Vertebrate host specificity of two avian malaria parasites of the subgenus Novyella: Plasmodium nucleophilum and Plasmodium vaughani

The susceptibility of wild-caught European passeriform birds to naturally isolated malaria parasites, Plasmodium (Novyella) nucleophilum and Plasmodium (Novyella) vaughani, was studied by means of intramuscular subinoculation of infected citrated blood. Plasmodium nucleophilum of the great tit, Parus major, was transmitted to 3 great tits, but 3 blackcaps (Sylvia atricapilla) were not susceptible. Plasmodium vaughani of the robin, Erithacus rubecula, was transmitted to 1 robin and 1 blackcap, but 1 dunnock, Prunella modularis, was not susceptible. The prepatent period was between 8 and 10 days in all experimental infections. Maximum experimental parasitemia (3.4% of red cells) was detected in great tits infected with P. nucleophilum 23 days postexposure. A light (<0.01%) transient parasitemia of P. vaughani developed in the robin and blackcap. This study is in accord with former experimental observations on host specificity of P. nucleophilum and P. vaughani, which are characterized by a wide, but selective, range of avian hosts. Two new host-parasite associations were recorded.     

The parasites of Anolis lizards the northern Lesser Antilles

Summary The communities of parasitic helminths from ten species of lizards on seven islands in the Caribbean were examined to ascertain the relative importance of predictable deterministic factors and unpredicatable colonization or extinction events in determining the structure of the parasite community. A simple graphical model of community structure is used as a null model to describe the features of a community that are dependent only upon the size of the host population and features of the life histories of the constituent parasite species. This model predicts that parasite species will exhibit a nested pattern of local and global relative abundance. The observed data correspond fairly well to this pattern. The absences of individual parasite species from communities where they might be expected to be present emphasizes the role of stochastic colonization and extinction events in delineating the constituent members of the community on any island.Statistical analysis of the distribution of parasite species per host illustrates that this pattern is random in habitats where parasite species diversity is low, but decreasingly variable in habitats where more diverse parasite communities occur. Increased parasite diversity also leads to an increase in the proportion of hosts that contain mixed species infections. Comparisons of worm burdens from single and mixed species infections within individual hosts suggest that interactions between parasite species only rarely leads to reduced worm burdens.     

The parasites of Anolis lizards in the northern Lesser Antilles

Summary The helminth communities from ten species of lizard on seven islands in the Caribbean were sampled by collecting one hundred specimens of each species. Nine genera of parasites were identified; these included six nematodes, two digeneans and an acanthocephalan. No relationship was discernible between parasite density or abundance and island area or altitude, although dry islands tend to have fewer species of parasites. Anolis lizards of the bimaculatus and wattsi series share similar parasites with four out of nine species common to both series. The parasite community of lizards on these islands is depauperate with respect to similar surveys on the larger islands of the Greater Antilles.On three of the islands lizards were sub-sampled by collecting from moist woodland and more xeric habitats. These data suggest that differences between habitats are as significant as differences between islands in determining parasite burdens. Worm burdens of the commonest parasite species, T. cubensis, increased monotonically with host body size and no evidence was found to suggest that these parasites affect either host survival or fecundity. The sex-ratio of this species correlated with mean abundance of the parasite, with females the dominant sex on islands or in habitats where the parasite was common. This pattern may reflect haplodiploid sexual determination in this species.     

Protective antigens of bloodstage Plasmodium knowlesi parasites

The simian malaria Plasmodium knowlesi provides many favourable features as an experimental model; it can be grown in vivo or in vitro. Parasites of defined variant specificity and stage of development are readily obtained and both the natural host and a highly susceptible host are available for experimental infection and vaccination trials. Proteins synthesized by erythrocytic P. knowlesi parasites are characteristic of the developmental stage, as are the alterations that the parasite induces in the red cell surface. Erythrocytic merozoites are anatomically and biochemically complex, their surface alone is covered by at least eight distinct polypeptides. Immune serum from merozoite-immunized rhesus recognizes many parasite components, especially those synthesized by schizonts. All of the merozoite surface components and some of the schizont-infected red cell surface antigens are recognized by such immune sera. Rhesus monkeys rendered immune by repeated infection may by contrast recognize comparatively few antigens; a positive correlation was established for these 'naturally' immunized monkeys between protection and antibody directed against a 74 000 molecular mass antigen. Immunization with this purified antigen confers partial protection. Other putative protective antigens have been identified by monoclonal antibodies that inhibit merozoite invasion of red cells in vitro. The antigens recognized by inhibitory monoclonal antibodies are synthesized exclusively by schizonts and are processed, at the time of schizont rupture and merozoite release, to smaller molecules that are present on the merozoite surface. The multiplicity of protective antigens is clearly demonstrated by the fact that seven distinct merozoite surface antigens are recognized by three different inhibitory monoclonals. None of the protective antigens identified are variant or strain specific.     

The saurian malarias of Venezuela: Haemosporidian parasites of gekkonid lizards

Telford S. P., Jr. 1978. The saurian malarias of Venezuela: haemosporidian parasites of gekkonid lizards. International Journal for Parasitology8: 341–353. Five haemosporidian species were found among 185 gekkonid lizards from Estados Portuguesa, Cojedes and Aragua, Venezuela, four of which were new to science. A pigmented Plasmodium species is described from Gonatodes taniae of Estado Aragua. It produces 8–20 merozoites in variably shaped schizonts, and elongate, irregularly margined prematuration gametocytes which contract to form round to broadly elongate mature gametocytes. Phyllodactylus ventralis of Estado Portuguesa is parasitized by two new unpigmented malarial species. One produces 11–35 merozoites in schizonts which are often rounded or elongated, occasionally fan-shaped. Gametocytes are always elongated and usually lie diagonally across one end of the host cell or laterally to the nucleus. The second species forms rounded mature schizonts nearly filled with 14–32 merozoites. The sexual stages are usually round or oval, rarely elongate. Plasmodium aurulentum Telford, 1971 was found in Thecadactylus raplcaudus of Estados Portuguesa and Cojedes. A single Thecadactylus from Cojedes was infected by a haemosporidian species of uncertain generic identity which resembles a parasite found earlier in a Panamanian gecko.     

Fractionation of Plasmodium chabaudi-infected erythrocytes into parasites and ghosts

We have developed a new procedure for subfractionation of Plasmodium chabaudi-infected erythrocytes into parasites and ghosts. Trophozoite-infected erythrocytes enriched over a percoll-step (:1.10 g/cm3) are subjected to a glycerol-enhanced osmotic shock. This induces the release of parasites and the emergence of erythrocyte ghosts, which can be separated on a continuous percoll gradient (:1.02----1.10 g/cm3). The parasites are intact in terms of ultrastructure and incorporation of 14C-isoleucine. The erythrocyte ghosts are purified over a two-step percoll gradient (:1.01-1.02 g/cm3). Our method recovers about 40%-50% of the initial ghosts and 70%-95% of the initially freed parasites.     

Comparative thermal ecology of two lizards

Summary In a habitat judged to be energetically costly for thermoregulation, mean body temperatures (MBT's) ofAnolis sagrei are significantly higher than those ofA. distichus. As indexed by the slope of the regression of body temperatures (T_b) on substrate temperature (T_s),A. sagrei is more dependent upon environmental temperatures thanA. distichus.In a habitat judged to be less costly for thermoregulation and where interspecific competition for perch sites may be less, MBT's ofA. sagrei are significantly higher, proportionally more lizards occupy sunny perches, and the slope of the regression of T_b on T_s is significantly less, than for conspecifics in the costly habitat.As indexed by length-specific fat body weights, well-nourished lizards in the costly habitat have T_b's which are independent of environmental temperature; T_b's of poorly-nourished lizards are highly dependent upon environmental temperature. This relationship does not hold for lizards in the low-cost habitat.These results corroborate the hypothesis that energetic costs are important in controlling the extent to which lizards thermoregulate. In high-cost habitats lizards thermoregulate less precisely than in low-cost habitats. Lizards that exploit the habitat as if it were highly productive thermoregulate more precisely than lizards that exploit the environment as if it were of low productivity.     

Coevolutionary genetics of Plasmodium malaria parasites and their human hosts

Malaria has been invoked, perhaps more than any other infectious disease, as a force for the selection of human genetic polymorphisms. Evidence for genome-shaping interactions can be found in the geographic and ethnic distributions of the hemoglobins, blood group antigens, thalassemias, red cell membrane molecules, human lymphocyte antigen (HLA) classes, and cytokines. Human immune responses and genetic variations can correspondingly influence the structure and polymorphisms of Plasmodium populations, notably in genes that affect the success and virulence of infection. In Africa, where the burden from Plasmodium falciparum predominates, disease severity and manifestations vary in prevalence among human populations. The evolutionary history and spread of Plasmodium species inform our assessment of malaria as a selective force. Longstanding host-pathogen relationships, as well as recent changes in this dynamic, illustrate the selective pressures human and Plasmodium species place on one another. Investigations of malaria protection determinants and virulence factors that contribute to the complexity of the disease should advance our understanding of malaria pathogenesis.     

Kenny syndrome: description of additional abnormalities and molecular studies

An 18-month-old girl presented with clinical manifestations of Kenny syndrome including growth retardation, ophthalmologic abnormalities, a persistent open anterior fontanel, dysmorphic facies, anemia, radiologic skeletal abnormalities, and severe hypoparathyroidism. Analysis of restriction patterns of DNA with human parathyroid hormone (PTH) DNA probes revealed no gross abnormalities of the PTH gene that could contribute to the hypoparathyroidism. In addition to the previously described characteristics of the syndrome, hypoplastic nails, persistent neutropenia, abnormal T cell function and neonatal liver disease all occurred and may be additional manifestations of Kenny syndrome, requiring diagnostic or therapeutic consideration.     

Immunological relationship of Plasmodium inui with two other quartan malaria parasites, P. malariae and P. brasilianum

A series of monoclonal antibodies was produced against sporozoites of the OS strain of Plasmodium inui, a simian quartan malaria parasite, and used to characterize the circumsporozoite protein of this parasite. The results confirm that the immunodominant epitope of the circumsporozoite protein of P. inui is immunologically distinct from those of 2 other quartan parasites, the human P. malariae and simian P. brasilianum, which are identical.     

Features of autophagic cell death in Plasmodium liver-stage parasites

Analyzing molecular determinants of Plasmodium parasite cell death is a promising approach for exploring new avenues in the fight against malaria. Three major forms of cell death (apoptosis, necrosis and autophagic cell death) have been described in multicellular organisms but which cell death processes exist in protozoa is still a matter of debate. Here we suggest that all three types of cell death occur in Plasmodium liver-stage parasites. Whereas typical molecular markers for apoptosis and necrosis have not been found in the genome of Plasmodium parasites, we identified genes coding for putative autophagy-marker proteins and thus concentrated on autophagic cell death. We characterized the Plasmodium berghei homolog of the prominent autophagy marker protein Atg8/LC3 and found that it localized to the apicoplast. A relocalization of PbAtg8 to autophagosome-like vesicles or vacuoles that appear in dying parasites was not, however, observed. This strongly suggests that the function of this protein in liver-stage parasites is restricted to apicoplast biology.     

Rediscovery and Mitochondrial Relationships of the Dendrobatid Frog Colostethus humilis Suggest Parallel Colonization of the Venezuelan Andes by Poison Frogs

Colostethus humilis Rivero, ‘1978’1980 was rediscovered near the type locality. The species is redescribed, and data on its advertisement call are provided for the first time. Its morphology and colour pattern differ from other Andean dendrobatids. It shows morphological and bio-acoustic similarities to species of Colostethus from the Amazonian lowlands. A phylogenetic analysis of sequences of the mitochondrial 16S rRNA gene confirmed that C. humilis is related to Amazonian lowland Colostethus, rather than to other Andean poison frogs of the genera Nephelobates and Mannophryne. This indicates that several groups of basal dendrobatids independently have colonised the Venezuelan Andes.