Cryptosporidium: Identification and Genetic Typing

Genetic crosses within and between species of Cryptosporidium

Parasites and their hosts are engaged in reciprocal coevolution that balances competing mechanisms of virulence, resistance, and evasion. This often leads to host specificity, but genomic reassortment between different strains can enable parasites to jump host barriers and conquer new niches. In the apicomplexan parasite Cryptosporidium, genetic exchange has been hypothesized to play a prominent role in adaptation to humans. The sexual lifecycle of the parasite provides a potential mechanism for such exchange; however, the boundaries of Cryptosporidium sex are currently undefined. To explore this experimentally, we established a model for genetic crosses. Drug resistance was engineered using a mutated phenylalanyl tRNA synthetase gene and marking strains with this and the previously used Neo transgene enabled selection of recombinant progeny. This is highly efficient, and genomic recombination is evident and can be continuously monitored in real time by drug resistance, flow cytometry, and PCR mapping. Using this approach, multiple loci can now be modified with ease. We demonstrate that essential genes can be ablated by crossing a Cre recombinase driver strain with floxed strains. We further find that genetic crosses are also feasible between species. Crossing Cryptosporidium parvum, a parasite of cattle and humans, and Cryptosporidium tyzzeri a mouse parasite resulted in progeny with a recombinant genome derived from both species that continues to vigorously replicate sexually. These experiments have important fundamental and translational implications for the evolution of Cryptosporidium and open the door to reverse- and forward-genetic analysis of parasite biology and host specificity.

Cross-genera amplification and identification of Colpodella sp. with Cryptosporidium primers in fecal samples of zoo felids from northeast China

The protozoans include many intracellular human pathogens. Accurate detection of these pathogens is necessary to treat the diseases. In clinical epidemiology, molecular identification of protozoan is considered a more reliable and rapid method for identification than microscopy. Among these protozoans, Cryptosporidium considered being one of the important water-borne zoonotic pathogens and a major cause of a diarrheal disease named cryptosporidiosis in humans, domestic animals, and wild animals. This study was aimed to identify Cryptosporidium in zoo felids (N= 56) belonging to different zoo of China, but accidentlly Colpodella was encountered in the zoo felids sample and phylogenetic data confirmed this unexpected amplification from fecal samples using two-step nested-PCR. Phylogenetic analysis revealed the fact about the specific primers used previously by many researchers and cross-genera amplification. We came to know that genetically sequenced amplicon gives more accurate identification of species. This study suggests more investigation on Colpodella which has been neglected previously but gains the attention of researchers after identified from humans and animals and has been known to correlate with neurological symptoms in patients.

Development of an immunocompetent mouse model susceptible to Cryptosporidium tyzzeri infection

AIMS

Immunocompromised mice are extensively used in the screening of vaccines and drugs for Cryptosporidium, but this study model does not reflect the real status of infection in immunocompetent animals. This study aimed to provide an optimized animal model for future studies of Cryptosporidium vaccine.

METHODS AND RESULTS

Three mouse strains (ICR, BALB/c and KM) with or without immunosuppression were compared after challenge with Cryptosporidium tyzzeri (C tyzzeri). The results indicated that ICR mice shed a greater number of faecal oocysts (20 346 ± 203 oocysts/g) compared with BALB/c (2077 ± 142 oocysts/g) and KM mice (3207 ± 431 oocysts/g) after experimental infection with C tyzzeri (P < .001). However, ICR mouse model is uniquely effective for C tyzzeri, not for other Cryptosporidium spp. such as C parvum. ICR mice were then used to determine the immunoreactions and immunoprotection of P23-DNA vaccine (pVAX1-P23) to C tyzzeri experimental infection. The results showed that a significant increase in anti-P23 antibody levels was induced by the pVAX1-P23 vaccine. Compared to pVAX1, TB and blank control mice, pVAX1-P23 immunized mice produced specific spleen cell proliferation as well as enhanced IL-5, IL-12p70 and IFN-γ production in sera. After challenge with 5 × 10⁶ C tyzzeri oocysts, the oocyst shedding of the pVAX1-P23 immunized group was reduced by 69.94% comparing to the infection control.

CONCLUSION

These results provide an optimized animal model for the study of prophylactic vaccines and this model might be applied to other candidates against Cryptosporidium, not only for pVAX1-P23.

Prevalence and diversity of Cryptosporidium spp. in bamboo rats (Rhizomys sinensis) in South Central China

Cryptosporidium is one of the most prevalent zoonotic parasites and is responsible for the high burden of diarrheal disease across the globe. Rodents are globally overpopulated and are reservoirs for a variety of zoonotic pathogens. Bamboo rats are a common species of rodent that are bred for meat and wool in China. However, the genetic characterization of Cryptosporidium in bamboo rats in China is limited. The aim of this study was to determine the occurrence and genetic characterization of Cryptosporidium in bamboo rats from South Central China. From February2017to February 2018, 435 fecal samples were collected from bamboo rats in 13 farms located in 12 cities in South Central China. All fecal specimens were examined for Cryptosporidium by PCR, and through sequencing the partial small subunit of ribosomal DNA (SSU rRNA). C. parvum-positive samples were further subtyped through analysis of the 60-kDa glycoprotein (gp60) gene sequence. Meanwhile, all the new Cryptosporidium genotypes samples were selected for further sequence characterization at the 70-kDa heat shock protein (HSP70) gene and oocyst wall protein (COWP) gene as well as gp60 gene. Infection rates of 2.1% (9/435) were recorded for Cryptosporidium. Sequence analysis confirmed the presence of two Cryptosporidium species including C. parvum (n = 2), C. occultus (n = 1) and two new Cryptosporidium genotypes termed Cryptosporidium bamboo rat genotype I (n = 5) and Cryptosporidium bamboo rat genotype II (n = 1). Two subtypes of C. parvum were identified including IIdA15G1 and IIpA19 (one each).The discovery of zoonotic Cryptosporidium species/genotypes in bamboo rats suggests they have significant zoonotic potential and pose a threat to human health. The novel sequences discovered provide new insight into genotypic variations in Cryptosporidium in bamboo rats.

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This is the first report of the identification of Cryptosporidium in farmed bamboo rats in South Central China.

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2.1% (9/435) bamboo rats were PCR-positive for Cryptosporidium.

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Cryptosporidium parvum, C. occultus, Cryptosporidium bamboo rats I and II were identified.

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The possibility of transmission of Cryptosporidium between bamboo rats and humans was suggested.

DNA barcoding of Cryptosporidium

Cryptosporidium spp. (Apicomplexa) causing cryptosporidiosis are of medical and veterinary significance. The genus Cryptosporidium has benefited from the application of what is considered a DNA-barcoding approach, even before the term 'DNA barcoding' was formally coined. Here, the objective to define the DNA barcode diversity of Cryptosporidium infecting mammals is reviewed and considered to be accomplished. Within the Cryptosporidium literature, the distinction between DNA barcoding and DNA taxonomy is indistinct. DNA barcoding and DNA taxonomy are examined using the latest additions to the growing spectrum of named Cryptosporidium species and within-species and between-species identity is revisited. Ease and availability of whole-genome DNA sequencing of the relatively small Cryptosporidium genome offer an initial perspective on the intra-host diversity. The opportunity emerges to apply a metagenomic approach to purified field/clinical Cryptosporidum isolates. The outstanding question remains a reliable definition of Cryptosporidium phenotype. The complementary experimental infections and metagenome approach will need to be applied simultaneously to address Cryptosporidium phenotype with carefully chosen clinical evaluations enabling identification of virulence factors.

Use of a bioinformatic-assisted primer design strategy to establish a new nested PCR-based method for Cryptosporidium

BACKGROUND

The accurate tracking of Cryptosporidium in faecal, water and/or soil samples in water catchment areas is central to developing strategies to manage the potential risk of cryptosporidiosis transmission to humans. Various PCR assays are used for this purpose. Although some assays achieve specific amplification from Cryptosporidium DNA in animal faecal samples, some do not. Indeed, we have observed non-specificity of some oligonucleotide primers in the small subunit of nuclear ribosomal RNA gene (SSU), which has presented an obstacle to the identification and classification of Cryptosporidium species and genotypes (taxa) from faecal samples.

RESULTS

Using a novel bioinformatic approach, we explored all available Cryptosporidium genome sequences for new and diagnostically-informative, multi-copy regions to specifically design oligonucleotide primers in the large subunit of nuclear ribosomal RNA gene (LSU) as a basis for an effective nested PCR-based sequencing method for the identification and/or classification of Cryptosporidium taxa.

CONCLUSION

This newly established PCR, which has high analytical specificity and sensitivity, is now in routine use in our laboratory, together with other assays developed by various colleagues. Although the present bioinformatic workflow used here was for the specific design of primers in nuclear DNA of Cryptosporidium, this approach should be broadly applicable to many other microorganisms.

Deep-sequencing to resolve complex diversity of apicomplexan parasites in platypuses and echidnas: Proof of principle for wildlife disease investigation

The short-beaked echidna (Tachyglossus aculeatus) and the platypus (Ornithorhynchus anatinus) are iconic egg-laying monotremes (Mammalia: Monotremata) from Australasia. The aim of this study was to demonstrate the utility of diversity profiles in disease investigations of monotremes. Using small subunit (18S) rDNA amplicon deep-sequencing we demonstrated the presence of apicomplexan parasites and confirmed by direct and cloned amplicon gene sequencing Theileria ornithorhynchi, Theileria tachyglossi, Eimeria echidnae and Cryptosporidium fayeri. Using a combination of samples from healthy and diseased animals, we show a close evolutionary relationship between species of coccidia (Eimeria) and piroplasms (Theileria) from the echidna and platypus. The presence of E. echidnae was demonstrated in faeces and tissues affected by disseminated coccidiosis. Moreover, the presence of E. echidnae DNA in the blood of echidnas was associated with atoxoplasma-like stages in white blood cells, suggesting Hepatozoon tachyglossi blood stages are disseminated E. echidnae stages. These next-generation DNA sequencing technologies are suited to material and organisms that have not been previously characterised and for which the material is scarce. The deep sequencing approach supports traditional diagnostic methods, including microscopy, clinical pathology and histopathology, to better define the status quo. This approach is particularly suitable for wildlife disease investigation.