Intestinal protozoa searching for a disease or for a doctor?

Although highly prevalent in developing countries, intestinal parasitoses frequently afflict subjects in industrialized ones as well. However, besides the agents with a well-known clinical relevance and those with an open debate about it (Blastocystis hominis and Dientamoeba fragilis), limited information is available about neglected protozoan infections such as those caused by Cyclospora cayetanensis, Isospora belli, Enteromonas hominis, Iodamoeba buetschlii, Balantidium coli, and free-living amoebae. In our laboratory, from 2011 to 2018, conventional diagnosis of intestinal parasitosis (microscopic examination of fresh/concentrated faeces and cultivation in Robinson’s medium) was performed on 20,978 faecal samples belonging to 13,596 patients, all presenting with the clinical suspicion of intestinal parasitosis; real-time PCR assays for the differentiation of Entamoeba histolytica and E. dispar and for the detection of D. fragilis were also used when clinical manifestation and/or risk factors for parasitic infections were reported, and/or when diagnostic stages of intestinal parasites were detected by microscopy. Intestinal parasitosis was diagnosed in 2062 patients (15.2%), about half of whom were immigrants from developing countries; of these cases, 1957 caused by protozoa (14.4%). The most common intestinal protozoan detected was B. hominis (2047 cases), followed by D. fragilis (467 cases) and G. intestinalis (195 cases). Interestingly, only one case of infection by I. belli together with B. hominis was diagnosed in an HIV-positive patient with fever and diarrhea and documented absence of enteropathogenic agents (bacteria, parasites, viruses). The data presented confirm the importance of suspecting protozoan infections even in non-endemic areas, particularly in cases in which no pathogens other than protozoa are present, and indicates the value of adopting adequate diagnostic methods. Data regarding the detection of enteropathogenic agents other than parasites and data regarding cases of clinical symptoms resolved only after therapeutic intervention and eradication of the infection caused by B. hominis and/or D. fragilis will be discussed. Knowledge of the epidemiology of intestinal parasitosis is important for health care authorities all over the world, so that they can understand the role of an infectious agent in causing disease, and thus adopt appropriate control measures and provide adequate patient care