Enteric protozoa in the developed world: a public health perspective

Abstract

Several enteric protozoa cause severe morbidity and mortality in both humans and animals worldwide. In developed settings, enteric protozoa are often ignored as a cause of diarrheal illness due to better hygiene conditions, and as such, very little effort is used toward laboratory diagnosis. Although these protozoa contribute to the high burden of infectious diseases, estimates of their true prevalence are sometimes affected by the lack of sensitive diagnostic techniques to detect them in clinical and environmental specimens. Despite recent advances in the epidemiology, molecular biology, and treatment of protozoan illnesses, gaps in knowledge still exist, requiring further research. There is evidence that climate-related changes will contribute to their burden due to displacement of ecosystems and human and animal populations, increases in atmospheric temperature, flooding and other environmental conditions suitable for transmission, and the need for the reuse of alternative water sources to meet growing population needs. This review discusses the common enteric protozoa from a public health perspective, highlighting their epidemiology, modes of transmission, prevention, and control. It also discusses the potential impact of climate changes on their epidemiology and the issues surrounding waterborne transmission and suggests a multidisciplinary approach to their prevention and control.

Fig 1

Photomicrographs of six enteric protozoa. Plates 1 to 5 were stained with a modified iron-hematoxylin stain (incorporating a carbol fuschin staining step). Plate 6 was a wet preparation. (1) Cryptosporidium oocysts; (2a) Giardia intestinalis cysts; (2b) Giardia intestinalis trophozoite; (3a) Entamoeba histolytica cyst; (3b) Entamoeba histolytica trophozoite; (4) Cyclospora cayetanensis oocysts; (5) Dientamoeba fragilis binucleated trophozoite; (6) Blastocystis oocysts. Bars, 10 μm. (All graphics by Damien Stark.)

Fig 2

Complex interactions in the transmission and control of enteric protozoal infections. Infectious parasites are transmitted to humans through several routes, including contaminated food and water, inadequately treated sewage/sewage products, and livestock and domestic pet handling. Prevention and control strategies can be implemented at different levels of food production, liquid waste management, water quality control, and livestock and pet handling processes.