Abstract
Introduction: Cryptosporidium spp.is an intestinal protozoan that is transmitted through water and food, and causes severe diarrhea, Cryptosporidiosis is not limited to humans, as there are many species of Cryptosporidium that infect a wide range of vertebrate hosts such as mammals of all species, fish, reptiles and birds.
Methods: In the current study, during the period between September 2025 and February 2026, 180 fish species were collected from the markets of Al-Diwaniyah Province, 60 fish of each species, which included both farmed fish such as Cyprinus carpio and non-farmed fish such as Planiliza abu and Acanthopagrus latus, with the aim of isolating the parasite Cryptosporidium spp., identifying it microscopically and molecularly, and determining the most widespread species through genetic sequencing and drawing its phylogenetic tree.
Results: The overall infection rate of the three fish species with the Cryptosporidium spp. was 14%, with the highest infection rate recorded in Acanthopagrus latus at 18.3%, followed by the infection rate of Cyprinus carpio at 11.66%, while Planiliza abu recorded the lowest infection rate at 10%. The highest infection rate was recorded during the months of moderate temperature, reaching 13.03% in October, and no infection was recorded during February.The results of using Nested polymerase chain reaction N-PCR technology to examine 24 fecal samples collected from the fish included in the study, which gave a positive result by direct smear method, indicated that the percentage of the SSU rRNA gene with a molecular weight of 533 bp, specific to the Cryptosporidium spp., reached 50%, with 12 samples.DNA sequencing technology was also used, relying on the same gene to analyze the phylogenetic tree of the local isolates. MEGA 6 software was used to determine the degree of similarity between the fish isolates and the international isolates registered with the NCBI. The results of the phylogenetic tree analysis of the local isolates revealed five species: Cryptosporidium molnari, Cryptosporidium bollandi, Cryptosporidium xiaoi, Cryptosporidium parvum, and Cryptosporidium hominis. The samples were registered in the international gene bank under serial numbers PZ120392, PZ120393, PZ120394, PZ120395, PZ120396, PZ120397, PZ120398, PZ120399, PZ120400, PZ120401, PZ120402, PZ120403.The registration of Cryptosporidium molnari, Cryptosporidium bollandi, and Cryptosporidium xiaoi marks their first recorded presence in Iraqi fish.
Conclusion: This genetic diversity in Cryptosporidium reflects the parasite’s ability to adapt and spread in diverse aquatic environments. This serves as a vital indicator of water pollution levels and foreshadows potential health risks that may be transmitted to humans.