Intra-isolate variation of Cryptosporidium parvum small subunit ribosomal RNA genes from human hosts in England

Genetic diversity of Cryptosporidium spp. within a remote population of Soay Sheep on St. Kilda Islands, Scotland

This is the first report to characterize the genotypes and subtypes of Cryptosporidium species infecting a geographically isolated population of feral Soay sheep (Ovis aries) on Hirta, St. Kilda, Scotland, during two distinct periods: (i) prior to a population crash and (ii) as host numbers increased. Cryptosporidium DNA was extracted by freeze-thawing of immunomagnetically separated (IMS) bead-oocyst complexes, and species were identified following nested-PCR-restriction fragment length polymorphism (RFLP)/PCR sequencing at two Cryptosporidium 18S rRNA loci. Two hundred fifty-five samples were analyzed, and the prevalent Cryptosporidium species in single infections were identified as C. hominis (11.4% of all samples tested), C. parvum (9%), C. xiaoi (12.5%), and C. ubiquitum (6.7%). Cryptosporidium parvum was also present with other Cryptosporidium species in 27.1% of all samples tested. Cryptosporidium parvum- and C. hominis-positive isolates were genotyped using two nested-PCR assays that amplify the Cryptosporidium glycoprotein 60 gene (GP60). GP60 gene analysis showed the presence of two Cryptosporidium genotypes, namely, C. parvum IIaA19G1R1 and C. hominis IbA10G2. This study reveals a higher diversity of Cryptosporidium species/genotypes than was previously expected. We suggest reasons for the high diversity of Cryptosporidium parasites within this isolated population and discuss the implications for our understanding of cryptosporidiosis.

Cryptosporidium species detected in calves and cattle in Dagoretti, Nairobi, Kenya

A total of 1,734 cattle faecal samples from 296 dairy-keeping households were collected from urban settings in Nairobi, Kenya. Modified Ziehl-Neelsen staining method and an immunofluorescence assay were used to identify those samples with Cryptosporidium oocyst infection. Oocysts from positive faecal samples were isolated by Sheather's sucrose flotation method and picked from the concentrate using cover slips. Genomic DNA was extracted from 124 of the faecal samples that were positive for Cryptosporidium and was used as template for nested PCR of the 18S rRNA gene. Twenty-five samples (20 %) were PCR-positive for Cryptosporidium, and 24 of the PCR products were successfully cloned and sequenced. Sequence and phylogenetic analysis identified 17 samples (68 %) as Cryptosporidium parvum-like, four samples (16 %) as Cryptosporidium ryanae, three samples (12 %) as Cryptosporidium andersoni and one sample (4 %) as Cryptosporidium hominis. To the best of our knowledge, this is the first genotyping study to report C. parvum-like, C. andersoni and C. hominis in cattle from Kenya. The results of this study show Cryptosporidium infections in calves and cattle may be potential zoonotic reservoirs of the parasite that infects humans.

Evaluation of polymerase chain reaction as an additional tool for the diagnosis of low-intensity Schistosoma mansoni infection

The aim of the present study was to evaluate polymerase chain reaction (PCR) as an alternative tool for diagnosing schistosomiasis in individuals with low-level parasite burden from areas of low endemicity or under occasional risk of infection by Schistosoma mansoni. A total of 102 samples were tested in this study using 2 PCR assays utilizing distinct primer pairs. One of the primer pairs was targeted to a highly repeated 121-base pair sequence of S. mansoni, and the other was targeted to Schistosoma 28S rDNA. The samples were divided into 4 groups according to parasite burden of the individual as follows: 16 individuals with schistosomiasis excreting less than 10 eggs per gram of feces (EPG), 18 individuals excreting higher than 10 EPG, 22 individuals with reactive IgG-ELISA against S. mansoni soluble membrane antigen and negative coproscopy, and 46 controls samples including 25 individuals with other intestinal parasites and 21 individuals with negative parasitologic examination. The results obtained with stool samples from individuals with schistosomiasis showed a high sensitivity for PCR as S. mansoni DNA was detected in 91% (31/34) of the samples analyzed. No amplification was observed in 3 stool samples from individuals excreting below 10 EPG. The specificity of the test for both pairs of primers was 100%. In the group of seropositive individuals, S. mansoni DNA was detected in 59% (13/22) of fecal samples, corroborating the serologic results. Overall, PCR can be an important tool for detecting S. mansoni infection in individuals excreting few eggs in feces. Moreover, the determination of the infection through the detection of S. mansoni DNA in stool samples from seropositive individuals represents a new means of confirming the results of IgG-ELISA for schistosomiasis. Therefore, studies in this direction should be encouraged and extended.

A small outbreak of human cryptosporidiosis associated with calves at a dairy farm in Norway

Cryptosporidiosis is rarely diagnosed in Norway. This is the first report of a human outbreak in Norway and involved 3 calves and 5 people. Sequencing studies were performed. Although 4 of the people acquired their infections from the calves, the other probably became infected from other calves or contaminated pens.

90-kilodalton heat shock protein, Hsp90, as a target for genotyping Cryptosporidium spp. known to infect humans

Small-subunit (SSU) rRNA-based methods have been commonly used in the differentiation of Cryptosporidium species or genotypes. In order to develop a new tool for confirming the genotypes of Cryptosporidium species, parts of the 90-kDa heat shock protein (Hsp90) genes of seven Cryptosporidium species and genotypes known to infect humans (C. hominis, C. parvum, C. meleagridis, C. canis, C. muris, C. suis, and the cervine genotype), together with one from cattle (C. andersoni), were sequenced and analyzed. With the exception of C. felis from cats and C. baileyi from birds, the Hsp90 genes of all tested Cryptosporidium species were amplified. Phylogenetic analysis of the hsp90 sequences from all these species is congruent with previous studies in which the SSU rRNA, 70-kDa heat shock protein, oocyst wall protein, and actin genes were analyzed and showed that gastric and intestinal parasites segregate into two distinct clades. In this study, the secondary products of hsp90 produced after PCR-restriction fragment length digestion with StyI and HphI or with BbsI showed that parasites within the intestinal or gastric clade could be differentiated from each other. These data confirm the utility of the Hsp90 gene as a sensitive, specific, and robust molecular tool for differentiating species and/or genotypes of Cryptosporidium in clinical specimens.

Cryptosporidium hominis infection of the human respiratory tract

Cryptosporidium oocysts, observed in a natural sputum sample of a patient with HIV, were further studied by using DNA markers to determine the species of the parasite. C. hominis was identified as the species infecting the patient’s respiratory tract, a finding that strengthens evidence regarding this pathogen’s role in human disease.

Cryptosporidium parvum infections in Bergen, Norway, during an extensive outbreak of waterborne giardiasis in autumn and winter 2004

During a large waterborne giardiasis outbreak in Norway, many diarrheic patients were found to have Cryptosporidium infections. Gene sequencing identified these infections as Cryptosporidium parvum infections, although they were not identical. Whether these infections were due to a simultaneous outbreak of waterborne cryptosporidiosis or reflected background levels not normally detected is discussed.

Differential evolution of repetitive sequences in Cryptosporidium parvum and Cryptosporidium hominis

Cryptosporidium parvum and Cryptosporidium hominis are two morphologically identical species of Apicomplexan protozoa infecting humans. Although the genomes of these species are 97% identical, their host range is strikingly different. C. parvum infects humans and animals and is primarily a zoonotic infection, whereas C. hominis is typically not detected in animals. The extent of genetic polymorphism in both species has been surveyed locally, but not on a larger geographical scale. Herein, a collection of unrelated C. parvum and C. hominis isolates was genotyped using multiple, randomly distributed micro- and minisatellites. In average, minisatellites, consisting of tandemly repeated sequence motifs of 6-24 basepair, were more polymorphic than microsatellites. When the average number of micro- and minisatellite alleles per locus was used as a measure of heterogeneity, no difference between C. parvum and C. hominis was found. However, the frequency distribution of alleles in both species was significantly different and in 6 of the 14 loci the size of the C. parvum and C. hominis repeats did not overlap. Assuming that C. parvum and C. hominis evolved from a common ancestor, these observations suggest a differential evolution of repeat length at these loci.

Cryptosporidiosis: an update in molecular epidemiology

PURPOSE OF REVIEW

Molecular tools have been developed to detect and differentiate Cryptosporidium at the species/genotype and subtype levels. These tools have been increasingly used in the characterization of the transmission of Cryptosporidium spp. This review addresses the most recent developments in molecular epidemiology of cryptosporidiosis.

RECENT FINDINGS

The recent development of subtyping tools has led to better understanding of the population genetics and transmission of Cryptosporidium in humans. The population structure of C. parvum and C. hominis is apparently more complicated than previously suggested, with the likely existence of both clonal and panmictic populations. Thus, the transmission of C. parvum (genotype II) in humans is shown to be different in different areas, with zoonotic transmission important in certain places and anthroponotic transmission in others. The use of molecular tools has also led to the identification of geographic and temporal differences in the transmission of C. parvum and C. hominis, and better appreciation of the public health importance of other Cryptosporidium species/genotypes and the frequency of infections with mixed genotypes or subtypes.

SUMMARY

Factors involved in the transmission of human cryptosporidiosis are difficult to examine using conventional methods. The use of molecular tools has been helpful in the assessment of the zoonotic potential of various Cryptosporidium spp. and sources of human infections, and has started to play a significant role in the characterization of transmission dynamic in endemic and epidemic areas.