New features on the moults and morphogenesis of the human filaria Loa loa by using rodent hosts consequences.

The development of the human filaria Loa loa (Dirofilariinae, Onchocercidae), previously studied in monkeys, was studied using the non permissive hosts-mice and jirds. The development proved to be rapid: moult 3 occurred on day 8 post-inoculation, the adult stage was reached on day 25 and measured at that time 3-3.5 mm in length. As in the other filarioids, the female genital apparatus developed during the fourth stage. A critical analysis of the studies on the development of Onchocercid species was made. The optimal duration of the stages (i.g. the shortest time) was chosen for the comparison. It appeared that the duration of the stage 3 was a constant character in a given species whatever the experimental conditions, whereas moult 4 might be retarded in a non susceptible host. Comparison between the 18 developmental cycles of Onchocercidae in the vertebrate host was made. Two biological types could be distinguished: either the moult 3 occurred on day 2-3 and was followed apparently by a late moult 4 (> or = 50 days), or the moult 3 occurred after about one week of development and it was associated with a less long stage 4 (20-40 days). The first group includes Dirofilaria and Onchocerca, the second group brings together mainly Loa and the Onchocercinae of the Dipetalonema line and related genera (Acanthocheilonema, Brugia, Litomosoides, etc.). The groups thus formed suggest real relationships as they fit with the morphology of the infective stage and the results of a recent molecular analysis of the 5S DNA.