Residents of Daraweesh village in Sudan were monitored for Plasmodium falciparum infection and malaria morbidity in 3 malaria seasons from 1993 to 1996. Malaria parasites were detected microscopically and by polymerase chain reaction (PCR) in a series of cross-sectional surveys. PCR revealed submicroscopical infections during the dry season, particularly among individuals who had recovered from a malaria episode following successful drug treatment. Clinical and subclinical infections were contrasted by assaying for allelic polymorphism at 2 gene loci, MSP-1 and GLURP and 2 hypotheses examined with reference to these data: that clinical malaria is associated with infection with novel parasite genotypes not previously detected in that host, or alternatively, that clinical malaria episodes are associated with an increased number of clones in an infection. We detected more mixed infections among clinical isolates, but people carrying parasites during the dry season were not found to have an increased risk of disease in the following malaria season. There was a clear association of disease with the appearance of novel parasite genotypes.

The encapsulation of microfilariae in the haemocoels of mosquitoes combines both humoral and cellular reactions: the microfilariae are first encased in an acellular layer of melanin, followed by a cellular encapsulation by plasmatocytes. In this study, we demonstrated that cellular encapsulation of Brugia pahangi microfilariae in the haemocoel of the mosquito Anopheles quadrimaculatus was terminated by the formation of a basement membrane-like structure on the outermost surface of the cellular capsule. This structure occurred in the early stage of cellular encapsulation and was evident on the exterior surface of the plasmatocyte, when the active haemocytes were attaching to the already melanized microfilariae. The termination structure appears to be laid down by releasing the vesicle inclusions of haemocytes and has similarities in ultrastructure and cationic colloidal gold staining properties with that of mosquito basement membranes.

The aims of the study were to assess the effect of praziquantel on Schistosoma japonicum infection in pigs, and to elucidate the level of resistance to reinfection after treatment. Pigs were given a single infection with S. japonicum followed by a praziquantel treatment (40 mg/kg) week 8, reinfection week 12 and perfusion week 20 post-primary infection. Relevant control groups were included. Worm burdens, faecal and tissue egg counts, gross- and histopathology of the liver and specific liver enzymes were assessed. The results showed a 100% cure rate of praziquantel against S. japonicum in pigs. Worm nodules were present in equal numbers in the intestinal wall 4 and 14 weeks post-treatment. Treatment did not significantly reduce the number of tissue eggs neither 4 nor 14 weeks post-treatment. No worm nodules or worm-induced lesions were found in the livers of the treated pigs and the levels of liver enzymes were comparable in treated and non-treated infected pigs. Periportal and septal fibrosis regressed following treatment. Faecal egg counts were significantly reduced 2 (56%) and 4 (82%) weeks after treatment. Challenge infection 4 weeks post-treatment did not result in establishment of new worm pairs. Praziquantel proved to be highly effective against S. japonicum in pigs without causing pathological side-effects in the liver.

An aspartic proteinase precursor, herein named BYC (Boophilus Yolk pro-Cathepsin) was isolated from eggs of the hard tick, Boophilus microplus. As judged by electrophoresis on sodium dodecyl sulfate polyacrylamide slab gel (SDS–PAGE), purified BYC presented 2 bands of 54 and 49 kDa, bearing the same NH2-terminal amino acid sequence. By Western blot analysis, BYC was also found in the haemolymph, indicating an extraovarian site of synthesis. Several organs were incubated in culture medium with [35S] methionine, and only the gut and fat body showed synthesis of BYC polypeptides. Protein sequencing of both the NH2-terminal and an internal sequence obtained after cyanogen bromide (CNBr) cleavage of BYC revealed homology with several aspartic proteinase precursors. Incubation at pH 3·5 resulted in autoproteolysis of BYC, which produced the mature form of the enzyme, that displayed pepstatin-sensitive hydrolytic activity against haemoglobin. Western blot analysis using anti-BYC monoclonal antibodies showed proteolytic processing of BYC during embryogenesis and suggested activation of the enzyme during development. A role of BYC in degradation of vitellin, the major yolk protein of tick eggs, is discussed.

Saliva of blood-feeding arthropods promotes infection by the vector-borne pathogens they transmit. To investigate this phenomenon in vitro, cultures of mouse L cells were treated with a salivary gland extract (SGE) prepared from feeding ticks and then infected with vesicular stomatitis virus (VSV). At low input doses of VSV, viral yield was increased 100-fold to 10000-fold by 16–23 h post-infection compared with untreated cultures, and depending on the SGE concentration. SGE-mediated acceleration of viral yield corresponded with the earlier appearance of VSV nucleocapsid protein as detected by 2-dimensional electrophoresis of infected cells. The observation that physiological doses of virus (i.e. doses likely to be inoculated by an infected arthropod vector into its vertebrate host during blood-feeding) respond to SGE treatment in vitro provides a new opportunity for identifying the factors in tick saliva that promote virus transmission in vivo.

The competence of 7 different stocks of Rhipicephalus appendiculatus and R. zambeziensis to transmit 2 different stocks of Theileria parva was compared by feeding nymphae of each tick stock simultaneously on infected cattle and assessing the infections in the salivary glands of the resultant adult ticks. There were significant differences in the patterns of infection of the 2 stocks (T. parva Muguga and T. parva Boleni) in the different stocks of ticks, and these differences were shown to be reproducible. The Muguga tick stock from Kenya and the Zambia tick stock from Eastern Province had the highest infections of T. parva Muguga and T. parva Boleni respectively. The Zambia Southern Province tick stock and the Zimbabwe Mashonaland West tick stock had the lowest infections of T. parva Muguga and T. parva Boleni respectively. The difference in mean abundance of infection between the most and least efficient vector for T. parva Muguga was 63·3 while that for T. parva Boleni was 54·4 infected acini. The implications of these results for laboratory transmission of T. parva and for the epidemiology of theileriosis are discussed.

The polymerase chain reaction (PCR) method was used to characterize trypanosome infections in tsetse flies from 3 sleeping sickness foci in Cameroon. The predominant tsetse species found was Glossina palpalis palpalis. An average infection rate of 12·1% was revealed by microscopical examination of 888 non-teneral tsetse flies. PCR amplification analyses for trypanosome identification were carried out on 467 flies, with primer sets specific for Trypanosoma (Trypanozoon) brucei s.l., T. (Duttonella) vivax, T. (Nannomonas) simiae and forest type T. (Nannomonas) congolense. Of 467 flies 93 were positive by microscopical analysis while PCR succeeded in identifying 89 positive flies. Of the PCR-positive flies 34 (38·2%) were negative by microscopical examination. PCR amplification, when compared to the parasitological technique, gave a higher estimate of infection rate of trypanosomes in natural tsetse populations. The PCR technique did, however, fail to identify 40·9% (38/93) of the parasitologically positive flies. The reasons for this failure are discussed. The overall prevalence of mixed infections, assessed by PCR, was 37·1%; the majority (72·7%) involved T. brucei and forest type T. congolense.

A mechanism for eggshell production in Schistosoma mansoni has been proposed (Wells & Cordingley, 1991), and suggests that the release of eggshell protein globules from the vitelline cells occurs under alkaline conditions within the ootype followed by their subsequent fusion to form the eggshell. Fusion and tanning of these components produces eggshell which autofluoresces. The present study was carried out to determine whether a similar process operates in Fasciola hepatica. A number of drug treatments were used to disrupt key steps in the maturation of vitelline cells. Treatment with the calcium ionophore lasalocid (1×10−5m) led to the premature release of eggshell globules from the vitelline cells but not their fusion. Incubation in monensin (1×10−6m), a sodium ionophore and ammonium chloride (NH4Cl) (5×10−2m), a weak base, resulted in the premature fusion of eggshell protein globules within the vitelline cells and premature tanning of the eggshell protein material. The copper-containing enzyme, phenol oxidase, is thought to be involved in the tanning process during the production of eggs. Diethyldithiocarbamate (DDC, 1×10−3m) is a phenol oxidase inhibitor and treatment with this compound, in combination treatments with monensin and NH4Cl, prevented fusion of the vitelline cell globules and tanning of the shell protein material. The results of the study suggest that the mechanism for eggshell formation in F. hepatica is similar to that proposed for S. mansoni and may be common to other trematodes as well.

The effects of dietary urea supplementation and of a 10-week trickle infection regime, simulating chronic exposure to Haemonchus contortus, on the zymogenic population of the abomasa of Hampshire Down lambs was examined. At necropsy a variety of parameters including plasma pepsinogen concentrations, the wet weights of abomasal fundic mucosal pieces and the amounts of pepsinogen contained in them, were assessed. Tissue pepsinogen concentration was measured as the total, acid-stable proteolytic activity present in mucosal homogenates, as well as immunohistochemically. The immunohistochemical findings were quantified using computer-aided image analysis. Elevation of plasma pepsinogen concentrations in infected animals was of borderline significance (P=0·06). The fundic mucosae of infected animals were heavier (P<0·02) than those of control animals, but there was no overall change in the pepsinogen content of tissues. Immunohistochemistry revealed that infected animals had increased numbers of zymogenic cells, due to mucous cell hyperplasia and the adaptation of cells to produce both mucins and pepsinogen. The pepsinogen content of chief cells, the major source of pepsinogen in uninfected animals, was reduced in infected lambs. Image analysis confirmed that at a mid-point of the mucosa of infected animals there was increased pepsinogen-specific immunoreactivity that corresponded with areas of mucosal hyperplasia. Mucous cell hyperplasia might therefore allow the maintenance of pepsinogen secretion in infected animals even if chief cell output is reduced.

The effect of the nematode Toxocara canis on social behaviour and anxiety levels of adult male outbred (LACA) mice was examined following infection with a single dose of 2000 ova. The actual number of larvae recovered from the brain of each individual mouse was determined after behavioural testing. The effect of the parasite on mouse behaviour was analysed by both the initial dose administered (i.e. infected versus control) and the degree of infection in the brain. There was substantial variation in the number of larvae recovered from the brains of the individual mice and the magnitude of behavioural change was associated with the level of infection. Examination of social behaviour for both analyses revealed that the infection reduced levels of aggressive behaviour and increased levels of flight and defensive behaviours. High infection in the brain induced the greatest degree of behavioural change which decreased in mice with lower infections. In contrast the analysis of anxiety levels in mice by initial dose administered revealed no difference between infected and control mice. Mice with low infection in the brain, however, displayed a greater level of risk behaviour by spending more time in the vicinity of a predator odour and in the light area of a light/dark paradigm than control or high infection mice. The results suggest that the behaviour of mice infected with T. canis is influenced by the number of larvae accumulated in the brain. This may have important consequences for the conclusions drawn on the effect of this parasite on murine behaviour.