GIARDIASIS
It is an acute or chronic diarrheal disease, caused by a flagellated, protozoal parasite, Giardia-lamblia, transmitted by feco-oral route through contaminated water. The public health importance lies in the fact that it can lead to malabsorption and growth retardation among children and is often responsible for traveller’s diarrhoea. Magnitude: Giardiasis is worldwide in distribution. The prevalence rate is about 2 to 5 percent in the developed countries and about 20 to 30 percent in the developing countries.
Agent Factors
Agent
The causative agent is a flagellated, protozoal parasite called ‘Giardia lamblia’ (synonyms = Giardia duodenalis). It exists in two phases: trophozoite and cysts.
Trophozoite
Usually it colonizes in the duodenum. It has a spear-shaped body, dorsal surface is convex and ventral surface is concave with a sucking disc. Size of the trophozoite is 14 µ long and 7 µ broad. It is bilaterally symmetrical and all the organs are paired (such as two axostyles, two nuclei and four pairs of flagella). An acid environment causes the parasite to encyst.
Cyst
It is oval shaped, measuring 12 µ long and 7 µ broad. It has a median body with four nuclei.
Life cycle
The trophozoite multiplies in the duodenum by binary fission. When the condition is unfavorable, encystment occurs in the large intestine. The cell divides into two within the cyst. The cysts are excreted in the feces and survives for several weeks or months in the cool environment. The cysts constitutes the infective stage of the parasite. It is transmitted feco-orally through the contaminated water or food. Within 30 minutes of ingestion, the cyst hatches out two trophozoites, which then multiply in enormous numbers and colonize in the duodenum and the cycle continues.
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Reservoirs
Humans are the reservoirs. Some of the domestic animals have been found to be infected, such as cats, dogs, as well as sheep and cattle. They may be a source of infection for humans.
Mode of Transmission
Feco-oral route through contaminated food and water is the main mode of transmission. Person to person transmission occurs in groups with oral-anal sexual contact among children in day-care centers, male homosexuals and in custodial institutions.
Host Factors
Age incidence: Giardiasis can occur in any age group. But is more common among children, specially below 5 years.
Sex incidence: It is equal in both the sexes.
Nutritional status: It is four times more among malnourished children, compared to healthy counterpart.
Environmental factors: Favorable environmental factors are lack of protected water supply, lack of sanitary disposal of excreta, lack of personal hygiene and over-crowding.
Pathogenicity: With the help of sucking disc, the parasite attaches itself on the intestinal epithelial cells and leads to malabsorption of fat, resulting in steatorrhea (passage of stools with loss of fat). The parasite is also capable of producing, harm by its toxic effect (allergy), traumatic and irritative effect as well as by diverting the nutrients.
Incubation Period
Ranges from 3 to 20 days (Average = 1 week).
Clinical Features
Vary from asymptomatic to acute or chronic features.
• Asymptomatic cases: These are silent cases. They constitute the majority, specially in endemic areas. They act as carriers.
• Acute cases: They will have watery diarrhea, mild to severe, often with bulky, greasy, frothy, malodorous stools, free from blood and mucus, associated with upper abdominal pain, discomfort, distension, anorexia, weakness and excessive flatus. Rarely fever. Majority recover but about 30 to 40 percent cases become chronic.
• Chronic cases: Chronic diarrhoea with steatorrhea and profound weight loss is the feature. Fat malabsorption,
Vitamin B12 and Vitamin A deficiency can occur.
Complications
Include retardation of growth and development among children and malnutrition.
Diagnosis
It is by identifying cysts or trophozoites in the freshly passed stools.
Treatment
Giardiasis is usually self-limiting but the administration of anti-giardial drug reduces the severity of symptoms and the duration of illness. Three major groups of drugs are used for the treatment, as follows.
1. Nitroimidazole:
– Metronidazole—400 mg, thrice a day for 5 days.
– Tinidazole—2 g, single dose
2. Acidine:
– Mepacrine—100 mg, thrice a day for 5 to 7 days.
3. Nitrofurans:
– Furazolidine—100 mg, four times a day for 7 to 10 days.
Prevention and Control
Control measures include treatment of the cases and screening of the family members for the treatment of cyst passers. Preventive measures are provision of protected water supply by filtration and chlorination, sanitary disposal of excreta and maintenance of personal hygiene
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