Equine Flash Notes - Theiler's & Tyzzer's

Question 1

what is theiler’s disease?

Answer 1

idiopathic acute hepatitis from equine origin biologicals - most commonly tetanus antitoxin

Question 2

when is theiler’s disease seen in horses?

Answer 2

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

Question 3

what is the common presentation of theiler’s disease in horses?

Answer 3

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

Question 4

what is seen on lab work from a horse with theiler’s disease? what is seen post mortem?

Answer 4

increase in all liver enzymes, increased bilirubin, prolonged clotting profiles

small, flaccid liver with microscopic necrosis & bile duct proliferation

Question 5

how is theiler’s disease treated?

Answer 5

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

Question 6

how is theiler’s disease prevented?

Answer 6

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

Question 7

what is another name for tyzzer’s disease? what causes it?

Answer 7

dead foal disease - bacillus piliformis infection

Question 8

what clinical signs are seen with tyzzer’s disease?

Answer 8

fatal within 7-40 days - focal bacterial hepatitis

most are found dead/comatose

depression, anorexia, recumbency, increased temp, marked jaundice, convulsions

Question 9

what changes in labwork are seen in foals with tyzzer’s disease? what is seen post mortem?

Answer 9

jaundice if alive long enough

marked increased of SDH, LDH, ALP, AST, GGT, marked increase in bilirubin, profound hypoglycemia

marked jaundice, huge liver

Question 10

how is a definite diagnosis of tyzzer’s disease made?

Answer 10

giemsa or silver stained liver sections - long slender bacillus alone in stacks and/or bundles in the hepatocytes

Question 11

T/F: liver abscesses are more common in cattle but are found incidentally on necropsy of horses

Answer 11

true

Question 12

what are some examples of poisonous plants that cause pyrrolididine alkaloid toxicity?

Answer 12

crotalaria, senecio, amsinckia, heliotropium, & echium

Question 13

what is the pathophysiology of pyrrolizidine alkaloid toxicity?

Answer 13

alkaloids in the liver are metabolized into pyyroles - pyrroles inhibit mitotic division so megalocytes & death of hepatocytes occur leading to fibrosis & marked portal hypertension

Question 14

what clinical signs are seen in pyrrolizidine alkaloid toxicity of horses?

Answer 14

liver failure, weight loss, hepatoencephalopathy, icterus, & photosensitization

Question 15

what treatment is used for pyrrolizidine alkaloid toxicosis?

Answer 15

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

Question 16

what is the prognosis of pyrrolizidine alkaloid toxicity in horses?

Answer 16

poor to grave due to the tremendous amount of fibrosis

Question 17

how much of the liver must be destroyed before lab values will reflect these changes?

Answer 17

80% must occur - regeneration/recovery impossible after this point

Question 18

what are some common clinical signs seen in liver disease in horses?

Answer 18

icterus, weight loss, diarrhea, dermatitis, hepatoencephalopathy

Question 19

where is the preferred liver biopsy site in an adult horse?

Answer 19

right 14th ICS intersection with line from tuber coxae to point of shoulder

Question 20

what are poor prognostic indicators of liver disease in horses?

Answer 20

albumin <2.5, increased globulins, prothrombin time > 30% of normal, greatly decreased GGT & ALP with normal or decreased SDH or LDH, marked fibrosis

Question 21

what abx should be avoided in horses with liver disease? why?

Answer 21

tetracycline & chloramphenicol - avoid drugs metabolized by the liver

Question 22

elevation in bilirubin in horses indicates what?

Answer 22

liver disease, bile blockage, hemolysis, or a fasted horse

Question 23

what do increased bile acid levels in a horse indicate?

Answer 23

hepatic disease, cholestasis, or portosystemic shunting

Question 24

what are the pros & cons of doing a liver biopsy in a horse?

Answer 24

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

Question 25

an increase in GGT represents an acute or chronic liver issue in horses? what about an increase in SDH?

Answer 25

GGT - chronic

SDH - acute