Iranian J Parasitol: Vol. 7, No.1, 2012, pp.92-96 of 1 ×105 trophozoites ml-1 in the caped vials were used. Dose response bioassay Based on our preliminary experiment, from stock chitosan solution, different concentra- tions of chitosan including: 1250, 500, 250 and 125 μg ml-1 (equivalent to 0.125, 0.05, 0.025 and 0.0125% respectively) were pre- pared in stock suspensions of parasites. The control samples without chitosan were pre- pared as the same procedure discussed in chitosan solution preparation. Viability assessment Vials of treated samples were kept at 37 C and observed at 0, 3 and 6h post treatment (PT) using a light microscope to check dead trophozoites by assessing their motility. As- sessment was carried out in triplicate for each concentration as well the control and the percentage mortality was recorded. Sam- ples containing medium without chitosan were also assayed as negative controls. Statistical analysis All viability measurements were carried out in triplicate and the average of mortality rates were transformed to logarithms and submitted to analysis of variance using Gen- eralised Linear Model and Repeated Meas- ure Analysis (two-factor mixed model) using (SPSS 17.0 for Windows, SPSS Inc., Chica- go, IL) for observation of significant varia- tion among them. Values of P < 0.05 were considered significantly different. Results We first investigated the possible effects of low molecular weight chitosan on the mor- tality/survival of T. gallinae trophozoites in vitro. The results for the toxicity of different concentrations (1250, 500, 250 and 125 μg ml-1) of chitosan at 0, 3 and 6h PT are shown in Fig. 2. The final solvent concentration, that is the highest concentration, was achieved by a preliminary experiment. The results of this work demonstrated that there were significant differences (P < 0.05) be- tween the control samples and four different concentrations of chitosan at 0, 3 and 6h PT. As illustrated in Fig. 2, after 6h of exposure, all chitosan concentrations showed high mortality rate ranging from 96.3% to 100% which were significantly (P < 0.05) different form the control group (30%). Moreover, among chitosan used dosages, there was sig- nificant difference between concentrations at 0 and 6h, whereas, at 0 and 3h or 3 and 6h, it was not significant (P < 0.05). The maxi- mum trophozoites mortality rate (100%) was observed at 1250 μg ml-1 concentration after 3h PT. Fig. 1: Structures of chitin and chitosan 94 Available at: http://ijpa.tums.ac.ir