nona zabolinejad department of pathology, mashhad university of medical sciences, mashhad, ir iran fariba berenji department of parasitology & mycology, medical faculty, mashhad university of medical sciences, ir iran; department of parasitology, mashhad university of medical sciences, mashhad, ir iran. tel: +98-5118022235, fax: +98-5118547255 elham bayati eshkaftaki department of parasitology, shahrekord university of medical sciences, ir iran zahra badeii department of pediatrics, mashhad university of medical sciences, ir iran abdollah banihashem department of pediatrics, mashhad university of medical sciences, ir iran monavar afzalaqaei department of biostatistic and epidemiology, mashhad university of medical sciences, ir iran