Parasitized mates increase infection risk for partners

Individuals can gain fitness benefits and costs through their mates. However, studies on sexual selection have tended to focus on genetic benefits. A potentially widespread cost of pairing with a parasitized mate is that doing so will increase an individual's parasite abundance. Such a cost has been overlooked in systems in which parasites are indirectly transmitted. We manipulated the abundance of the nematode parasite Trichostrongylus tenuis, an indirectly transmitted parasite, within pairs of wild red grouse Lagopus lagopus scoticus in spring. Parasite levels were correlated within pairs before the experiment. We removed parasites from males, females, or both members of the pair and evaluated individual parasite uptake over the subsequent breeding period. At the end of the breeding season, an individual's parasite abundance was greater when its mate had not been initially purged of parasites. This cost appeared to be greater for males. We discuss the implications of our results in relation to the costs that parasites may have on sexual selection processes.     

Targeting of host cell lineages by vertically transmitted, feminising microsporidia

Feminising microsporidian parasites are transmitted vertically from generation to generation of their crustacean hosts. Little is known about the mechanisms underpinning vertical transmission, in particular, parasite transmission to the host gonad during host development. Here, we investigate the burden and distribution of two species of vertically transmitted, feminising microsporidia (Dictyocoela duebenum and Nosema granulosis) during early embryogenesis (zygote to eight-cells) of the Gammarus duebeni host. Parasite burden differs between the two parasites with N. granulosis being higher by a factor of 10. Whilst D. duebenum replicates during the first few host cell divisions, there is no increase in N. granulosis burden. Only merogonic parasite stages were observed in the host embryo. Distribution of both parasites was non-random from the two-cell embryo stage, indicating biased parasite segregation at host cell division. Dictyocoela duebenum burden was low in the germline and somatic gonad progenitor cells but was highest in the ectoderm precursors, leading us to propose that the parasite targets these cells and then secondarily infects the gonad later in host development. Targeting by N. granulosis was less specific although there was a persistent bias in parasite distribution throughout host cell divisions. Parasite burden was highest in the ectoderm precursors as well as the germline progenitors leading us to suggest that, in addition to using the ectodermal route, N. granulosis may also target germline directly. Biased segregation will be adaptive for these parasites as it is likely to lead to efficient transmission and feminisation whilst minimising virulence in the host.     

The virulence–transmission relationship in an obligate killer holds under diverse epidemiological and ecological conditions,but where is the tradeoff?

Parasite virulence is a leading theme in evolutionary biology. Modeling the course of virulence evolution holds the promise of providing practical insights into the management of infectious diseases and the implementation of vaccination strategies. A key element of virulence modeling is a tradeoff between parasite transmission rate and host lifespan. This assumption is crucial for predicting the level of optimal virulence. Here, I test this assumption using the water flea Daphnia magna and its castrating and obligate‐killing bacterium Pasteuria ramosa. I found that the virulence–transmission relationship holds under diverse epidemiological and ecological conditions. In particular, parasite genotype, absolute and relative parasite dose, and within‐host competition in multiple infections did not significantly affect the observed trend. Interestingly, the relationship between virulence and parasite transmission in this system is best explained by a model that includes a cubic term. Under this relationship, parasite transmission initially peaks and saturates at an intermediate level of virulence, but then it further increases as virulence decreases, surpassing the previous peak. My findings also highlight the problem of using parasite‐induced host mortality as a “one‐size‐fits‐all” measure of virulence for horizontally transmitted parasites, without considering the onset and duration of parasite transmission as well as other equally virulent effects of parasites (e.g., host castration). Therefore, mathematical models may be required to predict whether these particular characteristics of horizontally transmitted parasites can direct virulence evolution into directions not envisaged by existing models.     

Reduced susceptibility to pyrethroid insecticide treated nets by the malaria vector Anopheles gambiae s.l. in western Uganda

Background

Cloning of parasites by limiting dilution is an essential and rate-limiting step in many aspects of malaria research including genomic and genetic manipulation studies. The standard Giemsa-stained blood smears to detect parasites is time-consuming, whereas the more sensitive parasite lactate dehydrogenase assay involves multiple steps and requires fresh reagents. A simple PCR-based method was therefore tested for parasite detection that can be adapted to high throughput studies.

Methods

Approximately 1 μL of packed erythrocytes from each well of a microtiter cloning plate was directly used as template DNA for a PCR reaction with primers for the parasite 18s rRNA gene. Positive wells containing parasites were identified after rapid separation of PCR products by gel electrophoresis.

Results

The PCR-based method can consistently detect a parasitaemia as low as 0.0005%, which is equivalent to 30 parasite genomes in a single well of a 96-well plate. Parasite clones were easily detected from cloning plates using this method and a comparison of PCR results with Giemsa-stained blood smears showed that PCR not only detected all the positive wells identified in smears, but also detected wells not identified otherwise, thereby confirming its sensitivity.

Conclusion

The PCR-based method reported here is a simple, sensitive and efficient method for detecting parasite clones in culture. This method requires very little manual labor and can be completely automated for high throughput studies. The method is sensitive enough to detect parasites a week before they can be seen in Giemsa smears and is highly effective in identifying slow growing parasite clones.     

Veterinary parasitic vaccines: pitfalls and future directions

Most available antiparasitic drugs are safe, cheap and highly effective against a broad spectrum of parasites. However, the alarming increase in the number of parasite species that are resistant to these drugs, the issue of residues in the food chain and the lack of new drugs stimulate development of alternative control methods in which vaccines would have a central role. Parasite vaccines are still rare, but there are encouraging signs that their number will increase in the next decade. The modern paradigm is that an understanding of parasite genes will lead to the identification of useful antigens, which can then be produced in recombinant systems developed as a result of the huge investment in biotechnology. However, we should also continue to devote efforts to basic research on the host-parasite interface.     

Diagnosis of ecto- and endoparasites in laboratory rats and mice

Internal and external parasites remain a significant concern in laboratory rodent facilities, and many research facilities harbor some parasitized animals. Before embarking on an examination of animals for parasites, two things should be considered. One: what use will be made of the information collected, and two: which test is the most appropriate. Knowing that animals are parasitized may be something that the facility accepts, but there is often a need to treat animals and then to determine the efficacy of treatment. Parasites may be detected in animals through various techniques, including samples taken from live or euthanized animals. Historically, the tests with the greatest diagnostic sensitivity required euthanasia of the animal, although PCR has allowed high-sensitivity testing for several types of parasite. This article demonstrates procedures for the detection of endo- and ectoparasites in mice and rats. The same procedures are applicable to other rodents, although the species of parasites found will differ.     

Plasmodium yoelii: a differential fluorescent technique using Acridine Orange to identify infected erythrocytes and reticulocytes in Duffy knockout mouse

Both human malarial parasite Plasmodium vivax and mouse malaria parasite Plasmodium yoelii use Duffy protein as the receptor for invasion and they preferentially invade reticulocytes. Recently, it has been shown that P. yoelii invades mouse reticulocytes by a Duffy independent pathway. Parasite invasion is generally visualized by time consuming staining procedures with dyes like Giemsa or Wright-Giemsa. Fluorochromatic dye like Acridine Orange has been used for instantaneous detection of parasites in RBCs. Acridine Orange binds to both DNA and RNA but with different emission spectra; and the binding can be distinguished with a fluorescent microscope using a green or a red filter, respectively. We have used this differential emission of Acridine Orange to determine P. yoelii invasion into erythrocytes and reticulocytes of Duffy positive and Duffy knockout mice. Moreover, we show that this method can be used to determine the maturity of reticulocytes in the peripheral blood of anemic mice.     

The serodiagnosis of parasitic infections

Recently, the term of clinical immunoparasitology has been coined to indicate the application of immunological methods to the laboratory diagnosis of parasitic infections. In particular, serological diagnosis (indirect diagnosis) is useful especially in the cases of toxocarosis, trichinellosis, echinococcosis, cysticercosis, toxoplasmosis, amoebic abscess, some filariasis, visceral leishmaniasis, schistosomiasis. When possible, for infections caused by protozoa or helminths, the "gold standard" is represented by direct diagnosis performed by microscopic and/or macroscopic observation of the parasite. In any case, immunological results must be interpreted in consideration of the clinical picture of the patient and confirmed possibly by finding the parasite or its genome, even using molecular methods. Furthermore, since the presence of specific antibodies can reveal an acquired infection, but not necessarily a disease, it is particularly helpful, in addition to a qualitative evaluation, a quantitative one, by determining the serum antibody titre. After recovery, the antibody levels decrease, however, they may persist for long periods, for this reason they do not help in evaluating the treatment outcome. Interpretation of serological results may be difficult when the patients originate from areas where the suspected infection is endemic, in that case, a serum positivity could reflect an old exposition to the parasite, therefore it is not related to the present clinical status. Furthermore, serology may frequently result falsely negative in not immunocompetent subjects (organ transplanted, HIV positive individuals, premature babies, diabetics). Clinicians can interpret correctly the serological results only if the Parasitology laboratory inform them about the significant diagnostic values, the sensitivity and the specificity of the test in use. At present time, many diagnostic kits for immunoparasitology are commercially available, and industries are developing newer and newer ones (which are not always validated). In relation to this aspect, it should be helpful, for each of parasitic infection, to establish reference centers, not only to control the quality of commercial kits, but also as a reference point to those laboratories which use "in house" kits. To this regard, the recent establishment of a European Centre for Control of Infectious Diseases will help. The antigen characteristics (crude, E/S, recombinant, synthetic) for assays searching for antibodies (IHA, IFA, EIA, WB) of different classes, the controls to choose for these assays, the specimen requirements will be discussed. The recent findings on the serological diagnosis of intestinal protozoa infections, malaria, leishmaniasis, echinococcosis, cysticercosis, trichinellosis, toxocariasis, schistosomiasis, strongyloidiasis will be presented.     

Patterns of parasite abundance and distribution in island populations of Galápagos endemic birds

Parasite life-history characteristics, the environment, and host defenses determine variation in parasite population parameters across space and time. Parasite abundance and distribution have received little attention despite their pervasive effects on host populations and community dynamics. We used analyses of variance to estimate the variability of intensity, prevalence, and abundance of 4 species of lice (Insecta: Phthiraptera) infecting Galápagos doves and Galápagos hawks and 1 haemosporidian parasite (Haemosporida: Haemoproteidae) infecting the doves across island populations throughout their entire geographic ranges. Population parameters of parasites with direct life cycles varied less within than among parasite species, and intensity and abundance did not differ significantly across islands. Prevalence explained a proportion of the variance (34%), similar to infection intensity (33%) and parasite abundance (37%). We detected a strong parasite species-by-island interaction, suggesting that parasite population dynamics is independent among islands. Prevalence (up to 100%) and infection intensity (parasitemias up to 12.7%) of Haemoproteus sp. parasites varied little across island populations.     

Reports from the cutting edge of parasitic genome analysis.

This new feature in Parasitology Today will host reports from the laboratories involved in genomics of parasites, be that sequencing, mapping or 'functional genomics' - the mining and analysis of the sequence datasets, and the development of postgenomics tools to examine gene expression, response to drugs and population variability. It will publicize new technology to wider audiences, let communities of researchers know about novel resources (particularly those available through the World Wide Web) and highlight significant advances in the understanding of parasitic genomes through functional genomics.     

Pathology of malaria-infected mosquitoes

Concepts of the basic case reproduction rate of malaria, or the vectorial capacity of malaria vectors, tend to assume that the behaviour of infected and non-infected mosquitoes will be similar. However, recent years have seen a series of studies demonstrating that mosquitoes infected with malaria or other parasites show many pathological features with important effects on their behaviour and on the transmission dynamics of the parasite. Parasitology Today will be featuring a series of reports discussing these effects and attempting to unravel the expected effects on parasite transmission dynamics; this article sets the scene.     

Multi-host parasite species in cophylogenetic studies

Cophylogenetic studies examine the relationship between host and parasite evolution. One aspect of cophylogenetic studies that has had little modern discussion is parasites with multiple definitive hosts. Parasite species with multiple host species are anomalous as, under a codivergence paradigm, speciation by the hosts should cause speciation of their parasites. We discuss situations such as cryptic parasite species, recent host switching or failure to speciate that may generate multi-host parasites. We suggest methods to identify which of the mechanisms have led to multi-host parasitism. Applying the suggested methods may allow multi-host parasites to be integrated more fully into cophylogenetic studies.     

What would it take to describe the global diversity of parasites?

How many parasites are there on Earth? Here, we use helminth parasites to highlight how little is known about parasite diversity, and how insufficient our current approach will be to describe the full scope of life on Earth. Using the largest database of host–parasite associations and one of the world’s largest parasite collections, we estimate a global total of roughly 100 000–350 000 species of helminth endoparasites of vertebrates, of which 85–95% are unknown to science. The parasites of amphibians and reptiles remain the most poorly described, but the majority of undescribed species are probably parasites of birds and bony fish. Missing species are disproportionately likely to be smaller parasites of smaller hosts in undersampled countries. At current rates, it would take centuries to comprehensively sample, collect and name vertebrate helminths. While some have suggested that macroecology can work around existing data limitations, we argue that patterns described from a small, biased sample of diversity aren’t necessarily reliable, especially as host–parasite networks are increasingly altered by global change. In the spirit of moonshots like the Human Genome Project and the Global Virome Project, we consider the idea of a Global Parasite Project: a global effort to transform parasitology and inventory parasite diversity at an unprecedented pace.     

Patterns of association, nestedness, and species co-occurrence of helminth parasites in the greater kudu, Tragelaphus strepsiceros, in the Kruger National Park, South Africa, and the Etosha National Park, Namibia

The helminth parasites of the greater kudu from the Kruger National Park (KNP), South Africa, and the Etosha National Park (ENP), Namibia, were examined to determine the major patterns of spatial and demographic variation in community structure and to evaluate nonrandomness in parasite community assembly. Nonmetric multidimensional scaling ordination procedures were used to test for differences in parasite community composition between hosts of the 2 parks and between hosts of different demographic groups within KNP. Infracommunities within KNP were also examined for patterns of nonrandomness using 2 null models, i.e., nestedness and species co-occurrence. Infracommunities of KNP and ENP were significantly different from each other, as were infracommunities of different host demographic groups within KNP. Parasite species in the greater kudu from KNP displayed significant levels of nestedness and were found to co-occur less frequently than expected by chance; however, this lack of co-occurrence was significant only when all demographic groups were considered. When restricted to any particular age class, co-occurrence patterns could not be distinguished from random. Overall, these data suggest that biogeography and host demographics are important factors in determining community organization of helminth parasites in the greater kudu.     

Parasite Replication and the Evolutionary Epidemiology of Parasite Virulence

Parasite virulence evolution is shaped by both within-host and population-level processes yet the link between these differing scales of infection is often neglected. Population structure and heterogeneity in both parasites and hosts will affect how hosts are exploited by pathogens and the intensity of infection. Here, it is shown how the degree of relatedness among parasites together with epidemiological parameters such as pathogen yield and longevity influence the evolution of virulence. Furthermore, the role of kin competition and the degree of cheating within highly structured parasite populations also influences parasite fitness and infectivity patterns. Understanding how the effects of within-host processes scale up to affect the epidemiology has importance for understanding host-pathogen interactions.     

Plasmodium motility: actin not actin' like actin

Apicomplexan parasites such as Plasmodium and Toxoplasma display actomyosin-dependent motility in the absence of readily detectable actin polymers. Three recent studies indicate that parasite actin polymers, either harvested from parasites or formed from purified recombinant proteins, are exceptionally short ( approximately 100 nm). We propose that parasite motility could be directed by the transient formation of short actin filament scaffolds. Parasite actin polymers that support transmembrane receptors are pulled, by myosin interaction, backwards along the parasite periphery, resulting in forward movement.     

Apparent vector‐mediated parent‐to‐offspring transmission in an avian malaria‐like parasite

Parasite transmission strategies strongly impact host–parasite co‐evolution and virulence. However, studies of vector‐borne parasites such as avian malaria have neglected the potential effects of host relatedness on the exchange of parasites. To test whether extended parental care in the presence of vectors increases the probability of transmission from parents to offspring, we used high‐throughput sequencing to develop microsatellites for malaria‐like Leucocytozoon parasites of a wild raptor population. We show that host siblings carry genetically more similar parasites than unrelated chicks both within and across years. Moreover, chicks of mothers of the same plumage morph carried more similar parasites than nestlings whose mothers were of different morphs, consistent with matrilineal transmission of morph‐specific parasite strains. Ours is the first evidence of an association between host relatedness and parasite genetic similarity, consistent with vector‐mediated parent‐to‐offspring transmission. The conditions for such ‘quasi‐vertical’ transmission may be common and could suppress the evolution of pathogen virulence.     

Effects of waterborne zinc on reproduction, survival and morphometrics of Gyrodactylus turnbulli (Monogenea) on guppies (Poecilia reticulata)

Recent reviews indicate that pollutants in the surrounding macroenvironment directly influence the population dynamics, distribution and dispersal of fish ectoparasites, often leading to increased parasitism. The aim of the current study was to explore the effects of sublethal concentrations of waterborne zinc (up to 240 microg Zn/L) on survival, reproduction and morphometrics of Gyrodactylus turnbulli, a viviparous monogenean infecting the skin and fins of the guppy, Poecilia reticulata. Parasite survival and reproduction on the fish were recorded daily for individual parasites maintained in isolated containers. Both survival and reproduction were reduced in 30 and 120 microg Zn/L, compared with 0, 15, and 60 microg Zn/L indicating direct toxic effects of Zn on the parasite. However, as generation time was unaffected by Zn, we attribute the reduced reproduction to the shorter lifespan. Parasite survival off the fish was monitored hourly. Average lifespan of the detached parasites decreased linearly from 19.5 h in 0 microg Zn/L to 17.3h in 240 microg Zn/L, further supporting the direct toxic effect of Zn to the parasite. In addition, temporal dynamics of parasite morphometrics were monitored from mini-epidemics sampled after 1, 5, 10, and 15 days exposure to various Zn concentrations. All morphological parameters decreased significantly in response both to concentration and duration of exposure to waterborne Zn. Together these data clearly indicate that concentrations as low as 120 microg Zn/L are directly toxic to G. turnbulli.