Parasitic diseases are endemic in parts of the tropics, but there is no convincing evidence that their prevalence or incidence is increasing due to the HIV epidemic. Available scientific data on parasitic infections in patients with the Acquired Immunodeficiency Syndrome (AIDS) suggests a predominance of Pneumocystis carinii, Toxoplasma gondii and Cryptosporidium spp. For reasons which are unclear, parasitic infections such as Plasmodium falciparum, Strongyloides stercoralis and Entamoeba histolytica, where cell-mediated immune responses are also thought to be significant, do not appear to be opportunists of importance. It is being increasingly recognized that chemotherapy for parasitic diseases has a host-dependent component, although scientific data on this subject remain scanty. The management of opportunistic parasitic infections in patients infected with HIV is dogged by failures and relapses, aptly illustrating the notion of the relationship between chemotherapy and the immune response. This review discusses the immunity and chemotherapy of opportunistic parasite infections in patients infected with the Human Immunodeficiency Virus (HIV).

The humoral responses of Sprague–Dawley rats infected with Brugia pahangi were examined for up to 6 months after infection by ELISA, immunoblotting, and IFAT. In 2 experiments, 50% and 62·5% of rats developed patent, microfilaraemic infections. Mean adult worm burdens at autopsy were approximately 2% of the inoculum, and only patent rats yielded living adult worms. IgG antibody levels against crude somatic extracts (CSE) of all parasite stages and against adult excreted/secreted (ES) products were significantly higher in patent than non-patent rats. Both patent and non-patent rats produced anti-microfilarial surface antibody, as revealed by immunofluorescence. Immunostaining of Western blots by early infection sera showed no consistent difference in recognition of infective larval (L3) antigenic components by IgG or IgM antibody between eventually-patent and eventually-non-patent rats. By 26 weeks, however, patent rats recognized more components. The data suggest that antibodies against L3, adult, and microfilarial somatic antigens, ES antigens and microfilarial surface antigens do not correlate with the subsequent development of microfilaraemia in any individual rat.

Pectoral fins from juvenile rainbow trout (Oncorhynchus mykiss) were used in a bioassay, the object of which was to quantify the effect of simulated shadow stimuli on the transmission success of the cercariae. For a period of 60 min, parasites and fins were exposed to a sequence of computer-controlled shadow stimuli, continuous light or total darkness, and subsequently the number of infections was counted. Trials were conducted with cercariae 1, 12 and 24 h old. Within the constraints of the experimental procedure, shadows were found to increase significantly the number of infections achieved by the 12-h-old parasites. As the cercariae aged, their ability to infect host tissue declined. The relevance of these results to transmission in the natural environment is discussed.

Fluorescent lipophilic compounds can be used to label the surface membrane of Schistosoma mansoni by adding the compound in small amounts of organic solvents to aqueous medium in vitro. Under these conditions it is difficult to follow routes of distribution of the label. Here we have absorbed nitrobenzoxadiazolamine methylamino–(NBD)–ceramides to positively charged Dowex beads, and incubated the labelled beads with living parasites. The NBD–ceramide transfers to the surface membrane as a patch 50–100 μm in diameter, after which the label can be seen localized in the gut and in a very concentrated form in organelles within the oesophageal gland cells. Subsequently the labelled compound can be found in organelles within other body cells, including subtegumental cells. We show that the labelled ceramide has been transported from the patch in the surface membrane through internal membrane systems to the destination in the gut and oesophageal gland and not transported through the gut via the external medium. A different pattern was observed when NBD–cholesterol was used. The pharynx was rapidly labelled when NBD–cholesterol was added in medium with or without serum or attached to red blood cells only. Diffuse labelling of the surface membrane and oesophageal gland occurred. We have demonstrated a novel route of lipid transport within the parasite. The route requires the surface membrane to have very specialized regions to facilitate such transport.

Clones of Trypanosoma congolense which express resistance to the widely used trypanocide isometamidium chloride accumulate less of the drug than clones which are sensitive to drug treatment. A mathematical model has been developed which was able to predict theoretical lines representing the uptake kinetics in trypanosomes which were sensitive to isometamidium, as well as for resistant trypanosomes in which reduced accumulation was a result of either reduced uptake or enhanced efflux of the drug. Data from drug uptake experiments were then fitted to these theoretical lines. While the value for drug efflux could not be separated from the dissociation constant of the trypanosomes for isometamidium, it was demonstrated that reduced accumulation is not a result of reduced uptake of isometamidium by drug-resistant trypanosomes.

Trickle infections with a hamster-adapted strain of the hookworm Ancylostoma ceylanicum were studied by administering doses of 5–30 larvae twice weekly to inbred DSN hamsters. The worm burdens were regulated at very low levels, and this was found to be independent of the size of the infective dose. It is likely that there is some turnover of adult worms during trickle infection, as larvae of all stages were recovered from most time-points. This regulation is immunologically mediated and both the worm burdens and fecundity were increased in hamsters that were immunosuppressed by cortisone treatment. A trickle infection regime also induced a 67% protective immunity to a single subsequent challenge. The resistance that occurred during trickle infections was, however, incomplete, and some worms were found to survive in hamsters that had been repeatedly infected for over 10 weeks. Thus, although hamsters are capable of regulating the infection, some worms are capable of surviving the host immune effectors.

The miracidium of Sanguinicola inermis contains a stylet and rodlet complex located within the single apical gland, which lies between a pair of lateral glands. The miracidial stylet consists of an arrangement of hollow tubes, composed of microtubules, connected at their base to large secretory granules and opening anteriorly through the apical papilla. A single rodlet lies adjacent to the stylet base and at least 8 rodlets are arranged at the apical tip of the stylet. The surface plasma membrane of the apical papilla is drawn into knob-like projections and 2 ciliated sensory endings are associated with the papilla. The ultrastructure of the apical gland, especially the stylet and rodlet complex, is related to the requirement for sanguinicolid miracidia to penetrate the double barrier of fish and snail hosts.

Evidence has accrued to indicate that host defence mechanisms enhance the efficacy of many of the drugs used to treat infectious diseases. Because of this, and also because of the likelihood of increased pathogen loads in immunoincompetent hosts, some infections are less likely to be completely cured by normal regimens of chemotherapy in individuals with drastically impaired immune responsiveness. In such circumstances natural selection could result in the accelerated emergence of drug-resistant pathogens.

A simple technique is described for preparation of Giardia cysts from faecal samples, the growth of trophozoites in suckling mice and the isolation of trophozoites for genetic analysis by allozyme electrophoresis. In total, 125 new isolates of Giardia have been collected from human and animal sources over a wide geographical area of South Australia and the Northern Territory of Australia. A number of long-established axenized isolates of G. intestinalis belonging to Groups I and II also adapted to grow in suckling mice. These findings indicate that suckling mice are permissive hosts for a variety of genetically dissimilar but morphologically similar organisms of the G. duodenalis type and that this in vivo technique may be less selective than isolation by in vitro culture. The use of suckling mice has revealed that infections can be composed of mixed genotypes and that isolation and purification techniques can be selective. Allozymic interpretation is essential to reveal the genetic complexity of such mixtures

The survival, growth and development of Onchocerca lienalis 3rd-stage (L3) larvae implanted into mice within micropore chambers has been studied with a view to developing a vaccination model for studies of protective immunity in onchocerciasis. The influence of host genetics on worm recoveries and development (growth and moulting rate) was analysed in a panel of inbred mice (CBA, BALB/c, DBA/2, SJL, 129J, C57BL/10 (B10), C3H/He and NIH), together with mice of BALB and B10 backgrounds with different major histocompatibility complex (H-2) genes (BALB/c, BALB.K, BALB.B and B10, B10.D2/n, B10.BR, B10.S). Parasite recoveries and development were similar in all mouse genotypes tested. They were unaffected by procedures designed to block or modulate phagocytic cell function with carbon or carrageenan, or to suppress inflammation by treatment with hydrocortisone acetate. A comparison of chambers sealed with membranes designed to admit (5·0 μm pore size) or exclude (0·2 μm pore size) host cells demonstrated no effect on the percentage recovery of living larvae, although dead larvae were more frequently retrieved when cells were excluded. Recoveries and rates of development of larvae implanted into immunodeficient scid mice and athymic Hooded rats were similar to those recorded in immunocompetent controls. We conclude that host genetic factors and immunocompetence are not significant determinants of survival, growth or development of O. lienalis larvae implanted within micropore chambers into naive mice. Despite its limitations, the use of this system merits further investigation as an approach to the study of protective immunity against developing larvae in onchocerciasis.

Four histones, a, b, c, d from procyclic Trypanosoma brucei brucei, which show similarities with the amino acid composition of the core histones H3, H2A, H2B and H4, were isolated and cleaved with Endoproteinase Glu-C. The fragments were separated by FPLC reversed phase chromatography and a subset of the fragments (a5, a9, b6, c8, d3, d9, d11) was subjected to sequence analysis. A 54–71% identity was found in the sequences of the fragment c8 and the C-terminal half of H2B and of three fragments of protein d covering the N-terminal half as well as the C-terminal region of H4. The amino acid sequence of the fragment a9 showed a 57 and 54% identity with H3 sequences of Saccharomyces cerevisiae and Xenopus laevis. Neither the a5 nor the b6 sequence could be aligned with histone sequences of other eukaryotes. The significant differences of 21–48% between the T. b. brucei, histone sequences and those of calf thymus histones, which are more pronounced than the differences of Tetrahymena pyriformis and the higher eukaryote, resulted partially from replacements of amino acids with different properties and indicate specific patterns of histone–histone and/or histone–DNA contact sites in the nucleosome of T. b. brucei. These differences, together with the lack of a functional histone H1, may be sufficient to explain the lack of a salt-dependent formation of the nucleosome filament into the 30 nm fibre, which reflects alternative methods of organizing and processing the genetic information in the nucleus of the protozoan parasite and which may be of chemotherapeutic significance.

The regulatory role of tumour necrosis factor (TNF) was investigated in murine infection with tetrathyridia of Mesocestoides corti. Recombinant TNFα reduced macrophage larvicidal activity in vitro. M. corti primed mice for TNF release in response to bacterial lipopolysaccharide (LPS) in vivo. TNF activity was amplified 100-fold at 14 days post-infection (p.i.), with a further rise at day 28 p.i. Maximal inflammatory reaction was observed histologically in the liver at the height of TNF activity. Hepatic necrosis was located within inflammatory foci, but not within the vicinity of the parasite itself, suggesting that TNF may contribute to the pathogenesis of infection. Peritoneal cells from infected mice, when stimulated with tetrathyridia in vitro, showed a 4-fold increase in TNFα activity at day 14 p.i. However, when peritoneal cells were stimulated with LPS in vitro, a marked increase in TNFα secretion was observed at 2 months post-infection followed by a slow decline. It is suggested that impaired macrophage effector function, previously attributed to endogenous endotoxin, which gains access to peritoneal macrophages through an inability of the liver to detoxify endotoxin, may be mediated through TNFα.

To determine whether the relative abundance of immature Ixodes dammini (the vector of Lyme disease and human babesiosis) is related to habitat structure, we examined tick burdens on their main host, the white-footed mouse (Peromyscus leucopus), in 4 structurally diverse sites on Great Island, Massachusetts, USA. Vegetation structure at each site was quantified with respect to 25 habitat variables. Principal components analysis was used to reduce this set of habitat variables to seven new and orthogonal variables. Immature tick abundance varied widely among grids. Regression analysis of tick burdens on the habitat principal components showed that larval burdens were related strongly to the density of woody vegetation and negatively to herbaceous vegetation. Nymphal burdens were related negatively to herbaceous vegetation, but the relationship was not as strong as in the case of larvae. An experimental reduction in the abundance of white-tailed deer (Odocoileus virginianus), the main host of adult ticks, substantially reduced tick burdens and altered their relationships to habitat structure. Nymphal burdens were unrelated to habitat structure following deer removal. Manipulating habitat structure may have utility as a control strategy against this important vector.

To facilitate the completion of their life-cycle, many helminth parasites have evolved the ability to manipulate the behaviour of their intermediate host in order to make it more likely to be eaten by the parasite's definitive host. Here, we determined whether the cestode Eubothrium salvelini modifies the behaviour of its intermediate host, the copepod Cyclops vernalis, and makes it more susceptible to predation by brook trout, Salvelinus fontinalis, the parasite's final host. Following the experimental infection of copepods, the spontaneous activity of infected and control subjects was quantified weekly. In addition, we regularly quantified predation by individual brook trout fry on known numbers of infected and control copepods. At approximately the time when the cestode larvae became infective to fish (2–3 weeks following infection), the infected copepods started to swim more actively than uninfected controls. Also at that time, infected individuals became more likely to be captured by fish than uninfected ones. Copepod size and intensity of infection had no significant effect on their behaviour or their risk of being eaten by fish. Thus cestode- induced changes in copepod swimming activity can lead to infected copepods becoming highly vulnerable to fish predators, and may have resulted from selection on the parasite to increase its transmission success

An enzyme-linked immunosorbent assay (ELISA) using crude worm extracts (CWE) and mixtures of these as antigens of five Spanish isolates (P, C, B1, B2 and W) was developed for detecting homologous and heterologous experimental infections with these isolates between – 14 and 82 days post-infection (p.i.) in white and Iberian pigs. A total of 243 pigs (Ilberian or cross-bred with this race) with numerous parasitic infections were also screened for the presence of antibodies to a mixture of CWE of C, B1 and B2 isolate. The test showed a specificity of 93·1–98·9% depending on the cut-off values and a maximum sensitivity of 92·8–100% between days 34 and 82 p.i. A low grade of infectivity was shown in the T3 isolates compared to the T1 isolates (P, C, B1 and B2) but high cross-reactions were observed between all the isolates with minor differences between P and W isolates. The highest antibody response was found in P infections and the lowest in pigs infected with the W isolate. A clear association between the presence of several parasitic infections and false positive reactions was not found, but an important relation was shown between high background levels and the Iberian race in experimentally and conventionally raised pigs

Two-dimensional polyacrylamide gel electrophoresis was used to examine the differences in total protein composition between two motile stages and two sedentary stages of the potato cyst-nematode, Globodera rostochiensis. Using a sensitive silver stain, 542 reproducible protein spots were distinguished. A list of these spots is presented, showing their apparent molecular weights, estimated isoelectric points, and occurrences in the different developmental stages. When the protein patterns were compared, 401 spots were found to change their presence or size in one or more of the four developmental stages. It is therefore estimated that during the post-embryonic development of G. rostochiensis, 74% of the polypeptides undergo modulation of their synthesis, or are affected by protein degradation or modification. In the motile stages several abundant proteins were present, which disappeared or decreased in concentration in the sedentary stages. Some of these proteins are presumably muscle proteins, and their modulation may illustrate the degeneration of body-wall musculature in the sedentary stages. It is concluded that the potato cyst-nematode has a very dynamic protein metabolism.

The present study compares parasite-specific antibody responses in two Caribbean communities with high and low levels of Trichuris trichiura transmission. The age-dependency of antibody levels suggest that IgG1 and IgG2 levels relate to the current intensity of infection (as assessed by density of eggs in stool (e.p.g.) and reflect the age–intensity profile at the population level. IgG4, IgE and IgA levels persist into early adulthood and the subsequent decline is gradual. In the low transmission area, lower infection levels are reflected in lower parasite-specific antibody levels (of all isotypes) in the community as a whole. Despite a significantly greater past experience of infection in the high transmission area, antibody levels are not maintained at significantly higher levels throughout adulthood. The production of IgA appears to require a threshold for triggering, and a vigorous IgA response is maintained into early adulthood only in the high transmission village where peak intensity is greatest and the age-convexity of intensity is most marked. Experimental and theoretical studies focusing on the dynamic nature of host–helminth interactions in hosts exposed to high and low infection levels, and the putative role of acquired immunity, are discussed in relation to the data presented.

Spores of the bacterium Pasteuria penetrans adhered to second-stage juveniles of both Meloidogyne incognita and M. arenaria, but in standard attachment assays far fewer adhered to the latter species. Similarly, a polyclonal antibody was shown not to recognize the surface coat of M. arenaria but did recognize the surface coat of M. incognita. Although the incubation of whole, intact 2nd-stage juveniles of M. incognita in a series of detergents and protein-denaturing agents at room temperature did not reduce the number of spores adhering after exposure to the bacterium, incubation in buffer (PBS) alone at 100 °C for 2 min did. Immunoblotting of cuticle extracts onto nitrocellulose and probing the blots with antibody showed that the antibody recognized a large protein of Mr 80 kDa and a series of smaller proteins of approximately 43 kDa on M. incognita which were not recognized in extracts from M. arenaria. As incubation of the 2nd-stage juveniles in antibody prohibited spore attachment it is suggested that these proteins may be involved in spore adhesion. Large differences exist between M. incognita and M. arenaria in the amounts of surface-associated proteins on the 2nd-stage juvenile cuticle.