Scuticociliatosis is a severe disease in farmed flatfish. However, the causative agent is not always accurately identified. In this study, we identified two isolates of scuticociliates from an outbreak in cultured fine flounder Paralichthys adspersus. Scuticociliate identification was based on morphological data, examination of life stages and the use of molecular approaches. The isolates were compared with a strain of Philasterides dicentrachi from turbot Scophthalmus maximus and with a strain deposited in the American Type Culture Collection as Miamiensis avidus ATCC® 50180™. The use of morphological, biological and molecular methods enabled us to identify the isolates from the fine flouder as P. dicentrarchi. Comparison of P. dicentrachi isolates and M. avidus revealed some differences in the buccal apparatus. Unlike P. dicentrarchi, M. avidus has a life cycle with three forms: macrostomes (capable of feeding on P. dicentrarchi), microstomes and tomites. Additionally, we found differences in the 18S rRNA and α- and β-tubulin gene sequences, indicating that P. dicentrarchi and M. avidus are different species. We therefore reject the synonymy/conspecificity of the two taxa previously suggested. Finally, we suggest that a combination of morphological, biological, molecular (by multigene analysis) and serological techniques could improve the identification of scuticociliates parasites in fish.

The size of the infecting inoculum may influence the severity of malaria, but evidence is scarce. Malaria therapy records provide a unique source of information on induced malaria in people. The therapy was given to large numbers of neurosyphilis patients and the malaria was left untreated as long as possible. Data from patients treated at the Horton Hospital, Epsom 1923–60 with a single strain of vivax malaria were analysed to assess the influence of inoculum size on severity of disease. Malaria was induced by mosquito bite, blood inoculation or direct sporozoite inoculation. The different measures of inoculum size were inversely correlated with pre-patent period, as expected. Overall, information was available on a total of 563 non-immune patients who were not treated during the first 5 days of patent parasitaemia. No strong or consistent relationships were found between measures of inoculum size and any of the measures of severity used: neither parasitaemia levels, nor peak fevers, nor number of paroxysms of fever. In the largest data set, longer pre-patent periods were associated with tertian fever, spontaneous recovery and less use of modifying treatment. Difficulties in interpreting the results are discussed, particularly with respect to misclassification of both exposure and outcome variables. While an inoculum size-severity relationship cannot be ruled out, a strong relationship is very unlikely.

The following observations were made upon serial sections of a new monogenetic trematode, Hexacotyle extensicauda, which the writer has described in a previous paper (Dawes, 1940).

It is a common experience that mosquito larvae when they are brought into a laboratory to undergo their development, often fail to develop normally. At times a high mortality takes place, or the larvae lapse into a condition of suspended development continuing as larvae for months. The latter phase usually ends in death before pupation can take place. I have been puzzled to account for these manifestations for a very long time, and have conducted various experiments in the hope of discovering the cause. The general opinion on the matter, I think, is that there is “something wrong with the food supply,” but as a matter of fact larvae supplied with an ample diet often show the same state of affairs.

The uptake kinetics of a 14C-labelled trypanocidal compound isometamidium chloride (SamorinR, RMB Animal Health Ltd, UK) was measured in drug-resistant and drug-sensitive Trypanosoma congolense. It was established that drug uptake was significantly more rapid and quantitatively greater in drug-sensitive parasites. There was clear evidence that drug uptake in both the resistant and sensitive trypanosomes was by a specific, receptor-mediated process. This specific drug transport was energy-dependent, being sensitive to metabolic inhibition with SHAM/glycerol. Significant differences in drug transport were observed which could be correlated with resistance to isometamidium. The optimal pH for drug accumulation was lowered in the resistant trypanosomes; this finding, along with an observed change in specificity for the related compound homidium bromide, suggested that the specific receptor for isometamidium is altered in the resistant trypanosomes, possibly resulting in a reduction in drug uptake. In addition to these alterations in drug uptake, efflux of isometamidium also appears to occur in the resistant trypanosomes. Both a reduction in incubation temperature and metabolic inhibition increased the level of trypanosome-associated isometamidium in the resistant parasites. This was in contrast to observations using drug-sensitive parasites. Furthermore, the addition of calcium flux-modulating agents to the incubation medium also resulted in an increase in accumulation by the resistant parasites.

In previous papers one of us (Keilin, 1915, 1917) has shown that among cyclorrhaphous dipterous larvae there is a remarkable correlation between the anatomical structure of the larvae and their mode of life. Although the mode of life of the larvae is in correlation with such anatomical features as thickness and hardness of the body-wall, the development of sensory organs on the head, and the structure of the alimentary canal, it is in the bucco-pharyngeal armature that the most obvious and important adaptations are to be found. The most important of these adaptations may be mentioned briefly. In certain cyclorrhaphous dipterous larvae the ventral wall of the basal sclerite of the bucco-pharyngeal armature has a number of longitudinal ridges projecting into the lumen of the pharynx. These ridges are usually Y-shaped at their free borders, and form a series of longitudinal channels in the ventral region of the pharynx. In other cyclorrhaphous dipterous larvae such ridges are absent and the ventral wall of the pharynx is smooth. This character allows the larvae to be divided into two groups—“all cyclorrhaphous dipterous larvae parasitic on the most diverse animals or on plants, as well as carnivorous larvae, and larvae which suck the blood of mammals, never have ridges in their pharynx; on the contrary, ridges are always present in saprophagous larvae” (Keilin, 1915). All the larvae which are devoid of ridges and are either parasitic, carnivorous, pass their whole life in the uterus of the female, or are phytophagous, may be united into the group of biontophagous; all larvae which have ridges are saprophagous.

A main feature of the data here presented is the number of new records. For the sake of brevity these are tabulated below, under their respective headings.

Another feature is the wide geographical distribution of a large percentage of the parasites herein recorded, particularly of such forms as Zoogonoides viviparus (Olsson), Derogenes varicus (Mueller) and Hemiurus communis Odhn. The former has been recorded for St Andrews, Millport, Aberdeen, Plymouth, Northumberland, Liverpool, Galway, and also for foreign seas. Derogenes varicus has been recorded for St Andrews, Millport, Plymouth, Aberdeen, Northumberland, Galway, and for foreign seas. Hemiurus communis has been recorded for St Andrews, Millport, Plymouth, Northumberland, Liverpool, Aberdeen, Galway, and for foreign seas.

This suggests that the intermediate host of the larval stages of these parasites must be some common marine form, in all probability an invertebrate, which itself enjoys a very wide geographical distribution.

A further feature is the tendency of certain parasites to infect a variety of fish, the more notorious being Derogenes varicus (Mueller) and Hemiurus communis Odhn. Of the twenty-six species of marine fishes examined at Galway, eleven (42 per cent.) were found to harbour Derogenes various. The infected fishes were the bib (G. luscus), cod (G. morrhua), pollack (G. pollachius), dab (Pleuronectes limanda), plaice (P. platessa), tub (Trigla hirundo), grey gurnard (T. gurnardus), brill (Rhombus laevis), hake (Merluccius vulgaris), common sole (Solea vulgaris), common sea bream (Sparus centrodontus).

Hemiurus communis was found parasitising eight species of fish, i.e. 31 per cent, of the total number of species examined. The hosts affected were the bib (G. luscus), whiting (G. merlangus), cod (G. morrhua), pollack (G. pollachius), flounder (P. flesus), tub (T. hirundo), plaice (P. platessa), and the common sea bream (S. centrodontus).

At the moment it is a little premature to prophesy to what extent the discovery of encysted specimens of Prosorhynchus crucibulum (Rud.) in the gill tissues of the cod (Gadus morrhua) will assist in elucidating the life-history of this parasite. Mature specimens of Prosorhynchus crucibulum have previously been recorded as occurring in the alimentary canal of the conger eel (Conger niger). The writer discovered partly digested specimens of small cod to form a considerable bulk of the stomach contents of the conger eel.

The clamp sclerites of Pricea multae and other higher monogeneans was fuchsin-positive in Mallory's and Masson's triple stain, and the staining was not affected by detanning agents, suggesting some form of stabilization in the protein. The sclerites were positive in Millon's, Morner's and Xanthoproteic tests for aromatic amino acids, but negative in tests for sulphydryl and disulphide groups. Quinone, phenol and phenol oxidase were absent. They stained with basic dyes such as toluidine blue and methylene blue in the pH range of 3·5–9·5, and also exhibited bluish fluorescence in u.v. light which was not affected by lipid solvents, indicating the presence of dityrosine and recalling the protein present in the ligament cuticle of insects. These features indicate that the clampprotein is stabilized by the formation of dityrosine. It is suggested that this protein may be responsible for the biological properties of the clamp sclerites. This mode of stabilization by tyrosyl residues of the protein, resulting in the formation of dityrosine, is the first record of its kind to be reported in platyhelminths.

1. Seven organic sulphur compounds likely to be produced in the breakdown of cystine have been tested under field conditions as blowfly attractants. Two of them, ethyl mercaptan and dimethyl di-sulphide, when mixed with hydrogen sulphide or carbon dioxide formed powerful attractants for females of the blowflies Lucilia caesar (and L. illustris) and L. sericata.

2. In the majority of trials 10 ml. 0·2% ethyl mercaptan mixed with 10 ml. freshly saturated hydrogen sulphide solution was used as the control attractant. As a standard in field-trapping studies this material overcomes many of the disadvantages of meat baits.

3. Sodium carbonate, sodium bicarbonate, ammonium hydroxide, ammonium carbonate and indole, at various concentrations, did not activate the organic compounds. Furthermore, when added to the ethyl mercaptan-hydrogen sulphide preparation they did not increase its activity.

4. In the present experiments oviposition was rarely induced. When it did occur it was associated with the presence of indole.

5. L. caesar responded to attractants placed 2 ft. from the ground as well as to the same materials placed on the ground. Height alone, therefore, was not responsible for the fact that L. caesar did not respond to the attractants when they were placed on sheep.

6. The responses of blowflies to chemical attractants was linked with climatic conditions. Thus, under certain conditions Calliphora spp., particularly C. vomitoria, responded to these attractants.

7. The results obtained in the present investigation emphasize the attractive nature of sulphur-containing compounds and the possible importance of hydrogen sulphide and carbon dioxide as sensitizing agents of such compounds on sheep.

The histological changes in the gut of Chrysops silacea during the digestion of blood are the same as those described by Cragg in Tabanus.

Digestive enzymes are confined to the posterior half of the mid-gut. They comprise an active invertase, a weak amylase and an active tryptase and peptidase. These results are compared with those in Glossina and Calliphora.

The functions of the crop are discussed.

Many parasites, including all known viruses, characteristically lead an intracellular existence, and are known as ‘obligatory intracellular parasites’. It is, however, obvious that—whether the parasite is a virus, a bacterium, or a protozoon— transmission of infection from host to host, or from cell to cell within a single host, must involve an extracellular stage, however short in duration. This extracellular stage is, for the purpose of therapeutics of highest importance, since evidence accumulates that within the protecting walls of a cell parasites are relatively protected against chemotherapeutic agents and antibiotics, while susceptible to their action in the extracellular phase.

We measured seasonal changes in the prevalence of haematozoa (Leucocytozoon fringillinarum, Haemoproteus fringillae, and Trypanosoma avium) in free-ranging White-winged Crossbills, Loxia leucoptera, over 1·5 year in Fairbanks, Alaska, USA. This prevalence was low during early winter. L. fringillinarum prevalence increased in late winter/early spring, in the absence of vectors, suggesting relapse of latent infection. By contrast, the prevalence of T. avium and H. fringillae did not increase until mid-spring, coincident with the emergence of putative vectors and suggestive of new inoculations. The winter breeding period was not associated with lower body condition or elevated blood heterophil/lymphocyte ratios than the summer post-breeding period. Thus, birds unlikely perceived their breeding effort as particularly stressful. Adult males in May and June had low plasma testosterone and their blood prevalence of L. fringillinarum, but not other haemoparasites, was higher than in adult females. This difference may have resulted from sex differences in behaviour and/or plumage colouration – bright red in males, dull green/yellow in females. Species in which reproduction and vector abundance are seasonally dissociated may constitute important models for investigating the respective contribution of reproductive hormones, breeding effort, and vector abundance to patent and latent hemoparasitic infections and to new inoculations.

For Isospora (Protozoa: Eimeriidae) parasites of passerine birds, diurnal periodicity of oocyst output is a well-described phenomenon. From the temporal zone to the tropics, oocyst production is correlated with the light-dark cycle, peaking in the afternoon hours. However, nothing is known about the existence of diurnal periodicity of these parasites in the birds of High Arctic environments, under permanent light during summer. We sampled free-ranging Snow Bunting (Aves: Passeriformes), on Svalbard in summer and tested oocysts output of Isospora plectrophenaxia. Here we show that under the permanent light conditions of Arctic summer in the wild, Isospora plectrophenaxia, a parasite of the Snow Bunting, still keeps the 24-h rhythm of oocyst output with the peak in the post-meridiem hours, despite the absence of diurnal periodicity in host's activity. Our findings prove the ability of avian Isospora to invoke alternative cues for synchronizing the circadian rhythms. Possible cues and adaptive significance of diurnal periodicity of parasite output in High Arctic are discussed. The maintenance of synchronization and timing of the parasite life-cycle stages is under positive selection pressure even in permanent daylight in the Arctic.

Cryptosporidium parvum is the major cause of livestock and zoonotically-acquired human cryptosporidiosis. The ability to track sources of contamination and routes of transmission by further differentiation of isolates would assist risk assessment and outbreak investigations. Multiple-locus variable-number of tandem-repeats (VNTR) analysis provides a means for rapid characterization by fragment sizing and estimation of copy numbers, but structured, harmonized development has been lacking for Cryptosporidium spp. To investigate potential for application in C. parvum surveillance and outbreak investigations, we studied nine commonly used VNTR loci (MSA, MSD, MSF, MM5, MM18, MM19, MS9-Mallon, GP60 and TP14) for chromosome distribution, repeat unit length and heterogeneity, and flanking region proximity and conservation. To investigate performance in vitro, we compared these loci in 14 C. parvum samples by capillary electrophoresis in three laboratories. We found that many loci did not contain simple repeat units but were more complex, hindering calculations of repeat unit copy number for standardized reporting nomenclature. However, sequenced reference DNA enabled reproducible fragment sizing and inter-laboratory allele assignation based on size normalized to that of the sequenced fragments by both single round and nested polymerase chain reactions. Additional Cryptosporidium loci need to be identified and validated for robust inter-laboratory surveillance and outbreak investigations.

Although many parasites are transmitted between hosts by a suite of arthropod vectors, the impact of vector biodiversity on parasite transmission is poorly understood. Positive relationships between host infection prevalence and vector species richness (SR) may operate through multiple mechanisms, including (i) increased vector abundance, (ii) a sampling effect in which species of high vectorial capacity are more likely to occur in species-rich communities, and (iii) functional diversity whereby communities comprised species with distinct phenologies may extend the duration of seasonal transmission. Teasing such mechanisms apart is impeded by a lack of appropriate data, yet could highlight a neglected role for functional diversity in parasite transmission. We used statistical modelling of extensive host, vector and microparasite data to test the hypothesis that functional diversity leading to longer seasonal transmission explained variable levels of disease in a wildlife population. We additionally developed a simple transmission model to guide our expectation of how an increased transmission season translates to infection prevalence. Our study demonstrates that vector SR is associated with increased levels of disease reporting, but not via increases in vector abundance or via a sampling effect. Rather, the relationship operates by extending the length of seasonal transmission, in line with theoretical predictions.

We investigated variation in the abundance-prevalence relationships of fleas among 17 different flea-host associations as well as among different species of hosts and fleas in the Negev desert. We explored variation in the value of exponent of Taylor's power relationship with changes in flea community size and flea specialization (host specificity and seasonal pattern of activity). We tested if a simple epidemiological model can reproduce the pattern of the abundance-prevalence relationship. We confirmed aggregated distribution of fleas within a population of host species as well as across a whole host community and the existence of a positive relationship between local flea abundance and their prevalence. Prevalence, mean abundance and variance of abundance were significantly higher in host specific than host opportunistic fleas. When ecological specialization was considered, based on a seasonal pattern of activity, these parameters were higher in year-round-active than seasonal fleas. The degree of flea specialization and flea community richness affected the pattern of the relationship between mean abundance and its variance. Power law slopes decreased with increasing richness of flea community. A simple epidemiological model based on mean flea abundance and degree of aggregation, corrected for host sample size, can predict the observed pattern of prevalence. In some cases, observed flea prevalence was higher than that predicted from the epidemiological model. The discrepancy of the observed prevalence from that predicted by the model can be explained by either a relatively low negative effect of flea parasitism on a host (at least, in terms of pathology) or strong resistance of a host to flea parasitism or both.

We established experimental metapopulations of the flour beetle, Tribolium castaneum, and its ectoparasitic mite, Acarophenax tribolii, to investigate the effects of host migration rate and local host population size on the spread of mite infections. Global prevalence across our metapopulations was less than half the observed within-patch prevalence, so that spatial structure alone afforded a great deal of protection to hosts against parasite infection. Our results showed further that migration played a determining role in occupancy, the number of patches infected within a metapopulation, while host population size played a determining role in local prevalence, the fraction of hosts infected within local patches. Local and global prevalence appeared to reach equilibrium levels on 2 different time-scales. Local host prevalence reached equilibrium values within 30 days of receiving an infected host migrant. Global prevalence increased more slowly and was clearly dependent upon occupancy, the number of host patches with at least 1 infected host, which in turn depended on the level of host migration among host patches. The effect of population size was not limited to local prevalence in patches without spatial structure but extended to sets of patches across the metapopulation. Lloyd's index of patchiness differed significantly between metapopulations with small versus large numbers of hosts. Although parasites were aggregated on hosts for both local patch sizes, they tended to aggregate to a much greater degree at the smaller host patch size. We discuss our empirical findings in light of current epidemiological theory.

From a study of the organisms themselves, so far as this has been possible, and from an analysis of all accessible records relating to them, I conclude that there are four distinct species of coccidia which may parasitize man. These are: (1) Isospora hominis Rivolta, 1878 (emend.), discovered by Kjellberg in 1860. and recently investigated by Wenyon; (2) Eimeria wenyoni n.sp., a form discovered in 1915 by Wenyon; (3) Eimeria oxyspora n.sp., another new form, here described for the first time; (4) an undetermined species of Eimeria (?) which was discovered by Gubler in 1858. This last inhabits the human liver, whilst the three others probably live in the small intestine. Probably some seventy cases of infection with the Isospora have now been seen, mostly in persons who have been in the Near East; but the other parasites appear to be extremely rare, and little is known concerning their probable geographical distribution.

All these parasites are probably peculiar to man. There is no evidence that any of them is or can be parasitic in any other host. The prevailing belief that the coccidia of man are identical with those of rabbits, cats, or dogs, is therefore unfounded. Furthermore, there is as yet no good evidence to show that man may harbour any species of coccidia other than the four just enumerated. All these forms, however, require fuller investigation. They are here briefly and incompletely described from the data at present available.

There is at present no proof that the coccidia of man—with the probable exception of the species occurring in the liver—can produce a clinically recognizable pathological condition of “coccidiosis”: and as yet no method of treatment which will eradicate an infection with any species has been discovered.

Protoscoleces of Echinococcus granulosus were incubated in a 10 μm solution of monensin and their viability and the ultrastructure of their tegument were monitored over a 36 h period. The earliest effects of the lonophore, apparent within 15 min, involved a degree of cisternal swelling of the tegumentary Golgi complexes. Swelling became more pronounced with time and cytons eventually contained numerous large electron-lucent vesicles. Residual bodies indicative of autophagy were observed in the cytons and distal cytoplasm from 1 h onwards. All movement of protoscoleces ceased after 1 h and the surface of the soma subsequently became folded, possibly suggesting spastic paralysis. Later, vacuoles and large cytoplasmic blebs were observed in the distal cytoplasm and viability dropped rapidly after 12 h. All protoscoleces were dead at 36 h. The potential of monensin as an in vivo protoscolicidal agent is discussed.

The surface proteins and glycoproteins of red cells from Plasmodium berghei-infected blood have been radio-isotope labelled and compared with those of normal mouse erythrocytes using the following protein labelling probes: lactoperoxidase-catalysed radio-iodination of tyrosyl residues, periodate oxidation and NaB3H4 reduction of sialic acid and oxidation of galactosyl/N-acetylgalactosaminyl residues by galactose oxidase with subsequent NaB3H4 reduction. During P. berghei infection, new tyrosyl-labelled proteins with apparent molecular weights (Mr) of 60000, 54000, 40000 and 27500 appeared on the surface of most, if not all, red cells in the blood. Purified multinucleate cells (mostly reticulocytes) differed only in that they also had a surface protein with Mr of 83000. However, this molecule is thought to be specific to mouse reticulocytes rather than derived from parasites. In contrast to the relatively minor changes detected with radio-iodination, striking changes in glycoprotein radio-isotope labelling resulted from infection. All of the red cells in infected blood of greater than 20% parasitaemia lost their periodate-sensitive glycoprotein sialic acid. With some samples there was little change in glycoprotein labelling by the galactose oxidase method, provided neuraminidase was also added. Modification of the exocyclic hydroxyls of sialic acid is postulated to account for this. Other blood samples exhibited a dramatic loss of galactose oxidase-dependent labelling. It is suggested that these observations may relate to the excessive red cell destruction of uninfected as well as infected cells which has been inferred in many haemosporidial infections, including malaria.