This study analyses the anti-proliferative effect of lemongrass essential oil and its main constituent (citral) on all 3 evolutive forms of Trypanosoma cruzi. Steam distillation was used to obtain lemongrass essential oil, with chemical composition determined by gas chromatography (GC) and GC coupled to mass spectrometry (GC-MS). The IC50/24 h (concentration that reduced the parasite population by 50%) of the oil and of citral upon T. cruzi was determined by cell counting in a Neubauer chamber, while morphological alterations were visualized by scanning and transmission electron microscopy. Treatment with the essential oil resulted in epimastigote growth inhibition with IC50=126·5 μg/ml, while the IC50 for trypomastigote lysis was 15·5 μg/ml. The IC50/48 h for the Association Index (% macrophage infection×number of amastigotes per cell) was 5·1 μg/ml, with a strong inhibition of intracellular amastigote proliferation. Ultrastructural analysis demonstrated cytoplasmic and nuclear extraction, while the plasma membrane remained morphologically preserved. Our data show that lemongrass essential oil is effective against T. cruzi trypomastigotes and amastigotes, and that its main component, citral, is responsible for the trypanocidal activity. These results indicate that essential oils can be promising anti-parasitic agents, opening perspectives to the discovery of more effective drugs of vegetal origin for treatment of parasitic diseases. However, additional cytotoxicity experiments on different cell lines and tests in a T. cruzi-mouse model are needed to support these data.

Data are presented on 2 full epizootic cycles and the start of a third of Ligula intestinalis in roach Rutilus rutilus in a small lake, and the relationships of these cycles to the densities of rudd, Scardinius erythrophthalmus, and Great Crested Grebes, Podiceps cristatus, over 31 years. The parasite was introduced to the lake by P. cristatus in 1973 at a time when the roach population had increased in response to eutrophication to a level at which individual fish growth was stunted and the hithero dominant rudd population had declined in numbers as a consequence of inter-specific competition with roach. Ligula prevalence peaked at 28% in only 2 years: thereafter parasite-induced host mortality caused a decline in the roach population, releasing fish from stunting and allowing the rudd population to recover. The consequent improved growth of roach individuals and their short life-span reduced Ligula transmission rates and prevalence levels declined to approximately 1% although Ligula nevertheless persisted for a further 10 years. Following a massive winter-kill of the fish populations in 1984–1985, fish and Ligula numbers declined to barely detectable levels and the parasite disappeared from samples. Rudd recovered first, then roach and interspecific competition again led to a decline in rudd numbers. This increase in roach numbers led to a decrease in roach growth rates, which coincided with the re-colonization of the lake by Ligula. This second epizootic of Ligula peaked within 2 years in 1991–1992, when up to 78% of roach were infected with a maximum abundance of 2.2 parasites and intensity of 21 parasites. Heavy parasite-induced mortality of roach led to a decline in numbers, an improvement in individual growth rate and a reduction of Ligula transmission rates such that the epizootic died out in 1996. Similar conditions of roach numbers and growth prevailed at the start of a third cycle in 1998. The course of events over the second cycle was so similar to that of the first that it confirms the interpretations of that cycle. Comparison with other localities shows that epizootics of Ligula always coincide with rapid increases in roach numbers, for whatever cause, and stunted growth, which together attract piscivorous birds. At the start of a cycle Ligula is a major determinant of the population dynamics of the roach, but at the end of the cycle the fish population dynamics determine those of the parasite. The cycles are not regulated and the roach–Ligula system is inherently unstable.

Leishmania spp. are sandfly-transmitted protozoa parasites that cause a spectrum of diseases in humans. Many enzymes involved in Leishmania central carbon metabolism differ from their equivalents in the mammalian host and are potential drug targets. In this review we summarize recent advances in our understanding of Leishmania central carbon metabolism, focusing on pathways of carbon utilization that are required for growth and pathogenesis in the mammalian host. While Leishmania central carbon metabolism shares many features in common with other pathogenic trypanosomatids, significant differences are also apparent. Leishmania parasites are also unusual in constitutively expressing most core metabolic pathways throughout their life cycle, a feature that may allow these parasites to exploit a range of different carbon sources (primarily sugars and amino acids) rapidly in both the insect vector and vertebrate host. Indeed, recent gene deletion studies suggest that mammal-infective stages are dependent on multiple carbon sources in vivo. The application of metabolomic approaches, outlined here, are likely to be important in defining aspects of central carbon metabolism that are essential at different stages of mammalian host infection.

Variation in clinical accuracy of molecular diagnostic methods for cutaneous leishmaniasis (CL) is commonly observed depending on the sample source, the method of DNA recovery and the molecular test. Few attempts have been made to compare these variables. Two swab and aspirate samples from lesions of patients with suspected CL (n = 105) were evaluated alongside standard diagnosis by microscopic detection of amastigotes or culture of parasites from lesion material. Three DNA extraction methods were compared: Qiagen on swab and aspirate specimens, Isohelix on swabs and Boil/Spin of lesion aspirates. Recovery of Leishmania DNA was evaluated for each sample type by real-time polymerase chain reaction detection of parasitic 18S rDNA, and the diagnostic accuracy of the molecular method determined. Swab sampling combined with Qiagen DNA extraction was the most efficient recovery method for Leishmania DNA, and was the most sensitive (98%; 95% CI: 91–100%) and specific (84%; 95% CI: 64–95%) approach. Aspirated material was less sensitive at 80% (95% CI: 70–88%) and 61% (95% CI: 50–72%) when coupled to Qiagen or Boil-Spin DNA extraction, respectively. Swab sampling of lesions was painless, simple to perform and coupled with standardized DNA extraction enhances the feasibility of molecular diagnosis of CL.

This study determined the complete mitochondrial (mt) genome sequence of the canine heartworm, Dirofilaria immitisThe complete nucleotide sequence for the mitochondrial genome of Dirofilaria immitis is available from the EMBL database under the Accession Number AJ537512., and compared its structure, organization and other characteristics with Onchocerca volvulus and other secernentean nematodes. The D. immitis mt genome is 13814 bp in size and contains 36 of the 37 genes typical of metazoan organisms, and lacks the ATP synthetase subunit 8 gene. All of the genes are transcribed in the same direction. For the entire genome, the nucleotide contents are ∼55% (T), ∼19% (each for A and G) and ∼7% (C), which is very similar to those of the protein-coding genes. In the latter genes, most (∼69%) third codon positions have a T, but rarely (∼1–9%) have an A or a C. The C content (8–12%) is higher at the first and second codon positions compared with the third position (∼1%). These nucleotide biases have a significant effect on the codon usage patterns and, thus, on the amino acid composition of the proteins. The mt genome organization of D. immitis is essentially the same as that of O. volvulus, but is distinctly different from other secernentean nematodes sequenced thus far. Irrespective of transpositions of transfer RNA (trn) genes and the non-coding, AT-rich region, there are 4 gene- or gene block-translocations between the mt genome of D. immitis and those of Caenorhabditis elegans, Ascaris suum and the 2 human hookworms, Ancylostoma duodenale and Necator americanus. For D. immitis, the 22 trn genes have secondary structures typical of other secernentean nematodes, and possess a TV-replacement loop instead of a TΨC arm and loop. Like O. volvulus, the mt trnK and trnP of D. immitis use the anticodons CUU and AGG, whereas in other nematodes, UUU and UGG are employed, respectively. Also, the secondary structures of the 2 ribosomal RNA (rrn) genes are similar to the models for other nematodes. Overall, the availability of the complete D. immitis mt genome sequence provides a resource for future studies of the comparative mt genomics and of the population genetics and/or phylogeny of parasitic nematodes.

Some new species of Mastigophora and Sporozoa and a Microfilaria, parasitic in fish, frogs and toads in eastern Canada, are described and illustrated.

Trypanosoma percae n.var. canadensis from the yellow perch, Perca flavescens, is monomorphic, smaller, with a shorter, broader body and shorter free flagellum than Trypanosoma percae from European Perca fluviatilis. Trypanosoma myoxocephali n.sp. from the longhorn sculpin, Myoxocephalus octodecimspinosus, is small, with a narrow undulating membrane. It is the first trypanosome to be recorded from Myoxocephalus. Trypanosoma lavalia n.sp. from Bufo americanus is delicate, with a prominent undulating membrane with two myonemes. Trypanosoma gaumontis n.sp. from Bufo americanus is small, crook-like, with undulating membrane with deep folds and one myoneme very-near the bordering flagellum. There is no free flagellum. Trypanosoma montrealis n.sp. from Bufo americanus is long and sinuous, with very short free flagellum and without chromatoid granules in the cytoplasm.

Trypanosoma rotatorium (Mayer) is described from Rana catesbiana from eight sites, R. clamitans from three sites, and R. pipiens from three sites in Quebec Province. Trypanosoma inopinatum Ed. & Et. Sergent is recorded from Rana catesbiana and R. pipiens, A form similar in dimensions and morphology except for a much shorter free flagellum has been found in R. catesbiana from St Eustache.

Spirochaeta manitoui n.sp. is described from the blood of Rana catesbiana from Lake Manitou.

Lankesterella canadensis n.sp. from Rana catesbiana from Montreal and Lake Manitou is described and illustrated. Intracorpuscular forms have polar vacuoles, schizogony occurs in endothelial cells of the blood vessels of the liver and kidney, and multinucleate oocysts have been observed.

Haemogregarina myoxocephali n.sp. from the longhorn sculpin, Myoxocephalus octo-decimspinosus, and Haemogregarina urophysis n.sp. from the white hake, Urophysis tenuis, are described. Two other haemogregarines sens lat. from species of Rana and Bufoamericanus are described, Haemogregarina aeglifini Henry is recorded from a new host, Gadus callarias from off Labrador, Haemogregarina platessae Lebailly from Pseudopleuronectes americanus and Haemogregarina bigemina Laveran & Mesnil from the eel pout, Zoarces angularis, the hosts being new.

Plasmodium catesbiana n.sp. from Rana catesbiana from the Back River, Montreal, is a small species, with ‘signet ring’ and amoeboid trophozoites, schizonts with up to eight merozoites clustered round coarse pigment granules and gametocytes showing slight sexual dimorphism. Plasmodium bufonis n.sp. occurs in Bufo americanus from Laval des Rapides. The schizonts are large, oval, and give rise to eight merozoites arranged en barillet, the pigment usually being at one pole. Possibly micro- and macromerozoites may be produced. Macrogametocytes are oval and deep-staining; microgametocytes are vermicular. Both have pigment.

A haemosporidian, different from but probably allied to Haemogregarina bigemina, is described from the black sea bass, Centropristis striatus.

Haemoproteus laurentiae n.sp. occurs in Bufo americanus from the banks of the St Lawrence at Montreal South and at Lake Manitou. Its pigment is characteristic, consisting of rod-like or bacilliform distributed granules. Haemoproteus lavalia n.sp. from Bufo americanus, from Laval des Rapides, has pigment restricted to curved bands of rounded to somewhat angular granules. Uninucleate parasites have been observed in extremely few endothelial cells of the lungs. Haemoproteus lanoraiea n.sp. from Bufo americanus, from Lanoraie, has very pale yellow to light brown pigment granules, densely crowded at one pole and forming a compact granular cap. Oval parasites have been found in endothelial cells of the lungs.

Leucocytozoon salvelini n.sp., parasitic in the leucocytes of the speckled trout, Salve-linus fontinalis, is described.

Dactylosoma salvelini n.sp., parasitic in Salvelinus fontinalis from a Laurentian stream, is the second species of Dactylosoma to be described and the third to be notified from fish. It has fan- to wedge-shaped schizonts producing eight merozoites. Its gametocytes are not markedly different from one another in shape but differ in cytoplasmic staining and in nuclear structure. Dactylosoma sylvatica n.sp., parasitic in Rana sylvatica from near Quebec City, produces eight merozoites and has oval and reniform gametocytes.

The morphology of a Microfilaria from Rana sylvatica is described.

The effects of the Protozoa on the host cells are described for each organism, and some differential leucocyte counts for comparable normal and parasitized Amphibia are given in the concluding section.

Unrelated and initially unfamiliar male CFLP mice, maintained for different periods in groups of 6, differed in both their rate of clearance of Babesia microti and the time taken to reach peak parasitaemia in relation to their aggressive behaviour within groups prior to infection. Males maintained in groups for shorter periods and showing more aggression within their group were slower to clear infection and males showing more marked external evidence of aggressive interaction reached a peak of parasitaemia sooner. Serum IgG and corticosterone analyses were consistent with increased aggression causing stress-induced immunodepression but relationships with aggression and social status were not simple. Males showing more aggression tended to enter their groups with higher levels of corticosterone and, to a lesser extent, reduced levels of IgG compared with other mice. The results thus suggest that increased susceptibility to disease may be a cost to males aggressively maintaining high social status.

Survival curves for cercariae of Schistosoma mansoni maintained at different temperatures were determined. Between 15 and 35 °C the curves were of reverse sigmoid form and the probit transformation gave a statistically good fit. The slope of the regression lines fitted to the probit transformations increased exponentially as the temperature rose. Above 35 °C heat intolerance became important and increased exponentially as the temperature rose. Below 15 °C, cold intolerance caused an initial high level of mortality followed by an extended period with insignificant mortality. The glycogen content of whole cercariae and separated cercarial bodies and tails was measured during ageing. The glycogen content of whole cercariae declined exponentially during ageing. This was a product of exponential decreases in the glycogen content of both the body and the tail of the organism. The cercarial tail was shown to contain slightly over half of the total glycogen content. The rate of glycogen use was higher in the tail than in the body. A computer simulation model was used to demonstrate that the observed exponential use of glycogen could generate survival curves similar to those observed experimentally.

Following the introduction of E. granulosus into Australia with domestic animals during European settlement, the parasite quickly became established in the E. granulosus-naive native animals of the continent. The distribution of E. granulosus in wildlife in Australia is restricted by rainfall, but nevertheless the parasite is currently widespread and highly prevalent in many areas including numerous national parks and privately owned farms. The human population of Africa is rapidly increasing resulting in ever more pressure on wild-life populations and habitat. National parks, reserves and conservation areas now provide important tracts of preserved habitat for maintaining populations of wildlife that are also important in the maintenance of E. granulosus. In some parts of Africa, hydatid-infected humans provide a source of E. granulosus infection to wildlife definitive hosts. In many areas felids may also act as important definitive hosts for E. granulosus with the parasite being maintained in a prey/predator relationship between lions and a range of intermediate hosts. Populations of E. granulosus-infected wild-life both in Australia and Africa act as important reservoirs in perpetuating the transmission of E. granulosus to both domestic animals and humans. In Australia, E. granulosus-infected wild-life is infiltrating urban areas and currently represents a potentially important new public health problem.

Experiments are often carried out in the laboratory under artificial conditions. Although this can control for confounding factors, it may eliminate important factors that under natural conditions mediate the interaction under investigation. Here, we show that different results can be gained in the field and in the laboratory regarding host–parasite interaction. In the field, courting three-spined stickleback males, Gasterosteus aculeatus, were less often infected with plerocercoids of a cestode tapeworm, Schistocephalus solidus, than shoaling males. However, when a random sample of males was allowed to nest and court females in individual aquaria in the laboratory, both uninfected and infected males built nests and courted females. Moreover, while the few infected males that courted females in the field expressed less red nuptial coloration than uninfected courting males, there was no difference in redness between infected and uninfected males in the laboratory. We argue that the different results gained in the field and in the laboratory are due to differences in the cost of reproduction, due to differences in the resource pool of the males. The favourable conditions in the laboratory exclude factors such as predation risk, social interactions, and fluctuating environmental conditions that may use up resources in the field and mediate the effect of the parasite.

Malaria-immune human sera were tested for their ability to affect the infectivity of Plasmodium falciparum gametocytes to Anopheles stephensi mosquitoes. Transmission-reducing effects of the sera were associated with the presence of antibodies to the gamete surface protein, Pfs230. Enhancement of transmission, manifest as elevated numbers of oocysts relative to controls, was observed for a number of sera, but was not found to be associated with antibodies against Pfs230. These results confirm that Pfs230 is a possible candidate for inclusion in a transmission-blocking malaria vaccine.

Molluscan FMRFamide and two recently discovered platyhelminth FMRFamide-related peptides (FaRPs), GNFFRFamide from the cestode Moniezia expansa and RYIRFamide from the terrestrial turbellarian Artioposthia triangulata, cause dose-dependent contractions of individual muscle fibres from Schistosoma mansoni in vitro. The most potent FaRP tested was the turbellarian peptide RYIRFamide, which produced a concentration-dependent effect between 10−9 and 10−7 M. FMRFamide and GNFFRFamide were less potent, inducing contractions between 10−8–10−6 M and 10−7–10−5 M respectively. The contractile effect of each of these peptides was blocked by the presence of 1 µM FMR-DFamide. FMRF free acid did not elicit contraction of the muscle fibres. The FaRP-induced contractions did not occur if the Ca2+ was omitted and 0·5 µM EGTA was added to the extracellular medium. The FaRP-induced contractions were not blocked by the Ca2+ channel blockers nicardipine, verapamil or diltiazem, although high K+-induced contractions of these fibres were blocked by nicardipine. These data indicate the presence of FaRP receptors on schistosome muscle fibres and demonstrate their ability to mediate muscle contraction. The action of these endogenous flatworm peptides on schistosome muscle is the first demonstration of a direct excitatory effect of any putative neurotransmitter on the muscle of a flatworm, and establishes a role for FaRPs in neuromuscular transmission in trematodes. In addition, it provides the first evidence that the peptidergic nervous system is a rational target for chemotherapeutic attack in parasitic platyhelmiths.

Computer-aided reconstruction from serial sections has been used to analyse the 3-dimensional structure of entire amastigotes of Leishmania mexicana mexicana and to determine the number, arrangement and volume of each organelle. In two reconstructions, the lysosome-like ‘megasomes’ were the most numerous organelle, there being 34 in one amastigote, and they comprised as much as 15% of the total cell volume. In contrast, as few as 9 glycosomes were present, accounting for less than 1% of the cell volume. The unitary nature of the mitochondrion was confirmed and its complex basket-like structure was revealed. The spatial arrangement of the cell organelles is here displayed in stereo-pairs.

Parasites are integral components of marine ecosystems, a general observation accepted by parasitologists, but often considered of trifling significance to the broader community of zoologists. Parasites, however, represent elegant tools to explore the origins, distribution and maintenance of biodiversity. Among these diverse assemblages, host and geographic ranges described by various helminths are structured and historically constrained by genealogical and ecological associations that can be revealed and evaluated using phylogenetic methodologies within the context of frameworks and hypotheses for co-evolution and historical biogeography. Despite over 200 years of sporadic investigations of helminth systematics, knowledge of parasite faunal diversity in chondrichthyan and osteichthyan fishes, seabirds and marine mammals remains to be distilled into a coherent and comprehensive picture that can be assessed using phylogenetic approaches. Phylogenetic studies among complex host–parasite assemblages that encompass varying temporal and geographic scales are the critical context for elucidating biodiversity and faunal structure, and for identifying historical and contemporary determinants of ecological organization and biogeographic patterns across the marine biosphere. Insights from phylogenetic inference indicate (1) the great age of marine parasite faunas; (2) a significant role for colonization in diversification across a taxonomic continuum at deep and relatively recent temporal scales; and (3) a primary role for allopatric speciation. Integration of ecological and phylogenetic knowledge from the study of parasites is synergistic, contributing substantial insights into the history and maintenance of marine systems.

This paper adds new insight to a molecular phylogeny of Gyrodactylus, based on a complete sequence of the ITS rDNA region of 4 subgenera and a more detailed molecular analysis. We propose a hierarchical approach in elucidating the phylogeny of this species-rich genus. A total of 37 sequences (915–1239 bp) from 10 representative species from 4 out of 6 subgenera, as defined by Malmberg (1970), are included in the analysis. Genetic differences observed at the 5.8S locus provide objective criteria to separate (sub)genera, while deep genetic differences of the spacers form a sound basis for species-specific identification. We demonstrate that each Gyrodactylus subgenus possesses a unique sequence of the 5.8S gene. Thus, there is concordance between the 5.8S gene and the excretory system used by Malmberg (1970) as a diagnostic character of subgenus status. At the species level, there is a discrepancy between morphological and molecular variation. Whereas the morphological variation, expressed in the shape and size of the attachment apparatus, is very low, the molecular variation, expressed at the ITS1 and ITS2 regions, is very high. This can be attributed either to the fast evolving ITS region or to the fact that the genus consists of groups of a higher taxonomic level than previously recognized. Perspectives and limitations of using the ITS rDNA region for a molecular phylogeny of this genus are discussed.

When the eggs of the skin parasitic monogenean Entobdella soleae are subjected in the laboratory to alternating periods of light and darkness (LD 12:12, LD 6:18 or LD 18:6) at constant temperature (selected from the range 12–16 °C), hatching is rhythmical, most of the oncomiracidia emerging during the first 4 h of the period of illumination on each successive day.

Rhythmicity in response to alternating 12 h periods of light and darkness persists in a wide range of lighting conditions including natural daylight and in dim blue light, the latter being similar in intensity (65 nW/cm2) and in spectral quality to light at the depths where the host Solea solea lives.

The hatching rhythm persists with a periodicity of about 24 h in constant darkness and in constant light, provided that the eggs have been exposed previously to LD 12:12 until hatching begins. This indicates that there is a strong endogenous component to the rhythm.

Eggs laid and maintained in total darkness develop and hatch, but the oncomiracidia may emerge at any time during each 24 h period and there is little evidence of rhythmicity.

When alternate 12 h periods of light and darkness are reversed after the commencement of hatching, the hatching pattern also reverses after 24 h, so that emergence of larvae occurs at the beginning of the new illumination period.

Mechanical disturbance plays little or no part as a hatching stimulus.

Larvae, which had emerged from their eggs at some time between 20 and 80 min previously, responded to host skin, suggesting that an initial uninfective period is of short duration or absent.

Hatching soon after dawn may have high survival value for E. soleae in view of the host's activity pattern; soles are active at night and partly bury themselves in the sediment (where the eggs of the parasite lie) at dawn, and the fish is inactive and a stationary target during the day.

Ancylostoma duodenale and Necator americanus are extremely common species of soil-transmitted helminth which flourish where poverty and malnutrition prevail. Hookworms contribute significantly to iron-deficiency anaemia, which remains one of the world's major nutritional problems, through the feeding activities of intestinal stages leading to chronic blood loss into the gut. In this article, a mathematical model is proposed to explain how human iron metabolism may respond to hookworm infection of varying intensity. The model draws attention to the importance of the regulation of stored iron levels in the process. The results from the model are presented for the effects of hookworm infection on the iron metabolism of a healthy adult male. Calculations are also presented in which the effects of hookworms on the iron metabolism of a non-pregnant woman are compared with those of a pregnant woman. Use of the model may help develop a better understanding of the pathology of hookworm disease.

Two panels of H-2 recombinant strains of mice were used in an attempt to map the H-2-linked genes which control resistance to infection with Trichuris muris. Response phenotypes could be related to the presence of ‘resistance’ (q, b) or ‘susceptibility’ (k, d) alleles at I-A. The influence of these genes was modulated by other alleles, particularly q or d alleles, at the D end of the H-2. Absence of I-E molecules correlated with resistance to infection in some but not all strains studied. Thus the (B10.BR × B10.G) Fl strain which expressed I-Ek gene products was resistant to infection. A study of the time-course of infection in strains of mice expressing q alleles throughout the H-2 on 4 different genetic backgrounds (NIH, SWR, DBA and B10) revealed that most strains were resistant to infection. However, the DBA/1 strain exhibited differential responsiveness, 4 out of 6 individuals harbouring mature adult parasites on day 35 post-infection.

The commonly held view that the kinetoplastida, and in particular trypanosomes, are asexual is largely derived from the principle that an organism is asexual until proved sexual. If the basis for this view is examined in detail, it largely arises from the lack of morphologically distinguishable gametes, the difficulties encountered in visualizing chromosomes and a few experiments, using drug-resistant stocks, in which no recombination between stocks could be demonstrated. While it is clear that these organisms are able to reproduce asexually, the existence of a sexual cycle was, until recently, an entirely open question. The early work strongly suggests that any sexual process (in the species examined extensively at the morphological level) does not involve classical well-differentiated gametes and so must involve fusion of morphologically very similar cells. These findings taken together with the inability to visualize chromosomes and thereby identify meiosis, mean that classical methods are unable to detect any sexual process even if it did occur. This review examines the evidence provided by the experimental approaches which have been applied recently to the question of kinetoplastid sexuality. These approaches include isoenzyme studies and the analysis of possible genetic exchange by the use of selective markers (e.g. drug resistance). The results which these techniques have produced make it clear that the kinetoplastid protozoans cannot be regarded as a totally asexual group of organisms.

Transgenesis for Strongyloides and Parastrongyloides was accomplished in 2006 and is based on techniques derived for Caenorhabditis elegans over two decades earlier. Adaptation of these techniques has been possible because Strongyloides and related parasite genera carry out at least one generation of free-living development, with adult males and females residing in soil contaminated by feces from an infected host. Transgenesis in this group of parasites is accomplished by microinjecting DNA constructs into the syncytia of the distal gonads of free-living females. In Strongyloides stercoralis, plasmid-encoded transgenes are expressed in promoter-regulated fashion in the F1 generation following gene transfer but are silenced subsequently. Stable inheritance and expression of transgenes in S. stercoralis requires their integration into the genome, and stable lines have been derived from integrants created using the piggyBac transposon system. More direct investigations of gene function involving expression of mutant transgene constructs designed to alter intracellular trafficking and developmental regulation have shed light on the function of the insulin-regulated transcription factor Ss-DAF-16. Transgenesis in Strongyloides and Parastrongyloides opens the possibility of powerful new methods for genome editing and transcriptional manipulation in this group of parasites. Proof of principle for one of these, CRISPR/Cas9, is presented in this review.