In-Depth Notes on Parasitic Diarrhea in Veterinary Medicine

Learning Outcomes

• By the end of this session, students will be able to:
  • Describe the common parasitic causes of diarrhea in small and large animals
  • Understand the clinical presentation and pathogenesis
  • Differentiate between small and large bowel diarrhea
  • Determine the diagnostic approaches for specific parasites
  • Know the strategies for transmission prevention

What is Parasitic Diarrhea?

• Parasitic diarrhea occurs when parasites infect the gastrointestinal (G.I.) tract, leading to:
  • Damage to the mucosa
  • Disruption of normal absorption of fluids and electrolytes
• Causes:
  • Direct cellular invasion by parasites
  • Activation of immune responses
  • Changes in intestinal motility

Parasites Associated with Diarrhea

Protozoa:

• Coccidia:
  • Cystoisospora spp., Eimeria spp.
• Giardia:
  • G. Duodenalis (synonyms: G. intestinalis, G. lamblia)
• Tritrichomonas:
  • T. blagburni
• Cryptosporidium spp.

Nematodes:

• Hookworms:
  • Ancylostoma spp., Bunostomum spp., Uncinaria sp.
• Trichuris spp.
• Strongyloides spp.
• Trichostrongyles
• Strongyles

Parasites and Their Locations:

Small Intestine:

• Coccidia
• Tritrichomonas
• Trichuris
• Strongyles

Large Intestine:

• Coccidia
• Giardia
• Cryptosporidium
• Hookworms
• Strongyloides
• Trichostrongyles

Coccidia

Cystoisospora spp.

• Hosts: Cats & dogs (host-specific)
• Transmission: Direct, fecal-oral ingestion of sporulated oocysts; tissue of paratenic hosts containing encysted sporozoites
• Clinical Signs:
  • Asymptomatic
  • Watery diarrhea (rarely hemorrhagic)
  • Weight loss, dehydration

Eimeria spp.

• Hosts: Cattle, sheep, goats (host-specific)
• Transmission: Similar to Cystoisospora
• Clinical Signs:
  • Reduced feed consumption
  • Soft diarrhea (hemorrhagic)
  • CNS signs in cattle, lower wool quality in small ruminants

Giardia

• Species: Giardia duodenalis
• Hosts: Dogs, cats, ruminants; zoonotic potential (certain assemblages)
• Transmission: Direct, fecal-oral ingestion of infective cysts
• Clinical Signs:
  • Maldigestion, malabsorption
  • Malodorous diarrhea (pale, greasy, mucus appearance)
  • Weight loss, growth retardation

Cryptosporidium

• Species: Cryptosporidium parvum, C. canis, C. felis
• Hosts: Cattle, small ruminants, dogs & cats (C. parvum has zoonotic potential)
• Transmission: Direct, fecal-oral ingestion of sporulated oocysts
• Clinical Signs:
  • Watery diarrhea (yellowish with blood or mucus)
  • Dehydration, life-threatening in immunocompromised hosts

Hookworms

• Species: Ancylostoma caninum, A. braziliense, A. tubaeforme, Uncinaria stenocephala, Bunostomum spp.
• Hosts: Dogs, cats, ruminants
• Zoonotic potential: Cutaneous larva migrans
• Transmission:
  • Ingestion, skin penetration, paratenic hosts, transmammary transmission of infective L3 larvae
• Clinical Signs:
  • Anemia, weight loss, dark, tarry diarrhea
  • Dermatitis with erythema and pruritus (L3 skin penetration)

Strongyloides

• Species: Strongyloides stercoralis, S. papillosus, S. westeri
• Hosts: Dogs, cats, ruminants, horses; zoonotic potential (S. stercoralis causes CLM)
• Transmission: Ingestion of infective filariform larvae, skin penetration, transmammary, autoinfection in GI tract
• Clinical Signs:
  • Diarrhea (with blood), malabsorption, potentially verminous pneumonia

Trichostrongyles

• Species: Trichostrongylus colubriformis, Ostertagia ostertagia, Cooperia spp., Nematodirus spp.
• Hosts: Sheep, goats & cattle
• Transmission: Ingestion of infective L3 larvae
• Clinical Signs:
  • Anorexia, weight loss, diarrhea, dehydration, abomasal lesions

Diagnosis - Fecal Examination

• Direct Wet Mount/Smear: Protozoa motility; quick but low sensitivity
• Flotation Techniques: Eggs, larvae & cysts using various solutions
• Baermann Technique: For larval stages (e.g., Strongyloides)
• Histopathology: Identification of oocysts & nematodes in intestinal mucosa
• PCR & Antigen Detection: Higher sensitivity and specificity for specific parasites (e.g., Giardia, Cryptosporidium)
• Modified Acid-fast Staining: For Cryptosporidium detection

Case Discussion: Max's Symptoms

• Max, a 2-year-old male neutered Labrador Retriever, has intermittent diarrhea and other clinical signs potentially pointing to a Giardia infection. Diagnostic plan and advice upon confirmation would focus on treatment and preventive measures against future infections.

Summary

• Gastrointestinal parasites predominantly affect the small intestine but can also occur in the large intestine.
• Diarrhea is a common clinical sign associated with various nematode and protozoan parasites.
• Different appearances of diarrhea may relate to the type of parasite interaction.
• Various fecal diagnostic tests can confirm parasitic infections.