Biomedical subjects
Publications and source records attributed to I Landau.
The study of the sparrow Isospora in cell culture has demonstrated that during the extra-intestine life cycle, sporozoites undergo a primary division, resulting into two similar elements, whereas, in plain intra-intestinal cycle, the sporozoite is straightforwardly transformed into the first generation schizont.
Sporozoites of Plasmodium falciparum, obtained by membrane feeding of Anopheles freeborni or A. stephensi with cultured gametocytes, were used to infect monolayers of human hepatocytes. Fluorescent labelling with an African serum as well as Giemsa staining performed from day one to day 7 of cultures, demonstrated the presence of numerous hepatic schizonts measuring up to 40 micron.
Hipposideros larvatus of Thailand are parasitized by two new Haemosporidia : a) Nycteria brucechwatti n. sp. can be differentiated from all other Nycteria species by the schizonts which are the largest in the genus and by the absence of accessory chromatin dots in the gametocytes; Biguetiella minuta n. g. n. sp. has very small intra-hepatocytic schizonts (less than 15 micron) and gametocytes of the "falciparum" type. These two species are considered as vicariant forms of parasites of Miniopterus, namely Polychromophilus and Bioccala. The subgenus Bioccala is raised to genus status and problems related to the study of polyparasitic infections of the same host are discussed.
Light microscope and ultrastructural studies show that WR 225,448, an 8-aminoquinoline related to primaquine, causes substantial damage to developing pre-erythrocytic (EE) schizonts of Plasmodium yoelii yoelii in the liver of young rats. In addition to lesions of the mitochondria and nuclear membranes, secretory granules in the parasite fail to reach the surrounding host cell cytoplasm across the parasite membrane. The effective dose of WR 225,448 is much lower than that of primaquine. However, hepatic damage is also seen in treated animals. This may be the summation of damage produced by the experimental inoculation of a large quantity of infective salivary gland tissue from mosquitoes (which is also seen in untreated animals) plus toxic effects of the drug itself. Particular attention would have to be directed to this aspect in preclinical toxicity testing of the compound.
Plasmodium atheruri, a parasite of the African porcupine Atherurus africanus, is infective to splenectomised laboratory Rats and Mice, to Hamsters and to 2 exotic rodents which are easily bred in captivity: Calomys callosus and Meriones unguiculatus. Sporogony develops in Anopheles stephensi fed on Atherurus and on laboratory rodents; it is similar to that of the Rodent Plasmodia. Exoerythrocytic schizogony usually lasts 4 to 6 days but schizonts have been found in the liver of a porcupine at day 8. Schizogony in the blood (induced by inoculation of infected blood or by injections of sporozoites) follows two stages which are morphologically distinct: a) acute infections developing in clean Atherurus, following splenectomy of infected Atherurus or in laboratory rodents; it is characterized by large trophozoïtes, schizonts with 8 to 16 merozoites, gametocytes and infectivity to Anopheles. b) chronic infection which only occurs in the blood of Atherurus and follows the acute stage 15 to 21 days after its onset; it is characterized by small trophozoites and schizonts producing 4 merozoites. Thus it is thought that the chronic stage only occurs in the natural host when it is immunized. We think that, in nature, chronic schizogony maintains the parasitaemia through periods of low transmission and is followed by "recrudescences". The mechanisms that trigger the "recrudescences" are unknown but are probably connected with a decrease in the immune status of the host.
Wistar rats were injected intravenously with sporozoites from Anopheles stephensi infected with Plasmodium yoelii yoelii. The animals were subsequently treated with primaquine at doses of 30, 50 or 100 mg kg-1 at various times. Liver biopsies were made and the exoerythrocytic schizonts examined by light and electron microscopy between 45 and 50 hours. The action of the drug appeared to be principally on the parasite mitochondria, the membranes of which became thickened, then proliferated into multiple layers. Finally the whole organelles swelled up losing all structural organisation. Other parasite membranes were affected similarly and the peripheral enzyme granules disappeared. Following treatment the small, disrupted schizonts were apparently absorbed by their host cells which appeared unaffected by primaquine.
Human hepatocytes obtained by perfusion of a liver biopsy fragment, were infected in vitro with Plasmodium vivax sporozoites raised in Anopheles stephensi. On day 7 of culture, numerous hepatocytic schizonts ranging in size from 5 to 35 micrometers were observed. The schizont maturation was complete and led to the release of invasive merozoites as shown by in vitro infestation of human red cells layered on the hepatocytes cultures.
Hepatocytes isolated from an African rodent, Thamnomys gazellae, by perfusing the liver with a solution of collagenase were cultured in modified MEM medium, and infected in vitro by sporozoites of the 17 X strain of P. y. yoelii. 48 hrs. later, schizonts measuring 30 to 40 microns on average were observed in all cultures. Injection of culture supernatant, harvested on day 3, into Mice, was followed by a parasitaemia demonstrating that viable merozoites had been released by the schizonts.
P. falciparum sporozoïtes obtained by membrane-feeding of Anopheles stephensi with blood containing gametocytes were injected intravenously to the Monkey Cebus apella. 5 days later, a great number of exo-erythrocytic stages were found in the liver, and appeared to be morphologically similar to those described in man. The host specificity of the sporozoïte seems less restricted than that of the merozoïte.
Two out of four Psittacula roseata from Thaïland harboured a trypanosome: T. bakeri n. sp. Laboratory reared Culicoides nubeculosus were fed on one of them. The trypanosomes developed well in this arthropod and metatrypomastigotes were observed five days after the blood meal. The inoculation of crushed Culicoides into one of the trypanosome-free Psittacula gave rise to a parasitaemia after a prepatent period of eleven days. This provides more evidence that Culicoides can act as vectors of avian trypanosomes.
Histological and ultrastructural aspects of acute and chronic pre-erythrocytic schizonts of P. yoelii yoelii were studied with: a) acute schizonts in normal rodents; b) chronic schizonts induced in rodents receiving ethionine injections or on a low methionine diet; Experimentally induced chronic schizonts frequently have the same histological aspect as those observed in wild Thamnomys from Africa. The ultrastructural evolution of the vacuole system described by Seureau et al. in acute schizonts is discussed; new evidence is presented to support the hypothesis according to which the contents of the vacuoles are enzymatic in nature. Ultrastructural studies of chronic schizonts show alterations in the sites of synthesis (zones of rough endoplasmic reticulum small and not numerous, absent in the most delayed schizonts; vesicle system poorly developed and also disturbances of nuclear development (slow division, apparently inhibited in the most retarded forms.) A peripheral accumulation of vacuoles in many chronic schizonts without discharge of their contents to the parasitophorous space, might indicate an alteration of their membranes, leaving them unable to fuse with the schizont plasmalemma.
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Natural intestinal infection of Isospora in the domestic Sparrow was studied during one year on a farm in Normandy. This survey showed many species and constant multiple infections. Some species were present all year, others were found only at certain times of the year; intensity varied with species and season. Almost all of the Isosporans previously described from the Sparrow were assigned to Isospora lacazei (Labbé, 1893), but this species is shown here in to be a parasite of the Goldfinch. Twelve new species are described on the basis of morphology of fresh sporulated oocysts. The most useful characters are those of: a) the Stieda apparatus and its inclusions;' b) the polar granules (number and shape); c) the residual body (diffuse or well delineated). In addition, the size and shape of oocysts and sporocysts, the number and shape of cristalloids in the sporozoites can be used to differenciate species. The following observations were made on sporogony: a) each species develops at a particular level in the intestine but several species could be found at the same level. However there is a patchy distribution of the species such that no two species occurred in the same villus. b) synchronous excretion of oocysts noted by others was found: the first oocysts appear at the beginning of the afternoon, the last at night fall; each species was found to have a characteristic and limited period of excretion. All the species found belong to the same systematic group (Stieda apparatus "macropylar") which suggests that they arose from successive speciations from a single species and were not acquired from other passerines in the same habitat.
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Salivary glands of A. stephensi, containing P. yoelii' sporozoites, were disrupted and added to hepatocyte cultures originated from the liver of an adult Rat perfused with a collagenase solution. 47 h after this in vitro inoculation, numerous well-developed and normal-looking schizonts were found in the hepatocyte monolayer.
The gametogony and the tissue schizogony of Parahaemoproteus desseri are described in the natural host: Psittacula roseata; the schizonts develop in muscle fibres; they are large (up to 900 micrometer) and often sausage shaped with pseudo-septa. Experimental sporogony was studied in laboratory bred Culicoides nubeculosus (Ceratopogonidae). Oocysts are small and give rise to a small number of sporozoites. The morphological characteristics of the schizonts of our Parahaemoproteus are very similar to those of schizonts of Arthrocystis galli and therefore it is possible that the two genera are synonymous.
A frozen strain of Plasmodium yoelii nigeriensis is inoculated at 4 pm, midnight and 9 am onto inbred Mice. In all instances young gametocytes (type 0) appear in the blood only between 10 am and 6 pm. Although the erythrocytic schizogony occurs regularly during the whole circadian period, the latency increases progressively when the infective subinoculations are made at midnight, 4 pm and 9 am. Possibly, the infective merozoite can only enter the red blood cell around midnight.
A morphological study has been made of the gametocytes of P. yoelii (a parasite of Rodents belonging to the "vivax" group). The authors distinguish 4 types chronologically ordered. Moreover, morphology enables one to predict their infectivity. The morphological analysis represents a tool leading to new data on the biology of gametocytes: loss of infectivity as soon as the parasitaemia becomes high; infectivity restricted to the young stages; concentration of young stages in the blood ingested by the Mosquitoes; short periodicity and short lived infectivity.