Parasitic Gut Infections

Overview – Parasitic Gut Infections

Parasitic gut infections are a significant cause of global gastrointestinal disease, particularly in developing countries and among immunocompromised individuals. They are commonly transmitted via the faecal-oral route and caused by either protozoa or helminths. Symptoms vary from mild malabsorption to severe dysentery and can lead to long-term nutritional deficits. This page outlines the most clinically relevant parasitic gut infections and their diagnosis and management.

Definition

Parasitic gut infections are gastrointestinal illnesses caused by intestinal protozoa or helminths. They are usually acquired via ingestion of contaminated food or water, or direct contact with infective ova or larvae.

Aetiology

Protozoal Causes

  • Giardia lamblia
  • Cryptosporidium spp.
  • Entamoeba histolytica

Helminthic Causes

Transmission

  • Faecal-Oral Route – Ingestion of dormant cysts or oocysts in contaminated water or food
  • Skin Penetration – Common for helminths like Strongyloides and Ancylostoma

Pathogenesis

Giardia

  • Non-toxigenic; causes malabsorption by covering the brush border
  • Leads to fatty stools and chronic nutritional issues
PARASITIC GUT INFECTIONS - Giardia
https://www.cdc.gov/dpdx/giardiasis/index.html

Cryptosporidium

  • Invokes inflammatory changes in the gut wall
  • Damages villi → rapid crypt cell turnover → immature villi → poor absorption
  • Resistant to chlorination (→ outbreaks via public pools)
PARASITIC GUT INFECTIONS - Cryptosporidium
https://www.cdc.gov/dpdx/cryptosporidiosis/index.html

Entamoeba histolytica

  • Invasive amoeba → ulceration of intestinal mucosa
  • Results in amoebic dysentery (bloody diarrhoea)
PARASITIC GUT INFECTIONS - Amebiasis
https://www.cdc.gov/dpdx/amebiasis/index.html

Clinical Features

  • Diarrhoea (watery or bloody depending on organism)
  • Abdominal cramps
  • Malabsorption and steatorrhoea (esp. Giardia)
  • Chronic infection in immunocompromised (e.g. Cryptosporidiosis in AIDS)
  • Systemic complications: weight loss, anaemia, malnutrition

Investigations

  • Stool Microscopy – Detection of cysts/oocysts
  • Antigen Detection – For Giardia and Cryptosporidium
  • Stool PCR (where available)
  • Clinical context: travel history, immune status, outbreak patterns

Management

Protozoa

  • Giardia: Metronidazole
  • Cryptosporidium:
    • Self-limiting if immunocompetent
    • Nitazoxanide if persistent
  • Entamoeba histolytica: Metronidazole

Helminths

  • Albendazole – Broad-spectrum antihelminthic effective against most intestinal worms
  • Hygiene and sanitation improvements essential to prevent reinfection

Prevention

  • Boil water to eliminate cysts
  • Good personal hygiene practices
  • Avoid faecal contamination
  • Food safety and sanitation education in endemic regions

Complications

  • Chronic infection
  • Malabsorption → Malnutrition
  • Failure to thrive in children
  • Amoebic dysentery complications: intestinal perforation, liver abscess
  • Severe cryptosporidiosis in immunosuppressed

Differential Diagnosis

Summary – Parasitic Gut Infections

Parasitic gut infections are a diverse group of faecal-orally transmitted diseases caused by protozoa or helminths. Clinical presentations range from mild diarrhoea to chronic malnutrition and bloody dysentery. Accurate diagnosis via stool testing and targeted treatment (e.g. metronidazole or albendazole) are essential, especially in high-risk and immunocompromised populations. For more, see our Gastrointestinal Overview page.

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