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PubMed2005

Biochemical and genetic analysis of the distinct proliferating cell nuclear antigens of Toxoplasma gondii.

The apicomplexa parasite Toxoplasma gondii expresses two distinct proliferating cell nuclear antigens (PCNA) that exhibit distinct patterns of subcellular localization during tachyzoite growth. In all cell cycle phases, TgPCNA1 is concentrated in the nucleus, while TgPCNA2 is only concentrated in the nucleus during S-phase and uniformly distributed throughout the cell during mitosis and early G1-phase. TgPCNA1-GFP and native TgPCNA2 display a punctate staining pattern that is consistent with assembly into replication foci during S-phase; however, TgPCNA2 disassociates from replication foci before TgPCNA1-GFP. Consistent with the distinct pattern of TgPCNA2 cellular localization, homotypic TgPCNA2 interactions were primarily observed by yeast two-hybrid or co-immunoprecipitation analysis. Transgenic parasites in which the TgPCNA2 gene was disrupted displayed a slower growth rate in vitro; however, no difference in DNA polymerase activity, response to chemical mutagens, or recombinational frequency was observed in these mutant clones demonstrating that TgPCNA2 is non-essential in the tachyzoite developmental stage. Heterologous expression of TgPCNA1, but not TgPCNA2, was able to complement a POL30 cold-sensitive yeast strain suggesting that this isoform may serve as a major replisomal factor in T. gondii and is consistent with the failure to disrupt this gene in tachyzoites.

Animals↗
PubMed2005

Characterization of Plasmodium falciparum cGMP-dependent protein kinase (PfPKG): antiparasitic activity of a PKG inhibitor.

Cyclic GMP-dependent protein kinase (PKG) has been biochemically and genetically validated in Toxoplasma gondii as a primary target responsible for the antiparasitic activity of the trisubstituted pyrrole 4-[2-(4-fluorophenyl)-5-(1-methylpiperidine-4-yl)-1H pyrrol-3-yl] pyridine (Compound 1) [Biftu T, Feng D, Ponpipom M, et al. Synthesis and SAR of 2,3-diarylpyrrole inhibitors of parasite cGMP-dependent protein kinase as novel anticoccidial agents. Bioorg Med Chem Lett 2005;15:3296-301; Gurnett AM, Liberator PA, Dulski PM, et al. Purification and molecular characterization of cGMP-dependent protein kinase from Apicomplexan parasites. A novel chemotherapeutic target. J Biol Chem 2002;277:15913-22; Donald RGK, Allocco J, Singh SB, et al. Toxoplasma gondii cyclic GMP-dependent kinase: Chemotherapeutic targeting of an essential parasite protein kinase. Eukaryotic Cell 2002;1:317-28; Nare B, Allocco J, Liberator PA, Donald RGK. Evaluation of a cyclic GMP-dependent protein kinase inhibitor in treatment of murine Toxoplasmosis: Gamma interferon is required for efficacy. Antimicrob Agents Chemother 2002;46:300-7]. Compound 1 inhibits the growth of several related protozoan parasites of the subphylum Apicomplexa. Native PKG activity has been partially purified by cGMP-affinity and MonoQ ion exchange chromatography from Plasmodium falciparum (PfPKG). Biochemical fractions enriched for a 98kDa protein detected using anti-PKG antisera, contain cGMP-induced protein kinase activity that is sensitive to inhibition by Compound 1. To enable a more thorough characterization of PfPKG we expressed a synthetic cDNA incorporating T. gondii codon preference (Pf(Tg)PKG) in T. gondii parasites. The protein kinase activity of purified recombinant Pf(Tg)PKG is stimulated by cGMP, with significant cooperativity as demonstrated by a Hill coefficient of 2. Both substrate preference and inhibition of Pf(Tg)PKG kinase activity by Compound 1 are similar to that seen with native PfPKG, as well as PKG enzymes from Eimeria spp. and T. gondii. We conclude that PfPKG has biochemical and pharmacological properties that are similar to previously characterized apicomplexan PKG enzymes. Compound 1 is active against blood cell stages of P. falciparum cultured in vitro. In a Plasmodium berghei mouse model of infection, Compound 1 delays the onset of parasitemia but does not cure the parasite infection.

Animals↗
PubMed2006

Genome-scale protein expression and structural biology of Plasmodium falciparum and related Apicomplexan organisms.

Parasites from the protozoan phylum Apicomplexa are responsible for diseases, such as malaria, toxoplasmosis and cryptosporidiosis, all of which have significantly higher rates of mortality and morbidity in economically underdeveloped regions of the world. Advances in vaccine development and drug discovery are urgently needed to control these diseases and can be facilitated by production of purified recombinant proteins from Apicomplexan genomes and determination of their 3D structures. To date, both heterologous expression and crystallization of Apicomplexan proteins have seen only limited success. In an effort to explore the effectiveness of producing and crystallizing proteins on a genome-scale using a standardized methodology, over 400 distinct Plasmodium falciparum target genes were chosen representing different cellular classes, along with select orthologues from four other Plasmodium species as well as Cryptosporidium parvum and Toxoplasma gondii. From a total of 1008 genes from the seven genomes, 304 (30.2%) produced purified soluble proteins and 97 (9.6%) crystallized, culminating in 36 crystal structures. These results demonstrate that, contrary to previous findings, a standardized platform using Escherichia coli can be effective for genome-scale production and crystallography of Apicomplexan proteins. Predictably, orthologous proteins from different Apicomplexan genomes behaved differently in expression, purification and crystallization, although the overall success rates of Plasmodium orthologues do not differ significantly. Their differences were effectively exploited to elevate the overall productivity to levels comparable to the most successful ongoing structural genomics projects: 229 of the 468 target genes produced purified soluble protein from one or more organisms, with 80 and 32 of the purified targets, respectively, leading to crystals and ultimately structures from one or more orthologues.

Animals↗
PubMed2005

The katablepharids are a distant sister group of the Cryptophyta: A proposal for Katablepharidophyta divisio nova/ Kathablepharida phylum novum based on SSU rDNA and beta-tubulin phylogeny.

The katablepharids are a morphologically well-defined group of heterotrophic flagellates. Since their original description in 1939, they have been classified in the Cryptophyceae (Cryptophyta) based on their similar cell shape, flagellar orientation, and the presence of ejectisomes visible by light microscopy. However, electron microscopy suggests that the katablepharids are distinct from cryptomonads. A possible affinity with the Alveolata has been proposed which is mainly based on the resemblance of their feeding apparatus to the apical complex of the Apicomplexa or to the tentacles of the Ciliophora. In this study, we provide the first SSU rDNA and beta-tubulin molecular sequence data for two katablepharids: Katablepharis japonica sp. nov. and Leucocryptos marina. We reveal that the katablepharids are not closely related to the Alveolata; rather, phylogenetic reconstruction analyses of SSU rDNA and beta-tubulin suggest that the katablepharids are a distant sister group of the Cryptophyta. We therefore conclude that the katablepharids should be a group equivalent to the Cryptophyta and propose Katablepharidophyta divisio nova (ICBN)/Kathablepharida phylum novum (ICZN).

Animals↗
PubMed2003

Analysis of cross-reactivity of five new chicken monoclonal antibodies which recognize the apical complex of Eimeria using confocal laser immunofluorescence assay.

For Apicomplexa (members) the host cell invasion is realized with the help of the organelles located at the apical tip of parasites. In this research paper the characterization of five chicken monoclonal antibodies (mabs) produced against Eimeria acervulina sporozoites is described. All mabs reacted with molecules belonging to the apical complex of chicken Eimeria sporozoites. On immunofluorescence assay (IFA) one mab, 8E-1, recognized an apical tip molecule present on all chicken Eimeria sporozoites, two mabs (8D-2 and HE-4) recognized an antigen present on the apical tip of the same two Eimeria species (E. acervulina and E. brunetti), another mab (5D-11) recognized an antigen present on the apical tip of other two species (E. acervulina and E. maxima) while one mab (8C-3) identified antigens present on the sporozoites and sporocysts wall of only E. acervulina. Besides the apical tip antigens, two mabs (HE-4 and 8D-2) recognized some proteins located in the anterior half of the sporozoites. Collectively, these mabs proved that the apical complex of chicken Eimeria sporozoites share one or more antigens that are expected to play a role in host cell recognition and invasion.

Animals↗
PubMed2005

Hemorrhagic disease in dogs infected with an unclassified intraendothelial piroplasm in southern Brazil.

A hemorrhagic disease affecting dogs in Brazil, referred to popularly as "nambiuvú" (bloody ears) and believed to be transmitted by ticks, has been observed in animals infected with an organism described originally in 1910 as a piroplasm, and known locally as Rangelia vitalii. In this series of 10 cases, the disease was characterized by anaemia, jaundice, fever, spleno- and lymphadenomegaly, hemorrhage in the gastrointestinal tract, and persistent bleeding from the nose, oral cavity and tips, margins and outer surface of the pinnae. The ixodid ticks Rhipicephalus sanguineus and Amblyomma aureolatum infested affected dogs from suburban and rural areas, respectively. Laboratory findings included regenerative anaemia, spherocytosis, icteric plasma and bilirubinuria. Those intracellular organisms were found in bone marrow smears but not in blood smears. Microscopically, zoites were seen within the cytoplasm of blood capillary endothelial cells. Parasitized and non-parasitized endothelial cells were positive immunohistochemically for von Willebrand factor (vWF). Langhans-type multinucleate giant cells were observed in the lymph nodes and choroid plexus. There was prominent erythrophagocytosis by macrophages in the lymph node sinuses and infiltration of the medullary cords by numerous plasma cells. Ultrastructurally, this organism had an apical complex that included a polar ring and rhoptries but no conoid. This parasite was contained within a parasitophorous vacuole that had a trilaminar membrane with villar protrusions and was situated in the cytoplasm of capillary endothelial cells. This organism tested positive by immunohistochemistry for Babesia microti. This pathogen was also positive by in situ hybridization for B. microti. Tentative clinical diagnosis in these cases was based on the history, clinical picture, haemogram and favorable response to therapy, and confirmed through microscopic examination of smears from the bone marrow or histological sections of multiple tissues, especially lymph nodes where zoites were most frequently found. The disease was reproduced by intravenous inoculation of blood from a naturally infected dog into an experimental dog. The authors demonstrate in this study that this organism is a protozoa of the phylum Apicomplexa, order Piroplasmorida. This piroplasm seems to be different from Babesia since it has an intraendothelial stage. Molecular phylogenetic analysis is necessary to better characterize this parasite and clarify its taxonomic status.

Animals↗
PubMed2006

Chemotherapy against babesiosis.

Babesiosis is caused by a haemotropic protozoal parasite of the genus Babesia, member of the phylum Apicomplexa and transmitted by the bite of an infected tick. There are many Babesia species affecting livestock, dogs, horses and rodents which are of economic significance. Infections can occur without producing symptoms, but babesiosis may also be severe and sometimes fatal caused by the intraerythrocytic parasite development. The disease can cause fever, fatigue and haemolytic anemia lasting from several days to several months. There are a number of effective babesiacides, but imidocarb dipropionate (which consistently clears the parasitaemia; often the only available drug on the market) and diminazene aceturate are the most widely used. Some Babesia spp. can infect humans, particularly Babesia microti and Babesia divergens, and human babesiosis is a significant emerging tick-borne zoonotic disease. Clinical manifestations differ markedly between European and North American diseases. In clinical cases, a combination of clindamycin and quinine is administered as the standard treatment, but also administration of atovaquone-azithromycin is successful. Supportive therapy such as intravenous fluids and blood transfusions are employed when necessary. More specific fast-acting new treatments for babesiosis have now to be developed. This should be facilitated by the knowledge of the Babesia spp. genome and increased interest for this malaria-like parasite.

Animals↗
PubMed2006

Isolation of Besnoitia besnoiti from infected cattle in Portugal.

Besnoitia besnoiti, an obligate intracellular protozoan parasite belonging to the phylum apicomplexa, is the causative agent of bovine besnoitiosis. Besnoitiosis is responsible for significant losses in the cattle industry of Africa and Mediterranean countries due to the high morbidity rate, abortion and infertility in males. The acute stage of disease is associated with the proliferative forms (tachyzoites) and is characterized by fever, whimpery, general weakness and swelling of the superficial lymph nodes. During the following chronic stage, a huge number of cysts are formed mainly in the subcutaneous tissues. This process is non-reversible, and chronic besnoitiosis is characterized by hyper-sclerodermia, hyperkeratosis, alopecia and, in bulls, atrophy, sclerosis and focal necrosis that cause irreversible lesions in the testis. In this paper we report on the identification of large cysts in the skin of a cow and a bull in Portugal, which presented loss of hair and enlargement and pachydermis all over the body. The observation of a two-layered cyst wall within the host cell, the encapsulation of the host cell by a large outer cyst wall, and the subcutaneous localization of the cysts within the host, were characteristic for B. besnoiti. The parasites were isolated from the infected animals and successfully propagated in Vero cells without prior passages in laboratory animals. Morphological characterization of B. besnoiti tachyzoites and the amplification of the 149 bp segment from the internal transcribed spacer 1 (ITS1), aided with specific primers, confirmed the identification of B. besnoiti.

Animals↗
PubMed2002

Host cell invasion by the opportunistic pathogen Toxoplasma gondii.

Toxoplasma gondii is an obligate intracellular protozoan that infects an astonishing variety of vertebrate hosts including humans. Classified in the phylum Apicomplexa, T. gondii causes an opportunistic disease, toxoplasmosis, in individuals with immune dysfunction and congenital disease in infected infants. Re-emergence of toxoplasmosis as a life-threatening disease in patients with AIDS is anticipated in the wake of emerging multi-drug resistant strains of HIV. In immunodeficient patients, the available evidence suggests that tissue pathology associated with T. gondii infection is due to parasite-directed lytic destruction of individual host cells. The Toxoplasma lytic cycle begins when the parasite actively invades a target cell. In association with invasion, T. gondii sequentially discharges three sets of secretory organelles beginning with the micronemes, which contain adhesive proteins involved in parasite attachment to a host cell. Deployed as protein complexes, several micronemal proteins possess vertebrate-derived adhesive sequences that function in binding receptors on the surface of a target cell. Each protein in these adhesive complexes fulfills a specific role in movement through the secretory pathway, targeting to the micronemes, or adhesion. It is anticipated that these adhesive complexes recognize a variety of host receptors, including some that are expressed on multiple cell types, and that this diversity in host cell receptors contributes to the remarkably broad tissue- and host-range of T. gondii.

AIDS-Related Opportunistic Infections↗
PubMed2002

Theileria annulata: virulence and transmission from single and mixed clone infections in cattle.

Theoretically, parasite virulence should be higher for faster growing parasites, and higher in mixed infections compared to single-clone infections. Virulence should also be positively correlated to transmission rates. Theileria annulata provides a good model system for studying such hypotheses, as parasite replication causes harm to the host, and there is evidence suggesting that the genetic complexity of an infection might affect its virulence. Two clones of T. annulata were chosen, one fast growing and one slow growing in vitro and these were used to establish cattle infections, either alone, or in a mixed infection. Virulence was measured using lymph node expansion, temperature, and blood parameters as correlates. As predicted, the faster growing clone was found to produce higher virulence. Mixed infections did not show higher virulence than single-clone infections, but interactions within mixed infections resulted in more transmission stage production than seen in either of the single-clone infections. Index Descriptors and Abbreviations. Theileria annulata, Apicomplexa, mixed infections, virulence, growth rates, red blood cell, RBC; packed cell volume, PCV.

Animals↗
PubMed2003

Apicomplexan parasites contain a single lipoic acid synthase located in the plastid.

Apicomplexan parasites contain a vestigial plastid called apicoplast which has been suggested to be a site of [Fe-S] cluster biogenesis. Here we report the cloning of lipoic acid synthase (LipA) from Toxoplasma gondii, a well known [Fe-S] protein. It is able to complement a LipA-deficient Escherichia coli strain, clearly demonstrating that the parasite protein is a functional LipA. The N-terminus of T. gondii LipA is unusual with respect to an internal signal peptide preceding an apicoplast targeting domain. Nevertheless, it efficiently targets a reporter protein to the apicoplast of T. gondii whereas co-localization with the fluorescently labeled mitochondrion was not detected. In silico analysis of several apicomplexan genomes indicates that the parasites, in addition to the presumably apicoplast-resident pyruvate dehydrogenase complex, contain three other mitochondrion-localized target proteins for lipoic acid attachment. We also identified single genes for lipoyl (octanoyl)-acyl carrier protein:protein transferase (LipB) and lipoate protein ligase (LplA) in these genomes. It thus appears that unlike plants, which have only two LipA and LipB isoenzymes in both the chloroplasts and the mitochondria, Apicomplexa seem to use the second known lipoylating activity, LplA, for lipoylation in their mitochondrion.

Amino Acid Sequence↗
PubMed2001

Molecular comparison of the dense granule proteins GRA6 and GRA7 of Neospora hughesi and Neospora caninum.

Neospora hughesi is a recently described apicomplexan parasite that has been associated with several cases of equine protozoal myeloencephalitis. The biology of this new parasite is just beginning to be defined. Towards this understanding, we report important differences between the nucleotide and deduced amino acid sequences of the dense granule proteins GRA6 and GRA7 of N. hughesi and Neospora caninum. This information can be used to differentiate the two species and contribute to further understanding of the prevalence and biology of N. hughesi. The newly defined proteins of N. hughesi are referred to as NhGRA6 and NhGRA7 in keeping with the protocol for naming homologous proteins of the Apicomplexa. Genes of the two dense granule proteins of N. hughesi (isolate Nh-A1) and four different isolates of N. caninum were isolated via PCR and their DNA sequences were determined. Computer analysis indicated that the two gene sequences were identical among all four N. caninum isolates. However, the gene for NhGRA6 was found to be 96 nucleotides longer at the 3' end than that of NcGRA6, resulting in a protein product that is 32 amino acids larger than NcGRA6. Two tandem repeat sequences were identified at the 3' end of the NhGRA6 gene. These repeat sequences contributed to the lengthening of the carboxy terminus of NhGRA6 in comparison with that of NcGRA6. The larger size of NhGRA6 was further confirmed by Western blot analysis in which NcGRA6 monospecific antibodies recognised a protein of approximately 42 kDa in N. hughesi whole tachyzoite preparation but a protein of 37 kDa in N. caninum whole tachyzoite preparation. Analysis of GRA7 gene sequences indicated a 6 and 14.8% difference at nucleotide and amino acid sequence level, respectively, between NcGRA7 and NhGRA7. Despite the same number of residues in the deduced amino acid sequences of all the GRA7 proteins, Western blot analysis indicated a difference in the migration pattern of NhGRA7 in comparison with NcGRA7. Results of our study indicate that diagnostic tests based on differences in dense granule sequences and antigenicity may have potential to differentiate between N. hughesi and N. caninum. Such diagnostic tests would be valuable tools to aid in our understanding of the epidemiology of these parasites. Additionally, dense granule proteins are immunogenic and they may have potential as use in recombinant vaccines against neosporosis.

Amino Acid Sequence↗
PubMed2001

Multiple origin of the dihomoxenous life cycle in sarcosporidia.

Although their ssrRNA gene sequences are closely related, the lizard sarcosporidia (Apicomplexa, Sarcocystidae) Sarcocystis lacertae and Sarcocystis gallotiae posses heteroxenous and dihomoxenous life cycles, respectively. When aligned with available sarcosporidian ssrRNA genes, both species constitute a monophyletic clade that is only distantly related with sarcosporidia that have a viperid snake as their definitive host (Sarcocystis sp., Sarcocystis atheridis). To test the phyletic status of the dihomoxenous life style, Sarcocystis rodentifelis and Sarcocystis muris, two dihomoxenous parasites of mammals were included into this study. All studied species group together with former Frenkelia spp., Sarcocystis neurona and related marsupial and bird sarcosporidia in a monophyletic clade. However, the available dataset supports independent appearance of the dihomoxenous life cycle at least twice during the evolution of the Sarcocystidae.

Animals↗
PubMed2003

Organisation and sequence determination of glutamine-dependent carbamoyl phosphate synthetase II in Toxoplasma gondii.

Carbamoyl phosphate synthetase II encodes the first enzymic step of de novo pyrimidine biosynthesis. Carbamoyl phosphate synthetase II is essential for Toxoplasma gondii replication and virulence. In this study, we characterised the primary structure of a 28kb gene encoding Toxoplasma gondii carbamoyl phosphate synthetase II. The carbamoyl phosphate synthetase II gene was interrupted by 36 introns. The predicted protein encoded by the 37 carbamoyl phosphate synthetase II exons was a 1,687 amino acid polypeptide with an N-terminal glutamine amidotransferase domain fused with C-terminal carbamoyl phosphate synthetase domains. This bifunctional organisation of carbamoyl phosphate synthetase II is unique, so far, to protozoan parasites from the phylum Apicomplexa (Plasmodium, Babesia, Toxoplasma) or zoomastigina (Trypanosoma, Leishmania). Apicomplexan parasites possessed the largest carbamoyl phosphate synthetase II enzymes due to insertions in the glutamine amidotransferase and carbamoyl phosphate synthetase domains that were not present in the corresponding gene segments from bacteria, plants, fungi and mammals. The C-terminal allosteric regulatory domain, the carbamoyl phosphate synthetase linker domain and the oligomerisation domain were also distinct from the corresponding domains in other species. The novel C-terminal regulatory domain may explain the lack of activation of Toxoplasma gondii carbamoyl phosphate synthetase II by the allosteric effector 5-phosphoribosyl 1-pyrophosphate. Toxoplasma gondii growth in vitro was markedly inhibited by the glutamine antagonist acivicin, an inhibitor of glutamine amidotransferase activity typically associated with carbamoyl phosphate synthetase II, guanosine monophosphate synthetase, or CTP synthetase.

Animals↗
PubMed1999

Comparison of the major antigens of Neospora caninum and Toxoplasma gondii.

The Apicomplexa are a diverse group of parasitic protozoa with very ancient phylogenetic roots. Consistent with their phylogeny, the extant species share conserved proteins and traits that were found in their apicomplexan progenitor, but at the same time they have diverged to occupy different biological niches (e.g. host-range and cell type). Characterisation of gene and protein diversity is important for distinguishing between related parasites, for determining their phylogeny, and for providing insight into factors that determine host restriction, cell preference, and virulence. The value of molecular characterisations and comparisons between species is well illustrated by the close phylogenetic relationship between Neospora caninum and Toxoplasma gondii. These two organisms have nearly identical morphology and can cause similar pathology and disease. Consequently, N. caninum has often been incorrectly identified as T. gondii, thus demonstrating the need for studies addressing the molecular and antigenic composition of Neospora. In this review, we describe the major antigenic proteins that have been characterised in N. caninum. These show homology to T. gondii proteins, yet possess unique antigenic characteristics that distinguish them from their homologues and enable their use for specific serological diagnoses and parasite identification.

Animals↗
PubMed2000

Cryptosporidium parvum: the many secrets of a small genome.

The coccidium Cryptosporidium parvum is an obligate intracellular parasite of the phylum Apicomplexa. It infects the gastrointestinal tract of humans and livestock, and represents the third major cause of diarrhoeal disease worldwide. Scarcely considered for decades due to its apparently non-pathogenic nature, C. parvum has been studied very actively over the last 15 years, after its medical relevance as a dangerous opportunistic parasite and widespread water contaminant was fully recognised. Despite the lack of an efficient in vitro culture system and appropriate animal models, significant advances have been made in this relatively short period of time towards understanding C. parvum biology, immunology, genetics and epidemiology. Until recently, very little was known about the genome of C. parvum, with even basic issues, such as the number and size of chromosomes, being the object of a certain controversy. With the advent of pulsed field gradient electrophoresis and the introduction of molecular biology techniques, the overall structure and fine organisation of the genome of C. parvum have started to be disclosed. Organised into eight chromosomes distributed in a very narrow range of molecular masses, the genome of C. parvum is one of the smallest so far described among unicellular eukaryotic organisms. Although fewer than 30 C. parvum genes have been cloned so far, information about the overall structure of the parasite genome has increased exponentially over the last 2 years. From the first karyotypic analyses to the recent development of physical maps for individual chromosomes, this review will try to describe the state-of-the-art of our knowledge on the nuclear genome of C. parvum and will discuss the available experimental evidence concerning the presence of extra-chromosomal elements.

Animals↗
PubMed2003

Progress in malaria research: the case for phylogenetics.

Malaria, from the Italian for "bad air", is a term used to describe a human disease caused by any of four parasites of the genus, Plasmodium. There are in fact over 200 described species of Plasmodium that parasitize reptiles, birds, and mammals, and may or may not cause disease in these various hosts. In this chapter, we highlight important evolutionary studies that have been undertaken to determine the relatedness among these species and their place in the taxonomic hierarchy. We begin by providing an overview of our present understanding of the phylum to which malaria parasites belong--Apicomplexa. The unique characteristics of these parasites reflect both their adaptation to the parasitic life style as well as some vestigial remnants of their pre-parasitic evolutionary past. Phylogenetic analyses provide the means for discerning the means by which these characteristics have come into existence. We next discuss the systematics of the genus Plasmodium. Morphology, genomic structure and content as well as host affiliation of these parasites are all traits that have been used for establishing taxonomic arrangements. Molecular phylogenetics has proven to be an invaluable tool in this regard and so we discuss the current phylogenetic picture of the genus as well as the correspondence among the various datasets (morphology, molecules, and host-preference). Lastly, we present a detailed account of our current understanding of the evolutionary past of the most deadly of the human malaria species--P. falciparum.

Animals↗
PubMed2006

Phylogenetic analyses of parasites in the new millennium.

Phylogenetic analysis has changed greatly in the last decade, and the most important themes in that change are reviewed here. Sequence data have become the most common source of phylogenetic information. This means that explicit models for evolutionary processes have been developed in a likelihood context, which allow more realistic data analyses. These models are becoming increasingly complex, both for nucleotides and for amino acid sequences, and so all such models need to be quantitatively assessed for each data set, to find the most appropriate one for use in any particular tree-building analysis. Bayesian analysis has been developed for tree-building and is greatly increasing in popularity. This is because a good heuristic strategy exists, which allows large data sets to be analyzed with complex evolutionary models in a practical time. Perhaps the most disappointing aspect of tree interpretation is the ongoing confusion between rooted and unrooted trees, while the effect of taxon and character sampling is often overlooked when constructing a phylogeny (especially in parasitology). The review finishes with a detailed consideration of the analysis of a multi-gene data set for several dozen taxa of Cryptosporidium (Apicomplexa), illustrating many of the theoretical and practical points highlighted in the review.

Animals↗