Cryptosporidiosis in tourists returning from the Caribbean

Emerging Causes of Traveler's Diarrhea: Cryptosporidium, Cyclospora, Isospora, and Microsporidia

Travel is a risk factor for acquiring infection with a spore-forming protozoa: Cryptosopridium, Cyclospora, Microsporidia, and Isospora. Certain travel destinations have a high disease burden and intense exposure. Patients present with persistent diarrhea and a history of recent travel to a developing country in the tropics. Very mild infections may be underdiagnosed and may cause typical traveler's diarrhea. In a patient with a history of travel and persistent diarrhea unresponsive to the usual antibiotic and antidiarrhea treatment, stool studies for all four of these protozoa infections should be performed. If immune status is normal and the disease is mild, symptomatic therapy may suffice. Effective treatment is available for Cyclospora, Microsporidia, and Isospora.

Intestinal parasites

Although safe and efficacious broad-spectrum antiparasitic drugs have been developed, their availability for use in mass-treatment programs and for individual treatment worldwide can be limited by economic resources, existing manufacturing and distribution networks, and national regulations. Increasing population density, environmental pollution with human waste products, and global migration patterns will continue to promote transmission of human intestinal parasites in the foreseeable future because untreated or incompletely treated infected individuals can serve as roving reservoirs of infection for long-lived parasites. Asking primary care patients about possible geographic exposures and activities associated with an increased likelihood of intestinal parasite infection is an important part of the medical history. Many intestinal parasites can be treated effectively with oral medications, and treatment relatively early in the course of infection may prevent development of disease associated with chronic infections.

Parasites and Diarrhea. I: Protozoans and Diarrhea

Intestinal parasitism is extremely common, with approximately 70% of all people harboring one or more intestinal parasite. Parasitism and diarrhea are both hyperendemic in areas where sanitation is suboptimal. Many clinicians assume that the identification of intestinal parasites in patients with diarrhea implies that the parasites are the cause. This approach is frequently misguided. Some intestinal parasites such as Giardia lamblia and Entamoeba histolytica certainly do cause diarrhea. Others, for example Entamoeba coli and Ascaris lumbricoides, almost certainly do not. In addition, there are a number of other organisms that have been associated with diarrheal illness in some cases, which may or may not be important pathogens. In this article, we will review the role of protozoans as definite and possible causes of diarrhea. In Part II, we review the role of helminths in diarrhea.

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.

Duodenal morphology and intensity of infection in AIDS-related intestinal cryptosporidiosis

BACKGROUND

The pathogenesis of intestinal cryptosporidiosis is not known. Previous studies have shown that the intensity of infection varies between patients. The hypothesis of this study is that intestinal injury is related to the intensity of infection.

METHODS

The histological abnormalities associated with Cryptosporidium infection were evaluated in duodenal biopsy specimens from 18 patients with acquired immunodeficiency syndrome-associated cryptosporidiosis. The intensity of Cryptosporidium infection was assessed histologically in all patients as the percentage of mucosa covered by organisms and by quantitation of oocyst excretion in the stools of 14 patients.

RESULTS

Duodenal biopsy specimens from 13 patients (72%) showed normal villous architecture. In these patients, the inflammatory component of the lamina propria was either normal or moderately increased. This increase consisted mostly of lymphocytes and plasma cells. Five of 18 patients (28%) had flattening of the mucosa associated with a prominent neutrophilic infiltrate. The intensity of infection in patients with villous flattening as measured from biopsy specimens and stool was significantly higher than in those without flattening (92% vs. 12% mucosa occupied with organisms; 738 x 10(3) vs. 199 x 10(3) oocyst/mL stool) (P < 0.004 in both cases).

CONCLUSIONS

Most patients with intestinal Cryptosporidium infection had normal duodenal villous architecture. Severe duodenal morphological abnormalities, including flattening of the villi, were associated with high-intensity infections.

Intestinal parasites in returned travelers

Travelers returning from third-world countries may become infected with a variety of intestinal parasites. Although protozoan infections are more frequently seen, intestinal worms are also encountered. If considered in the differential diagnosis, these infections usually are readily diagnosed and treated.

Travelers' diarrhea. Prevention and treatment

Travelers' diarrhea affects almost half of all travelers from developed to developing nations. Its occurrence frequently alters planned activities. Enterotoxigenic Escherichia coli and other bacterial pathogens endemic to the area visited account for the majority of pathogens isolated. Newer research technologies are assisting in defining virulence properties and epidemiologic characteristics. Prudence exercised during travel remains the preferred mode of prevention, reserving antimicrobial prophylaxis for specific situations. Oral rehydration and early pharmacologic intervention with antimicrobial and antimotility agents significantly decrease length of illness when diarrhea occurs.

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.

Effects of time and watershed characteristics on the concentration of Cryptosporidium oocysts in river water

Water samples were collected from four locations on two rivers in Washington State and analyzed by membrane filtration-immunofluorescence assay to establish Cryptosporidium oocyst concentrations. Sampling locations were selected to evaluate effects of watershed character, from pristine mountain to downstream agricultural, on oocyst concentrations. Samples were collected at six biweekly intervals from late June to early September, with two additional sets of five samples taken on separate days (one set taken at bihourly intervals and one set taken simultaneously). Cryptosporidium oocysts were found in 34 of 35 samples at concentrations ranging from about 0.2 to 65 oocysts per liter. Oocyst concentrations were highest early in the sampling period, when they were influenced by postrainfall runoff, and decreased through the summer months. Oocyst concentrations found in ten samples collected on two days (5 samples per day) showed no short-term variations. Oocyst concentrations and oocyst production per square mile (ca. 2.6 km2) of watershed found in water draining a controlled public water supply watershed were the lowest observed. The concentrations and production rates for drainage from an adjacent, comparable, but uncontrolled watershed were nearly 10 times higher. The concentration and production rates of the downstream area influenced by dairy farming were nearly 10 times higher than rates at the upstream stations. The data showed clearly that oocyst concentrations were consistently observed above the detection limit of the analytical method, about 0.1 oocysts per liter; that oocyst concentrations were continuous as opposed to intermittent; and that watershed character and management affected surface water oocyst concentrations significantly.

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.

Epidemiological aspects of human cryptosporidiosis

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

A two-year survey of the incidence of heat-labile enterotoxin-producing Escherichia coli and other enteric pathogens in travellers returning to the Sheffield area

A case-controlled study of the incidence of heat-labile enterotoxin-producing Escherichia coli (LT+ETEC) and other enteric pathogens in travellers returning to the Sheffield area was conducted from May 1984 to April 1986. LT+ETEC were found in 35 (5.8%) of 600 travellers to developed countries (mainly popular Mediterranean holiday resorts), 36 (11.3%) of 320 travellers to less-developed countries, and 11 (0.9%) of 1282 control patients whose illness was not associated with recent travel abroad. A seasonal peak of LT+ETEC infection was observed only in travellers to developed countries, with infections being significantly commoner in August to October. There was no significant deviation from expected age/sex distribution of LT+ETEC infection. Strains of LT+ETEC from travellers produced more toxin than strains from control patients, strains from travellers to less-developed countries producing most of all.

Cryptosporidiosis in perspective

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

Cryptosporidium species, a protean protozoan

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Detection of Cryptosporidium in water by using polypropylene cartridge filters

Members of the genus Cryptosporidium are protozoan parasites that cause gastroenteritis in humans and animals and appear to be spread largely by the fecal-oral route. A method was developed for the concentration and detection of Cryptosporidium oocysts in water to assess their occurrence in the environment and potential for waterborne disease transmission. This method was developed by using spun polypropylene cartridge filters. Optimal conditions for concentration, filter elution, filter porosity, and detection were determined. Fluoresceinated monoclonal antibodies were used for oocyst detection. Experiments also were conducted to study the effect of flow rate, low oocyst numbers, and the addition of detergents on recovery and retention of oocysts. The method that was developed was sensitive enough to detect oocysts at levels of less than 1 per liter. Using this method, we isolated Cryptosporidium oocysts from secondarily treated sewage.

Parasitic diseases of the small intestinal tract

The epidemiology, clinical aspects, and treatment of human intestinal infections with Giardia, Cryptosporidium, coccidia and Strongyloides in industrialized countries are reviewed. In well-nourished and immunocompetent persons, inapparent infections or mild, transitory gastrointestinal upsets caused by these parasites are quite common. Some patients develop severe symptoms, such as profuse diarrhoea, dehydration, stool irregularities for weeks or months followed by weight loss and malabsorption of fat, vitamins and iron. In patients receiving immunosuppressive treatment or with lymphotropic viral infections, Cryptosporidium and Strongyloides can cause life-threatening or debilitating disease. By autoinfection or external reinfection these parasites can persist in the intestine for years. Clinicians should consider such infections in immigrants, travellers and former servicemen, even long after their stay in endemic areas, and also in the handicapped and children in day-care centres.

Cryptosporidium spp. and cryptosporidiosis

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Quantification of specific antibody response to Cryptosporidium antigens by laser densitometry

Cryptosporidium spp. is a protozoan parasite with worldwide distribution associated with diarrhea in immunocompromised patients (particularly those with acquired immunodeficiency syndrome [AIDS]) and in immunocompetent humans. Immunoglobulin M (IgM) and IgG antibody responses are readily detected by an enzyme-linked immunosorbent assay. To determine which Cryptosporidium antigens invoke antibody responses in humans, we performed polyacrylamide gel electrophoresis using purified oocysts, followed by Western blots with human sera from various populations. Of 40 sera from persons with cryptosporidiosis (24 AIDS and 16 non-AIDS patients), in 37 (93%) a 23,000-dalton antigen measured quantitatively by laser densitometry was recognized. Of 63 sera from IgM- or IgG-positive individuals, as determined by enzyme-linked immunosorbent assay, in 58 (92%) this same antigen was recognized. Up to three additional bands between 125,000 and 175,000 daltons were identified by some of these sera. These results suggest that most persons infected with Cryptosporidium spp. produce antibodies which recognize at least one common low-molecular-weight antigen. Isolation of this antigen will be useful in development of diagnostic tests and may be important in the study of immunity.