Although opportunistic parasitic infections are selflimiting in people with complete immunity and can cause infections with mild symptoms or be asymptomatic, they can even be life-threatening in immunocompromised people. Nowadays, with the increase of susceptible hosts and the outbreak of some factors that weaken or suppress the immune system, such as cancer and the acquired immunodeficiency virus (HIV), opportunistic infections are of particular importance. 1 In tropical and subtropical regions, the spread of parasitic protozoa is significant, and health programs aimed at eliminating and reducing the (opportunistic) parasite load in these regions are up to the end of the current decade. 2 As it is known, HIV infection is one of the deadliest diseases in recent decades, for which, unfortunately, no definitive treatment has been found. In this infection, the virus belonging to the Retroviridae family targets the cells of the immune system, complicating the host’s condition and making it susceptible to infections. Frequently, coinfections of cryptosporidium and microsporidia species have been reported in immunocompromised people. 3, 4 Microsporidiosis and cryptosporidiosis are associated with chronic diarrhea in immunocompromised patients,hence, different species of cryptosporidium and microsporidia protozoa act as lethal agents by causing gastrointestinal complications and severe diarrhea by dehydration.

Protozoan parasites are very important in drinking water production systems because their cystic forms are stable in the environment and resistant to conventional disinfection methods. The present study aimed to investigate protozoan parasites in the drinking water of different places in Samarra, Iraq. To this end, 100 samples of tap drinking water were collected from 10 places in Samarra, Iraq (i. e., Al-Sekek, Al-Kadesia, Alzeraa, Al-Shuhdaa, Al-Muthana, Al-Shorta, Al-Mamal, Al-Khedraa, Al-Efraz, and Al-Jubereaa), from the beginning of December to the end of February. After sample collection, water samples were examined to detect oocysts or cysts of protozoan parasites by using Direct wet smear, Lugol’, s iodine, and Modified Ziehle Nelseen stain methods. The results indicate that 80% of the samples under investigation were infected with protozoan parasites, and the ratio of diagnostic parasites in the samples under investigation was determined at 36% with Entamoeba histolytica, 23% with Giardia lamblia, and 21% with Cryptosporidium parvum. The findings reveal the presence of protozoan parasites in the drinking water of the area under study and specify the need for a rapid improvement of the monitoring systems for the treatment of drinking water to control diseases caused by these pathogens, as well as to identify the sources of contamination.