A Survey of the Larval Stages of Digenetic Trematodes in Freshwater Snails from the Al-Gharraf River, Northern Dhi Qar Province, Southern Iraq

Abstract

This study investigated the occurrence and infection rates of digenetic trematode cercariae in freshwater snails from four sites along the Al-Gharraf River, north of Dhi Qar Province, southern Iraq, from July to December 2025. A total of 633 snails, belonging to two species of the genus Melanopsis (M. costata and M. buccinoides), were randomly collected and examined by direct crushing to detect larval stages. A total of 67 infected individuals were recorded, representing an overall infection rate of 10.58%. Infection was restricted to Melanopsis spp., indicating host specificity and ecological preference. Morphological examination revealed three distinct cercarial types: pleurolophocercous, furcocercous, and echinostomatid. These larval forms are associated with members of the families Heterophyidae, Cyathocotylidae, and Echinostomatidae. The findings provide baseline data on trematode–snail interactions in the Al-Gharraf River and highlight the ecological role of freshwater snails as intermediate hosts in parasite transmission.

Keywords

• Cercariae
• intermediate host
• Melanopsis spp.
• parasitic diversity

Ethical Statement

Bu çalışma için etik kurul onayı gerekmemektedir.

Thanks

We extend our sincere thanks to the anonymous reviewers for their valuable feedback. This study was conducted as part of the first author's Master's thesis under the supervision of Asst. Prof. Dr. Moayad Mijbil Ubaid and Prof. Dr. Azhar Mohammad Al-Khazali. The research was entirely self-funded, with no financial support from the university or any external sources.

Güney Irak, Zikar Eyaleti'nin Kuzeyindeki Al-Gharraf Nehri'nde Bulunan Tatlı Su Salyangozlarında Digenetik Trematodların Larva Evrelerinin Araştırılması

Abstract

Bu çalışmada, Güney Irak'ta Dhi Qar Eyaleti'nin kuzeyinde yer alan Al-Gharraf Nehri boyunca seçilen dört örnekleme noktasındaki tatlı su salyangozlarında bulunan digenetik trematod serkaryalarının görülme sıklığı ve enfeksiyon oranları, Temmuz ile Aralık 2025 tarihleri arasında araştırılmıştır. Melanopsis cinsine ait iki türe (M. costata ve M. buccinoides) mensup, toplam 633 salyangoz, rastgele toplanmış ve larva evrelerinin belirlenmesi amacı güdülerek doğrudan ezme yöntemiyle incelenmiştir. İncelenen örneklerden 67'sinin enfekte olduğu belirlenmiş ve genel enfeksiyon oranı %10,58 olarak hesaplanmıştır. Enfeksiyon, yalnızca Melanopsis türlerinde saptanmış olup bu durum konak özgüllüğünü ve ekolojik tercihi göstermektedir. Morfolojik incelemeler sonucunda üç farklı serkarya tipi belirlenmiştir: pleurolophocercous, furcocercous ve ekinostomatid. Bu larva tiplerinin sırasıyla Heterophyidae, Cyathocotylidae ve Echinostomatidae familyalarına ait trematodlarla ilişkili olduğu belirlenmiştir. Elde edilen bulgular, Al-Gharraf Nehri'ndeki trematod–salyangoz etkileşimlerine ilişkin temel veriler sunmakta ve tatlı su salyangozlarının parazitlerin yaşam döngüsünde ara konak olarak üstlendikleri önemli ekolojik rolü ortaya koymaktadır.

Keywords

• Serkarya
• ara konak
• Melanopsis spp.
• parazitik çeşitlilik

Ethical Statement

Ethics committee approval is not required for this study.

Thanks

Değerli geri bildirimleri için isimsiz hakemlere içten teşekkürlerimizi sunarız. Bu çalışma, ilk yazarın Yüksek Lisans tezinin bir parçası olarak, Doç. Dr. Moayad Mijbil Ubaid ve Prof. Dr. Azhar Mohammad Al-Khazali'nin danışmanlığında yürütülmüştür. Araştırma tamamen öz kaynaklarla finanse edilmiş olup, üniversiteden veya herhangi bir dış kaynaktan mali destek alınmamıştır.

References

1. Al-Hussein, R.H. (2000). Study of the larval stages of digenetic trematode parasitizing snails, some branches of the Shatt al-Arab, and the physiological effects of the parasite Ornithobilharzia turkestesanicum on rabbits and mice. M.Sc. thesis, College of Science, University of Basra, 122 pp.
2. Al-Katea, S.T. (2020). Isolation and diagnosis of larval stages of gastropod parasites, nymphs, and mosquito larvae. M.Sc. thesis, College of Science, University of Basra, 105 pp.
3. Al-Mayah, S.H. (1998). A preliminary study on some larval flukes parasites of freshwater gastropods in Basrah, Iraq. Basrah Journal of Science, 16(1), 49–54.
4. Al-Sahaf, M. (1965). Iraq hydrology and hydrometry. Extended abstract of Cand Sci (Geogr) Thesis. Mosk. Gos. Univ, Moscow.
5. Al-Taee, S.-H., Jwair, H.J., & Al-Kubaisee, A.H.M. (2011). Exploration of aquatic snails infection with digenea in Al-Hussainea Creek, Kerbala City. Kerbala University Scientific Journal (Scientific), 9(3), 57–63.
6. Al-Waeli, A.B.M. (2014). Use of molecular technique and scanning electron microscope in freshwater snails’ taxonomy and their infection with larval trematoda in the middle and south of Iraq. Ph.D. thesis, College of Education, Al-Qadisiya University, 171 pp.
7. Amr, Z., Nasarat, H., & Neubert, E. (2014). Notes on the current and past freshwater snail fauna of Jordan. Jordan Journal of Natural History, 1(1), 83-115.
8. Arouna, N., & Remy, M. (2005). Studies on the morphology and compatibility between Schistosoma haematobium and the Bulinus sp. complex (Gastropoda: Planorbidae) in Cameroon. African Journal of Biotechnology, 4(9), 1010–1016. https://doi.org/10.4314/ajb.v4i9.71133

9. Blair, D. (1977). A key to cercariae of British strigeoids (Digenea) for which the life-cycles are known, and notes on the characters used. Journal of Helminthology, 51, 155–166.
10. Farahnak, A., & Shiekhian, R.M.I. (2004). A faunistic survey on the bird helminth parasites and their medically importance. Iranian Journal of Public Health, 33(3), 40–46.
11. Fried, B., & Graczyk, T.K. (1997). Advances in Trematode Biology. Boca Raton, CRC Press, 480 pp.
12. Ghareeb, N.R.A. (2025). Diversity and spatial and temporal distribution of gastropods and their relationship with environmental factors, with morphological identification of their associated parasites, in three streams of the Diyala River. M.Sc. thesis, College of Education, University of Diyala, 80 pp.
13. Heller, J., Mordan, P., Ben-Ami, F., & Sivan, N. (2005). Conchometrics, systematics and distribution of Melanopsis (Mollusca: Gastropoda) in the Levant. Zoological Journal of the Linnean Society, 144(2), 229-260.
14. Husain, R.J. (2023). Larval stages of trematodes in snails and their use as a bioindicator of water bodies quality in Maysan Governorate. Ph.D. thesis, College of Education, University of Basrah, 64 pp.
15. Husain, R.J., & Al-Mayah, S.H. (2024). Larval stages of digenetic trematode parasitizing freshwater snails in the water bodies of Maysan Governorate, Iraq. International Journal of Aquatic Biology, 12(1), 73–83. https://doi.org/10.22034/ijab.v12i1.2019
16. Kaewkes, S. (2003). Taxonomy and biology of liver flukes. Acta Tropica, 88(3), 177–186. https://doi.org/10.1016/j.actatropica.2003.05.001
17. Koprivnikar, J., Lim, D., Fu, C., & Brack, S.H.M. (2010). Effects of temperature, salinity, and pH on the survival and activity of marine cercariae. Parasitology Research, 106(5), 1167–1177. https://doi.org/10.1007/s00436-010-1779-0
18. Krailas, D., Namchote, S., Koonchornboon, T., Dechruksa, W., & Boonmekam, D. (2014). Trematodes obtained from the thiarid freshwater snail Melanoides tuberculata (Müller, 1774) as vector of human infections in Thailand. Zoosystematics and Evolution, 90(1), 57–86. https://doi.org/10.3897/zse.90.7306
19. Martin, W.E. (1961). Life cycle of Mesostephanus appendiculatus (Ciurea, 1916) Lutz, 1935 (Trematoda: Cyathocotylidae). Pacific Science, 15(2), 278–281.
20. Mohammad, K.M. (2015). The parasitic infection of the freshwater snails collected in central Iraq. International Journal of Current Microbiology and Applied Sciences, 4(3), 47–55.
21. Morley, N.J. (2012). Cercariae (Platyhelminthes: Trematoda) as neglected components of zooplankton communities in freshwater habitats. Hydrobiologia, 691, 7–19. https://doi.org/10.1007/s10750-012-1029-9
22. Poulin, R. (2006). Global warming and temperature-mediated increases in cercarial emergence in trematode parasites. Parasitology, 132(2), 143–151. https://doi.org/10.1017/S0031182005008693
23. Poulin, R., & Cribb, T.H. (2002). Trematode life cycles: short is sweet? Trends in Parasitology, 18(4), 176–183. https://doi.org/10.1016/S1471-4922(02)02262-6
24. Poulin, R., & Mouritsen, K.N. (2006). Climate change, parasitism and the structure of intertidal ecosystems. Journal of Helminthology, 80(2), 183–191. https://doi.org/10.1079/JOH2006341
25. Rankin, J.S. (1939). Cercariae pseudoburti n. sp., a strigeid cercaria from western Massachusetts. The Journal of Parasitology, 25(1), 87–91.
26. Roberts, L.S., & Janovy, J. (2022). Foundations of Parasitology (11th ed.). New York, McGraw-Hill Education.
27. Studer, A., Thieltges, D.W., & Poulin, R. (2010). Parasites and global warming: net effects of temperature on an intertidal host–parasite system. Marine Ecology Progress Series, 415, 11–22. https://doi.org/10.3354/meps08742
28. Sukontason, K., Unpunyo, P., Sukontason, K.L., & Piangjai, S. (2005). Evidence of Haplorchis taichui infection as pathogenic parasite: Three case reports. Scandinavian Journal of Infectious Diseases, 37, 388–390. https://doi.org/10.1080/00365540510034473
29. Tkach, V.V., Kudlai, O., & Kostadinova, A. (2016). Molecular phylogeny and systematics of the Echinostomatoidea Looss, 1899 (Platyhelminthes: Digenea). International Journal for Parasitology, 46(3), 171–185. https://doi.org/10.1016/j.ijpara.2015.11.001
30. Toledo, R., & Fried, B. (2019). Digenetic Trematodes. Switzerland, Springer. https://doi.org/10.1007/978-3-030-18616-6
31. U.S. Department of Agriculture. (2009). Fact Sheet-USDA at Work for Agriculture in Iraq. Retrieved from: http://www.fas.usda.gov/icd/iraq/Iraqfactsheet.asp.