Icosiella neglecta (Nematoda, Onchocercidae) in Ukraine: Occurrence, Hosts, Morphological and Molecular Characterisation

Icosiella neglecta (Diesing, 1851) is a filarial nematode infecting anuran amphibians in the western Palaearctic. In the present survey, we found I. neglecta in 27 out of 28 localities in eight regions of Ukraine. In those localities, 56.5 % of sampled green frogs (Pelophylax esculentus complex) were infected. The infection prevalence was similar in the two parental species, P. ridibundus (Pallas) and P. lessonae (Camerano), and their hybrid form, P. esculentus (Linnaeus), while the infection intensity was comparatively higher in P. ridibundus, as well as in the samples including both P. ridibundus and P. esculentus. Morphological examination of 40 females and 80 males of I. neglecta confirmed the consistency of main qualitative characters, whereas most metrical characters appeared to be rather variable and related to body length. Muscular oesophagus dimensions and spicule length in males were found to be the least variable. In the studied sample of males, 54 % had a longer spicule on the left side and a shorter one on the right side; the other 46 % had a longer spicule on the right side. Our molecular study using mitochondrial COI gene sequences confirmed the strong genetic similarity of I. neglecta populations in Ukraine and most other parts of its distribution area. A single nuclear 18S sequence generated was identical to one previously deposited in GenBank, originating from Ukraine.