Parasites and Biliary stones

Giardiasis ٥٧
Giardiasis
Epidemiology:
The transmission of Giardia is essentially feco-oral (Meyer and
Jarroll, 1980). Outbreaks of giardiasis have been linked to fecally
contaminated water supply, infected animals, and situations involving
person to person contact (as in nursing homes and day-care centers). The
sexual transmission of Giardia is exclusively seen in male homosexuals.
The incidence of Giardia is higher in developing countries where the
parasite persists and flourishes as a result of poverty, inadequate
sanitation, insufficient health care, and overcrowding (Hill, 1993).
The incidence of giardiasis is significantly higher in homosexual
males (4–18%) than in heterosexual controls. Sexual behaviors
responsible for the transmission of this organism include, digital anal
contact, and oral-genital contact after anal intercourse. There are many
reports of Giardia vaginitis and proctitis, suggesting that this parasite may
be transmitted by sexual activity (Levine, 1991). Other high-risk groups
are individuals with Crohn’s disease, chronic pancreatitis, achlorhydria,
cystic fibrosis, and the immunocompromised. A late summer and autumn
peak in incidence has been noted (Flanagan, 1992).
Life cycle:
Giardia cysts have a hyaline wall that protects them from extremes
of temperature and other environmental stressors. These cysts are not
killed by chlorination of water, and they also may be resistant to boiling
water at a high altitude. Cysts may survive in water for up to 3 months
(Wolfe, 1992). After ingestion and passage through the stomach,
excystation occurs in the proximal small intestine. This is thought to be
triggered by exposure to gastric acid and/or the subsequent exposure to