The physicochemical conditions of high-rate algal ponds were responsible for a more than 97% reduction in the infectivity of Cryptosporidium parvum oocysts in neonatal mice. The use of semipermeable bags of cellulose showed that pH, ammonia, and/or light seems to be a major factor for the inactivation of oocysts in wastewater, supporting the importance of alga-based systems for safer reuse of treated wastewater.Present conventional wastewater treatment is very expensive for application in rural areas and, moreover, does not guarantee the inactivation of Cryptosporidium parvum oocysts from sewage (3,12,16,18). The high-rate algal pond (HRAP) is a low-cost wastewater treatment system designed to achieve two goals: secondary wastewater treatment and algal biomass production. The HRAP is a combination of intensified oxidation ponds and an algal reactor. Algae supply the oxygen demand for bacterial degradation of organic matter, and bacteria excrete mineral compounds that provide the algae with nutrition. HRAPs have proved effective in removing organic matter (13) and in reducing bacterial contamination (8) and the number of nematode eggs (1), but no data are available on their role in removing Cryptosporidium oocysts, a subject of special interest when dealing with rural wastewater. We will focus this study on the effect of the HRAP physicochemical conditions on the viability of Cryptosporidium oocysts as measured with a neonatal mouse infectivity model. HRAP pilot plants. Two identical pilot plants fed with urban wastewater were used for this study (ponds A and B) (Fig. 1). The average physicochemical characteristics of the ponds during the study period are shown in Table 1.C. parvum oocysts. Oocysts were obtained from the feces of an experimentally infected lamb, purified according to the procedures of Arrowood and Sterling (2), and stored at 4°C in a 2.5% (wt/vol) aqueous potassium dichromate solution until use.Treatment of oocysts in HRAP. Regenerated cellulose semipermeable bags with 14,000-Da porosity were used for the experiment. These bags allowed oocysts to be in contact with the small ions present in the water while reducing the effect of other mortality factors such as bacterial and/or fungal contamination or predation. The bags were filled with 50 ml of sterile water and 10 8 oocysts. Two bags were placed in each pond for 3 (pond A) and 10 (pond B) days. Two other bags without oocysts were also placed in the ponds to test the osmotic interchange through the semipermeable membrane, and two bags with oocysts were stored at 4°C in sterile water and used as a control. At the end of the hydraulic retention time (HRT), the oocysts were washed and centrifuged with distilled water. The sediment was resuspended and adjusted to obtain 5 ϫ 10 5 oocysts/25 l.Bioassay for viability. Two hundred fifty-seven suckling mice from 21 individual litters (7 to 16 mice/litter) of NMRI mice were divided in four groups of 3-to 4-day-old mice, day 0 postinfection (p.i.). Mice in groups A (98 mice) and B (79 mice) were inoculated...

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Three ewes were immunized five times over a 2-month period prior to giving birth by intramuscular injection, oral administration and intramammary infusion of antigen and viable or freeze-dried Cryptosporidium parvum oocyst solution emulsified with Freund's complete and incomplete adjuvant. Two animals served as controls and another two as adjuvant controls. Serum was collected at first immunization and thereafter every 2 to 4 weeks. Colostrum and milk were collected as well. All samples were assayed for C. parvum-specific antibodies using an enzyme-linked immunosorbent assay methodology, and Western blotting was used to recognize the C. parvum antigens. Hyperimmunization resulted in a progressive and significant increase in specific anti-C. parvum serum IgG, IgA and IgM titres, with the highest values noted at the point of lambing. Titres decreased slightly in milk, although they were in all cases higher than those in the control animals. Moreover, some 30 bands of C. parvum were recognized.

In this study, a newborn mouse model of Cryptosporidium parvum infection is presented so as to evaluate therapeutic and prophylactic measures for controlling cryptosporidiosis in ruminants. Ninety-six suckling mice from ten litters were used. The mice in group I were infected with C. parvum oocysts, and the mice in group II served as non-infected controls. In both groups, intensity of infection and serum IgG, IgA and IgM responses were measured at 6, 9, 12 and 16 days post-infection (pi). Experimentally induced infection in mice proved to be similar to natural infections in lambs, kids and calves. Thus, the intensity of infection peaked at 9 days pi then decreased slightly, showing its lowest value at 16 days pi. This decline in the number of oocysts coincided with peaks in IgM and IgA. Finally, non-infected mice had no oocysts and did not show any increase in their anti-C. parvum antibody levels.

Hyperimmune anti-Cryptosporidium parvum ovine colostral whey (HOCW) was tested to determine whether it conferred passive immunity to newborn NMRI mice. Three HOCWs (groups IV-VI), 2 nonimmune colostral wheys (groups II and III), and PBS (group I) were administered once (experiment A) and 3 times (experiment B) daily from -1 to 15 days postinfection (PI). Mice in groups I-VI were inoculated with 5 x 10(5) oocysts (day 0 PI), and group VII mice acted as controls. The percentage and intensity of infection were measured at 6, 9, 12, and 16 days PI. In experiment A, HOCW did not reduce significantly the percentage and intensity of infection except for mice in group VI treated with HOCW with the highest titers of anti-C. parvum antibodies. In contrast, no infection was detected in between 18.7 and 62.5% of the mice in groups IV-VI in experiment B. Furthermore, in these groups, the intensity of the infection decreased significantly, ranging from 83.5 to 97.4%. Thus, HOCW did not completely avoid infection, but a high level of protection was observed, being proportional to the titer of specific antibodies and the amount of whey administered orally. Finally, group VII showed no presence of oocysts.