In the hybrid zone of the two mouse subspecies Mus musculus musculus and Mus musculus domesticus, mice with hybrid genotypes harbour, on the average, more helminth parasites (cestodes and nematodes) than mice of the two parental taxa. In order to determine the roles played by genetic parameters in this phenomenon, mice with recombined and parental genotypes were experimentally infected with the intestinal pinworm Aspiculuris tetraptera, a natural parasite of the house mouse. The results showed that the high susceptibility of the hybrid zone mice is genetically determined. In addition, this study shows the occurrence of variability among resistant parental populations.

Specific antisera, directed against the highly conserved C-terminal hexapeptide amide of mammalian pancreatic poly-peptide (PP) and the invertebrate peptide FMRFamide, have been used in conjunction with post-embedding, IgG-conjugated colloidal gold immunostaining to demonstrate peptide immunoreactivity at subcellular level in the nervous system of adult Diclidophora merlangi. Gold labelling revealed that immunoreactivity for PP and FMRFamide was localized exclusively in dense-cored vesicles occupying the majority of axons in the central nervous system. Double-labelling demonstrated an apparent co-localization of PP and FMRFamide in the same dense-cored vesicles. Antigen pre-absorption experiments indicated cross-reactivity of the two antisera as unlikely, and that some if not all of the PP/FMRFamide immunostaining in the parasite was due to a neuropeptide F-like peptide.

Fifty tetrathyridia of Mesocestoides corti showing various degrees of scolex fission during asexual multiplication were subjected to estimation of the total number of neurons in the central ganglia, using a ‘fractionator’ designed sampling scheme on every 10th Historesin section through the specimen. Neurons were stained with Cresyl fast violet and viewed by transmission light microscopy. Cells were only counted if a nucleolus was present. The animals were divided into groups according to their stage in the asexual reproduction process indicated by head shape and sucker number. Animals which had a narrow head with 4 suckers contained about 250 neurons. As their heads became wider, in preparation for fission, neurons were overproduced by up to 5-fold. As additional suckers were developed (8 in total), neurons were reduced to about 500. Finally, when the animals had 2 clearly discernible heads, with 4 suckers on each, the total number of neurons (per head) was again approximately 250. As the heads became wider again, neuron over-production recommenced. Exceptionally shaped animals with an X- or T-shaped single head were observed. These results suggest that there is a preparatory stage for neuronal regeneration, during which the basic population of neurons is about 250. This is followed by neuron over-production followed by a selective cell death of neurons which occurred during asexual multiplication. Another cycle for neuronal regeneration can occur before an animal completes its fission process.

This review addresses' changes in the ecology of vectors and epidemiology of vector-borne diseases which result from deforestation. Selected examples are considered from viral and parasitic infections (arboviruses, malaria, the leishmaniases, nlariases, Chagas Disease and schistosomiasis) where disease patterns have been directly or indirectly influenced by loss of natural tropical forests. A wide range of activities have resulted in deforestation. These include colonisation and settlement, transmigrant programmes, logging, agricultural activities to provide for cash crops, mining, hydropower development and fuelwood collection. Each activity influences the prevalence, incidence and distribution of vector-borne disease. Three main regions are considered – South America, West & Central Africa and South-East Asia. In each, documented changes in vector ecology and behaviour and disease pattern have occurred. Such changes result from human activity at the forest interface and within the forest. They include both deforestation and reafforestation programmes. Deforestation, or activities associated with it, have produced new habitats for Anopheles darlingi mosquitoes and have caused malaria epidemics in South America. The different species complexes in South-East Asia (A. dirus, A. minimus, A. balabacensis) have been affected in different ways by forest clearance with different impacts on malaria incidence. The ability of zoophilic vectors to adapt to human blood as an alternative source of food and to become associated with human dwellings (peridomestic behaviour) have influenced the distribution of the leishmaniases in South America. Certain species of sandflies (Lutzomyia intermedia, Lu. longipalpis, Lu. whitmani), which were originally zoophilic and sylvatic, have adapted to feeding on humans in peridomestic and even periurban situations. The changes in behaviour of reservoir hosts and the ability of pathogens to adapt to new reservoir hosts in the newly-created habitats also influence the patterns of disease. In anthroponotic infections, such as Plasmodium, Onchocerca and Wuchereria, changes in disease patterns and vector ecology may be more difficult to detect. Detailed knowledge of vector species and species complexes is needed in relation to changing climate associated with deforestation. The distributions of the Anopheles gambiae and Simulium damnosum species complexes in West Africa are examples. There have been detailed longitudinal studies of Anopheles gambiae populations in different ecological zones of West Africa. Studies on Simulium damnosum cytoforms (using chromosome identification methods) in the Onchocerciasis Control Programme were necessary to detect changes in distribution of species in relation to changed habitats. These examples underline the need for studies on the taxonomy of medically-important insects in parallel with long-term observations on changing habitats. In some circumstances, destruction of the forest has reduced or even removed disease transmission (e.g. S. neavei-transmitted Onchocerca in Kenya). Whilst the process of deforestation can be expected to continue, hopefully at a decreased rate, it is expected that unpredictable and sometimes rapid changes in disease patterns will pose problems for the public health services.

Previous studies from this laboratory have suggested the presence of antibody-binding molecules on the surface of Taenia crassiceps metacestodes. We now report the purification of a T. crassiceps Fcγ -binding protein which has an equivalent molecular size (96 kDa), is antigenically similar and exhibits significant amino acid sequence homology to schistosome paramyosin. The similarities in molecular weight of the T. crassiceps protein, Schistosoma mansoni paramyosin and antigen B of T. solium, the close amino acid sequence homologies between the T. crassiceps protein and S. mansoni paramyosin and between S. mansoni paramyosin and antigen B of T. solium, and the antigenic similarity of the T. crassiceps protein with paramyosin indicates that this family of platyhelminth proteins are closely related. The known characteristics of T. solium antigen B (collagen binding affinity; disruption of complement function) and the Fcγ -binding activity of the T. crassiceps molecule suggests that this class of proteins may be multifunctional, fulfilling not only a structural role but also as components interacting with the host immune system to increase parasite survival.

The presence of phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31), an enzyme at the branchpoint of glycolysis and the Krebs cycle was detected in the Filaria Molinema dessetae. This enzyme has not previously been identified in Helminths, which have so far been found to only possess a phosphoenolpyruvate carboxykinase (EC 4.1.1.32). This enzyme had a level of activity comparable to that of pyruvate kinase, and was relatively less active than enzymes such as malate dehydrogenase or lactate dehydrogenase. We propose here a method of purification of M. dessetae PEP-carboxylase. When purified to electrophoretic homogeneity, the enzyme had a molecular weight of 64 kDa. Kinetic studies indicated that the carboxylation reaction had an optimal pH of 5·8. The enzyme was inhibited by cations such as Fe2+, Zn2+, Cd2+, Cu2+ but required the presence of Mg2+ or Mn2+. The enzyme was thermostable. The apparent Km value of 2·38 mmol for phosphoenolpyruvate for the carboxylation reaction was higher than previously reported values. The Km value for KHCO3 was found to be 1·6 mmol. PEP-carboxylase did not catalyse the reverse reaction.

Establishment, survival and distribution of Leptorhynchoides thecatus (Acanthocephala) were investigated in largemouth bass, Micropterus salmoides, fed 10, 25, or 40 cystacanths and examined at 1, 3 or 5 weeks post-infection. Worms established widely in the alimentary tracts of bass but by 5 weeks post-infection had localized in the pyloric caeca and intercaecal region. Other individuals moved to parenteral sites where they remained immature, though viable. In the 10- and 25-level exposures, establishment and survivorship in the alimentary tract were roughly proportional to the dose of cystacanths. After 1 week post-infection in the 40-level exposure class, numbers of worms in the alimentary tract decreased significantly and parenteral occurrence increased significantly. Total survival of L. thecatus appeared to be density-independent. Maturation of worms was retarded temporarily as intensity of infection increased, but by 5 weeks post-infection worms from all doses were at roughly the same stage of development within sex. The caeca and intercaecal area apparently did not differ in their suitability for maturation.

The degradation of several protein substrates, including the blood proteins haemoglobin, albumin and fibrinogen, by proteinases present in extracts of adult Haemonchus contortus was examined over a broad pH range. These proteinases were further characterized on the basis of substrate specificity, inhibitor sensitivity and molecular size by spectrophotometric and substrate gel analysis. The majority of the proteinases capable of degrading the blood proteins tested were active at acidic pH and could be ascribed to the cysteine proteinase class. In addition, evidence is presented that these proteinases are differentially recognized and inhibited by immune sera and that parasites capable of withstanding protective host immune responses exhibit modified expression of proteinases.

Groups of South African, farm-reared merino lambs about 4 months old were vaccinated with extracts of adult Haemonchus contortus enriched with H11, an integral membrane protein from the parasite's intestinal microvilli, or with proteins soluble in Tween 20. The lambs were challenged with 5000 infective 3rd-stage larvae. Compared to the adjuvant-injected controls, lambs vaccinated with 350 μg/kg liveweight of the H11-enriched extract showed an 89% reduction in parasite egg production and an 88% reduction in total worm burden at post-mortem 35 days post-challenge. The H11-enriched extract contained some protein also present in the Tween 20 extract. Lambs vaccinated with 600 μg/kg of protein soluble in Tween 20 showed a 40% reduction in faecal egg counts and 51% reduction in total worm numbers 35 days post-challenge. Animals injected with 20 μg/kg of a sub-fraction containing H11 obtained from the H11 extract, showed a 71% reduction in egg output and total worm numbers.

The paper examines the possible contributions to be made by Geographic Information Systems (GIS) to studies on human and animal trypanosomiasis in Africa. The epidemiological characteristics of trypanosomiasis are reviewed in the light of the formula for the basic reproductive rate or number of vector-borne diseases. The paper then describes how important biological characteristics of the vectors of trypanosomiasis in West Africa may be monitored using data from the NOAA series of meteorological satellites. This will lead to an understanding of the spatial distribution of both vectors and disease. An alternative, statistical approach to understanding the spatial distribution of tsetse, based on linear discriminant analysis, is illustrated with the example of Glossina morsitans in Zimbabwe, Kenya and Tanzania. In the case of Zimbabwe, a single climatic variable, the maximum of the mean monthly temperature, correctly predicts the pre-rinderpest distribution of tsetse over 82% of the country; additional climatic and vegetation variables do not improve considerably on this figure. In the cases of Kenya and Tanzania, however, another variable, the maximum of the mean monthly Normalized Difference Vegetation Index, is the single most important variable, giving correct predictions over 69 % of the area; the other climatic and vegetation variables improve this to 82 % overall. Such statistical analyses can guide field work towards the correct biological interpretation of the distributional limits of vectors and may also be used to make predictions about the impact of global change on vector ranges. Examples are given of the areas of Zimbabwe which would become climatically suitable for tsetse given mean temperature increases of 1, 2 and 3 °Centigrade. Five possible causes for sleeping sickness outbreaks are given, illustrated by the analysis of field data or from the output of mathematical models. One cause is abiotic (variation in rainfall), three are biotic (variation in vectorial potential, host immunity, or parasite virulence) and one is historical (the impact of explorers, colonizers and dictators). The implications for disease monitoring, in order to anticipate sleeping sickness outbreaks, are briefly discussed. It is concluded that present data are inadequate to distinguish between these hypotheses. The idea that sleeping sickness outbreaks are periodic (i.e. cyclical) is only barely supported by hard data. Hence it is even difficult to conclude whether the major cause of sleeping sickness outbreaks is biotic (which, in model situations, tends to produce cyclical epidemics) or abiotic. The conclusions emphasize that until we understand more about the variation in space and time of tsetse and trypanosomiasis distribution and abundance we shall not be in a position to benefit from the advances made by GIS. The potential is there, however, to re-introduce the spatial and temporal elements into epidemiological studies that are currently often neglected.

The infection dynamics of Cyclops vicinus by the larvae of Bothriocephalus claviceps were studied experimentally. The mean number of procercoids/copepod rose to a plateau of approximately 14 as the density of eggs increased, whilst the number of copepods surviving decreased correspondingly. Copepods exposed to eggs of B. claviceps survived less well than controls, and those exposed to a higher density of eggs survived less well than those to a lower density. The mean number of parasites/copepod and the mortality of copepods were found to increase with the increasing time of exposure to eggs even when egg density was constant. These two parameters were also found to differ between gravid female copepods and unsexed young copepods. Young copepods suffered a higher parasite burden and thus a higher mortality, indicating that there are age or developmental-stage related differences in susceptibility of copepods to infection.

Indirect immunofluorescence studies using a rabbit polyclonal antiserum have been used to localize the presence of a 32 kDa glycoprotein in the region of the amphids of 2nd-stage juveniles of the root-knot nematode, Meloidogyne incognita. Similar immunoreactivity was also demonstrated in 5 other Meloidogyne species but was not found in representatives of 8 other nematode genera including the closely related cyst nematodes (Globodera and Heterodera). Immunoelectron microscopical studies have shown that the immunoreactivity in M. incognita is associated with the secretory material filling the amphidial channel and probably with the sheath cell.

The infectivity and distribution of Echinostoma trivolvis were studied in male, conventional and congenitally athymic nude mice, each infected with 30 metacercarial cysts. In conventional mice, worm recoveries at 6 and 8 days post-exposure were58·3 and 54·0%, respectively. Worm recovery declined to 44·0% by day 10, to 4·3% by day 13, and 0% by day 17. In athymic mice, worm recoveries at 6 and 8 days post-exposure were 61·7 and 36·3%, respectively. Worm recovery declined to 27·7% by day 10, to 0·7% by day 13, and 0% by day 17. The distribution of worms demonstrated a posteriad migration over time in both groups. Kinetic changes in the number of goblet and mucosal mast cells in the upper ileum of mice infected with E. trivolvis were examined. In conventional mice, the number of goblet cells increased rapidly to reach a peak at day 13 and then declined gradually. The number of goblet cells in athymic mice also increased to reach a peak at day 13, and then declined rapidly. However, the number of goblet cells in athymic mice was always less than that inconventional mice. The mast cell number in infected conventional mice increased rapidly to reach a peak at day 17 and then declined. There was no increase in the mast cell number of infected athymic mice throughout the experiment. Whereas common pathological changes occurred in the intestines of both mice groups infected with echinostomes some ultrastructural differences were observed in the gut epithelial cells of conventional versus athymic mice.

To understand the mechanism for the expulsion of Nippostrongylus brasiliensis from rats, age-dependent variations in the metabolism of reactive oxygen species in the parasite and the host intestines were examined. N. brasiliensis showed an age-dependent increase in its susceptibility to xanthine-xanthine oxidase and t−butyl hydroperoxide generated oxidants as well as to H2O2. Protection obtained with several scavengers suggested that the worms were damaged by the combined action of oxidants generated by the in vitro systems employed. The level of superoxide dismutase in the nematode and its release into the surroundings exhibited a marked depression with advancement of age. No such alteration was, however, recorded for catalase and glutathione peroxidase. An appreciable decrease in the level of reduced glutathione in older N. brasiliensis appears to render them prone to oxidant attack. The rat intestines, on the other hand, exhibited an appreciable depression in catalase and a reduced glutathione content with progress of the infection. Vitamin E levels were elevated. The release of O27 and H2O2 by the intestines was also found to be greater during later stages of the infection. The combined effect of the changes observed in N. brasiliensis and in the rat intestines may be at least partly responsible for expulsion of the nematode from the rats after day 10.

In order to identify Echinococcus multilocularis DNA in fox faeces for epidemiological purposes, we have developed a new method to prepare DNA suitable for PCR amplification. DNA isolation from fox excrement was performed according to a novel procedure involving lysis in KOH, phenol–chloroform extraction and a purification step on a matrix (Prep-A-Gene®). The target sequence for amplification was the E. multilocularis U1 snRNA gene. PCR products were indistinguishable for 32 different E. multilocularis isolates and no signal was observed after ethidium bromide staining with DNAs from other tapeworm species, including E. granulosus. The sensitivity of amplification was monitored by the addition of E. multilocularis DNA or eggs to faeces free of E. multilocularis and was estimated to be 1 egg per 4 g of faeces. PCR products were blotted onto nylon membranes and hybridized with an internal oligonucleotide probe in order to confirm the results. Twenty nine faecal samples from foxes shot in Franche-Comté (East France) were tested. Out of 10 samples from foxes in which no E. multilocularis adult worms could be observed after necropsy, 7 were PCR positive, showing that the PCR test is more sensitive than microscopical examination. Out of 19 samples from foxes harbouring E. multilocularis adult worms, 18 were PCR positive. The remaining PCR-negative sample could be due either to the misidentification of the species of adult worm (E. granulosus and E. multilocularis), or to DNA variation between different isolates of E. multilocularis. Further work in the field should be initiated in order to confirm these results.

A low molecular weight (15 kDa) surface antigen of the cattle filarial nematode, Setaria digitata, was earlier shown to be specifically recognized by the antibodies from human bancroftian filarial (Mf positive) patients' sera (Theodore & Kaliraj, 1990). The filarial specific antibodies bound to a 15 kDa peptide in preparative Western blots were eluted and employed in screening of candidate antigens expressed in the genomic library of Wuchereria bancrofti at the IgG4 subclass antibody level. A recombinant clone (λ WbG7) reacting strongly with filarial sera but poorly with sera from patients infected with non-filarial helminths was selected for further studies. The 2 kb DNA insert of the clone λ WbG7 was recloned into a pMAL vector and the recombinant clone pGT7 thus obtained was over-expressed and affinity purified. The purified 105 kDa fusion protein of the clone pGT7 was specific and was not recognized by the non-filarial sera at the IgG4 level. All microfilaraemic individuals were positive by IgG4 assay. However, similar attempts to diagnose by filarial-specific IgE assays failed to recognize microfilaraemic individuals. Moreover, by filarial-specific IgG4 assays, the endemic normals were distinctly divided into two groups, showing higher and lower recognition for this antigen indicating current and past/no infection. Among the filarial-IgG4 (assay)-positive ‘endemic normals’, 14% showed ‘microfilariae’ during repeated peripheral night blood examination, confirming the validity of the recombinant antigen, pGT7 based assay.

5-HT is a candidate for the excitatory transmitter at the neuromuscular junction in trematodes including Fasciola hepatica. This study has determined the response of a muscle strip preparation from Fasciola hepatica to 5-HT and a range of agonists that distinguish between the vertebrate receptor 5-HT subtypes. 5-HT increased the resting tone and the rhythmic activity of the muscle strip. Of the 19 compounds tested, only 10 had an effect similar to 5-HT and all but 2 of these were tryptamine compounds. 5-HT was more potent than tryptamine whilst 4-OH-tryptamine had no effect, suggesting that the response is mediated by a 5-HT rather than a tryptamine receptor. 5-Fluorotryptamine and 5-carboxyamidotryptamine were the most potent agonists. 8-OH-DPAT also mimicked the effect of 5-HT, though less potently. Assuming that these agents elicit their response through a common receptor, this suggests the presence of a 5-HT receptor with similar properties in terms of agonist recognition as the vertebrate 5-HT1 class of receptor involved in controlling Fasciola muscle motility.

Urbanization involves a physical change in which increasing proportions of populations live in urban settings, however defined. It also implies considerable changes in the ways in which these people live, how they earn their livelihoods, the food which they eat, and the wide range of environmental factors to which they are exposed. There is another underlying assumption that, increasingly, urban populations will be more healthy than their rural counterparts and that higher levels of urbanization will equate with better health status. This paper discusses some of the assumptions underlying this contention. It takes issue with certain of them, particularly the assumption that urbanization affects the health of all residents equally. It is manifestly evident that in many cities, particularly in the developing world, the poor are exposed to greater risks and have much lower health status than their richer neighbours. In addition, whilst urban residents may theoretically have a better access to health care and services than do residents in many rural areas, and whilst many indicators of health do appear better in more highly urbanized societies than ones less so, there are caveats. The paper introduces the concept of epidemiological transition, which suggests that, whilst life expectancy might be higher in many urbanized countries and in certain cities, the inhabitants are often merely suffering from different forms of ill-health, often chronic or degenerative, rather than infective. In certain cities in middle-income countries, residents, particularly the poor, are exposed to a double risk of both infection and chronic degenerative ailments. The paper concludes with a consideration of more general recent statements from the World Health Organization among others, on the impact of urbanization on health. The ‘Healthy Cities’ project is also discussed. WHO identifies a range of general determinants of urban health: physical, social, cultural and environmental. Many represent the by-products of modernization and especially industrialization. It is emphasized that urbanization, and the concentration of human beings into new areas in particular, can bring exposure to new risk factors for large numbers of people. The growth of infectious and parasitic disease in some urban settings must therefore be recognized, as must the emergence of chronic diseases, with the concomitant need for investment in new types of health and social care. However, a number of constraints militate against the achievement of improved urban health, especially in developing countries. The paper concludes by considering some important constraints: the very scale of urban health problems; the impacts of structural adjustment programmes which cut public expenditure on environmental health, health services and nutrition, thereby increasing the vulnerability of the poor; urban management problems; lack of political will; and the difficulties of measuring change in health and effects of policies.

Nine vervet monkeys and nine baboons were infected with eggs of Echinococcus granulosus per as. Six of the vervets and one of the baboons possessed hydatid cysts at autopsy, 15–28 months post-infection. The sequential IgG response to hydatid fluid and protoscolex antigens showed considerable inter-animal variation. Infected vervets and baboons became seropositive after an average of 8 months post-infection. Considerable fluctuation in the IgG response was observed, particularly to the hydatid fluid antigen which, in humans, may contribute to the existence of a significant proportion of seronegative individuals. Vervets, in particular, may be useful to study immunological events associated with exposure, development and resolution of hydatid disease in outbred human populations.

The localization and distribution of neuropeptides in the central nervous system of the pig roundworm, Ascaris suum, have been determined by an indirect immunofluorescence technique in conjunction with confocal microscopy. Antisera to 25 vertebrate peptides and two invertebrate peptides were used to screen the worm for immunoreactivity (IR). Immuno-staining was obtained with antisera to pancreatic polypeptide (PP), peptide YY (PYY), neuropeptide Y (NPY), gastrin, cholecystokinin (CCK), substance P (SP), atrial natriuretic peptide (ANP), salmon gonadotropin-releasing hormone (SGnRH), mammalian gonadotropin-releasing hormone (MGnRH), chromogranin A (CGA) and FMRFamide. The most extensive patterns of IR occurred with antisera to PYY, FMRFamide and gastrin. IR was evident in nerve cells and fibres in the ganglia associated with the anterior nerve ring and in the main nerve cords and their commissures; IR to FMRFamide also occurred in the posterior nerve ring. Immunostaining for the other peptides was confined to the nerve cords, with the number of immunoreactive nerve fibres varying from peptide to peptide.