A century ago, W. G. MacCallum identified distinct male and female forms in malaria parasites of both birds and humans. Since then, scientists have been puzzled by the high female-to-male ratios of parasites in Plasmodium infections and by the mechanism of sex determination. The sex ratio of malaria parasites was shown to become progressively more male as conditions that allow motility and subsequent fertilization by the male parasites become adverse. This resulted from an increased immune response against male gametes, which coincides with intense host erythropoietic activity. Natural and artificial induction of erythropoiesis in vertebrate hosts provoked a shift toward male parasite production. This change in parasite sex ratio led to reduced reproductive success in the parasite, which suggests that sex determination is adaptive and is regulated by the hematologic state of the host. (+info)
Chitinases of the avian malaria parasite Plasmodium gallinaceum, a class of enzymes necessary for parasite invasion of the mosquito midgut.
(2/72)
The Plasmodium ookinete produces chitinolytic activity that allows the parasite to penetrate the chitin-containing peritrophic matrix surrounding the blood meal in the mosquito midgut. Since the peritrophic matrix is a physical barrier that the parasite must cross to invade the mosquito, and the presence of allosamidin, a chitinase inhibitor, in a blood meal prevents the parasite from invading the midgut epithelium, chitinases (3.2.1.14) are potential targets of malaria parasite transmission-blocking interventions. We have purified a chitinase of the avian malaria parasite Plasmodium gallinaceum and cloned the gene, PgCHT1, encoding it. PgCHT1 encodes catalytic and substrate-binding sites characteristic of family 18 glycohydrolases. Expressed in Escherichia coli strain AD494 (DE3), recombinant PgCHT1 was found to hydrolyze polymeric chitin, native chitin oligosaccharides, and 4-methylumbelliferone derivatives of chitin oligosaccharides. Allosamidin inhibited recombinant PgCHT1 with an IC(50) of 7 microM and differentially inhibited two chromatographically separable P. gallinaceum ookinete-produced chitinase activities with IC(50) values of 7 and 12 microM, respectively. These two chitinase activities also had different pH activity profiles. These data suggest that the P. gallinaceum ookinete uses products of more than one chitinase gene to initiate mosquito midgut invasion. (+info)
Malaria parasite development in a Drosophila model.
(3/72)
Malaria is a devastating public health menace, killing over one million people every year and infecting about half a billion. Here it is shown that the protozoan Plasmodium gallinaceum, a close relative of the human malaria parasite Plasmodium falciparum, can develop in the fruit fly Drosophila melanogaster. Plasmodium gallinaceum ookinetes injected into the fly developed into sporozoites infectious to the vertebrate host with similar kinetics as seen in the mosquito host Aedes aegypti. In the fly, a component of the insect's innate immune system, the macrophage, can destroy Plasmodia. These experiments suggest that Drosophila can be used as a surrogate mosquito for defining the genetic pathways involved in both vector competence and part of the parasite sexual cycle. (+info)
Host specificity in avian blood parasites: a study of Plasmodium and Haemoproteus mitochondrial DNA amplified from birds.
(4/72)
A fragment of the mitochondrial cytochrome b gene of avian malaria (genera Haemoproteus and Plasmodium) was amplified from blood samples of 12 species of passerine birds from the genera Acrocephalus, Phylloscopus and Parus. By sequencing 478 nucleotides of the obtained fragments, we found 17 different mitochondrial haplotypes of Haemoproteus or Plasmodium among the 12 bird species investigated. Only one out of the 17 haplotypes was found in more than one host species, this exception being a haplotype detected in both blue tits (Parus caeruleus) and great tits (Parus major). The phylogenetic tree which was constructed grouped the sequences into two clades, most probably representing Haemoproteus and Plasmodium, respectively. We found two to four different parasite mitochondrial DNA (mtDNA) haplotypes in four bird species. The phylogenetic tree obtained from the mtDNA of the parasites matched the phylogenetic tree of the bird hosts poorly. For example, the two tit species and the willow warbler (Phylloscopus trochilus) carried parasites differing by only 0.6% sequence divergence, suggesting that Haemoproteus shift both between species within the same genus and also between species in different families. Hence, host shifts seem to have occurred repeatedly in this parasite host system. We discuss this in terms of the possible evolutionary consequences for these bird species. (+info)
Identification of novel Plasmodium gallinaceum zygote- and ookinete-expressed proteins as targets for blocking malaria transmission.
(5/72)
The development of transmission-blocking vaccines is one approach to malaria control. To identify novel Plasmodium zygote- and ookinete-secreted proteins as targets of blocking malaria transmission, monoclonal antibodies (MAbs) were produced against parasite-secreted proteins found in Plasmodium gallinaceum ookinete culture supernatants. Four MAbs-1A6, 2A5, 2B5, and 4B6-were identified that bound to P. gallinaceum zygotes and ookinetes in diverse patterns in terms of spatial localization on parasites, time course of antigen expression, and Western immunoblot patterns. MAbs 2A5 and 4B6 recognized more than one protein band as detected by Western immunoblot of P. gallinaceum ookinete supernatants. Beginning at 0 h postfertilization, MAb 2A5 recognized a diverse set of antigens; at 10 h postfertilization, MAb 4B6 recognized several antigens as well. MAb 1A6 recognized a single approximately 17-kDa protein, and 2B5 recognized a single approximately 32-kDa protein at 15 h postfertilization. In membrane feeding assays to assess the effect of these MAbs on P. gallinaceum infectivity for Aedes aegypti mosquitoes, the addition of MAbs 1A6 and 2B5 to infectious blood meals significantly inhibited oocyst development in the mosquito midgut. In contrast, MAb 2A5 seemed to enhance infectivity. These results demonstrate that Plasmodium ookinetes secrete proteins (in addition to previously characterized chitinases) that may be targets for blocking malaria transmission. Future investigation of ookinete-secreted neutralization-sensitive molecules should provide valuable insight into mechanisms by which ookinetes exit the blood meal, penetrate and transverse the peritrophic matrix, and invade the mosquito midgut epithelium. (+info)
Two functionally distinct organic osmolyte pathways in Plasmodium gallinaceum-infected chicken red blood cells.
(6/72)
Red cells infected with the human malaria parasite Plasmodium falciparum have an increased permeability to a range of small, structurally unrelated solutes via a malaria-induced pathway. We report here a similar pathway present in parasitised red cells from chickens infected with the avian malaria parasite, Plasmodium gallinaceum. Parasitised cells showed a marked increase in the rate of influx of sorbitol (76-fold) and, to a lesser degree, taurine (3-fold) when compared with red cells from uninfected chickens. Pharmacological data suggest that both sorbitol and taurine are transported via a single malaria-induced pathway, which is sensitive to inhibition by 5-nitro-2-(3-phenylpropylamino)benzoic acid (IC(50) approximately 7 microM). The malaria-induced pathway differed in its inhibition by a range of anion channel inhibitors when compared to the endogenous, volume-activated osmolyte pathway of chicken red cells. There were also differences in the selectivity of sorbitol and taurine by the two permeation routes. The data presented here are consistent with the presence of two distinct organic solute pathways in infected chicken red cells. The first is an endogenous volume-activated pathway, which is not activated by the parasite and the second is a malaria-induced pathway, similar to those that are induced by other types of malaria in other host species. (+info)
Diversification and host switching in avian malaria parasites.
(7/72)
The switching of parasitic organisms to novel hosts, in which they may cause the emergence of new diseases, is of great concern to human health and the management of wild and domesticated populations of animals. We used a phylogenetic approach to develop a better statistical assessment of host switching in a large sample of vector-borne malaria parasites of birds (Plasmodium and Haemoproteus) over their history of parasite-host relations. Even with sparse sampling, the number of parasite lineages was almost equal to the number of avian hosts. We found that strongly supported sister lineages of parasites, averaging 1.2% sequence divergence, exhibited highly significant host and geographical fidelity. Event-based matching of host and parasite phylogenetic trees revealed significant cospeciation. However, the accumulated effects of host switching and long distance dispersal cause these signals to disappear before 4% sequence divergence is achieved. Mitochondrial DNA nucleotide substitution appears to occur about three times faster in hosts than in parasites, contrary to findings on other parasite-host systems. Using this mutual calibration, the phylogenies of the parasites and their hosts appear to be similar in age, suggesting that avian malaria parasites diversified along with their modern avian hosts. Although host switching has been a prominent feature over the evolutionary history of avian malaria parasites, it is infrequent and unpredictable on time scales germane to public health and wildlife management. (+info)
Interactions of climate change with biological invasions and land use in the Hawaiian Islands: Modeling the fate of endemic birds using a geographic information system.
(8/72)
The Hawaiian honeycreepers (Drepanidae) represent a superb illustration of evolutionary radiation, with a single colonization event giving rise to 19 extant and at least 10 extinct species [Curnutt, J. & Pimm, S. (2001) Stud. Avian Biol. 22, 15-30]. They also represent a dramatic example of anthropogenic extinction. Crop and pasture land has replaced their forest habitat, and human introductions of predators and diseases, particularly of mosquitoes and avian malaria, has eliminated them from the remaining low- and mid-elevation forests. Landscape analyses of three high-elevation forest refuges show that anthropogenic climate change is likely to combine with past land-use changes and biological invasions to drive several of the remaining species to extinction, especially on the islands of Kauai and Hawaii. (+info)