Infectivity of Cryptosporidium muris (strain RN 66) in various laboratory animals

Oocyst production and immunogenicity of Cryptosporidium muris (strain MCR) in mice

Three-week-old ICR SPF mice were orally inoculated with one of 5 doses ranging from 2 x 10(2) to 2 x 10(6) oocysts of Cryptosporidium muris (strain MCR) per mouse. Oocyst inoculation was directly proportional to the amount of oocysts shed and was inversely proportional to the period required for peak oocyst production and to the prepatent period. Peak oocyst production occurred between fifteen and thirty-one days with a patent period from 61 to 64 days. Three days after all mice stopped shedding oocysts, they were orally challenged with a single dose of 2 x 10(6) oocysts of the same species. Marked seroconversion for IgG antibody accompanied recovery from mice inoculated with 5 x 10(5) oocysts. Mice administered with carrageenan excreted a small number of oocysts for 49.0 days on the average after challenge inoculation (ACI) and control mice for 14.2 days in a dose-independent fashion. Just before challenge infection, phagocytic activity of peritoneal macrophages (M phi) and the number of peripheral M phi were dramatically decreased. Mild challenge infection implies that the immunogenicity of C. muris (strain MCR) is very strong, despite M phi blocker carrageenan administration.

Resolution of cryptosporidial infection in mice correlates with parasite-specific lymphocyte proliferation associated with both Th1 and Th2 cytokine secretion

This study was designed to investigate and characterize T-cell responses which lead to elimination of a primary infection of Cryptosporidium muris in BALB/c mice. The proliferative response of spleen cells to parasite antigen was measured by uptake of 3H-thymidine and, in parallel, supernatants were removed from cells to measure levels of IFN-gamma, TNF, IL-2 and IL-4 by ELISA. Oocyst excretion in faeces was first detected on day 10 post infection (p.i.); the level of shedding subsequently increased until day 14 and then declined until no oocysts were detected by day 25. The proliferative response of spleen cells from infected animals was similar to control levels up to day 14 p.i. but increased significantly on day 21 and was even greater on day 26. IFN-gamma and IL-2 were detected initially on day 14 p.i. and significantly higher concentrations were found on days 21 and 26. IL-4 secretion was also detected, but not until day 21 p.i., and production of TNF was not found at any time. Depletion of T-cells or CD4+ cells from spleen cells cultured with antigen resulted in a significant decrease in the levels of cytokine detected. These results indicated, therefore, that in BALB/c mice there was a correlation between the development of immunity to C. muris infection and both a parasite antigen-specific proliferative response and Th1 and Th2 cytokine production by spleen cells.

Cryptosporidium muris: prevalence, persistency, and detrimental effect on milk production in a drylot dairy

A total of 1746 individual fecal samples were obtained from milking cows during three separate visits to a drylot dairy farm. In addition, 1240 fecal samples were also obtained from cows in four additional farms. Cryptosporidium muris was prevalent in all five herds sampled. Cows that were sampled more than once invariably remained in the same shedding category. Cows shedding C. muris oocysts produced significantly less milk (approximately 3.2 kg/d). After corrections for the effects of age, parity, pen, and DIM in a logistic regression model, mean daily milk production was significantly associated with shedding status.

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.

Quantitation of Giardia cysts and Cryptosporidium oocysts in fecal samples by direct immunofluorescence assay

The lack of quick, simple, and sensitive quantitative tests has impeded studies on infection patterns and treatment of Giardia spp. and Cryptosporidium spp. A quantitative direct immunofluorescence assay (FA) using a commercial FA kit was developed and evaluated. Recovery rates of the FA for Cryptosporidium oocysts in calf feces seeded with 1,000, 10,000, 100,000, and 1,000,000 oocysts per g were 14.8, 40.8, 84.2, and 78.2%, respectively. Interassay coefficients of variation were 10.6 to 47.1%. Recovery rates of the FA for Giardia cysts in feces seeded with 1,000, 10,000, and 100,000 cysts per g were 76.4, 96.9, and 89.6%, respectively. Interassay coefficients of variation were 7.4 to 22.1%. By comparison, recovery rates of Giardia cyst by sucrose gradient flotation were only 20.5, 51.2, and 42.9%, respectively. Counts of cysts-per-gram obtained by sucrose gradient flotation with samples from calves, lambs, and ewes were only 49.1 to 54.8% of those obtained by the FA. Zinc sulfate flotation detected only 36.4% of infections when there were < or = 1,000 cysts per g. The quantitative FA offers a useful technique for epidemiological and control studies of these two parasites.

Intestinal protozoa infections

This article reviews important intestinal protozoal infections in cats. Among intestinal protozoa, Giardia and coccidia are the most important infections. Giardiasis is a common problem in catteries, especially where young kittens run free on the floor. Overcrowding and high humidity favour the survival and transmission of Giardia. Diagnosis is made by fecal examination by direct or concentration methods. Metronidazole is the drug of choice for treating giardiasis. Among the coccidial parasites, Isospora felis and Cryptosporidium sp. are the common infections. Virtually all cats become infected with Isospora felis. The pathogenicity of I. felis is controversial. Cryptosporidium parvum infection is a zoonosis. Cryptosporidium is transmitted by direct fecal-oral cycle. Cryptosporidial infections appear to be clinical in immunosuppressed cats. No drug has been found satisfactory for treatment of cryptosporidiosis.

Freeze-fracture study of the site of attachment of Cryptosporidium muris in gastric glands

The mode and organization of the attachment site of Cryptosporidium muris to gastric glands of stomach were investigated by the freeze-fracture method. Cryptosporidium muris was enveloped by a double membrane, of host plasma membrane origin, which formed the parasitophorous vacuole. The outer membrane of the double membrane was continuous with host plasma membrane, while the inner membrane was connected with the anterior part of the parasite plasma membrane at the annular ring. The density of intramembranous particles (IMP) was severely altered at the above two junctures. The parasitophorous outer membrane showed low IMP-density when compared to the host plasma membrane, although both membranes were continuous at the dense band. The inner membrane had few IMP, whereas the parasite plasma membrane showed numerous IMP, although both membranes were continuous at the annular ring. The size of dense band and annular ring was similar in diameter. The feeder organelle was clearly visible as membrane folds in freeze-fracture and some of them were connected with small vesicles of cytoplasm, indicating that the feeder organelle may play an important role for incorporation of nutrients from the host cell.

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.

PCR cloning and nucleotide sequence determination of the 18S rRNA genes and internal transcribed spacer 1 of the protozoan parasites Cryptosporidium parvum and Cryptosporidium muris

The genes encoding 18S rRNA and internal transcribed spacer 1 (1TS1) of Cryptosporidium parvum and Cryptosporidium muris were amplified from oocysts by PCR utilizing primers complementary to conserved regions of the 5' end of 18S and 5.8S rRNA. PCR products were cloned and the complete nucleotide sequences of two clones of each Cryptosporidium species were determined. The 18S rRNA genes of C. parvum and C. muris showed more than 99% sequence identity.

Analysis of oocyst wall and sporozoite antigens from three Cryptosporidium species

A comparison was made of the antigenic composition of oocyst walls and sporozoites from Cryptosporidium baileyi from turkeys, C. muris from rodents, and C. parvum from ruminants, employing immunoblotting and immunofluorescence. In immunoblotting, oocyst antigens were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting (immunoblotting) and detected with rabbit polyclonal anti-C. muris or -C. parvum antibodies or murine monoclonal antibodies developed against C. parvum. Immunofluorescence was used to investigate the reactivity of these monoclonal antibodies with air-dried excystation mixtures of sporozoites and oocysts of the different species. The results from both types of experiment indicated that the three Cryptosporidium species could be differentiated immunologically. In comparison, few antigenic differences were found between a number of isolates of C. parvum in immunoblotting. There was also evidence to suggest that C. parvum and C. baileyi were more closely related antigenically to one another than to C. muris.

[Isolation and identification of Cryptosporidium from various animals in Korea. II. Identification of Cryptosporidium muris from mice]

Each of SPF mice(Scl: ICR strain, 3-week-old males) was inoculated with 5 x 10(4) oocysts of Cryptosporidium by stomach tube. The oocysts were large type one which was previously isolated from Korean mice, and passaged in 3-week-old SPF mice. The patterns of oocyst discharge were monitored daily, and in order to observe the ultrastructure of developmental stages the stomach of the mice was examined by transmission electron microscopy (TEM) at 4 weeks post-inoculation. The prepatent period for 6 mice was 5.6 days post-inoculation on the average, and the patent period was 63.2 days. The number of oocysts discharged per day from the mice reached peak on day 36.6 post-inoculation on the average. A large number of oocysts were found in fecal samples obtained from inoculated mice on days 30-50 post-inoculation. C. muris was larger than C. parvum at almost every developmental stages, the size difference being 1.4 times in oocysts, 2.4 times in sporozoites, 1.6 times in merozoites, and 1.5 times in microgametes. The ultrastructural features of the attachment site of C. muris to the mucus cells were remarkably different from those of C. parvum and its closely related species. The anterior projection of the protozoa (C. muris), the outer aspect of which was surrounded by a thick filamentous process of the host cell, has not been reported at any developmental stages of C. parvum or its closely related species. The size of the oocysts of strain RN 66 was larger than that of Korean mice origin. The above results reveal that the large type Cryptosporidium of Korean mice origin is identified as Cryptosporidium muris and this type was named as C. muris (strain MCR).

[Isolation and identification of Cryptosporidium from various animals in Korea. I. Prevalence of Cryptosporidium in various animals]

Cryptosporidium, a coccidian protozoa, commonly causes a self-limiting diarrheal illness in humans and animals. Fecal samples from various animals in Chonbuk district were observed using Sheather's flotation technique, Kinyoun's modified acid-fast staining, and osmic acid pre-fixed Giemsa staining. The oocysts were detected in 74 cages (29.6%) out of 250 cages of mature mice, 26 (13.3%) out of 195 mature house rats, 75(15.0%) out of 4-week-old 500 fowls, 98(19.9%) out of 6 to 8-month-old 500 pigs, and 111(22.2%) out of 2 to 5-year-old 500 dairy cattle, respectively. The degree of prevalence was slight in general, but actual prevalence was higher than infection rate because the detection rates were higher in repeated-preparation examinations in comparison to the first examination. Meanwhile, large and small types of oocysts were detected from mice, house rats, pigs, and cattle, and medium type from fowls.