ABSTRACT
Giardiasis may be asymptomatic or symptomatic with possible extra-intestinal complications such as maculopapular rashes, polyarthritis and urticaria. Diagnosis by stool examination may give false negative results. Accurate exclusion of giardiasis is important to differentiate it from other causes of these manifestations. To assess the employment of saliva for diagnosing G. lamblia infections. The study attempted to determine the presence of G. lamblia antigen in human saliva by immunodiffusion technique and the associated specific secretory IgA [sIgA] immune response by immunoblot technique. Samples of saliva were collected from 80 subjects; 40 Giardia-infected individuals [symptomatic and asymptomatic], 20 subjects infected with other intestinal parasites and 20 healthy individuals as control groups of similar age and sex. Giardia cysts were collected from stools of heavily infected individuals, excysted and the harvested forms were cultivated on TYI-S-33 medium to prepare trophozoite antigen. The latter was used to produce hyperimmune serum in rabbits that was employed to detect the presence of specific antigen [s] in saliva by double gel immunodiffusion technique. Cysts were also used for antigen preparation which was fractionated by SDS-PAGE and tested to detect sIgA by immunoblotting of saliva samples. G. lamblia antigen was not detected in the saliva of any of the individuals enrolled in the study. Secretory IgA was detected in 75% of all infected individuals with 75% sensitivity and 90% specificity and in 90% of symptomatic and 60% of asymptomatic infected individuals. Molecular weight [MW] bands of 170 and 133 kDa were recognized by specific salivary sIgA by immunoblot analysis. Sensitivity and specificity of the 170 kDa band recognition were 75% and 90%, respectively with 88.2% and 78.2% positive [PPV] and negative [NPV] predictive values, respectively. The 133 kDa band gave 42.5% sensitivity, 100% specificity with 100% PPV and 62.3% NPV. Absence of specific antigen in the saliva refutes the assumption that G. lamblia antigens may reach the blood and questions the possibility of tissue invasion. The 170 and 133 kDa of Giardia cysts antigens form together useful molecules for diagnosis of giardiasis by IgA immunoblotting