TURNOVER OF MICROFILARIAE IN SMALL MAMMALS .1. DISINTEGRATION OF MICROFILARIAE (LITOMOSOIDES-SIGMODONTIS) (FILARIOIDEA, NEMATODA) AFTER INTRAVENOUS-INJECTION INTO SIGMODON-HISPIDUS, THE COTTON RAT

After i.v. injection of 833 x 10(3) microfilariae (mf) per animal (150 g) into naive recipient cotton rats, at autopsy 15 min thereafter 30. 4 % of them could be recovered as a total: 19.1 % were proved in the p eripheral circulating blood (PCB) completely intact. 6.5 % were recove red by perfusion of the lungs, of which 3/5 were associated with adher ent macrophages and neutrophils or partly disintegrated. By perfusion of the liver only 3.8 % were obtained, in spite of the four times grea ter volume of blood, of which 2/3 had adherent cells or were partly di sintegrated. 0.7% and 0.3% were recovered from kidneys and spleen, res pectively. In patent animals with adult worms the permanently delivere d mf were distributed as follows: 41.6 % were proved in the PCB; by pe rfusion 19.1 % were obtained from the lungs and 32.9 % from the liver; the rest of 6.4 % were found in kidneys and spleen. In the capillary systems of lungs as well as the liver the proportion of normal mf (1/3 ), with adherent cells (1/3), partly disintegrated ones (1/5) and frag ments (1/20) were quite similar. In long term mf injection experiments using the same dosage the autopsy was done 30 min and 1, 2, 3 and 28 days p. inj. of mf into naive animals. 30 min p.inj. 56 % of the mf in jected could be recovered as a total: 28.6 % were obtained from the PC B, 16.0 % from the lungs and 7.1 % from the liver as normal mf (no per fusion), the rest of 4.1 % from heart muscle, kidneys and spleen. Alre ady after two days and pronounced after four weeks a shifting, most pr obably of aged mf after their normal sojourn, from the circulating blo od to the liver was observed. During the normal course of the filiaria sis, obviously, from the very first delivered mf a considerable propor tion will be rapidly disintegrated in the lungs and somewhat less in t he liver. At fully developed patency two communities of mf must be pos tulated: One fifth in the lungs being metabolized rapidly (median of l ife time 2 days), the others entering the circulating blood and being metabolized in the liver after their normal sojourn (median of circula tion time 7 days). Increasing levels of mf delivery by the adult worm load (fecundity) seems to be buffered by the mf accumulating in the lu ngs in order to maintain a moderate parasitaemia.