Sts capable of inducing these kind of lesions was not known until now. In fact, as it was previously observed, after 79983-71-4 infection with higher inocula (105?07) of the C. parvum Iowa strain [7,10], in the present study neoplastic lesions (LGIEN and HGIEN) were detected as early as day 45 P.I. both in the stomach and in the ileo-caecal region of Dex treated SCID mice challenged 
with intended doses of 100, 10 or even one oocyst, and these lesions could also evolve in an invasive adenocarcinoma progressing through 1676428 all layers of the stomach and ileo-caecal region. Consistently, we observed that 
in mice inoculated with low inocula the parasite excretion increased fast, reaching a mean of SR-3029 site oocyst shedding of more than 10,000 oocyst/g of feces at 45 days P.I.. It seems that the few oocysts inoculated to mice had an important multiplication, and that an increase in oocyst inoculated doses raise the level of infectivity but not necessarily the shedding of parasites and the pathological outcome. In experimental infections of immunocompetent animals, different observations have been reported. In cattle, after inoculation with as little as one red blood cell infected with Babesia bovis, another apicomplexan parasite, there was an increase in the prepatent period (as we also observed) but the high morbidity and mortality of animals was not altered in comparison to those infected 25837696 with higher inocula [18]. These findings are in contrast to those for infections with the haemoparasite Theileria parva, where infection of cattle with a low inoculum resulted in decreased severity of disease and lower mortality [19]. Interestingly, in studies of Eimeria infection of chickens and rats, it was especially noticeable that with the greatest infecting dose, the number of oocysts produced per oocyst inoculated was smaller [20]. On the other hand, in our previous study, the oocyst shedding after inoculation with 105 oocysts was much higher [8].Nevertheless, natural lot to lot variability of the Iowa isolate was demonstrated before by a review of 22 dose response studies in a mouse model over a period of 3 years [21]. Our findings presented here confirm a great parasite amplification effect in mouse tissues after a low challenge of oocysts, and provide supplementary evidence of the role of C. parvum in the induction of digestive cancer. The DNA detection of parasites through qPCR corroborates that C. parvum is present in target organs and may lead to neoplasia. In some cases the amount of Cryptosporidium DNA present in tissues was not quantifiable in all three qPCR runs but it is well known that the isolation of genetic material from paraffin-embedded tissue sections can yield low amounts of DNA, which could be fragmented, degraded or folded with proteins [22]. It is also possible to have differences in the amounts of Cryptosporidium DNA extracted from one section of the organ to another one due to a variable distribution of parasites all along the gastro-intestinal tract. Additionally, inhibitions of the PCR reaction may occur due to the presence of large quantities of host DNA. The ability of C. parvum to infect mice with one oocyst and to develop digestive adenocarcinoma suggests that other mammalian species including humans could be as susceptible to this process as Dex-treated SCID mice are, especially when they are severely immunocompromised. In conclusion, the high infectious power of Cryptosporidium oocysts associated to its cancerogenic role was confirmed. For th.Sts capable of inducing these kind of lesions was not known until now. In fact, as it was previously observed, after infection with higher inocula (105?07) of the C. parvum Iowa strain [7,10], in the present study neoplastic lesions (LGIEN and HGIEN) were detected as early as day 45 P.I. both in the stomach and in the ileo-caecal region of Dex treated SCID mice challenged with intended doses of 100, 10 or even one oocyst, and these lesions could also evolve in an invasive adenocarcinoma progressing through 1676428 all layers of the stomach and ileo-caecal region. Consistently, we observed that in mice inoculated with low inocula the parasite excretion increased fast, reaching a mean of oocyst shedding of more than 10,000 oocyst/g of feces at 45 days P.I.. It seems that the few oocysts inoculated to mice had an important multiplication, and that an increase in oocyst inoculated doses raise the level of infectivity but not necessarily the shedding of parasites and the pathological outcome. In experimental infections of immunocompetent animals, different observations have been reported. In cattle, after inoculation with as little as one red blood cell infected with Babesia bovis, another apicomplexan parasite, there was an increase in the prepatent period (as we also observed) but the high morbidity and mortality of animals was not altered in comparison to those infected 25837696 with higher inocula [18]. These findings are in contrast to those for infections with the haemoparasite Theileria parva, where infection of cattle with a low inoculum resulted in decreased severity of disease and lower mortality [19]. Interestingly, in studies of Eimeria infection of chickens and rats, it was especially noticeable that with the greatest infecting dose, the number of oocysts produced per oocyst inoculated was smaller [20]. On the other hand, in our previous study, the oocyst shedding after inoculation with 105 oocysts was much higher [8].Nevertheless, natural lot to lot variability of the Iowa isolate was demonstrated before by a review of 22 dose response studies in a mouse model over a period of 3 years [21]. Our findings presented here confirm a great parasite amplification effect in mouse tissues after a low challenge of oocysts, and provide supplementary evidence of the role of C. parvum in the induction of digestive cancer. The DNA detection of parasites through qPCR corroborates that C. parvum is present in target organs and may lead to neoplasia. In some cases the amount of Cryptosporidium DNA present in tissues was not quantifiable in all three qPCR runs but it is well known that the isolation of genetic material from paraffin-embedded tissue sections can yield low amounts of DNA, which could be fragmented, degraded or folded with proteins [22]. It is also possible to have differences in the amounts of Cryptosporidium DNA extracted from one section of the organ to another one due to a variable distribution of parasites all along the gastro-intestinal tract. Additionally, inhibitions of the PCR reaction may occur due to the presence of large quantities of host DNA. The ability of C. parvum to infect mice with one oocyst and to develop digestive adenocarcinoma suggests that other mammalian species including humans could be as susceptible to this process as Dex-treated SCID mice are, especially when they are severely immunocompromised. In conclusion, the high infectious power of Cryptosporidium oocysts associated to its cancerogenic role was confirmed. For th.
