Showing papers in "Parasitology in 1993"
TL;DR: This review addresses changes in the ecology of vectors and epidemiology of vector-borne diseases which result from deforestation from viral and parasitic infections where disease patterns have been directly or indirectly influenced by loss of natural tropical forests.
Abstract: 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, filariases, 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.(ABSTRACT TRUNCATED AT 400 WORDS)
344 citations
TL;DR: 6 oligonucleotide probes, corresponding to species-specific regions, were designed and demonstrated to provide unequivocal identification of each of the 6 species either by direct detection of parasite sr RNA or by hybridization to amplified parasite srRNA genes.
Abstract: The complete small subunit ribosomal RNA (srRNA) gene of Theileria parva was cloned and sequenced. Two primers were designed which permitted the specific amplification of part of the Theileria srRNA gene from Theileria-infected cell line samples which were predominantly (> 95%) bovine DNA. The sequence of the central (variable) region of the srRNA genes of T. annulata, T. taurotragi, T. mutants and two unidentified parasites referred to as Theileria sp. (buffalo) and Theileria sp. (Marula) were obtained. An alignment of the sequences was generated from which 6 oligonucleotide probes, corresponding to species-specific regions, were designed. These probes were demonstrated to provide unequivocal identification of each of the 6 species either by direct detection of parasite srRNA or by hybridization to amplified parasite srRNA genes. The probes were not able to distinguish buffalo-derived T. parva, the causal agent of Corridor disease, from cattle-derived T. parva, the causal agent of East Coast fever.
174 citations
TL;DR: The antigenic and ultrastructural similarities between N. caninum and the protozoal parasites isolated from aborted bovine foetuses in this study support the proposition that these parasites belong to the genus Neospora.
Abstract: A Neospora sp. was isolated from the brains of two aborted bovine foetuses and grown continuously in vitro in bovine cell cultures. A comparison of the antigenic reactivity of in vitro cultivated tachyzoites with polyclonal antisera to Neospora caninum, Hammondia hammondi or Toxoplasma gondii revealed that the bovine protozoal isolates were similar to N. caninum and antigenically distinct from T. gondii. Tachyzoites of both bovine isolates had similar ultrastructural features, including an apical polar ring, conoid, electron-dense rhoptries and micronemes. The orientation of the micronemes, presence of micropores and a large number of electron-dense granules in the posterior portion of the bovine isolate tachyzoites differed from previous descriptions of N. caninum in vivo. Tachyzoites of the bovine isolates were ultrastructurally more similar to in vitro cultivated N. caninum tachyzoites than to tachyzoites of T. gondii or H. hammondi. The antigenic and ultrastructural similarities between N. caninum and the protozoal parasites isolated from aborted bovine foetuses in this study support the proposition that these parasites belong to the genus Neospora.
166 citations
TL;DR: Although excystation was maximal after incubation for 4 h, sporozoites tended to lyse over this period, and maximum sporozoite recovery occurred after 30 min, and a number of recommendations are given for in vitroExcystation of C. parvum oocysts.
Abstract: Protocols for in vitro excystation of oocysts of Cryptosporidium parvum, including different chemical pre-incubation steps, were compared to examine some of the biochemical triggers involved in excystation and to define an in vitro excystation protocol of a reproducibly high efficiency. Pre-incubation steps which increased the permeability of the oocysts were found to enhance excystation dynamics and pre-treatment of oocysts with saliva was found to decrease the permeability and reduce excystation. Although excystation was maximal after incubation for 4 h, sporozoites tended to lyse over this period, and maximum sporozoite recovery occurred after 30 min. The results obtained are discussed in relation to excystation protocols adopted by different research groups and a number of recommendations are given for in vitro excystation of C. parvum oocysts.
158 citations
TL;DR: Two clones of the human malaria parasite Plasmodium falciparum were grown in vitro under conditions permitting the development of gametocytes, suggesting that gametes in the original mixture fed to mosquitoes had undergone random mating.
Abstract: Two clones of the human malaria parasite Plasmodium falciparum, denoted 3D7 and HB3, were grown in vitro under conditions permitting the development of gametocytes. The two clones differ in their allelic forms of two antigen genes MSP1 and MSP2. The alleles can be distinguished as size differences of polymerase chain reaction (PCR) amplified fragments of repetitive regions of each gene. Mosquitoes (Anopheles stephensi) were fed on a mixture of these gametocytes. A total of 128 oocysts was isolated from the midguts of infected mosquitoes from 9 crossing experiments between the clones. DNA extracted from these oocysts was amplified by PCR. Oocysts which contained both alleles of each gene (MSP1 and MSP2) had developed from heterozygotes produced by cross-fertilization events between 3D7 and HB3 gametes. The remaining oocysts contained single alleles of each gene, in parent clone combinations, and these had developed from homozygotes formed by self-fertilizations. The results suggest that gametes in the original mixture fed to mosquitoes had undergone random mating.
126 citations
TL;DR: It is shown that Ascaris from humans and pigs are involved in separate transmission cycles in Guatemala, and patterns of phylogenetic similarity and geographical distribution of these haplotypes suggest that they are the result of two historical introgressions of mtDNA between the two host-associated Ascar is populations.
Abstract: In Guatemalan villages people commonly rear pigs, and both hosts may be infected with Ascaris. This study was designed to ask whether both humans and pigs are potential hosts in a single parasite transmission cycle in such villages, or alternatively, if there are two separate transmission cycles, one involving pigs and one involving human hosts. Parasites were collected from both host species from locations in the north and south of Guatemala. Allelic variation in the nuclear genome of Ascaris was measured using enzyme electrophoresis, while mitochondrial DNA (mtDNA) sequence variation was quantified using restriction mapping. Low levels of enzyme polymorphism were found in Ascaris, but allele frequencies at two loci, mannose phosphate isomerase and esterase, suggest that there is little gene exchange between parasite populations from humans and pigs. MtDNA haplotypes fall into two distinct clusters which differ in sequence by 3-4%; the two clusters broadly correspond to worms collected from humans and those collected from pigs. However, some parasites collected from humans have mtDNA characteristic of the 'pig Ascaris' haplotype cluster, while some parasites collected from pigs have mtDNA characteristic of the 'human Ascaris' haplotype cluster. These shared haplotypes are unlikely to represent contemporary cross-infection events. Patterns of phylogenetic similarity and geographical distribution of these haplotypes suggest, instead, that they are the result of two historical introgressions of mtDNA between the two host-associated Ascaris populations. The results clearly demonstrate that Ascaris from humans and pigs are involved in separate transmission cycles in Guatemala.
125 citations
TL;DR: A novel procedure for the immunofluorescent investigation of Plasmodium falciparum is described, which indicates that there is an apparent asynchrony in chromosomal multiplication within a single parasite.
Abstract: We describe a novel procedure for the immunofluorescent investigation of Plasmodium falciparum. This has allowed us to visualize clearly microtubular structures and their changing conformation through the erythrocytic cell-cycle, to the stage of cytodifferentiation leading to merozoite release. The images of spindle development we observed, together with an analysis of nuclear body numbers in large numbers of parasites, indicate that there is an apparent asynchrony in chromosomal multiplication within a single parasite. Using antibodies specific for post-translational modification of alpha-tubulin, we also demonstrate that the C-terminal tyrosine-containing epitope of P. falciparum alpha-tubulin I is similar to that of other organisms. Lysine-40 in the same molecule, a target for highly specific in vivo acetylation in some organisms, is unmodified in the blood stages we examined here. After in vitro acetylation of this residue, however, the epitope to which it contributes was recognized by antibody, showing that the conformation of this part of the molecule is also conserved, despite a lack of primary sequence homology immediately downstream of the target lysine residue.
114 citations
TL;DR: A model is proposed for susceptibility to trypanosome infection based on the generation of GlcNAc by RLO endochitinase activity in tsetse pupae inhibiting midgut lectin in teneral flies.
Abstract: SUMMARY Rickettsia-like organisms (RLO) from tsetse midguts and mosquito cell cultures showed high levels of endochitinase activity. A line of Glossina morsitans morsitans highly susceptible to midgut trypanosome infection and with high incidence of RLO infection showed significantly greater chitinolytic activity than G. austeni which had low RLO incidence and were correspondingly refractory to midgut infection. Midgut infection rates of Trypanosoma brucei rhodesiense in G. m. morsitans showed a dose-related increase when flies were fed iV-acetyl-D-glucosamine (GlciVAc) in the infective meal and for 4 subsequent days. A model is proposed for susceptibility to trypanosome infection based on the generation of GlciVAc by RLO endochitinase activity in tsetse pupae inhibiting midgut lectin in teneral flies.
113 citations
TL;DR: How important biological characteristics of the vectors of trypanosomiasis in West Africa may be monitored using data from the NOAA series of meteorological satellites is described, to lead to an understanding of the spatial distribution of both vectors and disease.
Abstract: 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.
110 citations
TL;DR: Oocyst frequency distribution analysis shows that under natural conditions of transmission intensity, significant numbers of fully susceptible mosquitoes will not be infected under conditions where the mean infection is as high as 250 oocysts, and failure to infect is not therefore an absolute indicator of refractoriness.
Abstract: Oocyst prevalence and intensity have been recorded in 349 laboratory infections of Anopheles stephensi with Plasmodium berghei Intensity and prevalence of infection are shown to be predictably related The structure and heterogeneity in the infections has been analysed with the objective of describing the biological mechanisms by which the observed negative binomial oocyst distributions are generated The analysis has revealed that the most likely processes lie within the population dynamic events of malaria within the mosquito, namely gametogenesis, fertilization and mortality The distribution is similar in all Plasmodium – mosquito combinations examined so far, whether they are of laboratory (P gallinaceum in Aedes aegypti) or field (P vivax in An albimanus and P falciparum in An gambiae sl and An funestus) origin Further we conclude that there is competition between parasites in the vector Oocyst frequency distribution analysis shows that under natural conditions of transmission intensity, and even under the best laboratory conditions, significant numbers (> 10%) of fully susceptible mosquitoes will not be infected under conditions where the mean infection is as high as 250 oocysts Failure to infect is not therefore an absolute indicator of refractoriness In assessing transmission data it is shown that sample sizes should not be less than 50, and ideally 100 mosquitoes, if reliable data are to be obtained In the field it is suggested that difficulties in determining the low natural intensity of oocyst infections indicate that prevalence estimates are a useful and accessible parameter to measure In determining the impact of transmission blocking mechanisms we predict that under conditions where high oocyst intensities prevail, large reductions in intensity will be required before a reduction in prevalence can be expected ie here it will be necessary to measure intensity of infection Conversely, under conditions where low oocyst intensities prevail, a rapid reduction in prevalence will occur with little concurrent reduction in intensity ie prevalence determination will be the more sensitive estimate
108 citations
TL;DR: A highly repetitive, tandemly arranged DNA sequence and oligonucleotide primers, for use in polymerase chain reaction (PCR) amplification are described, which can be used for specific identification of the trypanosome and its distinction from others within the Nannomonas subgenus.
Abstract: Trypanosoma (Nannomonas) congolense comprises morphologically identical but genetically heterogeneous parasites infective to livestock and other mammalian hosts; three different genotypes of this parasite have been described previously. Restriction enzyme fragment length polymorphisms (RFLPs) in both kinetoplast DNA minicircle and nuclear DNA sequences, and randomly amplified polymorphic deoxyribonucleic acid (RAPD) patterns have been used here to demonstrate the existence of another type of T. (N.) congolense that is genotypically distinct from those that have so far been characterized at the molecular level. A highly repetitive, tandemly arranged DNA sequence and oligonucleotide primers, for use in polymerase chain reaction (PCR) amplification are described, which can be used for specific identification of the trypanosome and its distinction from others within the Nannomonas subgenus.
TL;DR: The prediction that species richness and diversity' of intestinal helminth communities in eels would change over time in response to habitat changes was tested over a period of 13 years in a small stream subjected to extensive human management.
Abstract: The prediction that species richness and diversity of intestinal helminth communities in eels would change over time in response to habitat changes was tested over a period of 13 years in a small stream subjected to extensive human management. Nearly all measures of helminth community structure adopted indicated a decline in richness and diversity over the first 6 years followed by a recovery over the last few years to levels unexpectedly close to those at the start of the investigation. Changes in total number of species suggested that the component community was far richer (from 3–9 species) at the end of the period. By contrast, changes in diversity and dominance measures revealed less variation than expected and suggested that there was an underlying stability of community structure characterized by high dominance by a single species, although the identity of this changed, low diversity and a large proportion of the eel population harbouring 0 or only 1 species. A similar pattern of changes was recorded in the infra-communities, where values of species richness and diversity were very similar at the commencement and termination of the study. It appeared that those helminths that colonized in the recovery period contributed to community richness but had little impact on community structure. The helminth communities clearly did change in response to habitat changes, and the evidence for a fixed number of niches and an underlying constancy in helminth community structure in eels is evaluated.
TL;DR: 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.
Abstract: 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.(ABSTRACT TRUNCATED AT 400 WORDS)
TL;DR: The information processing model of human cognition is outlined and IQ and DQ are explained and a speculative hypothesis concerning the psychological effects of parasitic infection is sketched.
Abstract: The paper considers briefly the nature of cognition and its relationship to intelligence. The information processing model of human cognition is outlined and IQ and DQ are explained. The literature dealing with the effects of malnutrition and parasitic infection on cognitive performance and development in children is selectively reviewed. A speculative hypothesis concerning the psychological effects of parasitic infection is sketched and brief consideration is given to models and measures in research on development.
TL;DR: 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), and the target sequence for amplification was the E. multilocularis U1 snRNA gene.
Abstract: 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-Comte (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.
TL;DR: qinghaosu (QHS, artemisinin) and its derivatives on Leishmania major replication in vitro and on the disease development in mice infected with L. major developed significantly smaller lesions and parasite loads when treated with the compounds.
Abstract: We have investigated the effect of qinghaosu (QHS, artemisinin) and its derivatives on Leishmania major replication in vitro and on the disease development in mice infected with L. major. Artemisinin is effective against promastigotes in vitro, with an ED50 (50% effective dose) at 7.5 x 10(-7) M. Both artemisinin and artemether are leishmanicidal for amastigotes in infected murine macrophages in vitro, with ED50 at 3 x 10(-5) M and 3 x 10(-6) M respectively. These compounds have no effect on the viability of macrophages or on the phytohaemaglutinin-induced proliferation of normal spleen cells, even at 10(-4) M. BALB/c mice infected in the footpad with L. major developed significantly smaller lesions and parasite loads when treated with the compounds. Intra-lesion injection of the compounds was the most effective route. The intramuscular and oral routes were also effective; however, intravenous injection with artesunate was not effective.
TL;DR: It is concluded that community-level treatment and control of schistosomiasis in areas where the infection, protein-energy malnutrition, and anaemia are common are to be encouraged and are likely to improve child growth, appetite, physical fitness and activity levels and to decrease anaemia and symptoms of the infection.
Abstract: This article reviews studies that examine the negative effects of urinary and intestinal schistosomiasis on the following nutritional parameters in humans: urinary and faecal blood and iron loss, anaemia and haemoglobin levels, proteinuria, child growth and adult protein-energy status, physical fitness, physical activity, appetite and symptomatology. The conclusions reached are (1) that community-level treatment and control of schistosomiasis in areas where the infection, protein-energy malnutrition, and anaemia are common are to be encouraged and are likely to improve child growth, appetite, physical fitness and activity levels and to decrease anaemia and symptoms of the infection, and (2) that further studies are needed to determine how much and by what means decreases in and treatment of schistosomal infection may improve nutritional status, cognitive and school performance and attendance, and work capacity and productivity in communities with different amounts of parasitism and malnutrition.
TL;DR: A mathematical model is proposed to explain how human iron metabolism may respond to hookworm infection of varying intensity, drawing attention to the importance of the regulation of stored iron levels in the process.
Abstract: Ancylostoma duodenale and Necator americanus are extremely common species of soil-transmitted helminth which flourish where poverty and malnutrition prevail. Hookworms contribute significantly to iron-deficiency anaemia, which remains one of the world's major nutritional problems, through the feeding activities of intestinal stages leading to chronic blood loss into the gut. In this article, a mathematical model is proposed to explain how human iron metabolism may respond to hookworm infection of varying intensity. The model draws attention to the importance of the regulation of stored iron levels in the process. The results from the model are presented for the effects of hookworm infection on the iron metabolism of a healthy adult male. Calculations are also presented in which the effects of hookworms on the iron metabolism of a non-pregnant woman are compared with those of a pregnant woman. Use of the model may help develop a better understanding of the pathology of hookworm disease.
TL;DR: This review strongly indicates that A. lumbricoides infection definitely retards childhood growth and a better nutritional status in terms of growth, lactose tolerance, vitamins A and C, and albumin levels were observed than among Ascaris-infected or untreated children even in cross-sectional or non-randomized studies.
Abstract: The present review will examine epidemiological perspectives and be confined mainly to the results of those field studies published since 1975 in order to provide concrete scientific evidence of the effect of ascariasis on childhood malnutrition, particularly on growth. The field studies were done in many developing countries from Africa, Asia and Latin America, using cross-sectional and intervention studies in which anthelmintics were employed, with different dosing frequency and follow-up periods ranging from 33 days to 2 years. In general, a better nutritional status in terms of growth, lactose tolerance, vitamins A and C, and albumin levels were observed among Ascaris-free or treated than among Ascaris-infected or untreated children even in cross-sectional or non-randomized studies. More importantly, the improvement in weight or height after chemotherapeutic treatment was found to be significant particularly in those randomized controlled studies with an initially high prevalence of ascariasis and malnutrition, a low prevalence of other intestinal parasites, repetitive and regular treatments of children with tetramisole, levamisole or pyrantel, within a period of 12 or 24 months. Reasons for failures to detect improved growth in some studies are provided. This review strongly indicates that A. lumbricoides infection definitely retards childhood growth.
TL;DR: Analysis of the kinetics of protein synthesis of schistosomula labelled after transformation revealed four different phases, which may relate to the developmental processes occurring in vivo.
Abstract: The lung schistosomulum of Schistosoma mansoni is the target of protective immunity in mice singly vaccinated with irradiated cercariae. Since the effector responses are T cell-mediated, their initiation requires the release of antigens from the intact parasite. We have used the technique of biosynthetic labelling with [35S]methionine, before and after transformation of the cercariae, to analyse the kinetics of protein synthesis and release by the schistosomulum. In addition, the proteins present in the soluble fraction of the parasite and those released during in vitro culture have been characterized. During a 7-day culture period schistosomula derived from labelled cercariae lost proteins most rapidly within the first 3 h after transformation. Two proteins of molecular weight 61 and 20 kDa were dominant and may correspond to areas of proteolytic activity. Analysis of the rate of protein synthesis of schistosomula labelled after transformation revealed four different phases, which may relate to the developmental processes occurring in vivo. During the first 24 h, synthesis was very low, increasing to a plateau and then rising to a peak at day 8; therefore the rate declined rapidly. Whilst some stage-specific synthesis of proteins was detected in the soluble fractions of the parasite bodies, the pattern of proteins released by cultured larvae was remarkably uniform. At least 15 proteins were detected by autoradiography with bands at 61, 45 and 20 kDa being particularly prominent. These proteins merit further study as potential mediators of the protective immune response.
TL;DR: For its burgeoning importance as a worldwide health problem, both with the HIV virus as a direct intestinal pathogen and with the opportunistic gut infections occurring in the immunocompromised host, AIDS represents the emerging context of the impairment of nutritional status by intestinal pathogens.
Abstract: Gastrointestinal pathogens are of three varieties, those that can, and often do, take the life of the host, those that infect transiently and rarely are life-threatening, and those (parasites) that establish a relatively prolonged residence or colonization of the host's alimentary tract. In the case of the second form, if infections are recurrent, both catabolic effects during the episode and failure to digest foods and/or absorb nutrients results. Similarly, catabolic wastage through activation of the acute phase response, and interference with the host's acquisition of nutrients by maldigestion, malabsorption, intestinal losses and competition with the parasite burden can impair growth and nutrition with helminthic infections. Growth and nutrition with respect to all of the macronutrients and virtually all of the micronutrients have been documented to be adversely affected by gastrointestinal pathogens. For its burgeoning importance as a worldwide health problem, both with the HIV virus as a direct intestinal pathogen and with the opportunistic gut infections occurring in the immunocompromised host, AIDS represents the emerging context of the impairment of nutritional status by intestinal pathogens.
TL;DR: 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.
Abstract: 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.
TL;DR: The investigation of Price & Clancy (1983), which demonstrated a significant positive correlation between total helminth species number per host species and geographical range of freshwater fish host species in Britain, was re-examined using a different measure of parasite species richness.
Abstract: The investigation of Price & Clancy (1983), which demonstrated a significant positive correlation between total helminth species number per host species and geographical range of freshwater fish host species in Britain, was re-examined using a different measure of parasite species richness. Re-calculation of the correlations between the two parameters after controlling for the effect of the composition of the list of fish by excluding, on biological and distributional grounds, 2 species of agnathans and 7 species of introduced teleosts, and for the effect of sampling effort by using helminth richness in the richest component community of each fish species rather than check-list data, reveals no significant relationship between helminth species richness and host range. Habitat and an omnivorous host diet now appear more significant determinants of helminth richness than the accumulation of parasites by predation. The findings provide little support for the interpretation of the relationship between helminth species richness and host range in terms of island biogeographic theory, but do support an alternative explanation in terms of the colonization time hypothesis, i.e. that helminth species richness is related to the time since the fish host arrived in Britain.
TL;DR: The results showed that the high susceptibility of the hybrid zone mice is genetically determined and the occurrence of variability among resistant parental populations is shown.
Abstract: 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.
TL;DR: Two mathematical models are developed that investigate the transmission dynamics of Theileria parva by the ixodid tick Rhipicephalus appendiculatus to cattle in endemically stable areas and the impact of each method on the transmission of infection is evaluated.
Abstract: Two mathematical models are developed that investigate the transmission dynamics of Theileria parva by the ixodid tickRhipicephalus appendiculatus to cattle in endemically stable areas. A method of estimating the rate of infection to cattle ofT. parva at the endemically stable state is given. Empirical estimates of ail the parameters in the model are available. The degree to which animals that have recovered from theileriosis (the ‘carrier’ state) are able to transmit the infection to tick nymphs or larvae is a crucial determinant of the dynamics of infection in a herd. Two control methods influencing the transmission of infection are considered – infection and treatment immunization and the reduction in tick feeding by acaricide application. The impact of each method on the transmission of infection is evaluated. Future developments and the data required to predict the dynamics of T. parva infections in cattle and ticks are discussed.
TL;DR: Reinfection with hookworm following chemotherapy was studied over 2 years in a rural village in Madang Province, Papua New Guinea; there was significant predisposition to hookworm infection; the strength of this predisposition did not vary significantly between age or sex classes.
Abstract: Reinfection with hookworm (Necator americanus) following chemotherapy was studied over 2 years in a rural village in Madang Province, Papua New Guinea. The prevalence of hookworm infection had returned to pre-treatment levels after 2 years, and the geometric mean hookworm burden had returned to 58% of the pre-treatment value. The rate of acquisition of adult worms was independent of host age, and was estimated as a geometric mean of 2.9-3.3 worms/host/year (arithmetic mean 7.9-8.9 worms/host/year). There was significant predisposition to hookworm infection; the strength of this predisposition did not vary significantly between age or sex classes.
TL;DR: The results suggest that increased susceptibility to disease may be a cost to males aggressively maintaining high social status and that males showing more aggression tended to enter groups with higher levels of corticosterone and, to a lesser extent, reduced levels of IgG compared with other mice.
Abstract: Unrelated and initially unfamiliar male CFLP mice, maintained for different periods in groups of 6, differed in both their rate of clearance of Babesia microti and the time taken to reach peak parasitaemia in relation to their aggressive behaviour within groups prior to infection. Males maintained in groups for shorter periods and showing more aggression within their group were slower to clear infection and males showing more marked external evidence of aggressive interaction reached a peak of parasitaemia sooner. Serum IgG and corticosterone analyses were consistent with increased aggression causing stress-induced immunodepression but relationships with aggression and social status were not simple. Males showing more aggression tended to enter their groups with higher levels of corticosterone and, to a lesser extent, reduced levels of IgG compared with other mice. The results thus suggest that increased susceptibility to disease may be a cost to males aggressively maintaining high social status.
TL;DR: 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, showing a reduction in parasite egg production and total worm numbers.
Abstract: 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 micrograms/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 micrograms/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 micrograms/kg of a sub-fraction containing H11 obtained from the H11 extract, showed a 71% reduction in egg output and total worm numbers.
TL;DR: Of the 41 cases diagnosed by the three diagnostic techniques combined 31 were detected by the dipstick assay making it the most sensitive technique employed, the combined diagnostic approach did not, however, diagnose all cases.
Abstract: A dipstick dot ELISA for detection of Taenia-specific coproantigens was developed. The test was based on a sandwich ELISA using antibodies raised against adult Taenia solium. Antibodies were adsorbed to nitrocellulose paper previously adhered to acetate plastic to form dipsticks. Once blocked with 5% skimmed milk and dried the antibody-coated dipsticks were stable for several weeks at room temperature. Both micro and dot ELISA formats were genus specific although the dot ELISA was less sensitive than the micro ELISA based on the same antiserum. During field studies, in which the majority of samples were tested in rural villages soon after collection, 3728 samples were tested. All samples were also examined by microscopy using formol ether concentration and individuals questioned to determine whether they were aware of being infected. After the initial diagnostic work individuals were treated with taeniacidal drugs for worm recovery. Use of the coproantigen test significantly increased the number of cases diagnosed. Of the 41 cases diagnosed by the three diagnostic techniques combined 31 were detected by the dipstick assay making it the most sensitive technique employed. The specificity of the dipstick assay was 99·9% with a positive predictive value of 88·%. The combined diagnostic approach did not, however, diagnose all cases. The coproantigen test was fast and easy to use. Further improvements may make the dipstick test suitable for wide-scale use in field studies and diagnostic laboratories.
TL;DR: The epidemiology of trypanosome infections of Glossina pallidipes was studied at a riverine site in the Zambezi Valley, Zimbabwe for a period of 13 months, finding that the rate of infection decreases with age, and that infected flies have higher mortality rates, and/or that a significant fraction of the population is resistant to infection.
Abstract: The epidemiology of trypanosome infections of Glossina pallidipes was studied at a riverine site in the Zambezi Valley, Zimbabwe for a period of 13 months. Over 9000 flies were captured using a single trap. These flies were dissected, screened for trypanosome infection, sexed, and aged using both wing fray and (for females) ovarian category indices. Midgut infections were identified to species using recently developed DNA probes. The overall prevalence of mature infections was 5·5%, comprising 3·1% Trypanosoma vivax-type and 2·4% T. congolense-type (which included very low prevalences of T. brucei, T. simiae and another Nannomonas species). The prevalence of infection increased with age. For T. vivax-type infections in flies aged by ovarian category this relationship could be described by a simple ‘catalytic’ model assuming a constant per capita rate of infection. For T. congolense-type infections this model tended to over-estimate prevalence in older age classes, implying that the rate of infection decreases with age, and/or that infected flies have higher mortality rates, and/or that a significant fraction of the population is resistant to infection. Prevalences of infection also varied between months. This variation was more marked for T. vivax-type infections and was negatively correlated with both temperature and rainfall. The shape of the age-prevalence relationship, however, did not vary significantly between months. These observations are not fully explained by variation in the age-structure of the tsetse population and are consistent with temporal variation in the rate of infection (rather than in the trypanosome developmental period or in effects of infection on fly mortality). Possible causes of this variation are discussed.