Lacteal immunity to enteric cryptosporidiosis in mice: immune dams do not protect their suckling pups

PI3K inhibitors are finally coming of age

Overactive phosphoinositide 3-kinase (PI3K) in cancer and immune dysregulation has spurred extensive efforts to develop therapeutic PI3K inhibitors. Although progress has been hampered by issues such as poor drug tolerance and drug resistance, several PI3K inhibitors have now received regulatory approval - the PI3Kα isoform-selective inhibitor alpelisib for the treatment of breast cancer and inhibitors mainly aimed at the leukocyte-enriched PI3Kδ in B cell malignancies. In addition to targeting cancer cell-intrinsic PI3K activity, emerging evidence highlights the potential of PI3K inhibitors in cancer immunotherapy. This Review summarizes key discoveries that aid the clinical translation of PI3Kα and PI3Kδ inhibitors, highlighting lessons learnt and future opportunities.

Diagnostic biomarkers in murine Cryptosporidiosis: dose- and age-related infection

Increasing prevalence of Cryptosporidium raises the importance to explore different aspects of its infection. In the absence of reproducible in vitro culturing, animal model is the only experimental method to study Cryptosporidium. Our study evaluated Cryptosporidium infection using coproscopy, copro-antigen and copro-DNA for early detection of murine cryptosporidiosis. Hundred and forty albino mice (neonates and adult) were divided into two groups, control group received sterile PBS solution, and infected groups were inoculated with molecularly characterized Cryptosporidium parvum oocysts and further subdivided into three subgroups for infectious dose response detection. Mice fecal samples were collected every 4 h on the first day and then daily and examined for fecal oocysts, copro-antigen and copro-DNA. Four mice from each subgroup were killed at 12, 24 and 48 h post-infection (P-I), and their intestines were examined for cryptosporidial mucosal DNA. Cryptosporidium copro-antigen and copro-DNA were detected 4 and 8 h P-I in infected neonatal and adult mice, respectively, and intestinal mucosal DNA was detected after 12 h in both. Microscopy was able to detect oocysts 48 h P-I. Inoculated C. parvum oocysts were recovered in feces of infected mice without genotypic changes. Neonate mice showed higher susceptibility for cryptosporidial infection than adults without statistical differences for the given infectious doses. Both copro-immunoassay and copro-nPCR assays can early detect Cryptosporidium infection; however, nPCR was able to identify Cryptosporidium species, making nPCR a reliable biomarker for early detection in murine model.

The Mammary Gland in Mucosal and Regional Immunity

The mammary gland (MG) lacks a mucosa but is part of the mucosal immune system because of its role in passive mucosal immunity. The MG is not an inductive site for mucosal immunity. Rather, synthesis of immunoglobulin (Ig)A by plasma cells stimulated at distal inductive sites dominate in the milk of rodents, humans, and swine whereas IgG1 derived from serum predominates in ruminants. Despite the considerable biodiversity in the role of the MG, IgG passively transfers the maternal systemic immunological experience whereas IgA transfers the mucosal immunological experience. Although passive antibodies are protective, they and other lacteal constituents can be immunoregulatory. Immune protection of the MG largely depends on the innate immune system; the monocytes–macrophages group together with intraepithelial lymphocytes is dominant in the healthy gland. An increase in somatic cells (neutrophils) and various interleukins signal infection (mastitis) and a local immune response in the MG. The major role of the MG to mucosal immunity is the passive immunity supplied to the suckling neonate.

COMPARATIVE EFFECT OF NEOSPORA CANINUM INFECTION IN BALB/c MICE AT THREE DIFFERENT GESTATION PERIODS

Neospora caninum has been recognized as a major cause of infectious bovine abortion worldwide. In the present study, the effect of N. caninum infection in mice at the 3 gestation periods (first, second, and third period) was investigated. In dams, tissue distribution of N. caninum was evaluated by nested polymerase chain reaction. In the progeny, fetal mortality, stillbirth, litter size, neonatal mortality/morbidity, vertical transmission, and parasite burden in neonatal tissues were evaluated. Pregnant BALB/c mice were infected subcutaneously with 2 x 10(6) NC-1 tachyzoites on days 0, 7, or 14 of gestation. Dams from each group were sequentially killed during gestation and postpartum (PP). Pups were killed on days 1 and 7 PP. Infection on day 0 of gestation produced a high vertical transmission rate, although no changes in fetal mortality, stillbirth, and littermate size were observed. The highest level of vertical transmission, together with an increase in fetal mortality and stillbirth and a decrease in litter size, were observed when infection was done on day 7 of gestation. Finally, infection on day 14 of gestation produced the lowest vertical transmission. Furthermore, infection at any time during gestation compromised the postnatal development of pups, because neonates from infected dams showed less body weight and a delay in the hair development.

Molecular targets for detection and immunotherapy in Cryptosporidium parvum

Cryptosporidium parvum is an obligate protozoan parasite responsible for the diarrheal illness cryptosporidiosis in humans and animals. Although C. parvum is particularly pathogenic in immunocompromised hosts, the molecular mechanisms by which C. parvum invades the host epithelial cells are not well understood. Characterization of molecular-based antigenic targets of C. parvum is required to improve the specificity of detection, viability assessments, and immunotherapy (treatment). A number of zoite surface (glyco)proteins are known to be expressed during, and believed to be involved in, invasion and infection of host epithelial cells. In the absence of protective treatments for this illness, antibodies targeted against these zoite surface (glyco)proteins offers a rational approach to therapy. Monoclonal, polyclonal and recombinant antibodies represent useful immunotherapeutic means of combating infection, especially when highly immunogenic C. parvum antigens are utilized as targets. Interruption of life cycle stages of this parasite via antibodies that target critical surface-exposed proteins can potentially decrease the severity of disease symptoms and subsequent re-infection of host tissues. In addition, development of vaccines to this parasite based on the same antigens may be a valuable means of preventing infection. This paper describes many of the zoite surface glycoproteins potentially involved in infection, as well as summarizes many of the immunotherapeutic studies completed to date. The identification and characterization of antibodies that bind to C. parvum-specific cell surface antigens of the oocyst and sporozoite will allow researchers to fully realize the potential of molecular-based immunotherapy to this parasite.

Mucosal defences against orally acquired protozoan parasites, emphasis on Toxoplasma gondii infections

Protozoan parasites that gain access to the host through the mucosal tissue of the alimentary tract may influence the development of intestinal inflammatory disorders. Despite the diversity of the extracellular and intracellular protozoan pathogens discussed in this review, our current understanding of the mechanisms involved in the immune response indicates that a common exuberant immune response to rid the host of these agents is elicited. This robust inflammatory response is orchestrated both by cells from parenchymatous origin such as intestinal epithelial cells and by cells from the haematopoietic system such as macrophages, dendritic cells and lymphocytes. This inflammatory immune response is controlled by a series of regulatory mechanisms in most species. When this balance is no longer evident, an inflammation of the intestine may occur, leading to acute gastritis and diarrhoea and that would add pathological effects to those because of the pathogen itself.

Prevalence of and risk factors involved in the spread of neonatal bovine cryptosporidiosis in Galicia (NW Spain)

An epidemiological study was carried out on farms in Galicia (NW Spain) to investigate the prevalence of and the risk factors associated with the spread of infection by Cryptosporidium parvum in calves of less than 3 weeks of age. A total of 22 cattle farms (10 beef herds and 12 dairy herds) were visited once every 21 days between January and December 2000. A faecal sample was collected directly from the rectum of each of the 844 calves born during the study period. Each sample was studied macroscopically to establish its consistency as liquid, soft or solid, and the presence of mucus or blood noted. C. parvum oocysts were identified by direct microscopic examination and the intensity of infection established semiquantitatively as slight, moderate or severe. Of the 844 calves, 404 were found to have the parasite in their faeces, i.e. the prevalence was 47.9%. Statistical analysis of the risk factors such as general characteristics of the farm and the housing conditions of the calves, revealed three variables that significantly effect the risk of cryptosporidial infection in suckling calves: the method of cleaning, the type of flooring and the frequency of cleaning.

Prevalence of and risk factors for shedding of Cryptosporidium parvum in Holstein Freisian dairy calves in central México

A total of 31 dairy farms from three states in central México were selected for this study in order to determine the prevalence of and risk factors for Cryptosporidium parvum shedding in young Holstein Freisian calves. Fecal samples were obtained once from each calf for acid-fast staining for detection of C. parvum oocysts. Information on each calf and on each dairy's management practices regarding the maternity pen, calf hutches and calf feeding was obtained by personal interview using a standardized questionnaire. Of the 31 dairies, 29 had one or more calves shedding C. parvum oocysts. The overall point prevalence was 25% (128/512). Dairy calves from the states of Hidalgo, Jalisco, and México had overall point prevalences of 28% (51/185), 29% (33/112) and 20% (44/215), respectively. Day of age was strongly associated with the risk of shedding C. parvum oocysts, with a maximum risk of shedding at approximately 15 days of age. Using mixed-effects logistic regression with herd as the random effect, feeding starter grain to calves, sweeping out the maternity pen, and using hay bedding in the maternity pen were significantly associated with increased odds of shedding C. parvum oocysts. We speculate that the association between feeding starter grain to calves and the higher odds of shedding C. parvum is linked to an increased duration rather than a higher incidence density of shedding. In addition, the association between sweeping the maternity pen and the increased odds of shedding C. parvum may be attributable to dairy personnel using the same broom for cleaning calf hutches and the maternity pen, thereby cross-contaminating oocysts from infected to newborn calves.

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.

Cryptosporidium parvum infection in T-cell receptor (TCR)-alpha- and TCR-delta-deficient mice

Mice deficient in either alpha beta or gamma delta T cells were more susceptible to infection with the protozoan parasite Cryptosporidium parvum than were control mice. Both neonatal and adult alpha beta-T-cell-deficient mice developed chronic infection. Gamma delta-T-cell-deficient neonatal mice were more susceptible than control mice but were able to clear the infection. Adult gamma delta-T-cell-deficient mice were not susceptible to infection. These data indicate that alpha beta T cells are important for resistance to C. parvum while gamma delta T cells have a less critical role.

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).

The infectivity of Cryptosporidium parvum in healthy volunteers

BACKGROUND

Small numbers of Cryptosporidium parvum oocysts can contaminate even treated drinking water, and ingestion of oocysts can cause diarrheal disease in normal as well as immunocompromised hosts. Since the number of organisms necessary to cause infection in humans is unknown, we performed a study to determine the infective dose of the parasite in healthy adults.

METHODS

After providing informed consent, 29 healthy volunteers without evidence of previous C. parvum infection, as determined by the absence of anti-cryptosporidium-specific antibodies, were given a single dose of 30 to 1 million C. parvum oocysts obtained from a calf. They were then monitored for oocyst excretion and clinical illness for eight weeks. Household contacts were monitored for secondary spread.

RESULTS

Of the 16 subjects who received an intended dose of 300 or more oocysts, 14 (88 percent) became infected. After a dose of 30 oocysts, one of five subjects (20 percent) became infected, whereas at a dose of 1000 or more oocysts, seven of seven became infected. The median infective dose, calculated by linear regression, was 132 oocysts. Of the 18 subjects who excreted oocysts after the challenge dose, 11 had enteric symptoms and 7 (39 percent) had clinical cryptosporidiosis, consisting of diarrhea plus at least one other enteric symptom. All recovered, and there were no secondary cases of diarrhea among household contacts.

CONCLUSIONS

In healthy adults with no serologic evidence of past infection with C. parvum, a low dose of C. parvum oocysts is sufficient to cause 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.

Treatment of experimental ovine cryptosporidiosis with ovine or bovine hyperimmune colostrum

Ovine or bovine colostrums with different antibody titers were tested for their ability to prevent cryptosporidiosis in five groups of neonatal lambs experimentally infected with 10(6) Cryptosporidium parvum oocysts 2 days after birth (Day 0). In a control group (Group 1), six lambs were deprived of ewe colostrum and exclusively fed with milk replacer. Two groups of six lambs were allowed to suckle their non-hyperimmunized (Group 2) or hyperimmunized (Group 3) dams throughout the experiment. Two groups of seven lambs were separated from their dams at birth before suckling and fed with non-hyperimmune (Group 4) or hyperimmune (Group 5) bovine colostrum; for 7 days they received 50 ml of colostrum completed by milk replacer twice a day, then they were fed with milk replacer exclusively. Control lambs became infected and developed clinical cryptosporidiosis with diarrhea on Days 4-9 post inoculation, oocyst shedding and mortality (2/6). In all the treated groups, the colostrum prevented mortality and clinical cryptosporidiosis. The mortality (5/7) observed in Group 5 was not due to cryptosporidiosis but anemia. In treated groups, specific antibodies were detected on Day 0 after 2 days of colostrum intake and varied little in time for IgM and IgG in spite of the parasite development, whereas they appeared later in the control group, on Day 4 for IgM, Day 11 for IgA and Day 14 for IgG. In all groups, the response which was the most consistent was the IgA response which evolved from Days 11 to 18 in association with the decline of oocyst shedding. Our results show that whatever the serum antibody titers were, the specific C. parvum circulating antibodies have no influence on the control of cryptosporidiosis. The prophylaxis or the treatment of cryptosporidiosis require high titers of specific C. parvum antibodies in the gut lumen during a sufficiently long period.

Neutralisation of Cryptosporidium parvum sporozoites by immunoglobulin and non-immunoglobulin components in serum

Sporozoites of Cryptosporidium parvum were incubated in 1:10 dilutions of immune or non-immune, heat-inactivated lamb serum specimens or serum fractions. The infectivity of treated sporozoites was assessed by inoculating them, per rectum, into five-day-old rats followed by histological examination of their intestines at either three or five days after infection. The infectivity of sporozoites treated with heat-inactivated whole sera was greatly reduced. This neutralisation had both specific and non-specific components. The former was associated with the IgG fraction of hyperimmune serum raised against sporozoites and the latter with a heat-stable, non-dialysable component present in both IgG-depleted hyperimmune serum and uninfected gnotobiotic serum.

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.

Immune responses to Cryptosporidium muris and Cryptosporidium parvum in adult immunocompetent or immunocompromised (nude and SCID) mice

Adult murine models of Cryptosporidium infection involving Cryptosporidium muris and C. parvum were used to study immunity to cryptosporidiosis in the mammalian host. Immunocompetent BALB/c or C57BL/6 mice developed a highly patent infection with the RN 66 strain of C. muris but overcame the infection and were immune to reinfection. In contrast, severe combined immunodeficiency (SCID) mice or nude mice had a chronic infection lasting at least 109 days. The development of the C. muris infection appeared to be confined to the gastric epithelium in immunocompetent and immunocompromised mice. SCID mice injected intraperitoneally with histocompatible spleen or mesenteric lymph node cells from uninfected BALB/c mice were able to recover from the C. muris infection. The protective effect of donor spleen cells was not reduced by depletion of the B cell population but was significantly reduced by depletion of Thy.1 cells. Treatment of C57BL/6 or BALB/c mice during infection with a gamma interferon-neutralizing monoclonal antibody, but not a tumor necrosis factor-neutralizing monoclonal antibody, resulted in a significant increase in oocyst production. In the C. parvum model, a severe and eventually fatal chronic infection with a cervine isolate was established in SCID mice, with parasitization occurring in the ileum, cecum, and colon. SCID mice injected with unprimed BALB/c spleen cells prior to inoculation of C. parvum oocysts were resistant to infection. These results suggested that the two animal models should be valuable in the study of immunity to cryptosporidial infection.

Cryptosporidiosis in adult and neonatal mice with severe combined immunodeficiency

Cryptosporidium parvum causes protracted diarrhoea in immunodeficient hosts. To characterize the role that T and B lymphocytes play in the eradication of the parasite from the intestinal mucosa, the course of infection in mice with severe combined immunodeficiency (SCID) was studied. Twenty-nine SCID and 26 BALB/c adult mice received 10(6) oocysts intragastrically. The course of infection in the two strains was similar until 2 months after inoculation, when moderate numbers of organisms were identified in the villous and crypt mucosa of the ileum and proximal colon of SCID mice. Three months after inoculation, SCID mice developed wasting and progressive intestinal and biliary tract disease. At 5 months, mortality of 72 and 0 per cent, respectively, was observed in the SCID and BALB/c mice. Twenty-four SCID and 26 BALB/c neonatal mice were also inoculated with C. parvum. Cryptosporidiosis occurred in SCID and BALB/c mice within 2 weeks of inoculation. Subsequently, BALB/c, but not SCID mice, eradicated the parasite from their intestinal mucosa. SCID mice developed progressively severe cryptosporidiosis which killed all animals within 7 weeks. Responses mediated by B or T cells, or both, appeared to play a role in eradicating C. parvum from the intestinal mucosa, since SCID mice were more severely affected than BALB/c mice. The different course of infection in adult and neonatal SCID mice indicated that other age-related factors also played a role in containing C. parvum infection.

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.

Cryptosporidiosis: Pathogenesis and immunology

Cryptosporidium parvum is an increasingly recognized agent of intestinal infection in normal and immunocompromised humans, and in many other animals. The intraepithelial cell infection results in villous atrophy, mild submucosal inflammation, reduction of brush-border enzymes and a characteristic persistent watery diarrhea. The infection is self-limiting in immunocompetent hosts, probably because of specific acquired immunity; specific serum and secretory antibody responses develop that may be required for clearance and protection against reinfection. Passive milk antibody, especially i f in high titers, may be partially protective but severe, persistent infection in athymic rodents and humans with AIDS demonstrate that T cells are essential for controlling the infection. Specific anti-bodies and lymphocyte extracts have been tested in cases of cryptosporidiosis but the interpretation of the results remains controversial. Here, Shu-Xian Zu, Guo-Dong Fang, Ronald Foyer and Richard Guerrant emphasize that effective treatment and prevention remain dependent on advances in our understanding of the host cell-parasite relationship.

Coccidian infections in AIDS. Toxoplasmosis, cryptosporidiosis, and isosporiasis

Cryptosporidium sp. and Isospora belli are coccidian protozoan parasites that were long recognized as pathogens for many animal species. The medical community became acquainted with these organisms with the advent of AIDS. Both parasites are associated with persistent, debilitating enteritis and, in the case of Cryptosporidium, biliary tract involvement in patients with AIDS. For the immunocompetent host, infection with these two pathogens usually results in self-limited diarrhea. Cryptosporidiosis appears to occur more often than isosporiasis, but the true prevalence of both infections for various populations of humans is unknown. Clinically, cryptosporidiosis is indistinguishable from isosporiasis. Diagnosis is based on finding the acid-fast (red staining oocyst in stained fecal specimens). There is no known effective therapy for cryptosporidiosis, whereas patients with isosporiasis respond promptly to treatment with trimethoprim-sulfamethoxazole. Patients with AIDS and isosporiasis have a high relapse rate after achieving complete remission and therefore need to be maintained on suppressive therapy. Much more needs to be learned about these two fascinating, "newly recognized" parasites.

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.

Characterization of bovine cellular and serum antibody responses during infection by Cryptosporidium parvum

Cellular and serum antibody responses of calves were monitored for 23 days after oral inoculation of the calves with oocysts of Cryptosporidium parvum. In vitro blastogenic responses of peripheral blood lymphocytes were assessed after stimulation with a C. parvum preparation. Specific lymphocyte blastogenic responses to the parasite were detected 2 days after inoculation. Parasite-specific antibody titers were demonstrable 7 days after inoculation with oocysts and achieved peak levels 9 days after inoculation, coinciding with oocyst shedding at 5 to 10 days after inoculation. Both lymphocyte and antibody responses remained elevated until the termination of the experiment. Immunoblotting the C. parvum preparation with serum from an infected calf revealed six major parasite antigens. Five of these antigens reacted on immunoblots from 7 to 14 days after inoculation with oocysts. A parasite antigen of approximately 11,000 molecular weight demonstrated intense reactivity on immunoblots from 7 to 23 days after inoculation. The 11,000-molecular-weight antigen also reacted on immunoblots with parenterally raised antioocyst and antisporozoite rabbit sera. These results indicate that cell-mediated as well as humoral immune responses are initiated by cryptosporidial infection in calves and that the 11,000-molecular-weight parasite antigen is immunodominant.

Susceptibility of mast cell-deficient W/Wv mice to Cryptosporidium parvum

Mast cell-deficient W/Wv infant mice were similar to normal mice in their susceptibility to and recovery from infection with the intestinal protozoan Cryptosporidium parvum. W/Wv adult mice were significantly more susceptible to primary infection than were normal adult mice, but both groups recovered at a similar rate.

Some infectious causes of diarrhea in young farm animals

Escherichia coli, rotaviruses, and Cryptosporidium parvum are discussed in this review as they relate to enteric disease in calves, lambs, and pigs. These microorganisms are frequently incriminated as causative agents in diarrheas among neonatal food animals, and in some cases different strains or serotypes of the same organism cause diarrhea in humans. E. coli causes diarrhea by mechanisms that include production of heat-labile or heat-stable enterotoxins and synthesis of potent cytotoxins, and some strains cause diarrhea by yet undetermined mechanisms. Rotaviruses and C. parvum induce various degrees of villous atrophy. Rotaviruses infect and replicate within the cytoplasm of enterocytes, whereas C. parvum resides in an intracellular, extracytoplasmic location. E. coli, rotavirus, and C. parvum infections are of concern to producers, veterinarians, and public health officials. These agents are a major cause of economic loss to the producer because of costs associated with therapy, reduced performance, and high morbidity and mortality rates. Moreover, diarrheic animals may harbor, incubate, and act as a source to healthy animals and humans of some of these agents.

Immunotherapeutic efficacy of bovine colostral immunoglobulins from a hyperimmunized cow against cryptosporidiosis in neonatal mice

Infection with Cryptosporidium parvum, a ubiquitous protozoan parasite of virtually all mammals, can cause mild to severe diarrhea in immunocompetent hosts and life-threatening diarrhea in immunocompromised hosts. Passive immunotherapy of experimentally infected animals and naturally infected humans with hyperimmune bovine colostrum has been reported to be efficacious, whereas chemotherapy has not. In this study, the efficacy of specific immunoglobulin isotypes purified from bovine colostrum from a cow hyperimmunized with Cryptosporidium parvum was assessed in neonatal BALB/c mice. Mice were orally infected with oocysts and treated with whole whey immunoglobulin G1 (IgG1), IgG2, IgA, or IgM at six intervals from 22 to 66 h postinfection. In histologic sections of intestine examined at 72 h postinfection, the reduction in number of intestinal stages in treated mice versus untreated controls was very highly significant (P less than 0.0001). The greatest reduction in parasite number was found in mice treated with IgG1, IgA, or whey.

Cryptosporidium parvum (Apicomplexa: Cryptosporidiidae) oocyst and sporozoite antigens recognized by bovine colostral antibodies

Colostral whey from seven hyperimmunized and two control cows (hyperimmune bovine colostrum) was examined by Western immunoblotting for the presence of antibody against oocysts and sporozoites of Cryptosporidium parvum, using rabbit anti-bovine immunoglobulin A (IgA), IgG1, IgG2, and IgM antibodies, followed by a horseradish peroxidase goat anti-rabbit polyvalent antibody. Although considerable variation was found in binding activity between cows on different immunization protocols, IgA and IgG1 in whey recognized a greater variety of C. parvum antigens than did IgG2 and IgM. A band at 9 to 10 kilodaltons appeared unique in that it was recognized only by IgA.

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.

Cryptosporidiosis and AIDS

Cryptosporidiosis in patients with AIDS presents as a chronic enteritis, with biliary complications in about 10% of sufferers. The disease is persistent and progressively fatal. Due to the widespread prevalence of the parasite in the community and amongst domesticated animals, persons with AIDS are constantly at risk. Treatment is extremely difficult in view of the apparent lack of a specific anticryptosporidial drug. Methods of immunomodulation are worth considering, but the main recourse may have to be a prolonged regimen of rehydration and parenteral nutrition. However, if T helper cell function improves, the disease may go into remission or the parasite could be eliminated. Vaccination of those at risk is not feasible at present.

Cryptosporidiosis in guinea pigs: an animal model

Cryptosporidia from natural cryptosporidiosis in guinea pigs were experimentally transmitted to both adult and juvenile guinea pigs. Cryptosporidia were associated with the villi of the ileum, jejunum, and duodenum. Both juveniles and adults were equally susceptible to cryptosporidia, as determined by decreases in villus height, increases in crypt depth, and decreases in villus height/crypt depth ratios, when compared with uninoculated animals. When multiple paired comparisons were made between 2 and 10 days postinoculation, there were significant decreases in villus height/crypt depth ratios with time. A dose study showed that 6-week-old guinea pigs were all infected with doses as low as 325 oocysts per animal. When sampled at weekly intervals postinoculation, guinea pigs had significant evidence of infection up to 2 weeks but had recovered completely by 4 weeks. Guinea pigs mounted a specific humoral immune response against cryptosporidia, as measured by an immunoperoxidase technique. Guinea pigs challenged by reinoculation with cryptosporidial oocysts were completely refractory to reinfection. These studies show that cryptosporidiosis in guinea pigs is a useful small animal model of this disease.

Effects of immune colostrum and orally administered antisporozoite monoclonal antibodies on the outcome of Cryptosporidium parvum infections in neonatal mice

A neonatal BALB/c mouse model of cryptosporidiosis was used to examine the potential passive transfer of immunity via immune colostrum and oral treatment with anticryptosporidial monoclonal antibodies. Neonates suckled by dams that recovered from Cryptosporidium parvum infections were equally susceptible to infection as their control counterparts suckled by naive dams. Parasite loads among the control and immune colostrum-fed mice were indistinguishable. Neonates receiving orally administered antisporozoite monoclonal antibodies were equally susceptible to infections compared with the control and immune colostrum-fed mice. Parasite loads among the mice receiving daily oral treatment with monoclonal antibody mixtures exhibited significantly lower parasite loads compared with the control mice (P less than 0.05).

[Resistance to Naegleria fowleri infection passively acquired from immunized splenocyte, serum or milk]

A pathogenic free-living amoeba, Naegleria fowleri, causes primary amoebic meningoencephalitis to human and experimental animals. This infection is rare, but the mortality is very high. Nowadays, drug treatment or active immunization of human or mice are being tried with partial effectiveness. This study shows passive immunization effect by transfer of immunized spleen cells, serum, or milk from immunized mother in mouse experimental model. Young BALB/c mice were immunized intraperitoneally with 2-3 X 10(6) trophozoites of N. fowleri, and spleen cells and sera were collected for injection to recipient mice. There were seven transfer groups, i.e., immunized mouse serum, spleen cells, serum and spleen cells, normal mouse serum, spleen cells, serum and spleen cells, and control group. Three days later, BALB/c mice were inoculated with 1 x 10(4) trophozoites of N. fowleri intranasally. After infection, decreased mortality and prolonged survival time of mice were noted in immunized groups compared with non-immunized control group. The groups injected with immunized spleen cells or normal serum showed lower mortality than that of controls but showed no changes of serum IgG level. The groups injected with immunized serum or normal spleen cells showed increased serum IgG level after immunization but hundred percent mortality was observed. Mother mice were immunized intraperitoneally with 2-3 X 10(6) trophozoites of N. fowleri at the end of pregnancy and weaning period. Soon after the delivery, litters born of non-immunized mother were matched with immunized mother for feeding immune milk. After three weeks, the litters were infected with 1 X 10(4) trophozoites of N. fowleri or sacrificed for serum collection to measure the IgG levels.(ABSTRACT TRUNCATED AT 250 WORDS)

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.