Diarrhea Causes & Diagnosis

E. coli

• bacterial (Gram -)

• zoonotic + foodborne

• affects neonates - less common in horses, more common in poultry & <1wk calves

• clinical signs: watery ± bloody D+ caused by toxin production

• usually foodborne in SA

Salmonella

• bacterial

• zoonotic + foodborne

• primarily affects adult horses, pigs, cows, & poultry - most common cause of D+ in adult horses & cattle

• clinical signs: colitis, fever, septicemia

• major public health concern (multi-drug resistance), usually foodborne in SA, S. pullorum eradicated from US poultry

Salmonella pullorum

• high mortality rates in young poultry

• eradicated from commercial poultry stock in US

• vertical & horizontal transmission, survivors become subclinical carriers

• display huddling, anorexia, weakness, white diarrhea

• diagnosed via serum submission

Campylobacter

• bacterial (C. jejuni jejuni)

• zoonotic + foodborne

• affects most species, SA & poultry (meat) important sources of human infection

• causes acute watery-bloody D+ w/mucus ± bile lasting 5-15 days

• often found in clinically normal LA

Clostridium

• bacterial

• zoonotic

• primarily affects piglets, calves, & foals

• clinical signs: enterotoxemia caused by toxins

Brachyspira

• bacterial

• primarily affects poultry + adult swine

• clinical signs: mucohemorrhagic D+, lesions in LI

• mostly eradicated in commercial swine

Lawsonia intracellularis

• bacterial

• primarily affects weanling horses + adult swine

• clinical signs: “garden hose gut,” hemorrhagic D+, SQ edema, PLE

• often subclinical in pigs

Mycobacterium avium paratuberculosis

• bacterial

• primarily affects ruminants

• clinical signs: D+, weight loss, decreased production

• SR unlikely to have D+

Rotavirus

• RNA virus

• primarily affects young animals, mainly cause of D+ foals

• clinical signs: D+ ± V+, depression, dehydration

Coronavirus

• RNA virus

• primarily affects swine (TGE) & poultry

• clinical signs: yellow D+, V+, high mortality

• often asymptomatic-mild in other species

Pestivirus

• RNA virus

• primarily affects ruminants (BVDV) & swine (swine fever)

• clinical signs: D+, fever, depression, decreased production, abortion, death

• causes swine fever (highly infectious, often fatal, eradicated from US)

Parvovirus

• DNA virus

• primarily affects dogs

• survives well in environment

Roundworm

• parasite

• primarily affects SR

• clinical signs: mild D+, potbelly, weight loss, poor coat

• commonly passed from mother to young

Hookworm

• parasite

• zoonotic

• primarily affects young SA

Whipworm

• parasite

• primarily affects adult pigs

• reside in LI, whole group needs treated if 1 is +

Tapeworm

• parasite

• primarily affects dogs, sheep, cattle, & horses

Coccidia

• parasite (intracellular), protozoa

• primarily affects young animals

• clinical signs: pasty D+ decreased growth

• low mortality

Cryptosporidium

• parasite, protozoa

• zoonotic

• primarily affects calves & lambs

• clinical signs: malabsorptive D+ w/straining ± blood, dehydration, lethargy

• shedding starts at days of age

Giardia

• parasite, protozoal

• primarily affects SA

• clinical signs: malabsorptive D+

• intermittent shedding

Histoplasmosis

• fungal

• primarily affects SA

• clinical signs: chronic D+, pale MM, fever, weight loss, peripheral lymphadenopathy

  • cats: tachypnea + cutaneous signs

  • dogs: hepatomegaly + ascites

• endemic in US

Dietary causes of diarrhea

• diet change can impact all species

• SA: dietary indiscretion

• ruminant: carb-rich diet

• swine: mycotoxins, grain overload

• poultry: excess minerals/starch/toxins/treats (+ non-pathologic color changes via diet)

• equine: high fructan green grass in spring, overeating grain/toxic plants

Environmental causes of diarrhea

• extreme weather

• overcrowding/unsanitary conditions

Overview of infectious diarrheal agents

• bacteria: common at herd level, toxins lead to secretory diarrheas

• virus: common at herd level, villi damage leads to malabsorptive ± secretory diarrheas

• parasites: more common in younger animals

• fungi: less common, gut microbial imbalance

Small vs large bowel diarrhea

• intermittent high volume liquid D+ ± melena, causes weight loss, often self-limiting

vs

• tenesmus/urgency, increased frequency, mucous ± hematochezia

Functional categories of diarrhea

• osmotic: often bacterial, intestines push out water to “flush” bugs through, often acute + severe

• malabsorption: often viral, bugs cause blunting of enterocytes, often chronic

• hyper-secretory

• hyper-motility: often dietary indiscretion

Who to test for diarrhea

• early & untreated clinically representative cases

• severely/systemically affected cases

• fresh dead

• multiple animals from epidemiologically distinct locations

• ± control animals

• ± environmental samples

When to test for diarrhea

• SA: fecal float on most cases, parvo ELISA for puppies; advanced testing for chronic/unresponsive cases, unique signs, 10+% population affected, or sudden death

• swine: 3+% morbidity/0.5+% mortality in piglets, unresponsive/rapidly spreading w/increased mortality in adults

• cattle: 20+% morbidity in calves, increased death/decreased production in adults

• equine: any sick foal, 1+ day w/colic in adults

• poultry: 5% deviation from normal mortality, 1/3+ droppings abnormal, poor litter quality

Outbreak

• more cases than expected for a defined population, place, & period

• does not require known pathogen

Diagnostic hierarchy

1. immediate population assessment: PE + area inspection + POC testing

2. etiologic investigation: advanced send-out testing + necropsy

3. cause: environmental/food/water testing + repeat testing

Antemortem sample collection

• 2g+ fresh feces (can hold for 2 days)

• fecal swabs for neonates (keep moist w/transport media)

• 2-3ml blood in red + purple top tubes

Postmortem sample collection

• same samples as antemortem collection PLUS

• fresh tissues: intestines & contents, spleen

• fixed tissues: fore-stomachs, liver, intestines, mesenteric lymph nodes (especially if purulent)

Types of population diagnostics

• feces: culture, smear/stain, float, PCR

• blood: PCR, virus isolation, ELISA (red top), CBC/chem

• tissue: smears, cultures, histopath, virus isolation

Virus therapeutic emphasis

• fluids + monitoring

• isolation & vaccination of healthy animals

Bacteria therapeutic emphasis

• fluids + NSAIDs

• systemic antimicrobials when indicated

• toxin (need to be demonstrated for Gram +) & source control

• not every shedder needs treatment

Helminth therapeutic emphasis

• targeted dewormers (whole-group may accelerate parasitic resistance)

• pasture/environment management

Protozoal therapeutic emphasis

• coccidiostats

• supportive care (crypto)

• environmental clean-up + hygiene

Nutritional/toxic therapeutic emphasis

• remove/correct/minimize exposure

• restore fluids + nutrition

Common disinfectants for diarrheal outbreaks

• halogens: chlorine to treat water

• peroxygen compounds

• phenols

• quaternary ammoniums