Survival of rodent malaria merozoites in the lymphatic network: Potential role in chronicity of the infection

Experiments performed during the lost few years, lead us to hypothesise the existence of latent asexual forms of murine Plasmodium. In the present rep ort we examined the organs of infected animals and describe novel structure s, which we call merophores, containing merozoites which have resisted lysi s seen with other asexual stage parasites. We propose that these merozoites represent a latent form of the parasite. Merophores were also found in the lymphatic circulation, and were demonstrated by subinoculation to have ret ained their viability. Depending on the parasite species two types of merop hores were observed. For P. yoelii nigeriensis merophore socks, with the la tent merozoites found inside vesicles, were usually observed Merophore leuc ocytes, where latent merozoites dispersed in the cytoplasm of macrophages o r neutrophils, were solely seen with P. vinckei petteri. Both structures we re seen in P. chabaudi chobaudi infections. Merophores were found in lymph nodes of rodents after the asexual parasitaemia had apparently subsided. Th ey were formed soon after schizogony, principally in the spleen, either by pitting or by macrophage phagocytosis, Merophore numbers appeared to be pro portional to the number of maturing schizonts. We propose that merophore fo rmation and their circulation in the lymphatics play an important role in t he pattern of recrudescences and chronicity of rodent malaria infections, i t is further suggested that the lymphatic network, a privileged pathway for many parasites, might play a similar role in human malaria infections.