RESUMEN
OBJECTIVE: To assess the effect of malnutrition on the development of giardiasis in Sprague-Dawley rats, using different inoculum sizes of Giardia lamblia cysts. MATERIAL AND METHODS: An experimental study was conducted between 1995 and 1999 at Centro de Investigación, Alimentación y Desarrollo (Center for Research, Food, and Development), in Hermosillo, Sonora, Mexico. The study population consisted of two groups of six to eight experimental units that were fed two different diets and inoculated five different concentrations of Giardia lamblia cysts. Data were collected on excretion of cysts, weight gain, food intake, bowel contents, and macro and microscopic lesions in the intestinal mucosa. Statistical analysis consisted of analysis of variance and residuals. RESULTS: Animals fed with a diet meeting nutritional requirements required an infecting inoculum of 60 cysts, while malnourished rats required only six cysts to develop mucosal lesions. CONCLUSIONS: Weight gain monitored during ten days was not a good indicator of Giardia lamblia infection. Infection depended on cyst inoculum size as well as on the nutritional status of the tested animals.