This episode begins organism-specific parasitology with protozoa that primarily infect the gastrointestinal and urogenital tracts. Drawing from Murray’s Chapter 72, it explores transmission, pathogenesis, and clinical presentation.

Key intestinal protozoa include:

* Giardia lamblia - malabsorption and chronic diarrhoea

* Entamoeba histolytica - invasive colitis and liver abscess

* Cryptosporidium species - watery diarrhoea, severe in immunocompromised hosts

In the urogenital tract:

* Trichomonas vaginalis - sexually transmitted infection causing vaginitis and urethritis

Transmission occurs through contaminated water, food, faecal–oral spread, or sexual contact. Many infections remain luminal, but some protozoa invade mucosa and disseminate.

Conceptually, these organisms demonstrate how single-celled parasites can produce both localised and invasive disease. Clinically, travel history, water exposure, and sexual history guide suspicion.

Key Takeaways

* Intestinal protozoa are commonly waterborne

* Giardia causes malabsorption

* Entamoeba can cause invasive colitis and liver abscess

* Cryptosporidium causes severe disease in immunocompromised hosts

* Trichomonas is sexually transmitted

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