Increased virulence due to multiple infection in Daphnia leads to limited growth in 1 of 2 co-infecting microsporidian parasites

Recent outbreaks of various infectious diseases have highlighted the ever-present need to understand the drivers of the outbreak and spread of disease. Although much of the research investigating diseases focuses on single infections, natural systems are dominated by multiple infections. These infections may occur simultaneously, but are often acquired sequentially, which may alter the outcome of infection. Using waterfleas (Daphnia magna) as a model organism, we examined the outcome of sequential and simultaneous multiple infections with 2 microsporidian parasites (Ordospora colligata and Hamiltosporidium tvaerminnensis) in a fully factorial design with 9 treatments and 30 replicates. We found no differences between simultaneous and sequential infections. However, H. tvaerminnensis fitness was impeded by multiple infection due to increased host mortality, which gave H. tvaerminnensis less time to grow. Host fecundity was also reduced across all treatments, but animals infected with O. colligata at a younger age produced the fewest offspring. As H. tvaerminnensis is both horizontally and vertically transmitted, this reduction in offspring may have further reduced H. tvaerminnensis fitness in co-infected treatments. Our findings suggest that in natural populations where both species co-occur, H. tvaerminnensis may evolve to higher levels of virulence following frequent co-infection by O. colligata.

A walk on the wild side: A review of the epidemiology of Toxocara canis and Toxocara cati in wild hosts

Toxocara species are cosmopolitan nematode parasites of companion, domestic and wild hosts. Of the 26 known species of Toxocara, only Toxocara canis and Toxocara cati are definitively zoonotic. The significance of wild carnivores as definitive hosts of T. canis and T. cati respectively, has received far less attention compared to domestic dogs and cats. Complex environmental changes have promoted increasing contact between wildlife, domestic animals and humans that can enhance the risk of pathogen spillover. This review lists a total of 19 species of wild canid host that have been shown to act as definitive hosts for T. canis and a total of 21 species of wild felid host. In general, the number of publications focusing on felid host species is fewer in number, reflecting the general paucity of data on T. cati. The wild canids that have received the most attention in the published literature include the red fox (Vulpes vulpes), the wolf (Canis lupus), and the golden jackal (Canis aureus). The wild felid species that has received the most attention in the published literature is the Eurasian lynx (Lynx lynx). Some non-canid and non-felid hosts also act as definitive hosts of Toxocara species. Certainly, red foxes would appear to be the most significant wild species in terms of their potential to transmit Toxocara to domestic dogs and humans via environmental contamination. This can be explained by their increasing population densities, encroachment into urban areas and their dietary preferences for a wide range of potential paratenic hosts. However, a major challenge remains to assess the relative importance of wild hosts as contributors to environmental contamination with Toxocara ova. Furthermore, one major constraint to our understanding of the significance of wildlife parasitism is a lack of access to samples, particularly from rare host species.

Caring for Canines: A Survey of Dog Ownership and Parasite Control Practices in Ireland

Dogs are an important part of life for many people. Dog ownership can confer various health benefits to their owners, but it also presents some risks. In order to establish if dog owners were aware of these risks, an online survey of dog ownership practices was carried out. The survey was open during the month of January 2022 and received 662 responses regarding 850 individual dogs. Overall, 52% of people reported deworming their dog between zero and twice a year, which is unlikely to reduce the risk of infection to humans. The majority of dog owners (71%) reported disposing of faeces correctly; however, when comparing urban and rural environments, 33% of those in rural environments did not dispose of their dogs' faeces at all, compared with 3% of people in urban locations. People who obtained their dog during the pandemic brought their dog to the vet and dewormed them more frequently than those who obtained their dog before the pandemic. There were no differences in how faeces was disposed of between these groups. These results indicate that we, as researchers and veterinarians, have much work to do in terms of educating dog owners about the ways in which we can reduce the risk of infection to ourselves and our communities.

The Invasive Bank Vole (Myodes glareolus): A Model System for Studying Parasites and Ecoimmunology during a Biological Invasion

The primary driver of the observed increase in emerging infectious diseases (EIDs) has been identified as human interaction with wildlife and this increase has emphasized knowledge gaps in wildlife pathogens dynamics. Wild rodent models have proven excellent for studying changes in parasite communities and have been a particular focus of eco-immunological research. Helminth species have been shown to be one of the factors regulating rodent abundance and indirectly affect disease burden through trade-offs between immune pathways. The Myodes glareolus invasion in Ireland is a unique model system to explore the invasion dynamics of helminth species. Studies of the invasive population of M. glareolus in Ireland have revealed a verifiable introduction point and its steady spread. Helminths studies of this invasion have identified enemy release, spillover, spillback and dilution taking place. Longitudinal studies have the potential to demonstrate the interplay between helminth parasite dynamics and both immune adaptation and coinfecting microparasites as M. glareolus become established across Ireland. Using the M. glareolus invasion as a model system and other similar wildlife systems, we can begin to fill the large gap in our knowledge surrounding the area of wildlife pathogen dynamics.

Lessons from studying roundworm and whipworm in the mouse: common themes and unique features

Ascaris lumbricoides, the roundworm, and Trichuris trichiura, the whipworm, are human intestinal nematode parasites; both are soil-transmitted helminths, are often placed together in an epidemiological context and both remain neglected despite high prevalence. Our understanding of parasitic disease continues to be enhanced through animal models. Despite the similarities between whipworm and roundworm, there are key differences between the two species and these have influenced the application of their respective animal models. In the case of T. trichiura, the fact that a murine equivalent, T. muris completes its life cycle in a mouse model has greatly enhanced our knowledge of whipworm biology, pathogenicity and immunology. In contrast, A. lumbricoides and its porcine equivalent, Ascaris suum, lack a rodent model in which the life cycle is completed. However, evidence continues to accumulate demonstrating that mice represent useful models of early Ascaris infection, a key stage of the life cycle. The use of mouse models for both Ascaris and Trichuris has a long history with early pioneers discovering fundamental aspects of each parasite's biology. Novel technologies and perspectives, as outlined in this special issue, demonstrate how through the prism of mouse models, we can continue to explore the similarities and differences between roundworms and whipworms.

Distinct hepatic myeloid and lymphoid cell repertoires are associated with susceptibility and resistance to Ascaris infection

The soil-transmitted helminth Ascaris lumbricoides infects ~800 million people worldwide. Some people are heavily infected, harbouring many worms, whereas others are only lightly infected. The mechanisms behind this difference are unknown. We used a mouse model of hepatic resistance to Ascaris, with C57BL/6J mice as a model for heavy infection and CBA/Ca mice as a model for light infection. The mice were infected with the porcine ascarid, Ascaris suum or the human ascarid, A. lumbricoides and immune cells in their livers and spleens were enumerated using flow cytometry. Compared to uninfected C57BL/6J mice, uninfected CBA/Ca mice had higher splenic CD4+ and γδ T cell counts and lower hepatic eosinophil, Kupffer cell and B cell counts. Infection with A. suum led to expansions of eosinophils, Kupffer cells, monocytes and dendritic cells in the livers of both mouse strains and depletions of hepatic natural killer (NK) cells in CBA/Ca mice only. Infection with A. lumbricoides led to expansions of hepatic eosinophils, monocytes and dendritic cells and depletions of CD8+, αβ, NK and NK T cells in CBA/Ca mice, but not in C57BL/6J mice where only monocytes expanded. Thus, susceptibility and resistance to Ascaris infection are governed, in part, by the hepatic immune system.

Warming can alter host behavior in a similar manner to infection with behavior-manipulating parasites

Parasites are ecologically ubiquitous and, by modifying the physiology and behavior of their host organisms, act as key regulators of the dynamics and stability of ecosystems. It is, however, as yet unclear how parasitic relationships will act to moderate or accelerate the ecological impacts of global climate change. Here, we explore experimentally how the effects of parasites on both the physiology and behavior of their hosts can be moderated by warming, utilising a well-established aquatic host-parasite model system-the ecologically important amphipod Gammarus duebeni and its acanthocephalan parasite Polymorphus minutus. We show that, while only warming affected measured components of host physiology, parasite infection and warming both supressed predator-avoidance behavior of the host independently, yet in a similar manner. Six degrees of warming altered geotactic behaviors to the same extent as infection with behavior-manipulating parasites. These results indicate a novel mechanism by which parasites impact their ecosystems that could be critical to predicting the ecological impacts of warming. Our findings highlight the need for holistic knowledge of interaction networks, incorporating multiple interaction types and behaviors, to predict the effects of both warming and parasitism on the dynamics and stability of ecosystems.

Whipworm and roundworm infections

Trichuriasis and ascariasis are neglected tropical diseases caused by the gastrointestinal dwelling nematodes Trichuris trichiura (a whipworm) and Ascaris lumbricoides (a roundworm), respectively. Both parasites are staggeringly prevalent, particularly in tropical and subtropical areas, and are associated with substantial morbidity. Infection is initiated by ingestion of infective eggs, which hatch in the intestine. Thereafter, T. trichiura larvae moult within intestinal epithelial cells, with adult worms embedded in a partially intracellular niche in the large intestine, whereas A. lumbricoides larvae penetrate the gut mucosa and migrate through the liver and lungs before returning to the lumen of the small intestine, where adult worms dwell. Both species elicit type 2 anti-parasite immunity. Diagnosis is typically based on clinical presentation (gastrointestinal symptoms and inflammation) and the detection of eggs or parasite DNA in the faeces. Prevention and treatment strategies rely on periodic mass drug administration (generally with albendazole or mebendazole) to at-risk populations and improvements in water, sanitation and hygiene. The effectiveness of drug treatment is very high for A. lumbricoides infections, whereas cure rates for T. trichiura infections are low. Novel anthelminthic drugs are needed, together with vaccine development and tools for diagnosis and assessment of parasite control in the field.

Seroprevalence estimates for toxocariasis in people worldwide: A systematic review and meta-analysis

Background

Human toxocariasis is an important neglected disease. We performed a systematic review and meta-analysis study to estimate the global and regional prevalence of anti-Toxocara serum antibodies (referred to as ‘T-seroprevalence’) in human populations around the world.

Methods

We searched five international databases (PubMed, EMBASE, Web of Science, SciELO and Scopus) for seroprevalence studies published from 1 January 1980 to 15 March 2019. We used random effect models to calculate the overall T-seroprevalence (with 95% CIs) in all six WHO regions and worldwide. We also conducted subgroup and linear meta-regression analyses to evaluate the impact of socio-demographic, geographical and climatic parameters on seroprevalence.

Results

We identified 250 eligible studies (253 datasets) comprising 265,327 participants in 71 countries for inclusion in the present meta-analysis. The estimated global T-seroprevalence rate was 19.0% (95%CI, 16.6–21.4%; 62,927/265,327); seroprevalence was highest in the African region (37.7%; 25.7–50.6%) and lowest in the Eastern Mediterranean region (8.2%; 5.1–12.0%). The pooled seroprevalence for other WHO regions was 34.1% (20.2–49.4%) in the South-East Asia; 24.2% (16.0–33.5%) in the Western Pacific; 22.8% (19.7–26.0%) in the American; and 10.5% (8.5–12.8%) in the European regions. A significantly higher T-seroprevalence was associated with a lower income level; lower human development index (HDI); lower latitude; higher humidity; higher temperature; and higher precipitation (P-value < 0.001). Potential risk factors associated with seropositivity to Toxocara included male gender; living in a rural area; young age; close contact with dogs, cats or soil; consumption of raw meat; and the drinking of untreated water.

Conclusions

The present findings indicate high levels of infection with, or exposure to Toxocara spp. in many countries, which calls for increased attention to human toxocariasis and improved measures to prevent adverse health risks of this disease.

There have been many epidemiological studies on the seroprevalence of Toxocara infection or toxocariasis in humans in individual countries, but there has been no systematic review/meta-analysis to estimate the extent of Toxocara infection or exposure in human populations worldwide. By reviewing 250 studies of 265,327 people from 71 countries, we provide the first comprehensive global estimates of T-seroprevalence in humans to date. The findings indicate that almost one fifth (19%) of the world’s human population is seropositive to Toxocara. The highest seroprevalence rates were found in Africa (37.7%) and the lowest in the Eastern Mediterranean region (8.2%). Individual countries with high HDIs and high income levels usually had low T-seroprevalence rates. Our findings also showed that T-seroprevalence varies markedly among countries, according to geographical location (coordinates) and climatic features. Evidence from this study indicates that human toxocariasis is a prevalent, neglected tropical disease and potentially one of major importance to global public health. Our study emphasizes the need for governmental authorities to pay increased attention to the risks and socioeconomic impact of HT in many countries around the world, and for them to design and implement HT prevention or control programs, considering risk predictors identified here.

The role of the liver in the migration of parasites of global significance

Many parasites migrate through different tissues during their life-cycle, possibly with the aim to enhance their fitness. This is true for species of three parasite genera of global importance, Ascaris, Schistosoma and Plasmodium, which cause significant global morbidity and mortality. Interestingly, these parasites all incorporate the liver in their life-cycle. The liver has a special immune status being able to preferentially induce tolerance over immunity. This function may be exploited by parasites to evade host immunity, with Plasmodium spp. in particular using this organ for its multiplication. However, hepatic larval attrition occurs in both ascariasis and schistosomiasis. A better understanding of the molecular mechanisms involved in hepatic infection could be useful in developing novel vaccines and therapies for these parasites.

The liver proteome in a mouse model for Ascaris suum resistance and susceptibility: evidence for an altered innate immune response

Background

Ascariasis is a neglected tropical disease that affects 800 million people worldwide. Whereas most people only experience light worm burden, some people experience heavy worm burdens even after several rounds of chemotherapy, a phenomenon known as predisposition. Such heavy infections are associated with more severe symptoms and increased chronic morbidity.

Methods

In order to investigate potential mechanisms that may explain the observed predisposition, we infected mice with the porcine ascarid Ascaris suum using an established mouse model with two different mouse strains, where the C57BL/6J strain is more susceptible to infection and therefore a model for heavy infection and the CBA/Ca strain is more resistant and thus a model for light infection. At day 7 post-infection we investigated the liver proteome, using shotgun mass spectrometry, of both infected and control mice of each strain.

Results

We identified intrinsic differences, between the two mouse strains, in both oxidative phosphorylation proteins and proteins involved in retinol metabolism. Additionally, we found differences between the two mouse strains in activation of the complement system, where the CBA/Ca strain has higher protein abundances for lectin pathway proteins and the C57BL/6J strain has higher protein abundances for complement inhibiting proteins. The CBA/Ca strain had a higher abundance of proteins involved in the activation of the complement cascade via the lectin pathway. In contrast, the C57BL/6J strain demonstrated a higher abundance of proteins involved in arresting the complement pathway.

Conclusions

We observed clear differences between the two mouse strains both intrinsically and under infection.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3655-9) contains supplementary material, which is available to authorized users.

A comparison of helminth infections as assessed through coprological analysis and adult worm burdens in a wild host

Coprological analysis is the most widely used diagnostic tool for helminth infection in both domestic and wild mammals. Evaluation of the efficacy of this technique is rare, due to the lack of availability of adult worm burden. Where information is available the majority of studies are in small ruminants and seldom in a wild host. This study of 289 wild badgers is the first to report the relationship between faecal egg/larval counts and adult worm burden in badgers whilst also evaluating the reliability of coprological analysis as a diagnostic tool for hookworm (Uncinaria criniformis) and lungworm (Aelurostrongylus falciformis) infection. The prevalence of hookworm and lungworm infection, as assessed through adult worm burden was 59.2% and 20.8% respectively. For both species of helminth, infection was consistently under-reported by coprological analysis compared to adult worm burden with a reported 41% sensitivity for hookworm and 10% for lungworm. A significant positive relationship was found between faecal counts and adult worm burden for both species of helminths. Additionally the density –dependent relationship often reported in helminth infection appears to be weak or non-existent in this study, up to the observed worm intensity of 500.

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Hookworm infection is endemic within the Irish badger population.

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Lungworm infection is also common in Irish badgers.

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Coprological analysis has a low sensitivity for diagnosing infection compared to adult worm burden.

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Faecal is a reliable indicator of intensity of infection.

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Density-dependence is weak, or non-existent up to the observed intensity of 500 worms.

Human toxocariasis

Parasitic nematodes of the genus Toxocara are socioeconomically important zoonotic pathogens. These parasites are usually directly transmitted to the human host via the faecal-oral route and can cause toxocariasis and associated complications, including allergic and neurological disorders. Although tens of millions of people are estimated to be exposed to or infected with Toxocara spp, global epidemiological information on the relationship between seropositivity and toxocariasis is limited. Recent findings suggest that the effect of toxocariasis on human health is increasing in some countries. Here we review the salient background on Toxocara and biology, summarise key aspects of the pathogenesis, diagnosis, and treatment of toxocariasis, describe what is known about its geographic distribution and prevalence, and make some recommendations for future research towards the prevention and control of this important disease.

Helminths in organ transplantation

With transplantation becoming an increasingly routine form of treatment for diverse populations, and with international travel becoming ever more accessible and affordable, the danger of transplantation-mediated helminth infections, exacerbated by coincident immunosuppression, must be considered. In this Review, we attempt to catalogue all clinically-relevant helminthiases that have been reported to coincide with transplantation, whether by transplantation-mediated transmission, reactivation of latent infections in an immunosuppressed context, or possible de-novo infection during the immunosuppressed peritransplant period. Helminthiasis has been reported in cases of kidney, liver, bowel, pancreas, heart, lung, and stem-cell transplant, and blood transfusion. For each helminthiasis, known risk factors, symptoms, and suggested options for screening and treatment are given. We conclude that helminths are a small but important and potentially severe source of disease after transplantation, and, with options for diagnosis and treatment, these pathogens warrant greater consideration during organ implantation. The achievement of immunological tolerance using helminth-derived products is also an exciting future prospect.

Reduced helminth parasitism in the introduced bank vole (Myodes glareolus): More parasites lost than gained

Introduced species are often less parasitised compared to their native counterparts and to ecologically similar hosts in the new environment. Reduced parasitism may come about due to both the loss of original parasites and low acquisition of novel parasites. In this study we investigated the intestinal helminth parasites of the introduced bank vole (Myodes glareolus) in Ireland. Results were compared to data from other European studies and to the intestinal helminth fauna of an ecologically similar native rodent in Ireland, the wood mouse (Apodemus sylvaticus). The helminth fauna of introduced bank voles exhibited low diversity with only 3 species recovered: Aspiculuris tianjinensis; Aonchotheca murissylvatici and Taenia martis larvae. In particular, no adult parasites with indirect life-cycles were found in bank voles suggesting that indirectly transmitted parasites are less likely to establish in invasive hosts. Also, the results of this study add support to the enemy release hypothesis.

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Helminth parasitism was assessed in native wood mice and invasive bank voles.

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Parasite diversity in invasive voles was significantly less than in native mice.

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First record of Aspiculuris tianjinensis and Taenia martis in Ireland.

The significance of cerebral toxocariasis: a model system for exploring the link between brain involvement, behaviour and the immune response

Toxocara canis is a parasitic nematode that infects canines worldwide, and as a consequence of the widespread environmental dissemination of its ova in host faeces, other abnormal hosts including mice and humans are exposed to infection. In such abnormal or paratenic hosts, the immature third-stage larvae undergo a somatic migration through the organs of the body but fail to reach maturity as adult worms in the intestine. The presence of the migrating larvae contributes to pathology that is dependent upon the intensity of infection and the location of the larvae. A phenomenon of potential public health significance in humans and of ecological significance in mice is that T. canis larvae exhibit neurotrophic behaviour, which results in a greater concentration of parasites in the brain, as infection progresses. Toxocara larval burdens vary between individual outbred mice receiving the same inocula, suggesting a role for immunity in the establishment of cerebral infection. Although the systemic immune response to T. canis has been widely reported, the immune response in the brain has received little attention. Differential cytokine expression and other brain injury-associated biomarkers have been observed in infected versus uninfected outbred and inbred mice. Preliminary data have also suggested a possible link between significant memory impairment and cytokine production associated with T. canis infection. Mice provide a useful, replicable animal model with significant applicability and ease of manipulation. Understanding the cerebral host-parasite relationship may shed some light on the cryptic symptoms of human infection where patients often present with other CNS disorders such as epilepsy and mental retardation.

Ascaris co-infection does not alter malaria-induced anaemia in a cohort of Nigerian preschool children

BACKGROUND

Co-infection with malaria and intestinal parasites such as Ascaris lumbricoides is common. Malaria parasites induce a pro-inflammatory immune response that contributes to the pathogenic sequelae, such as malarial anaemia, that occur in malaria infection. Ascaris is known to create an anti-inflammatory immune environment which could, in theory, counteract the anti-malarial inflammatory immune response, minimizing the severity of malarial anaemia. This study examined whether Ascaris co-infection can minimize the severity of malarial anaemia.

METHODS

Data from a randomized controlled trial on the effect of antihelminthic treatment in Nigerian preschool-aged (6-59 months) children conducted in 2006-2007 were analysed to examine the effect of malaria and Ascaris co-infection on anaemia severity. Children were enrolled and tested for malaria, helminths and anaemia at baseline, four, and eight months. Six hundred and ninety subjects were analysed in this study. Generalized linear mixed models were used to assess the relationship between infection status and Ascaris and Plasmodium parasite intensity on severity of anaemia, defined as a haemoglobin less than 11 g/dL.

RESULTS

Malaria prevalence ranged from 35-78% over the course of this study. Of the malaria-infected children, 55% were co-infected with Ascaris at baseline, 60% were co-infected four months later and 48% were co-infected eight months later, underlining the persistent prevalence of malaria-nematode co-infections in this population. Over the course of the study the percentage of anaemic subjects in the population ranged between 84% at baseline and 77% at the eight-month time point. The odds of being anaemic were four to five times higher in children infected with malaria compared to those without malaria. Ascaris infection alone did not increase the odds of being anaemic, indicating that malaria was the main cause of anaemia in this population. There was no significant difference in the severity of anaemia between children singly infected with malaria and co-infected with malaria and Ascaris.

CONCLUSION

In this cohort of Nigerian preschool children, malaria infection was the major contributor to anaemia status. Ascaris co-infection neither exacerbated nor ameliorated the severity of malarial anaemia.

Ascaris and ascariasis

Ascaris lumbricoides and Ascaris suum are widespread parasitic nematodes of humans and pigs respectively. Recent prevalence data suggests that approximately 1.2 billion people are infected. Adult worms exhibit an overdispersed frequency distribution in their hosts and individuals harbouring heavy burdens display associated morbidity. In this review, we describe the parasite, its distribution and measures undertaken to control infection.

Investigating the underlying mechanism of resistance to Ascaris infection

The generative mechanism(s) of predisposition to Ascaris infection are currently unknown. While many factors play a role in interindividual infection intensity, much focus has been placed on the host's immunological response to infection and the underlying genetics. The present review describes the research conducted that has examined various immunological parameters and genetic factors that may play a role in resistance to ascariasis. We also discuss the contribution that animal models have made to our understanding of resistance to the parasitic roundworm and their role in possible future work.

Identification of a high diversity of Cryptosporidium species genotypes and subtypes in a pediatric population in Nigeria

A longitudinal study was conducted to determine the epidemiology of Cryptosporidium in 1,636 children in Nigeria. Oocyst prevalence ranged from 15.6% to 19.6% over one year. Cryptosporidium hominis (34), C. parvum (25), C. parvum/C. hominis (4), C. meleagridis (5), Cryptosporidium rabbit genotype (5), Cryptosporidium cervine genotype (3), and C. canis (1) were identified by polymerase chain reaction-restriction fragment length polymorphism analysis. Glycoprotein 60 subgenotyping showed that 28 amplifiable C. hominis isolates consisted of 12 subtypes that belonged to 5 subtype families (Ia, Ib, Id, Ie, and 1 novel subtype family, Ih) and 23 amplifiable C. parvum isolates consisted of 6 subtypes that belonged to 4 subtype families (IIa, IIc, Iii, and IIm). Three C. meleagridis isolates sub-genotyped by sequence analysis of the small subunit ribosomal RNA gene fragment were type 1. This study is the first one to genetically characterize Cryptosporidium species and subtypes in Nigeria and highlights the presence of a high Cryptosporidium diversity in this pediatric population.

Patterns of soil-transmitted helminth infection and impact of four-monthly albendazole treatments in preschool children from semi-urban communities in Nigeria: a double-blind placebo-controlled randomised trial

Background

Children aged between one and five years are particularly vulnerable to disease caused by soil-transmitted helminths (STH). Periodic deworming has been shown to improve growth, micronutrient status (iron and vitamin A), and motor and language development in preschool children and justifies the inclusion of this age group in deworming programmes. Our objectives were to describe the prevalence and intensity of STH infection and to investigate the effectiveness of repeated four-monthly albendazole treatments on STH infection in children aged one to four years.

Methods

The study was carried out in four semi-urban villages situated near Ile-Ife, Osun State, Nigeria. The study was a double-blind placebo-controlled randomised trial. Children aged one to four years were randomly assigned to receive either albendazole or placebo every four months for 12 months with a follow-up at 14 months.

Results

The results presented here revealed that 50% of the preschool children in these semi-urban communities were infected by one or more helminths, the most prevalent STH being Ascaris lumbricoides (47.6%). Our study demonstrated that repeated four-monthly anthelminthic treatments with albendazole were successful in reducing prevalence and intensity of A. lumbricoides infections. At the end of the follow-up period, 12% and 43% of the children were infected with A. lumbricoides and mean epg was 117 (S.E. 50) and 1740 (S.E. 291) in the treatment and placebo groups respectively compared to 45% and 45% of the children being infected with Ascaris and mean epg being 1095 (S.E. 237) and 1126 (S.E. 182) in the treatment and placebo group respectively at baseline.

Conclusion

Results from this study show that the moderate prevalence and low intensity of STH infection in these preschool children necessitates systematic treatment of the children in child health programmes.

Trial Registration

Current controlled trials ISRCTN44215995.

The migration of Ascaris suum larvae, and the associated pulmonary inflammatory response in susceptible C57BL/6j and resistant CBA/Ca mice

Ascariasis is an important infection in humans (Ascaris lumbricoides) and pigs (Ascaris suum) and individuals appear to be predisposed to either heavy or light worm burdens. These extremes of susceptibility and resistance are represented in a mouse model by 2 strains of mice, CBA mice showing high resistance to infection and C57BL/6 which are highly susceptible, as reflected in worm burdens in the lungs 6-7 days after infection. In an attempt to identify the point at which the difference between these 2 strains is first manifested, we quantified worm burdens at key stages during infection leading up to the pulmonary stage of development. Thus mice were inoculated with fully embryonated A. suum eggs and larval burdens were enumerated in the large intestine and rectum, liver and lungs of the 2 strains at 6 h post-inoculation (p.i.) and on each of days 1-8 p.i. inclusively. A higher percentage of the total inoculum was recovered from the intestine/rectum of C57BL/6j mice in contrast to CBA/Ca mice at 6 h p.i. Larvae were recovered from the intestinal contents and also whilst actively migrating through the large intestinal wall. The number of larvae recovered was significantly reduced in CBA/Ca mice in contrast to C57BL/6j mice between the phase of migration from the liver and arrival in the lungs. The combined results of the inoculation of mice with corticosteroids and the examination of the change in profile and number of leukocytes present in bronchoalveolar lavage fluid suggested that the pulmonary inflammatory immune response was not prominently involved in primary protection of mice to A. suum infection in the latter days of infection in the lungs. The susceptible C57BL/6j mice produced a BAL response almost twice as intense as that of resistant CBA/Ca mice with stronger neutrophil, lymphocyte and eosinophil but not macrophage components, suggesting that the difference in worm burdens between the strains was generated earlier in the course of infection. These results were further corroborated by a histological examination of the lung tissues which showed that the passage of the larval stages of A. suum through the mouse lungs was associated with a marked inflammatory response in both strains. Again, C57BL/6j mice exhibited increased inflammation relative to CBA/Ca mice. Hence some hepatic/post-hepatic factor that varies between the 2 strains, but exerts its effect before the lung phase plays a critical role in determining the success of larvae through the host tissues. The possible sites of this host defence are reviewed.

Utilization of brown troutSalmo truttabyAcanthocephalus clavulain an Irish lake: is this evidence of a host shift?

The population biology of the fish acanthocephalanAcanthocephalus clavulawas described from 161 wild brown trout,Salmo truttasampled over a two-year period in Clogher Lake in the west of Ireland. Overall prevalence of the parasite was 86% and the mean abundance was 53 worms per fish. Despite the presence of large numbers of worms in the trout very few females (2%) attained full reproductive maturity. This suggests that trout is an accidental host. A sample of yellow eels,Anguilla anguillawas examined at a different time from the same lake. The prevalence ofA. clavulawas 97% and the average abundance was 8 worms per fish. In contrast to the situation in trout, the proportion of female worms attaining full reproductive maturity was 61% fulfilling the expected characteristic of a preferred definitive host. The possible explanations for the very high abundance ofA. clavulain trout are discussed and include the influence of fluctuations in host populations, host diet and the absence of a potential competitor.

A murine model for cerebral toxocariasis: characterization of host susceptibility and behaviour

Toxocara canis, the parasitic roundworm of dogs, can infect a number of paratenic hosts, such as mice and humans, due to the widespread dissemination of its ova in the environment. In these paratenic hosts, larvae have been shown to exhibit a predilection for the central nervous system, resulting in an increasing number of parasites migrating to the brain as infection progresses. In an initial experiment, we investigated the differential brain involvement of T. canis in 7 strains of inbred mice, and chose 2 strains, susceptible (BALB/c) and resistant (NIH) to cerebral infection. In a second experiment, both strains were investigated in terms of course of migration, larval accumulation, and behavioural response to T. canis infection. Results revealed that infected BALB/c mice took significantly longer to drink from a water source (following a period of deprivation), compared with control mice, indicating some degree of memory impairment. Cerebral larval recoveries from both strains of mice demonstrated variation between the two experiments, suggesting that larval burdens may not be a reliable indicator of susceptibility or resistance to T. canis infection. The percentage of total recovered larvae in each organ may be a better representation of larval distribution. Our model system may provide insights into the impact of chronic geohelminth infection on cognitive development.

The development of a mouse model to explore resistance and susceptibility to early Ascaris suum infection

Ascaris suum and Ascaris lumbricoides exhibit an over-dispersed frequency distribution in their host populations in both the adult and larval stages. The impact of host factors on this observed distribution is still poorly understood and difficult to investigate in the natural host populations. The use of a mouse model has been supported by the observations that the larval migratory pattern, in this host, mimics the pattern observed in the pig. We explored the extrinsic factors that might affect the quantitative recovery of larvae during this migration in order to standardize a model system facilitating accurate future assessment of host genetic variation on this phase of the infection. In Exp. 1 larvae accumulated in the livers of both C57BL/6j and BALB/c mice up to and including days 4-5 p.i. and then declined in both strains until day 9. Loss of larvae from the livers corresponded to arrival in the lungs and maximum accumulation on day 7 p.i. but recovery was considerably higher in C57BL/6j mice. It was concluded that day 7 recoveries gave the best indication of relative resistance/susceptibility to this parasite. In Exp. 2 A/J, BALB/c, CBA/Ca, C57BL/6j, C3H/HeN, DBA/2, NIH, SJL, and SWR mice were compared. C57BL/6j mice were identified as the most susceptible strain and CBA/Ca mice as having the most contrasting phenotype, but with a similar kinetic pattern of migration. Finally, in Exp. 3, a strong positive correlation between the size of the inoculum and the mean worm recovery from the lungs was found in CBA/Ca and C57BL/6j mice, but the difference between these strains was highly consistent, 66.6-80%, regardless of the initial dose. These results demonstrate that, using our protocols for infection and recovery, between-experiment variation in A. suum worm burdens is minimal, and that C57BL/6j mice are highly susceptible to infection compared to other strains. The mechanistic basis of this susceptibility in relation to the resistance of other strains is unknown, but the possibilities are reviewed.

Comparison of morphological characters in Irish and English populations of the acanthocephalan Pomphorhynchus laevis (Müller, 1776)

Pomphorhynchus laevis is believed on ecological evidence to exist as three strains in the British Isles. However, the strains have never been shown to be capable of being distinguished using morphological characters. A morphological comparison was made between a sample of P. laevis from Salmo trutta in L. Feeagh in the west of Ireland and a sample from Leuciscus cephalus in R. Culm in the south of England. The length and width of the trunk, neck, bulb, proboscis and hooks were measured. The number of hooks per row, the number of rows and the positions of the stoutest and longest hooks were also recorded. A Principal Components Analysis based on the morphological measurements confirmed the separation of the two populations and showed that two characters successfully identified the populations: the position of the stoutest hook and the ratio of numbers of anterior to posterior hooks.

Evidence for the hypothesis of strain formation inPomphorhynchus laevis(Acanthocephala): an investigation using mitochondrial DNA sequences

A hypothesis has been erected stating that in the British Isles the acanthocephalan,Pomphorhynchus laeviscan be separated into 3 strains, an English, Irish and marine strain. Ecological and morphological evidence exists in support of this hypothesis. An investigation at the molecular level was conducted in order to test the validity of the existing evidence. A mitochondrial gene, subunit I of cytochrome c oxidase was partially sequenced from 3 Irish populations ofP. laevis, 1 Scottish population and 3 English populations.P. laevissequences from brown trout from Ireland, England and Scotland were very similar, showing a mean sequence divergence of 0·7%. Sequences from two populations ofP. laevisfrom English chub and bullhead were also similar to each other (0·35% divergence). These two groups of sequences, the brown trout group and the chub/bullhead group were 2·2% different. These data confirm the existence of at least 2 strains in Ireland and Britain, although there is evidence to suggest that these strains are defined by their host species rather than by their geographical distributions.

Ocular Toxocariasis in Schoolchildren

Ocular toxocariasis in humans is typically a unilateral disease caused by second-stage larvae of the Toxocara species. Serological evidence of widespread infection in humans provides little information on clinical disease. There is only a single previous estimate of the prevalence of ocular toxocariasis (from Alabama). The present survey examined the extent of consultant-diagnosed toxocaral eye disease among a population of schoolchildren. More than 120,000 participants were surveyed by questionnaire and follow-up. Two sets of control subjects from the same school and from the same county were compared with persons who had ocular toxocariasis. The prevalence of consultant-diagnosed toxocaral eye disease was 6.6 cases per 100,000 persons when only cases regarded as definite by the consultant ophthalmologist were included. This increased to 9.7 cases per 100,000 persons when both definite and strongly suspected cases were included. Geophagia and a history of convulsion were associated with toxocaral eye disease in both of the case-control studies.

Interspecific interactions between Acanthocephala in the intestine of brown trout: are they more frequent in Ireland?

The aim of this paper was to test the hypothesis that when the 2 species of Acanthocephalan Pomphorhynchus laevis and Acanthocephalus clavula are found concurrently within the intestine of brown trout under field conditions, they have the potential to interact negatively. Evidence has shown that Acanthocephala are more likely to exhibit negative interactions with their own and other species, under both field and experimental conditions. Furthermore, the likelihood of these interactions is increased in Ireland because of the absence of certain definitive hosts and the fact that concurrent infections by two or more species of Acanthocephala are more commonly observed in fish. Data collected from wild and stocked brown trout and from 2 lakes provided an opportunity to compare the 2 potentially interacting helminth species in their fundamental and realized niche and several pieces of convincing evidence are provided here to support the hypothesis. A significant negative association between the numbers of each species found in individual fish was reported and this was consistent for both wild and stocked trout. Furthermore, an analysis of the proportions of low, moderate and high intensity infections in single and concurrent infections revealed a significant reduction in increasing intensities in concurrent infections compared to single infections. Finally, strikingly different patterns of niche inhabitation were observed, particularly for P. laevis in the presence of A. clavula in wild trout. Results from the niche width analysis also support the observations on average position in single and concurrent infections. The niche width of P. laevis when it co-occurred with A. clavula decreased markedly in high intensity infections compared to low intensity infections.

Comparison of the macroparasite communities of wild and stocked brown trout (Salmo trutta L.) in the west of Ireland

The aim of the present study was to compare the helminth infra and component communities of wild and stocked brown trout in Lough Feeagh, in the west of Ireland, and also to examine the establishment and development of helminth communities in stocked brown trout. Fish were sampled in May, August and November 1997 and 1998 and an additional sample of wild brown trout was examined in April 1997. In total 217 wild trout and 122 stocked trout were examined. The acanthocephalans Acanthocephalus clavula and Pomphorhynchus laevis were the first parasite species to infect stocked trout in May 1997. In May 1998 both acanthocephalan species along with the trout specialists Eubothrium crassum and Crepidostomumfarionis were the first to infect trout. Mean species richness values for stocked trout increased from May to November, in 1997 and 1998. For wild trout, mean species richness values increased from April to November, in 1997 and decreased from May to November in 1998. The parasite communities of wild trout were richer than those of stocked trout in May of both years. In August the parasite communities recorded for wild and stocked trout were similar in terms of the number of species present but differed in terms of structure, and in November the parasite communities of stocked trout were richer than those of wild trout.

Dimeric inhibins in girls from birth to adulthood: relationship with age, pubertal stage, FSH and oestradiol

OBJECTIVE

Inhibin B is produced by granulosa cells in small antral follicles under the influence of FSH, whilst inhibin A is produced by larger follicles and the corpus luteum. The aims of our study were to investigate how these inhibins change from birth to late adolescence in girls, to derive reference data and to explore their relation with pubertal stage, FSH, oestradiol and each other.

STUDY DESIGN AND SUBJECTS

Blood samples were collected from: (a) 345 girls aged 0--18 years to obtain age-related reference data, and (b) 80 pre-menarcheal girls with full pubertal staging, of whom 40 were on GH treatment at the time of sampling.

MEASUREMENTS

Dimeric inhibins A and B were measured by double antibody enzyme-linked immunosorbent assay (ELISA), FSH by immunoradiometric assay (IRMA) and oestradiol by radioimmunoassay.

RESULTS

Median inhibin B was low until age 6 years, slightly higher from 6 to 10 years, then increased from 10 to 12 years to reach a plateau from 12 to 18 years. Inhibin A was usually detectable in girls younger than 3 months but thereafter became undetectable in most samples until after age 10 years, when median levels rose progressively to 14 years, then stabilized from 14 to 18 years. Both inhibins displayed considerable scatter about the median throughout infancy, childhood and adolescence. Girls aged 0--10 years showed a positive correlation between inhibins A and B (P < 0.0001), whereas those aged 14--18 years showed an inverse relationship (P < 0.001), indicating the onset of ovulatory cycles. Age-related reference ranges and data for calculation of SD scores are presented. GH-treated girls at pubertal stage B2 (but not at B1 or B3--5) had higher inhibin B and FSH levels than untreated girls and were excluded from further analysis. Both inhibins A and B increased during puberty (P < 0.0001) and were positively correlated with each other (P < 0.01). Both inhibins were also positively correlated with FSH in pre-pubertal girls (P < 0.05) but not at pubertal stages B3--5.

CONCLUSIONS

Although median levels of inhibins A and B remained low until after age 10 years in girls, the increased levels of both inhibins in individual samples, together with their positive relationship with FSH, provide further evidence of sporadic follicular development throughout infancy and childhood under the influence of FSH. The increase in both inhibins during puberty and their changing relationship with FSH are in keeping with the concept of follicular growth being dependent on the duration of FSH elevation above a critical threshold rather than the degree of elevation per se.

Inhibin B in boys from birth to adulthood: relationship with age, pubertal stage, FSH and testosterone

OBJECTIVE

Inhibin B in males is produced principally by Sertoli cells under the influence of FSH and is thought to have a role in feedback regulation of FSH. The aims of our study were to investigate how inhibin B changes from birth to late adolescence in boys, to derive reference data and to explore its relation with pubertal stage, FSH and testosterone.

DESIGN AND SUBJECTS

Blood samples were collected from (i) 366 boys aged 0--18 years to obtain age-related reference data; (ii) 195 boys who had full pubertal staging; and (iii) a cohort of 15 boys studied longitudinally as they approached and entered early puberty.

MEASUREMENTS

Dimeric inhibin B was measured by double antibody enzyme-linked immunosorbent assay (ELISA), FSH by immunoradiometric assay (IRA) and testosterone by an extraction radioimmunoassay.

RESULTS

Inhibin B was high in infant boys, decreased gradually to a nadir at 6--10 years of age, then increased rapidly in early adolescence to reach a new plateau at 12--17 years. It was detectable in all samples. Age-related reference ranges and data for calculation of SD scores are presented. In prepubertal boys, inhibin B correlated positively with age (P < 0.001), but not with FSH. Inhibin B increased progressively from pubertal stages G1 to G3 but then decreased slightly at stages G4 to G5 (P less-than-or-equal 0.01). At stage G2, inhibin B correlated positively with testosterone (P < 0.01) but not with FSH. From stage G3 onwards, inhibin B correlated inversely with FSH (P < 0.01) but lost its relationship with testosterone. In the cohort of boys studied longitudinally, inhibin B increased progressively prior to pubertal onset and further on entry into early clinical puberty (P < 0.05). Testosterone also increased over this period (P < 0.05) but FSH showed no significant change.

CONCLUSIONS

The two peaks of inhibin B during infancy and early puberty appear to reflect the two periods of Sertoli cell proliferation in normal human males. During mid-childhood, a relatively constant amount of inhibin B is secreted constitutively. The early FSH-independent increase in inhibin B that precedes clinical puberty and continues to stage G2 may be stimulated by testosterone or other factors from Leydig cells. The inverse relationship between inhibin B and FSH that subsequently develops from mid-puberty onwards is consistent with the establishment of a negative feedback loop at this time.

The public health importance of Ascaris lumbricoides

Numerous studies have shown that anthelminthic treatment can be effective in improving growth rates when given to malnourished children with ascariasis. Recent investigations have also indicated that Ascaris infections can affect mental processing in some school children. Poor socio-economic conditions are among the key factors linked with higher prevalences of ascariasis, as are defaecation practices, geophagia, cultural differences relating to personal and food hygiene, occupational necessity, agricultural factors, housing style, social class and gender. Chemotherapy is currently the major tool used for the strategic control of ascariasis as a short-term goal. In the long term, improvements in hygiene and sanitation are thought to aid long-term control considerably. Targeted treatment, especially when aimed at schoolchildren, has been a major focus of recent control efforts in some areas. Universal treatment reaches more people and thus decreases further aggregate morbidity, especially in nutritionally vulnerable preschool-age children. Selective treatment requires technical effort to identify heavily infected individuals; acceptance by the community may vary in less educated populations when some individuals receive treatment and others do not. Child-targeted treatment may be more cost-effective than population treatment in reducing the number of disease cases and, in high transmission areas, expanding coverage of a population can be a more cost-effective strategy than increasing the frequency of treatment.

The public health significance of Trichuris trichiura

An estimated 1049 million persons harbour T. trichiura, including 114 million preschool-age children and 233 million school-age children. The prevalence of T. trichiura is high and may reach 95% in children in many parts of the world where protein energy malnutrition and anaemias are also prevalent and access to medical care and educational opportunities is often limited. The Trichuris dysentery syndrome (TDS) associated with heavy T. trichiura, which includes chronic dysentery, rectal prolapse, anaemia, poor growth, and clubbing of the fingers constitutes an important public health problem, as do lighter but still heavy infections, even if not strictly TDS, especially in children. The profound growth stunting in TDS can be reversed by repeated treatment for the infection and, initially, oral iron. However findings from Jamaica strongly suggest that the significant developmental and cognitive deficits seen are unlikely to disappear without increasing the positive psychological stimulation in the child's environment. The severe stunting in TDS now appears likely to be a reaction at least in part to a chronic inflammatory response and concomitant decreases in plasma insulin-like growth factor-1 (IGF-1), increases in tumor necrosis factor-alpha (TNF-alpha) in the lamina propria of the colonic mucosa and peripheral blood (which likely decrease appetite and intake of all nutrients) and a decrease in collagen synthesis. Improvements in cognitive performance have been found after treatment for relatively heavy infections (without chronic dysentery) in school-going children; it is unclear precisely how much T. trichiura interferes with children's ability to access educational opportunities, but treatment of infections whenever possible is obviously sensible. The blood loss that can occur in T. trichiura infection is likely to contribute to anaemia, particularly if the child also harbours hookworm, malaria and/or has a low intake of dietary iron. Community control is important, particularly for the individuals within a population who harbour heavy worm burdens; this means children, with special attention to girls who will experience increased iron requirements and blood loss due to menstruation, pregnancies, and lactation. Mebendazole and albendazole, both of which are on the WHO Essential Drugs List, are very effective against T. trichiura; multiple doses are needed to attain complete parasitological cure in all cases. However the goal of control programmes in endemic areas is morbidity reduction, which follows when intensity of infection is significantly reduced.

The influence of inoculum size and time post-infection on the number and position of Toxocara canis larvae recovered from the brains of outbred CD1 mice

Outbred CD1 mice were administered doses of 1000 and 3000 Toxocara canis eggs and postmortem took place on days 7, 42 and 120 post-infection. Mice were killed by cervical dislocation and brains were sagitally bisected and fixed in 10% neutral buffered formalin prior to histological preparation and examination. The number of T. canis larvae were counted per brain and per section and the number of larvae cited for the first time per section were also recorded. These observations were compared by dose administered and by day of postmortem. The total number of larvae per brain and per section was higher for the 3000 dose compared to the 1000 dose. A different pattern emerged for the number of larvae observed in the brain over the three postmortem days depending upon the dose received. For the 1000 dose larval numbers increase from day 7 to day 120 whereas for the 3000 dose the opposite trend occurs. Larvae were assigned to one of five regions in the brain - the telencephalon, diencephalon, cerebellum, medulla, pons and brain stem and the olfactory bulb. Larvae did not show a random distribution in the brain. The majority of larvae were recorded from the telencephalon and the cerebellum. The percentage of sections with larvae in them is higher for the 3000 dose compared to the 1000 dose for all regions of the brain. For the majority of regions, the percentage of sections with larvae in them increases between day 7 and 42 and then decreases by day 120 and this is most pronounced for the cerebellum. For the telencephalon and diencephalon only, more larvae were detected on the right hand side of the brain compared to the left hand side. Statistical analysis revealed that dose and brain region are significant factors which influence the number of larvae observed in histological sections of the brain but day post-infection is not.

Toxocara in the mouse: a model for parasite-altered host behaviour?

The objective of this paper is to critically evaluate the significance of parasite-altered host behaviour in the Toxocara mouse model particularly in the light of the Manipulation Hypothesis. Murine behaviours were examined in both outbred and inbred strains of mice infected with different doses of Toxocara canis ova. Behaviours investigated included activity, exploration, response to novelty, anxiety, learning, memory and social behaviour. Subsequent modifications to the behaviour of infected mice were investigated with respect to dose administered and larval accumulation in the brain. There was substantial variation in the number of larvae recovered from brains of individual mice, which received similar doses of Toxocara ova. Furthermore, the numbers of larvae recovered at different doses differed significantly between an outbred and inbred strain of mouse. Alterations in infected host behaviour occurred and were related to the number of larvae recovered from the brain. For social behaviour in outbred mice, a high infection in the brain reduced levels of aggressive behaviour and increased levels of flight and defensive behaviours. In contrast, outbred mice with a low infection in the brain displayed a greater level of risk behaviour in respect of predator odour and the light/dark box compared to control or high infection mice. Post-infection, outbred mice were more immobile whereas inbred mice showed reduced immobility and increased digging and climbing. Impaired learning ability was observed in outbred mice with moderate and high levels of infection in the brain compared to control and low infection mice. Toxocara infection has an impact upon a diverse range of murine behaviours with little evidence for a specific and hence an adaptive alteration. Many of the effects on murine host behaviour by Toxocara are likely to be pathological side effects of infection rather than as a consequence of adaptive host-manipulation. Observed changes in murine behaviour may be relevant to human toxocariasis.

Relationship between three intensity levels of Toxocara canis larvae in the brain and effects on exploration, anxiety, learning and memory in the murine host

Outbred LACA mice were administered low (100 ova), medium (1000 ova), high (3000 ova) and trickle (4x250 ova) doses of Toxocara canis ova and the effect of infection was examined with respect to the number of larvae recovered from the brain and their behaviour. Recovery of larvae from the brain was generally low with the % recovery expressed in terms of the total dose administered being highest for the 3000 dose (6.1%) and 1000 dose (6%), followed by the 100 (4.4%) and trickle (3.5%) doses. The variation in larval recoveries was large between individual mice receiving similar doses. The level of infection in the brain was lower in mice receiving a multiple as opposed to an equivalent single dose of ova. Mice were then divided into three larval intensity groupings based upon the number of larvae recovered from their brain. The ranges for the groups were as follows: low intensity group, 0-15 larvae; moderate intensity group, 27-55 larvae; high intensity group, 66-557 larvae. Three behavioural tests were carried out on control and infected mice. Exploration and response to novelty was examined using a 'T' maze and learning was investigated by means of a water-finding task. Anxiety was measured using an elevated plus maze apparatus. Infected mice were less explorative and less responsive to novelty in the 'T' maze and this was particularly pronounced for the heavily infected mice. In the elevated plus maze, infected mice displayed reduced levels of anxiety to aversive and exposed areas of the maze, particularly in the case of the moderate and high intensity mice. There was evidence for impaired learning ability in the water task apparatus for moderate and high intensity mice. In general, the effects of infection on behaviour were more pronounced in the moderate and high intensity groups compared to the low intensity group.

Influence of mouse strain, infective dose and larval burden in the brain on activity in Toxocara-infected mice

Outbred LACA mice and inbred NIH mice were administered low (100 ova), medium (1000 ova), high (3000 ova) and trickle (4x250 ova) doses of Toxocara canis ova and the effect of infection on activity was examined with respect to: (i) the dose of ova administered and (ii) the number of larvae recovered from the brain. Larval recovery from the brain was significantly reduced in NIH mice compared to LACA mice for the 1000, 3000 and trickle doses. Mice from each strain were divided into larval intensity groupings based upon the number of larvae recovered from their brain. Activity for each mouse was measured pre- and post-infection by observing its behaviour in the home cage. Activity was assessed by monitoring six different independent categories of murine behaviour - ambulation, grooming, rearing, digging, climbing and immobility. Within each behavioural category, the duration of time spent at each behaviour per mouse within one thousandth of a second, the number of short bouts performed and the number of long bouts of behaviour performed were recorded over a 20 min period. Activity of LACA and NIH mice differed prior to infection. LACA mice spent more time immobile compared to NIH mice, which ambulated and climbed more. Variations in activity were also observed between groups of mice prior to infection. The effect of infection differed by strain, by dose and by larval intensity. Post-infection LACA mice became more immobile and ambulated less. NIH mice showed reduced immobility, but while ambulation decreased digging and climbing increased post-infection. Short bouts of activity remained unchanged among LACA mice post-infection but showed an increase for some behaviours in NIH mice.

Asymptomatic shedding of Cryptosporidium oocysts by red deer hinds and calves

Levels of Cryptosporidium infection in a group of red deer were monitored over a period of 1 year. Faecal samples were examined on an approximate monthly basis from adult hinds and calves for the presence of Cryptosporidium oocysts. The water-ether sedimentation method followed by sucrose flotation and a monoclonal antibody identification procedure were used. It was found that apparently healthy adult deer were shedding low numbers of oocysts in their faeces throughout the year and that there appeared to be a periparturient increase in the numbers of oocysts shed. Samples taken from 6-month-old deer calves, both in-house and on pasture, had low numbers of Cryptosporidium oocysts, indicating that the calves were also asymptomatically shedding oocysts.

Experimental infections of farmed eels with different Trypanosoma granulosum life-cycle stages and investigation of pleomorphism

Trypanosoma granulosum, a flagellate protozoon commonly found in the blood of the European eel Anguilla anguilla, was injected experimentally into uninfected eels purchased from a local farm. In order to investigate the infectivity of different stages in the life cycle, trypanosomes from various sources were used for inoculation. Infectivity was greatly reduced in in vitro culture stages inoculated at 20 C. Isolated bloodstream stages injected into groups of animals held at 12 and 20 C could be detected for over 70 days but did not appear to multiply. Naturally infected Hemiclepsis marginata, a piscivorous leech known to serve as vector, produced detectable, single-peak infections in eels held at 20 C. Infections were characterized by a prepatent stage and a phase of rising parasitemia. Peak infection intensities ranged between 1 and 7 x 10(4) trypanosomes/ml. Trypanosomes in the bloodstream of eels experimentally infected with leeches, divided at a very low rate during the early stages of infection. Small morphs present during the early phase of rising parasitemia were gradually replaced by larger trypanosomes. The overall length frequency distribution of trypanosomes was unimodal.

Natural immunity to Ascaris lumbricoides associated with immunoglobulin E antibody to ABA-1 allergen and inflammation indicators in children

Children putatively immune to the large roundworm Ascaris lumbricoides were identified in an area of Nigeria where infection is hyperendemic. Immunity was associated with higher levels of serum ferritin, C-reactive protein, and eosinophil cationic protein, indicating ongoing acute phase or inflammatory processes. In contrast, children who were susceptible to the infection had little serological evidence of inflammation despite their high parasite burdens. Immunoglobulin G (IgG) antibody activity in all subclasses was present in high titer in most children but appeared to have no protective function. Despite exceptionally high total IgE levels, there was no evidence that atopic responses to local common allergens was associated with natural immunity to Ascaris. Among those individuals who produced IgG antibody to recombinant ABA-1 allergen of Ascaris, the naturally immune group had significantly more IgE antibody to the allergen than did those susceptible to the infection. IgE antibody responses in conjunction with innate inflammatory processes therefore appear to associate with natural immunity to ascariasis.

The relationship between numbers of larvae recovered from the brain of Toxocara canis-infected mice and social behaviour and anxiety in the host

The effect of the nematode Toxocara canis on social behaviour and anxiety levels of adult male outbred (LACA) mice was examined following infection with a single dose of 2000 ova. The actual number of larvae recovered from the brain of each individual mouse was determined after behavioural testing. The effect of the parasite on mouse behaviour was analysed by both the initial dose administered (i.e. infected versus control) and the degree of infection in the brain. There was substantial variation in the number of larvae recovered from the brains of the individual mice and the magnitude of behavioural change was associated with the level of infection. Examination of social behaviour for both analyses revealed that the infection reduced levels of aggressive behaviour and increased levels of flight and defensive behaviours. High infection in the brain induced the greatest degree of behavioural change which decreased in mice with lower infections. In contrast the analysis of anxiety levels in mice by initial dose administered revealed no difference between infected and control mice. Mice with low infection in the brain, however, displayed a greater level of risk behaviour by spending more time in the vicinity of a predator odour and in the light area of a light/dark paradigm than control or high infection mice. The results suggest that the behaviour of mice infected with T. canis is influenced by the number of larvae accumulated in the brain. This may have important consequences for the conclusions drawn on the effect of this parasite on murine behaviour.

Community study of toxoplasma antibodies in urban and rural schoolchildren aged 4 to 18 years

To estimate the prevalence of toxoplasma antibodies in schoolchildren and their association with clinical and environmental data, antibody titres were measured in 1276 children aged 4 to 18 years attending primary and secondary schools. Environmental and clinical data were obtained by questionnaire. Altogether 12.8% (163/1276) of children had antibodies to Toxoplasma gondii with no difference between the sexes. Seroprevalence was higher in country children (16.6% (50/302)) than town children (10.2% (75/737)). The proportion testing positive increased with age in both town and country children. No association with cat ownership was found. Toxoplasma seropositivity was associated with a positive toxocara titre, having had a bitch whelp in the past two years, and having an unwormed dog at home. Lack of energy or tiredness in the last 12 months were the only clinical features associated with a positive titre.