Exam 3: Diarrhea in Horses

describe a complete history for adult horse diarrhea

• vaccination

• deworming

• drug administration

• presence of other clinical cases on the farm

• previous cases of Salmonella or PHF

• types of feeds

• changes of feed

• duration of signs

what are the common clinical signs that go with diarrhea

• remember that severe acute diarrhea is a medical emergency

• lethargy

• fever

• colic

• anorexia/hyporexia

• clinical signs of endotoxemia → tachycardia, tachypnea, abnormal MM

• deydration

• abnormal GI auscultation

how is colic described generally

• inflammatory mediators associated with colitis can stimulate pain receptors

• some horses with diarrhea can develop ileus, may cause intestinal distension with fluid and can lead to NG reflux

• abdominal discomfort in a diarrhea case is usually transient, pain gives way to profuse diarrhea

describe the possible clinical signs with colitis

• typical = fever, depression, and signs of endotoxemia usuall precede diarrhea by 2-5 days

• sometimes diarrhea never occurs in colitis patients that have minimal damaged mucosa

• in a few severe cases, severe acute shock and death occur before clinical signs in diarrhea are seen, called colitis X

what diagnostics should all acute diarrhea cases hav

• CBC

• chem

• venous blood gas

• blood lactate as prognostic indicator

• abdominal ultrasound

• fecal testing

what diagnostics may be used in select cases of acute diarrhea

• abdominocentesis if peritonitis is suspected

• NG intubation if abdominal pain

• rectal palpation if horses is distended and painful

how does colitis present on CBC

• increased PCV

• neutropenia that may be followed by neutrophila

• left shift and toxic changes

• fibrinogen mild hyper with severe colonic inflammation

how does colitis present on chemistry

• hyponatremia

• hypochloremia

• hypokalemia

• hypocalcemia

• metabolic acidosis

how does azotemia present with colitis

• pre-renal azotemia in most cases due to dehydration and hypovolemia

• renal azotemia caused by acute hemodynamic renal failure
  -can occur with prolonged entotoxemic hypotension and hypovolemia, esp if patient has received NSAIDs or aminoglycosides

how does total protein change with colitis

• normal = fluid losses are absent or minor

• increased when fluid losses only

• decreased when substantial colon damage causes protein loss, with acute diarrhea indicates a guarded prognosis

how is abdominal ultrasound used for colitis

• examine the large intestines for edema and thickness

• evaluate motility
  -fluid filled colon and cecum typically noted

• eamine peritoneal fluid quality and quantity

what are infectious causes of colitis in adult horses

• salmonella

• clostridium

• Neorickettsia risticii

• parasites (strongyles)

• coronavirus

what are non-infectious causes of colitis in adult horses

• toxic (NSAIDs, cantharadin, heavy metals)

• nutritional (carbohydrate overload, lush forage, sudden change in diet composition)

• sand enteropathy

• IBD, neoplasia, organ dysfunction

how is chronic diarrhea defined

• diarrhea of greater than 2 weeks duration

• results from disease of the large intestines, though many also affect small intestines resulting in weight loss

• greater diagnostic challenge

• usually fluid and electrolyte loss less of a problem

what is the organism that causes equine salmonellosis

• THE most important infectious cause of colitis in horses

• family Enterobacteriacae

• gram negative facultative anaerobic rod

• flagella = motile

• surface pilli = adheres to surfaces

what are the four syndromes caused by equine salmonellosis

• severe acute diarrhea

• mild infections

• bacteremia/septicemia

• asymptomatic +/ shedding

• after infection, horses shed for 3 weeks to months

what is meant by salmonella being invasive

• causes severe mucosal and interstitial damage

• attaches to intestinal epithelial cells

• injects signaling proteins into cell causing forced entry

• escapes destruction once inside the cell

• invades intestinal macrophages to be spread systemically

what are the toxins of salmonella

• cytotoxin- damages cells and alters permeability

• exotoxin- causes intestinal hypersecretion

• endotoxin- severe intestinal inflammation

what are the risk factors for equine salmonellosis

• age- neonates

• stress such as prolonged transport, heat exposure, abdominal surgery

• alterations in enteric microflora such as antibiotics, diet changes, fasting, colic

• other disease, especially respiratory disease where antibiotics may be used

how is salmonella diagnsed

• 5 fecal cultures all 24hrs apart from each other is the gold standard, but is slow

• fecal PCR is more rapid but risk of false positive and cannot rune sensitivity

how is C. difficile in horses generally defined

• can be cultured in healthy horses without disease

• important cause of antibiotic-associated diarrhea

• ANY antibiotic use can cause this kind of colitis

what is the pathogenesis of C. difficule

• toxin producing strains, A and B

• mucosal damage causing necrosis, intestinal inflammation

what are the risk factors for C. difficile

• mare with a foal being treated with antibiotics for R. equi

• hospitalization, including exposure to contaminated environment, change in diet, surgical fasting, antibiotic therapy

how is C. difficile diagnosed

• fecal toxin detection

• fecal PCR

• NO CULTURE

what are the important types of C. perf in horses

• Type A

• Type C

describe C. perf type A in horses

• predominant type ID in normal and diarrheic horses

• alpha toxin with potent hemolytic properties

• causes bloody diarrhea, rapid death without outward diarrhea

• Beta-2 toxin and CPE toxin ma also play a role

describe C. perf type C in horses

• can cause severe diarrhea, sepsis and death in newborn foals

• some foals die before onset of diarrhea

• beta toxin is necrotizing that forms membrane pores in GI cells

• causes necrotizing enterocolitis

• can cause death from absorption of toxins from intestines into the blood

ho is C. perf diagnosed

• fecal toxin detection

• Fecal PCR panel to detect toxin producing genes

• NO CULTURE

describe the organism that causes Potomac horse fever

• Neorickettsia risticii

• gram negative rickettsial bacteria

• obligate intracellular organism

• complex life cyctle

• infe ts colonic macrophages and monocytes

what is the epidemiology of Potomac Horse fever

• serology is not reliable

• seasonal- May to november, peaks mid to late summer

generally describe N. risticii

• definitive host thought to be trematode flukes

• infected flukes parasitize many different intermediate hosts such as snails, insects, insectivores, non-equine mammals

describe the transmission and pathophysiology of N. risticii

• ingestion of insects, snails, or trematodes harboring the organism

• patho is poorly understood, but has predilection for the cecum and large colon, direct contact with contaminated feces not likely a major route of transmission

how do you diagnose Potomac Horse fever

• PCR is test of choice, but must be collected BEFORE antibiotics
  -fecal sample may be fridge not frozen
  -post mortem = fresh or formalin fixed colon tissue

• serology is not reliable

generally describe equine coronavirus

• RNA virus

• sporatic cause of diarrhea in adult horses

• fecal oral

• disease usually occurs during cool months

what are the clinical signs of equine coronavirus

• usually resolve in 2-4 days

• anorexia, lethargy, fever most common

• colic, diarrhea, neurological signs

how is equine coronavirus diagnosed

• fecal PCR is test of choice, 4 days after infection,duration of shedding 11 days

• chemistry for hyperammonemia iin horses with neurological signs

what antibiotics should NEVER be given to adult horses

• Clindamycin

• Macrolides

• Lincomycin

what is the pathophysiology and diagnosis of antimicrobial associated diarrhea

• disruption of normal intestinal microflora

• allows pathogens to overgrow

• dx with history of antibiotic therapy

how is NSAID associated colitis defined

• one of the clinical syndromes of NSAID toxicity

• all NSAIDs are capable of causing colitis, Phenylbutazone most likely

• overdose most common in ponies and foals

define right dorsal colitis

• unknown why NSAIDs have preference for this spot

• high or low doses, long or short term use

what are the clinical signs of right dorsal colitis

• lethargy

• decreased appetits

• colid

• diarrhea

• ± tachycardia, tachypnea, dehydration, weight loss

• ulceration throughout GI tract, mouth, esophagus and or right dorsal colon

how is right dorsal colitis diagnosed

• often presumptive based on history

• bloodwork may show anemia, hypoproteinemia, hypoalbuminemia, hypocalcemia

  • ultrasound

how does parasitism typically present

• chronic weight loss or chronic diarrhea

• L3 larva can damage the intestinal all and cause intestinal inflammation

what are possible causes of parasitism in horses

• Cyathostomes (small strongyles) are more common due to resistance

• large strongyles are less common and largely eradicated by ivermectin

describe larval encysting in parasitism

• some L3 larva that penetrate the gut wall encyst → hypobiosis

• encysted larvae can simultaneousl mature and emerge from the colon at once with certain environmental cues

• leads to massive release of inflammatory mediators → acute diarrhea/colitis

how is parasitism diagnosed

• no antemortem method to diagnose encysted cyathostomes

• fecal egg counts may or may not be increased

• do fecal egg counts as a part of herd parasite program
  -if 10% of herd >200epg → indicate a high level of pasture contamination

what is the pathogenesis of cathardin GI tox

• toxic to mucosal cells of the intestine

• excreted by the kidney and damages kidney and mucosa of bladder an urethra

what are the clinical signs of cantharidin tox

• gastroenteritis causing colic and severe diarrhea

• oral ulceration

• AKI

• mycardial necrosis causing arrhythmia

• ulcerative cystitis causing hematuria

• synchonous diaphragmatic flutter due to low calcium

how is canthardidin tox diagnoed

• chemistry will show azotemia, extremely decreased calcium, decreased magnesium, decreased protein

• UA shows hematuria

• tox testing

• examine hay source

describe carbohydrate overload

• sudden increase in consumption of readily digestible CHO, accidental or intentiona

• leads to change in colonic microflora
  -CHO fermentation in the hindgut → osmotic diarrhea
  -increases lactic acid producing bacteria in the large intestine
  -lactic acid decreases GI pH which also damages colonic epithelium and leads to mucosal inflammation

what is sand enteropathy

• horses consuming small amounts of sand over a long period of time and accumulates in the colon

• can cause impaction and chronic diarrhea

how do you diagnose sand enteropathy diagnosis

• auscultation for sand sounds

• abdominal rads

• fecal sand test in rectal sleeve

• rule out