TURNOVER OF MICROFILARIAE IN SMALL MAMMALS .2. DISINTEGRATION OF MICROFILARIAE (ACANTHOCHEILONEMA-VITEAE) (FILARIOIDEA, NEMATODA) AFTER INTRAVENOUS-INJECTION INTO THE JIRD, MERIONES-UNGUICULATUS

After i.v. injection of 305 x 10(3) microfilariae (mf) per animal (50 g) into naive jirds, 50.8% of them could be recovered at autopsy 15 mi n later. Of these, 65.8% were calculated to be in the peripheral circu lating blood (PCB) and were completely intact; 18.6% were recovered by perfusion of the lungs and 13.6% from the liver. In both organs about half the mf were associated with adherent lymphocytes and neutrophils but a few were partly disintegrated. Only 2.6% were recovered from th e kidneys and the spleen. In long-term injection experiments using the same inoculum size the autopsy was done 15 min and 1, 3 and 6 weeks p ost-injection (p.i.) of mf into naive jirds. Throughout the experiment al period the density of mf remained more or less constant in the PCB, but 3 weeks p.i. the density in the lungs increased up to 14 times to that in the PCB, whereas in the liver it decreased at the same time t o a density similar to that in the PCB. In patent animals with adult w orms delivering mf these were distributed as follows: 34.7%, were calc ulated to be in the PCB; 24.4% were obtained by perfusion from the lun gs and 22.0% from the liver; the rest were found in the kidneys (16.6% ) and spleen (2.3%). In the lungs and the liver about 5/6 were associa ted with adherent cells, partly disintegrated or as fragments. In view of the fact that very few mf become disintegrated immediately after i .v. injection and also from their extremely long sojourn in the PCB, a low turnover rate of mf is presumed. The limited fecundity of the fem ale adults combined with the 20 weeks median circulation time of injec ted mf in the PCB supports this view.