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

Advances in therapeutic and vaccine targets for Cryptosporidium: Challenges and possible mitigation strategies

Cryptosporidium is known to be the second most common diarrheal pathogen in children, causing potentially fatal diarrhea and associated with long-term growth stunting and cognitive deficits. The only Food and Drug Administration-approved treatment for cryptosporidiosis is nitazoxanide, but this drug has not shown potentially effective results in susceptible hosts. Therefore, a safe and effective drug for cryptosporidiosis is urgently needed. Cryptosporidium genome sequencing analysis may help develop an effective drug, but both in vitro and in vivo approaches to drug evaluation are not fully standardized. On the other hand, the development of partial immunity after exposure suggests the possibility of a successful and effective vaccine, but protective surrogates are not precise. In this review, we present our current perspectives on novel cryptosporidiosis therapies, vaccine targets and efficacies, as well as potential mitigation plans, recommendations and perceived challenges.

Cryptosporidiosis in children in the Indian subcontinent

Cryptosporidiosis is a leading cause of diarrheal disease among children under two in developing countries. Previous estimates have shown a high burden of cryptosporidial diarrhea in children from Sub-Saharan Africa and South Asia. Asymptomatic cryptosporidial infections which go undetected and untreated have been shown to result in significant malnutrition. In this review, we carried out a literature search of studies published on cryptosporidiosis in children in the Indian subcontinent from 1983 to 2016. Of the 154 publications identified, 54 were included for final analysis with both hospital-based and community-based studies. There were wide variations in reported prevalence rates from hospital studies and highlight the need to be carry out these studies with uniform sampling and molecular tools for detection, especially in countries with a dearth of information. Community-based studies, however, showed similarities in spite of differences in when (the late 1990s up until recently) and where (South India or Bangladesh) they were conducted. When more sensitive detection methods were used, cryptosporidial diarrhea accounted for 7%–9% of all diarrhea episodes and 20%–30% of children in these cohorts experienced at least one cryptosporidial diarrheal episode. High rates of asymptomatic infections with increased detection by serology and multiple infections (symptomatic and asymptomatic) were also documented in all cohorts. This overview brings to light the high burden of disease associated with cryptosporidiosis in children in the subcontinent and the gaps in knowledge to be addressed.

Systemic and Mucosal Immune Responses to Cryptosporidium-Vaccine Development

Cryptosporidium spp is a major cause of diarrheal disease worldwide, particularly in malnourished children and untreated AIDS patients in developing countries in whom it can cause severe, chronic and debilitating disease. Unfortunately, there is no consistently effective drug for these vulnerable populations and no vaccine, partly due to a limited understanding of both the parasite and the host immune response. In this review, we will discuss our current understanding of the systemic and mucosal immune responses to Cryptosporidium infection, discuss the feasibility of developing a Cryptosporidium vaccine and evaluate recent advances in Cryptosporidium vaccine development strategies.

A review of the global burden, novel diagnostics, therapeutics, and vaccine targets for cryptosporidium

Cryptosporidium spp are well recognised as causes of diarrhoeal disease during waterborne epidemics and in immunocompromised hosts. Studies have also drawn attention to an underestimated global burden and suggest major gaps in optimum diagnosis, treatment, and immunisation. Cryptosporidiosis is increasingly identified as an important cause of morbidity and mortality worldwide. Studies in low-resource settings and high-income countries have confirmed the importance of cryptosporidium as a cause of diarrhoea and childhood malnutrition. Diagnostic tests for cryptosporidium infection are suboptimum, necessitating specialised tests that are often insensitive. Antigen-detection and PCR improve sensitivity, and multiplexed antigen detection and molecular assays are underused. Therapy has some effect in healthy hosts and no proven efficacy in patients with AIDS. Use of cryptosporidium genomes has helped to identify promising therapeutic targets, and drugs are in development, but methods to assess the efficacy in vitro and in animals are not well standardised. Partial immunity after exposure suggests the potential for successful vaccines, and several are in development; however, surrogates of protection are not well defined. Improved methods for propagation and genetic manipulation of the organism would be significant advances.

Biochemical and functional characterization of CpMuc4, a Cryptosporidium surface antigen that binds to host epithelial cells

Cryptosporidium spp. are intracellular apicomplexan parasites that cause outbreaks of waterborne diarrheal disease worldwide. Previous studies had identified a Cryptosporidium parvum sporozoite antigen, CpMuc4, that appeared to be involved in attachment and invasion of the parasite into intestinal epithelial cells. CpMuc4 is predicted to be O- and N-glycosylated and the antigen exhibits an apparent molecular weight 10kDa larger than the antigen expressed in Escherichia coli, indicative of post-translational modifications. However, lectin blotting and enzymatic and chemical deglycosylation did not identify any glycans on the native antigen. Expression of CpMuc4 in Toxoplasma gondii produced a recombinant protein of a similar molecular weight to the native antigen. Both purified native CpMuc4 and T. gondii recombinant CpMuc4, but not CpMuc4 expressed in E. coli, bind to fixed Caco-2A cells in a dose dependent and saturable manner, suggesting that this antigen bears epitopes that bind to a host cell receptor, and that the T. gondii recombinant CpMuc4 functionally mimics the native antigen. Binding of native CpMuc4 to Caco2A cells could not be inhibited with excess CpMuc4 peptide, or an excess of E. coli recombinant CpMuc4. These data suggest that CpMuc4 interacts directly with a host cell receptor and that post-translational modifications are necessary for the antigen to bind to the host cell receptor. T. gondii recombinant CpMuc4 may mimic the native antigen well enough to serve as a useful tool for identifying the host cell receptor and determining the role of native CpMuc4 in host cell invasion.