Experimental cryptosporidiosis in laboratory mice

Strategies for the control of Cryptosporidium parvum infection in calves

Cryptosporidium parvum is a protozoan parasite that is now recognized as one of the leading causes of diarrhea in young calves. To date, there are no drugs or preventive measures available for the control of this disease. We have developed an oral vaccine that, when given to calves at birth, protects against experimental challenge with C. parvum. However, when field tested on a large dairy operation with heavy endemic C. parvum infection, the vaccine failed to provide protection. The difference in these results is most likely due to uncontrolled early (probably within hours of birth) exposure to C. parvum on the farm versus controlled exposure at 1 wk of age in the experimental trials. The successful control of C. parvum in the field may require vaccines that generate a rapid (within the first few days of life) cell-mediated immune response in the calf. Successful use of such a vaccine will also require improved hygiene and management practices to minimize the exposure of calves to C. parvum in the initial days of life, thus allowing time for protective immune responses to be generated. Careful attention to hygiene in the management of sick calves is also critical to minimize the spread of the parasite to other animals.

Profiles of healing and nonhealing Cryptosporidium parvum infection in C57BL/6 mice with functional B and T lymphocytes: the extent of gamma interferon modulation determines the outcome of infection

This study describes healing and nonhealing models of Cryptosporidium parvum infection with adult mice that have functional T and B lymphocytes. In our nonhealing model, mice on a C57BL/6 background which have a targeted disruption in the gamma interferon (IFN-gamma) gene (GKO mice) are utilized. C. parvum-infected GKO mice shed extremely high levels of oocysts and displayed overwhelming infection of the entire small intestine. The majority of these mice succumbed within 2 to 3 weeks due to severe acute infection and profound mucosal destruction. In our healing murine model, C57BL/6J mice treated with a single injection of the neutralizing anti-IFN-gamma monoclonal antibody XMG 1.2 prior to infection were used. These mice developed two peaks of oocyst shedding but were ultimately free of parasites on day 30 of infection. Again, the small intestine was the primary site of infection. Mesenteric lymph node (MLN) cells isolated from C. parvum-infected nonhealing GKO mice proliferated and secreted interleukin 2 (IL-2) but not IFN-gamma or IL-4 in response to ex vivo restimulation with intact C. parvum sporozoites or a C. parvum sporozoite antigen preparation. In contrast, parasite-specific MLN cells isolated from healing C57BL/6J mice secreted IL-2 and IFN-gamma but not IL-4. These results suggest that IFN-gamma, either directly or indirectly, is important for resistance to and resolution of cryptosporidiosis. Moreover, these models now allow the analysis of parasite-specific cell-mediated and humoral mucosal immune responses to determine what constitutes protective immunity to C. parvum.

Characterization of secretory IgA responses in mice infected with Cryptosporidium parvum

Mice inoculated at 5, 21 and 28 days of age with 10(6) or 10(7) Cryptosporidium parvum oocysts became infected but did not exhibit any clinical signs of disease. Specific IgA antibodies were detected in faecal extracts from all infected mice by an indirect immunofluorescent assay. These antibodies first appeared between 11 and 37 days post-infection (dpi) and persisted until the end of the experiment at 55 dpl. They appeared earlier in older mice than in newborn mice. Reduction and resolution of oocyst shedding was not directly related, however, to IgA antibody levels in infected mice. Reactive C. parvum antigens were identified by immunoblotting techniques using faecal and serum samples from infected mice. IgA copro-antibodies reacted specifically with two antigens of 26 and 33 kDa, which were also identified by IgG antibodies in mouse serum. The role of these antibodies in the resolution of infections and the subsequent protection against challenge is unknown.

Specific interferon-gamma, IgA and IgM responses after experimental infection of neonatal calves with Cryptosporidium parvum

The in vitro interferon-gamma production by peripheral blood mononuclear cells and the local antibody build up was monitored in neonatal calves experimentally infected with Cryptosporidium parvum and in negative controls of the same age. From day 6 p.i. on, an infection-induced interferon-gamma response was observed in lymphocyte cultures after stimulation with Cryptosporidium oocyst antigen preparation. Only the Cryptosporidium-infected calves developed local IgA and IgM responses from day 6 p.i. on, with peak values at day 10 p.i. These antibodies disappeared quickly, perhaps due to the strict hygienic measures and consequently the absence of a continuous antigenic stimulation.

Viability of Cryptosporidium parvum during ensilage of perennial ryegrass

The survival of Cryptosporidium parvum during ensilage of perennial ryegrass was examined in laboratory silos with herbage prepared in one of three different ways; either untreated, inoculated with a strain of Lactobacillus plantarum or by direct acidification with formic acid. The pH values of all silages initially fell below 4.5, but only formic acid-treated silage remained stable at less than pH 4 after 106 d, with the pH of the untreated and inoculant-treated silages rising to above 6. The formic acid-treated silage had a high lactic acid concentration (109 g kg-1 dry matter (DM)) and low concentrations of propionic and butyric acids after 106 d. However, the untreated and inoculant-treated silages showed an inverse relationship, with low lactic acid concentrations and high concentrations of acetic, propionic and butyric acids. These silages also contained ammonia-N concentrations in excess of 9 g kg-1 DM. In terms of the viability of Cryptosporidium parvum oocysts very few differences were seen after 14 d of ensilage with ca 50% remaining viable, irrespective of treatment and total numbers had declined from the initial level of 5.9 x 10(4) to 1 x 10(4) g(-1) fresh matter. Total oocyst numbers remained approximately the same until the end of the ensiling period, with the percentage of viable oocysts declining to 46, 41 and 32% respectively for formic acid, inoculant and untreated silages. The results are discussed in terms of changes occurring during the silage fermentation, in particular the products which may influence the survival of Cryptosporidium and implications for agricultural practice and the health of silage fed livestock.

Survival of Cryptosporidium muris (strain MCR) oocysts under cryopreservation

We have successfully maintained Cryptosporidium muris by cryopreservation. Oocysts were suspended in distilled water, stored at -20 degrees C for 24 hrs, and then cryopreserved at -70 degrees C. Cryopreserved specimens were slowly thawed at 5 degrees C. Oocysts, which had been cryopreserved for 15 months without cryoprotective agents, retained their infectivity by the mouse titration method. Oocysts stored at 5 degrees C in 2.5% potassium dichromate failed to retain their infectivity beyond 6.5 months.

Effects of low temperatures on viability of Cryptosporidium parvum oocysts

Microcentrifuge tubes containing 8 x 10(6) purified oocysts of Cryptosporidium parvum suspended in 400 microliters of deionized water were stored at 5 degrees C for 168 h or frozen at -10, -15, -20, and -70 degrees C for 1 h to 168 h and then thawed at room temperature (21 degrees C). Fifty microliters containing 10(6) oocysts was administered to each of five to seven neonatal BALB/c mice by gastric intubation. Segments of ileum, cecum, and colon were taken for histology from each mouse 72 or 96 h later. Freeze-thawed oocysts were considered viable and infectious only when developmental-stage C. parvum organisms were found microscopically in the tissue sections. Developmental-stage parasites were not found in tissues from any mice that received oocysts frozen at -70 degrees C for 1, 8, or 24 h. All mice that received oocysts frozen at -20 degrees C for 1, 3, and 5 h had developmental-stage C. parvum; one of 6 mice that received oocysts frozen at -20 degrees C for 8 h had a few developmental-stage parasites; mice that received oocysts frozen at -20 degrees C for 24 and 168 h had no parasites. All mice that received oocysts frozen at -15 degrees C for 8 and 24 h had developmental-stage parasites; mice that received oocysts frozen at -15 degrees C for 168 h had no parasites. All mice that received oocysts frozen at -10 degrees C for 8, 24, and 168 h and those that received oocysts stored at 5 degrees C for 168 h had developmental-stage parasites. These findings demonstrate for the first time that oocysts of C. parvum in water can retain viability and infectivity after freezing and that oocysts survive longer at higher freezing temperatures.

Helicobacter felis as a cofactor alone or together with stress in cryptosporidial activation in mice

Cryptosporidiosis is caused by a protozoan parasite, mainly found in animals, which usually results in transient, mild gastroenteritis in humans but can cause severe and prolonged disease in immunocompromised individuals. Immunocompetent mice, naturally infected with Cryptosporidium muris, were used to investigate the effects of inoculation with Helicobacter felis and of stress on the activity of the C. muris infection, as indicated by histopathological examination of their stomachs. The results indicate that both H. felis inoculation and/or stress activate C. muris and cause gastric inflammation. The extent of the activation of C. muris depends on the duration of the stress.

Rapid antigen detection assay for identification of Chlamydia trachomatis infection

A rapid antigen detection test was compared with direct fluorescent-antibody staining and with tissue culture isolation for the detection of Chlamydia trachomatis infections in 507 women. The sensitivities observed were 75, 76, and 84%, respectively, with specificities of > 99%.

Murine infection model for maintenance and amplification of Cryptosporidium parvum oocysts

Propagation of Cryptosporidium parvum is problematic because in vitro development of the parasite is poor and animals are only briefly susceptible as neonates. At present oocysts of the parasite are usually procured by passage in neonatal sheep or cattle. In the present study, large numbers of oocysts of C. parvum could be isolated following infection of dexamethasone-treated adult C57BL/6 mice. The amount of immunosuppressive drug and the regimen of administration were critical for successful maintenance of the parasite, however. Routinely, 10 mice (age, 8 to 12 weeks) were injected four times on alternate days with 1.0 mg of dexamethasone, and the last injection was given on the same day as oral inoculation with 10(6) oocysts. By using a simplified procedure for oocyst purification from mouse feces, approximately 10(9) oocysts were obtained. This model is inexpensive and comparatively safe to handle, and the numbers of animals inoculated can be varied to obtain the required number of oocysts. Thus, this murine infection model would be a suitable alternative to the use of neonatal calves or sheep for efficient oocyst propagation.

Evaluation of maduramicin and alborixin in a SCID mouse model of chronic cryptosporidiosis

Two polyether ionophores, maduramicin and alborixin, were evaluated for anticryptosporidial activity in a severe combined immune deficient (SCID) mouse model of cryptosporidiosis. Groups of SCID mice were inoculated with 10(6) oocysts of bovine origin by oral gavage. Maduramicin or alborixin was administered beginning 4 weeks postinfection at 3 mg/kg of body weight per day. Maduramicin treatment resulted in a 96% reduction in fecal parasite load over the 3-week treatment period (P < 0.003). This reduction correlated with decreases in tissue parasite loads observed in histological sections of the small intestine (P < 0.000002) and the colon (P < 0.000006). A significant decrease in oocyst shedding was also observed after a 3-week treatment with alborixin (71% reduction, P < 0.01). Maduramicin was also evaluated in a relapsing model of cryptosporidiosis in which the infection was observed to recur after treatments were discontinued. Some toxicity, as demonstrated by weight loss, was observed with both maduramicin and alborixin. Both drugs exhibited significant anticryptosporidial activities with concomitant moderate toxicity. These polyether ionophores should be valuable as positive controls in compound evaluation studies and as lead compounds for chemical optimization (modification).

Age-related resistance in ovine cryptosporidiosis: patterns of infection and humoral immune response

The phenomenon of age-related resistance to infection with Cryptosporidium parvum has been well characterized in rodent models, and its existence has been demonstrated in calves. To determine whether this is a genuine age effect in a fully susceptible animal model or the result of infection with related pathogens inducing a nonspecific immunity, and to examine several parameters associated with severity of clinical diseases, lambs maintained in a parasite-free environment were infected with C. parvum oocysts at increasing ages. A marked decrease in the severity of clinical symptoms was observed as the age at infection increased, though the kinetics of both fecal and serum antibody responses were similar in all age groups, suggesting that mechanisms other than humoral response may play an important role in the development of age-related resistance. This study demonstrates the first experimental evidence for age-related resistance to ovine cryptosporidiosis and examines parameters which may influence the acquisition of resistance to infection.

Cryptosporidium muris in adult mice: adoptive transfer of immunity and protective roles of CD4 versus CD8 cells

The aim of this study was to investigate the role of the CD4 and CD8 T cells in immunity to cryptosporidia by using Cryptosporidium muris and a mouse model of infection. Two approaches were used, each involving the use of rat anti-T-cell surface marker monoclonal antibodies (MAbs). In the first, the adoptive transfer of immunity was studied by using the CB.17 SCID mouse (which lacks T and B cells) as the host; in the second, the effect on susceptibility of BALB/c mice to infection was examined following depletion of T cells or subsets of T cells. In adoptive immunity experiments, the conditions which differentiated between resistance associated with reconstitution of SCID mice with naive BALB/c lymphocytes and the transfer of immunity with primed lymphocytes from infected animals were determined. Primed spleen or mesenteric lymph node cells conferred better protection to recipients than naive cells when obtained from donors which had developed resistance to infection. Adoptive immunity was abrogated when Thy.1 cells or CD4 cells were depleted from primed cells, while depletion of CD8 cells could reduce the level of protection. In the study of C. muris in BALB/c mice, treatment with either anti-Thy.1 plus anti-Lyt.1 or anti-CD4 MAbs increased susceptibility to a primary infection as determined by the size and duration of oocyst production, but an anti-CD8 MAb produced an increase only in oocyst shedding. Thus, both CD4 and, to a lesser extent, CD8 cells appeared to be involved in resistance to primary and secondary C. muris infection.

Mechanisms of innate and acquired resistance to Cryptosporidium parvum infection in SCID mice

SCID mice, which lack T and B cells, were used as hosts to investigate the nature of both T cell-independent and T-cell-dependent immune responses to infection with Cryptosporidium parvum. We found previously that SCID mice developed chronic infections in which the level of oocyst excretion was low up to about eight weeks post-infection but then increased significantly to cause morbidity and death after 13 weeks. In the present study, weekly administration of an anti-IFN-gamma monoclonal antibody (MoAb) resulted in a shortened prepatent time, significant increase in oocyst excretion and early onset of disease and death. These results suggested an immunologically mediated resistance to C. parvum in the SCID host which required the production of IFN-gamma. Attempts to demonstrate a role for TNF in nonspecific immunity were unsuccessful as injection of mice at weekly intervals with an anti-TNF MoAb failed to alter the course of infection. In contrast to the chronic infection observed in the mice above, SCID mice reconstituted with spleen cells from naive BALB/c mice were able to recover. Depletion of CD4+ cells from the donor population abrogated this protective effect. Mice receiving spleen cells depleted of CD8+ cells were able to recover but the patent infection was prolonged compared with those obtained in mice receiving unfractionated cells. These results demonstrate that CD4+ cells are necessary for the development of immunity to C. parvum infection in reconstituted SCID mice, but, in addition, that CD8+ cells also make a significant contribution to this immunity.

Susceptibility of major histocompatibility complex (MHC) class I- and MHC class II-deficient mice to Cryptosporidium parvum infection

Major histocompatibility complex (MHC) class I-deficient and MHC class II-deficient mice lack functional CD8 T cells and CD4 T cells, respectively. These mice were evaluated for infection following oral administration of 10(7) Cryptosporidium parvum oocysts. MHC class II-deficient (but not MHC class I-deficient) mice dosed with C. parvum oocysts at 3 to 5 days of age remained infected 8 weeks postexposure. MHC class II-deficient mice exposed to C. parvum oocysts at 5 to 6 weeks of age were significantly more susceptible to infection than control mice (P < 0.0001).

Cryptosporidiosis: multiattribute evaluation of six diagnostic methods

Six diagnostic methods (Giemsa staining, Ziehl-Neelsen staining, auramine-rhodamine staining, Sheather's sugar flotation, an indirect immunofluorescence procedure, and a modified concentration-sugar flotation method) for the detection of Cryptosporidium spp. in stool specimens were compared on the following attributes: diagnostic yield, cost to perform each test, ease of handling, and ability to process large numbers of specimens for screening purposes by batching. A rank ordering from least desirable to most desirable was then established for each method by using the study attributes. The process of decision analysis with respect to the laboratory diagnosis of cryptosporidiosis is discussed through the application of multiattribute utility theory to the rank ordering of the study criteria. Within a specific health care setting, a diagnostic facility will be able to calculate its own utility scores for our study attributes. Multiattribute evaluation and analysis are potentially powerful tools in the allocation of resources in the laboratory.

Survival of Cryptosporidium parvum oocysts under various environmental pressures

The survival of various isolates of Cryptosporidium parvum oocysts under a range of environmental pressures including freezing, desiccation, and water treatment processes and in physical environments commonly associated with oocysts such as feces and various water types was monitored. Oocyst viability was assessed by in vitro excystation and by a viability assay based on the exclusion or inclusion of two fluorogenic vital dyes. Although desiccation was found to be lethal, a small proportion of oocysts were able to withstand exposure to temperatures as low as -22 degrees C. The water treatment processes investigated did not affect the survival of oocysts when pH was corrected. However, contact with lime, ferric sulfate, or alum had a significant impact on oocyst survival if the pH was not corrected. Oocysts demonstrated longevity in all water types investigated, including seawater, and when in contact with feces were considered to develop an enhanced impermeability to small molecules which might increase the robustness of the oocysts when exposed to environmental pressures.

Resistance of severe combined immunodeficient mice to infection with Cryptosporidium parvum: the importance of intestinal microflora

Cryptosporidium parvum is a protozoan parasite which colonizes intestinal epithelium, causing transient diarrheal illness in immunocompetent hosts and severe chronic disease in immunocompromised hosts. We examined the resistance of severe combined immunodeficient mice, either bearing intestinal flora or germfree, to intestinal infection with C. parvum. Infection was not readily detected in flora-bearing adult severe combined immunodeficient mice until 5 to 7 weeks following oral challenge with C. parvum. In contrast, germfree adult severe combined immunodeficient mice were heavily infected 3 weeks following challenge. These data support the hypothesis that resistance of adult mice to C. parvum infection does not require a specific immune response but can be mediated by nonspecific mechanisms associated with the presence of intestinal flora.

Experimental Cryptosporidium parvum infections in immunosuppressed adult mice

Five strains of adult mice were immunosuppressed with the synthetic glucocorticosteroid dexamethasone (DEX), administered either orally or intraperitoneally. The strains of mice used were C57BL/6N, DBA/2N, CBA, C3H/HeN, and BALB/cAnN. All mice were evaluated for susceptibility to Cryptosporidium parvum after intragastric inoculation with 10(6) oocysts per mouse. The DBA/2N, CBA, C3H/HeN, and BALB/cAnN mice given 0.25 micrograms of DEX per g per day orally (the dose and route previously used to infect rats with C. parvum) failed to develop chronic infections. However, the C57BL/6N mice sustained light infections during the entire 28-day experiment. The five strains of mice were also administered DEX intraperitoneally at concentrations ranging from 62.5 to 500 micrograms/day. Only the C57BL/6N mice given DEX at 125 micrograms/day developed chronic infections which persisted over 10 weeks, suggesting that the genetic background of the mouse plays a role in determining susceptibility to cryptosporidosis following immunosuppression with DEX. We believe that the C57BL/6N mouse model will prove to be superior to other animal models for evaluating potential anticryptosporidial agents, as well as for elucidating the immunological defects that allow C. parvum to establish chronic infections, because of cost effectiveness and ease in maintenance, breeding, and handling. We also evaluated the C3H/HeJ/beige mouse (lacks natural killer cell activity) and the C57BL/6N mouse maintained on a low-protein diet to induce immunosuppression. Neither of these mice exhibited heavy cryptosporidial infections.

Cryptosporidium parvum: investigation of sporozoite excystation in vivo and the association of merozoites with intestinal mucus

Enteric cryptosporidiosis was studied in the small intestine of five-day-old sucking mice after infection with 10(6) Cryptosporidium parvum oocysts. It was shown that excystation and the majority of subsequent endogenous stages occurred predominantly in the ileum. During the first three days of infection the number of merozoites collected in ileal washings increased over 100-fold to approximately 10(6) merozoites per mouse on the third day. In contrast to control mice, wash fluid from infected mice contained numerous strands of dislodged mucus. Estimates of mucus in the ileal washings of infected mice were similar to those made in controls until day 4 after infection when they increased and remained high throughout the remainder of the experiment. This study describes a method whereby ileal mucus washings from C parvum infected infant mice could be used as a rich source of merozoites.

Persistent cryptosporidiosis in horses with severe combined immunodeficiency

Cryptosporidial infections were established in five young foals with severe combined immunodeficiency following oral administration of 10(8) Cryptosporidium parvum oocysts. All foals shed oocysts (average of 8 x 10(6) to 2 x 10(8)/g of feces) until death. Inflammation and C. parvum organisms were observed in the common bile duct, duodenum, jejunum, and ileum. Since foals with severe combined immunodeficiency lack functional T and B lymphocytes and are incapable of antigen-specific immune responses, they are well suited for evaluating the pathogenesis and treatment of persistent cryptosporidiosis.

Cryptosporidiosis

Before 1982, only eight case reports of human cryptosporidiosis and fewer than 30 papers on Cryptosporidium spp. appeared in the biomedical literature. At that time, cryptosporidiosis was thought to be an infrequent infection in animals and rarely an opportunistic infection in humans. The concept of Cryptosporidium spp. as pathogens has changed dramatically within the past 8 years because of improved diagnostic techniques, increased awareness within the biomedical community, and the development of basic research programs in numerous laboratories. Presently, greater than 1,000 publications including over 400 case reports in the biomedical literature address Cryptosporidium spp. and cryptosporidiosis. Cryptosporidium parvum is now thought to be one of the three most common enteropathogens causing diarrheal illness in humans worldwide, especially in developing countries. It is likely that cryptosporidiosis was previously included in the 25 to 35% of diarrheal illness with unknown etiology. Because of the severity and length of diarrheal illness and because no effective therapy has been identified, cryptosporidiosis is one of the most ominous infections associated with AIDS. The role of C. parvum as an enteropathogen is well established; documentation of its role as a cause of hepatobiliary and respiratory diseases is now appearing in the literature. Our present understanding of the natural history, epidemiology, biology, and immunology of Cryptosporidium spp. as well as the clinical features, pathogenicity, and treatment of cryptosporidiosis are reviewed here.

Inhibition of Cryptosporidium parvum in neonatal Hsd:(ICR)BR Swiss miceby polyether ionophores and aromatic amidines

Cryptosporidicidal effects of two polyether ionophores (maduramicin and alborixin), a fluorinated 4-quinolone (enrofloxacin), and three analogs of pentamidine were evaluated in a suckling mouse bioassay. Treatment with all compounds except enrofloxacin and one of the pentamidine analogs [1,3-di(4-imidazolinophenoxy)propane] resulted in significant (P less than 0.05) reductions in oocyst excretion.

Biological nature of Cryptosporidium sp. isolated from a cat

A small type of Cryptosporidium oocysts was isolated from a naturally infected cat and its biological nature was investigated. In cats experimentally inoculated with Cryptosporidium oocysts, long-lasting shedding of the oocysts occurred after a prepatent period of 8-10 days, and a number of peaks of oocyst count appeared at intervals of several days to a few weeks, earlier in the infection course. Cryptosporidium infection in cats is likely to pass from an acute to a chronic stage. During the chronic stage, prednisolone injection into the cats gave rise to a recurrence of proliferation of the parasite along with a marked increase in the number of oocysts shed. None of the infected cats showed clinical symptoms. Infection experiments using Cryptosporidium oocysts were unsuccessful in several species of animals such as mice, rats, guinea pigs, dogs, suckling mice and mice previously injected with prednisolone or hydrocortisone.

In vitro cultivation of Cryptosporidium parvum and screening for anticryptosporidial drugs

Sporozoites of Cryptosporidium parvum which were excysted in vitro from oocysts isolated from calves or patients with acquired immune deficiency syndrome underwent development in monolayers of the mouse fibroblast cell line L929. Asexual multiplication occurred, with the maximum numbers of parasites usually being observed between 24 and 48 h after infection. Gametocytes were also found, but their numbers were relatively small compared with those of the asexual stages. A study was made of the effect on parasite development of 20 antimicrobial agents, most of which were anticoccidial or antimalarial agents. The majority of the drugs had a limited inhibitory effect on parasite development, but usually only at high concentrations. The two most active drugs were monensin and halofuginone, which reduced parasite multiplication by more than 90% at high concentrations. In the case of monensin, however, inhibition of parasite development at higher concentrations was due, at least in part, to a toxic effect of the drug on the host cells.

Resistance of calves to Cryptosporidium parvum: effects of age and previous exposure

Cryptosporidium parvum is a coccidian parasite that causes diarrheal disease in many vertebrate species, including young (less than or equal to 1 month old) calves. Older calves and adult cattle are resistant to infection. In this study, newborn calves were raised in isolation from C. parvum for 1 week to 3 months before experimental challenge with the parasite. Calves orally challenged with C. parvum at 1 week of age shed oocysts in their feces and had diarrhea after challenge exposure. When these calves were rechallenged at 1 and 3 months of age, they neither shed oocysts nor had diarrhea. There was no significant increase in the mean anticryptosporidium enzyme-linked immunosorbent assay serum antibody titer in these calves following any of the challenge exposures. Calves orally inoculated with C. parvum for the first time at 1 month of age shed oocysts, had diarrhea after challenge exposure, and were resistant to rechallenge at 3 months of age. These calves had a twofold increase in serum antibody titer after the first challenge and no increase after the second challenge. Calves orally inoculated with C. parvum for the first time at 3 months of age shed oocysts, and two of seven animals had diarrhea. These calves had a 10-fold increase in serum antibody to C. parvum after exposure. This study demonstrates that calves raised in isolation from C. parvum remain susceptible to challenge until at least 3 months of age. Furthermore, within this time period, initial exposure and recovery renders calves resistant to further challenge with the parasite. The data also suggest that exposure of young calves to C. parvum may inhibit the development of a serum antibody response to the parasite.

New mouse models for chronic Cryptosporidium infection in immunodeficient hosts

Cryptosporidium sp. causes fulminant diarrhea and chronic infection in immunocompromised, particularly human immunodeficiency virus-infected, persons. The lack of in vitro cultivation and a suitable animal model has limited development of effective treatment. We describe two new mouse models of chronic symptomatic cryptosporidiosis in adult athymic mice and in T-cell subset-depleted mice. A progressive infection, fatal within 4 months, occurred in most adult athymic mice; a few developed stable infections. Symptoms included dehydration, weight loss, intermittent diarrhea, and jaundice. Pathologic abnormalities and organisms localized in the intestine in stable infections but involved the hepatobiliary tree and pancreas in others. Lymphoid cells from histocompatible, Cryptosporidium sp.-immune mice cured infected nude mice. Identical infections occurred in neonatally infected BALB/c mice treated with anti-CD4 monoclonal antibodies alone or also with anti-CD8 monoclonal antibodies; the mice were cured when the monoclonal antibody treatments were stopped. These models will be useful in definition of the immune defects that permit chronic cryptosporidiosis to develop and in assessment of treatment modalities.

Epidemiological aspects of human cryptosporidiosis

The coccidian protozoan parasiteCryptosporidiumhas been described in many host species since its discovery in the early part of the century, but it remained obscure until the recognition by veterinary workers in the 1970s of its importance as a cause of scours in young livestock animals [1–4].

Experimental cryptosporidiosis in hamsters

A new laboratory animal model for experimental cryptosporidiosis is described. Adult immunosuppressed hamsters were infected per os with 0.5 x 10(5) and 1 x 10(5) Cryptosporidium oocysts of calf origin. The mean numbers of oocysts shed per gram of feces per day and the patterns of infection are described. The susceptibility to Cryptosporidium infection, the total number of oocysts shed (a thousand times the infective dose), and the ease of handling in laboratory conditions make hamsters a good animal model for cryptosporidiosis.

Susceptibility of germfree or antibiotic-treated adult mice to Cryptosporidium parvum

Adult mice are more resistant than neonatal mice to intestinal colonization with the protozoan parasite Cryptosporidium parvum. Development of a mature intestinal flora may play a role in this resistance. We compared susceptibilities to colonization with C. parvum in adult conventional mice, adult germfree mice, and adult conventional mice treated with oral antibiotics to deplete the intestinal flora. Germfree mice of both CD1 and BALB/c strains were colonized at day 7 following inoculation with C. parvum oocysts isolated from the feces of an infected, diarrheic calf. Age-matched conventional mice of the same strains were comparatively resistant to colonization. Conventional mice treated with antibiotics remained resistant to colonization. These results suggest that the microflora in the intestine was not the sole determinant of resistance or susceptibility to colonization. The germfree adult mouse as an experimental model of cryptosporidiosis is discussed.

Cryptosporidiosis in perspective

In this review I have examined the vast literature which has accumulated on Cryptosporidium, particularly in the past 3 years, in an attempt to highlight areas in which progress has been made in relation to the organism and the disease, and to indicate areas in which knowledge is still lacking. Since 1982, a global effort by scientists and clinicians has been directed towards determining the nature of the disease in humans and the relative contribution of cryptosporidiosis to gastroenteritis. From published data, the incidence of diarrhoea is 1-5% in most developed countries, and 4-7% in less developed countries, when measured throughout the year and in all age groups. The frequency of cryptosporidiosis is highest in children aged between 6 months and 3 years, and in particular locations (e.g., day-care centres) and at particular times of the year. Although susceptibility to infection is life-long, one suspects that the lower prevalence among older children and adults is due to immunity acquired from frequent exposure. Other important factors contributing to higher prevalence are the season--it is more frequent in a wet, warm climate--association with travel to particular destinations, poor hygiene, intimate contact with certain animals, and congregation of large numbers of young previously unexposed children in day-care centres. The association between cryptosporidiosis and giardiasis presumably results from the existence of a common source of infection. The immune status of the host appears to be a major determinant of whether the infection is self-limiting or persistent. It is clear that both branches of the immune system are required for complete recovery, since T-lymphocyte dysfunction or hypogammaglobulinaemia can both lead to persistent illness. Chronic diarrhoea and malabsorption attributed to cryptosporidiosis also occur in the absence of evidence of immune defect. The importance of respiratory tract infection in humans, other than in the terminal stages of chronic illness, requires investigation. The infection has now been identified in all classes of vertebrates; it has been observed in all domestic animals including pets, and a wide range of wildlife including birds. Cryptosporidiosis seems to cause diarrhoea in young ruminants, less frequently in pets. In birds the parasite has been observed in the gastrointestinal tract, without ill effect, and in the respiratory tract, in which clinical symptoms of variable severity have been described. The mucosal response of the gastrointestinal tract to infection appears to vary among mammals and may be the key to the variable clinical manifestations observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of cyclophosphamide-rat model of cryptosporidiosis

A cyclophosphamide-treated-rat model for cryptosporidiosis is described. The optimal conditions for inducing a cryptosporidial infection in rats were a 50 mg/kg dose of cyclophosphamide per day in the drinking water for a minimum of 14 days before inoculation with 10(4) or more infectious oocysts. Eighteen days after inoculation, 80% or more of the animals were infected. Cryptosporidia were attached to the terminal 24 cm of the small intestine, and the immunosuppressed animals remained infected as long as they received cyclophosphamide. However, the intestinal infection cleared within 7 to 10 days after cyclophosphamide was withdrawn. Oocysts continued to be detected in the feces for an additional 5 to 7 days after cryptosporidia were no longer visibly attached to the ideal enterocytes. This study characterized an animal model that can be used to investigate the pathogenesis of and evaluate therapeutic regimens for cryptosporidiosis in the immunocompromised host.

Infectivity and neutralization of Cryptosporidium parvum sporozoites

Cryptosporidiosis, a diarrheal disease of calves and humans caused by the coccidian parasite Cryptosporidium parvum, is terminated in hosts with normal immune systems. To assess the mechanisms of immunity in cryptosporidiosis, it is necessary to isolate and quantitate sporozoites, the infective stage of Cryptosporidium spp. Here we report the (i) separation of infective C. parvum oocysts from calf feces by ether extraction, sieving, and hypochlorite treatment; (ii) separation of viable C. parvum sporozoites from intact and excysted oocysts by anion-exchange chromatography; and (iii) quantitation of sporozoite infectivity in vivo by direct intraintestinal injection of isolated sporozoites in 7-day-old BALB/c mice. When isolated sporozoites were incubated with heat-inactivated immune bovine serum, 25 times the 50% infective dose for 7-day-old mice was completely neutralized. Sporozoites incubated with preimmune bovine serum were infectious for 7-day-old mice.

Abomasal cryptosporidiosis in cattle

A 6-week-old calf and nine feedlot steers shed oocysts similar to Cryptosporidium muris-like oocysts. There were massive populations of this Cryptosporidium in the peptic glands of most of these animals. The oocysts were larger and more oval than the frequently reported type which is generated in the intestines of many animal species and thought to be similar to Cryptosporidium parvum. The pattern of shedding of this newly discovered Cryptosporidium in the steers was continuous over a period of months whereas the C. parvum-like oocysts cease to be shed 1 to several weeks after onset. The nature of the host-parasite interaction in abomasal cryptosporidiosis is yet to be determined. Morphologic changes that resulted from the interaction were an approximate 10% increase in abomasal mucosal thickness, widening of gland lumens in the middle region, and atrophy of epithelium in the same region.

Experimental intrauterine infection of adult BALB/c mice with Cryptosporidium sp

Inoculation of adult, female BALB/c mice with 2 X 10(5) bleach-treated Cryptosporidium sp. oocysts isolated from calf feces resulted in infection of the uterine mucosa in more than 50% of the animals. Cryptosporidium sp. completed the entire life cycle in the uterus, and infectious oocysts were passed into the vagina. Two methods of application were used to establish intrauterine infection. The inoculum was either injected into the uterus after abdominal surgery or intracervically instilled. Mice were susceptible at all phases of the sexual cycle, but the highest infection rates were obtained during estrus and diestrus. Parasites were demonstrated as early as 5 days postinfection. Phagocytic cells in the uterine lumen and in the vagina contained Cryptosporidium sp. Phagocytosis may be an important immune response and a mechanism of parasitic clearance. These results suggest that Cryptosporidium sp. is a potential pathogen of the reproductive tract.

Separation of cryptosporidium oocysts from fecal debris by density gradient centrifugation and glass bead columns

A method was developed to obtain purified cryptosporidium oocysts from fecal samples. Oocysts were initially collected by centrifugation through a sucrose density gradient and further purified by passage through glass bead columns. The purified oocysts were antigenically active and sufficiently pure for immunological studies.

Experimental cryptosporidiosis in mice, calves and chicken

Experimental infections attributed solely to Cryptosporidium were carried out in newborn SPF mice, calves and chicken in order to study the prepatency, patency and incubation periods, describe the clinical symptoms and find and describe any correlations between the association of Cryptosporidium with the intestinal mucosa and presence of pathological lesions. The paper also gives the clinical and paarsitological parameters of Cryptosporidium infection of calves from a field survey and compares them to the results of experimental study.

Sporadic cryptosporidiosis in a rural population is asymptomatic and associated with contact to cattle

Fecal samples each followed by a completed questionnaire were obtained from 233 persons representing 80 households. Using the formalinether concentration method combined with the acid-fast staining oocysts of Cryptosporidium were found in 7 (3 %) persons. 63 persons had contact to cattle, and asymptomatic cryptosporidiosis was diagnosed in 6 of them. Cryptosporidiosis was not found in any of the 51 persons with contact to some other animal but not cattle, and none of the 7 Cryptosporidium positive persons had been traveling abroad. We also obtained fecal samples from 15 calves from 7 households. Six of the calves (40 %) harbored Cryptosporidia and manifest enteritis was detected in those under age of 1 month. Five out of 14 farms had problems of neonatal calf diarrhea. Human cryptosporidiosis was more frequent on such problem farms. The results indicate that in rural population, human cryptosporidiosis is mainly asymptomatic and occurs mainly in residents of cattle-rearing farms.