The Current Molecular Epidemiological Scenario of Cryptosporidium, Giardia and Blastocystis in Spain. Implication for Public Health

Abstract

The enteric protozoan parasites Cryptosporidium spp. and Giardia duodenalis are major contributors to the burden of gastrointestinal diseases globally. Both pathogens primarily affect children living in resource-poor settings with limited or no access to clean water and sanitation facilities, but are also significant public health threats in developed countries. Additionally, Cryptosporidium spp. and G. duodenalis are common causes of waterborne and foodborne outbreaks of gastrointestinal disease globally. Besides, the Stramenopile Blastocystis sp. is the most common eukaryotic organism reported in the human gut. Although its pathogenicity is a topic of debate, there is increasing evidence demonstrating that this protist can be associated with gastrointestinal disorders (diarrhoea, irritable bowel syndrome) and extra-intestinal manifestations, including urticaria. Because Cryptosporidium spp., G. duodenalis and Blastocystis sp. share the same transmission (faecal-oral) route, are able to infect a wide range of animal species other than humans with variable host specificities, and their infective forms are environmentally resilient, the study of these pathogens should be ideally approached under the One Health umbrella. In this context, molecular-based methods including PCR and sequencing provide powerful tools to investigate the epidemiology and transmission of these parasites. In Spain, cryptosporidiosis and giardiosis, but not blastocystosis, are notifiable diseases. However, the true incidence of these infections remain largely unknown because underdiagnosing and underreporting. Symptomatic cryptosporidiosis and giardiosis disproportionally affect children under four years of age, but we know now that subclinical infections are also common in apparently healthy individuals of all age groups. However, molecular data regarding the frequency and diversity of these pathogens are limited and spatially and temporally discontinuous. This chapter aims to provide, from a public veterinary health perspective, an updated account on the epidemiology of Cryptosporidium, G. duodenalis and Blastocystis in Spain, with an emphasis on the description of the species/genotypes circulating in symptomatic and asymptomatic human populations. Current knowledge on the presence of these pathogens in production (livestock), companion (dogs and cats) and wildlife animal species is also discussed, including their potential role as natural reservoirs of human infections, and the available evidence of zoonotic (and anthroponotic) transmission events.