Substance P receptor antagonist reverses intestinal pathophysiological alterations occurring in a novel ex-vivo model of Cryptosporidium parvum infection of intestinal tissues derived from SIV-infected macaques

BACKGROUND: Cryptosporidium infection leads to life-threatening diarrhea in AIDS patients. Pathogenesis of cryptosporidiosis is due to intestinal physiological alterations. We devised an ex-vivo model using ex-vivo Cryptosporidium parvum infection of jejunal tissues derived from SIV-infected macaques and studied the role of substance P (SP) in the pathogenesis of cryptosporidiosis. METHODS: We measured jejunal SP protein levels using ELISA, and electrophysiological alterations using the Ussing chamber technique in an ex vivo model of Cryptosporidium infection. Paraformaldehyde-fixed jejunum from SIV-infected macaques with and without naturally occurring cryptosporidiosis was studied for SP protein expression by immunohistochemistry and fluorescence deconvolution microscopy. RESULTS: Ex-vivo Cryptosporidium-infected tissues and tissues from SIV-infected macaques with naturally occurring cryptosporidiosis demonstrated elevated SP protein levels compared with tissues from SIV-infected animals without ex-vivo C. parvum infection or tissues from SIV-infected animals that have no evidence of cryptosporidiosis. In our ex-vivo model of Cryptosporidium infection, we demonstrated pathophysiological alterations that were blocked by SP-receptor antagonist treatment. CONCLUSIONS: These studies suggest that SP-receptor antagonists could prove useful for treatment of AIDS-related cryptosporidiosis.     

Supplementation with Lactobacillus reuteri or L. acidophilus reduced intestinal shedding of cryptosporidium parvum oocysts in immunodeficient C57BL/6 mice.

The effect of L. acidophilus supplementation to reduce fecal shedding of Cryptosporidium parvum oocysts was compared to L. reuteri using C57BL/6 female mice immunosuppressed by murine leukemia virus (strain LP-BM5) inoculation. After 12 weeks post LP-BM5 inoculation, 15 immunosuppressed mice each were randomly assinged to one of the following treatment groups: historical control (group A), LP-BM5 control (group B), C. parvum (group C), L. reuteri plus C. parvum (group D) or L. acidophilus plus C. parvum (group E). Mice were pre-fed the L. reuteri or L. acidophilus bacteria strains daily for 13 days, challenged with C. parvum oocysts and thereafter fed the specified Lactobacillus regimens daily during the experimental period. Animals supplemented with L. reuteri shed fewer (p<0.05) oocysts on day-7 post C. parvum challenge compared to controls. Mice supplemented with L. acidophilus also shed fewer (p<0.05) oocysts on days 7 and 14 post-challenge compared to controls. Overall, Lactobacillus supplementation reduced C. parvum shedding in the feces but failed to suppress the production of T-helper type 2 cytokines [interleukin-4 (IL-4), IL-8)] which are associated with immunosuppression. Additionally, Lactobacillus supplementation did not restore T-helper type 1 cytokines (interleukin-2 (IL-2) and gamma interferon (IFN-gamma), which are required for recovery from parasitic infections. Altered T-helper types 1 and 2 cytokine production as a consequence of immunodysfunction permitted the development of persistent cryptosporidiosis while mice with intact immune system were refractory to infection with C. parvum. Reduction in shedding of oocysts observed in the Lactobacillus supplemented mice during deminished IL-2 and IFN-gamma production may be mediated by factors released into the intestinal lumen by the Lactobacillus and possibly other host cellular mechanisms. These observations suggest that L. reuteri or L. acidophilus can reduce C. parvum parasite burdens in the intestinal epithelium during cryptosporidiosis and may serve potential benefits as probiotics for host resistance to intestinal parasitic infections. L. acidophilus was more efficacious in reducing fecal shedding than L. reuteri and therefore may also have implication in the therapy of cryptosporidiosis during immunosuppressive states including human AIDS.     

Protection of calves against cryptosporiosis by oral inoculation with gamma-irradiated Cryptosporidium parvum oocysts

The purpose of this study was to determine whether gamma-irradiated Cryptosporidium parvum oocysts could elicit protective immunity against cryptosporidiosis in dairy calves. Cryptosporidium parvum Iowa strain oocysts (1 x 10(6) per inoculation) were exposed to various levels of gamma irradiation (350-500 Gy) and inoculated into 1-day-old dairy calves. The calves were examined daily for clinical signs of cryptosporidiosis, and fecal samples were processed for the presence of C. parvum oocysts. At 21 days of age, the calves were challenged by oral inoculation with 1 x 10(5) C. parvum oocysts and examined daily for oocyst shedding and clinical cryptosporidiosis. Calves that were inoculated with C. parvum oocysts exposed to 350-375 Gy shed C. parvum oocysts in feces. Higher irradiation doses (450 or 500 Gy) prevented oocyst development, but the calves remained susceptible to C. parvum challenge infection. Cryptosporidium parvum oocysts exposed to 400 Gy were incapable of any measurable development but retained the capacity to elicit a protective response against C. parvum challenge. These findings indicate that it may be possible to protect calves against cryptosporidiosis by inoculation with C. parvum oocysts exposed to 400-Gy gamma irradiation.     

A comparison of fecal percent dry matter and number of Cryptosporidium parvum oocysts shed to observational fecal consistency scoring in dairy calves

Evaluation of dairy calf feces is often used in research and for clinical decision making to assess severity of diarrhea. However, this has not been validated for agreement between dry matter content and observed fecal consistency. Therefore, a comparison of observed fecal consistency score to fecal percent dry matter and Cryptosporidium parvum oocyst shedding was performed to assess the accuracy of observational scoring as a measure of diarrhea and its association with number of oocysts shed. Fecal samples from 20 dairy calves experimentally infected with C. parvum oocysts were collected daily post-infection and scored on a scale from 1 to 4, with 1 being normal feces to 4 being severe diarrhea. An aliquot of each sample was analyzed for percent dry matter and Cryptosporidium oocyst counts by using immunofluorescent microscopy. Fecal consistency scores of 1, 2, 3, and 4 had median percent dry matter of 20.9, 16.3, 9.6, and 5.8, respectively. Using percent dry matter assessed by fecal consistency scoring were significantly different from each other (P < 0.001). A higher fecal consistency score also was associated with a greater number of Cryptosporidium oocysts shed (P < 0 .0001). Scores of 1, 2, 3, and 4 had median oocyst counts of 0, 0, 1.3 × 10?, and 2.8 × 10?, respectively. These results suggest that observational scoring is a useful proxy to assess diarrhea in dairy calves.     

Time gap between oocyst shedding and antibody responses in mice infected with Cryptosporidium parvum

We observed the time gap between oocyst shedding and antibody responses in mice (3-week-old C57BL/6J females) infected with Cryptosporidium parvum. Oocyst shedding was verified by modified acid-fast staining. The individually collected mouse sera were assessed for C. parvum IgM and IgG antibodies by enzyme-linked immunosorbent assay from 5 to 25 weeks after infection. The results showed that C. parvum oocysts were shed from day 5 to 51 post-infection (PI). The IgM antibody titers to C. parvum peaked at week 5 PI, whereas the IgG antibody titers achieved maximum levels at week 25 PI. The results revealed that IgM responses to C. parvum infection occurred during the early stage of infection and overlapped with the oocyst shedding period, whereas IgG responses occurred during the late stage and was not correlated with oocyst shedding. Hence, IgM antibody detection may prove helpful for the diagnosis of acute cryptosporidiosis, and IgG antibody detection may prove effective for the detection of past infection and endemicity.     

Infection of immunosuppressed C57BL/6N adult mice with a single oocyst of Cryptosporidium parvum

The present study was designed to determine the minimum number of Cryptosporidium parvum oocysts capable of producing patent infections in immunosuppressed C57BL/6N adult mice. Sixty-four female mice were divided into 6 groups of 8 mice each, except group 1 that contained 24 mice. Mice in groups 1-3 were immunosuppressed with dexamethasone and inoculated with 1, 5, and 10 oocysts per mouse, respectively. The accuracy of the inoculum size was microscopically confirmed. Mice in groups 4-6 served as controls: they received either only oocyst inoculation (group 4), or immunosuppression (group 5), or no treatments (group 6). Fecal oocyst shedding was monitored daily for each mouse using an indirect immunofluorescent assay. Parasite colonization in the terminal ileum of each mouse was evaluated histologically. Four of 24 mice in group 1 developed patent infections, with a prepatent period of approximately 6 days. All mice in groups 2 and 3 developed patent infections, with prepatent periods ranging from 4 to 7 days. Mice in groups 4-6 remained uninfected. Parasite colonization was observed in the terminal ilea of all mice in groups 1-3 that shed fecal oocysts. The present study experimentally demonstrates that a single viable oocyst can induce patent C. parvum infections in immunosuppressed C57BL/6N adult mice and indicates that this mouse model could be used for the parasite genotype or isolate cloning.     

Immunotherapy of cryptosporidiosis in immunodeficient animal models.

Immunotherapy for persistent infection caused by Cryptosporidium parvum was attempted in two immunodeficient animal models. BALB/c Athymic (nude) mice were infected with two oral doses of 2 x 10(7) C. parvum oocysts, and subsequently treated with monoclonal antibody (MAb) 17.41 that neutralizes sporozoites and merozoites. Persistent infection was established in all exposed mice. Daily oral treatment with MAb 17.41 for 10 days significantly reduced (p less than 0.005) the number of C. parvum organisms observed by microscopic study of intestinal tracts of infected mice. Young horses with severe combined immunodeficiency (SCID) also developed persistent infection following oral exposure with 10(8) C. parvum oocysts. In contrast to nude mice, SCID foals exhibited diarrhea associated with oocyst shedding. Two foals were treated orally with MAb 18.44 and immune serum, both of which neutralized C. parvum sporozoites and merozoites. Oocyst shedding patterns did not significantly differ from those in five SCID foals treated with nonimmune reagents. The results obtained indicate that SCID foals are a useful large animal model of clinical disease associated with persistent C. parvum infection, and that nude mice are a convenient animal model for testing therapeutic potential of antibodies in persistent cryptosporidial infection.     

Cryptosporidium infection in an adult mouse model. Independent roles for IFN-gamma and CD4+ T lymphocytes in protective immunity.

Cryptosporidium is a protozoan parasite that can cause chronic life-threatening diarrhea in immunocompromised persons. Host immune responses are poorly understood, an impediment to development of effective therapy. In mice, normal adult BALB/c animals resist infection whereas chronic symptomatic cryptosporidiosis develops in adult nude mice and in neonatally infected BALB/c mice treated with anti-CD4 mAb. To define further the immune defects that allow mice to be infected with Cryptosporidium, adult BALB/c mice were treated with cytolytic anti-CD4 or anti-CD8 or with neutralizing anti-IFN-gamma or anti-IL-2 mAb. Chronic infection, manifested by continuous shedding of sparse but statistically significant numbers of oocysts, occurred with anti-CD4 +/- anti-CD8 mAb treatment although anti-CD8 mAb treatment alone did not allow infection. Treatment with anti-IFN-gamma mAb greatly enhanced oocyst shedding but infection was self-limited. Treatment with a combination of anti-CD4 and anti-IFN-gamma mAb permitted both chronic infection and shedding of large numbers of oocysts. Furthermore mice treated initially with anti-CD4 mAb showed a substantial increase in oocyst shedding when later treated with anti-IFN-gamma mAb; and mice treated initially with both mAbs showed a decline in oocyst shedding when anti-IFN-gamma mAb was stopped. Anti-IFN-gamma mAb treatment of congenitally athymic adult BALB/c mice led to an approximately a 75-fold increase in oocyst shedding. Treatment of adult BALB/c mice with anti-IL-2 mAb did not permit Cryptosporidium infection. These results suggest that redundant immunologic mechanisms limit Cryptosporidium infection such that both CD4+ cells and IFN-gamma are required to prevent initiation of infection whereas either alone can limit the extent (IFN-gamma) or duration (CD4+ T cells) of infection. They also suggest that production of IFN-gamma by a non-T cell contributes to host immunity.     

Lack of detectable shedding of Cryptosporidium parvum oocysts by periparturient dairy cattle

We examined whether periparturient dairy cattle shed Cryptosporidium parvum oocysts within 12 hr of calving on 3 commercial dairy farms endemic for calfhood cryptosporidiosis. Using a diagnostic method that can detect as few as 1 oocyst per gram of feces, we found no evidence of C. parvum oocysts in 86 fecal samples collected within 12 hr of calving from 43 dairy cows.     

Treatment with agmatine inhibits Cryptosporidium parvum infection in infant mice

Cryptosporidium parvum is an intracellular protozoan parasite that causes enteric infection and diarrhea in a wide range of mammalian hosts, including humans and economically important livestock species. There are no effective vaccines or drug treatments available for cryptosporidiosis. Cryptosporidium parvum utilizes a unique metabolic pathway for the synthesis of polyamines, forming agmatine as an intermediary metabolite. We treated infant mice with oral doses of agmatine for 2 days before, the day of, and 5 days following experimental infection with C. parvum. Mice treated with agmatine were significantly less infected with C. parvum than were control mice receiving phosphate-buffered saline. Mice treated with agmatine only on the day of experimental infection with C. parvum were also significantly less infected than were control mice. These data suggest that exogenous agmatine alters the metabolism of C. parvum sufficient to interfere with its ability to colonize the mammalian intestine.     

Effects of dexamethasone and dehydroepiandrosterone in immunosuppressed rats infected with Cryptosporidium parvum.

Treatment of rats immunosuppressed with dexamethasone and inoculated with Cryptosporidium parvum oocysts were treated with dehydroepiandrosterone. A significant reduction in cryptosporidial activity was observed as determined by oocyst shedding and colonization of host tissue by parasites. Dexamethasone treatment alone resulted in decreases in T-, B- and natural killer (NK) cell responses and antibody production that, with the exception of NK-cell activity, were all reversed after administration of dehydroepiandrosterone.     

Role of intraepithelial lymphocytes in mucosal immune responses of mice experimentally infected with Cryptosporidium parvum

In order to investigate the role of intestinal intraepithelial lymphocytes (IELs) in host defense against Cryptosporidium parvum infection, conventionally bred immunocompetent (ImCT) ICR mice and immunosuppressed (ImSP) littermates were infected orally with 10(6) C. parvum oocysts. Then fecal oocyst excretion, the number and location of IELs, and their T lymphocyte subsets were observed on days 4, 7, 10, 13, 16, and 20 postinfection (PI). Uninfected ImCT and ImSP mice were used as controls. The starting point of oocyst excretion was day 4 PI in both ImCT- and ImSP-infected mice. The highest oocyst excretion occurred on day 7 PI in both groups, though the number of oocysts excreted was 3 times greater in ImSP than in ImCT mice. In ImCT mice, IELs greatly increased in number on days 16 and 20 PI (P < 0.05), but the increase was minimal in ImSP mice. IELs changed their location from the basal area to intermediate and apical areas of villous epithelial cells during the early stage of infection. In ImCT-infected mice, IEL phenotypes also changed; whereas CD4+ cells increased temporarily on day 7 PI (P < 0.05), CD8+ cells increased significantly on days 16 and 20 PI (P < 0.05). The results strongly suggest that IELs play a significant role in host defense against C. parvum infection, with helper T cells initiating control of the infection and cytotoxic T cells eliminating the parasites.     

Efficacy of beta-cyclodextrin against experimental cryptosporidiosis in neonatal lambs

The efficacy of beta-cyclodextrin against experimental Cryptosporidium parvum infection was evaluated in neonatal lambs. The animals were treated by oral administration of the drug at 1 g/kg of body weight during 3 consecutive days. Preventive treatment was started within 1 day of birth, and therapeutic treatment was initiated at the onset of diarrhea following confirmation of infection. Disease development and drug efficacy were evaluated by monitoring the presence or absence of diarrhea and oocyst shedding from birth until 30 days of age. Weight gains at 15 and 30 days of age were also recorded. Beta-cyclodextrin was highly effective as a prophylactic treatment; 1 animal did not acquire the infection, diarrhea was prevented in infected animals, and there was a considerable decrease in oocyst shedding. The therapeutic treatment was effective in decreasing the severity of diarrhea and the duration of oocyst shedding. The animals tolerated the drug well, and there was a significant increase in their body weights.     

Development of patent infection in immunosuppressed C57Bl/6 mice with a single Cryptosporidium meleagridis oocyst

The ability of Cryptosporidium meleagridis to produce patent infection was studied in adult C57BL/6 mice that were immunosuppressed with dexamethasone phosphate provided in the drinking water at a dosage of 16 microg/ml. Four days after the onset of immunosuppression, mice were orally challenged with 1, 3, 10, or 1,000 C. meleagridis TU1867 oocysts per mouse. The mice were monitored daily for 18 days postinoculation for oocyst shedding. Five of 10 mice given a single oocyst, 4 of 5 mice given 3 oocysts, and all 9 mice given either 10 or 1,000 oocysts became infected and began shedding oocysts 5-7 days after challenge and continued to shed oocysts until the end of the experiment on day 18 postchallenge. Approximately 10(7) oocysts per mouse per day were excreted, regardless of the challenge dose. Neither the noninfected, immunosuppressed nor the inoculated, nonimmunosuppressed control mice shed oocysts. The excreted oocysts were confirmed to be those of C. meleagridis by polymerase chain reaction-restriction fragment length polymorphism analysis. We show that C. meleagridis, originally classified as an avian pathogen but recently found in humans with cryptosporidiosis, can produce patent infection in mice infected with a single oocyst. Moreover, we demonstrate that the immunosuppressed C57BL/6 adult mouse is an ideal host for the propagation of clonal populations of C. meleagridis isolates for laboratory studies.     

Pomegranate (Punica granatum) peel is effective in a murine model of experimental Cryptosporidium parvum

Cryptosporidiosis, a major health issue for neonatal calves, is caused by the parasite Cryptosporidium parvum, which is highly resistant to drug treatments. To date, many anti-parasitic drugs have been tested, but only a few have been shown to be partially effective in treating cryptosporidiosis. Previous studies have indicated that pomegranate (Punica granatum) possesses anti-plasmodium, anti-cestode, and anti-nematode activities. Therefore, the aim of this study was to evaluate the effect of P. granatum peel on suckling mice infected with experimental C. parvum. At 4days of age, 72 neonatal albino mice were randomly divided into five groups: G1: healthy controls, G2: infected/untreated controls, G3: uninfected/distilled water-treated, G4: uninfected/P. granatum peel-treated, and G5: infected/P. granatum peel-treated. Mice were experimentally-infected by oral administration of 1×10(3)C. parvum oocysts per animal. On day 7 post-inoculation (pi), treated mice received an aqueous suspension of P. granatum peel orally (3g/kg body weight). The presence of diarrhea, oocyst shedding, and weight gain/loss, and the histopathology of ileal sections were examined. Infected mice treated with the P. granatum peel suspension showed improvement in all parameters examined. Additionally, these mice did not exhibit any clinical symptoms and no deaths occurred. Oocyst shedding was very significantly reduced in the P. granatum-treated mice by day 14 pi (P<.05), and was completely eliminated by day 28 pi. The mean weight gain of the P. granatum-treated mice was significantly higher than that of the infected/untreated controls throughout the study (P<.01). Histopathological analysis of ileal sections further supported the clinical and parasitological findings. The histological architecture of villi from the P. granatum-treated mice on day 14 pi showed visible improvement in comparison with the infected/untreated controls, including renewed brush borders, reduced numbers of C. parvum trophozoites, and reduced lymphatic infiltration. On day 28 pi, tissues of the P. granatum-treated mice were very similar to those of healthy control mice. These results suggest that P. granatum peel is a promising anti-coccidial therapeutic treatment that lacks negative side effects.     

NF-kappaB-mediated expression of iNOS promotes epithelial defense against infection by Cryptosporidium parvum in neonatal piglets

Cryptosporidium sp. parasitizes intestinal epithelium, resulting in enterocyte loss, villous atrophy, and malabsorptive diarrhea. We have shown that mucosal expression of inducible nitric oxide (NO) synthase (iNOS) is increased in infected piglets and that inhibition of iNOS in vitro has no short-term effect on barrier function. NO exerts inhibitory effects on a variety of pathogens; nevertheless, the specific sites of iNOS expression, pathways of iNOS induction, and mechanism of NO action in cryptosporidiosis remain unclear. Using an in vivo model of Cryptosporidium parvum infection, we have examined the location, mechanism of induction, specificity, and consequence of iNOS expression in neonatal piglets. In acute C. parvum infection, iNOS expression predominated in the villous epithelium, was NF-kappaB dependent, and was not restricted to infected enterocytes. Ongoing treatment of infected piglets with a selective iNOS inhibitor resulted in significant increases in villous epithelial parasitism and oocyst excretion but was not detrimental to maintenance of mucosal barrier function. Intensified parasitism could not be attributed to attenuated fluid loss or changes in epithelial proliferation or replacement rate, inasmuch as iNOS inhibition did not alter severity of diarrhea, piglet hydration, Cl- secretion, or kinetics of bromodeoxyuridine-labeled enterocytes. These findings suggest that induction of iNOS represents a nonspecific response of the epithelium that mediates enterocyte defense against C. parvum infection. iNOS did not contribute to the pathogenic sequelae of C. parvum infection.     

Experimental activation of cryptosporidiosis in mice by immunosuppression

Cryptosporidium, a coccidian parasite first described by Tyzzer (1907) from a laboratory mouse, has become an important human enteric pathogen causing overwhelming diarrhea especially in immunocompromised patients such as AIDS. This parasite has been reported from over 20 countries and is recognized as a cosmopolitan species. In Korea, however, there has been no report on human as well as animal cryptosporidiosis. This study was performed so as to verify the presence of Cryptosporidium in Korea by activating the parasite from laboratory mice by immunosuppression. Total 65 conventionally-bred ICR mice including a control (5 mice) and 3 experimental groups (20 each) were used for this study. Group I was immunosuppressed with prednisolone injection (1 mg IM, every other day) for 7 weeks. Group II (prednisolone injection and tetracycline administration) and Group III (prednisolone injection and trimethoprim-sulfamethoxazole administration) were prepared to observe the effect of antibacterial agents on the activation of cryptosporidiosis. In fecal examinations of mice Cryptosporidium oocysts (4-6 microns in size) were detected from 1 week after the start of immunosuppression and the mice began to die. In H-E stained tissue sections of the lower jejunum, numerous very small (2-4 microns), dense, ovoid or spherical, slightly basophilic bodies were seen attached on the free border of mucosal epithelial cells. In scanning and transmission electron microscopic observations, these organisms were identified as various developmental stages of Cryptosporidium. The species is considered to be C. parvum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Indinavir reduces Cryptosporidium parvum infection in both in vitro and in vivo models

The use of highly active antiretroviral therapy in persons with acquired immunodeficiency syndrome has reduced the prevalence of infection with Cryptosporidium parvum and the length and severity of its clinical course. This effect has in most cases been attributed to the recovery of the host immunity; however, some works suggest that human immunodeficiency virus protease inhibitors, indinavir in particular, which is one of the human immunodeficiency virus protease inhibitors used in highly active antiretroviral therapy, may be capable of controlling Microsporidia and Cryptosporidium infections, which are refractory to other treatments. The objective of the present study was to investigate the effect of human immunodeficiency virus protease inhibitors on C. parvum infections. Since preliminary experiments using ritonavir, saquinavir, and indinavir showed a drastic reduction of C. parvum infection both in vivo (neonatal Balb/c mice) and in vitro (human ileocecal adenocarcinoma tumour cell line) models, indinavir alone was tested in successive experiments. In vitro, the treatment of the sporulated oocysts with different concentrations of indinavir reduced the percentage of human ileocecal adenocarcinoma tumour cell line infected cells in a dose-dependent manner. For established infection, the treatment with 50 microM of indinavir decreased the percentage of infected cells in a time-dependent manner. In vivo, mice treated with indinavir at the same time they were infected with the oocysts showed a 93% reduction in the number of oocysts present in the entire intestinal contents and a 91% reduction in the number of intracellular parasites in the ileum. For established infection, indinavir treatment reduced the number of oocysts in the entire intestinal content by about 50% and the number of intracellular parasites in the ileum by about 70%. These data show that indinavir directly interferes with the cycle of C. parvum, resulting in a marked reduction in oocyst shedding and in the number of intracellular parasites. Protease inhibitors could be considered as good candidates for the treatment of cyptosporidiosis in immunosuppressed persons.     

Anti-cryptosporidial drug activity screened with an immunosuppressed rat model

Cryptosporidium parvum, a coccidian parasite can cause mild or severe self-limiting diarrhea in immunocompetent humans, but chronic and life-threatening in immunocompromised individuals. An immunosuppressed rat model with persistent cryptosporidiosis was used to investigate the anti-cryptosporidial activity of drugs. Using curative procedures, no activity was found with 6 antibiotics assayed, including spiramycin (31-100%). Mepacrine at a dose of 100 mg/kg had mild activity (19%), while lasalocid (10 mg/kg) and sulfadimethoxine (60 mg/kg) exhibited a 0.1% and 13%, activity respectively. This experimental immuno-suppressed rat model appears suitable for screening candidate drugs either for preventive or curative treatment of cryptosporidiosis.