Friday, October 14, 2016
Which of the following statements about giardiasis is true?
A) Transmission occurs through fecal–oral contamination.
B) Chlorination of drinking water kills the cyst.
C) Diagnosis can be achieved by peripheral blood smears.
D) The cyst form is responsible for symptoms.
E) Asymptomatic carriers do not require treatment.
Answer and Discussion
The answer is A.
Giardia lamblia is the causative agent in parasitic giardiasis. Most cases are asymptomatic. However, these patients pass infective cysts and must be treated.
Symptoms occur 1 to 3 weeks after infection and include foul-smelling watery diarrhea, flatulence, abdominal cramps and distention, and anorexia.
Outbreaks in day schools, nursing homes, and institutions for the mentally retarded are common. Transmission is through a fecal–oral route.
The infective form is the cyst, and trophozoites are responsible for the symptoms. Cysts are transmitted in contaminated food or water. Giardia cysts are resistant to chlorination; therefore, filtration is used to clear cysts from drinking water supplies. Giardia is sensitive to heat, thus bringing water to a boil is effective before consumption.
Diagnosis is accomplished by detecting cysts or the parasite in the stool (usually three samples) or in duodenal contents (by using endoscopy, the swallowed-string test, or Enterotest).
Treatment includes metronidazole and furazolidone. The medication is available in suspension, making it useful for children. Close contacts should also be tested, especially when recurrent infections are found. Although Giardia is most commonly associated with beavers, there is evidence of sporadic transmission between infected dogs and people.