Host immunity will result in increased homozygosity at immunogenic loci if they encode products that elicit allele-specific immune responses. This increased homozygosity can be detected by comparison to ‘neutral’ (i. e. unselected) loci in the same genome which act as controls for the various epidemiological factors, such as biting rate, which affect homozygosity. Numerical results suggest that homozygosity should be 20 to 500 % higher at immunogenic loci, a result which is robust to changes in host death rate and the degree of linkage between the immunogenic and neutral loci. The same logic applies to loci which encode drug resistance: treated individuals with resistant infections will transmit zygotes homozygous for the resistance allele. It is argued that this increased homozygosity at putative immunogenic loci can act as a diagnostic feature to test using field data. The method also serves as a potentially very powerful method of identifying immunogenic and drug-resistant loci in laboratory studies of species such as the murine malaria Plasmodium chabaudi.

Iron overload in BALB/c mice by treatment with ferric ammonium citrate promotes the hepatic development of Plasmodium yoelii in vivo and in vitro. This was the result of increased penetration of the parasite into hepatocytes since no effect was observed on parasite transformation or maturation. These results could explain why in endemic regions iron supplementation led, in certain studies, to an increase in clinical episodes of malaria and in the prevalence of malaria infection.

We have extracted a protein of 14 kDa from purified oocyst walls of several Eimeria species. Polyclonal antibodies were raised in rats against the 14 kDa proteins of E. acervulina and E. tenella. On immunoblots these antisera reacted in a highly specific manner with the homologous 14 kDa antigens, but not with heterologous antigens. In addition, specific binding of the two antisera to oocyst wall fragments of E. acervulina and E. tenella was demonstrated by immunofluorescence. Partial amino-terminal sequences comprising 20 amino acid residues were obtained from the 14 kDa oocyst wall proteins of E. acervulina and E. tenella. They are characterized by an abundance of amino acids containing hydroxyl groups in their side chains (serine, tyrosine, threonine). Binding of the oocyst wall protein of E. tenella by peanut agglutinin indicates the presence of O-linked carbohydrates.

Neospora caninum and N. caninum-like organisms are cyst-forming coccidian parasites known to cause neuromuscular disorders in dogs and abortion in cattle. In this article we report on the use of the polymerase chain reaction (PCR) for the detection of DNA from N. caninum. After determining the sequence of the internal transcribed spacer 1 (ITSl) of N. caninum and Toxoplasma gondii, and part of the sequences for & species of Sarcocystis, we designed a primer set for the amplification of a 279-base-pair fragment of ITSl from N. caninum. The PCR system made possible the specific detection of 5 N. caninum organisms and no amplification was observed from any of the other cyst-forming coccidia tested, including the closely related T. gondii. Furthermore, we were also able to demonstrate the presence of N. caninum in brain and lung tissue samples from experimentally infected mice. Our data also link the 5-8S rRNA gene for T. gondii and N. caninum to the 16S-like rRNA gene, within the rDNA unit.

Neospora caninum is a recently identified coccidian parasite which was, until 1988, misdiagnosed as Toxoplasma gondii. It causes paralysis and death in dogs and neonatal mortality and abortion in cattle, sheep, goats and horses. The life-cycle of Neospora has not yet been elucidated. The only two stages identified so far are tissue cysts and intracellularly dividing tachyzoites. Very little is known about the biology of this species. We have set up a fluorescence-based adhesion/invasion assay in order to investigate the interaction of N. caninum tachyzoites with bovine aorta endothelial (BAE) cells in vitro. Treatment of both host cells and parasites with metabolic inhibitors determined the metabolic requirements for adhesion and invasion. Chemical and enzymatic modifications of parasite and endothelial cell surfaces were used in order to obtain information on the nature of cell surface components responsible for the interaction between parasite and host. Electron microscopical investigations defined the ultrastructural characteristics of the adhesion and invasion process, and provided information on the intracellular development of the parasites.

Acetylcholinesterase (ACHE) is present in the muscle and on the tegument of schistosomes. Molecular forms of schistosome AChE were examined because particular AChEs are found in tissues of distinct function elsewhere. The dimeric globular form (G2) is the only form evident in adult Schistosoma haematobium: 32 % of the muscle AChE is hydrophilic and 61 % is membrane associated. A substantial amount of this enzyme is phosphatidylinositol (PI) anchored since it could be released by PI-specific phospholipase C from both muscle and tegumental membranes.

A rapid, visually read, dot-ELISA developed for the detection and differentiation of trypanosome species in tsetse flies (Glossina spp.), was field tested alongside the standard fly dissection method on a ranch in south eastern Kenya. Of 104 G. pallidipes dissected, 2 were found to be infected with trypanosomes in their midguts. By the dissection method the infecting trypanosome species could not be identified, as both flies had no salivary gland infections. However, using the dot-ELISA, the 2 flies were shown to be infected with Trypanosoma congolense in their midguts. The midguts of an additional 6 (5·8%) of the 104 G. pallidipes tested positive for T. congolense in the dot-ELISA, even though no trypanosomes were seen on dissection. The infection rate for this fly species as determined using the dot-ELISA, therefore, was 7·7% for T. congolense in midgut infections compared to 1·9% identified by fly dissection. The salivary glands and mouthparts of the 6 additional tsetse flies identified by dot-ELISA were all negative as determined by the 2 techniques. None of 390 G. longipennis flies dissected and examined for trypanosomes in the midgut, salivary glands and mouthparts was shown, by this method, to be infected. Using the dot-ELISA, however, 17 (4·4%) of the flies tested positive for T. congolense in the midgut, whilst the salivary glands and mouthparts of the same flies were negative. Thus, the dot-ELISA appears to be more sensitive than the fly dissection method under field conditions. Moreover, the dot-ELISA can be performed in the field without electricity. It is simple to perform, and was not affected by high ambient temperatures (22–32°C), or by contamination of reactants with dust.

Models have predicted that directly transmitted macroparasites may influence the abundance of forage plants in herbivore grazing systems by reducing the food intake of their host. Evidence of parasite-induced alterations in host food intake is, however, limited mainly to sheep, cattle and laboratory rodents. We estimated the effect of naturally acquired parasite infections on the appetite of reindeer. Food intake was significantly lower in infected reindeer compared to animals in which the parasites had been experimentally removed. Among the infected animals there was a significant negative relationship between intensity of the directly transmitted macroparasites (i. e. gastrointestinal nematodes) and mean food intake, indicating that the lower food intake was caused by these parasites. The time-specific onset of depression in food intake is also consistent with seasonality in the pathogenic effect from gastrointestinal nematodes. This shows that parasite-induced changes in herbivore food intake is not restricted to agricultural systems, and implies that parasites may have impact on the dynamics of a wide range of herbivore plant communities.

The presence of retinol-binding protein (RBP) activity in Onchocerca cervicalis adult worms and interaction with ivermectin has been studied using high pressure size exclusion chromatography (HPSEC). Four distinct peaks of [3H]-retinol incorporation were obtained corresponding to approximate molecular weights of 150, 67, 19·7 and 4–6 kDa, the 2 smaller Mr peaks accounting for most of the binding activity. Competition for binding using non-labelled retinol at 200-fold molar excess indicated that specific binding of retinol occurred only to the 19–7 kDa fraction. Competition by ivermectin also inhibited binding of [3H]-retinol to the third peak. Following incubation with [3H]-ivermectin & peaks of similar molecular weights were also detected by HPSEC in soluble adult worm homogenate, However, in this case the 150 kDa fraction was most prominent. Both non-labelled ivermectin and non-labelled retinol at 200-fold molar excess reduced binding of [3H]-ivermectin to all & fractions. These data indicate that the putative Onchocerca RBP has an approximate molecular weight of 19·7 kDa, that retinol also binds to 3 additional fractions non-specifically, that the pattern of binding of ivermectin to adult worm material is quantitatively and qualitatively different from the binding exhibited by retinol, and that ivermectin interferes with the binding of retinol to the 19·7 kDa Onchocerca protein.

This paper demonstrates that the activities of glycogen phosphorylase (GP), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are reduced in adult worms of the filarial nematode Litomosoides carinii recovered from pyri-doxine-deficient cotton rats when compared to worms recovered from pyridoxine-sufficient controls. GP, ALT and AST activities were determined in adult worms L. carinii recovered from cotton rat hosts over a 20-week experimental period. Activities of GP, ALT and AST in the parasite showed a direct correlation with the dietary pyridoxine intake of their host. Throughout the experiment, enzyme activities were significantly lower (P < 0·001) in worms from rats fed a pyridoxine-free diet ad libitum that in worms from rats fed either a stock colony diet, a pyridoxine-free diet ad libitum with daily supplementation of 100 μg pyridoxine or limited amounts of pyridoxine-free diet with daily supplementation of 100 μg pyridoxine. The lower than normal activity of GP, ALT, AST and other enzymes dependent on the biologically active derivative of pyridoxine, the coenzyme pyridoxal-5-phosphate (PLP), interferes with the protein, carbohydrate and lipid metabolism of L. carinii and may in part cause the reduced establishment, development and growth of the parasite in pyridoxine-deficient hosts.

The effect of Anguillicola crassus (Nematoda) on gas composition in the swimbladder of eels (Anguilla anguilla) was studied using mass spectrometry in feral eels from two German rivers and in experimentally infected eels. In both naturally and experimentally infected eels significant correlations were observed between the proportion of oxygen in the swimbladder and level of infection with Anguillicola crassus. In swimbladders of naturally infected feral eels the contribution of oxygen to swimbladder gas was reduced by 36–62·9% and in experimentally infected eels it was reduced by 11·4–57% compared to uninfected controls. The proportion of CO2 appeared to be lower in infected swimbladders compared to uninfected ones. However, this change was not significant. The findings are discussed in relation to an altered structure of the swimbladder wall due to the parasite.

The response of individual adult males of the potato cyst nematodes, Globodera rostochiensis and G. pallida, to sex pheromones from adult females was investigated using electrophysiological techniques. Each male nematode was pierced with an electrode close to the cephalic region and then exposed to pheromones from virgin females. Cellular responses in the form of action potentials were recorded as spike activity. The spike frequency produced by G. rostochiensis and G. pallida males increased significantly after the application of their homospecific pheromone. The spike frequency produced by G. pallida males also increased significantly after the application of G. rostochiensis female sex pheromone. In contrast, males of G. rostochiensis showed no significant response to G. pallida female sex pheromone. The electrophysiological results support and considerably extend information from agar plate behavioural bioassays.

An electrophysiological preparation of Ascaris suum pharyngeal muscle suitable for recording changes of input conductance using a 2-microelectrode current clamp and pharmacological study is described. The preparation is shown to contain a glutamate-gated Cl (ion sensitive) channel sensitive to the avermectin analogue, milbemycin D. The application of glutamate produces a dose-dependent increase in Cl conductance and the effect of glutamate is potentiated by milbemycin D. Milbemycin D also produced a dose-dependent increase in input conductance.

The somatic muscle cells of the parasitic nematode Ascaris suum possess GABA receptors that gate chloride conductances in a similar fashion to the mammalian GABAA receptor subtype. These receptors mediate muscle relaxation and are the site of action of the anthelmintic piperazine. The properties of this receptor differ from the properties of the GABA-gated chloride receptors in the mammalian host, in particular they are not as sensitive to mammalian GABA receptor antagonists such as bicuculline and picrotoxin. Using two-electrode intracellular electrophysiological recording techniques from Ascaris muscle cells, we have tested the potency of a series of azole derivatives for their ability to block the chloride-dependent GABA response. The lead compound, SN606078, 2-(2,6-dichloro-4-trifluromethylphenyl)-4-(4,5-dicyano-lH-imidazol-2-yl)-2H-l,2,3-triazoIe, and 4 structurally related compounds reversibly blocked the conductance increase elicited by 30 μM GABA with IC50s of less than 10 μM. SN606078 (10 μM) decreased the slope of the dose-response curve for GABA, suggesting a non-competitive mechanism of action. In two-electrode voltage clamp experiments, 10μM SN606078 blocked the outward current elicited by 20 μM GABA in a voltage-dependent manner with 72 ± 2% inhibition at −20 mV and 49±6% inhibition at −40 mV. These observations indicate that SN606078 may act as an open-channel blocker of the GABA-gated chloride channel in A. suum.