diseases Flashcards
considerations of infectious horse diseases
Systems affected and severity – Prognosis if your horse gets the disease – Vaccine available?
• Reliability of vaccine
– Is there a vector or a seasonality?
• Or is the organism always present in the environment?
communicable
directly transmitted from sick to healthy
vector-borne
carried by insects or other animals
infectious but not usually contagious
organisms present in the soil
equine encephalitis transmission
songbirds are infected with the disease but fight it off in a few days, mosquitoes bite the infected bird and become infected for life, an infected mosquito bites the horse and transmits the virus (horses do not get high enough level to infect mosquitoes), results in inflammation of the brain
western equine encephalitis
Mostly west of Mississippi – Extends into Canada and Mexico
Venezuelan equine encephalitis
Mostly South and Central America
– Also, Mexico, Texas
• Occasionally appears in other southern states • Last US outbreak 1971 • Last Mexico outbreak 1993
eastern equine encephalitis clinical signs
“Sleeping sickness”– Fever – Loss of Coordination – Head Pressing – Circling – Poor prognosis
• Supportive care only • Most horses die or have permanent damage
EEE prevention
Vaccine available
– Effective if given at appropriate time
• Spring • Peak season July – Sept • Immunity lasts up to 1 year
– Must vaccinate every year
– Usually sold in combination with other vaccines
• 4-way, 5-way, etc.
– Avoid exposure to mosquitoes
West Nile Virus
Encephalitis new to US
– Originated in Africa – Also causes disease in humans, birds
• Now found all over lower 48 states • Vector-borne - mosquitoes • Reservoir is birds • Similar life cycle to EEE • Not all infected horses develop disease
west nile virus clinical signs
West Nile Virus
– Loss of coordination – Muscle twitching (face and muzzle) – Weakness – Falling down – Prognosis better than EEE
• 30-40% mortality • Supportive care only • Some recover completely
west nile virus prevention
Vaccine available
– Effective if given at appropriate time
• Spring • Peak season July – Sept • Immunity lasts up to 1 year
– Must vaccinate every year
• 3 types of vaccine on the market
– Killed virus – Recombinant (canarypox virus) – Inactivated flavivirus
– Avoid exposure to mosquitoes
tetanus
Caused by bacteria – Clostridium tetani – Lockjaw – No vector – Present in soil (spores) – Thrives in closed wounds • Anaerobic – Bacteria produces toxin that causes disease – Horses highly susceptible
tetanus clinical signs
Stiffness, rigidity
– Sawhorse stance
• Sensitive to noise • Convulsions • Paralysis • Prognosis poor
– Supportive care – 80% mortality – Usually due to respiratory failure
tetanus prevention
Vaccine available
– Immune system neutralizes toxin – Wounds can occur year round – Give annually – Usually in combination with other vaccines – Tetanus toxoid
• To produce protective antibodies
– Tetanus antitoxin
• Antibodies given directly to unvaccinated horses
• Accompanied by tetanus toxoid vaccine
botulism
Caused by bacteria
– Clostridium botulinum– No vector – Acquired via forages or puncture wounds – Present in soil and decaying material • Anaerobic = grows in closed wounds • Dead rodents baled along with hay • Round bales of hay
– Kentucky is endemic area – Bacteria produces multiple toxins
botulism clinical signs
Weakness, tremors • Respiratory paralysis • Inability to swallow • In foals, inability to suckle
– “Shaker foal syndrome”
• Prognosis poor without treatment
– Antitoxin can be administered if diagnosed early enough and horse can eventually recover
botulism prevention
Vaccine available • C. botulinum toxoid • Given as a series, then annually • Foals are especially susceptible
– Vaccinate dam 4-6 weeks prior to foaling – Start vaccinating foal at 2-3 months old
• Vaccine not effective against wound botulism
– Different toxin than forage botulism
rabies
Caused by virus
– Rhabdovirus
• “Hydrophobia”
• Vectors are other animals
– Bats, skunks, raccoons, dogs – Transmitted by biting – Can infect any warm-blooded animal
• Not common in horses, but always fatal
rabies clinical signs
Fever, depression • Excess salivation • Excitability • Paralysis • By the time signs appear it is too late to
prevent or treat • Cannot be diagnosed in a living animal
rabies prevention
Vaccine available • Given annually • Recommended in Kentucky
– Eastern strain rabies in raccoons
• Administered by veterinarian
– Can provide proof of vaccination
• Cannot be diagnosed in a living animal
– Vaccinated horses will test positive for antibodies in blood
equine infectious anemia (EIA)
EIA (swamp fever)
– Caused by a virus (lentivirus) – Many similarities to HIV/AIDS – Attacks immune system – Mutates easily, “hides” in liver – Body can’t rid itself of infection – No cure
• No vaccine
EIA clinical signs
Acute
– Fever, depression, pale mucus membranes – Destruction of red blood cells – Viremic (high levels of virus in blood)
Chronic
– Cycles resembling acute phase – Weight loss (poor doer) – Viremia can fluctuate, but tends to be lower than acute EIA
Inapparent carrier
– Appears healthy
– May carry the virus for years with no effects
– Can relapse to chronic state – Will be detected by routine testing – Not usually viremic while in this state
EIA epidemiology
Virus spread by biting flies
– Primarily horse flies – Rarely, deer flies
• Mechanical transmission
– Fly bites infected horse – Horse reacts – Fly bites another horse – Virus spread on fly mouth parts – Can spread virus for about 200 yards before blood dries
EIA testing
Antibody tests on blood
– Coggin’s test (AGID) – ELISA (faster) – A positive test indicates current infection
• Reportable disease
– Euthanasia – Slaughter??? – Quarantine
• Horse must be branded with the letter A • Kept away from other horses (> 200 yards)
EIA control
Today EIA has low incidence in KY
• Most states require testing for entry, sales and gatherings of horses
• Remove carriers from population
• Trace-back investigations of horses exposed to carriers
• Do not reuse needles or syringes when vaccinating horses
– Mechanical transmission of blood and virus
respiratory diseases
Typical symptoms
– Fever
– Nasal discharge
• First clear, then progressively cloudy
– Depression, lack of appetite – Cough – Muscle pain – Can be caused by viruses or bacteria
influenza
Caused by virus • Highly contagious from horse to horse • No vector • Aerosol dispersal
– Sneezing – Coughing – Infects via mucus membranes
• Nasal passages, eyes
• Affects horses of all ages
influenza clinical signs
Classic respiratory disease clinical signs
• Cough can last up to 3 weeks
• Damages respiratory tract
– Horses need time to recover – Restrict exercise for 3 weeks – Prone to secondary bacterial infections
influenza prevention
Quarantine sick horses
– Aerosol transmission – Soap and water are effective at killing virus
• Virus has lipid envelope • Avoid mechanical transmission
• Segregate new arrivals for 2 weeks • Vaccinate
– Intramuscular – Intranasal – Immunity is short-lived
rhinophneumonitis
Caused by virus
– Equine herpes virus – Strains EHV 1 and EHV 4
• Primarily a respiratory disease • Also abortion in pregnant mares • Also neurological disease • No vector • Contagious from horse to horse
– Aerosol and mechanical transmission
rhino clinical signs (classic respiratory)
Classic respiratory signs
– EHV 1 and EHV 4
• Most horses recover completely but herpes viruses remain latent in body
• Can re-emerge in times of stress
• Abortion usually occurs
– 2-12 weeks after infection with EHV 1 – 7-11 months gestation – Sometimes infected foals are born alive
but die shortly thereafter
rhino clinical signs (neurological)
Neurological form of herpes
– EHV 1 (mutant strain) – Causes vasculitis of neurological tissues – Inflammation that compromises blood-
brain-barrier – Can take the form of an epidemic – Prognosis
• Good recovery often seen in horses that remain standing
• Prognosis poor for horses with more severe disease
rhino prevention
Same as for influenza
• Vaccination
– Broodmares
• 5, 7 and 9 months gestation • Use vaccine labeled for EHV 1 (abortion)
– Performance horses
• Every 3-4 months during competition season
– Recreation horses
• 2 twice per year, if at all
– Current vaccines on market do not appear to protect against the neurological strain
strangles
Caused by Streptococcus bacteria • Also called distemper • High morbidity, low mortality • Contagious from horse to horse – Highly contagious – Nasal discharge • No vector • Affects horses of all ages – Young horses
strangles clinical signs
Fever (103o – 106o) • Nasal discharge • Swollen lymph nodes
– Submandibular – Retropharyngeal – Difficulty swallowing – Respiratory noise – Abscess
– Rupture
strangles treatment
Rest in a warm, dry stall
• Hot compresses help speed the rupture of abscesses
• Flush abscesses with diluted iodine solution
• Antibiotic treatment carries risks
– Severe cases only – Can prolong the course of disease – Can result in “bastard strangles”
strangles prevention
Hygiene/biosecurity during an outbreak
– Quarantine sick horses – Have separate caretakers for sick horses – Wash everything used on sick horses – Control flies (mechanical transmission
• Test for negative nasal swab before reintroducing recovered horses
• Wash sick horse facilities with Nolvasan and let stand for at least 20 days
Natural immunity is long-lasting
• Some horses are carriers
• 2 types of vaccines available
– Intramuscular (abscesses at injection site) – Intranasal (one occurrence of disease)
• Not highly effective
• Required at some stables with horses that compete
potomac horse fever
Disease of the intestinal tract
– Diarrhea, enteritis
• Caused by Neorickettsia risticii
– Formerly called Ehrlichia risticii
• Multiple strains of N. risticii
• Bacteria lives inside an aquatic parasite
– Found in snails, insects
• Caddisflies, mayflies, damselflies, dragonflies and stoneflies, etc.
PHF occurs in most regions of the US and Canada
– Originally described near Potomac River
• Seasonal peaks in July-Sept.
– Flying aquatic insects
• 16-33% of horses with no history of PHF have serum antibodies that indicate previous infection
potomac horse fever clinical signs
Fever (103o – 106o)
– Loss of appetite, depression – Colic, diarrhea – Laminitis
• Treatment
– Oxytetracylcine – Supportive care, fluids
• Prognosis varies
potomac horse fever prevention
Transmission to horses not well understood
– Avoid attracting insects to your barn
• Overnight lighting increases risk
– Vaccination
• Vaccine efficacy questionable • Only one strain of N. rististii in vaccines • May not lessen severity of case • 2x/year recommended schedule
incubating disease carrier
Early in disease process • Subclinical • Important source of agent
convalescent disease carrier
Animal continues to shed for a period foIlowing recovery
• Less important than incubating carrier
host characteristics
Resistant
– Will not get sick with natural exposure – Inherent or innate – Acquired natural or artificial
• Immune
– Protected against disease – Antibodies – Not absolute
• Susceptible
types of immunity
Passive
– Colostrum , injections (example: antitoxin) – Short-lived (weeks to months)
• Artificial
– Vaccines and toxoids – Antibody titer (level)
• Active
– Results from natural infection – Can be induced with a vaccine
vaccines
Given after passive immunity wanes
– Mare’s antibodies will reduce response from foal
– First given as a series – ~1 month apart – Boostered thereafter – Annual vaccination for adult horses – Some more often
killed (inactivated) vaccine
Pathogen mixed with adjuvant
– Adjuvant stimulates stronger response than you would get from killed pathogen alone
– Less complete response than with natural infection
– Need to booster – Safe (no live organism) – Stable in storage
modified (attenuated) live vaccine
Mild or weakened form of pathogen – More complete stimulation of immunity
• Longer-lasting
– Can spread to others in herd
– Some disadvantages
• Can occasionally cause disease (reversion) • Viability must be maintained • More difficult to store
recombinant vaccine
Genes encoding pathogen proteins inserted into a safe virus
– Infection process Is similar to modified live vaccine
– More complete stimulation
• Longer-lasting
– Less likely to cause disease
– In rare cases they can cause disease in immunocompromised animals
DNA vaccines
Genes encoding pathogen proteins injected into horse
– Illicits production of proteins by the horse
• Recognized as foreign • Attacked by immune system
– Won’t cause disease
• No actual pathogen is involved
– So far, shown to be safe and effective in horses
• West Nile Virus Vaccine
response to vaccine
Primary response (first vaccine)
– Allows body to recognize foreign proteins
• Secondary response (booster(s))
– Takes advantage of memory – Stronger response
• Once in the bloodstream antibodies decay over time
– ~4-5 months for IgG from killed vaccines
vaccination risks
Introduction of foreign substance into body carries some risks
• Mild symptoms of disease • Abscesses at injection site • Infections (Clostridium) • Reversion • Anaphylaxis (Very rare)
– Rapid, deadly – Requires epinephrine
vaccination strategies to consider
Considerations by disease
– Severity – Risk of disease (also source) – Potential losses
• Horses • Days of use • Cost of treatment
– Efficacy of vaccine
– Cost of vaccine
• How many horses to vaccinate?Considerations by farm
– Classes of horses
• Broodmares • Foals • Competitive
– Animal density – Biosecurity practices – Herd immunity – Recurring diseases
• Strangles
herd immunity
• Not all animals in a herd need to be immune to prevent an outbreak
– Generally, 2O-3O% need to be susceptible for contact-transmitted epidemic
– If a disease organism is introduced it will not get far
– Unvaccinated animals are protected by herd immunity
• Reduced odds of encountering the disease
colic
The term “colic” refers to a condition that causes abdominal pain
• Not infectious or contagious • Multiple types of colic
– Multiple causes – Differing levels of severity
• Different risk factors for different types of colic
• Disease of high concern for horse owners
colic clinical signs
Elevated respiration rate and pulse • Lack of interest in food, water • Kicking or nipping at belly or sides • Rolling • Stretched stance • Lip curling • Sweaty • Not passing manure
colic and GI tract anatomy
Equine gastrointestinal tract
– Long, involved – Relies on rapid passage of forages – Must handle dried forages (hay) – Requires lots of water – Often incomplete digestion of
concentrates – leads to gas, acid – Small, frequent meals ideal – Horse cannot vomit
sand colic
Caused by eating sand – Colic occurs in cecum and colon – Inflammation and impaction
gas colic
Caused by over-consumption of sugars and starches
– Microbes ferment and produce gas – Painful but can be self-resolving
impaction colic
Flow of digesta slows or stops – Can be serious – Related to diet changes and dehydration
verminous colic
Caused by parasites damaging GI tract or forming an obstruction
– Large and small strongyles – Tapeworms – Ascarids
spasmodic colic
Painful, overactive peristalsis (smooth muscle contractions in intestines)
serious types of colic
Torsion or twist
– Intestines become twisted and flow of digesta is blocked
• Intussusception
– Part of intestine telescopes within itself or into another section
• Strangulating lipomas (benign tumors)
– Older horses
• These are life-threatening and usually require surgery
treating colic
Observe your horse, take TPR
• Call vet
– May not need to come but should be aware
• Walk horse if it is rolling violently
– Consider your own safety – Don’t over do it and exhaust your horse
• Administer analgesic
– With consultation from vet
• Monitor for manure passageIf colic persists vet will need to examine the horse
– Vital signs, gum color – Rectal palpation to check for mass – Listen to gut sounds – May pass a nasogastric tube (belly tap)
• Relieves pressure in stomach
– May administer water or mineral oil – Analgesic – May recommend surgery
colic surgery considerations
If colic surgery is recommended
– Consider duration of problem – Time to clinic – Nature of problem – Age of horse – Potential cost $$$$$$$$ – Prognosis – Value of the horse to you
risk factors for colic
Breed or use
• Lack of access to water
– Cold weather, group housing
• Sudden changes in diet • Confinement (stall) • Poor parasite control program • Parturition • Overconsumption of concentrates • Long periods between feedings
water after exercise
Long believed to be risky
• No association proven to exist
– Dehydration a risk factor for impaction – Thirst not triggered by sweating
• Horses recover hydration best when offered water within 15-20 minutes
– Ambient temperature – First with electrolytes or NaCl – Then plain water
colic prevention
Provide the most natural feeding and housing situation possible
– Free choice forage – Access to water (heated in winter) – Turnout or exercise
• Make feed changes gradually • Don’t overfeed concentrates • Manage parasites effectively
