Rediscovery and redescription of Plasmodium pifanoi and description of two additional Plasmodium parasites of Venezuelan lizards

Plasmodium pifanoi Scorza and Dagert B., known only from the type host, Ameiva ameiva, is redescribed from Kentropyx calcarata collected in Territorio Amazonas, Venezuela. Schizonts, 6.2 x 4.5 (4-8 x 3-6), produce on average 11.9 (7-16) merozoites. Gametocytes average 12.4 x 6.0 (8-16 x 4-10), with length x width (LW) 72.9 (52-112) and L/W 2.18 (1.1-3.3), and always contain 1-5 prominent vacuoles. Macrogametocytes in active infection are longer than microgametocytes, with greater LW, but gametocytes in chronic infection are not sexually dimorphic in dimension and are slightly smaller. Two additional malarial parasites are described from K. calcarata. Plasmodium lepidoptiformis has small schizonts, 4.6 x 3.2 (3-6 x 2.5-3), that produce 5.1 (4-8) merozoites and commonly resemble a butterfly in appearance. Gametocytes are elongate, 9.0 x 4.3 (7-10 x 3-6), with LW 38.3 (24-51) and L/W 2.2 (1.3-3.3), and sexually dimorphic, with macrogametocytes longer than microgametocytes, with greater LW. Plasmodium minasense calcaratae is characterized by very small, usually fan-shaped, schizonts. 3.4 x 2.6 (2.5-4.5 x 2.0-3.0), that produce 3.9 (3-4) merozoites. Gametocytes are spherical or ovoid, 6.7 x 5.0 (4.5-9.0 x 3.0-7.0), with LW 33.7 (15-54) and L/W 1.4 (1.0-2.3), with no sexual dimorphism in dimensions.     

Two malaria parasites (Apicomplexa: Plasmodiidae) of the Australian skink Egernia stokesii

The Australian skink Egernia stokesii is parasitized uncommonly by Plasmodium circularis n. sp. and by Plasmodium mackerrasae. Plasmodium circularis is distinguished from all other plasmodiids by immature schizonts that encircle host cell nuclei, forming an unbroken ring from apparent fusion of the attenuated ends. Mature schizonts contract into halteridial or dumbbell-shaped forms 15.6 x 4.3 microm, LW 66.2 microm2, with 19-52 nuclei. Rounded or oval gametocytes are 9.0 x 7.3 microm, LW 66.9 microm2, and L/W 1.24. Gametocyte LW is 2.63 x host erythrocyte nucleus size and 1.79X uninfected erythrocyte nuclei. Plasmodium mackerrasae occurs in high prevalence and often massive parasitemia in E. stokesii. Schizonts, often oblong, elongate, or oval, are 5.1 x 3.7 microm, LW 19.8 microm2, with 7.2 merozoites. Immature gametocytes, elongate with terminal nucleus, may produce multiple infections of 6 or more parasites. Mature gametocytes, usually rounded, are 5.8 x 4.6 microm, LW 26.7 microm2, and L/W 1.29. Gametocyte size is 0.98 x host erythrocyte nucleus size and 1.03 x uninfected erythrocyte nuclei. Phanerozoites, in endothelium or connective tissue of most organs, may appear in large numbers in circulating blood as seemingly intact bodies of regular form, similar to or larger than phanerozoites seen in sections. Previously unreported phenomena for hemosporidian parasites include extremely large, highly irregular exoerythrocytic schizonts, in circulating blood, perhaps torn from endothelial lining of blood vessels and sinuses, and a visible flooding of free merozoites into the blood stream.     

A Haemocystidium species from the East African gecko Lygodactylus capensis grotei

Haemocystidium lygodactyli n. sp. parasitizes Lygodactylus capensis grotei (Gekkonidae) in Tanzania. Mature gametocytes in acute phase of infection average 16.3 x 5.7 microm (11-20 x 4-9.5 microm), with LW 93.0 (62-140 microm2) and L/W ratio 2.94 (1.2-3.9). Gametocytes usually lateral, lateropolar, or halteridial in position. There was no significant sexual dimorphism in gametocyte dimensions. Nuclei discrete in both sexes at maturity, with a rounded nucleolus usually present in microgametocytes. In chronic infection, gametocytes were 18.1 x 8.7 microm (8-25 x 5-11 microm), with LW 156.8 microm2 (80-250) and L/W 2.16 (1.1-3.6). When gametocytes from the chronic infection were compared with the same sex in acute infection, length did not differ, but differences were present between the same sex in each comparison of width, LW, and L/W. Macrogametocytes and microgametocytes in chronic phase were broader, larger, and less elongate and most commonly halteridial. Meronts were found only in endothelium and connective tissue of lung. Elongate to oval in shape, the larger meronts filled with nuclei were 12.2 x 6.9 microm (10.0 x 5.0-16.0 x 9.0), with LW 50-144 microm2 (85.1). In 1 initial infection followed for 49 days, apparently mature gametocytes appeared by day 28 postcapture. Binucleate parasites were present from day 14 throughout the course of infection, with their frequency increasing from 5% of immature parasites to 34% of mature gametocytes. Binucleate mature gametocytes were found in 1 other infection, where 14% had 2 nuclei. Sex ratio varied from 51 to 63% in favor of macrogametocytes.     

Studies on African saurian malarias: Plasmodium holaspi n. sp. from the flying lacertid Holaspis guentheri

The African flying lizard Holaspis guentheri (Lacertidae) from the Uluguru Mountains, Tanzania was found infected by an undescribed malarial parasite, Plasmodium holaspi n. sp. Gametocytes were elongate, approximately twice the size of host cell nuclei, and showed prominent, irregular pigment granules. Schizonts were oblong or formed as rosettes, approximated the host cell nucleus in size, and produced 8-18 merozoites. Maturing gametocytes contained large masses or blocks of chromatin which can obscure sexual differentiation by staining reaction, while young gametocytes and asexual stages almost always occupy marginal positions in host cells. These characteristics distinguish P. holaspi from all other saurian Plasmodium species. This is the first malarial parasite described from African lacertid species.     

Redescription of Haemoproteus mesnili (Apicomplexa: Plasmodiidae) and its meronts, with description of a second haemosporidian parasite of African cobras

Haemoproteus mesnili (Bouet 1909) Wenyon 1926 is redescribed from the spitting cobra, Naja nigricollis nigricollis, of Tanzania. Mature gametocytes in the acute phase of infection averaged 17.7 X 7.3 jim, with LW 128.1 jim-, and L:W ratio 2.52. Nuclei were visible in both sexes. Both sexes were heavily pigmented, with 31-62 black granules dispersed in macrogametocytes; 20-46 granules were often clumped or concentrated near ends of microgametocytes. The halteridial form was present in 28% of active-phase gametocytes, but in only 8% of those in chronic phase. A few large, possibly first generation, meronts were present in cardiac muscle; uninucleate parasites within parasitophorous vacuoles in splenic cells produced small rounded or ovoid meronts, 12.2 x 9.6 microm, with 12-16 deeply basophilic, square-to-rectangular cytomeres. Meronts with 17-32 cytomeres were 16.9 x 11.9 microm. Meronts, 20 x 16 to 26 x 22 microm, contained 51-57 cytomeres. Mature meronts were ovoid, 13.7 x 11.5 microm, with many rounded merozoites. Haemoproteus balli n. sp, found in an Egyptian cobra, Naja haje haje of Kenya, differs from H. mesnili in average gametocyte dimensions, 10.8 x 7.7 microm; LW, 83.2 microm2; L/W ratio, 1.42; absence of halteridial forms; sparse pigmentation (3-10 granules); and presence of a broad peripheral band, apparently chromatin, along one side of microgametocytes.     

A population of Pasmodium colmbiense sp. n. in the iguanid lizard, Anolis Auratus.

Plasmodium colombiense sp. n. is described from 274 naturally infected Anolis auratus from western Colombia. Host blood pictures, parasitemia, parasite structure, infection states, and host population dynamics are correlated. Local epidemics occur, but in contrast to temperate zone species there is little regional synchronization. Active infections occur year-around, being somewhat more common in dry seasons; however, chronic infections predominate. Mature schizonts have 3 to 14, usually 6, 8, or 10 merozoites, reduced to 4 to 6 in chronic infections. Gametocytes are round to oblong, measuring 6 by 5 mu, and the pigment in microgametocytes occurs in a single peripheral vacuole. Parasitemia averaged 2.5% and seldom surpassed 20 to 30%. Infections cause significant anemia, and parasites in active infections are most common in immature erythrocytes. Host response is similar to avian or primate infections, including erythropoiesis, phagocytosis, and interference with parasite growth.     

Plasmodium knowlesi: studies on invasion of rhesus erythrocytes by merozoites in the presence of protease inhibitors

The effect of protease inhibitors on invasion of rhesus erythrocytes by Plasmodium knowlesi merozoites was evaluated. Chymostatin, N-alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK), and L-1-tosylamide-2-phenylethylchloromethyl ketone (TPCK) inhibited invasion. Leupeptin, antipain, pepstatin, and phenylmethylsulfonyl fluoride (PMSF) had no effect. TLCK and TPCK inhibited attachment of merozoites to host erythrocytes. Chymostatin had no adverse effect on attachment, and in its presence junction formation between the merozoite and host erythrocyte occurred. Both chymostatin and leupeptin inhibited normal rupture of schizont-infected erythrocytes. It is suggested that proteolytic activity may be important both in the rupture of schizont-infected erythrocytes and in the invasion of erythrocytes by malaria parasites.     

Two additional Hepatozoon species (Apicomplexa: Hepatozoidae) from the southern black racer, Coluber constrictor priapus (Serpentes: Colubridae), in northern Florida

Hepatozoon priapus n. sp. from Coluber constrictor priapus has robust gamonts with broadly rounded ends, 18.0 x 4.2 microm (17.0-20.0 x 3.5-6.0), with LW 76.4 microm2 (59-105) and L/W 4.31 (2.9-5.4). The nucleus is always present in second quarter of gamont, seldom extend into first quarter but often into third quarter, 6.0 x 3.0 (5.0-7.0 x 2.5-4.0), with LW 17.9 (13.7-21.0). Erythrocyte cytoplasm is always thin, appearing dehemoglobinized, with infected cells always distorted. Infected erythrocytes are much longer and wider than uninfected cells, with longer nuclei. Oocysts are spherical to ovoid, 92.5 x 86.0 (55-123 x 47-115) and L/W 1.08 (1.0-1.3), contain 14.0 (6-31) sporocysts. Sporocysts, which are also spherical to ovoid, 26.3 x 23.3 (19-50 x 16-38), LW 641.2 (320-1,500) and L/W 1.13 (1.0-2.2), contain 12.6 (5-18) sporozoites. Hepatozoon confusus n. sp., also from C. constrictor priapus, has slender gamonts with rounded ends, 15.6 x 4.1 (14.0-17.0 x 3.5-5.0), with LW 64.3 (52-80) and L/W 3.82 (2.8-4.4). The nucleus is always present in second quarter of gamont, commonly extending into first and third quarters, 5.0 x 2.7 (2.5-4.4 x 4.0-6.0), with LW 13.5 (11.0-16.5). Erythrocyte cytoplasm is sometimes thin, appearing partially dehemoglobinized, with infected cells usually distorted. Infected erythrocytes are longer than uninfected cells but similar in width, with erythrocyte nuclei longer. Oocysts are spherical to ovoid, 115.5 x 108.9 (52-278 x 50-278), with L/W 1.06 (1.0-1.2), and contain 25.0 (7-111) sporocysts. Sporocysts are spherical to ovoid, 27.6 x 25.2 (21-38 x 20-33), LW 701.3 (420-1,125) and L/W 1.09 (1.0-1.4), containing 20.2 (12-32) sporozoites.     

Plasmodium (Sauramoeba) pelaezi n. sp., a malaria parasite of the mexican iguanid lizardUrosaurus bicarinatus bicarinatus (Dumeril, 1856) (Sauria: Iguanidae)

A new Mexican species of saurian malaria parasite,Plasmodium (Sauramoeba) pelaezi, is described from the iguanid lizardUrosaurus bicarinatus bicarinatus. Two out of 12 specimens collected at Chila de la Sal (Puebla, México) were found infected. The species is characterized by round and oval gametocytes. Schizonts are mostly round with a single mass of pigment and with 16 merozoites in mature forms. Gametocytes cause shrinkage of infected cells and schizonts render the host cell nuclei spherical.     

Additional Fallisia spp. (Apicomplexa: Plasmodiidae) of Neotropical lizards

Fallisia biporcati n. sp. parasitises thrombocytes and lymphocytes of Anolis biporcatus and A. lionotus in Panama. Round or oval schizonts average 13.3 × 11.5 (10.5–16 × 9–13) m, with LW 153.8 (94–208) m², and produce 38.3 (28–60) merozoites. Gametocytes are variably shaped, from round or oval to nearly triangular or rectangular, and average 12.6 × 9.0 (10–15 × 6–12) m, with LW 113.1 (82–150) m² and L/W ratio 1.43 (1.0–2.2). Thrombocytes and lymphocytes of A. poecilopus in Panama are parasitised by F. poecilopi n. sp. Schizonts, oval to elongate in shape, 7.7 × 4.7 (5.5–9 × 3–6) m, with LW 36.5 (22–54) m², are filled with 31.0 (20–51) tiny nuclei or merozoites. Gametocytes are 10.1 × 8.0 (7.5–14 × 6–11) m, with LW 82.0 (45–132) m², round to elongate with L/W ratio 1.27 (1.0–1.6). F. thecadactyli n. sp. parasitises thrombocytes and lymphocytes of Thecadactylus rapicaudus in Panama and Venezuela. Oval, oblong, or triangular schizonts average 10.3 × 8.0 (7–13 × 5–12) m, with LW 86.6 (37–156) m², and produce 40.2 (26–61) merozoites. Gametocytes are round, oval, triangular or elongate, 10.4 × 7.0 (7–15 × 5–11) m, with LW 74.8 (40–154) m² and L/W ratio 1.51 (1.1–2.2). F. dominicensis n. sp. parasitises thrombocytes of A. cybotes on Hispaniola. Schizonts, 6.0 × 4.8 (4–8 × 3–7) m, with LW 29.1 (12–56) m², round, oval, elongate, oblong or lentiform in shape, produce 12.4 (8–22) merozoites. Gametocytes are 6.6 × 5.0 (5–9 × 4–7) m , with LW 33.8 (20–56) m², round, oval or elongate, and L/W ratio of 1.34 (1.1–2.0).     

Hepatozoon polytopis n. sp. parasitic in two genera and species of colubrid snakes in southern Florida

Hepatozoon polytopis, described from Coluber constrictor priapus from Palm Beach County, Florida, has short, usually broad gamonts 12.8 x 4.6 microm (10.0-15.0 x 3.5-6.0), with LW 58.5 microm2 (42-84) and L/W 2.84 (1.8-3.7). Nuclei commonly extend into first quarter of gamont (45%), are always present in second quarter, and seldom in third quarter (11%), with dimensions 4.5 x 3.4 (3.0-6.0 x 2.5-4.5) and LW 15.1 (10.0-24.0). Spherical to ovoid oocysts, 122.1 x 104.9 (62-240 x 57-190), with L/W 1.17 (1.0-1.9), contain 31.3 (3-103) sporocysts. Spherical to ovoid sporocysts, 38.0 x 33.9 (28-73 x 25-58), with LW 1,325.1 (756-4,168) and L/W 1.12 (1.0-1.4), contain 42.9 (22-64) sporozoites. Thamnophis sauritus sackenii from Palm Beach County is infected also by H. polytopis, as indicated from similar gamont dimensions and verified by isolation of an identical haplotype of the 18S ribosomal RNA gene from both host species.     

Haematozoa of fishes in Humboldt Bay, California.

Five hundred seven fish representing 45 species from Humboldt Bay, California (USA) were examined for blood parasites. Four fish (less than 1%) from two species were infected. Haemogregarina leptocotti sp. n. is described from one of 33 staghorn sculpin (Leptocottus armatus). Haemogregarina roelofsi sp. n. is described from three of 15 black rockfish (Sebastes melanops). Gametocytes of H. leptocotti sp. n. averaged 6.1 x 2.1 microns with a 2.7 x 1.7 microns oval nucleus; those of H. roelofsi sp. n. averaged 5.5 x 2.7 microns with a 2.5 x 2.2 microns rectangular nucleus. Neither species of parasite had distinct chromatin granules, a polar cap, or more than one gametocyte in an infected cell. Haematozoa are relatively rare in fishes of the northeastern Pacific Ocean.     

Development and ultrastructure of first-generation meronts of Sarcocystis cruzi in calves fed sporocysts from coyote feces

The development of Sarcocystis cruzi Hasselmann (syn. S. fusiformis Railliet) meronts was studied in seven 7- to 10-day-old calves filled 4, 7, 11, 15, 22, 25 and 28 days postinoculation (DPI) with 5 x 10(7) sporocysts from feces of coyotes. No meronts were found 4 and 7 DPI. Young and intermediate meronts with 1-16 nuclei were found in endothelial cells of arteries in mesenteric lymph nodes, but not in kidneys 11 DPI. Mature meronts were noted in endothelial cells of arteries, arterioles, or capillaries of many organs of calves killed 15 to 25 DPI. No first-generation meronts were found 28 DPI. By electron microscopy, all stages of the first-generation merogony were found free within the host cell cytoplasm and not within a parasitophorous vacuole. The appearance of intranuclear spindles preceded the formation of merozoites by endopolygeny. Mature meronts measured 41.0 x 17.5 (34-50 x 15-24) microgram, contained approximately 100-350 merozoites, and had 2 to 4 relatively small residual bodies, 2.8 microgram in diameter. Merozoites measured 6.3 x 1.5 (5.5-7 x 1 microgram) and contained most of the organelles characteristically found in coccidian merozoites. Micropores were observed in merozoites, but not in young and intermediate meronts. Merozoites were seen free in the lumen of blood vessels, in intracellular areas, and free within the host cell cytoplasm.     

Endogenous development of Eimeria minasensis in experimentally infected goats

The endogenous development of Eimeria minasensis was studied in 9 coccidia-free goat kids inoculated with 10(5) sporulated oocysts/kg body weight. Kids were killed 4, 7 (2 animals), 10, 13, 16, 18, 19, and 22 days after inoculation (DAI). In tissue sections of the intestines stained with hematoxylin and eosin and examined by light microscopy, 2 generations of meronts, gamonts, gametes, and oocysts were found. The first generation of meronts developed in cells deep in the lamina propria of the jejunum and ileum. Mature giant meronts (299.4x243.8 microm) found 16 DAI were visible to the naked eye and contained a large number of crescent-shaped merozoites. The second generation of meronts developed in the epithelial cells of crypts of the ileum and above the host cell nuclei. Mature meronts (11.5x10.1 microm) with 18-28 comma-shaped merozoites were first seen 16 DAI. Gametogenesis took place in epithelial cells of the crypts and villi of the terminal part of the ileum, cecum, and colon. Macrogametes (27.8x17.6 microm), mature microgamonts (21.3x17.0 microm), microgametes, and oocysts (30.5x19.4 microm) were found 19 DAI. Sexual stages were below the host cell nucleus.     

Plasmodium tenue Laveran and Marullaz, 1914

SYNOPSIS. Plasmodium tenue was described briefly by Laveran and Marullaz in 1914, and seems to have been studied by no one since. Indeed only Wenyon reports having seen it. The discoverers saw it in the blood of Liothrix luteus (a babbler, but often mistakenly called a Pekin robin or Chinese nightingale). Partly because of the small size of the parasite and partly because it had been found in a "robin," it has since been generally thought to be a synonym for Plasmodium vaughani , so common in America robins. Plasmodium tenue usually produces 4 merozoites per segmenter, but often as many as 6; rarely it apparently gives rise to only 2 or 3. Gametocytes are elongate, and neither sexual nor asexual stages displace the host cell nucleus. Altho very similar to Plasmodium rouxi in structure, and also to certain other recently found members of the group, it seems to be a valid species of the subgenus Novyella. Canaries seem insusceptible, at least to blood-induced infection, and its structure and behavior have therefore been studied in the original host, of which a number of individuals have been found infected. By contrast, canaries are readily susceptible to Plasmodium rouxi , and also to P. vaughani. In vaughani malaria, whether in the robin or canary, larger asexual stages usually have a conspicuous refractile granule.     

A new Haemocystidium (Apicomplexa: Plasmodiidae) species of the dhub lizard, Uromastyx aegyptia microlepis , in Abu Dhabi, distinguished by the absence of pigment

The spiny-tailed lizard, Uromastyx aegyptia microlepis , in Abu Dhabi is parasitized by Haemocystidium apigmentada n. sp., and 2 species of Hepatozoon . The elongate gametocytes of H. apigmentada are 13-19 × 6-9 μm, with length × width (LW) 90-133 μm(2), and L/W ratio 1.56-3.17. Gametocyte dimensions do not differ by sex. Gametocytes are unpigmented. Hepatozoon species 1 has gamonts with a consistently terminal nucleus, with dimensions of 13-16 × 4.5-7 μm, LW of 58-104 μm(2), and L/W ratio of 2.00-3.22. Hepatozoon species 2 gamonts have a broad nucleus at the midbody, and dimensions of 13-15.5 × 5-7 μm, LW of 71-109 μm(2), and L/W ratio of 1.93-3.00.     

Hepatozoon ursi n. sp. (Apicomplexa: Hepatozoidae) in Japanese black bear (Ursus thibetanus japonicus)

Morphological and genetic features of a new Hepatozoon species, Hepatozoon ursi n. sp., in Japanese black bear (Ursus thibetanus japonicus) were studied. Schizogonic developmental stages were observed in the lungs of Japanese black bears. The schizonts were sub-spherical in shape and 45.7+/-4.6 x 42.7+/-4.5 microm in size. Each mature schizont contained approximately 80-130 merozoites and 0-5 residual bodies. The merozoites were 7.0+/-0.7 x 1.8+/-0.3 microm in size. Intraleukocytic gametocytes were slightly curved, cigar-like in shape and had a beak-like protrusion at one end. The size of the gametocytes was 10.9+/-0.3 x 3.3+/-0.2 microm. The analyses of the18S rRNA gene sequences supported the hypothesis that H. ursi n. sp. is different from other Hepatozoon species. Mature Hepatozoon oocysts were detected in two species of ticks (Haemaphysalis japonica and Haemaphysalis flava) collected on the bears infected with H. ursi n. sp. Two measured oocysts were 263.2 x 234.0 microm and 331.8 x 231.7 microm, respectively. The oocysts contained approximately 40 and 50 sporocysts, respectively. The sporocysts were sub-spherical in shape and 31.2+/-2.5 x 27.0+/-2.9 microm in size. Each sporocyst contained at least 8-16 sporozoites, with the sporozoites being 12.2+/-1.4 x 3.5+/-0.5 microm in size. H. ursi n. sp. is the first Hepatozoon species recorded from the family Ursidae.     

Plasmodium falciparum: increased and multiple invasion during short periods of time

We describe how to obtain an increased merozoite invasion of Plasmodium falciparum into human erythrocytes during short periods of time. Using this procedure, infected erythrocytes show multiple invasions (2-4 merozoites per erythrocyte), amplifying, several times, the effects of parasite entry into host cells. The procedure yields synchronous cultures (2-h age range) with parasitemia as high as 15%. It is possible to reach parasitemia of 50% or higher allowing for a 6-h invasion period.     

Babesia bovis merozoites invade human, ovine, equine, porcine and caprine erythrocytes by a sialic acid-dependent mechanism followed by developmental arrest after a single round of cell fission

Babesia bovis infections have only been observed in bovine species in contrast to Babesia divergens that also can infect humans, sheep and rodents. Using an in vitro assay that assesses invasion of erythrocytes by free merozoites after a 1-h incubation period, it was shown that specificity is not determined by host-specific interactions associated with invasion. Human erythrocytes were invaded more efficiently than bovine erythrocytes whereas erythrocytes of sheep, pigs and horses were invaded only slightly less efficiently. In contrast, goat erythrocytes were refractory to efficient invasion. Significant differences in invasion efficiency into erythrocytes from different individuals of the same species were observed. Erythrocytes from all species, except for goats, supported intracellular development of newly invaded merozoites and high numbers of duplicated parasites, located in a morphologically normal accole position, were present. Only in bovine erythrocytes did subsequent rounds of invasion, leading to increased parasitaemia, take place. This suggests that host specificity is determined by factors operating late in the erythrocytic stage of the B. bovis life cycle. Incubation of erythrocytes with neuraminidase prior to invasion led to a decrease in invasion efficiency of 80%. This effect was observed for several species. The removal of either (2-3)-linked or (2-6)-linked sialic acid residues gave similar levels of reduction whereas simultaneous removal did not show an additive effect. Pre-incubation of merozoites with N-acetylneuraminyl-lactose decreased invasion efficiency by 45% whereas addition just prior to invasion had no significant effect. The results demonstrate that invasion is dependent on the presence of sialic-acid containing membrane receptors on erythrocytes that interact with merozoite ligands that are probably already accessible during pre-incubation prior to invasion.     

Fine Structural Observations of the Erythrocytic Stages of Plasmodium chabaudi Landau, 1965*

SYNOPSIS. Electron microscopic examination of Plasmodium chabaudi in mouse erythrocytes revealed many characteristics resembling those observed in other mammalian malarial parasites. A double unit membrane surrounds the trophozoite cytoplasm which contains many ribonucleoprotein particles, a limited amount of endoplasmic reticulum and membraned organelles including sausage-shaped vacuoles and multilaminated membraned bodies. More or less circular double membraned vacuoles, possibly cross sections of the sausage-shaped vacuoles, are common. Typical protozoan mitochondria are lacking. The limiting membrane of the merozoites is triple-layered. Paired organelles and small dense bodies are found in the merozoites along with dense granular masses in the nuclei. Trophozoites have cytostomal structures as well as invaginations of the plasma membrane at sites where no cytostomes are evident. Digestion appears to occur in single membrane-bound vesicles which contain one to several pigment grains. P. chabaudi frequently contains multiple food vacuoles and has polymorphism manifested in part by the presence of cytoplasmic extensions and of nuclei with a variety of shapes. Several apparently free forms are noted, often accompanied by a thin rim of host cytoplasm. “Appliqué” forms are common among the trophozoites as are forms in which 2 or more trophozoites are joined together. Finally, alterations in the host cytoplasm resembling the socalled Maurer's clefts are frequent. Ferritin-containing vacuoles also appear in the host cell.