Parasitology Lecture Notes

Giardia

• Giardia duodenalis (aka Giardia intestinalis, Giardia lamblia) is an intestinal flagellate.
• Second most common parasitic cause of diarrhea worldwide.
• Mostly undiagnosed in the tropics.
• Exists in two forms: cysts and trophozoites.

Cysts

• Cysts are hardy and infective.
• Cysts can survive in cold water for months.
• Cysts can be stained with iodine for easy identification.
• Ovoid shape is characteristic.

Trophozoites

• Trophozoites cannot survive in the environment.
• Trophozoites can be passed in stool.
• Trophozoites are pear-shaped organisms.
• Trophozoites can be stained with trichrome.

Symptoms

• Acute: Watery stools and floating, fatty stools.
• Chronic: Fat malabsorption syndrome, leading to fat loss and deficiency of fat-soluble vitamins (A, D, E, K).
• Can stunt growth.

Diagnosis

• Stool exams are used for diagnosis.
• Antigen kits are available.
• Fluorescent stains or rapid diagnostic tests (RDTs) can be employed.
• Multiplex PCR panels are available for detection.
• DFA commercial kits are available and are more sensitive for low cyst concentrations.

Treatment

• Treatment is the same as for amebiasis; use Iodoquinol.

Trichomonas vaginalis

• A sexually transmitted disease caused by a protozoan parasite.
• There is no cyst stage.
• Most common non-viral STD.
• Males are typically asymptomatic, while females are symptomatic.
• Replicates via binary fission.