Giardíase

              Referência: Yamanaka, A., Jorge, S.G., Soares, E.C., Almeida, J.R.S., Mesquita, M.A., Zeitune, J.M.R., Sakamoto, T, Tanaka, M.: Giardiasis. Endoscopia Digestiva ( Japão ) 11(3): 469-71, 1999

Dr. Ademar Yamanaka
Dr. Stéfano Gonçalves Jorge

HISTORY

            Giardia lamblia is the most commom protozoan isolated from the gastrointestinal tract in humans. It was first observed and described in 1681, by Anton Van Leeuwenhoek¹, being the first intestinal protozoa identified. In 1859, Vilem Lambl published the first drawings of the trophozoite and the cyst forms of the parasite. Being so commom in the gastrointestinal tract, with ou without diarrhea, the discussion about the true nature of the parasite last for decades: “Is it a enteropathogen or a simple comensal ?” Finally, some studies demonstrating the development of diarrhea in humans and animals after the exposion to Giardia cleared the question². It is now considered a true enteropathogen by the World Health Organization³.

MICROBIOLOGY

            There are three species of Giardia: agilis ( amphibians ), muris ( rodents, birds and reptiles ) and intestinalis ( mammals, birds and reptiles )⁴. The name Giardia lamblia is not correct, but its use is universaly accept among health care workers. Giardia is a flagellated protozoa whose life cicle can be divided in two stages: a motile and multiplying form, the trophozoite and the resistent form, the cyst. The cyst can survive in water and food, and is relatively resistant to chlorination procedures⁵, difficulting erradication and prevention of the disease. In fact, the cysts were detected in 81% of raw water⁶ and in 17% of filtered water⁷ samples.

Giardiasis occurs after ingestion of contaminated water or food, or by person-to-person transmission. Only 10 to 100 cysts are necessary⁸. When ingested, the cyst passes through the acid environment of the stomach, which triggers excystation. Into the proximal intestine, after exposure to pancreatic secretions, the excystation begins. Usually two trophozoites emerges from each cyst.

The trophozoite has four flagella simmetrically placed and a concave ventral surface that contains the atachment organelle, called the ventral disk. After excystation, the trophozoites moves close to the epitelium, generally in the proximal intestine, often deep in the crypts. It multiplies by binary fission, depending of nutrients. The exposion to high concentrations of bile salts can promote encystation. The cysts are eliminated with feces, contaminates water or food and can be ingested for another individual. Those cysts may be ingested by domestic and wild animals, which are considered reservoir of human infection⁹.

EPIDEMIOLOGY

            Giardiasis occurs worldwide. Its prevalence rises in developing contries , especially in children¹⁰. It can reach from 20% to 30% in the developing world, and from 2% to 5% in the industrialized countries⁹. Groups at high risk of giardiasis are: children and infants ( especially those at day care facilities^11-12), homosexuals^13-15, institutionalized individuals, campers¹⁶, travelers¹⁷ and immunocompromised¹⁸ ( common variable immunodeficiency is the most commonly reported ).

PATHOLOGY

            Giardia is found predominantly in the proximal small intestine, but can be found in stomach¹⁹, terminal ileum, colon²⁰ and gallbladder²¹. There are several hypothesis about the pathogenesis of chronic diarrhea in giardiasis. It is accepted that diarrhea occurs by the colnization and multiplication of the trophozoites in the lumen of small intestine. Despite it, the very majority of individual infected is asymptomatic. It can be explained by host factors, parasite load and variable virulence of specific Giardia isolates^{9, 22}.

            The light microscopic features of giardiasis in the proximal small intestine are commonly mild to moderate parcial villous atrophy, with a mild to moderate increase in crypt depth⁸. It can be found increase in inflamatory cells in the lamina propria and in the epithelium, shortening and disruption of microvilli and lymphangiectasia²³. The histological changes observed in giardiasis are, in fact, inespecific²⁴.

            The gastric giardiasis is strongly correllated with chronic atrophic gastritis, often showing intestinal metaplasia and H. pylori infection^{19, 34}. It is believed that a decrease in gastric acidity is essential for the colonization of Giardia into the stomach.

SYMPTOMS

            The incubation period for acute giardiasis is between 1 to 2 weeks. Diarrhea occurs in more than 90% of individuals^{17, 25}. It usually begins with abdominal discomfort, nausea, anorexia and flatulence. Those are followed by explosive and watery diarrhea, with abdominal cramps. Usually, is self-limited within 2 to 4 weeks.

            The cronic giardiasis can present with diarrhea, loose stools, constipation, fatigue, weight loss, eructation, bloatedness, flatulence, nausea, vomiting and epigastric pain²⁶. It can mimic a inflamatory bowel disease²⁷. There is no evidence of a role of giardiasis in nonulcer dyspepsia²⁸.

            The nutrition insufficiency is the major complication of giardiasis. In adults, it produces minor consequences, with symptoms that can completely revert with treatment. In children, however, the nutricional insuficiency can produce growth and development impairment.

DIAGNOSIS

            The search for trophozoites and cysts of Giardia in fresh stool is still the most used method. As the trophozoites can survive only for a brief period in feces, he is only found in examinations of fresh stool from watery diarrheas. For a more sensitive screening, it is necessary five or six stools, because cyst excretion varies in intensity day to day²⁹.

            Trophozoites can be identified by endoscopic brush biopsy of the proximal small intestine³⁰ or by histopathologic samples. Those can also be detected in duodenal juice.

            The enzyme immunoassay for copro-antigen detection reveals to be almost as sensitive as microscopy of stool³¹, and can become less expensive³². However, the complaints of a patient with giardiasis are usually inespecific. The direct examination of stools can provide not only the diagnosis of giardiasis – it can demonstrate the presence or not of other parasites.

            DNA-based detection methods of Giardia in stools has some difficulties due the large amount of other DNA and inibitory substances, as the difficult of lysing cysts. The results shows sensitivity and specificity below the microscopic detection³³.

TREATMENT

            Three major classes of drugs are used for giardiasis: nitroimidazole derivatives, acridine dyes such as mepacrine and nitrofurans such as furazolidone. Metronidazole and tinidazole are the drugs of Choice because the short treatmente period. In treatment failures, a second-line drug may be required⁹.

PREVENTION

            There are several reasons why giardiasis will never erradicate. Giardia is widely distributed through mammals and others, the cysts can survive even in the absence of animals resevoir and the vast majority of humans infected are asymptomatic. All efforts in prevent giardiasis must focus on hygiene education, detection of parasites in drinking water and a search for a vaccine. As the most parasitary infections, the most profound symptom of the disease is felt in the development countries: children without access to clean water and education, who can not grow or develop as they could.

REFERENCES

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