The identification and discrimination of 2 closely related and morphologically similar species of Gyrodactylus, G. salaris and G. thymalli, were assessed using the statistical classification methodologies Linear Discriminant Analysis (LDA) and k-Nearest Neighbours (KNN). These statistical methods were applied to morphometric measurements made on the gyrodactylid attachment hooks. The mean estimated classification percentages of correctly identifying each species were 98·1% (LDA) and 97·9% (KNN) for G. salaris and 99·9% (LDA) and 73·2% (KNN) for G. thymalli. The analysis was expanded to include another 2 closely related species and the new classification efficiencies were 94·6% (LDA) and 98·0% (KNN) for G. salaris; 98·2% (LDA) and 72·6% (KNN) for G. thymalli; 86·7% (LDA) and 91·8% (KNN) for G. derjavini; and 76·5% (LDA) and 77·7% (KNN) for G. truttae. The higher correct classification scores of G. salaris and G. thymalli by the LDA classifier in the 2-species analysis over the 4-species analysis suggested the development of a 2-stage classifier. The mean estimated correct classification scores were 99·97% (LDA) and 99·99% (KNN) for the G. salaris–G. thymalli pairing and 99·4% (LDA) and 99·92% (KNN) for the G. derjavini–G. truttae pairing. Assessment of the 2-stage classifier using only marginal hook data was very good with classification efficiencies of 100% (LDA) and 99·6% (KNN) for the G. salaris–G. thymalli pairing and 97·2% (LDA) and 99·2% (KNN) for the G. derjavini–G. truttae pairing. Paired species were then discriminated individually in the second stage of the classifier using data from the full set of hooks. These analyses demonstrate that using the methods of LDA and KNN statistical classification, the discrimination of closely related and pathogenic species of Gyrodactylus may be achieved using data derived from light microscope studies.

Newly transformed schistosomula and day 8 lung parasites, derived from optimally irradiated cercariae, were used to immunize groups of C57B1/6 mice via 4 different injection routes. Schistosomula administered intradermally induced high levels of protection, comparable with that achieved by percutaneous vaccination. Intermediate levels were elicited by delivery of parasites via intraperitoneal or intratracheal routes. In contrast, intravenous injection of schistosomula to the lungs resulted in little or no resistance. Attenuated day 8 schistosomula administered intradermally were at least as immunogenic as irradiated cercariae. The fate of radio-isotope labelled attenuated lung schistosomula, injected via the various routes, was examined by compressed organ autoradiography. After intradermal vaccination, a proportion of parasites migrated from the site of injection to the draining lymph node and lungs. Conversely, schistosomula administered via the other 3 routes persisted to varying degrees at the injection site, but little onward migration was observed. We suggest that successful vaccination requires that some attenuated parasites migrate to, and sequester in, lymph nodes draining the vaccination site; persistence at the site of administration alone is not an adequate stimulus.

1. The period which elapses between a blood-meal and oviposition on the part of the female bed-bug affects the duration of the egg stage. Eggs laid soon after the meal take longer to hatch than those laid later. It is supposed that embryonic development of eggs inside the female occurs at a rate relatively greater than that of oviposition.

2. Atmospheric humidity is without effect on the duration of the egg stage. Although the temperature-velocity graph appears to be fairly linear between 18 and 30° C. the thermal constants show considerable variation.

3. A daily alternation of temperature with a range of 10° C, between the threshold and optimum temperatures results in an acceleration of development; this can, however, be accounted for by the non-linearity of the temperature-velocity relationship, if the usual methods of thermal summation are used.

4. Eggs have been exposed to temperatures between 1 and 12° C. and the time taken to hatch on subsequent incubation at 23° C. has been ascertained. When these times are compared with times for hatching of control eggs kept at 23° C. from oviposition there is some evidence that a slight amount of development may occur at as low a temperature as 4° C.; i.e. 9° below the developmental-hatching threshold. Times after exposure are shorter than times for control eggs.

5. Thermal summation, however, suggests that temperatures between 13 and 11·7° C. result in a retardation of development since the times after exposure at which hatching occurs at 23° C. are longer than would be expected.

6. The method of thermal summation is criticized mainly on the grounds that it assumes that a temperature has the same accelerating effect on all stages of embryonic development. A retardation of development such as that mentioned in the preceding paragraph may be either a true retardation or due to errors resulting from the assumption that the reciprocal of the time for complete development represents the true amount of daily development at all stages of embryonic growth.

7. The lowest constant temperature at which complete development with hatching, of eggs laid at 23° C, can occur is 13° C. I have called this temperature the developmental-hatching threshold. The developmental threshold may be as low as 4° C, while the hatching threshold is at approximately 8° C.

8. Alternating temperatures such as occur in English houses are unlikely to affect the position of the developmental-hatching threshold. Atmospheric humidity does, however, affect it and 75–90% r.h. appear to be the only humidities at which development with hatching can take place at a constant temperature of 13° C.

9. Mortalities near the developmental-hatching threshold appear to depend also on the temperature at which eggs are laid (or perhaps the temperatures at which they develop within the female). Eggs laid at 15° C. and incubated at 15° C. and 7% r.h. suffer 97·1% mortality while those laid at 23° C. and incubated under identical conditions have 32·9% mortality.

10. If eggs are laid at 23° C. and are incubated at 15, 18 and 23° C. until nearly ready to hatch, the percentage hatch at temperatures near the batching threshold is higher with those eggs previously kept at 18° C. than with those from 15 or from 23° C. At 8° C, the lowest observed temperature for hatching, preliminary incubation at 15° C. is probably more favourable than one at 23° C.

11. Mortality of eggs above 13° C. is only slightly affected by atmospheric humidity over the optimal range. But the effects are more noticeable near the upper and lower temperature limits. 99–100% r.h. appears to be associated with a higher mortality than 90% r.h. The extreme temperature limits for eggs laid at 23° C. are 13 and 37° C. With eggs laid at 15° C. the range is restricted at both upper and lower temperature limits compared with the range for eggs laid at 23° C. The temperature of oviposition, whether it is 15 or 25° C, seems to make no difference to mortalities between 18 and 28° C.

12. The mortalities of eggs exposed for varying periods to temperatures between 1 and 13° C. and various humidities are discussed. By means of probits estimates of the times for 50 and 99·99% mortalities have been made for each of the temperature and humidity combinations.

13. Exposure for 50% mortality is affected slightly by humidity below 13° C, but no simple law relating survival to humidity has been found either above or below 13° C. Variations in temperature within the range 0—34° C. are likely to influence survival more than the humidity variations possible within this temperature range.

14. At constant saturation deficiencies the eggs survive longer at the higher temperatures between 1 and 13° C. The median exposure for death (i.e. exposure for 50% mortality) increases by 1·5–1·8 days per 1° C. rise of temperature.

15. The scatter of mortalities about the median exposure for death as measured by the regression coefficient of probits on exposure times is slightly influenced by humidity, but is not affected by temperatures between 1 and 13° C. Much of the variation in the slopes of the mortality curves is thought to be due to inherent variation in the eggs themselves.

16. With eggs laid at 23° C. and exposed to temperatures below 13° C. the longest exposure necessary to produce 99·99% mortality (as judged by subsequent incubation at 23° C.) was estimated at 79.8 days. This occurred at 12·1° C. and 73% r.h. The actual observed times for exposure for 100% mortality are somewhat shorter than the estimated times.

17. Eggs with embryos in an advanced state of development are more quickly killed by exposure to 7·7° C. and 90% r.h. than are newly laid eggs.

18. Ovipositional temperatures of 15, 18 and 23° C. produced no different effects on the mortality rates of eggs exposed to 10° C. and 90% r.h.

19. Future problems and the ecological significance of the experimental results are discussed.

To assess ectoparasite impact on individuals and populations of Gerbillus andersoni allenbyi under natural conditions, I addressed the following questions. Do ectoparasites affect their host fitness and, if so, how? Do ectoparasites affect host population level? Does this parasite–host interaction support the traditional concept of parasite evolution towards avirulence? For this purpose, host infestation, infection, survival, haematological indices, and physical condition were recorded. A field experiment which included manipulating host infestation while recording host survival was conducted to determine the causal relations between these variables. G. a. allenbyi was infested by 2 fleas (Synosternus cleopatrae and Stenoponia tripectinata), 5 mesostigmatid mites (Androlaelaps centrocarpus, A. hirsti, A. insculptus, A. marshalli and Hirstionyssus carticulatus), 1 tick (Rhipicephalus sanguineus), and 1 louse (Polyplax gerbilli). Ectoparasite burden significantly reduced host survival and red blood cell indices (red cell concentration, haemoglobin concentration and haematocrit). Ectoparasite burden did not significantly affect white blood cell concentration. Gerbils were not infected by haemoparasites or gut helminths which potentially could cause anaemia. The causal relationship between S. cleopatrae burden and host survival was established by manipulation of host infestation. Both ectoparasite removal and initial level of infestation significantly affected host survival. Ectoparasites that caused anaemia were not associated with host physical condition (PC), measured as weight/length3. None of the red blood cell indices was correlated with host PC. These results suggest both that host PC was not affected by ectoparasite burden and that exsanguination leading to anaemia was the main effect of the ectoparasites. Ectoparasite pressure on the host population (based on the ectoparasite effects as estimated by statistical models, combined with dispersion of the infestation within the host population) changed seasonally and was greatest when host density was the highest. A large segment of the gerbil population was affected by ectoparasites during the entire year. An explanation for the evolution of parasite virulence, contrasting parasites that evolve towards increased virulence with parasites that evolve towards avirulence is presented. This classification is primarily based on whether parasite impact is equated with a higher efficiency of host exploitation, or whether it is a ‘side effect’ of parasite biology.

Two species of Schizotrypanum, T. (S.) dionisii and T. (S.) vespertilionis, were identified from British bats. Laboratory studies on stocks of isolated trypanosomes from 5 species of bat (Pipistrellus pipistrellus, Nyctalus leisleri, N. noctula, Eptesicus serotinus and Myotis brandti) indicated that the predominant species was T. d. dionisii. Collections and dissection of the bat bug Cimex pipistrelli from bat roosts revealed flagellate infection in a total of 12 out of 20 bugs; 7 of these bugs had metacyclic trypanosomes present. C. pipistrelli and the human bed bug, C. lectularius were reared in the laboratory and allowed to feed on wild-caught bats known to be infected with T. d. dionisii. Development occurred in both species of Cimex. Cimex spp. could be used to detect subpatent Schizotrypanum infections by xenodiagnosis. This technique was used to test the parasitological status of bats collected in the wild or reared in captivity. On a single occasion an apparent transmission of T. d. dionisii to an uninfected (by xenodiagnosis) laboratory reared bat was achieved. A stock of Schizotrypanum isolated from a wild-caught C. pipistrelli collected in a N. leisteri roost was identified by DNA buoyant density centrifugation as T. (S.) vespertilionis. A P. pipistrellus known to be infected with T. d. dionisii was found to have cyst-like structures in thoracic skeletal muscle containing amastigotes. The study provided the strongest evidence yet that C. pipistrelli is the vector of Schizotrypanum in British bats.

Cells of Cryptocaryon irritans at different life history stages were studied using both light and electron microscopy. The characteristics of several organelles were revealed for the first time at the ultrastructural level. It was confirmed that the cytostome of trophonts, protomonts and theronts was surrounded by cilium–palp triplets rather than ciliary triplets. The nematodesmata underlying the circumoral dikinetids were single bundles, whereas these were always paired in Prorodontids. Toxicysts were present in late-stage tomonts and theronts, but were absent in trophonts and protomonts. We posited that toxicysts might play a role in infection and invasion of host-fish tissue by theronts. The adoral brosse was unlike that of any other family of the class Prostomatea based on its location and morphology. Membranous folds were present in trophonts, protomonts and theronts. These folds were longer and more highly developed in C. irritans than in exclusively free-living prostome ciliates suggesting that they might be linked to parasitism in C. irritans. Trophonts, protomonts and theronts had multiple contractile vacuoles. The basic ultrastructure of the contractile vacuole of C. irritans was similar to that of other kinetofragminophoran ciliates. They might play different roles in different stages of the life cycle since their ultrastructure varied among trophonts, protomonts and theronts.

Trichomonas vaginalis is a parasitic protozoan that causes trichomonosis, a sexually-transmitted disease, with serious sequelae to women and men. As the host–parasite relationship is complex, it is important to investigate biochemical aspects of the parasite that contribute to our understanding of trichomonal biology and pathogenesis. Nucleoside triphosphate diphosphohydrolase 1 (NTPDase 1), which hydrolyses extracellular ATP and ADP, and ecto-5′-nucleotidase, which hyrolyses AMP, have been characterized in laboratory isolates of T. vaginalis. Here we show that the extracellular ATP[ratio ]ADP hydrolysis ratio varies among fresh clinical isolates, which presented higher ATPase and ADPase activities than long-term-grown isolates. Growth of parasites in iron-replete and iron-depleted medium resulted in different, albeit minor, patterns in extracellular ATP and ADP hydrolysis among isolates. Importantly, some isolates had low or absent ecto-5′-nucleotidase activity, regardless of environmental conditions tested. For isolates with ecto-5′-nucleotidase activity, high- and low-iron trichomonads had increased and decreased levels of activity, respectively, compared to organisms grown in normal TYM-serum medium. This suggests a regulation in expression of either the enzyme amounts and/or activity under the control of iron. Finally, we found no correlation between the presence or absence of dsRNA virus infection among trichomonad isolates and NTPDase and ecto-5′-nucleotidase activities.

We monitored temporal changes in the magnitude of altered host behaviour in minnows (Pimephales promelas) experimentally infected with metacercariae of a brain-encysting trematode (Ornithodiplostomum ptychocheilus). This parasite develops and then encysts in a region of the brain that mediates the optomotor response (OMR), an innate behaviour that links visual stimuli with motor performance. The OMR of infected and uninfected minnows was evaluated between 0 and 10 weeks post-infection (p.i.), an interval spanning the development period of metacercariae to infectivity in birds. Trials involved monitoring the time an individual minnow spent following a spinning drum that had been painted with alternating black and white stripes. At 2 and 4 weeks p.i., infected minnows followed the drum 40% less often than controls. Differences between controls and infected fish declined thereafter, and were undetectable by 10 weeks p.i. Both control and infected fish habituated equally rapidly to the spinning drum. However, the difference in performance between controls and infected fish was 29% for experienced fish and 48% for fish that had never experienced the drum. Because maximum parasite-induced reduction in OMR coincided with the period of maximum parasite development, the behavioural effects are most likely due to unavoidable pathology in the brain associated with developing larvae.

We have examined metabolic rate, lipid and carbohydrate of female Aedes aegypti during 10 days following a malaria-infected bloodmeal. In parallel, we determined bloodmeal size, portions retained and diuresed, and subsequent fecundity. We found that mosquitoes obtained identical masses of blood when feeding on an infected or control host. However, infected mosquitoes lost more mass during diuresis and retained a smaller mass. Infection led to a significant reduction in fecundity, the extent of which could not be explained by the difference in post-diuresis bloodmeal mass alone. We found no differences in lipid or carbohydrate content between infected and control mosquitoes during the 10 days post-infection, although infected mosquitoes had a lower body mass than controls. Metabolic rates were not different between groups, except during blood digestion, where the metabolic rate was lower in infected mosquitoes. These results suggest that infection by malaria does not lead to an increase in metabolic rate during the phases of midgut invasion and sporogony. However, infection does have a measurable effect on fecundity and subsequent body mass of the infected females.

Chronic Plasmodium falciparum malaria infections in a Sudanese village, in an area of seasonal and unstable malaria transmission, were monitored and genetically characterized to study the influence of persistent infection on the immunology and epidemiology of low endemicity malaria. During the October–December malaria season of 1996, 51 individuals out of a population of 420 had confirmed and treated P. falciparum malaria in the village of Daraweesh in eastern Sudan. In a cross-sectional survey carried out in December 1996, an additional 6 individuals were found to harbour a microscopically negative but polymerase chain reaction (PCR)-positive P. falciparum infection. On 1 January 1997, a cohort of 43 individuals aged from 9 to 53, recruited from this group of recently malaria-infected individuals agreed to donate fortnightly blood samples for the next 9 months, the first 6 of which constitute the long Sudanese dry season when transmission falls to undetectable levels. Each blood sample was tested for the presence of persistent malaria infection by microscopy and PCR. Parasite-positive samples were genotyped using PCR assays that detect allelic polymorphism at the MSP-1, MSP-2 and GLURP marker gene loci. Of 43 individuals 16 were found to maintain chronic P. falciparum infections which were continuously genetically characterized.

The prevalence of vector-borne parasites varies greatly across host species, and this heterogeneity has been used to relate infectious disease susceptibility to host species traits. However, a few empirical studies have directly associated vector-borne parasite prevalence with exposure to vectors across hosts. Here, we use DNA sequencing of blood meals to estimate utilization of different avian host species by Culex mosquitoes, and relate utilization by these malaria vectors to avian Plasmodium prevalence. We found that avian host species that are highly utilized as hosts by avian malaria vectors are significantly more likely to have Plasmodium infections. However, the effect was not consistent among individual Plasmodium taxa. Exposure to vector bites may therefore influence the relative number of all avian Plasmodium infections among host species, while other processes, such as parasite competition and host-parasite coevolution, delimit the host distributions of individual Plasmodium species. We demonstrate that links between avian malaria susceptibility and host traits can be conditioned by patterns of exposure to vectors. Linking vector utilization rates to host traits may be a key area of future research to understand mechanisms that produce variation in the prevalence of vector-borne pathogens among host species.

Common bird species were screened during May and June 2007 on Barbados for haemosporidian parasites (Haemosporida) of the genera Haemoproteus and Plasmodium to determine whether the low parasite diversity reported in previous studies might have reflected limited sampling. PCR screening and DNA sequencing revealed a single predominant lineage of Haemoproteus identified as H. coatneyi. Sixty-two out of 257 birds were infected with Haemoproteus spp. on Barbados in 2007. Fifty-nine of the infections were identified as H. coatneyi (lineage HC), the only lineage recovered in the previous study in 1993. Two of the infections recovered from the bananaquit (Coereba flaveola) were identified as Haemoproteus spp. (lineage HD), which is the prevalent haemosporidian parasite in C. flaveola on Grenada. We discuss the possibility of infrequent colonization events and absence of vectors as explanations for Barbados's low avian haemosporidian diversity. In our study, the parasites were absent from the southeast of the island, whereas they were abundant in several host species in the northwest. Accordingly, environmental and host population genetic differences were also investigated between the areas with and without parasites. No host genetic differences were found between the parasite-free and the parasite-afflicted regions. However, the parasite-free region is slightly warmer and drier, and it supports less vegetation than the parasite-afflicted region. The influence that this harsher environment may have on vector survival is discussed.

Aquaculture, including both freshwater and marine production, has on a world scale exhibited one of the highest growth rates within animal protein production during recent decades and is expected to expand further at the same rate within the next 10 years. Control of diseases is one of the most prominent challenges if this production goal is to be reached. Apart from viral, bacterial, fungal and metazoan infections it has been documented that protozoan parasites affect health and welfare and thereby production of fish in marine aquaculture. Representatives within the main protozoan groups such as amoebae, dinoflagellates, kinetoplastid flagellates, diplomonadid flagellates, apicomplexans, microsporidians and ciliates have been shown to cause severe morbidity and mortality among farmed fish. Well studied examples are Neoparamoeba perurans, Amyloodinium ocellatum, Spironucleus salmonicida, Ichthyobodo necator, Cryptobia salmositica, Loma salmonae, Cryptocaryon irritans, Miamiensis avidus and Trichodina jadranica. The present report provides details on the parasites’ biology and impact on productivity and evaluates tools for diagnosis, control and management. Special emphasis is placed on antiprotozoan immune responses in fish and a strategy for development of vaccines is presented.

Novel tools for early diagnosis and monitoring of schistosomiasis are urgently needed. This study aimed to validate parasite-derived miRNAs as potential novel biomarkers for the detection of human Schistosoma japonicum infection. A total of 21 miRNAs were initially validated by real-time-polymerase chain reaction (RT-PCR) using serum samples of S. japonicum-infected BALB/c mice. Of these, 6 miRNAs were further validated with a human cohort of individuals from a schistosomiasis-endemic area of the Philippines. RT-PCR analysis showed that two parasite-derived miRNAs (sja-miR-2b-5p and sja-miR-2c-5p) could detect infected individuals with low infection intensity with moderate sensitivity/specificity values of 66%/68% and 55%/80%, respectively. Analysis of the combined data for the two parasite miRNAs revealed a specificity of 77.4% and a sensitivity of 60.0% with an area under the curve (AUC) value of 0.6906 (P = 0.0069); however, a duplex RT-PCR targeting both sja-miR-2b-5p and sja-miR-2c-5p did not result in an increased diagnostic performance compared with the singleplex assays. Furthermore, the serum level of sja-miR-2c-5p correlated significantly with faecal egg counts, whereas the other five miRNAs did not. Targeting S. japonicum-derived miRNAs in serum resulted in a moderate diagnostic performance when applied to a low schistosome infection intensity setting.

The pig is a natural host of Schistosoma japonicum and a useful animal model of human disease. In the present study mRNA levels of Th1 (IFN-γ) and Th2 (IL-10 and IL-4) cytokines were assessed by RT-PCR within tissues from infected pigs. Twelve Danish crossbred pigs were infected by intramuscular injection or orally with 1000 cercariae. Six other pigs served as non-infected controls. Liver and intestinal tissues were collected 10 weeks post-infection, and analysed for their relative levels of cytokine mRNA. Infected pigs developed a Th2 response as characterized by the increased level of mRNA encoding for IL-4 and IL-10 in their large intestine (caecum and colon). In contrast, levels of IFN-γ did not differ between control and infected animals although variation between animals was observed. When comparing the immune response of orally and intramuscularly infected animals, we found that orally infected pigs produced higher IL-4 and IL-10 levels in their caecum and colon respectively. This stronger Th2 response correlated with a previously reported delay in maturation of infection following oral infection. The cytokine expression levels in tissue samples taken from lesion sites and in nearby areas, without obvious lesions, were then compared. Subsequent to an oral infection, the Th2 type cytokine production was higher in the lesion sites of the liver. In conclusion, this study is the first demonstration of IL-4 and IL-10 cytokine response in pig tissues during S. japonicum infection.

When every individual has an equal chance of mating with other individuals, the population is classified as panmictic. Amongst metazoan parasites of animals, local-scale panmixia can be disrupted due to not only non-random mating, but also non-random transmission among individual hosts of a single host population or non-random transmission among sympatric host species. Population genetics theory and analyses can be used to test the null hypothesis of panmixia and thus, allow one to draw inferences about parasite population dynamics that are difficult to observe directly. We provide an outline that addresses 3 tiered questions when testing parasite panmixia on local scales: is there greater than 1 parasite population/species, is there genetic subdivision amongst infrapopulations within a host population, and is there asexual reproduction or a non-random mating system? In this review, we highlight the evolutionary significance of non-panmixia on local scales and the genetic patterns that have been used to identify the different factors that may cause or explain deviations from panmixia on a local scale. We also discuss how tests of local-scale panmixia can provide a means to infer parasite population dynamics and epidemiology of medically relevant parasites.

HIV-1 and parasitic infections co-circulate in many populations, and in a few well-studied examples HIV-1 co-infection is known to amplify parasite transmission. There are indications that HIV-1 interacts significantly with many other parasitic infections within individual hosts, but the population-level impacts of co-infection are not well-characterized. Here we consider how alteration of host immune status due to HIV-1 infection may influence the emergence of novel parasite strains. We review clinical and epidemiological evidence from five parasitic diseases (malaria, leishmaniasis, schistosomiasis, trypanosomiasis and strongyloidiasis) with emphasis on how HIV-1 co-infection alters individual susceptibility and infectiousness for the parasites. We then introduce a simple modelling framework that allows us to project how these individual-level properties might influence population-level dynamics. We find that HIV-1 can facilitate invasion by parasite strains in many circumstances and we identify threshold values of HIV-1 prevalence that allow otherwise unsustainable parasite strains to invade successfully. Definitive evidence to test these predicted effects is largely lacking, and we conclude by discussing challenges in interpreting available data and priorities for future studies.

Plasmodium knowlesi has risen in importance as a zoonotic parasite that has been causing regular episodes of malaria throughout South East Asia. The P. knowlesi genome sequence generated in 2008 highlighted and confirmed many similarities and differences in Plasmodium species, including a global view of several multigene families, such as the large SICAvar multigene family encoding the variant antigens known as the schizont-infected cell agglutination proteins. However, repetitive DNA sequences are the bane of any genome project, and this and other Plasmodium genome projects have not been immune to the gaps, rearrangements and other pitfalls created by these genomic features. Today, long-read PacBio and chromatin conformation technologies are overcoming such obstacles. Here, based on the use of these technologies, we present a highly refined de novo P. knowlesi genome sequence of the Pk1(A+) clone. This sequence and annotation, referred to as the ‘MaHPIC Pk genome sequence’, includes manual annotation of the SICAvar gene family with 136 full-length members categorized as type I or II. This sequence provides a framework that will permit a better understanding of the SICAvar repertoire, selective pressures acting on this gene family and mechanisms of antigenic variation in this species and other pathogens.

Heat shock is believed to be a developmental inductor of differentiation in Leishmania. Furthermore, heat shock genes are extensively studied as gene models to decipher mechanisms of gene regulation in kinetoplastids. Here, we describe the organization and expression of the HSP70 loci in representative Leishmania species (L. infantum, L. major, L. tropica, L. mexicana, L. amazonensis and L. braziliensis). With the exception of L. braziliensis, the organization of the HSP70 loci was found to be well conserved among the other Leishmania species. Two types of genes, HSP70-I and HSP70-II, were found to be present in these Leishmania species except for L. braziliensis that lacks HSP70-II gene. Polymorphisms in the HSP70 locus allow the differentiation of the Old and New World species within the subgenus Leishmania. A notable discrepancy between our data and those of the L. major genome database in relation to the gene copy number composing the L. major HSP70 locus was revealed. The temperature-dependent accumulation of the HSP70-I mRNAs is also conserved among the different Leishmania species with the exception of L. braziliensis. In spite of these differences, analysis of the HSP70 synthesis indicated that the HSP70 mRNAs are also preferentially translated during heat shock in L. braziliensis.

The epidemiology of the sucking lice Echinophthirius horridus was studied over a 4 year period in which their harbour seal hosts experienced marked inter-annual changes in food availability. Prevalence and intensity of infection varied in relation to host age but not sex. Burdens were highest on immature seals, but both prevalence and intensity of infection were significantly higher in years when food availability was low. Observed intra-population variations in ectoparasite dynamics suggested that reported geographical differences in the prevalence of E. horridus may have resulted from methodological differences. In contrast to previous studies of other pinnipeds, lice were also absent on weaned pups, suggesting that E. horridus is transferred horizontally. No significant differences were found in the haematological parameters of infected and uninfected hosts. Nevertheless, there was a significant negative correlation between intensity of infection and several erythrocyte parameters, suggesting that high burdens of lice may compromise diving ability.