Abstract
Background:
Cryptosporidium is a parasite that affects birds and humans, it plays role in potential zoonotic interspecies transmission. adequate diagnosis is important to study the epidemiological diversity of this genus.

Aim:
This study aimed to diagnose the species of Cryptosporidium in domestic pigeons (Columba livia domestica) in Nasiriyah city in Iraq, by using nested polymerase chain reaction (Nested PCR).

Methods:
Seventeen fecal samples from domestic pigeons were collected. Nested polymerase chain reaction targeting the 18S rRNA gene was done to detect and molecularly characterize the parasite, and we study the genetic similarities with known Cryptosporidium species in humans and birds in gene bank.

Results:
The rate of infection Pigeons was high 64.7%, the Cryptosporidium was detected in 11 out of 17 samples. Three species were detected : C. meleagridis, C. baileyi, and C. avium. The present study confirms for the first time the presence of Cryptosporidium avium in domestic pigeons in Iraq using molecular analysis. The samples showed a high genetic similarity of 98.50%–99.0% with known human species, indicating a close genetic relationship. This is the first molecular identification of C. avium parasites in pigeons in Nasiriyah, with one sample showing a 99.45% match with the species isolated from birds. Minor genetic mutations were also observed in the 18S rRNA gene, indicating slight genetic diversity that may be related to the adaptation of the parasite.

Conclusion:
This study highlights the presence and diversity of Cryptosporidium parasites in domestic pigeons in Iraq, emphasizing the potential for parasite transmission between birds and humans. These findings provide a foundation for future research into transmission pathways and infection.

Key words: Columba livia domestica; C. avium; C. baileyi; C. meleagridis; Nested PCR.