Endemic Cryptosporidium and Giardia lamblia infections in a Thai orphanage

Co-infection risk assessment of Giardia and Cryptosporidium with HIV considering synergistic effects and age sensitivity using disability-adjusted life years

Co-infection with multiple pathogens, especially the spread of Giardia and Cryptosporidium in source water among those with immunodeficiency, is common worldwide, which will result in an increase in overall risk. In this study, the quantitative microbial risk assessment model was used to estimate the cumulative risk of co-infection with Giardia and Cryptosporidium promoted by HIV, considering age sensitivity. The sensitivity of population segments with different ages was estimated by the optimization method, based on clinical data of cryptosporidiosis and giardiasis with age structure. The factors of co-infection enhancement were used to quantify HIV synergism with the action of other pathogens. The removal rates of Giardia and Cryptosporidium through water treatment were estimated by a model involving turbidity and particles. The results showed that children (0-4 years) were 17.911-fold more sensitive to infection with Giardia than adults (15-64 years), and that with Cryptosporidium was 10.592-fold. Removal rates of these parasites in water treatment plants in major cities in China were estimated to be 2.03 log₁₀. Considering the HIV-synergistic and age-susceptibility effects, the cumulative risk of exposure to Giardia or Cryptosporidium was about 38.781 × 10^-6DALYs (Disability-adjusted life years) per person per year, which was much higher than the reference risk level recommended by the World Health Organization (10^-6DALYs). The methodology and results of this study will be useful in better evaluating and reducing the burden due to infection of Giardia and/or Cryptosporidium in China and other countries.

Persistent Occurrence of Cryptosporidium hominis and Giardia duodenalis Subtypes in a Welfare Institute

Few data are available on the transmission dynamics of intestinal protozoa in children in welfare institutes. In this study, fecal specimens were collected from 396 children in a welfare institute in Shanghai, China during December 2011 (207 specimens), June 2012 (78 specimens), and September 2013 (111 specimens), and examined for Cryptosporidium spp., Giardia duodenalis, and Enterocytozoon bieneusi by PCR analysis of the small subunit rRNA, triosephosphate isomerase, and internal transcribed spacer genes, respectively. The Cryptosporidium hominis and G. duodenalis assemblage A identified were further subtyped by multilocus sequence typing. Altogether, Cryptosporidium was detected in 39 (9.8%) children, with infection rates of 11.6% (24/207), 9.0% (7/78), and 7.2% (8/111) in December 2011, June 2012, and September 2013, respectively. Infection rates were higher in children of 0-12 months (20.4% compared to 0-7.3% in other age groups, P = 0.0001) and those with diarrhea (17.9% compared to 7.7% in those with no diarrhea, P = 0.006). In contrast, G. duodenalis was detected in 161/396 (40.7%), with infection rates of 48.3% (100/207), 35.9% (28/78), and 29.7% (33/111) in December 2011, June 2012, and September 2013, respectively. There were no significant gender- or diarrhea-associated differences, but the G. duodenalis infection rate in children of 13-24 months (50%) was significantly higher than in the age groups of 0-12 months and > 48 months (29.8-36.5%, P = 0.021). Co-infection of Cryptosporidium and G. duodenalis was seen in 19 (4.8%) children, but no E. bieneusi infection was detected in this study. All Cryptosporidium-positive specimens belonged to the subtype IaA14R4 of C. hominis, while all G. duodenalis-positive specimens belonged to sub-assemblage AII. Both were the same subtypes in a previous outbreak of cryptosporidiosis and giardiasis in a hospital ward hosting children from the welfare institute. Results of the study indicate that there was a persistent occurrence of limited C. hominis and G. duodenalis subtypes in the small enclosed community, with differences in age distribution and association with diarrhea occurrence between cryptosporidiosis and giardiasis.

Natural History of Cryptosporidiosis in a Birth Cohort in Southern India

In an Indian birth cohort, we demonstrate a high and early burden of cryptosporidiosis by polymerase chain reaction and serology. Reinfection was common and infections clustered in a subset of children. Prior infection provided some protection against subsequent infection, but not disease.

Background.

Cryptosporidium is a leading cause of moderate to severe childhood diarrhea in resource-poor settings. Understanding the natural history of cryptosporidiosis and the correlates of protection are essential to develop effective and sustainable approaches to disease control and prevention.

Methods.

Children (N = 497) were recruited at birth in semiurban slums in Vellore, India, and followed for 3 years with twice-weekly home visits. Stool samples were collected every 2 weeks and during diarrheal episodes were tested for Cryptosporidium species by polymerase chain reaction (PCR). Serum samples obtained every 6 months were evaluated for seroconversion, defined as a 4-fold increase in immunoglobulin G directed against Cryptosporidium gp15 and/or Cp23 antigens between consecutive sera.

Results.

Of 410 children completing follow-up, 397 (97%) acquired cryptosporidiosis by 3 years of age. PCR identified 1053 episodes of cryptosporidiosis, with an overall incidence of 0.86 infections per child-year by stool and serology. The median age for the first infection was 9 (interquartile range, 4–17) months, indicating early exposure. Although infections were mainly asymptomatic (693 [66%]), Cryptosporidium was identified in 9.4% of diarrheal episodes. The proportion of reinfected children was high (81%) and there was clustering of asymptomatic and symptomatic infections (P < .0001 for both). Protection against infection increased with the order of infection but was only 69% after 4 infections. Cryptosporidium hominis (73.3%) was the predominant Cryptosporidium species, and there was no species-specific protection.

Conclusions.

There is a high burden of endemic cryptosporidiosis in southern India. Clustering of infection is suggestive of host susceptibility. Multiple reinfections conferred some protection against subsequent infection.

A cysteine protease inhibitor rescues mice from a lethal Cryptosporidium parvum infection

Cryptosporidiosis, caused by the protozoan parasite Cryptosporidium parvum, can stunt infant growth and can be lethal in immunocompromised individuals. The most widely used drugs for treating cryptosporidiosis are nitazoxanide and paromomycin, although both exhibit limited efficacy. To investigate an alternative approach to therapy, we demonstrate that the clan CA cysteine protease inhibitor N-methyl piperazine-Phe-homoPhe-vinylsulfone phenyl (K11777) inhibits C. parvum growth in mammalian cell lines in a concentration-dependent manner. Further, using the C57BL/6 gamma interferon receptor knockout (IFN-γR-KO) mouse model, which is highly susceptible to C. parvum, oral or intraperitoneal treatment with K11777 for 10 days rescued mice from otherwise lethal infections. Histologic examination of untreated mice showed intestinal inflammation, villous blunting, and abundant intracellular parasite stages. In contrast, K11777-treated mice (210 mg/kg of body weight/day) showed only minimal inflammation and no epithelial changes. Three putative protease targets (termed cryptopains 1 to 3, or CpaCATL-1, -2, and -3) were identified in the C. parvum genome, but only two are transcribed in infected mammals. A homology model predicted that K11777 would bind to cryptopain 1. Recombinant enzymatically active cryptopain 1 was successfully targeted by K11777 in a competition assay with a labeled active-site-directed probe. K11777 exhibited no toxicity in vitro and in vivo, and surviving animals remained free of parasites 3 weeks after treatment. The discovery that a cysteine protease inhibitor provides potent anticryptosporidial activity in an animal model of infection encourages the investigation and development of this biocide class as a new, and urgently needed, chemotherapy for cryptosporidiosis.

Serum IgG responses and seroconversion patterns to Cryptosporidium gp15 among children in a birth cohort in south India

The correlates of protective immunity to cryptosporidiosis are not well understood. This study was conducted to assess the effect of maternal serum IgG against Cryptosporidium gp15 on responses to this antigen in children with (cases) and without (controls) PCR-confirmed cryptosporidial diarrhea. Maternal sera (n = 129) and sera from cases (n = 39) and controls (n = 90) collected at 3.5, 9, and 24 months of age were tested for serum IgG against Cryptosporidium gp15 by enzyme-linked immunosorbent assay (ELISA). Seroconversion patterns were evaluated by estimating probabilities of seroconversion along three time points based on the transition pathways by using a first-order Markov chain process and empirical Bayesian estimates. There was no difference in serum IgG levels or seropositivity rates to gp15 between cases and controls across all time points in children or in IgG levels to this antigen between mothers of cases and controls. The most common transition pathway can be described as a seronegative child at 3.5 months who seroconverts at 9 months and remains seropositive at 24 months. This pattern remained stable irrespective of the serological status of the mother or the case or control status of the child. Children were most likely to be exposed to Cryptosporidium for the first time between the ages of 3 and 9 months, and most of the children seroconverted by 24 months. The high degree of seroconversion among control children is suggestive of high rates of asymptomatic transmission in this region.

Serum antibody responses to polymorphic Cryptosporidium mucin antigen in Bangladeshi children with cryptosporidiosis

Cryptosporidium is a significant cause of diarrheal disease in children in developing countries. The sporozoite antigen Muc4 is important for infection of host cells, and could be a candidate vaccine antigen. However, this antigen is polymorphic between Cryptosporidium hominis and C. parvum. We investigated antibody responses to C. hominis Muc4 and C. parvum Muc4 antigen in children in Bangladesh infected with C. hominis. Antibody responses were compared between children with cryptosporidial diarrhea (cases) and uninfected children with diarrhea (controls). There was a significant IgM response to Muc4 from both species in cases compared with controls, which increased over time, and was higher in children with persistent diarrhea. Despite sequence polymorphisms, antibody responses to C. hominis Muc4 and C. parvum Muc4 were significantly correlated. These results suggest that the human antibody response to Muc4 is cross-reactive between species, but in young children does not mature to an IgG response within the period observed in this study.

Recognition and prevention of hospital-associated enteric infections in the intensive care unit

The objectives of this article were to review the causes and extent of hospital-associated infectious diarrhea and associated risks in the general hospital ward and intensive care unit (ICU), to compare microorganisms with similar symptoms to aid in recognition that will lead to timely and appropriate treatment and control measures, and to propose infection prevention protocols that could decrease human process errors in the ICU. This literature review describes epidemiology, comparison of microbial characteristics for potential hospital-associated enteric pathogens, diagnosis, and prevention, especially if important in the ICU, and particularly in regard to Clostridium difficile. Enteric organisms that most commonly cause hospital-associated infectious diarrhea in acute care settings and the ICU are C. difficile, rotavirus, and norovirus, although others may also be important, particularly in developing countries. To recognize and control infectious diarrhea successfully in the ICU, intensivists should be aware that epidemiology, risks, and prevention measures may differ between these microorganisms. In addition, intensivists should be ready to implement systems changes related to notification, isolation precautions and prevention, and environmental cleaning in the ICU.

Polymorphic mucin antigens CpMuc4 and CpMuc5 are integral to Cryptosporidium parvum infection in vitro

Cryptosporidium, a waterborne enteric parasite, is a frequent cause of diarrheal disease outbreaks worldwide. Thus far, the few antigens shown to be important for attachment to and invasion of the host cell by Cryptosporidium are all mucin-like glycoproteins. In order to investigate other antigens that could be important for Cryptosporidium host-parasite interactions, the Cryptosporidium genome databases were mined for other mucin-like genes. A single locus of seven small mucin sequences was identified on chromosome 2 (CpMuc1 to -7). Reverse transcriptase PCR analysis demonstrated that all seven CpMucs were expressed throughout intracellular development. CpMuc4 and CpMuc5 were selected for further investigation because of the significant sequence divergence between Cryptosporidium parvum and C. hominis alleles. Rabbit anti-CpMuc5 and -CpMuc4 antibodies identified several polypeptides in C. parvum lysates, suggestive of proteolytic processing of the mucins. All polypeptides were larger than the predicted molecular weight, which is suggestive of posttranslational processing, most likely O-glycosylation. In immunofluorescence assays, both anti-CpMuc4 and -CpMuc5 antibodies reacted with the apical region of sporozoites and revealed surface-exposed epitopes. The antigens were not shed during excystation but did partition into the aqueous phase of Triton X-114 extractions. Consistent with a role in attachment and invasion, CpMuc4 and CpMuc5 could be detected binding to fixed Caco-2A cells, and anti-CpMuc4 peptide antibodies inhibited Cryptosporidium infection in vitro. Sequencing of CpMuc4 and CpMuc5 from C. hominis clinical isolates identified several polymorphic alleles. The data suggest that these antigens are integral for Cryptosporidium infection in vitro and may be potential vaccine candidates.

Prevalence and molecular characterization of human and bovine Cryptosporidium isolates in Thailand

This study was performed to determine the prevalence and genotypes of Cryptosporidium species among HIV patients and cattle in Thailand. Stool specimens were collected from 46 HIV patients from Prabat Nampu Temple, Lop Buri Province in central Thailand. Two hundred fecal samples from dairy cattle were collected from seven farms in Chon Buri Province, the eastern part of Thailand. Each sample was concentrated by Sheather's sucrose flotation technique and stained by acid fast stain (AFS) for the identification of oocysts by microscopy. All HIV stool samples and 83 fecal specimens from cattle were further tested using nested polymerase chain reaction (PCR) targeting the 18S SSUrRNA gene to characterize the detected species. In HIV patient samples, the detection rate was 28.7% by AFS and 4.35% by nested PCR. In cattle samples, the detection rate was 13% by AFS and 9.63% by nested PCR. After DNA sequencing results, we identified the genotypes of the Cryptosporidium from seven of the PCR positive samples. All were found to be C. parvum. The findings presented here represent the first genetic identification of Cryptosporidium species in cattle in Thailand.

Environmental risk factors for Cryptosporidium infection in an island from Western Venezuela

Few investigations have been conducted on risk factors for Cryptosporidium infection in communities from developing countries. A study was conducted to determine the prevalence and risk factors for cryptosporidiosis in San Carlos island, Venezuela. A sample of 515 subjects (mean age +/- SD: 21.4 +/- 17.8 years) was surveyed. Single fecal specimens were collected and modified Ziehl-Neelsen carbolfuchsin staining of formalin-ether concentrate stools were examined for identification of the parasite. Infections with Cryptosporidium (67 of 515, 13%) were common. Prevalence of the parasite varied among sectors of the community; 34 of 67(50.7%) cases of cryptosporidiosis clustered in two sectors with extreme poverty. Variables strongly associated with a higher risk for the infection (p < 0.01) were residing in these sectors versus the remainder, living in a hut or small residence versus a brick or larger house, using an area of backyard rather than a toilet or latrine for defecation, and having contact with soil contaminated with human feces. Crowding was also a risk (p < 0.05). Contact with human feces contaminated-soil may be an important mode of transmission and poverty a predisposing factor for the infection.

A rapid method for extracting oocyst DNA from Cryptosporidium-positive human faeces for outbreak investigations

We describe a rapid method for extracting and concentrating Cryptosporidium oocysts from human faecal samples with subsequent DNA preparation for mainstream PCR applications. This method consists of extracting faecal lipids using a modified water-ether treatment and releasing DNA from semi-purified oocysts by freeze thawing in lysis buffer. Following immunomagnetisable separation (IMS), recovery rates of 29.5%, 43.2% and 49.8% were obtained from oocyst-negative solid, semi-solid and liquid faeces, respectively, seeded with 100 +/- 2 C. parvum oocysts, which were enumerated by flow cytometry. A retrospective analysis was conducted on 92 positive human faecal samples including 78 oocyst-positive cases from 2 UK cryptosporidiosis outbreaks (outbreak A = 34 samples, outbreak B = 44 samples) and 14 oocyst-positive, sporadic cases. We used primers targeting the Cryptosporidium oocyst wall protein gene (COWP; STN-COWP), the 18S rRNA (direct PCR) and the dihydrofolate reductase gene (dhfr, MAS-PCR) fragments to evaluate extracted DNA by PCR. PCR inhibitors were present in 20 samples when template was co-amplified with the 18S rRNA gene primers and an internal control. Template dilution (1/5) in polyvinylpyrrolidone (10 mg ml(-1), pH 8.0) transformed four PCR-negative samples to PCR-positive and increased amplicon intensity in previously positive samples. Eighteen of 20 PCR-negative samples produced visible amplicons when Taq polymerase concentration in the STN-COWP PCR was increased from 2.5 to 5 U. The STN-COWP PCR assay amplified 90 of 92 samples (97.8%) and the MAS-PCR assay amplified 70 of 92 samples (76.1%) tested. In the absence of inhibitors, DNA equivalent to 3 C. parvum oocysts was amplified.

Longitudinal analysis of cryptosporidium species-specific immunoglobulin G antibody responses in Peruvian children

Cryptosporidium species are ubiquitous in the environment and are frequently detected in the stools of children who live where sanitation conditions are poor. To better characterize the immune response to these parasites, we monitored immunoglobulin G (IgG) antibody levels in a cohort of children from Lima, Peru. Two new enzyme-linked immunosorbent assays based on the C. parvum (bovine, subtype IIa) Iowa strain 17-kDa and 27-kDa antigens were used to measure IgG antibody levels in longitudinal serum samples. Antibody responses were detected during infections with C. parvum, C. felis, and C. meleagridis and with four different subtypes of C. hominis. We also noted that the magnitude of the antibody response was related to the number of previous infections and that older children generally had higher levels of antibodies to the two C. parvum antigens. Antibody responses were not associated with infections with either Cyclospora sp. or Giardia sp. We believe the antibody assays will be important tools for monitoring the success of future public health interventions.

Epidemiology and clinical features of Cryptosporidium infection in immunocompromised patients

Cryptosporidium spp. are a major cause of diarrheal disease in both immunocompetent and immunodeficient individuals. They also cause waterborne disease in both the United States and United Kingdom. Studies on the mechanisms of immunity to cryptosporidiosis indicate the importance of the T-cell response. The spectrum and severity of disease in immunocompromised individuals with cryptosporidiosis reflect this importance since the most severe disease is seen in individuals with defects in the T-cell response. The most commonly studied group is that of patients with AIDS. These patients suffer from more severe and prolonged gastrointestinal disease that can be fatal; in addition, body systems other than the gastrointestinal tract may be affected. The widespread use of antiretroviral therapy does appear to be having a beneficial effect on recovery from cryptosporidiosis and on the frequency of infection in human immunodeficiency virus-positive patients. Other diseases that are associated with increased risk of severe cryptosporidiosis, such as primary immunodeficiencies, most notably severe combined immunodeficiency syndrome, are also predominantly associated with T-cell defects. Of the remaining groups, children with acute leukemia seem to be most at risk from cryptosporidiosis. There is less evidence of severe complications in patients with other malignant diseases or in those receiving immunosuppressive chemotherapy.

Cryptosporidiosis in Kuwaiti children: seasonality and endemicity

OBJECTIVE

To detect the incidence of cryptosporidial infection in children presenting with gastrointestinal symptoms at the local hospital in Kuwait.

METHODS

Over a period of 3 years, September 1995 to August 1997, a single fecal sample from 3549 children was analyzed by modified saframin-methylene blue (SM-B) staining and a direct immunofluorescence test for the presence of Cryptosporidium oocysts.

RESULTS

Cryptosporidium oocysts were detected in 51 (10%) children with diarrhea. Prevalence was highest (73%) in children > 2 years of age compared with children < 2 years of age. The maximum number of cases, 38 of 51 (75%), was seen during the months January to April, indicating a marked seasonal variation. Polyparasitism was common in children with diarrhea; however, 43 of the 51 (84%) children with cryptosporidiosis had cryptosporidium infection only. Blastocystis hominis and Endolimax nana were the most common parasites detected (38% and 15%, respectively). Forty-seven of the 51 (90%) children with cryptosporidiosis were Kuwaiti and gave no history of travel abroad, suggesting that the infection was acquired indigenously. Sociodemographic information on children with cryptosporidiosis suggests three possible modes of transmission of infection: drinking contaminated water stored in overhead water tanks, person to person, or contact with infected animals.

CONCLUSION

In this study, we observed water-borne transmission of cryptosporidium infection in children with diarrhea. The infection is seasonal and endemic.

Cryptosporidium infection in Bedouin infants assessed by prospective evaluation of anticryptosporidial antibodies and stool examination

An enzyme-linked immunosorbent assay system using oocyst lysate as antigen was used to detect serum- specific antibody responses to Cryptosporidium parvum between 1989 and 1994 in consecutive sera obtained at birth, and at the age of 6, 12, and 23 months, from 52 infants living in a Bedouin town located in the south of Israel. The serologic tests revealed high levels of immunoglobulin G anti-Cryptosporidium at birth that dropped significantly by the age of 6 months and then rose continuously to a geometric mean titer of 481 at age 23 months. The serum immunoglobulin M Cryptosporidium antibodies rose continuously from nearly undetectable levels at birth to a geometric mean titer of 471 (157-fold increase) at age 23 months. All the subjects already showed at 6 months a significant rise in immunoglobulin M. A significant rise in immunoglobulin A titers was detected in 48% and 91% of subjects at 6 and 23 months, respectively. By monthly surveillance, microscopy using the modified Ziehl-Neelsen method and confirmed by indirect immunofluorescence assay detected Cryptosporidium antigens in only 11% at age 6 months and 48% at age 23 months. The extent of exposure to Cryptosporidium immediately after birth as detected by serology is much higher than that predicted by frequent prospective assessment of stool samples.

[Giardiasis and cryptosporidiosis in day-care centers in the municipality Campinas SP]

The prevalence of the Giardia duodenalis and Cryptosporidium parvum infections were studied in children 2-60 months old (n = 310) grouped to sex and age, enrolled in 8 day-care centers. Giardiasis was found in 42 (13.5%) of the children and, was most frequent in the age group corresponding to 19-24 months old although children at the first six months of life also presented positive faecal samples. Statistical analysis indicated no association between sex (p > 0.05) and prevalence for Giardia infection. C. parvum was detected in 20 (6.4%) of the children. Children seven to twelve months old showed the greatest prevalence of this parasite. There were not oocysts in the stools from the children 25-30 months and from those older than 36 months. Oocytes were detected in 4 children from the 0-6 months old group. There was no significative difference on sex (p = 0.09) and day-care-facility (p = 0.068) for C. parvum infection while age was associated with infection (p = 0.004). Epidemiological aspects were studied by familiar inquiry, by parasitological examinations of stools from the contact-members of each case and from animals present at the residence. Prevalence for C. parvum was higher when at least one of the parents was a professional in the Human Health Centers (73.6% positives), when there was report of concomitant disease (52.6% positives) and when diarrhoea was the main symptom at the collection of the faecal specimens (78.9% positives). Faecal examinations of the domestic animals were negatives for these two parasites.

Seroepidemiology of cryptosporidiosis in children in Papua New Guinea and Australia

Enzyme immunoassays (EIA) were used to measure serum antibodies to Cryptosporidium in four immunocompetent adults with recent proven cryptosporidial infection, 379 healthy children and 73 adult volunteers in Melbourne, Australia, and 205 children in Papua New Guinea (PNG) (47 healthy children; 158 with pneumonia). Antibodies peaked 3-6 weeks after infection and fell to baseline within a few months. A high level (5000 EIA units/ml) or a significant change between paired sera, of IgG or IgM, were taken as evidence of recent infection and found in 24% of PNG children and in 8% of children and 5% of adults in Melbourne. Among PNG children with pneumonia who had high cryptosporidial antibody levels, those with measles (6/8) were significantly more likely (P = 0.002) to have diarrhoea than the remainder (4/28). Symptomatic cryptosporidiosis may be associated with transient immune suppression due to viral infection. This study indicates that serological surveys can contribute to an understanding of the epidemiology of cryptosporidosis.

Severe cryptosporidiosis in children with normal T-cell subsets

Though Cryptosporidium spp. is considered to cause only a self-limiting illness in immunocompetent children, data from Guinea Bissau suggest that cryptosporidiosis may be a significant cause of deaths in developing countries. An impaired cellular immune function could explain the severe course of cryptosporidiosis in these children. We therefore investigated in a community study whether pre-infectious CD4/CD8 status had an impact on incidence and severity of cryptosporidiosis. Of 168 children below two years of age 21 experienced Cryptosporidium-infection within 156 days after blood sampling, but no tendencies of pre-infectious impaired cellular immune function was found in the cases compared with controls, nor did nine children who acquired persistent diarrhoea or three who died have impaired CD4/CD8 status.

Epidemiology of equine Cryptosporidium and Giardia infections

Prevalence and infection patterns of Cryptosporidium and Giardia infections in horses were studied by a direct immunofluorescence staining method. Faecal examinations of 222 horses of different age groups revealed Cryptosporidium infection rates of 15-31% in 66 foals surveyed in central Ohio, southern Ohio and central Kentucky, USA. Only 1 of 39 weanlings, 0 of 46 yearlings, and 0 of 71 mares were positive. Giardia infection was found in all age groups, although the infection rates for foals were higher (17-35%). Chronological study of infection in 35 foals showed that foals started to excrete Cryptosporidium oocysts between 4 and 19 weeks and Giardia cysts between 2 and 22 weeks of age. The cumulative infection rates of Cryptosporidium and Giardia in foals were each 71%. Some foals were concurrently infected with both parasites and excretion of oocysts or cysts was intermittent and long-lasting. The longest duration of excretion was 14 weeks for Cryptosporidium and 16 weeks for Giardia. Excretion of Cryptosporidium oocysts stopped before weaning, while excretion of Giardia cysts continued thereafter. Infected foals were considered the major source of Cryptosporidium infection in foals, whereas infected mares were deemed the major source of Giardia infection in foals. The high infection rate of Giardia in nursing mares suggested a periparturient relaxation of immunity. The results indicated that Cryptosporidium and Giardia infections are common in horses.

Pathways to the impairment of human nutritional status by gastrointestinal pathogens

Gastrointestinal pathogens are of three varieties, those that can, and often do, take the life of the host, those that infect transiently and rarely are life-threatening, and those (parasites) that establish a relatively prolonged residence or colonization of the host's alimentary tract. In the case of the second form, if infections are recurrent, both catabolic effects during the episode and failure to digest foods and/or absorb nutrients results. Similarly, catabolic wastage through activation of the acute phase response, and interference with the host's acquisition of nutrients by maldigestion, malabsorption, intestinal losses and competition with the parasite burden can impair growth and nutrition with helminthic infections. Growth and nutrition with respect to all of the macronutrients and virtually all of the micronutrients have been documented to be adversely affected by gastrointestinal pathogens. For its burgeoning importance as a worldwide health problem, both with the HIV virus as a direct intestinal pathogen and with the opportunistic gut infections occurring in the immunocompromised host, AIDS represents the emerging context of the impairment of nutritional status by intestinal pathogens.

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.

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.