Light microscopy of stained blood films is still the mainstay of malaria diagnosis in many regions, but its pre-eminence is threatened by accurate and sensitive rapid diagnostic tests (RDTs) based on immunochromatography which are now widely used in the field. In well-resourced regions, nucleic acid detection easily out performs microscopy and RDTs. This paper reviews the main in vitro methods for parasite detection and considers future trends in diagnostics, both for sophisticated laboratory settings and for field use.

Schistosomiasis in China has been substantially reduced due to an effective control programme employing various measures including bovine and human chemotherapy, and the removal of bovines from endemic areas. To fulfil elimination targets, it will be necessary to identify other possible reservoir hosts for Schistosoma japonicum and include them in future control efforts. This study determined the infection prevalence of S. japonicum in rodents (0–9·21%), dogs (0–18·37%) and goats (6·9–46·4%) from the Dongting Lake area of Hunan province, using a combination of traditional coproparasitological techniques (miracidial hatching technique and Kato-Katz thick smear technique) and molecular methods [quantitative real-time PCR (qPCR) and droplet digital PCR (ddPCR)]. We found a much higher prevalence in goats than previously recorded in this setting. Cattle and water buffalo were also examined using the same procedures and all were found to be infected, emphasising the occurrence of active transmission. qPCR and ddPCR were much more sensitive than the coproparasitological procedures with both KK and MHT considerably underestimating the true prevalence in all animals surveyed. The high level of S. japonicum prevalence in goats indicates that they are likely important reservoirs in schistosomiasis transmission, necessitating their inclusion as targets of control, if the goal of elimination is to be achieved in China.

The infectivity and distribution of Echinostoma trivolvis were studied in male, conventional and congenitally athymic nude mice, each infected with 30 metacercarial cysts. In conventional mice, worm recoveries at 6 and 8 days post-exposure were58·3 and 54·0%, respectively. Worm recovery declined to 44·0% by day 10, to 4·3% by day 13, and 0% by day 17. In athymic mice, worm recoveries at 6 and 8 days post-exposure were 61·7 and 36·3%, respectively. Worm recovery declined to 27·7% by day 10, to 0·7% by day 13, and 0% by day 17. The distribution of worms demonstrated a posteriad migration over time in both groups. Kinetic changes in the number of goblet and mucosal mast cells in the upper ileum of mice infected with E. trivolvis were examined. In conventional mice, the number of goblet cells increased rapidly to reach a peak at day 13 and then declined gradually. The number of goblet cells in athymic mice also increased to reach a peak at day 13, and then declined rapidly. However, the number of goblet cells in athymic mice was always less than that inconventional mice. The mast cell number in infected conventional mice increased rapidly to reach a peak at day 17 and then declined. There was no increase in the mast cell number of infected athymic mice throughout the experiment. Whereas common pathological changes occurred in the intestines of both mice groups infected with echinostomes some ultrastructural differences were observed in the gut epithelial cells of conventional versus athymic mice.

Studies of foraging strategies are often complicated by competing goals of the forager. In contrast, non-feeding infective juvenile entomopathogenic nematodes forage exclusively for a single host. Two questions were posed: (1) what is the relationship between metabolic rate, energy reserves and foraging strategy and (2) when a foraging strategy fails, will an infective-stage parasite switch strategies? Three species of entomopathogenic nematodes were stored in water and changes in their behaviour, metabolic rate, energy reserves, and infectivity were measured throughout the storage period. Steinernema carpocapsae ambushes insect hosts, whereas S. glaseri and Heterorhabditis bacteriophora cruise forage. Steinernema carpocapsae was least active and had the lowest metabolic rate. Heterorhabditis bacteriophora was more active and had the highest metabolic rate. Steinernema glaseri was most active and had an intermediate metabolic rate. Neither cruising species changed foraging strategy. Steinernema carpocapsae decreased nictation (a behaviour associated with ambushing only) and increased their locomotory rate. Any change in searching strategy occurred without assessment of the profitability or distribution of potential hosts, but the advantage this confers is unknown.

Climate change in the Arctic is anticipated to alter the ecology of northern ecosystems, including the transmission dynamics of many parasite species. One parasite of concern is Ostertagia gruehneri, an abomasal nematode of Rangifer ssp. that causes reduced food intake, weight loss, and decreased pregnancy rates in reindeer. We investigated the development, availability, and overwinter survival of the free-living stages of O. gruehneri on the tundra. Fecal plots containing O. gruehneri eggs were established in the Northwest Territories, Canada under natural and artificially warmed conditions and sampled throughout the growing season of 2008 and the spring of 2009. Infective L3 were present 3–4 weeks post-establishment from all trials under both treatments, except for the trial established 4 July 2008 under warmed conditions wherein the first L3 was recovered 7 weeks post-establishment. These plots were exposed to significantly more time above 30°C than the natural plots established on the same date, suggesting a maximum temperature threshold for development. There was high overwinter survival of L2 and L3 across treatments and overwintering L2 appeared to develop to L3 the following spring. The impact of climate change on O. gruehneri is expected to be dynamic throughout the year with extreme maximum temperatures negatively impacting development rates.

Up to the present very few authors have directed their attention to factors influencing the emergence of larval trematodes from their snail hosts. Cort (1922) has made a study of the escape of cercariae from their hosts and the writer (1931) has examined the effect of light and temperature on the emergence of three species of larval trematodes from three species of fresh-water molluscs. More recently, Giovannola (1936) has investigated the effect of a reversal of light and darkness on the periodicity of emission of cercariae from three species of host snails. All these studies have been made on freshwater molluscs. In the case of molluscs living between tide-marks on the shore, in addition to variation in temperature there exists another variable factor, namely, the salinity of the water. Many rock-pools situated in the intertidal zone are small and will therefore be subject to considerable variations in temperature and salinity at different times of the year and even for short periods of up to 12 hr. during individual days. In the summer months the temperature of the water in these pools may rise to a high degree and the high temperature would be maintained for a longer period near high-water mark than near low-water mark, where the period of exposure is less. Similarly, the decrease in temperature would be very marked during the cold winter months. As the water in the exposed pools evaporates the salinity increases and high up on the shore, between successive tides on hot summer days, it may become twice that of normal sea water. The pools are also exposed to rain and in the same period the salinity of the water may decrease considerably if the precipitation is heavy. The light factor would be the same for molluscs living in fresh and in salt water, but the reaction of various species of larval trematodes to the presence or absence of light varies. Some emerge from their hosts in larger numbers during the daytime, others during the night and some indiscriminately during periods of light and darkness.

Genetic proximity between two karyotypic groups of Trypanosoma congolense was investigated using as hybridization probes: (i) total genomic DNA, (ii) a 35 nucleotide long synthetic oligonucleotide, and (iii) non-variant antigen type (non-VAT) specific complementary DNAs. The phylogenetic relationship between Trypanosoma brucei and T. evansi, both of which are accepted species in the subgenus Trypanozoon, was used as a reference to assess the phylogenetic proximity of the two groups of T. congolense. Results indicate that some morphologically indistinguishable T. congolense populations differ in a variety of molecular and genetic properties: molecular karyotypes, majority of the DNA sequences, and the restriction enzyme sites in the genomic environments of various conserved genes. The implications of these findings for trypanosome evolution and T. congolense epidemiology are discussed.

This review considers three case studies based on macroparasites of anurans: (a) natural infections in the permanently-aquatic Xenopus laevis which represent the worm burdens acquired, and the implications for pathology, when hosts are exposed to continuous, year-round, transmission; (b) the desert toad, Scaphiopus couchii, which experiences invasion very briefly each year and provides a simplified system involving only a single significant infection (Pseudodiplorchis americanus); (c) the mesic Bufo bufo which has been the subject of experimental laboratory studies designed to measure the effects of Rhabdias bufonis infection on host growth, physical performance and survival. Experimental manipulation of both Scaphiopus and Bufo provide quantitative data on disease effects of macroparasites, including precise measurements of parasite-induced host mortality. Field data for Xenopus and Scaphiopus show that, despite high initial worm burdens from efficient transmission, infection levels at parasite maturity are modulated below those leading to significant disease. Experimental data for Scaphiopus and Bufo have documented the time-course and magnitude of this decline in intensities, and there is circumstantial evidence for Scaphiopus that this regulation is host-mediated. Immunological studies on Xenopus show that disease effects of the pathogenic Pseudocapillaroides xenopodis are exacerbated in thymectomised hosts and reversed by implantation of thymuses from MHC-compatible donors. Thus, whilst factorial experiments can demonstrate the potential of helminths to cause significant disease and mortality in anuran host-macroparasite interactions, powerful post-invasion regulation of worm burdens appears to exert a strong control of parasite-induced disease in natural host populations.

We have performed restriction endonuclease digestion of nuclear DNAs, combined with gel electrophoresis and molecular hybridization to characterize different Trypanosoma brucei brucei stocks and to identify trypanosome species. Cloned DNA complementary to the messenger RNAs (mRNAs) for different variable surface glycoproteins (VSGs) of T. b. brucei stock LUMP 227 was used to examine differences in genomic DNAs from T. b. brucei stocks and from various other trypanosome species. These cDNA reagents differentiated the stocks of T. b. brucei and also distinguished the trypanosome species. Our data also show that a T. b. brucei nuclear DNA fragment used as a probe in molecular hybridization analysis provides an appropriate marker in determining trypanosome species. We have extended our analysis of trypanosome nuclear DNA by developing a simple and rapid spot test, for the identification of trypanosome species, which can be carried out using crude materials such as isolated parasites, infected whole blood and tsetse saliva. The procedure is species-specific, sensitive to the level of 104 organisms and is suitable for use under field conditions. Thus, with appropriate sequences for hybridization, the procedure has obvious applications for the diagnosis of African trypanosomiasis.

In a manner similar to many other groups of organisms, the tapeworm order Proteocephalidea poses a difficult phylogenetic problem if treated on the basis of single-gene analysis. Since the biogeography and host distribution of proteocephalideans make these tapeworms a potentially interesting model for evolutionary and co-evolutionary studies, we tried to resolve their phylogenetic relationships by applying a multi-gene approach. The ITS2 sequences and V4 hypervariable loop of 18S rRNA were obtained for 43 and 35 proteocephalidean taxa, respectively, and combined with other sequences available in the GenBank. The phylogenetic analysis of the combined DNA set was confronted with characters derived from ITS2 secondary structures. Using this approach, a species-rich Neotropical lineage of proteocephalideans could be reliably resolved. The phylogenetic relationships within this group show a high degree of phylogeny-independent host distribution. The reconstruction of ITS2 secondary structure revealed a universal 4-domain arrangement, which is conserved across a wide range of Neodermata. Several motifs of the secondary structure could be mapped to the phylogenetic tree as possible clade synapomorphies.

Density-dependent constraints on parasite growth, survival or reproduction are thought to be important in preventing the unchecked increase in parasite numbers within individual hosts or host populations. While it is important to know where, and with what severity, density dependence is acting within the parasite life-cycle, interpretation of data from natural infections is difficult. In this paper, we present a Monte Carlo simulation technique for examining such data for evidence of density dependence. We also describe how this technique may be used to distinguish among mechanisms hypothesized to generate density-dependent phenomena.

The nematodes described here were collected by biologists of the Australian National Antarctic Research Expedition based at the subantarctic stations at Macquarie Island and Heard Island, over the years 1948–51.

Antibody responses to Ascaris lumbricoides worm antigens were examined by ELISA in a case-control study of 2 groups of Bangladeshi children, one of which had been shown over a period of 12 months to be consistently lightly infected (controls) and the other consistently heavily infected (cases). The children showed a wide range in intensity of infection; children identified as cases were on average 4 times more heavily infected than the controls. There were no significant differences in weight, height, mid-upper arm circumference and skinfold thickness between the case or control subjects at the time blood samples for analyses by ELISA were collected. Children with repeatedly heavy infections with A. lumbricoides had higher concentrations of antibody isotypes to the antigens of A. lumbricoides than children who are repeatedly lightly infected. IgG1, IgG4 and IgE to worm antigens occurred in significantly higher concentrations in heavily infected subjects. This suggests that these antibody responses simply reflect the intensity of infection and may not play a significant role in protecting against heavy infections.

Polychromophilus murinus, a malaria parasite of Chiroptera is reported from Myotis daubentoni in England. The vector was suspected to be the ectoparasitic Nycteribiid fly, Nycteribia kolenatii. N. kolenatii collected from wild-caught M. daubentoni were found to have oocysts on the midgut and sporozoites in the salivary glands. Wild-caught N. kolenatii were maintained on two wild-caught M. daubentoni harbouring heavy (patent) infections of P. murinus; both oocysts and sporozoites were found in these flies. The mature oocysts measured 52–71 μm in diameter. Sporozoites were straight or slightly crescentic and had a mean length of 7·4 μm. Electron microscopy of immature and mature oocysts revealed a morphology similar to that of malaria parasites. Sporozoites were also similar in structure to Plasmodium sporozoites and were found in the epithelial cells of the salivary gland and within the lumen; a cytostome was present and transverse sections revealed 21 microtubules arranged evenly around the periphery. Sporozoites were observed within the basement membrane of the salivary gland of N. kolenatii; such sporozoites appeared to be penetrating the gland, a process hitherto not described in malaria parasites. Rickettsia-like bodies were found within the cytoplasm of the epithelial cells of the salivary gland. Exflagellation of microgametocytes was achieved. An ultrastructural study of the gametocytes revealed a structure similar to that described in other Haemoproteidae. A common feature of infected erythrocytes was a projecting erythrocyte membrane. Attempts to find schizogony in impression smears and sections of tissues of two infected M. daubentoni were not successful.

1. Introduction: We have little understanding of the true rôle of parasitic insects in the maintenance of the natural equilibrium chiefly because few efforts have been made to interpret the available data.

2. This is especially true concerning the problem of host relations which is in many ways of fundamental importance.

3. To solve the problem of host relations we ought to be able: (a) to deduce from a study of the host the composition of its parasitic fauna; (b) to deduce from a study of the parasite the composition of its host list.

This would necessitate (1) the definition of the “typical” or “ideal” parasite of any given host; (2) the definition of the typical or ideal host of any given parasite; (3) the establishment of a correlation between such definitions and morphological or systematic data in such a way that conclusions could be drawn concerning species whose habits had not yet been the subject of direct observation.

The object of the present paper is the examination of this problem.

4. The problem of the host relations is simply the problem of a particular kind of animal association. From analogy with other problems of this type, we may deduce that the idea of formulating a definition of the “typical parasite” of a given host is fallacious. A consideration of the data in regard to the parasitic fauna of various hosts confirms this as does experimental evidence. The attraction exerted by the host on the various members of its fauna is not necessarily identical or even similar.

5. The only feasible method of attacking the problem is therefore the analysis of the behaviour of parasites with the object of defining their “typical hosts.”

6. An experimental study of the host relations of Melittobia acasta Walk. was conducted in the laboratory and an attempt made by the analysis of the characters of the various species accepted or refused by the parasite, to formulate a definition of the normal host.

7. The nature of the hyperparasitic and gregarious habits are discussed in connection with the habits of Melittobia. An effort is made to discuss the true causes of the phenomena.

8. A study of the variations in oviposition habit in relation to the particular characteristics of various hosts shows that these variations, though complex and very difficult to explain in relation to the efficient causes involved, are easily explained if considered in relation to the object of the behaviour.

9. A general definition of the host of Melittobia acasta was formulated on the basis of the observations and experiments performed.

10. Attempts to simplify the definition and discover for the phenomenon of attraction some simple stimulus, completely failed.

11. A critical examination of the definition of the normal host of Melittobia shows that though it indicates the general trend of behaviour in the species studied, it is at once too narrow to include all possible hosts and too broad to exclude all species which might be refused.

12. A detailed study of the extensive data available on the host relations of the Tachinid Compsilura concinnata Meig. confirms the above results and shows that the typical host cannot be defined in relation to either morphological or physico-chemical characters.

13. It is shown further (a) that the fauna of systematically related parasites though sometimes similar are not necessarily so and may be very different; (b) that parasites so similar as to be morphologically inseparable in most or all stages of development may have different host relations.

14. A scientific treatment of host relations along ecological lines whether (a) by the establishment of an empirical correlation between systematic position and habitat or (b) by the definition of the parasite in terms of its habitat is thus impossible.

15. It follows that the acts of the parasite are not strictly determined if considered simply in relation to the physico-chemical and morphological properties of the host.

16. The reason for this is the fact that the choice of hosts is primarily a phenomenon of the psychological order which can be understood only by analogy with a similar process, such as the choice of food, in regard to which direct knowledge can be obtained by introspection.

17. A comparison along these lines leads to the conclusion that the choice of hosts, like the choice of food, is not a phenomenon which can be referred to any constant and definite efficient cause exterior to the organism; in certain cases the substances selected differ entirely in their properties and are identical as causes of behaviour only in that they are all agreeable to the organism concerned. In other words, the cause of behaviour is one only upon the psychological plane. Both food and hosts may be considered in relation to their suitability in relation to a given organism, but again the only category in which all types of food and hosts can be grouped is that of assimilable substances. The cause of behaviour considered from this angle is one only upon the physiological plane.

18. Pursuing the analysis of the process of food or host selection one finds, that this process occurs as if the suitability of substances as food or as hosts, obviously not in itself perceptible, were deduced by the animal from the perceptible qualities, though we have no reason to suppose that any conscious judgment occurs in the animal mind. This conception which corresponds exactly to the classical idea of instinct is the only one which seems to fit all the facts of the case.

19. An apparent objection to the views here advanced, based on the fact that the choice of the habitat in many animals seems to have been expressed with sufficient adequacy in terms of simple factors having certain quantitative values owes what force it possesses to the fact that the factors considered are those affecting the tactile sense in various ways, this sense being that in which the qualities of the object perceived affect the sentient subject most acutely so that his sensory impressions of pain and pleasure, ultimate sources of his actions, are more nearly measures of the qualities perceived than is the case with other senses. It is to be noted further that the objects of the tactile sense are essentially less varied than in such senses as taste, smell and sight, and that many stimuli classed as gustatory or visual are in reality tactile.

In view of the undeniable adaptive power possessed by organisms, it is however doubtful whether tactile impressions really constitute a valid measure of tangible qualities, or that movements induced by tactile pleasure and pain can be considered for a given organism as due to certain constant values of these qualities as measured by physical instruments. The results obtained up to the present do not constitute by any means a sufficient answer to this difficulty and have in any event but little bearing upon the problem of host selection which there is no reason to consider as determined by impressions of the tactile order.

20. There is therefore no reason to suppose that the accumulation of data on the host relations of entomophagous parasites will ever lead to the discovery of laws of parasite distribution permitting us to correlate the properties of parasites with those of their hosts so that we can predict in advance the host list of a given parasite or the parasitic fauna of a given host. The data collected may suggest interesting hypotheses or facilitate greatly operations of the practical order, but they have in themselves, only an empirical significance. The laws underlying the problem of host relations are not capable of expression in scientific terms nor discoverable by scientific methods.

21. From this it follows that in problems involving the practical utilisation of entomophagous parasites, as for example, when these species are transferred from one country to another, we have no means of predicting results because it is impossible for us to foretell the behaviour of the parasite with regard to the possible host insects of the new area. It would therefore be futile to make the execution of such projects dependent upon investigations in the native home of the parasite and designed to supply advance information as to the results obtainable. Such studies, while no doubt of great interest and value, cannot lead to any certain conclusions in regard to the question at issue, which experiment alone will solve.

Immune responses that kill pathogens or reduce their reproductive rate are generally important in protecting hosts from infection and disease. Pathogens that escape the full impact of such responses will survive, and any heritable genetic basis of this evasion will be selected. Due to the memory component of vertebrate immune responses, pathogens with rare alleles of a target antigen can have an advantage over those with common alleles, leading to the maintenance of a polymorphism. At the genetic level, there ought to be detectable signatures of balancing selection in the genes encoding these antigens. Here, methods for identifying these selective signatures are reviewed. Their practical utility for identifying which antigens are targets of protective immune responses is discussed.

The course of single infections of Nematodirus battus was studied and the developmental phases of the fourth larval stage described. The third moult occurred between days 2 and 4 after infection and the fifth between days 8 and 10. The period of maximum larval penetration of the intestinal mucosa occurred around day 4 and most of the larvae had returned to the mucosal surface by day 6, during the middle of the fourth-stage. Some larvae remained deep in the mucosa and moulted to the fifth-stage in this site.

The relationship between growth and morphological development was not constant and was different in worm populations from different sites. Some larvae grew very rapidly during the early fourth-stage and then entered a period of lethargus while continuing to develop sexually, while others grew and developed throughout the larval stage.

The worms recovered from the second 30% of the small intestine were consistently smaller and less advanced morphologically than those from the first 30%. The worms in the posterior region of the small intestine were preferentially lost from the mucosa in the third- and fourth-stages between days 2 and 4 and from the mucosal surface as adults between days 12 and 16.

Two nucleoproteins with similar chemical composition have been isolated from the leaves of tobacco plants infected with tobacco necrosis virus. One of these is crystalline and has a sedimentation constant of 130 × 10−13; the other is amorphous and its principal component has a sedimentation constant of 58 × lO−13.

Each preparation will infect plants at a dilution of 1 in 108 and will precipitate specifically with antiserum at a dilution of 1 in 3·2 × 105.

The nature of the difference between preparations in the two states is obscure and it has not proved possible to convert the one into the other.

A recombinant Echinococcus multilocularis antigen (II/3–10), which had previously been shown to exhibit immunodiagnostic characteristics highly specific for human alveolar echinococcosis, and the corresponding native parasite antigen, were further characterized with immunochemical and molecular biological methods. Immunoblot analysis using a polyclonal antiserum raised in rabbits against the recombinant protein, and subsequent Northern hybridization analysis, revealed that the native antigen was expressed by E. multilocularis at the adult as well as at the metacestode stage. In metacestodes, the antigen was shown by using indirect immunofluorescence and the same antiserum to be localized within the germinal layer and membrane structures of developing protoscolices. Electrophoretic analyses revealed remarkable differences in the apparent molecular weight of the antigen under reducing and non-reducing conditions. In further immunoblot analyses, anti-II/3–10 antibodies identified the corresponding epitopes on bands with identical Mr in all E. multilocularis isolates investigated (European, Asian and North American). By Southern hybridization analyses of the respective gene, phylogenetically related sequences were shown to be present in other helminth species such as E. granulosus and several Taenia spp. In the same respect, immunoblotting revealed that anti-II/3–10 antibodies reacted with antigens of different Mr from various E. granulosus isolates and some other cestode species, indicating the presence of shared and thus potentially cross-reacting epitopes. The relevance of these findings for the immunodiagnostic performance of the recombinant antigen is discussed.

The potential for the non-coding intergenic rDNA spacer (IGS) to DNA fingerprint Giardia duodenalis isolates was investigated. Conserved PCR primers, specific for the flanking large and small rDNA genes, were used to amplify the IGS from 52 in vitro-cultured Giardia isolates. Four distinct IGS–PCR size groups (1·35–1–6 kb) were observed, which correlated closely with the major genetic assemblages established previously for the same isolates using isoenzyme analysis. IGS–PCR size groups A (1·42 kb), C (1·4 kb) and D (1·35 kb) corresponded to isoenzyme assemblage A, and IGS–PCR group B (1·6 kb) to isoenzyme assemblage B. Amplified products from IGS–PCR size groups A and B, which contained 50/52 isolates, were subsequently digested with 8 different restriction enzymes and their profiles compared. Analysis separated isolates within each IGS–PCR size group into 2 distinct clusters which correlated almost exactly with the same genetic groups established previously using isoenzyme electrophoresis. Within each cluster, both methods exhibited a similar capacity to distinguish between Giardia genotypes although they established different genetic relationships between individual isolates. Much of the variability associated with the IGS was attributed to isolates harbouring multiple IGS- sequence types. Restriction analysis of IGS–PCR products amplified from cloned and parent lines of a human isolate BAH 39, which contains multiple IGS variants, showed that trophozoite populations are homogeneous with respect to the types of IGS-variants they maintain. Furthermore, in vitro culture of the cloned isolate BAH39c9 over a 6-year period also failed to reveal variation in IGS–PCR digestion profiles. These results suggest that IGS–PCR RFLP profiles are inherently stable. IGS–PCR analysis was successfully applied to 11 Giardia cyst samples highlighting the potential for this approach to genotype Giardia isolates without the need for in vitro culture.