A survey of Plasmodium falciparum infection and clone multiplicity in Ghanaian children was carried out to study the effect of the onset of the malaria transmission season on disease incidence. Fortnightly blood samples were collected from 40 children living in the rural town of Dodowa, between February and August 1998. P. falciparum parasite densities were calculated and PCR genotyping was carried out using the polymorphic MSP-1 and MSP-2 genes as target loci for the estimation of the number of parasite clones in each sample. The average clone number was estimated using maximum likelihood techniques and the minimum number of clones per patient was analysed for the effects of age, sex, season, minimum number of clones per child, level of parasitaemia and parasite genotype. The statistical analysis indicated that the more clones a child carried, the more likely they were to have a clinical malaria episode. This was true after adjusting for age and season effects and for the measured circulating parasitaemia. The probability of clinical disease also increased if the MSP-1 MAD 20 and the MSP-2 FC 27 alleles were present. This longitudinal analysis thus indicates that the probability of a Ghanaian child having a symptomatic malaria episode is positively associated with both increasing numbers and novel types of P. falciparum clones.

Taenia crassiceps is a cestode parasite of wild and domestic animals that rarely affects humans; it has been widely used as an experimental model. The asexual proliferation by budding is a useful attribute of T. crassiceps cysticerci, which allows the various strains to be maintained indefinitely in the peritoneal cavity of inbred mice. Over the last 50 years, experimental results using larval and adult stages of T. crassiceps have yielded much information on the morphology, infectivity, proliferation dynamics, host immune response, endrocrinological responses and vaccine research, all of which have contributed to our knowledge of cestode biology.

Many zoonotic disease agents are transmitted between hosts by arthropod vectors, including fleas, but few empirical studies of host-vector-microparasite dynamics have investigated the relative importance of hosts and vectors. This study investigates the dynamics of 4 closely related Bartonella species and their flea vectors in cyclic populations of field voles (Microtus agrestis) over 3 years. The probability of flea infestation was positively related to field vole density 12 months previously in autumn, but negatively related to more recent host densities, suggesting a dilution effect. The 4 Bartonella species exhibited contrasting dynamics. Only B. grahamii, showed a distinct seasonal pattern. Infection probability increased with field vole density for B. doshiae, B. taylorii and BGA (a previously unidentified species) and with density of coexisting wood mice for B. doshiae and B. grahamii. However, only the infection probability of BGA in spring was related to flea prevalence. B. doshiae and BGA were most common in older animals, but the other 2 were most common in non-reproductive hosts. Generally, host density rather than vector abundance appears most important for the dynamics of flea-transmitted Bartonella spp., possibly reflecting the importance of flea exchange between hosts. However, even closely related species showed quite different dynamics, emphasising that other factors such as population age structure can impact on zoonotic risk.

Haemonchus contortus worm populations isolated from naturally infected sheep at the Pastoral Research Laboratory, Armidale, N.S.W., were found to contain approximately 20% of worms resistant to a 50 mg/kg dose of thiabendazole. Following 3 generations of selection with 50 mg/kg thiabendazole the number of worms removed by the anthelmintic was too small to detect differences between treated and control groups. After more than 15 generations of selection, matings between males from the selected strain and non-resistant females produced resistant males and females in equal numbers. Thus, thiabendazole resistance does not appear to be sex-linked. A dose–response assay on the F2 adults indicated that worms from female resistant × male non-resistant crosses were more resistant than F2 adults of the reciprocal cross. An in vitro technique that identified thiabendazole-resistant eggs by their ability to hatch in a solution containing thiabendazole and 0·1% NaCl solution was also used to study the inheritance of resistance. F1 eggs had similar LC50's to the resistant parents. F2 and back-cross eggs from an original mating of thiabendazole-resistant females × non-resistant males had a higher LC50 than F2 and back-cross eggs from the reciprocal mating, indicating a degree of matroclinous inheritance of resistance. However, the resistant parents had tolerances to thiabendazole exceeding those of F2. F3 eggs had a resistance distribution that ranged from that of the resistant to the non-resistant parent. No significant deviation from linearity was observed in any of the dose–response lines. These results indicate that thiabendazole resistance in H. contortus worms is inherited as an autosomal and semi-dominant trait.

Two morphologically novel Kudoa species are characterized from brain tissue of fish, Kudoa chaetodoni n. sp. from Chaetodon unimaculatus (Chaetodontidae) and Kudoa lethrini n. sp. from Gymnocranius audleyi and Lethrinus harak (Lethrinidae). Additionally we characterized a 5-spore valve (SV) Kudoa species from the brain of Sillago ciliata (Sillaginidae). Intriguingly, its 18S rDNA sequence was identical to that of the 7 SV Kudoa yasunagai extracted from the brain of a paralichthyid halibut in Japan. These 2 species may either prove to be con-specific, even though morphology and distribution differ, or demonstrate the limit of specific resolution in the small subunit rDNA gene region. Small subunit rDNA sequences from these new species were used in molecular phylogenetic analyses of kudoids to examine congruence of phylogeny with tissue tropism, geographical distribution, and host specificity. There was significant correlation between tissue tropism in the form of well-supported brain and heart-infecting clades. Host specificity and geographical distribution showed some correlations with genotype.

The cestode Schistocephalus solidus is a simultaneous hermaphrodite that grows in 2 intermediate hosts and reproduces rapidly within a few days in the gut of a bird. Reproduction takes place by self- or cross-fertilization. Here, it was tested whether egg production differs between S. solidus that reproduce alone and those that are allowed to reproduce in pairs. Egg production in an in vitro system was found to depend on the cestodes' social situation. When kept alone, larger cestodes produced larger eggs. This was not so when kept in pairs – the difference between these 2 reproductive modes being highly significant in this respect. Further experiments revealed that, within the first 3 days, these hermaphrodites produced a larger total egg mass when kept alone than when kept in pairs. This was also reflected by the energy contents of the cestodes after this time-span: selfers had used up more energy than paired worms. Furthermore, S. solidus appeared to adjust its investment per egg depending on whether the offspring will be the result of self- or cross-fertilization. Selfers produced larger numbers of eggs, but these eggs were smaller and contained even smaller embryos per given egg size than eggs of potentially outbreeding cestodes. Selfed eggs reached lower hatching rates. Although this is to be expected from inbreeding depression it may also be an effect of the reduced maternal investment per egg. The observed phenotypic plasticity in the reproduction of S. solidus is discussed within 4 evolutionary frameworks: local mate competition adjusted for hermaphrodites, the hermaphrodite's dilemma, bet-hedging, and sib-competition.

We used the PCR–SSCP method followed by sequencing in order to assess the genetic variability of coding and non- coding parts of the genome of Echinococcus granulosus (Cestoda; Taeniidae) and to test whether or not the parasite populations are mainly self-fertilizing. For this, we analysed a sample of 110 E. granulosus metacestode isolates collected from different geographical regions (Southern Brazil, Europe and Australia) and from different intermediate hosts (ovine, bovine, human, macropod, swine and equine). Using appropriate controls, we were able to identify 4 strains in that sample (sheep, cattle, pig and horse strains). The high degree of genetic differentiation between strains, but not within, and the monomorphism found in most loci (EgAg4, EgActII, EgHbx2 and EgAg6 – non-coding – EgAgB/1 and EgND1 – coding) indicated that they are largely selfed. On the other hand, outcrossing was also shown to occur, since 5 potential hybrid genotypes between cattle and sheep strains were found in populations of Southern Brazil, but absent in other geographical areas. We suggest that both processes are adaptive. The article also reports, for the first time, the occurrence of the E. granulosus cattle strain in South America.

A Polymerase Chain Reaction (PCR) and Southern blot hybridization for the detection of Theileria annulata are described. The PCR used primers amplifying a 785 base-pair fragment of the T. annulata gene which encodes the 30 kDa major merozoite surface antigen, Tams1. The sensitivity of the PCR in bovine blood was 1 piroplasm in 1 μl of blood. T. buffeli, T. parva, Babesia bigemina, B. bovis and B. divergens were not detected. The PCR detected down to 1 infected acinus/tick in resting and partially fed adult Hyalomma anatolicum anatolicum ticks and was negative for T. lestoquardi and T. equi, which are transmitted by this tick but are not infective to cattle. The specificity of the PCR was checked using 30 stocks of T. annulata, all of which were detected. Three stocks of T. lestoquardi, 4 of T. equi and 1 each of T. buffeli, T. parva, B. bigemina, B. bovis and B. divergens were used to ascertain there were no cross-reactions. A nested PCR using separate primers for the first reaction and the same primers for the second reaction detected T. annulata to the same sensitivity and specificity in saponin-extracted DNA samples stored for long periods at −20 °C.

The need for a vaccine(s) against cutaneous leishmaniasis and the populations at risk for whom such vaccines should be developed are briefly discussed. The current human vaccine studies are reviewed, as are some experimental mouse studies with emphasis on Leishmania major infection relevant to vaccine development. Based on the information available from the mouse model and those data which are being sought in human studies, the benign nature of the cutaneous disease, the ease with which L. major can be manipulated to yield the required material, and the ongoing practice of leishmanization which allows rapid evaluation of candidate vaccine(s), it is suggested that a vaccine, at least against L. major, is imminent in the not too distant future.

1. Pimpla ruficollis is a parasite of the pine shoot moth Rhyacionia (Evetria) buoliana Schiff. (Eucosmidae) which emerges from its host a considerable time before the next generation of larvae are ready for oviposition. It seems that during this period the parasites leave the pine trees and feed on the flowers of certain Umbelliferae and probably other plants. Only after 3 or 4 weeks do they return to the pine trees where the shoots now contain larvae ready for egg laying.

2. It has been shown by means of olfactometer experiments that during this first period of the adult life, the parasites are repelled by the odour of oil of Pinus sylvestris. At this time the ovaries are very small and are probably not ready for the production of eggs. After the third or fourth week of life the females become attracted by the oil of P. sylvestris and the ovaries are now relatively large.

3. Since Geraniol is known to be a constituent of certain conifers, this substance was also tested. It was, however, found to be invariably repellent to the parasites.

4. There is some evidence that conclusions reached as a result of experiments with P. ruficollis also apply to the ophionine ichneumonid Eulimneria rufifemur.

Anopheles stephensi mosquitoes showed a reduction in fecundity over 3 successive gonotrophic cycles, after becoming infected with Plasmodium yoelii nigeriensis. This effect could be observed at high oocyst burdens (> 75) or at low oocyst burdens (mean of 4·36). Mean bloodmeal size of the infected mosquitoes was significantly reduced only when feeding upon a mouse with a high gametocytaemia and the conversion of the bloodmeal into eggs by the infected mosquitoes was disrupted. Patterns of infected mosquito mortality, over the 3 gonotrophic cycles, varied with severity of infection. Although in 1 case increased mortality and decreased bloodmeal size may have affected fecundity, this could not have accounted for all of the observed fecundity reduction. We propose that other, unknown parasite related factors, are involved.

SSU ribosomal sequences of trypanosomes from Brazilian cattle and water buffalo were used to infer phylogenetic relationships between non-pathogenic T. theileri and allied species parasitic in artiodactyls. T. theileri trypanosomes from distinct geographical regions in Brazil and from other countries were tightly clustered into the ‘clade T. theileri’ distant from the ‘T. brucei clade’ of pathogenic parasites of artiodactyls, and also distinct from trypanosomes of other mammals. The existence of this monophyletic assemblage (T. theileri clade) composed only by isolates from artiodactyl species justifies the continued recognition of the subgenus T. (Megatrypanum) with T. theileri as its type species. Phylogenies based on SSU and ITS1 ribosomal sequences produced the same branching pattern with isolates from different mammalian hosts clustered in 5 lineages: A, related to water buffalo; B, C and D, to cattle; E, to fallow deer. The pattern of host specificity allied to some congruence between host and parasite phylogenies suggested association of these trypanosomes with their respective hosts. Segregation of cattle isolates into three lineages revealed an overall geographical structure. Moreover, positioning of trypanosomes infecting tabanids in the T. theileri clade is consistent with the role of these flies as important vectors of these trypanosomes.

The author has summarized the history of discovery, the mechanism and the clinical significance of antibody-dependent enhancement (ADE) of HIV infection. ADE has two major forms: (a) complement-mediated antibody-dependent enhancement (C-ADE) and (b) complement-independent Fc receptor-dependent ADE (FcR-ADE). The most important epitope responsible for the development of C-ADE-mediating antibodies is present in the immunodominant region of gp41 while antibodies mediating FcR-ADE react mainly with V3 loop of gp120. There are at least three fundamentally different hypotheses for the explanation of ADE in vitro: (a) increased adhesion of HIV-antibody-(complement) complexes to FcR or complement receptor carrying cells; (b) facilitation of HIV-target cell fusion by complement fragment deposited on the HIV-virions and (c) complement activation products may have a non-specific stimulatory effect on target cells resulting in enhanced virus production. FcR-ADE and C-ADE have been measured in vitro mostly by using FcR-carrying and complement receptor-carrying cell lines, respectively; no efforts have been made to standardize these methods. Several data support the possible clinical significance of FcR-ADE and C-ADE: (a) Cross-sectional and longitudinal studies indicate a correlation between the amounts of FcR-ADE and C-ADE-mediating antibodies and clinical, immunological and virological progression of the HIV-disease; (b) ADE may facilitate maternal–infant HIV-1 transmission; (c) According to experiments in animal models, ADE are present and may modify the course of SIV (simian immunodeficiency) infection as well. The author raises a new hypothesis on the mechanism of the in vivo effect of C-ADE. According to the hypothesis, C-ADE-mediating antibodies exert their effect through enhancement of HIV propagation and consequent facilitation of the progression of HIV disease. Finally, according to observations from animal experiments and human clinical trials it cannot be excluded that ADE-mediating antibodies may develop, diminish the beneficial effect or may be harmful in volunteers vaccinated with HIV-1 candidate vaccines.

The sexual development of the microgametocyte of Plasmodium yoelii nigeriensis may be subdivided into microgametogenesis which includes exflagellation, dispersal of the gametes and fertilization. Under our experimental conditions microgametogenesis takes about 8–15 min at 20 °C, the duration of this period being inversely related to temperature. Exflagellation takes less than 1 min, subsequent dispersal of gametes may continue for 40 min. We find that exflagellation is totally inhibited in vitro by temperatures of 30 °C and above, and by certain invertebrate tissue culture media. Exflagellation may occur within a persistent host cell plasmalemma, which seriously impedes the escape of the 8 microgametes. Microgametes move by sinusoidal or helical waves which may be rapid (10 waves/s), slow (< 1 wave/s) or they may be immobile. Microgamete activity, which is alternately rapid/slow or slow/immobile, declines linearly with time. Fertilization which takes less than 1 min results from characteristic behavioural changes by the microgamete; vibratory waves are responsible for the penetration of the macrogamete by the microgamete. The microgamete completely enters the macrogamete and therein continues its cyclical activity.

An experiment is described in which the effects of age, previous infection, pregnancy and lactation on some reactions of cattle to infection with Ostertagia ostertagi were studied. It was found that an acquired resistance to the establishment of worms developed more rapidly in 20-month-old heifers than in calves, that it was unaffected by pregnancy of the host but that it was largely lost by heifers in early lactation. The rate at which populations were turned over, i.e. the mean life-span of worms through the late 4th and 5th stages was unaffected by the factors studied. Although, in the conditions of the experiment, development of the worms was not arrested in susceptible calves, both age of the host and its previous experience of infection were significant causes of arrest, and in previously infected 20-month-old cattle 86% of the worms of a challenge infection were arrested. Pregnancy did not affect the proportion of worms that was arrested but in lactating heifers only marginally more worms were arrested than in calves. Worms that were not arrested grew more rapidly in calves and in lactating heifers than in empty heifers or those in mid-pregnancy.

Cystic echinococcosis, caused by Echinococcus granulosus, is an emerging disease in many parts of the world and, in particular, in eastern Europe and the former Soviet Union. This paper examines the abundance of infection of E. granulosus in the definitive host in southern Kazakhstan. Observed data are fitted to a mathematical model in order to decide if the parasite population is partly regulated by definitive host immunity and to define parameters in the model. Such data would be useful to develop simulation models for the control of this disease. Maximum likelihood techniques were used to define the parameters and their confidence limits in the model and the negative binomial distribution was used to define the error variance in the observed data. The results indicated that there were 2 distinct populations of dogs in rural Kazakhstan which had significantly different exposures to E. granulosus. Farm dogs, which are closely associated with livestock husbandry, particularly sheep rearing, had a relatively high mean abundance of 631 parasites per dog and a prevalence rate of approximately 23%. The best fit to the model indicated that there was significant herd immunity in the dog at this infection pressure. In contrast, village dogs which were more likely to be kept as pets had a much lower mean abundance of parasites of only 27 parasites per dog and a lower prevalence of 5·8%. With this village population of dogs, the best fit indicated negligible herd immunity.

Neurocysticercosis continues to be a major health burden on humans living in many regions of the world, despite the availability of highly effective taeniacides and identification of the cause, Taenia solium, as being potentially eradicable. Several T. solium control trials have been undertaken, generally achieving limited success and none that has been fully documented has achieved what was demonstrated to be a sustainable level of disease control. Pigs act as intermediate hosts for T. solium and two new control tools have become available for application in pigs – single-dose oxfendazole treatment of porcine cysticercosis and the TSOL18 vaccine. Three potential intervention scenarios for pigs are compared for control of cysticercosis, using either oxfendazole or vaccination. A control scenario involving vaccination plus oxfendazole treatment delivered at 4 monthly intervals was predicted to achieve the best outcome, with no pigs slaughtered at 12 months of age having viable T. solium cysticerci. Now that new control tools are available, there are opportunities to concentrate research attention on evaluation of novel control scenarios leading to the implementation of effective and sustainable control programmes and a reduction in the global burden of neurocysticercosis.

Marteilia refringens is a major pathogen of the European flat oyster, Ostrea edulis Linnaeus. Since its description, the life-cycle of this protozoan parasite has eluded discovery. Attempts to infect oysters experimentally have been unsuccessful and led to the hypothesis of a complex life-cycle involving several hosts. Knowledge of this life-cycle is of central importance in order to manage oyster disease. However, the exploration of M. refringens life-cycle has been previously limited by the detection tools available and the tremendous number of species to be screened in enzootic areas. In this study, these two restrictions were circumvented by the use of both molecular detection tools and a mesocosm with low biodiversity. Screening of the entire fauna of the pond for M. refringens DNA was systematically undertaken using PCR. Here, we show that the copepod Paracartia(Acartia) grani is a host of M. refringens. Not only was DNA of M. refringens consistently detected in P. grani but also the presence of the parasite in the ovarian tissues was demonstrated using in situ hybridization. Finally, successful experimental transmissions provided evidence that P. grani can be infected from infected flat oysters.

Observations have been made on the development and survival of the free-living stages in faeces deposited out of doors at different times of year, and on the migration of infective larvae to the surrounding herbage. Laboratory experiments were performed to assist in the interpretation of the field observations. Studies were made on the rate of development to the infective stage in faeces kept at different temperatures. The rates at which eggs and larvae of Strongylus vulgaris, S edentatus, S. equinus and Trichonema nassatum developed on faecal-agar cultures at different temperatures were compared. Studies were also made on the effect of desiccation of faeces on the development and survival of the free-living stages. The results of these observations are discussed in relation to the development of herbage infestations on British pastures.