Trypanosoma cruzi: skin-penetration kinetics of vector-derived metacyclic trypomastigotes

In order to investigate the natural route of infection of nude and normal BALB/c mice with Trypanosoma cruzi via the skin, a drop of vector faeces/urine containing metacyclic trypomastigotes was placed onto the puncture site of a bite from Triatoma infestans. The periods of exposure, i.e. until removal of flagellates from the skin, and the time elapsed until surgical removal of the skin around the puncture were varied. After 15 min of exposure, T. cruzi developed in all nude mice without surgery, and in four of 10 mice if the puncture region of the skin was removed directly after exposure. In a shaved puncture region, 5 min of exposure were sufficient to infect all normal BALB/c mice without surgery and one of four mice with direct removal of the puncture region. Longer periods of exposure or time until removal of the skin only sometimes resulted in higher infection rates. Prepatent periods and the development of parasitaemia varied irrespective of the period of exposure or the period until skin removal at the puncture site. The importance of these findings is that they clearly prove that T. cruzi can rapidly invade the host via the puncture site of the bite of the vector and that at least some parasites are immediately transported away from this site.