RESUMEN
Schizonts of all rodent Plasmodium studied (Plasmodium yoelii, P. chabaudi, P. vinckei) show a characteristic morphology when they are completely mature: rounded or slightly elongate merozoites, completely detached from the pigment mass. At this stage, they are localized principally in the spleen and the lungs but, in impression smears of these organs they show two different aspects. In the spleen, schizonts are either inside the host erythrocyte or extraglobular but still close to a pigment mass; free merozoites are rare. In the lungs, on the contrary, merozoites are often free and dispersed; electron microscopy showed them to lie against the endothelium. Work by physiologists has shown the blood circulation in the alveoli to be much slowed down. Free merozoites, lined against the endothelium of relatively rigid capillaries, are in the best possible conditions to make contact with the intact red blood cells. Lungs appear to be the privileged site for the invasion of erythrocytes by the merozoites.
Asunto(s)
Eritrocitos/parasitología , Pulmón/parasitología , Malaria/patología , Plasmodium/crecimiento & desarrollo , Animales , Capilares/parasitología , Capilares/patología , Capilares/ultraestructura , Pulmón/ultraestructura , Malaria/sangre , Ratones , Plasmodium chabaudi/crecimiento & desarrollo , Plasmodium yoelii/crecimiento & desarrollo , Alveolos Pulmonares/irrigación sanguínea , Circulación Pulmonar , Especificidad de la EspecieRESUMEN
Experiments performed during the last few years, lead us to hypothesise the existence of latent asexual forms of murine Plasmodium. In the present report we examined the organs of infected animals and describe novel structures, which we call merophores, containing merozoites which have resisted lysis 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 retained their viability. Depending on the parasite species two types of merophores were observed. For P. yoelii nigeriensis merophore sacks, with the latent merozoites found inside vesicles, were usually observed. Merophore leucocytes, where latent merozoites dispersed in the cytoplasm of macrophages or neutrophils, were solely seen with P. vinckei petteri. Both structures were seen in P. chabaudi chabaudi infections. Merophores were found in lymph nodes of rodents after the asexual parasitaemia had apparently subsided. They were formed soon after schizogony, principally in the spleen, either by pitting or by macrophage phagocytosis. Merophore numbers appeared to be proportional to the number of maturing schizonts. We propose that merophore formation and their circulation in the lymphatics play an important role in the pattern of recrudescences and chronicity of rodent malaria infections. It is further suggested that the lymphatic network, a privileged pathway for many parasites, might play a similar role in human malaria infections.
Asunto(s)
Sistema Linfático/parasitología , Malaria/parasitología , Plasmodium/patogenicidad , Animales , Enfermedad Crónica , Resistencia a Medicamentos , Sistema Linfático/ultraestructura , Masculino , Ratones , Microscopía Electrónica , Ratas , EsplenectomíaRESUMEN
A host harbouring many parasite species of the same genus is a phenomenon frequently observed in numerous parasitic infections. This is the case for the Plasmodium parasites of Muridae in Central Africa, where three different parasite species are found in the same rodent host species. It is highly likely that these three Plasmodium species are transmitted simultaneously by the same vector. We and others have shown that the maturation periods of the various asexual and sexual stages in the rodent, differ amongst the three parasites. In this article we propose that these differences are the product of complex adaptations which result, for all three Plasmodium species, in a maximum peak of infectivity to the insect vector occurring around 3 a.m., the period of highest activity of the nocturnal host rodent.
Asunto(s)
Muridae/parasitología , Plasmodium/fisiología , Animales , República Centroafricana , Malaria/transmisión , Maduración Sexual , Factores de TiempoRESUMEN
Vesicles containing apparently healthy merozoites from mature schizonts were observed in the spleen and lymph nodes of mice parasitized by Plasmodium yoelii nigeriensis. They differed from all parasitic stages undergoing digestion by the macrophage and from mature schizonts of the blood. Up to 40 merozoites from three mature schizonts may be seen in the same compartment. They are thought to be accumulations of latent merozoites.