New biomarkers in the diagnosis of parasitic diseases: The example of Cryptosporidium spp. and Giardia duodenalis

Parasitic diseases are one of the most common infections in the world and cause millions of illnesses and deaths each year. In the past, most of these infections were predominantly associated with tropical or subtropical regions. However, today, factors such as changes in climate and vector ecology, significant increases in international travel, human and animal migrations, and the increase in the number of animals that serve as mechanical and biological vectors of parasites have caused some parasitic diseases to become more prominent worldwide.  This situation forces scientists to search for new and rapid biomarkers for early diagnosis of parasitic diseases. Biomarkers are biological indicators used to objectively measure and evaluate an organism's normal biological processes, disease processes or responses to therapeutic interventions. Biomarkers, also defined as changes in the constituents of tissues or body fluids, provide us with various parameters for the homogeneous classification of a disease and disease-related risk factors and can contribute to our basic knowledge of the underlying pathogenesis of the disease. Today, although variables such as clinical symptoms, clinical history, travel history and geographical location of patients are important in the detection and diagnosis of parasitic diseases, the diagnosis of these diseases is primarily based on various laboratory methods (such as microscopy and molecular methods). Besides molecular techniques, the discovery of new biomarkers using tissues or biological fluids from hosts infected with parasitic agents is attracting attention. Cryptosporidium spp. and Giardia duodenalis, an intestinal protozoan pathogen, are the leading causes of growth deficiency and even death in children and diarrhea in healthy adults. Therefore, the detection of these two pathogens has become a high priority, both to prevent potential outbreaks and to prevent the devastation they can cause in sick individuals. This review aims to draw attention to new biomarkers that are or could be used in the diagnosis of Cryptosporidium spp. and Giardia duodenlis protozoan parasites.