Genomic Heterogeneity of Cryptosporidium parvum Isolates From Children in Bangladesh: Implications for Parasite Biology and Human Infection

Cryptosporidium species are a major cause of diarrhea and associated with growth failure. There is currently only limited knowledge of the parasite's genomic variability. We report a genomic analysis of Cryptosporidium parvum isolated from Bangladeshi infants and reanalysis of sequences from the United Kingdom. Human isolates from both locations shared 154 variants not present in the cattle-derived reference genome, suggesting host-specific adaptation of the parasite. Remarkably 34.6% of single-nucleotide polymorphisms unique to human isolates were nonsynonymous and 8.2% of these were in secreted proteins. Linkage disequilibrium decay indicated frequent recombination. The genetic diversity of C. parvum has potential implications for vaccine and therapeutic design. Clinical Trials Registration. NCT02764918.

Nonsterile immunity to cryptosporidiosis in infants is associated with mucosal IgA against the sporozoite and protection from malnutrition

We conducted a longitudinal study of cryptosporidiosis from birth to three years of age in an urban slum of Dhaka Bangladesh. Fecal DNA was extracted from monthly surveillance samples and diarrheal stool samples collected from 392 infants from birth to three years. A pan-Cryptosporidium qPCR assay was used to identify sub-clinical and symptomatic cryptosporidiosis. Anthropometric measurements were collected quarterly to assess child nutritional status. 31% (121/392) of children experienced a single and 57% (222/392) multiple infections with Cryptosporidium. Repeat infections had a lower burden of parasites in the stool (Cq slope = -1.85; p<0.0001) and were more likely to be sub-clinical (Chi square test for trend; p = 0.01). Repeat infections were associated with the development of growth faltering (Pearson correlation = -0.18; p = 0.0004). High levels of fecal IgA antibodies against the Cryptosporidium Cp23 sporozoite protein at one year of life were associated with a delay in reinfection and amelioration of growth faltering through three years of life (HAZ IgA high responders -1.323 ± 0.932 versus HAZ -1.731 ± 0.984 p = 0.0001). We concluded that nonsterile immunity to cryptosporidiosis in young children was associated with high levels of mucosal IgA anti-Cp23 and protection from diarrhea and growth faltering. Trial Registration: NCT02764918.

Case-Control Study of Cryptosporidium Transmission in Bangladeshi Households

Background

Cryptosporidium is a leading contributor to diarrheal morbidity and mortality in under-5 children worldwide. As there is no vaccine and no effective drug therapy in young children for this infection, preventing infection is critical. We undertook a pilot case-control study to define the extent of person-to-person transmission of cryptosporidiosis within an urban and a rural community in Bangladesh.

Methods

We enrolled 48 case families with a Cryptosporidium-infected child aged 6–18 months. Controls were age- and sex-matched Cryptosporidium-negative children in 12 households. Children and household members were followed for 8 weeks with weekly illness survey and stool testing with quantitative polymerase chain reaction for Cryptosporidium.

Results

In the 24 urban case families, the secondary attack rate was 35.8% (19/53) vs 0% (0/11) in controls (P = .018, χ² test). In contrast, in the 24 rural case families, the secondary attack rate was 7.8% (5/64) vs 0% (0/21) in controls (P = .19, χ² test). Genotyping by gp60 demonstrated infection with the same subspecies in 5 families, and evidence of transmission in 2. Serologic response to Cryptosporidium infection was associated with younger age, longer duration of infection, and Cryptosporidium hominis gp60_IbA9G3R2 infection.

Conclusions

In the urban site, the high rate of secondary infection and infection with the same subspecies within families suggests that person-to-person transmission is a major source of Cryptosporidium infection for young children living in this region. Molecular genotyping can be applied to determine transmission of Cryptosporidium in endemic regions. Further work is needed to understand the differences in parasite transmissibility and immunity to different genotypes.

Genetic Diversity of Cryptosporidium hominis in a Bangladeshi Community as Revealed by Whole-Genome Sequencing

We studied the genetic diversity of Cryptosporidium hominis infections in slum-dwelling infants from Dhaka over a 2-year period. Cryptosporidium hominis infections were common during the monsoon, and were genetically diverse as measured by gp60 genotyping and whole-genome resequencing. Recombination in the parasite was evidenced by the decay of linkage disequilibrium in the genome over <300 bp. Regions of the genome with high levels of polymorphism were also identified. Yet to be determined is if genomic diversity is responsible in part for the high rate of reinfection, seasonality, and varied clinical presentations of cryptosporidiosis in this population.

Species-Specific Immunodetection of an Entamoeba histolytica Cyst Wall Protein

Entamoeba histolytica causes intestinal disease in endemic settings throughout the world. Diagnosis of E. histolytica infection would be improved by the identification of biomarkers that are expressed by cysts of E. histolytica, but not by cysts of closely related commensal species of Entamoeba. Herein, we describe two novel monoclonal antibodies (1A4 and 1D3) produced against a spacer region of the E. histolytica Jacob2 lectin, an outer cyst wall protein. These reagents demonstrated no cross-reaction to E. dispar recombinant antigen and low picomolar molecular detection limits when paired in ELISA sandwich assays. In an immunofluorescence microscopy assay, the α-Jacob2 murine antibodies labeled cysts of three xenically cultured E. histolytica isolates but did not label cysts of three E. bangladeshi isolates. Monoclonal antibody 1A4 did not cross-react with xenic cultures of three E. dispar isolates, demonstrating specificity to E. histolytica, while monoclonal antibody 1D3 cross-reacted with two out of three E. dispar isolates. Both antibodies labeled cysts in formalin-fixed slides, a potential logistical advantage in some settings. The monoclonal antibody 1A4 was also used in an immunofluorescence microscopy assay with formalin-fixed stool specimens. Seven out of ten ELISA-positive stool specimens exhibited 1A4-labeled cyst-like objects, compared to one out of seven ELISA-negative specimens. These results demonstrate that antibodies generated against the flexible spacer of E. histolytica Jacob2 lectin recognize and bind to Jacob2 protein in whole cysts and are capable of differentiating Entamoeba species in fixed specimens. Thus, Jacob2 is a promising biomarker for use in diagnosing E. histolytica infection.