Erythrocytic and merogonic stages of Hepatozoon ridibundae sp. nov. infecting the Arabian ranid frogs, Rana ridibunda in Saudi Arabia with reflections on the haemogregarine complex.

The prevalence and levels of parasitaemia of haemogregarine infection among Arabian ranid frogs, Rana ridibunda, in Saudi Arabia was studied for the first time. Erythrocytic and merogonic stages of Hepatozoon ridibundae sp. nov. in the intermediate vertebrate host, R. ridibunda were described by light microscopy. The erythrocytic parasites were differentiated into small form (trophozoite) measuring 14.6 +/- 0.3 x 3.8 +/- 0.4 microm and the mature form (gamont) which was banana-shaped with hooked anterior end and blunt broad posterior end and measuring 19.8 +/- 1.8 x 5.2 +/- 0.6 microm. The gamonts of the present parasite induced nuclear fragmentation or segmentation in host erythrocytes. Merogony, of the ectomerogonic type, took place in the liver parenchyma cells. Two meront types were observed. Small meronts (micromeronts) yielded 2-6 (average 4) large merozoites (macromerozoites) measuring 16.6 +/- 0.6 x 6.2 +/- 0.5 microm in size. Large meronts (macromeronts) yielded 18-30 (average 24) elongated merozoites (micromerozoites) measuring 15.2 +/- 0.3 x 3.8 +/- 0.4 microm. A partial systematic revision of the haemogregarine complex was discussed in the view of the diagnostic characteristic features of the 6 recognized haemogregarine genera.