BIODIVERSITY RESEARCH: Parasites of exotic species in invaded areas: does lower diversity mean lower epizootic impact?

Aim Exotic species may serve as vectors for the introduction of parasites from their native range and may also become infected by parasites already present in invaded areas, but the total number of parasites infecting such exotic species in their invaded areas is typically less than that in their native range. We tested whether the diversity of parasites associated with exotic species in the native and invaded areas is related to the epizootic impact these parasites cause. Location Global. Methods We examined the diversity and epizootic impact of 384 parasite taxa associated with 22 exotic freshwater invertebrate species. The epizootic impact of each parasite was rated based on whether it had been documented to cause a major pathological impact on a large proportion of an infected host population (other than the invader under consideration). Results The total number of parasites associated with an exotic host in its native range was about twice that of all parasites associated with it in its entire invaded range. This was mainly because of the loss in the invaded areas of low impact parasites, whereas the average number of high impact parasites per host in these areas did not differ statistically from that in the native range. Main conclusions Our study suggests similar levels of adverse impact of parasites of exotic species in both their native and invaded areas. In addition to the introduction of highly pathogenic exotic parasites, other mechanisms that may be involved include (1) acquisition by the invaders of new high impact parasites in the invaded ranges, (2) high abundance of the invaders in their new ranges and (3) susceptibility of novel hosts to exotic parasites because of the ‘naive host syndrome’.     

Enhanced transmission of drug-resistant parasites to mosquitoes following drug treatment in rodent malaria

The evolution of drug resistant Plasmodium parasites is a major challenge to effective malaria control. In theory, competitive interactions between sensitive parasites and resistant parasites within infections are a major determinant of the rate at which parasite evolution undermines drug efficacy. Competitive suppression of resistant parasites in untreated hosts slows the spread of resistance; competitive release following treatment enhances it. Here we report that for the murine model Plasmodium chabaudi, co-infection with drug-sensitive parasites can prevent the transmission of initially rare resistant parasites to mosquitoes. Removal of drug-sensitive parasites following chemotherapy enabled resistant parasites to transmit to mosquitoes as successfully as sensitive parasites in the absence of treatment. We also show that the genetic composition of gametocyte populations in host venous blood accurately reflects the genetic composition of gametocytes taken up by mosquitoes. Our data demonstrate that, at least for this mouse model, aggressive chemotherapy leads to very effective transmission of highly resistant parasites that are present in an infection, the very parasites which undermine the long term efficacy of front-line drugs.     

The Immune Response of Hemocytes of the Insect Oncopeltus fasciatus against the Flagellate Phytomonas serpens

The genus Phytomonas includes parasites that are etiological agents of important plant diseases, especially in Central and South America. These parasites are transmitted to plants via the bite of an infected phytophagous hemipteran. Despite the economic impact of these parasites, many basic questions regarding the genus Phytomonas remain unanswered, such as the mechanism by which the parasites cope with the immune response of the insect vector. In this report, using a model of systemic infection, we describe the function of Oncopeltus fasciatus hemocytes in the immune response towards the tomato parasite Phytomonas serpens. Hemocytes respond to infection by trapping parasites in nodular structures and phagocytizing the parasites. In electron microscopy of hemocytes, parasites were located inside vacuoles, which appear fused with lysosomes. The parasites reached the O. fasciatus salivary glands at least six hours post-infection. After 72 hours post-infection, many parasites were attached to the salivary gland outer surface. Thus, the cellular responses did not kill all the parasites.     

Virulence, drug sensitivity and transmission success in the rodent malaria, Plasmodium chabaudi

Here, we test the hypothesis that virulent malaria parasites are less susceptible to drug treatment than less virulent parasites. If true, drug treatment might promote the evolution of more virulent parasites (defined here as those doing more harm to hosts). Drug-resistance mechanisms that protect parasites through interactions with drug molecules at the sub-cellular level are well known. However, parasite phenotypes associated with virulence might also help parasites survive in the presence of drugs. For example, rapidly replicating parasites might be better able to recover in the host if drug treatment fails to eliminate parasites. We quantified the effects of drug treatment on the in-host survival and between-host transmission of rodent malaria (Plasmodium chabaudi) parasites which differed in virulence and had never been previously exposed to drugs. In all our treatment regimens and in single- and mixed-genotype infections, virulent parasites were less sensitive to pyrimethamine and artemisinin, the two antimalarial drugs we tested. Virulent parasites also achieved disproportionately greater transmission when exposed to pyrimethamine. Overall, our data suggest that drug treatment can select for more virulent parasites. Drugs targeting transmission stages (such as artemisinin) may minimize the evolutionary advantage of virulence in drug-treated infections.     

Establishment of exotic parasites: the origins and characteristics of an avian malaria community in an isolated island avifauna

Knowledge of the processes favouring the establishment of exotic parasites is poor. Herein, we test the characteristics of successful exotic parasites that have co-established in the remote island archipelago of New Zealand, due to the introduction of numerous avian host species. Our results show that avian malaria parasites (AM; parasites of the genus Plasmodium) that successfully invaded are more globally generalist (both geographically widespread and with a broad taxonomic range of hosts) than AM parasites not co-introduced to New Zealand. Furthermore, the successful AM parasites are presently more prevalent in their native range than AM parasites found in the same native range but not co-introduced to New Zealand. This has resulted in an increased number and greater taxonomic diversity of AM parasites now in New Zealand.     

Factors Enhancing the Host-Cell Penetration of Toxoplasma gondii

The penetration into HeLa cells of Toxoplasma gondii was studied with a cell culture technique. The influence on the rate of penetration and the number of penetrating Toxoplasma parasites was tested by use of preparations of disintegrated parasites mixed with test parasites. These preparations were found to contain factors enhancing the penetrating rate of the parasites. This effect was demonstrable by use of untreated parasites as well as parasites lacking active motility owing to a previous exposure to Formalin. The preparations of disintegrated parasites contained, in addition, components inhibitory to the penetration-enhancing factors. These inhibitory components were able to reduce the penetrating capacity of normal Toxoplasma parasites, suggesting that the studied enhancing factors may play a role in the natural process of penetration. The efficacy of various techniques for disintegration of Toxoplasma parasites was investigated for release of penetration-enhancing factors from Toxoplasma parasites. The methods used resemble those used for liberation of lysosomal enzymes. Reduced osmotic pressure was obviously not adequate for release of enhancing factors, whereas the freezing and thawing procedure, sonic treatment, and irradiation produced high yields. It was difficult to evaluate the effect of incubation at acid pH on release of enhancing activity, because the penetration-promoting factors seemed unstable on both the acid and the alkaline sides of pH 7.6.     

Overexpression of leucyl aminopeptidase in Plasmodium falciparum parasites. Target for the antimalarial activity of bestatin

Malaria aminopeptidases are important in the generation and regulation of free amino acids that are used in protein anabolism and for maintaining osmotic stability within the infected erythrocyte. The intraerythrocytic development of malaria parasites is blocked when the activity of aminopeptidases is specifically inhibited by reagents such as bestatin. One of the major aminopeptidases of malaria parasites is a leucyl aminopeptidase of the M17 family. We reasoned that, when this enzyme was the target of bestatin inhibition, its overexpression in malaria cells would lead to a reduced sensitivity to the inhibitor. To address this supposition, transgenic Plasmodium falciparum parasites overexpressing the leucyl aminopeptidase were generated by transfection with a plasmid that housed the full-length gene. Transgenic parasites expressed a 65-kDa protein close to the predicted molecule size of 67.831 kDa for the introduced leucyl aminopeptidase, and immunofluorescence studies localized the protein to the cytosol, the location of the native enzyme. The product of the transgene was shown to be functionally active with cytosolic extracts of transgenic parasites exhibiting twice the leucyl aminopeptidase activity compared with wild-type parasites. In vitro inhibitor sensitivity assays demonstrated that the transgenic parasites were more resistant to bestatin (EC50 64 microM) compared with the parent parasites (EC50 25 microM). Overexpression of genes in malaria parasites would have general application in the identification and validation of targets for antimalarial drugs.     

基于部分18S rDNA, 28S rDNA和COI基因序列的索科线虫亲缘关系

通过PCR扩增获得我国常见昆虫病原索科线虫6属10种18S rDNA、28S rDNA(D3区)和COI基因序列,结合来自GenBank中6属10种索科线虫的18S rDNA同源序列,用邻接法和最大简约法构建系统进化树。结果显示:12属索科线虫分为三大类群,第一大类群是三种罗索属线虫(Romanomermis)先聚在一起,再与两索属(Amphimermis)和蛛索属(Aranimermis)线虫聚为一支;在第二大类群中,六索属(Hexamermis)、卵索属线虫(Ovomermis)和多索属(Agamermis)亲缘关系最近,先聚在一起,再与八腱索属(Octomyomermis)和Thaumamermis线虫聚为一支。第三大类群由索属(Mermis)和异索属(Allomermis)线虫以显著水平的置信度先聚在一起,再与蠓索属(Heleidomermis)和施特克尔霍夫索属(Strelkovimermis)线虫聚为一支。从遗传距离看,基于3个基因的数据集均显示索科线虫属内种间差异明显小于属间差异,武昌罗索线虫(R.wuchangensis)和食蚊罗索线虫(R.culicivorax)同属蚊幼寄生罗索属线虫,其种间的遗传距离最小。     

Isolation of Plasmodium berghei by hemolysin lysis of infected erythrocytes and evidence for a parasite hexokinase.

A rapid and simple procedure has been developed for the isolation of Plasmodium berghei parasites from infected-mouse erythrocytes employing the heat stable hemolysin produced by Pseudomonas aeruginosa. Using parasites isolated by this method, the presence of a parasite specific hexokinase has been demonstrated, providing an explanation for the increased glucose consumption observed with infected cells. Enzyme assays and serology were employed in determining the purity and yield of purified parasites. The enzyme assays showed that about 25% of the parasites in infected RBCs were recovered in the purified state. The purified parasites were not agglutinated by rabbit-anti-mouse RBC serum which indicated the purified parasites were not contaminated by RBC components.     

Mobile genetic elements colonizing the genomes of metazoan parasites

A substantial fraction of the genome of most eukaryotes, including those of metazoan parasites, is predicted to comprise repetitive sequences. Mobile genetic elements (MGEs) will make up much of these repetitive sequences, particularly the interspersed sequences. This article reviews information on MGEs that have colonized the genomes of metazoan parasites (i.e. parasites of parasites). Helminth and mosquito genomes, in particular, are compared with those of better-understood model organisms. MGEs from the genomes of metazoan parasites can be expected to have practical uses in transgenesis and epidemiological studies.     

Internalization of surface anionic sites and phagosome-lysosome fusion during interaction of Toxoplasma gondii with macrophages

The participation of cell surface anionic sites on the interaction between tachyzoites of Toxoplasma gondii and macrophages and the process of phagosome-lysosome fusion were analyzed using cationized ferritin as a marker of cell surface anionic sites and albumin-colloidal gold as a marker for secondary lysosomes. Incubation of either the macrophages or the parasites with cationized ferritin before the interaction increased the ingestion of parasites by macrophages. Anionic sites of the macrophage's surface, labeled with cationized ferritin before the interaction, were internalized together with untreated parasites. However, after interaction with glutaraldehyde-fixed or specific antibody-coated parasites, the cationized ferritin particles were observed in endocytic vacuoles which did not contain parasites. Macrophages previously labeled with albumin-gold at 37 degrees C, were incubated in the presence of cationized ferritin at 4 degrees C and then incubated with untreated or specific antibody-coated parasites. After interaction with opsonized parasites, the colloidal gold particles were observed in the parasitophorous vacuoles while the cationized ferritin particles were observed in cytoplasmic vesicles. However, when the interaction was carried out with untreated parasites, the parasitophorous vacuoles exhibited ferritin particles while the colloidal gold particles were observed in cytoplasmic vesicles. These observations, in association with studies previously reported, suggest that the state of the parasite surface determines the mechanism of parasite entry into the macrophage, the composition of the membrane lining the parasitophorous vacuole and the ability of lysosomes to fuse with the vacuoles.     

PHYLOGENETIC RELATIONSHIPS AMONG PAPER WASP SOCIAL PARASITES AND THEIR HOSTS (HYMENOPTERA: VESPIDAE; POLISTINAE)

Abstract— Cladistic analyses of data from allozyme polymorphisms in paper wasp social parasites and their hosts do not support the hypothesis that social parasites are most closely related to their hosts. Electrophoretic data are adduced for nine species of Polistes , including all three known species of social parasites ( Sulcopolistes ) and their hosts. Three different coding methods are investigated; in no case do the social parasites cluster most closely with their hosts. Rather, there is limited evidence that they form a monophyletic group. However, formal taxonomic recognition of Sulcopolistes is not justified, as it renders Polistes sensu stricto paraphyletic. Although the social parasites are not most closely related to their hosts, hosts and parasites belong in the same subgenus and share many characteristics that may have facilitated the exploitation and deception practised by the parasites on the hosts.     

Phylogenetic relationships of haemosporidian parasites in New World Columbiformes, with emphasis on the endemic Galapagos dove

DNA-sequence analyses of avian haemosporidian parasites, primarily of passerine birds, have described the phylogenetic relationships of major groups of these parasites, which are in general agreement with morphological taxonomy. However, less attention has been paid to haemosporidian parasites of non-passerine birds despite morphological and DNA-sequence evidence for unique clades of parasites in these birds. Detection of haemosporidian parasites in the Galapagos archipelago has raised conservation concerns and prompted us to characterise the origins and diversity of these parasites in the Galapagos dove (Zenaida galapagoensis). We used partial mitochondrial cytochrome b (cyt b) and apicoplast caseinolytic protease C (ClpC) genes to develop a phylogenetic hypothesis of relationships of haemosporidian parasites infecting New World Columbiformes, paying special attention to those parasites infecting the endemic Galapagos dove. We identified a well-supported and diverse monophyletic clade of haemosporidian parasites unique to Columbiformes, which belong to the sub-genus Haemoproteus (Haemoproteus). This is a sister clade to all the Haemoproteus (Parahaemoproteus) and Plasmodium parasites so far identified from birds as well as the Plasmodium parasites of mammals and reptiles. Our data suggest that the diverse Haemoproteus parasites observed in Galapagos doves are not endemic to the archipelago and likely represent multiple recent introductions.     

Brugia malayi: transient transfection by microinjection and particle bombardment

To develop a method for the introduction of DNA into filarial parasites, several methods that have proven successful in other organisms were evaluated for their ability to transform Brugia malayi. Luciferase activity was detectable in embryos bombarded with gold particles coated with a construct consisting of a luciferase reporter gene under the control of the 5S rRNA intergenic spacer (SL promoter). Similar results were seen in adult parasites and infective larvae bombarded with this construct, or in adult female parasites microinjected with the plasmid. In similar experiments employing the SL promoter driving a green fluorescent protein (GFP) reporter, expression of the reporter was detectable in the intrauterine embryos of the microinjected adult parasites, and in the sub-cuticular tissues of biolistically transfected adult female parasites. A similar pattern of GFP expression to that seen in the SL promoter construct transfected parasites was noted in parasites transfected with constructs consisting of the upstream domain derived from an aspartyl aminoacyl tRNA synthetase gene of B. malayi. The ability to transfect B. malayi embryos may provide a foundation for studies of the regulation of gene expression and function in these organisms.     

Echinococcus granulosus: the establishment of the metacestode is associated with control of complement-mediated early inflammation

In this work we studied the evolution of early inflammation, complement activation and parasite survival/death along the establishment phase of Echinococcus granulosus metacestode. Using a chamber model of infection in mice, we examined cell infiltration and C3 deposition on individual parasites during their development from protoscoleces to cystic forms. We found that the intensity of the initial inflammation decreased around undamaged but not around damaged parasites: at 43dpi undamaged parasites were mostly associated with poor/mild inflammation while damaged parasites with a strong inflammation. In addition, whereas complement activation participated in the induction of early inflammation, the deposition of C3 on undamaged parasites progressively diminished. Interestingly, we observed some parasites in pre-cystic stage with no/poor C3 deposition at 3dpi. Overall, these results indicated that the establishment and survival of the hydatid cyst is associated with the control of complement and, consequently, of local inflammation at the initial phases of infection.     

Lysosomes of Toxoplasma gondii and Their Possible Relation to the Host-Cell Penetration of Toxoplasma Parasites

Lysosome-like structures of Toxoplasma gondii were observed by means of vital staining with acridine orange and by the Gomori technique. These structures were found scattered over the cytoplasm but were often located at one end of the parasite. In comparison with parasites of the inoculum used for infecting HeLa cell cultures, the toxoplasma which had penetrated the HeLa cells revealed a markedly lower percentage of parasites showing lysosomal staining. After the penetration, the number of parasites with demonstrable lysosomes increased successively and, at the time for release of newly formed parasites (at 24 hr), the majority of the parasites demonstrated lysosome-like bodies in the cytoplasm. The observations are discussed with special reference to the mechanism of host-cell penetration.     

Differential responses to related hosts by nesting and non-nesting parasites in a brood-parasitic duck

Host-parasite relatedness may facilitate the evolution of conspecific brood parasitism, but empirical support for this contention remains inconclusive. One reason for this disparity may relate to the diversity of parasitic tactics, a key distinguishing feature being whether the parasite has a nest of her own. Previous work suggests that parasites without nests of their own may be of inferior phenotypic quality, but because of difficulties in identifying these parasitic individuals, little is known about their host selection criteria. We used high-resolution molecular maternity tests to assign parasitic offspring to known parasites with and without their own nests in a population of Barrow's goldeneyes (Bucephala islandica). We determined whether parasite nesting status, host-parasite relatedness and distance between host and parasite nests affected the probability of parasitizing a host and the number of eggs laid per host. We also investigated whether nesting parasites, conventionally nesting females and non-nesting parasites differed regarding their age, structural size, body condition, nesting phenology or total brood size. The probability of engaging in parasitism increased with host-parasite relatedness and spatial proximity to host nests for nesting and non-nesting females alike. However, nesting parasites increased the number of eggs donated with relatedness to the host, while non-nesting parasites did not do so. Non-nesting parasites laid fewer eggs in total, but did not differ by any of the other quality measures from conventional nesters or nesting parasites. Our study provides the first demonstration that nesting and non-nesting parasites from the same population may use different host selection criteria.     

Response to Preuss and Zuccarello (2020): biological definitions that can be unambiguously applied for red algal parasites

In response to a comment in this issue on our proposal of new terminology to distinguish red algal parasites, we clarify a few key issues. The terms adelphoparasite and alloparasite were previously used to identify parasites that infected close or distant relatives. However, most red algal parasites have only been studied morphologically, and molecular tools have shown that these binary terms do a poor job at representing the range of parasite–host relationships. We recognize the need to clarify inferred misconceptions that appear to be drawing from historical terminology to contaminate our new definitions. We did not intend to replace the term adelphoparasite with neoplastic parasites and the term alloparasites with archaeplastic parasites. Rather, we seek to establish new terms for discussing red algal parasites, based on the retention of a native plastid, a binary biological trait that is relatively easy to identify using modern methods and has biological implications for the interactions between a parasite and its host. The new terminology can better account for the spectrum of relationships and developmental patterns found among the many independently evolved red algal parasites, and it is intended to inspire new research, particularly the role of plastids in the survival and evolution of red algal parasites.     

Schistosoma mansoni: migration potential of normal and radiation attenuated parasites in naive guinea pigs

Compressed tissue autoradiography using [75Se]selenomethionine labelled parasites has been used to investigate the migration potential of normal and radiation attenuated cercariae of Schistosoma mansoni in naive guinea pigs. By Day 14 after infection. 44% of normal parasites were detected as reduced silver foci in the liver; this value corresponded well with the number of liver parasites recovered by retrograde perfusion of the hepatic portal system on Day 42 (42% of the challenge). In contrast, cercariae subjected to 50 krad of gamma irradiation failed to migrate out of the skin. The migration capacity of 20 krad irradiated parasites was less severely affected in that about half of the challenge parasites reached the lungs, but virtually none moved to the liver. These data are discussed in relation to the kinetics of immunity induced in guinea pigs by infection or vaccination with normal or radiation attenuated parasites.     

Comparison of in vitro-cultured and wild-type Perkinsus marinus. I. Pathogen virulence

Perkinsus marinus is a highly contagious pathogen of the eastern oyster Crassostrea virginica. Until recently, transmission studies have employed wild-type parasites isolated directly from infected oysters. Newly developed methods to propagate P. marinus in vitro have led to using cultured parasites for infection studies, but results suggest that cultured parasites are less virulent than wild-type parasites In this paper, we report results of experiments designed to quantify differences between wild-type and cultured P. marinus virulence and to test the following hypotheses: (1) in vitro-cultured parasites are less virulent than wild-type parasites; (2) virulence decreases gradually during in vitro culture; (3) virulence of in vitro cultures can be restored by in vivo passage; (4) virulence changes with culture phase. Our results demonstrate that parasites freshly isolated from infected hosts are much more virulent than those propagated in culture, indicating a potential deficiency in the culture medium used. Virulence was lost immediately in culture and, for that reason, the practice of repassing cultured cells through the host to restore virulence does not work for P. marinus. Virulence was also associated with culture phase: log-phase parasites were significantly more virulent than those obtained from lag- or stationary-phase cultures.