Equine Flash Notes - Theiler's & Tyzzer's Flashcards
what is theiler’s disease?
idiopathic acute hepatitis from equine origin biologicals - most commonly tetanus antitoxin
when is theiler’s disease seen in horses?
occurs 4-10 weeks after last tetanus antitoxin administration
occur in late summer/fall - suggested infectious or blood borne agent involved, seasonal occurrence with multiple horses involved
what is the common presentation of theiler’s disease in horses?
malaise/weight loss weeks to months before acute signs
acute hepatoencephalopathy, icterus, photodermatitis, rapidly progressive signs, & death within 2-5 days after initial clinical signs
what is seen on lab work from a horse with theiler’s disease? what is seen post mortem?
increase in all liver enzymes, increased bilirubin, prolonged clotting profiles
small, flaccid liver with microscopic necrosis & bile duct proliferation
how is theiler’s disease treated?
treat like liver failure - sedate with xylazine, decrease blood ammonia levels, correct acidosis slowly, dietary management, vitamin b1/folic acid/vit k weekly, protect from the sun when grazing
how is theiler’s disease prevented?
avoid using tetanus antitoxin - use only on horses with wounds who are not immunized or those of questionable vaccine history & foals of mares not immunized during late gestation
what is another name for tyzzer’s disease? what causes it?
dead foal disease - bacillus piliformis infection
what clinical signs are seen with tyzzer’s disease?
fatal within 7-40 days - focal bacterial hepatitis
most are found dead/comatose
depression, anorexia, recumbency, increased temp, marked jaundice, convulsions
what changes in labwork are seen in foals with tyzzer’s disease? what is seen post mortem?
jaundice if alive long enough
marked increased of SDH, LDH, ALP, AST, GGT, marked increase in bilirubin, profound hypoglycemia
marked jaundice, huge liver
how is a definite diagnosis of tyzzer’s disease made?
giemsa or silver stained liver sections - long slender bacillus alone in stacks and/or bundles in the hepatocytes
T/F: liver abscesses are more common in cattle but are found incidentally on necropsy of horses
true
what are some examples of poisonous plants that cause pyrrolididine alkaloid toxicity?
crotalaria, senecio, amsinckia, heliotropium, & echium
what is the pathophysiology of pyrrolizidine alkaloid toxicity?
alkaloids in the liver are metabolized into pyyroles - pyrroles inhibit mitotic division so megalocytes & death of hepatocytes occur leading to fibrosis & marked portal hypertension
what clinical signs are seen in pyrrolizidine alkaloid toxicity of horses?
liver failure, weight loss, hepatoencephalopathy, icterus, & photosensitization
what treatment is used for pyrrolizidine alkaloid toxicosis?
euthanasia if severe fibrosis of the liver
if appetite is still present & only a little fibrosis - sedate with xylazine, glucose IV, decrease blood ammonia, dietary management
what is the prognosis of pyrrolizidine alkaloid toxicity in horses?
poor to grave due to the tremendous amount of fibrosis
how much of the liver must be destroyed before lab values will reflect these changes?
80% must occur - regeneration/recovery impossible after this point
what are some common clinical signs seen in liver disease in horses?
icterus, weight loss, diarrhea, dermatitis, hepatoencephalopathy
where is the preferred liver biopsy site in an adult horse?
right 14th ICS intersection with line from tuber coxae to point of shoulder
what are poor prognostic indicators of liver disease in horses?
albumin <2.5, increased globulins, prothrombin time > 30% of normal, greatly decreased GGT & ALP with normal or decreased SDH or LDH, marked fibrosis
what abx should be avoided in horses with liver disease? why?
tetracycline & chloramphenicol - avoid drugs metabolized by the liver
elevation in bilirubin in horses indicates what?
liver disease, bile blockage, hemolysis, or a fasted horse
what do increased bile acid levels in a horse indicate?
hepatic disease, cholestasis, or portosystemic shunting
what are the pros & cons of doing a liver biopsy in a horse?
pros - safe, simple, & good for diagnosing diffuse/zonal diseases (toxicities, infectious, & metabolic liver disease)
cons - don’t do if you suspect liver abscesses & easy to miss focal lesions such as abscesses, granulomas, neoplasia, & flukes
an increase in GGT represents an acute or chronic liver issue in horses? what about an increase in SDH?
GGT - chronic
SDH - acute
