Morpho-molecular analysis of Cystoisospora canis isolated from dogs in Sulaymaniyah province, Iraq.

Cystoisospora (formerly known as Isospora) are apicomplexan intracellular parasites that frequently infect the small intestine of dogs, causing diarrhea, abdominal discomfort, and, in severe cases, death, particularly in young dogs. The research designed to determine the frequency of cystoisosporiasis, identify the species, and evaluate the genetic diversity of the 18S rRNA gene among isolates in Sulaymaniyah, Iraq. The research was carried out in the province of Sulaymaniyah between July and December of 2024. A total of 258 fecal specimens from dogs were collected and examined to diagnose Cystoisospora spp. infection. The traditional Sheather's fecal flotation method was used for the detection of Cystoisospora canis oocysts, while polymerase chain reaction (PCR) and 18S rRNA gene sequencing were performed for molecular confirmation and sequence analysis of C. canis. The infection rate of cystoisosporiasis was 20/258 (7.75%), with the infection occurring significantly more often (P < 0.05) in stray dogs (11.35%) compared to domestic dogs (3.42%), in dogs with watery diarrhea (26.31%) versus those with semi-formed and formed feces (8.89% and 1.54%, respectively), and in puppies (11.45%) compared to adults (3.94%). Comparison and analysis of partial 18S rRNA gene sequences of the protozoa were performed on 20 local isolates identified in the study region. Five of these isolates showed similarity to sequences previously deposited in GenBank, while fifteen isolates exhibited nucleotide variations in the partial 18S rRNA gene sequences compared with previously reported isolates and were documented for the first time in this research area. Phylogenetic analyses revealed a close relationship between C. canis from different countries. These findings provide essential baseline data for dog owners and the veterinary community regarding the presence of this canine coccidian and its risk factors. Additionally, the research offers a valuable molecular dataset for C. canis, crucial for understanding phylogenetic relationships and identifying these protozoans.