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Biomedical subjects

C R Sterling

Publications and source records attributed to C R Sterling.

At least 37 records · Page 2Linked to original sources
PubMed1997

Pathologic and clinical findings in patients with cyclosporiasis and a description of intracellular parasite life-cycle stages.

Cyclospora cayetanensis has been observed in the feces of persons with prolonged diarrhea. A description of the symptoms and histopathologic findings for patients with cyclosporiasis is presented. The intracellular life-cycle stages of these parasites in the enterocytes of patients will also be described. Seventeen Peruvian patients positive for Cyclospora organisms were surveyed and underwent endoscopy, and their symptoms were recorded. Patients presented with gastrointestinal symptoms, including diarrhea, flatulence, weight loss, abdominal discomfort, and nausea. Jejunal biopsies showed an altered mucosal architecture with shortening and widening of the intestinal villi due to diffuse edema and infiltration by a mixed inflammatory cell infiltrate. There was reactive hyperemia with vascular dilatation and congestion of villous capillaries. Parasitophorous vacuoles contained sexual and asexual forms. Type I and II meronts, with 8-12 and 4 fully differentiated merozoites, respectively, were found at the luminal end of epithelial cells. These findings demonstrate the complete developmental cycle associated with host changes due to Cyclospora organisms.

Animals↗
PubMed1997

Epidemiology and treatment of Cyclospora cayetanensis infection in Peruvian children.

Cyclospora cayetanensis was detected in fecal specimens from 63 (1.1%) of 5,836 Peruvian children studied over 2 years; the protozoan was detected by modified acid-fast staining and autofluorescence under ultraviolet light. The highest prevalence occurred among children between 2 and 4 years of age. Thirty-two percent (20) of the 63 C. cayetanensis-infected children were symptomatic. Nineteen infected children were enrolled in a double-blind, placebo-controlled trial of a 3-day course of trimethoprim-sulfamethoxazole (TMP-SMZ; 5/25 mg/[kg x d]). Children were followed up with daily stool examinations (mean number of samples examined per child +/- SE, 19 +/- 4). The mean duration of oocyst excretion +/- SE was 4.8 +/- 1.2 days for TMP-SMZ recipients compared with 12.1 +/- 6.1 days for placebo recipients (P < .02). The prevalence of C. cayetanensis infection decreases during winter months and as children age; it decreases precipitously by adulthood. In children in areas of endemicity, C. cayetanensis usually causes mild disease that is often asymptomatic. TMP-SMZ therapy significantly decreases the duration of oocyst excretion.

Adolescent↗
PubMed1997

Waterborne protozoan pathogens.

Protozoan parasites were the most frequently identified etiologic agents in waterborne disease outbreak from 1991 to 1994. The waterborne parasites Giardia lamblia, Naegleria fowleri, Acanthamoeba spp., Entamoeba histolytica, Cryptosporidium parvum, Cyclospora cayetanesis, Isospora belli, and the microsporidia are reviewed. For each parasite, the review includes history, life cycle, incidence, symptoms, and therapy. Clinical detection methods are compared, and emerging technologies are discussed. Information on the association of these parasites with waterborne outbreaks is reviewed. Current information on protozoan parasites identified as etiological agents in waterborne outbreaks is discussed. Water industry issues related to recent disease outbreaks are examined in the context of water quality testing regulations for G. lamblia and those proposed for C. parvum. The review identifies the limitations of the American Society of Testing and Materials water-testing method for these parasites. An overview of federal regulations affecting the water industry and laboratories that test for water quality is also provided. The article highlights the importance of the clinical laboratory as a frontline defense for the detection of infectious organisms. The review points to the need for clinical laboratories, physicians, and public health personnel to cooperatively plan and assess the challenge of meeting this potential public health threat.

Acanthamoeba↗
PubMed1997

Cryptosporidium infections in Mexican children: clinical, nutritional, enteropathogenic, and diagnostic evaluations.

Using an indirect immunofluorescence assay on stool samples, we found a 6.4% prevalence of cryptosporidiosis among 403 children less than five years of age with acute diarrhea in Mexico City over a one-year period. The prevalence was highest (11.4%) during the rainy summer months. Most Cryptosporidium parvum cases occurred in infants less than one year of age. Cryptosporidium parvum was more common in malnourished children (P < 0.05) and in nonbreast-fed infants less than six months of age (P < 0.01). Neither dwelling characteristics nor the presence of domestic animals at home were associated with C. parvum infection. Enteropathogenic bacteria were found in 26.8% of the children; Escherichia coli, Salmonella, and Shigella being the most frequently identified. None of 100 serum samples tested showed antibodies against human immunodeficiency virus. When compared with immunofluorescence, the acid-fast technique showed a sensitivity of 76.9% and a specificity of 98.9%, with a predictive positive value of 83.3%. It was concluded that 1) monoclonal antibody-based immunofluorescence is a better diagnostic tool than the acid-fast technique, 2) the prevalence of cryptosporidiosis in this population was similar to that of other developing countries, 3) clinical manifestations were nonspecific, and 4) C. parvum was more common in malnourished children and in nonbreast-fed infants.

Animals↗
PubMed1997

Isolation of Cryptosporidium parvum and Cyclospora cayetanensis from vegetables collected in markets of an endemic region in Peru.

Cryptosporidium parvum and Cyclospora cayetanensis are protozoan pathogens that cause prolonged diarrhea in both immunocompetent and immunocompromised hosts. Cryptosporidium parvum can be transmitted via the fecal-oral route, while the exact mechanisms of transmission of Cyclospora cayetanensis have not been fully determined. Humans appear to be the sole host for the latter and a distinct seasonality has been observed in endemic areas around the world. Samples of vegetables were collected at several small markets in a periurban slum in Peru during the seasons of high and low incidence. The vegetables were washed, the supernatants were collected and centrifuged, and the pellets were resuspended in a solution of 2.5% potassium dichromate. Pellets were examined using direct microscopic observation, acid-fast staining, and immunofluorescent assays for C. parvum and Cyclospora cayetanensis oocysts. Samples were collected during three time periods: the season of low incidence, the beginning of the season of high incidence, and end of the season of high incidence. Of the total vegetables examined, 14.5% contained C. parvum oocysts and 1.8% had Cyclospora oocysts. Thus, market vegetables may provide a route by which Cryptosporidium and Cyclospora can be transmitted. Our study also suggests that washing vegetables does not completely remove Cryptosporidium and Cyclospora oocysts.

Animals↗
PubMed1996

Cryptosporidium parvum: intensity of infection and oocyst excretion patterns in healthy volunteers.

Data about human Cryptosporidium parvum infection have originated from travelers, community and day care center outbreaks, and persons infected with the human immunodeficiency virus. In addition, experimental infection in 29 antibody-negative, healthy, adult volunteers generated information on the dose-infection response of C. parvum (Iowa strain). In that report, low inocula were sufficient to cause infection in 18 and illness in 7 persons. To further define the duration and intensity of infection in this population, oocyst shedding patterns were investigated in the 18 subjects infected with C. parvum. Oocyst quantitation revealed that volunteers with diarrheal illness (n = 7) excreted more oocysts over the course of the infection than did volunteers without diarrhea (n = 11; P < .05). Symptomatic subjects were more likely to shed oocysts on consecutive days. Further, a statistical nonsignificant inverse trend (r2 = .330, P = .136) was seen between challenge dose and total excreted oocysts. This paradox may relate to receptor saturation or a toxic effect on cells, parasites, or both afforded by a high inoculum.

Animals↗
PubMed1996

Cryptosporidium parvum metalloaminopeptidase inhibitors prevent in vitro excystation.

Cryptosporidium parvum arginine aminopeptidase (RAP) was studied during in vitro excystation. Specific RAP inhibitors were identified by using C. parvum extracts. Amastatin, a series of alpha-aminoboronic acids, and the chelating agents EDTA and 1,10-phenanthrolene, but not endoproteinase inhibitors, blocked enzymatic activity. RAP inhibitors found to be effective in soluble enzymatic assays were then studied for their effect on in vitro excystation. 1,10-Phenanthrolene, amastatin, and H-boronorleucine (pinacol) inhibited excystation by 84, 57, and 61%, respectively, compared with solvent-treated control oocysts. Sporozoites remained viable within the oocyst as determined by propidium iodide and fluorescein diacetate dye uptake, suggesting that alpha-aminoboronic acids were not directly lethal to the parasite.

Aminopeptidases↗
PubMed1996

Incomplete dominance of the low antibody response to Cryptosporidium parvum antigens in mice selected for high and low antibody responsiveness.

The humoral antibody response to Cryptosporidium was investigated in mice genetically selected for high (H) and low (L) antibody responsiveness. Groups of 4-5 mice from two different selections, general primary (GP) and general secondary (GS), were studied. Following immunization with Cryptosporidium parvum antigens, the maximum levels of IgG in the HGP (X +/- SD = 1.13 +/- 0.35, N = 5) in the HGS (0.42 +/- 0.15, N = 4) lines, and of IgM in the HGP line (0.86 +/- 0.53, N = 5) were significantly higher than those in their L counterparts (0.04 +/- 0.02, N = 5; 0.05 +/- 0.02, N = 4 and 0.24 +/- 0.07, N = 5, respectively). These findings were similar to those reported for other immunogens. However, the IgG (0.22 +/- 0.05, N = 4) and the IgM (0.33 +/- 0.08, N = 4) responses to immunization of F1 (LGP x HGP) hybrids indicated an incomplete dominance of the low response, in contrast to the incomplete dominance of the high response described for many other antigens and representing an important exception. In addition, the H, L and F1 mice did not develop detectable infections when inoculated with live Cryptosporidium oocysts, supporting the view that a reduced or zero antibody production itself is not enough to permit the establishment of Cryptosporidium infection in adult mice.

Animals↗
PubMed1995

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.

Adult↗
PubMed1995

A molecular-based magnet test for malaria.

The molecular-based magnet test for malaria is shown to be more sensitive than the thin blood film test. The globally used thin blood film test is less sensitive because it uses preparation steps that result in the reduction of the absolute number of diagnostically pertinent erythrocytes. Several reports of diagnostic error with the thin film test and the thick film test have appeared in the literature. In marked contrast to the commonly accepted tests, the magnet test concurrently partitions and concentrates the infected erythrocytes present in the initial sample. The magnetic test permits a brief and sensitive microscopic-based enumeration of the malaria-infected erythrocytes in the enriched sample. Diagnostically pertinent hemozoin is simply identified through two of its specific molecular properties: paramagnetism and birefringence. The former property mediates the capture and enrichment of malaria-infected erythrocytes within the magnetic flux and the latter property manifests the characteristic birefringence demonstrated by polarized light.

Animals↗
PubMed1994

Arginine aminopeptidase, an integral membrane protein of the Cryptosporidium parvum sporozoite.

Cryptosporidium parvum oocysts were studied for the expression of aminopeptidase by using amino acids bound to the synthetic fluorescent substrate 7-amino-4-trifluoromethyl coumarin. After 1 h of incubation, intact oocysts showed no activity; however, homogenization and solubilization with Triton X-114 followed by phase separation yielded a 22-fold increase in aminopeptidase activity in the detergent fraction. With arginyl-6-amino-2-styrylquinoline as a substrate, aminopeptidase activity was observed in permeabilized oocysts and freshly excysted sporozoites but not on intact oocysts or empty oocyst membranes after excystation. These results suggest that C. parvum expresses an arginine aminopeptidase that is an integral protein of the sporozoite membrane.

Aminopeptidases↗
PubMed1994

Bovine antibody against Cryptosporidium parvum elicits a circumsporozoite precipitate-like reaction and has immunotherapeutic effect against persistent cryptosporidiosis in SCID mice.

Control of cryptosporidiosis is currently hampered by the absence of drugs or vaccines proven consistently effective against Cryptosporidium parvum. On the basis of observations that anti-C. parvum antibody has therapeutic effect against cryptosporidiosis, cows were immunized with C. parvum to produce hyperimmune colostral antibody. An antibody-rich fraction was prepared and differentiated from control (nonhyperimmune) antibody by enzyme-linked immunosorbent assay, immunofluorescence assay, immunoelectron microscopy, and in vitro neutralizing titer against DEAE-cellulose-isolated C. parvum sporozoites. Oocyst, purified sporozoite, and merozoite antigens recognized by hyperimmune antibody were defined by Western blot (immunoblot). Hyperimmune antibody recognized antigens common to oocysts, sporozoites, and merozoites, as well as stage-specific antigens. Upon incubation with hyperimmune antibody, sporozoites underwent distinct morphologic changes characterized by progressive formation and eventual release of membranous sporozoite surface antigen-antibody complexes, similar to the malaria circumsporozoite precipitate reaction. The infectivity of sporozoites having undergone this reaction was neutralized. The reaction was minimal or absent on sporozoites incubated with control antibody. To determine therapeutic effect in vivo, persistent C. parvum infection was established in adult severe combined immune-deficient (SCID) mice by oral inoculation with 10(7) oocysts. At 5 weeks postinfection, infected mice were treated for 10 days with hyperimmune or control antibody by inclusion in drinking water and daily gavage. Fecal oocyst shedding and infection scores in the gastrointestinal tract and gall bladder/common bile duct in hyperimmune antibody-treated mice were significantly lower than those in the control antibody-treated mice. Hyperimmune bovine antibody prepared against C. parvum may provide a first-generation therapy for control of cryptosporidiosis. Additionally, the defined antigens can be evaluated as subunit immunogens to produce better-characterized polyclonal antibody for control of cryptosporidiosis or as targets for monoclonal antibody-based immunotherapy.

Animals↗
PubMed1994

A new coccidian parasite (Apicomplexa: Eimeriidae) from humans.

A new coccidian parasite has been found in stool specimens of humans with and without diarrhea. The oocyst of this parasite measures 8.6 microns in diameter (7.7-9.9 microns), with ovoid sporocysts 4.0 x 6.3 (3.3-4.4 x 5.5-7.1) microns. Each oocyst has 2 sporocysts and each sporocyst contains 2 sporozoites. Based on these characteristics and the structures observed by electron microscopy, this parasite has been classified in the genus Cyclospora. We propose the name Cyclospora cayetanensis n. sp. for this new human parasite.

Animals↗
PubMed1993

Cyclospora species--a new protozoan pathogen of humans.

BACKGROUND: Organisms referred to as "cyanobacterium-like bodies" have now been identified worldwide in the feces of both immunocompetent and immunocompromised patients with diarrhea. Organisms with a similar appearance have been isolated from Peruvian patients since 1985. From 1988 to 1991 we studied prospectively two cohorts of infants and young children infected with this organism. We now attempt to identify it. METHODS: Fecal samples were collected weekly from the children and examined with the use of acid-fast staining and staining with a monoclonal antibody specific for cryptosporidium. Stools positive for cyanobacterium-like bodies were preserved in potassium dichromate and exposed to conditions allowing coccidian sporulation and excystation. Both unsporulated and sporulated oocysts were fixed by freeze-substitution techniques and then examined by electron microscopy. RESULTS: Organisms isolated from the feces of Peruvian patients and two patients from the United States were identified as belonging to the coccidian genus cyclospora, after sporulation and excystation of the oocysts according to standard techniques. Complete sporulation occurred within 5 to 13 days in oocysts maintained in potassium dichromate at 25 or 32 degrees C. Complete excystation resulted in the liberation of two sporozoites from the two sporocysts within each oocyst (cryptosporidia have four naked sporozoites within each oocyst). The presence of organelles characteristic of coccidian organisms was confirmed by electron microscopy. CONCLUSIONS: We have identified organisms of the genus cyclospora that are remarkably similar to cryptosporidia in their morphologic features and the diarrheal disease that they produce in humans. The complete life cycle and epidemiology of this new protozoan parasite remain to be described.

Aged↗
PubMed1993

Role of CD4+ TH1- and TH2-cell-secreted cytokines in cryptosporidiosis.

Cryptosporidium parvum is now recognized as an important gastrointestinal pathogen around the world. Unfortunately, control measures for cryptosporidiosis are currently not well defined and very little is known about the immunological events relevant to the control of infection. Cytokine depletion experiments were conducted by injecting adult BALB/c mice with monoclonal antibodies directed to IL-2, IL-4, and IL-5, prior and during C. parvum infection. Faecal oocyst excretion and intestinal parasite number were monitored from day 4 to day 31 post-infection. Mice injected with monoclonal antibodies to IL-5 or IL-4/IL-5, but not IL-4 alone, harboured significantly higher numbers of both intestinal parasites and excreted oocysts. It is concluded that IL-5 complemented with IL-4 appears to be an important TH2-dependent mechanism for controlling cryptosporidiosis. Nevertheless, we suggest that cytokines secreted by both TH1 and TH2 cells may operate in concert in controlling cryptosporidiosis, triggering different functional mechanisms in a dynamic and simultaneous up- and down-regulatory fashion.

Animals↗
PubMed1992

Regulation of tyrosine hydroxylase gene transcription rate and tyrosine hydroxylase mRNA stability by cyclic AMP and glucocorticoid.

Tyrosine hydroxylase mRNA is induced in rat pheochromocytoma PC18 cells by cAMP analogs and glucocorticoids. Previous studies have shown that these increases in tyrosine hydroxylase mRNA are due at least in part to stimulation of the tyrosine hydroxylase gene. However, the involvement of post-transcriptional mechanisms in the regulation of tyrosine hydroxylase mRNA by these inducing agents has not been investigated. In the present study, using nuclear run-on assays we show that the relative transcription rate of the tyrosine hydroxylase gene is stimulated 2-5-fold within 20 min after treatment of PC18 cells with cAMP analogs or dexamethasone and that the rate of transcription remains elevated 2-3-fold for at least 24 hr in the continual presence of these inducing agents. Pulse-labeling experiments using 4-thiouridine indicate that the rate of synthesis of tyrosine hydroxylase mRNA is increased approximately 3-fold or 10-fold after treatment with either a cyclic AMP analog or dexamethasone, respectively. These increases in rates of synthesis agree well with the fold increases in tyrosine hydroxylase mRNA levels after treatment with these inducers. Treatment of the cells with cycloheximide lowers the basal relative transcription rate of the tyrosine hydroxylase gene 2-3-fold; however, the relative transcription rate of the tyrosine hydroxylase gene is still elevated in cells treated with either dexamethasone or cAMP analogs in the presence of cycloheximide, compared with the transcription rate of the gene in cells treated with cycloheximide alone. These results indicate that protein synthesis is not required for the short term regulation of the gene by these inducing agents. The apparent t1/2 for tyrosine hydroxylase mRNA has been estimated by two different procedures, approach to steady state kinetics and pulse-chase analysis. Both procedures yield an estimated apparent t1/2 of approximately 6-9 hr for tyrosine hydroxylase mRNA under basal culture conditions. Dexamethasone does not substantially alter this apparent t1/2 value; however, cAMP appears to lower this apparent t1/2 value transiently. Our results suggest that cAMP and glucocorticoid regulate tyrosine hydroxylase mRNA levels primarily by stimulating the transcription rate of the tyrosine hydroxylase gene; however, cAMP may also regulate the stability of the mRNA for a short period of time, such that it is induced more rapidly in the cells.

Animals↗
PubMed1992

Identification and partial purification of a lectin on the surface of the sporozoite of Cryptosporidium parvum.

A human-derived isolate of Cryptosporidium parvum from a symptomatic patient with the acquired immunodeficiency syndrome was expanded in vivo by infecting a neonatal calf with 10(8) oocysts. Sporozoites were isolated from 4 x 10(10) oocysts harvested from this single infection, and the characteristics of mixed hemagglutination (HA) with rabbit erythrocytes were determined. Sporozoite HA was inhibited by bovine submaxillary mucin (BSM), hog gastric mucin, and orosomucoid, but not by simple sugars, including sialic acid. Carbohydrate-inhibitable HA (lectin) activity increased with sporozoite lysis and was associated with the sporozoite membrane fractions. The ability of intact sporozoites to form rosettes around erythrocytes indicates that the HA (lectin) is, at least in part, present on the parasite surface. Hemagglutination (lectin) activity was partially purified from sporozoite lysates by affinity chromatography with BSM coupled to Sepharose-4B. Best elution was obtained with ethylene glycol and NaCl, which resulted in enrichment of 6 bands compared to the crude starting lysate (Mr = 60, 24, 22, 20, and 15 kDa and a 40-kDa doublet). Our results indicate that an HA (lectin) activity is present on the surface of intact sporozoites where it could play a role in cell-to-cell interactions with eukaryotic targets.

Acquired Immunodeficiency Syndrome↗