Cryptosporidiosis: the complexity of intestinal pathophysiology

A Retrospective Cohort Study of an Outbreak of Cryptosporidiosis among Veterinary Students

An outbreak of gastrointestinal illness occurred among a cohort of 56 veterinary technology and 100 veterinary science students at Massey University over an eight-week period in 2013. This coincided with calving in New Zealand’s seasonal dairy farming system and a time when calves with diarrhoea are commonly seen by veterinarians. Laboratory and epidemiological investigations were instigated by MidCentral Public Health Service (MCPHS) in conjunction with the Institute of Veterinary, Animal and Biomedical Sciences (IVABS) at Massey University. Eighty students responded to a questionnaire of which 19 met the case definition, a 24% attack rate. Faecal specimens from seven students contained Cryptosporidium oocysts and Cryptosporidium parvum IIa A18G3R1 was identified from one of the specimens. The inferred median incubation period was five days (range 1–12 days). All of the cases were self-limiting, characterized by diarrhoea, abdominal cramps, and in some cases vomiting, headache, and fever. Having contact with calves with diarrhoea was significantly associated with increased adjusted odds of being a case (OR 10.61, 95% CI 1.87–108.29 for one week of contact; OR 55.05, 95% CI 3.80–1931.18 for two weeks of contact). Outbreaks of cryptosporidiosis had occurred previously among veterinary students at Massey University, but the extremely high infectivity of C. parvum resulted in student illness despite enhanced hygiene precautions.

Development and validation of a cell culture based assay for in vitro assessment of anticryptosporidial compounds

In vitro culture of Cryptosporidium parvum oocysts in HCT-8 cells was combined with immunofluorescent labelling and digital image analysis to quantify the development of the parasite by detecting and measuring the labelled area in the respective cell cultures. The number of inoculated oocysts and the labelled area correlated reliably and significantly (R (2), 0.98-0.99). The effects of various concentrations of halofuginone bromide (0.00039 to 50 microM) and monensin (0.00225 to 0.144 microM) on in vitro parasite development were determined in further trials in cultures inoculated each with 10(5) oocysts. Monensin reduced the detected area in a dose-dependant manner. In comparison to the untreated controls, the area positive for C. parvum in the cultures treated with 0.144 to 0.009 microM monensin reached a maximum of 17%, and inhibition of 40% was observed at 0.0045 microM. Halofuginone bromide also efficiently inhibited parasite in vitro reproduction, albeit at higher concentrations. At 12.5 microM or more, inhibition was at least 90%; 0.05 microM still yielded 80% inhibition, whereas at concentrations below 0.00625 microM, labelled areas abruptly increased. Both drugs appeared efficient under in vitro conditions; the applied system is suited to screen drugs for their anti-cryptosporidial capacity.

Neutrophils do not mediate the pathophysiological sequelae of Cryptosporidium parvum infection in neonatal piglets

Cryptosporidium parvum is a minimally invasive protozoal pathogen of intestinal epithelium that results in villus atrophy, mucosal lipid peroxidation, diarrhea, and diminished barrier function. Influx of neutrophils is a consistent feature of human and animal cryptosporidiosis, and yet their contribution to the pathological sequelae of infection has not been investigated. Accordingly, we used an established neonatal piglet model of C. parvum infection to examine the role of neutrophils in disease pathogenesis by inhibiting their recruitment and activation in vivo using a monoclonal anti-CD18 antibody. Infected piglets were treated daily with anti-CD18 or isotype control immunoglobulin G and euthanized at peak infection, at which time neutrophil infiltrates, lipid peroxidation, severity of infection, and intestinal barrier function were quantified. C. parvum infection resulted in a significant increase in mucosal neutrophil myeloperoxidase activity that was prevented by treatment of piglets with anti-CD18 antibody. Neutrophil recruitment was dependent on mucosal superoxide formation (prevented by treatment of infected piglets with superoxide dismutase). Neutrophils did not contribute to peroxynitrite formation or peroxidative injury of C. parvum-infected mucosa and had no impact on the severity of epithelial infection, villus atrophy, or diarrhea. The presence of neutrophils in C. parvum-infected mucosa was associated with enhanced barrier function that could not be attributed to mucosal elaboration of prostaglandins or stimulation of their synthesis. These studies are the first to demonstrate that neutrophilic inflammation arising in response to infection by a noninvasive epithelial pathogen results in physiologic rather than pathological effects in vivo.

Significance of Cryptosporidium as an aetiology of acute infectious diarrhoea in elderly Indians

OBJECTIVE

To explore the significance of Cryptosporidium isolation in elderly Indian with acute infectious diarrhoea and its clinical correlates.

DESIGN

A hospital-based clinico-aetiological study of 120 patients aged 60 years or older, 25 adults younger than 60 years and 25 children up to age 14 with acute diarrhoea, and 57 apparently healthy elderly individuals.

RESULTS

Cryptosporidium was isolated in 22 older patients with diarrhoea (18.3%) and was highly significant (P < 0.01) compared with healthy age-matched controls. Of these patients 66% had a history of close contact with animals. Most (68%) Cryptosporidium infections occurred during the rainy season. Among the elderly patients 17% suffered from vomiting and abdominal pain, 31% were febrile; none were severely dehydrated. Stools numbered three to nine per day with duration of 5-17 days. Stool leucocytes were <6/hpf and no RBCs were seen. Isolation of Cryptosporidium in older persons was associated with diabetes mellitus (22.7%), tuberculosis (9.0%), malignancy (4.5%) and coronary artery disease (4.5%).

CONCLUSION

Cryptosporidium is an important cause of diarrhoea in elderly Indians, especially those with close contact with animals. The infection has a mild clinical course, is self-limiting and does not cause dysenteric stool. Its effect on nutrition requires further study.

An outbreak of cryptosporidiosis among veterinary science students who work with calves

The authors describe an outbreak of cryptosporidiosis among students working with calves as part of their veterinary science technology program. After an off-campus provider identified an index case, school authorities requested cryptosporidium (crypto) as part of the stool ova and parasite examination of all students presenting to the college health center with significant gastroenteritis. Thirteen students submitted stool specimens that were examined for crypto; 7 were positive, and all were from veterinary science students. One of the calves used in the program also tested positive for crypto. All of the students were immunocompetent and recovered uneventfully. The outbreak was contained by strictly enforcing infectious-disease precautions in the calf barn. The authors recommend considering crypto as a cause of gastroenteritis, especially among farm-animal workers, and urge strict infectious disease precautions for those who attend to livestock.

Prevalence and etiology of gastroduodenal ulcer in HIV-positive patients: a comparative study of 497 symptomatic subjects evaluated by endoscopy

OBJECTIVE

In 497 HIV-positive (+) patients with upper digestive tract symptoms, 23 (5%) had gastroduodenal ulcers (GDU) at upper endoscopy.

METHODS

To establish the causes of GDU in this setting, 16 of these patients who had had comprehensive histological evaluation (group I) were compared with 20 HIV+ subjects with upper gastrointestinal symptoms but without ulcer (group II), and with 16 seronegative patients with GDU (group III). Eighty-one percent of group I subjects and 90% of group II patients had C3 AIDS. The presence of gastritis and Helicobacter pylori, fungi, mycobacteria, viruses (especially cytomegalovirus [CMV] and herpes simplex [HSV]), and parasites was determined in all three groups by histopathological and microbiological studies.

RESULTS

The prevalence of chronic active gastritis was 13/16 (81%) in group I, 12/20 (60%) in group II, and 15/16 (94%) in group III. It was associated with H. pylori in group III, and with opportunistic pathogens in groups I and II and with none in group III. H. pylori was detected in 5/16 patients (31%) in group I, in 12/20 (60%) in group II, and 11/16 (69%) in group III. Cytomegalovirus was histologically diagnosed in 8/16 patients (50%) in group I and in 1/20 (5%) in group II. This virus was the only factor shown to be significantly associated with GDU in these cases (p = 0.0046). Cryptosporidium was found in 2/16 (12.5%) patients in group I, in 1/20 (5%) in group II, and in none in group III. Differences between groups I and II were not statistically significant. No other organisms were observed in the three groups.

CONCLUSIONS

Gastroduodenal ulcers were infrequent in HIV+ subjects with upper digestive tract symptoms and CMV was the only organism significantly associated with GDU in HIV+ patients. Among HIV+ patients, H. pylori was an uncommon cause of ulcer. Among HIV+ subjects with ulcer, chronic active gastritis was more common than H. pylori and it was associated with other pathogens. Finally, HIV+ patients with GDU should have endoscopic biopsies to detect opportunistic infections, especially CMV, because H. pylori infection is uncommon.

Human intestinal epithelial cells respond to Cryptosporidium parvum infection with increased prostaglandin H synthase 2 expression and prostaglandin E2 and F2alpha production

Cryptosporidium parvum is an important cause of diarrhea in humans and several animal species. Prostaglandins play a central role in regulating intestinal fluid secretion in animal models of cryptosporidiosis, but their cellular sources and mechanisms of induction are unclear. Here, we show that C. parvum infection directly activates prostaglandin H synthase 2 expression and prostaglandin E2 and F2alpha production in human intestinal epithelial cells.

Cryptosporidium parvum infection of human intestinal epithelial cells induces the polarized secretion of C-X-C chemokines

Cryptosporidium parvum infects intestinal epithelial cells and does not invade deeper layers of the intestinal mucosa. Nonetheless, an inflammatory cell infiltrate that consists of neutrophils and mononuclear cells is often present in the lamina propria, which underlies the epithelium. This study investigated the host epithelial cell response to C. parvum by assessing in vitro and in vivo the expression and production of proinflammatory cytokines by intestinal epithelial cells after infection. The human colon epithelial cell lines HCT-8 and Caco-2 and human intestinal xenografts in SCID mice were infected with C. parvum. The expression and secretion of the C-X-C chemokines interleukin-8 (IL-8) and GROalpha were determined by reverse transcription-PCR analysis and enzyme-linked immunosorbent assay. Our results demonstrate that upregulated expression and secretion of IL-8 and GROalpha after C. parvum infection of intestinal epithelial cells first occurred 16 to 24 h after infection and increased over the ensuing 1 to 2 days. The kinetics of C-X-C chemokine production by C. parvum-infected epithelial cells contrast markedly with the rapid but transient expression of C-X-C chemokines by epithelial cells infected with invasive enteric bacteria. C-X-C chemokine secretion in C. parvum-infected epithelial cells occurred predominantly from the basolateral surface in polarized monolayers of Caco-2 cells grown in Transwell cultures, whereas cell lysis occurred at the apical surface. The basolateral secretion of IL-8 and GROalpha from C. parvum-infected epithelial cells suggests that C-X-C chemokines produced by those cells contribute to the mucosal inflammatory cell infiltrate in the underlying intestinal mucosa.

Diarrheal diseases associated with HIV infection

Diarrhea is a major complication of HIV infection and adversely impacts health care costs, quality of life, and even survival of patients. There is a wide variety of potential causes of diarrhea in HIV-infected patients, and the number of pathogens found continues to increase with time. In addition, there is some controversy concerning the role of some organisms in the pathogenesis of diarrhea and the appropriate diagnostic evaluation of affected patients. This article reviews our current understanding of these pathogens and some of the diagnostic and therapeutic approaches for diarrhea associated with HIV infection.

Cryptosporidiosis: an emerging, highly infectious threat

Cryptosporidium parvum, a leading cause of persistent diarrhea in developing countries, is a major threat to the U.S. water supply. Able to infect with as few as 30 microscopic oocysts, Cryptosporidium is found in untreated surface water, as well as in swimming and wade pools, day-care centers, and hospitals. The organism can cause illnesses lasting longer than 1 to 2 weeks in previously healthy persons or indefinitely in immunocompromised patients; furthermore, in young children in developing countries, cryptosporidiosis predisposes to substantially increased diarrheal illnesses. Recent increased awareness of the threat of cryptosporidiosis should improve detection in patients with diarrhea. New methods such as those using polymerase chain reaction may help with detection of Cryptosporidium in water supplies or in asymptomatic carriers. Although treatment is very limited, new approaches that may reduce secretion or enhance repair of the damaged intestinal mucosa are under study.

Jejunal water and electrolyte transport in human cryptosporidiosis

Cryptosporidiosis may have severe clinical consequences in both immunocompromised and immunocompetent individuals. However, pathophysiological mechanisms that are responsible for diarrhea are poorly understood. We performed jejunal perfusion studies in patients with human immunodeficiency virus-related cryptosporidial diarrhea to measure water and electrolyte transport in vivo. Five patients with human immunodeficiency virus-related cryptosporidiosis and nine healthy volunteers were studied using a triple-lumen steady-state jejunal perfusion technique. Stool volume measurement and distal duodenal biopsy showed that the patients had diarrhea (600-1500 ml/24 hr) and morphological abnormalities of small intestinal mucosa. Net water, sodium, and chloride movement in the jejunum was not significantly different from healthy controls. In these patients with watery diarrhea and morphological mucosal abnormalities, we found no evidence that cryptosporidial diarrhea was due to a secretory state in the proximal small intestine. We conclude that diarrhea may be due to secretion of electrolytes and water efflux more distally or to other abnormalities of gastrointestinal function.

Parasitic diseases in immunocompromised hosts. Cryptosporidiosis, isosporiasis, and strongyloidiasis

Cryptosporidiosis and isosporiasis are intestinal infections caused by the protozoan parasites Cryptosporidium parvum and Isospora belli, respectively. HIV infection and other immunodeficiency diseases predispose human subjects to severe and prolonged cryptosporidiosis. There is also evidence that HIV infection predisposes to chronic isosporiasis. Strongyloidiasis is caused by a nematode worm, Strongyloides stercoralis. Administration of corticosteroids to patients with chronic low-grade S. stercoralis infection can trigger a fulminant, life-threatening form of strongyloidiasis.

The pathogenesis of cryptosporidiosis

Human infection with the protozoan parasite Cryptosporidium parvum has recently emerged as a global public health problem. Although infection is unrelenting in patients classically regarded as immunocompromised, a tantalizing observation is that infection with this parasite results in both acute self-limited as well as chronic diarrhea in young children. Recent data have begun to elucidate multiple potential mechanisms by which parasitism of the intestinal epithelium may yield an intestinal secretory response. However, a central issue for future studies is to understand how Cryptosporidium infection in young children results in such a broad spectrum of clinical presentation. An answer to this question is likely to result through a dual understanding of how systemic or enteric immunity impacts on intestinal secretory responses and how intra-cellular parasitism alters intestinal epithelial cell function and signals the submucosal intestinal compartment. The virulence factors of Cryptosporidium mediating these events need to be identified. Douglas Clark and Cynthia Sears here review the current understanding of the pathogenesis of intestinal secretion in response to Cryptosporidium infection, and discuss key questions requiring additional study.

Cryptosporidium and cryptosporidiosis

The tiny, iodine- and chlorine-resistant protozoan oocysts of Cryptosporidium parvum, long recognized by veterinarians, have become increasingly noted as a cause of watery diarrhea in developed and developing countries throughout the world. For immunocompromised patients, particularly those with AIDS, this diarrhea can be severe and life-threatening. Clovis Martins and Richard Guerrant here discuss the increasing recognition of this important pathogen in immunocompetent patients as well, and outline new challenges to improved water treatment, immunologic and antiparasite chemotherapy.

Intestinal function and injury in acquired immunodeficiency syndrome-related cryptosporidiosis

BACKGROUND/AIMS

The pathogenesis of the diarrhea in acquired immunodeficiency syndrome (AIDS)-related cryptosporidiosis is not known. The hypothesis of this study was that the intestinal dysfunction and injury are related to the number of organisms infecting the intestinal mucosa. The aim of this study was to study the influence of intensity of infection on intestinal function and injury in AIDS-related cryptosporidiosis.

METHODS

In 16 patients with AIDS with intestinal Cryptosporidium infection, the intensity of infection was quantified by counting the total number of fecal oocysts excreted in 24 hours and by determining the percent of duodenal epithelium covered by organisms. Intestinal function was assessed by vitamin B12 absorption and serum D-xylose test. Intestinal injury was assessed by morphology of duodenal mucosa, differential urinary excretion of lactulose and mannitol, and fecal alpha 1-antitrypsin clearance. Measurements were repeated after treatment with paromomycin.

RESULTS

Vitamin B12 and D-xylose absorption negatively correlated with intensity of infection. Villus atrophy occurred only in patients with oocyst excretion of > 10(8) oocyst/24 hours. Lactulose/mannitol urinary excretion ratio showed a positive correlation with intensity of infection. Intestinal function and injury improved in patients whose oocyst counts were reduced by treatment with paromomycin.

CONCLUSIONS

Cryptosporidium infection in patients with AIDS causes malabsorption and intestinal injury in proportion to the number of organisms infecting the intestine.

Temporal changes in permeability and structure of piglet ileum after site-specific infection by Cryptosporidium parvum

BACKGROUND/AIMS

Cryptosporidiosis is an important enteric infection associated with diarrhea in humans. The structural and functional basis for diarrhea is poorly understood. The aim of the study was to determine the structural and functional basis of diarrhea in cryptosporidiosis during evolving host cell-parasite interactions in the intestine.

METHODS

We used the piglet model for temporal studies of alterations in intestinal epithelial structure and function that occurred 12-48 hours postinoculation. Segments of intestine were directly inoculated in vivo, harvested, and studied in vitro using Ussing chamber techniques.

RESULTS

Villus architectural alterations corresponded to the extent of infection. Increased numbers of lamina propria inflammatory cells were evident at 36 hours postinoculation. Solute and macromolecular permeability was not increased. Glucose-responsive short-circuit current was diminished at 48 hours postinoculation. The short-circuit current response to theophylline was the same in control and infected tissues.

CONCLUSIONS

We conclude that passive solute and macromolecular permeability in infected tissues is not significantly increased during parasite-host cell interactions 12-48 hours postinoculation. Electrogenic glucose stimulated Na+ absorption, a function principally of villus absorptive cells, is impaired, and electrogenic Cl- secretion, a function of crypt epithelial cells, remains the same. These findings parallel structural observations that include loss of the Na+/glucose-transporting villus epithelium without loss of crypt epithelium.

Cryptosporidium parvum infection of Caco-2 cell monolayers induces an apical monolayer defect, selectively increases transmonolayer permeability, and causes epithelial cell death

Caco-2 cells were grown on permeable filters and infected with Cryptosporidium parvum. Infection rates exceeded 50% of target cells with a sufficient inoculum dose of parasites. Infection induced a dose- and time-dependent fall in transmonolayer resistance, which was closely related to both the inoculum dose and the number of parasites detected by immunofluorescence. Caco-2a, MDBK, and MDBK subclone F5D2 evidenced similar declines in resistance when grown and infected under similar circumstances. Caco-2 monolayers became permeable to molecules of < or = 1,000 Da but continued to remain impermeable to exogenously added, or endogenously produced, proteins of > or = 1,881 Da. We found that infected monolayers released up to 50% of the total cellular lactase dehydrogenase into apical media, but not basal media, and that the vital dye propidium iodide avidly stained infected cells, and often parasites, when added to the apical reservoir. Cryptosporidium infection of Caco-2 monolayers increases transmonolayer permeability, induces an apical cellular and monolayer defect, and causes cell death.

Blastocystis hominis infection and intestinal injury

Blastocystis hominis is an enteric protozoan associated with clinical illness. To determine the prevalence of intestinal injury in patients with B. hominis infection, the authors prospectively evaluated 18 patients with B. hominis infection by endoscopy and a test of intestinal permeability. Seventeen patients had gastrointestinal symptoms. Colonic mucosa appeared normal by lower endoscopy in 12 of 13 patients, and was friable slightly in 1. Duodenal mucosa was normal by upper endoscopy in nine patients. Pathologic examination of mucosal biopsy specimens did not demonstrate evidence of mucosal invasion. 51Cr-edetic acid (51Cr-EDTA) was given to the 18 patients with stools positive for B. hominis and to 32 healthy control subjects. Approximately 100 uCi of 51Cr-EDTA was given orally after an overnight fast, and urine was collected for the following 24 hours. Mean 24-hour urinary excretion of 51Cr-EDTA, calculated as a percent of the administered dose, was 1.31% (0.34-2.76%) in patients with B. hominis infection and 1.99% (0.59-3.48%) in the control subjects. The intestinal permeability to 51Cr-EDTA in blastocystis-infected individuals was not increased, but was decreased significantly compared with healthy subjects (p < 0.005). Therefore, in a group of symptomatic patients with B. hominis infection, endoscopy typically did not show evidence of significant intestinal inflammation, and results of intestinal permeability testing with 51Cr-EDTA did not suggest impaired barrier function of the intestinal mucosa. The clinical literature on B. hominis infection and intestinal injury is reviewed.