic?
no
give 3 symptoms of severe cases of equine encephalitis
- hyperesthesia (increased sensitivity to stimulation)
- aggression
- excitability
when does death usually occur in a case of equine encephalitis?
2-7 days after recumbency (aka sleeping sickness, horses are called sleepers)
if a horse recovers from equine encephalitis, what is observed and what are these horses called?
will have residual CNS signs; horses called sleepers or dummies
why is recumbency so bad for horses?
weight is pressing on the cardiovascular system; also not eating or drinking
how is equine encephalitis diagnosed? (2)
- rise in plasma antibodies against the disease suggests a case
- virus isolation in the brain is definitive diagnosis
describe treatment of equine encephalitis
supportive care mainly; treat to control fever, inflammation, and discomfort
what strains of equine encephalitis do we vaccinate for in the southeast US?
both eastern and western
describe vaccination against equine encephalitis; give special case for southeast US and why
1st dose for foals from vaccinated mares at 3-6 months
2nd dose 4-6 weeks after 1st
3rd dose at around 10-12months
(in SE US; may give 1st dose at 3 months old because it warms up earlier here; akso may give boosters every 6 months)
then vaccinate again at 1 year of age and then give annual boosters
what is equine infectious anemia also called? what is it known for causing?
swamp fever; causing red blood cell destruction
what kind of virus causes equine infectious anemia (EIA)? how transmitted?
worldwide retrovirus; transmitted by blood-sucking and biting external parasites (horse flies common vector!) and blood-contaminated needles
other than vectors and fomites, what is a third way that EIA can be transmitted?
vertical transmission; through the placenta by a mare to her fetus
where is the highest incidence of equine infectious anemia? give percentage
80% of cases are in the southeast US, although the general eastern US gets lots of cases too
is there a vaccine for equine infectious anemia?
nope
describe occurrence of clinical signs of equina infectious anemia and then 9
clinical signs are recurrent;
1. fever
2. anemia
3. depression
4. anorexia
5. weakness
6. leg and ventral edema (from decreased movement9
7. icterus
8. abnormal bleeding
bonus 9!: unthrifty!!
is death common from a case of EIA? what is the usual outcome and why?
death not common; horses become lifelong carriers becayse no vaccine or treatment
what is the risk of an EIA infected horse?
becomes a source of infection for other horses
if a horse tests positive for EIA, what must be done? (2)
- the lab must report it to the state veterinarian
2.the horse must be either euthanized or permanently quarantined at a sufficient distance from other horses so horse flies can’t transmit between infected and healthy
regarding equine infectious anemia, what are horse owners required to do yearly?
yearly blood test; either coggins or ELISA test
regarding equine infectious anemia, what are horse owners required to have when traveling from state to state, between horse shows, or traveling at all?
either a negative coggins or a negative ELISA; MUST HAVE AT LEAST ONE
what is equine rhinopneumonitis also called?
equine herpes virus, or viral abortion
what causes equine rhinopneumonitis? (2)
equine herpes virus, either
type-1 (EHV-1) or
type 4 (EHV-4)
what is caused by both EHV1 and EHV4
respiratory disease in horses
what is also caused by EHV1, other than respiratory disease?
can cause abortions or neurological disease
describe equine herpes virus, include transmission (3)
- highly contagious disease
- transmitted by inhalation of infectious aerosols and
- direct contact with infected secretions on utensils or in drinking water (fomites)
in what kind of conditions/ages is equine herpes virus more common?
in younger horses (less than 3 years old) in crowded conditions
describe the prevalence of equine herpes virus in many horse populations and how most mature horses handle it
endemic in many horse populations; most mature horses develop some level of immunity
give 4 initial clinical signs of equine herpes virus, then 3 symptoms observed as the virus progresses
initially:
1. fever
2. mild respiratory tract disorder
3. cough
4. nasal discharge
as progresses:
1. stiffness
2, weakness
3. ataxia
when do and what symptoms appear with equine herpes virus (incubation period and initial presentation)
after an incubation period of 2-10 days, the symptoms of the respiratory subtype begin with fever and a bacterial infection (referred to as the snots)
what can EHV1 cause (big bad news bears)
may cause abortion storms with no other clinical signs
how does EHV1 cause abortions? when will this usually occur?
foals dies from asphyxiation by premature separation of the placenta; usually occurs during months 8-11 of pregnancy
when in the disease course would abortion occur from EHV1?
day 10-20 of infection, following clinical or subclinical infection and immediately before or during development of neurological signs
describe diagnosis of equine herpes virus
difficult to diagnose; requires detecting antigen or culturing the viruses from either nose and throat swabs or from blood PCR
what is equine herpesvirus myeloencephalopathy?
a genetic variation of EHV1 caused by a single point mutation that results in more significant neurological disease
do any vaccines claim to protect against equine herpesvirus myeloencephalopathy? what is the only ray of hope?
no vaccines have a label claim to prevent this; but it is suggested that vaccines may assist in limiting the spread of outbreaks of EHM by limiting nasal shedding of EHV1 and lowering dissemination of infection
what are the 3 strains of EHV1?
D752, N752, and H752
what is the “wild type” strain of EHV1? describe what this means
N752, considered the normal variant (abortion storms and resp tract disease often seen) but this is misleading because this strain CAN cause neurologic disease, just less likely
which strain of EHV1 is typically associated with EHM? what is it sometimes called because of this?
D752; sometimes called the neurotropic strain
describe the H752 strain of EHV1
a newer third variant that seems to interact with D752 to make horse more susceptible to neurological EHM
what is recrudescence?
a second, more intense relapse of symptoms after a seeming recovery due to the presence of another stress
how is equine rhinopneumonitis treated?
with supportive therapy (fluids and anti-inflammatories) and rest
what are the 2 types of available vaccines for equine herpes virus? describe protection of both
modified live or killed virus vx
both provide protection against the respiratory form of the disease
describe limitation of protection with the modified live vaccine for equine herpes virus; then say what is used then in pregnant mares
may not give good protection against abortion, so used killed virus vx in pregnant mares!
how are equine herpes virus vaccines often given?
in a combo that have EHV1 and EHV4, plus sometimes also influenza virus
describe vaccination protocol against equine herpes virus in foals
begin vaccinating at 3 months, then boost at 5-6 months, then yearly boosters
describe vaccination protocol against equine herpes virus in pregnant mares
vaccinate with killed virus vaccine in the 5th, 7th, and 9th month of gestation
what are the 2 types of viruses that cause equine influenza?
myxovirus A and subtypes 1 and 2
what does the prefix myxo mean?
mucus production
in what age horses is equine influenze most common and why?
2-3 year olds, they are under stress from riding and training and also in groups
what is considered to be the most important viral respiratory tract disease in horses in training centers, race tracks, and shows?
equine influenza
when do clinical signs begin in equine influenza?
1-3 days after inhalation of the virus
what can equine infleunza cause, transmission wise?
explosive outbreaks that spread rapidly; only takes one infected horse
give 7 clinical signs of equine influenza
- fever
- dry, hacking, persistent cough
- muscle soreness
- depression
- loss of appetite
- clear nasal discharge early in disease course
- leg edema from decreased movement (in stalls and also low energy)
what is usually the most common sign of equine influenza and how long does it last?
the cough; persists for 1-3 weeks
in the absence of secondary complications, what is the outcome of a case of equine influenza?
the respiratory lining regenerates and recovery occurs in about 3 weeks
what are 3 secondary complications that can occur due to equine influenza?
- bacterial pneumonia that leads to thick, purulent nasal discharge
- bronchitis
- pleurisy: inflammation and fluid buildup between pleural membranes
how is equine influenza spread?
by inhalation of contaminated water droplets moving through the air from contaminated facilities or objects (fomites help)
how long can horses shed the equine influenza virus?
for 10-14 days
how is equine influenza diagnosed?
observation of increased serum influenza antibody titer in samples taken 1-2 days after symptom onset
describe treatment of equine influenza
rest and supportive therapy
describe vaccination against equine influenza
begin at 6 months of age, give again at 9 months, then yearly (foals receiving amply amounts of colostrum should be okay to wait to vx at 5-6 months)
if a mare is vaccinated against equine influenza yearly, when in her pregnancy should she be revx?
1-2 months before foaling
if a horse is in constant contact with other horses (traveling, showing) how often should you vx for equine influenza?
every 3 months
what are 2 other names for strangles?
- equine distemper
- shipping fever
what is strangles?
an acute, highly contagious disease of the upper respiratory tract
what is the causative agent of strangles?
streptococcus equi, a bacteria
how long is the incubation period for strangles?
3-8 days
what are 5 symptoms of strangles?
- fever
- depression
- inappatance
- nasal discharge (mucopurulent)
- infected or abscessed lymph nodes
describe lymph nodes in strangles (2)
- the lymph nodes under the jaw swell, which can create difficulty swallowing
- hot, painful, and usually rupture within 7-14 days
how does a horse stand when it has strangles? describe the larynx
stands with head extended; larynx painful upon palpation
why is strangles called strangles?
the lymph node swelling under the jaw may be enough to cause respiratory obstruction and difficulty breathing
how is strangles diagnosed?
a culture of S. equi using a selective transport medium such as a strepswab and then using PCR to identify
describe treatment of strangles (6)
- isolation
- lancing of abscessed lymph nodes
- antibiotics
- hot compresses
- sanitation
- supportive care
why is antibiotic use controversial in treatment of strangles? when is this usually used?
the worry is whether it will be effective or just prolong the processes until the horse clears the infeciton on its own; may be used if a whole group of horses get it at once to reduce labor and time of care
describe the strange history of vaccination against strangles
formerly was an injectable available, but it caused local reactions and didn;t always work, so then we switched to the intranasal (Pinnacle) in 1998 that is still used today, but now this is also the Strangvac injectable, which is a fusion of recombinant proteins and is only used in Europe; additionally there is Strepvac II, which is another current, good injectable
what age horses are more susceptible to strangles?
young (shocker)
what environments can S. equi survive in? (3)
- water
- pastures
- fences
when does recovery occur in strangles? how long before the horse can go back to work?
recovery: 1-2 weeks after abscess rupture or 3-6 weeks after onset of clinical signs
back to work: allow 4-6 weks after recovery
what is essential to presenting the spread of strangles? what should you do after a case?
hygiene! disinfect stalls with chlorahexadine and then don’t use for 2 months after a case
what are 2 complications of strangles? describe
- bastard strangles: widespread lymph node abscessation, penumonia, septicemia, heart damage, brain abscesses
- allergic reaction in older horses resulting in purpura hemorrhagica, widespread hemorrhage on body membranes and subcutaneous edema
what was potomac horse fever formerly called?
equine monocyte ehrlichiosis
what is the causative organism of potomac horse fever?
Neorickettsia risticii
what kind of disease is potomac horse fever? (2)
- seasonal- in the summer time
- GI tract: enterocolitis
when and where was potomac horse fever first recognized as a disease?
in 1979 near the potomac river in maryland
where is potomac horse fever reported? (3)
- most regions of the US
- canada
- europe
what is potomac horse fever characterized by? (give 4 symptoms in this)
acute onsent and 2-10 days of
1. fever
2. ataxia
3. depression
4. decreased intestinal sounds
what can some severe cases of potomac horse fever result in? (5)
- some can develop a severe diarrhea (pipestream) that leads to severe dehydration
- laminitis in some cases
- ventral and leg edema
- leukopenia (decreased WBC count)
- fetal infection and abortions
list 2 reservoirs/hosts of potomac horse fever
- small animals MAY serve as reservoirs/hosts
- trematodes and flukes ARE reservoirs
how is potomac horse fever transmitted? (3)
- aquatic insect such as mayflies, caddisflies, or dragonflies
- horses ingest snails or aquatic insects that carry N. risticii
- horses ingest the larval stage of the fluke, aquatic insect, or snail while grazing, or a flying insect that has landed in drinking water
describe treatment of potomac horse fever
- antibiotics: IV oxitetracycline
- possible fluid and electrolyte treatment if severe diarrhea
how is potomac horse fever diagnosed?
PCR detection in blood or feces
describe vaccination against potomac horse fever (3)
- initial series of 2 injections, with a booster every 6 months to 1 year
- vaccinate horses in endemic areas or if they are being transported to those areas
- efficacy of vx is questionable
what is rabies also known as?
hydrophobia
what kind of disease is rabies? how transmitted?
viral disease transmitted through saliva of carnivores by bite of rabid animal
what is the primary source of rabies infections in georgia (2)
raccoons and bats
give 3 other commons sources of rabie infections (not just in georgia)
foxes, skunks, possums
how do animals often infect horses with rabies?
by biting or licking open wounds
when are rabies cases more frequent?
spring and summer months
describe the symptoms of rabies in horses
appear after incubation period of 3 weeks to 3 months; symptoms extremely variable in horses, may just look lethargic
when does death occur with rabies?
usually 5 days after onset of clinical signs
what does the virus do in rabies?
irritates the CNS and destroys nerves, resulting in paralysis and death
what are the 2 symptom forms of rabies in horses?
- paralytic “dumb” form
- furious form
describe the paralytic “dumb” form of rabies in horses (4)
- changes in horse’s disposition, peculiar look in eyes
- horse appears to be confused with jaw hanging open
- causes lameness or weakness in one leg until horse becomes recumbent and has convulsions
- horse drools and acts choked
describe the furious form of rabies in horses (2)
- excessive salivation and abnormal aggression, with excitable and exaggerated movement
- actions are uncontrollable
describe vaccination against rabies
vaccine available and should be used in endemic areas; one initial injection and then yearly boosters
what is the causative agent of west nile virus?
a flavivirus
what is west nile virus?
a mosquito-borne disease that cuases encephalomyelitis (inflammation of brain and spinal cord)
when and where was west nile virus discovered?
first in Uganda in 1937, then in New York in 1999
describe the prevalence of west nile virus in the US in december of 2004, just 5 years after it was discovered in the US
found in all 48 (at the time) states and canada
describe fatality rate of west nile virus
35% fatality once horse shows clinical signs
what percentage of horses that survive west nile virus will still exhibit residual effects?
40%
what are 10 symptoms of west nile virus?
- stumbling/tripping
- muscle weakness or twitching
- partial paralysis
- inappatance
- depression/lethargy
- head pressing
- circling
- inability to swallow
- inability to stand
- fever, convulsions, coma
how is west nile virus diagnosed?
serologic test
describe the infeciton cycle of west nile virus
begins with infected birds (reservoirs), the mosquitoes bite birds and become infected, then feed on horses or humans
after being bitten by an infected mosquito, how long is the incubation period of west nile virus in a hrose
3-15 days
describe treatment of west nile virus
supportive therapy (fluids, anti-inflammatory drugs)
describe prevention of west nile virus (2)
- mosquito control
- Fort Dodge Innovator (1st vx developed)
describe vaccination against west nile virus
Fort Dodge Innovator; give innitial vaccine, follow with booster 3 weeks later, then annual booster
what is equine protozoal myeloencephalitis caused by?
the protozoa sarcocystis neurona
what are 5 symptoms of EPM?
- incoordination
- weakness
- ataxia
- weight loss
- muscle atrophy (often unilateral)
describe what kind of horses are affected by EPM most
more common in younger horses bc weaker immune system but can affect horses of all ages
when does infection of EPM occur?
after horse ingests S. neurona sporocysts in grain or hay
what kind of host are horses in EPM?
dead end hosts; can’t transmit to anyone else
what is the definitive host of EPM? describe transmission cycle
possums are definitive hosts; they are scavengers, so will eat armadillos, skunks, cats, and raccoons, all of which can carry S. neurona, and then pick up the sporocysts, possums are then attracted to horse grain and hay and shed infective egg-like sporocysts S. neurona in the feed for horses to pick up
once S. neurona sporocysts are ingested by horses, what happens? (2)
- migrate from intestinal tract into the bloodstream
- cross the blood brain barrier and attack the CNS
describe the onset of EPM disease
can be slow or suddent, depending on type of CNS damage
do all horses that exposed to S. neurona develop the disease?
nope; some horses mount an immune response and are not affected
describe diagnostics of EPM, generally
tests are based on the presence of antibodies to the parasite, the presence of which means that the horse was exposed to the organism, but want to rule out other neuro diseases and problems first
describe the Western blot test to diagnose EPM
if negative wester blot on blood sample, horse does not have EPM, but a positive western blot requires cerebrospinal fluid, but confirms the disease and WAS considered the gold standard
what is the current gold standard for diagnosing EPM in a horse? (3)
- first observable neurologic signs consistent with EPM
- next rule out disease with similar neuro signs to EPM
- then a positive serum to SCF ration that indicated intrathecal (within CNS) antibody production against S. neurona is definitive diagnosis
other than western blot and CSF, list and describe two other diagnostics for EPM
- IFAT (serum and CSF): immunofluorescent antibody test, looks for antibodies against the whole parasite and is suggested to (but not proven) have better accuracy than the western blot
- SAG2, 4/3 ELISA: looks for antibodies against surface antigens detected in ELISA; searches for antibodies to three separate proteins in the CNS on the outer surface of S. neurona
what is the only definitive way to siagnose EPM in horses?
finding protozoa in the CNS on post-mortem exam
describe treatment of EPM (3)
- use Marquis (Bayer), an anti-protozoal drug that is administered once daily (orally) for 28 days or more, depending on severity and clinical signs; the cost is approx $1,200-1,400 per month
- or Rebalance
- or Protazil
what are the 4 core vaccines that are always given, no matter the location, travel/activity, season, or type of horse?
- rabies
- eastern/western encephalitis
- west nile virus
- tetanus
