Giardiasis - It is caused by the protozoan flagellate Giardia intestinalis, which lives in upper parts of human intestine. It perches on living cells of intestinal wall with adhesive discs, absorbing nutrition from food passing by, growing and multiplying. They interfere with digestion, causing pain, diarrhea, headache and fever. Preventive measures include consuming boiled water, maintaining hygiene and sanitation as well as practicing personal hygiene.