A specific extracellular proteinase, degrading selectively the cecropin-based defence system of insects, is secreted into the larval body during parasitism of the greater wax moth by the Heterorhabditis bacteriophora/Photorhabdus luminescens complex and by phase 1 of P. luminescens. The proteolytic digestion of insect inducible cecropin-like immune molecules was demonstrated by the disappearance of the Galleria mellonella cecropins and purified Hyalophora cecropin B peptide PAGE bands upon exposure to infected extracts, and a similar abrogation of antibacterial activity using an agar diffusion assay. Proteolytic activity of infected extracts produced by nematode/bacterial complex and phase 1 variant of P. luminescens was shown to be correlated with cecropin-inhibitory activity, suggesting that this anti-cecropin agent may be responsible for the ability of bacteria to establish infection and the insecticidal nature of H. bacteriophora. Antibacterial activity of Galleria lysozyme and that of chicken egg-white lysozyme to which P. luminescens is insensitive, was unaffected by H. bacteriophora proteinase.

Antibodies to a non-repeat region of the Plasmodium falciparum antigen Pf155/RESA were investigated for their capacity to inhibit parasite cytoadherence to melanoma cells and parasite growth in vitro. The activities of these antibodies were studied since the target region in Pf155/RESA includes a cytoadherence-related motif also found in loop 3 and 7 of human erythrocyte band 3 protein. Overlapping multiple antigen peptides (MAPs) together spanning residues 199–220 of Pf155/RESA were used to raise antibodies in rabbits. Analysis of the fine specificity of these antibodies revealed that antibodies raised against largely overlapping sequences displayed highly different specificity patterns. Similarly, striking differences were seen when analysing the biological effect of antibodies to these MAPs. Antibodies to the cytoadherence-related motif of Pf155/RESA, as well as antibodies raised against a MAP based on a corresponding band 3 motif, inhibited cytoadherence but not parasite growth. In contrast, antibodies to sequences adjacent to the Pf155/RESA cytoadherence motif inhibited parasite growth in vitro but had no effect on cytoadherence.

A decline in serum thyroxine (T4) occurs in Nya[ratio ]NYLAR female mice infected with Toxoplasma gondii. To ascertain whether the hypothyroxinaemia might be the result of primary thyroid dysfunction, 2 parameters of thyrofollicular cell function were monitored to determine (a) if the cell surface membrane receptors for thyroid-stimulating hormone (TSH) were operative, and (b) whether the cyclic adenosine monophosphate (cAMP)-dependent cascade of intracellular events leading to the release of T4 was responsive to exogenous cAMP. Our results indicated that both parameters were intact and functional in the infected-mouse thyrocytes. However, the elicited T4 responses were distinctly diminished in magnitude, reflecting a lack of readily available thyroidal T4 reserves. Because the continuing synthesis, storage, and release of T4 is dependent on the pulsatile stimulation of the thyroid by TSH, we suggest that the depletion of T4 reserves is likely due to perturbation of the pulsatile release of TSH from the pituitary, rather than to primary thyroid malfunction.

Mice infected with Toxoplasma gondii manifest a rapid decline in serum thyroxine (T4) levels. To locate the locus of the hypothyroxinaemia, the integrity of the pituitary–thyroid axis of infected mice was assessed by a thyrotropin-releasing hormone (TRH) assay. A rise in serum T4 after inoculation of TRH implies the release of thyrotropin (thyroid-stimulating hormone) from a functionally intact pituitary. Administration of a single, large-dose (1 μg) bolus of TRH to infected mice induced a positive, although subnormal, T4 response. In contrast, when infected mice were pre-treated with a series of low-dose (5 ng) pulses of TRH prior to the bolus challenge, the T4 response was markedly enhanced. We suggest that the multiple inoculations of low-dose pulses of TRH ‘primed’ the pituitary (and secondarily the thyroid) and led to replenishment of their readily available hormone reserves and the heightened response to stimulation. These observations indicate that the locus of thyroid dysfunction is in the hypothalamus, not the pituitary or thyroid, and apparently involves impairment of the pulsatile release of TRH.

A new and simple colorimetric method has been developed for determining activity in vitro against Giardia intestinalis. The microtitre plate assay is based upon the nucleoside hydrolase activity released from G. intestinalis by lysis. Action of the nucleoside hydrolase on the substrate analogue, 4-nitrophenyl β-d-ribofuranoside (NPR), gives rise to a coloured product which may be determined directly by the change in absorbance. A number of other such nucleoside analogues can be similarly used, but NPR is the preferred substrate, since it gives high enzymic activity at a relatively low substrate concentration. The IC50 values determined using this method for the known anti-giardials metronidazole, tinidazole and furazolidone were consistent with previously published values. The method is simple, does not involve radioisotopes or complex instrumentation, and thus provides a convenient method for screening potential anti-giardial agents.

The sequences for the entire intergenic spacer (IGS) and 3′ end region of the large subunit (28S) ribosomal RNA gene are presented for Schistosoma intercalatum, S. haematobium and S. mansoni. The IGS was found to have at least 2 size formats for S. intercalatum and S. haematobium and the region for all 3 species contains numerous repeats and evidence of recombination. An A+T rich sequence found in S. intercalatum and S. haematobium is described and its possible function and origins are discussed. The amplification of this region by means of the polymerase chain reaction can be used to discriminate clearly between the 3 species involved in this study. The putative end of the 28S gene is identified.

In order to investigate the molecular taxonomy within Trypanosoma cruzi, the ribosomal small subunit (18S) gene was amplified by polymerase chain reaction (PCR) from a selection of 21 stocks and 3 outgroup taxa. Amplification products were digested with 10 restriction enzymes; restriction fragments were separated by polyacrylamide gel electrophoresis and profiles were visualized by silver staining. Upon analysis of such riboprint profiles, an estimate of pairwise phenetic distance between stocks of T. cruzi was calculated. Upon principal coordinate analysis of this data matrix, a tendency towards a bi-polar grouping of stocks was observed. These 2 groups were predominantly either zymodeme 1 stocks or zymodeme 2 stocks. The position of zymodeme 3 stocks remained intermediate between the 2 groups but did not form a coherent group by themselves. It would therefore appear premature to warrant division of T. cruzi into 2 discrete taxa or subspecies until the relationships of further zymodeme 3 stocks are elucidated.

To test the homogeneity of 18S sequences within Trypanosoma cruzi, riboprint profiles were separated by temperature gradient gel electrophoresis (TGGE). Upon interpretation of melting curves of fragments within a riboprint profile, there appeared to be two 18S sequence types within each stock examined. Two similar types were also observed within outgroup taxa Trypanosoma conorhini, Trypanosoma rangeli and Leishmania braziliensis. From DNA hybridization studies, these fragments were shown to have homology to the 18S V1 region. There are therefore two 18S V1 regions, differing in sequence, present in all taxa examined. When only a single 18S sequence is used to represent each taxa for phylogenetic inference, comparisons may be between paralogous and not orthologous copies of this region, such that, inferred relationships may merely reflect a gene history. This seriously questions the current molecular phylogeny of these protozoa using 18S data.

The maturation and quantification of Theileria lestoquardi (T. hirci) parasites in unfed and partially fed adult Hyalomma anatolicum anatolicum ticks was studied using (1) methyl green pyronin (MGP) staining of salivary glands, (2) in vitro infection of peripheral blood mononuclear cells (PBM) with parasites harvested from infected ticks and (3) a semi-quantitative polymerase chain reaction (PCR). With MGP staining the greatest infection rate was seen in unfed ticks. Feeding resulted in a gradual reduction in the number of infected acini with a concomitant increase in the maturity of the parasites. In vitro infection of sheep PBM with titrated ground-up tick supernate (GUTS) demonstrated that infectivity peaked between 2 and 4 days of tick feeding whereas GUTS prepared from unfed ticks was not infective. The polymerase chain reaction (PCR) was both sensitive and specific, detecting T. lestoquardi DNA in unfed and partially fed ticks, with a maximum sensitivity of 0·022 infected acinus/tick in 2-day fed ticks, though it gave no indication of the infectivity of the parasite.

A 120 kDa antigen produced by juvenile female Litomosoides sigmodontis (Juv-p120) was isolated and purified. The amino acid composition of the molecule was determined. Juv-p120 was shown to be highly modified with N,N-dimethyl-aminoethanol (28·4 mol%). Treatment of Juv-p120 with potassium hydroxide (β-elimination) or with sodium m-periodate leads to the destruction of epitopes recognized by antibodies immune affinity-purified with isolated Juv-p120. Juvenile L. sigmodontis were shown to release Juv-p120 into the pleural cavity of infected Mastomys coucha before the onset of patency.

The macroparasites Cephenemyia trompe (Modeer) and Hypoderma (=Oedemagena) tarandi (L.) (Diptera: Oestridae), Linguatula arctica Riley, Haugerud and Nilssen (Pentastomida: Linguatulidae), Elaphostrongylus rangiferi Mitskevich (Nematoda: Protostrongylidae), and abomasal nematodes (Nematoda: Trichostrongylidae) were sampled in semidomestic reindeer calves (Rangifer tarandus (L.)) (ca. 8 months of age) in northern Norway in 1988 (n=160) and 1989 (n=191). Each parasite showed an aggregated (clumped) distribution among the hosts and fitted the negative binomial distribution. Analyses of interspecific associations in intensities showed that there was no consistent covariation among the parasites apart from a weak correlation (Kendall's tau 0·104, P=0·007) between the 2 oestrids C. trompe and H. tarandi. This lack of covariation reveals that the parasites were distributed independently of each other, and suggests that innate host resistance is not a dominant factor that has a significant simultaneous effect on all parasites. The aggregated distribution of each parasite species is hypothesized to be caused by (1) random events and heterogeneities in host behaviour that create unequal transmission (exposure) rates, or (2) by heterogeneities in parasite specific immunocompetence among host individuals. Factors in hypothesis (1) are probably the most important at low transmission rates.

A new category of signalling molecules – transmitter gases – has appeared. Nitric oxide (NO) is generated by nitric oxide synthase (NOS) and diffuses as a short-lived transcellular messenger through the plasma membrane. NADPH-diaphorase (NADPH-d) is a marker enzyme for NO-producing neurons. In this study the pattern of NADPH-d stained neurons in Diphyllobothrium dendriticum is described and compared to the pattern of aminergic and peptidergic neuronal elements and to that of the musculature stained with TRITC-labelled phalloidin. NADPH-d staining was observed in neurons in the bilobed brain and along the 2 main nerve cords and in nerve fibres close to the body musculature and the musculature of the reproductive ducts, the walls of the testicular follicles and in sensory endings in the tegument. The NADPH-d staining reaction and the 5-HT or FMRFamide immunoreactivities occur in separate sets of neurons.