Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

In this study with the filarial model Litomosoides sigmodontis, we demonstrate that the worms ingest host red blood cells at a precise moment of their life-cycle, immediately after the fourth moult. The red blood cells (RBC) were identified microscopically in live worms immobilized in PBS at 4 °C, and their density assessed. Two hosts were used: Mongolian gerbils, where microfilaraemia is high, and susceptible BALB/c mice with lower microfilaraemia. Gerbils were studied at 12 time-points, between day 9 post-inoculation (the worms were young 4th stage larvae) and day 330 p.i. (worms were old adults). Only the very young adult filarial worms had red blood cells in their gut. Haematophagy was observed between days 25 and 56 p.i. and peaked between day 28 and day 30 p.i. in female worms. In males, haematophagy was less frequent and intense. Similar kinetics of haematophagy were found in BALB/c mice, but frequency and intensity tended to be lower. Haematophagy seems useful to optimize adult maturation. These observations suggest that haematophagy is an important step in the life-cycle of L. sigmodontis. This hitherto undescribed phenomenon might be characteristic of other filarial species including human parasites.

The small size of many parasitic organisms requires the use of election microscopy for adequate elucidation of their structure. While both transmission and scanning electron microscopy can provide complementary results which allow considerable degree of structural correlation, each technique has its inherent limitations. Since previous studies have demonstrated that soft X-ray microscopy could be used to study parasitic protozoa and provide new information, the objective of this study was to determine whether soft X-ray microscopy could also be used to elucidate the morphology of small metazoa to complement the data obtained by other microscopy techniques.

Newborn larvae, approximately 7 μm × 110 μm in size, of parasitic nematode Trichinella spiralis were used as a model system. Some of the larvae, deposited by adult females maintained in vitro, were isolated and processed for examination by transmission and scanning electron microscopy as described in our previous studies, others were fixed in 4% glutaraldehyde (Millonig's buffer) and examined in the X-ray microscope XM-1, and in the BioRad MRC 1024 confocal laser (krypton/argon) microscope of the Advanced Light Source, Berkeley National Laboratory.