Observations that growth of Plasmodium falciparum in vitro is inhibited by high temperatures have led to hypotheses that malaria fever may influence the parasite population dynamics, regulating parasite density and synchronizing parasite growth. In order to investigate the fever hypotheses, we have developed an age-structured coupled Markov chain model that describes the parasite erythrocyte cycle and its interaction with the host fever response. We estimated the model parameters using data collected from laboratory parasite cultures that were exposed to febrile or normal temperature. Using the experimental parameter values, quantitative predictions were made of the effect of fever in determining the parasite population dynamics. It was concluded from the model behaviour that, during the primary infection of a non-immune host, a typical episode of fever can effect density-dependent regulation of the parasite population, maintaining cycles of parasitaemia and promoting synchronous parasite growth.

After infection with sporozoites of the protozoon Theileria parva (Tp) bovine T cells are readily transformed to permanent growth in vivo and in vitro. Their transformed state depends on the constant presence of the parasite but membrane signals remain important. Non-receptor tyrosine kinases play a critical role in the transduction of membrane signals in haematopoietic cells. We have investigated Src-family kinases in bovine T cells transformed by Tp. The T cell receptor-associated tyrosine kinase p60fyn had high activity in all cell lines tested. In addition, weak phosphorylation of 2 novel bands was observed associated with Fyn. In contrast to Fyn, enzymatic activity of p56lck, which in T cells has an essential role in signalling, was low. Furthermore, 1 of 3 Tp transformed cell lines was completely devoid of p56lck indicating that the enzyme is not necessary for the Tp dependent growth of the T cells. In addition to p60fyn and p56lck weak enzymatic activity of 1 splice variant of p53/56lyn was observed after infection of T cells with Tp. These data show that growth transformation by Tp influences kinase activity in bovine T cells. However, they also prove that p56lck does not play an essential role in the transformation mechanism.

Failure of snail reinfection by Schistosoma mansoni has been demonstrated in susceptible Biomphalaria glabrata infected with 1 miracidium and subsequently re-exposed to 1 or 5 homologous parasite larvae. The acquisition of ‘resistance’ to secondary parasite infection was time dependent since complete inhibition was observed at 2 weeks and longer following monomiracidial exposure. This phenomenon was still observed in snails challenged 8 weeks after primary infection. Histological observations revealed that sporocysts from the challenge infection were free of encapsulation, their development was stopped and they degenerated slowly in the absence of haemocytic reaction of the host. Under the hypothesis of an acquired homologous resistance mechanism, this strongly suggests that 1 or several unidentified humoral factors are responsible for the non-development of the sporocysts from the challenge infection. However, considering the time-dependent nature of the phenomenon, an intraspecific larval antagonism process between sporocysts resulting from the primary infection and those from the challenge infection may be involved.

The relocation of several thousand members of the Kamba tribe from the Kyulu Hills to the Thange valley near Masongaleni in Kenya provides an excellent opportunity to study the development of the immune response to schistosomiasis mansoni in a population with little or no previous experience of the infection. An adjacent, well-established Kamba community with similar patterns of water contact provides a suitable endemic control population. The immigrants were, uniquely, examined shortly after their arrival in the endemic area, while the prevalence of infection was still low. At this time faecal egg counts peaked atypically around 30 years of age. Over the next 12–18 months infection increased rapidly, especially among teenagers, producing a pattern of infection more typical of endemic communities. This substantially narrows estimates of the time required to develop the important determinants of the age–intensity profile, supporting the notion that changes related to age per se, rather than duration of infection, dominate. Age-dependent factors might include behaviour or physiology, including immune response. This paper provides the background for continuing longitudinal studies on the development of immunological responses to this parasite.

In this paper we investigate whether the assortative mating between individuals of the same genetic entity (i.e. coming from the same geographical area) of Echinostoma caproni, reported in a previous paper, may be explained by a post-zygotic isolating mechanism. The fecundity of the adults of 2 parental genetic entities and of their hybrids (i.e. F1, F2, F3) was quantified through 3 successive generations. Whereas the number of eggs released by F1 hybrids is similar to that of the mid-parent, that of recombinant hybrids (F2–3 hybrids) is significantly lower than that of F1 and that of the mid-parent. Since these results seem to demonstrate hybrid breakdown, 2 important factors maintaining reproductive isolation, i.e. pre-mating reproductive isolation and low hybrid fecundity, may influence the evolution of E. caproni.

Gyrodactylus salaris, an important pathogen of Atlantic salmon Salmo salar, has been shown to be highly sensitive to factors in host serum and mucus, being killed rapidly (50% within 1h) by serum at a dilution of 1[ratio ]200. The time needed for killing was inversely proportional to serum concentration. Similar effects were noted using host mucus, which contained approximately 1/20th of the anti-Gyrodactylus activity of serum. Serum activity was abolished completely by heating at 45°C for 30 min, and by addition of EDTA, but not by EGTA+1 mm magnesium ions. Activity was not dependent on whether the serum was from infected or naive fishes, nor was it species specific. Attempts to pre-coat parasites in salmon anti-Gyrodactylus antibodies also failed to enhance the activity of fresh serum. These observations suggest that killing is due to the complement system of the host, acting via the alternate pathway. G. salaris appears to be exceptionally sensitive to complement, being killed at concentrations which could be experienced in vivo. The role of complement in the protection of fishes against gyrodactylid infection therefore deserves further investigation.

Recent work has shown that mice with subclinical parasitic infections suffer impaired spatial learning and memory, as assayed in an open-field water maze. Although the mechanism underlying this effect is not clear, the phenomenon has been reported following infection with both a protozoan parasite (Eimeria vermiformis) and a gastrointestinal nematode (Heligmosomoides polygyrus). In a variety of experiments, we examined the effects of a different gastrointestinal nematode, Strongyloides ratti, on the ability of rats and mice to learn a spatial or a discrimination task. Animals were tested at various stages post-infection, with different levels of infection, using different lines of S. ratti and with varying experimental protocols. All animals learned the tasks, but we found no evidence of an effect of S. ratti infection on learning or memory. Even rats infected with approximately 5000 S. ratti larvae, a dose which has an impact on rat body size, showed no deficit in learning ability. Various reasons for the conflict between our results and those previously reported for E. vermiformis and H. polygyrus are discussed. Our results show that impaired learning and memory following parasitic infection is not a ubiquitous or at least easily replicated phenomenon.

The ascaridoid nematode of cats from Kuala Lumpur, Malaysia, previously identified morphologically as Toxocara canis, was characterized using a molecular approach. The nuclear ribosomal DNA (rDNA) region spanning the first internal transcribed spacer (ITS-1), the 5·8S gene and the second internal transcribed spacer (ITS-2) was amplified and sequenced. The sequences for the parasite from Malaysian cats were compared with those for T. canis and T. cati. The sequence data showed that this taxon was genetically more similar to T. cati than to T. canis in the ITS-1, 5·8S and ITS-2. Differences in the ITS-1 and ITS-2 sequences between the taxa (9·4–26·1%) were markedly higher than variation between samples within T. canis and T. cati (0–2·9%). The sequence data demonstrate that the parasite from Malaysian cats is neither T. canis nor T. cati and indicate that it is a distinct species. Based on these data, PCR-linked restriction fragment length polymorphism (RFLP) and single-strand conformation polymorphism (SSCP) methods were employed for the unequivocal differentiation of the Toxocara variant from T. canis and T. cati. These methods should provide valuable tools for studying the life-cycle, transmission pattern(s) and zoonotic potential of this parasite.

The impact of mixed, nematode infection upon a group of animals will depend upon the number of nematodes present, how they are distributed among hosts and whether individuals that are heavily parasitized with one species are more likely to be heavily parasitized with other species. A survey of over 500 six-month-old, Scottish Blackface lambs from a single farm in Southwest Strathclyde identified 7 different categories of nematodes in the abomasum and small intestine. There were considerable differences among years and among nematodes in the prevalence and mean intensity of infection. Ostertagia circumcincta was present in nearly all lambs and judged by prevalence and intensity is one of the most successful of all parasitic nematodes. Each category of nematodes had a skewed distribution; most animals had relatively few worms but a small proportion had many worms. The variances of the number of nematodes in each category were approximately equal to the square of the mean. The counts of adult O. circumcincta followed a negative binomial distribution, but the negative binomial distribution did not provide a good description of the observed values for the other species. These other species had a lower prevalence and possibly some sheep were not exposed to infection. There was no significant genetic variation among lambs in the number of nematodes present and therefore the differences among these lambs were unlikely to be a consequence of genetic differences in host susceptibility. Lambs with increased numbers of one species were more likely to have increased numbers of the other species, but the correlations were weak and may reflect covariation in exposure to different parasites.

Diagnostic PCR primers for Trichinella were constructed. Twelve pairs of primers were designed based on the sequences of random amplified polymorphic DNA, and 4 pairs of primers were designed based on the reported sequences of complementary DNA encoding excretory–secretory glycoproteins. With these primers, 31 samples of DNA from different strains of Trichinella including 5 species (Trichinella spiralis, Trichinella britovi, Trichinella nativa, Trichinella nelsoni and Trichinella pseudospiralis) and 3 phenotypes of uncertain taxonomic level (Trichinella T5, T6 and T8) were tested with PCR. Genus Trichinella can be identified by 4 different primer pairs (SB147D, SB372A, SB153, or Ts43). Trichinella spiralis can be identified by the presence of a 673 bp amplicon in PCR with the primer pair SB147B. Trichinella nelsoni can be identified using primer pair SB147F or by the presence of 673 bp and ca. 380 bp amplicon in PCR with the primer pair SB147B. Trichinella pseudospiralis can be identified by 2 primer pairs (SB147E or SB372B). Trichinella T5 can be identified by the primer pair SB147G. Trichinella T8 can be identified by its positivity by the primer pair SB147C and its negativity by the primer pair SB372C. A group of Trichinella species (T. britovi, T. nativa and Trichinella T6) can be identified by the primer pair SB372C.

Species of Echinococcus (Cestoda: Taeniidae) require 2 mammalian hosts to complete their life-cycle; a carnivorous definitive host, and a herbivorous or omnivorous intermediate host. For most species of Echinococcus, the definitive host range is restricted to 1 or a few species, but the intermediate host range is very broad. Programmes to control hydatid disease attempt to break the life-cycle of the parasite and their effectiveness is therefore enhanced by an understanding of local patterns of transmission. Although it is known that the rostellar hooks of protoscoleces may be influenced by the species of intermediate host in which they develop, the application of this knowledge to infer transmission cycles has been limited, because the intermediate host effect has not been isolated from other environmental and genetic components of phenotypic variance. This study presents a method for separating these potentially confounding genetic and environmental effects, by combining quantitative genetic analyses of hook traits with data on population structure from neutral genetic markers. The method was applied to 5 hook traits (hook number, total length of large hooks, blade length of large hooks, total length of small hooks, blade length of small hooks) measured on protoscoleces from 2 intermediate host types (sheep and macropod marsupials) in Australia. Although genetic variance was similar for all traits, they differed markedly in the extent of environmental variance attributed to development in different host types. Total length of small hooks was the trait most affected, with 49–60% of phenotypic variance being explained by environmental differences between intermediate host species. Blade length of small hooks was least affected, with none of the phenotypic variance due to intermediate host origin. These data suggest that hook measurements of adult worms from naturally infected definitive hosts could be used to determine the intermediate host species from which infection was acquired, if the appropriate traits are measured.

The study was conducted to evaluate a mAb-based coproantigen detection assay for monitoring fox prevalence of Echinococcus multilocularis infections in the Shiretoko National Park in Hokkaido, Japan. Eight fox families, each consisting of 2–4 adults and their pups, were selected because their territories have been determined. Faeces of each family (total n=537) were collected monthly from April to October, 1994. Detection of coproantigen and taeniid eggs was recognized in 58 and 27 faeces, respectively, but mostly restricted in 1 family, in which coproantigen ELISA OD values had dual peaks, one in June and the other in October, whereas taeniid eggs were detected only from April to July. Fox pup faeces (n=51) collected around the dens used by the positive family were all coproantigen and taeniid egg negative except for 1 faeces. These results suggest that the prevalence and infection pressure in the study area were low and the infected family terminated the infection in the summer and acquired a new one in the early autumn, 1994. This monitoring method for fox infection will be a practical management tool for E. multilocularis infection, especially at the tourist spots in Hokkaido where close contact of fox with humans is frequently observed.