Is Necator americanus approaching a mutualistic symbiotic relationship with humans?

Controlled Infection of Humans with the Hookworm Parasite Necator americanus to Accelerate Vaccine Development : The Human Hookworm Vaccination/Challenge Model (HVCM)

In this chapter, we describe the scientific, technical, clinical and regulatory aspects of establishing a controlled human hookworm infection (CHHI) model in non-endemic and endemic geographical regions, to facilitate a pathway towards accelerated vaccine development. The success achieved in establishing the CHHI platform specifically allows the Human Hookworm Vaccine Initiative (HHVI) to accelerate its progress by establishing a human hookworm vaccination/challenge model (HVCM) in a hookworm endemic area of Brazil. The HVCM will permit the rapid and robust determination of clinical efficacy in adults, allowing for early selection of the most efficacious human hookworm vaccine (HHV) candidate(s) to advance into later-stage pivotal paediatric clinical trials and reduce the overall number of participants required to assess efficacy (Diemert et al. 2018).

An Absence of Epstein-Barr Virus Reactivation and Associations with Disease Activity in People with Multiple Sclerosis Undergoing Therapeutic Hookworm Vaccination

Background: Epstein–Barr virus (EBV) infection is strongly associated with multiple sclerosis (MS). Helminth infection can downregulate antiviral immune responses, potentially protecting against MS, but with a theoretical risk for reactivating latent EBV infection. Objective: To investigate parameters of EBV infection and their relationship with disease activity in people with MS (PwMS) therapeutically vaccinated with Necator americanus (hookworm). Methods: Sequential serum samples from 51 PwMS; 26 therapeutically infected (25 larvae) with N. americanus and 25 controls were tested for EBV virus capsid antigen (VCA) IgG and IgM, EBV nuclear antigen-1 (EBNA-1) IgG, and EBV early antigen (EA) IgG. Disease activity was assessed by periodic MRI. Significance was set at p < 0.05. Results: All PwMS were EBV VCA IgG and EBNA-1 IgG positive, and 35.2% were EBV EA IgG positive. EBV antibody levels were generally stable, and EBV reactivation in PwMS was not demonstrated by significant increases in IgG titre over 12 months. Disease activity was most frequent in PwMS possessing high levels of EBV VCA IgG (>600 units/mL) or EBNA-1 IgG (>150 units/mL); however, there was no association with hookworm treatment. Interpretation: Therapeutic hookworm vaccination was not associated with EBV reactivation. Multiple sclerosis disease activity was associated with high levels of EBV VCA IgG or EBNA-1 IgG.

Trichinella spiralis Infection Mitigates Collagen-Induced Arthritis via Programmed Death 1-Mediated Immunomodulation

Helminth infection induces Th2-biased immune responses and inhibitory/regulatory pathways that minimize excessive inflammation to facilitate the chronic infection of helminth in the host and in the meantime, prevent host hypersensitivity from autoimmune or atopic diseases. However, the detailed molecular mechanisms behind modulation on inflammatory diseases are yet to be clarified. Programmed death 1 (PD-1) is one of the important inhibitory receptors involved in the balance of host immune responses during chronic infection. Here, we used the murine model to examine the role of PD-1 in CD4+ T cells in the effects of Trichinella spiralis infection on collagen-induced arthritis (CIA). Mice infected with T. spiralis demonstrated higher expression of PD-1 in the spleen CD4+ T cells than those without infection. Mice infected with T. spiralis 2 weeks prior to being immunized with type II collagen displayed lower arthritis incidence and significantly attenuated pathology of CIA compared with those of uninfected mice. The therapeutic effect of T. spiralis infection on CIA was reversed by blocking PD-1 with anti-PD-1 antibody, associated with enhanced Th1/Th17 pro-inflammatory responses and reduced Th2 responses. The role of PD-1 in regulating CD4+ T cell differentiation and proliferation during T. spiralis infection was further examined in PD-1 knockout (PD-1-/-) C57BL/6 J mice. Interestingly, T. spiralis-induced alteration of attenuated Th1 and enhanced Th2/regulatory T cell differentiation in wild-type (WT) mice was effectively diminished in PD-1-/- mice characterized by recovered Th1 cytokine levels, reduced levels of Th2 and regulatory cytokines and CD4+CD25+Foxp3+ cells. Moreover, T. spiralis-induced CD4+ T cell proliferation suppression in WT mice was partially restored in PD-1-/- mice. This study introduces the first evidence that PD-1 plays a critical role in helminth infection-attenuated CIA in a mouse model by regulating the CD4+ T cell function, which may provide the new insights into the mechanisms of helminth-induced immunomodulation of host autoimmunity.

The physicochemical fingerprint of Necator americanus

Necator americanus, a haematophagous hookworm parasite, infects ~10% of the world's population and is considered to be a significant public health risk. Its lifecycle has distinct stages, permitting its successful transit from the skin via the lungs (L3) to the intestinal tract (L4 maturing to adult). It has been hypothesised that the L3 larval sheath, which is shed during percutaneous infection (exsheathment), diverts the immune system to allow successful infection and reinfection in endemic areas. However, the physicochemical properties of the L3 larval cuticle and sheath, which are in direct contact with the skin and its immune defences, are unknown. In the present study, we controlled exsheathment, to characterise the sheath and underlying cuticle surfaces in situ, using atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). AFM revealed previously unseen surface area enhancing nano-annuli exclusive to the sheath surface and confirmed greater adhesion forces exist between cationic surfaces and the sheath, when compared to the emergent L3 cuticle. Furthermore, ToF-SIMS elucidated different chemistries between the surfaces of the cuticle and sheath which could be of biological significance. For example, the phosphatidylglycerol rich cuticle surface may support the onward migration of a lubricated infective stage, while the anionic and potentially immunologically active heparan sulphate rich deposited sheath could result in the diversion of immune defences to an inanimate antigenic nidus. We propose that our initial studies into the surface analysis of this hookworm provides a timely insight into the physicochemical properties of a globally important human pathogen at its infective stage and anticipate that the development and application of this analytical methodology will support translation of these findings into a biological context.

Helminth Immunomodulation in Autoimmune Disease

Helminths have evolved to become experts at subverting immune surveillance. Through potent and persistent immune tempering, helminths can remain undetected in human tissues for decades. Redirecting the immunomodulating "talents" of helminths to treat inflammatory human diseases is receiving intensive interest. Here, we review therapies using live parasitic worms, worm secretions, and worm-derived synthetic molecules to treat autoimmune disease. We review helminth therapy in both mouse models and clinical trials and discuss what is known on mechanisms of action. We also highlight current progress in characterizing promising new immunomodulatory molecules found in excretory/secretory products of helminths and their potential use as immunotherapies for acute and chronic inflammatory diseases.

Clinical trials of helminth therapy in autoimmune diseases: rationale and findings

Some helminths are major human pathogens. Recently, however, increased understanding of the immunoregulatory responses induced by this class of parasites, in combination with epidemiologic and animal studies, suggests that helminths may have therapeutic potential in autoimmune diseases (AD) and other conditions. This article reviews the rationale for and results of clinical trials to test the safety and efficacy of helminth therapy in AD. Also discussed are future prospects for investigation and the possibility that helminth treatment may serve as a probe to help reveal the pathogenesis of AD.

The crowding effect in Ancylostoma ceylanicum: density-dependent effects on an experimental model of infection

This study compared the course of Ancylostoma ceylanicum infection in hamsters infected with different inocula and the consequences for the host and helminth populations. The average of adult worms recovered, according to the number of third stage larva used, were 28.0, 24.8, 24.6, and 24.8% to inocula size of 25 L3, 75 L3, 125 L3, and 250 L3, respectively. The size of the inoculum did not affect the establishment, survival, or fecundity of adult helminths. Reductions in the red blood cell and hemoglobin levels in the infected group were inversely proportional to the number of white blood cells. Moreover, differential cell counting revealed a positive correlation between the worm load and leucocyte numbers. The humoral response against excretion-secretion antigens was more robust and sensitive compared with the response against crude extract, with no direct linear correlation with the number of worms. The effect of the population density was more evident in females.

Parasites and immunotherapy: with or against?

Immunotherapy is a sort of therapy in which antibody or antigen administrates to the patient in order to treat or reduce the severity of complications of disease. This kind of treatment practiced in a wide variety of diseases including infectious diseases, autoimmune disorders, cancers and allergy. Successful and unsuccessful immunotherapeutic strategies have been practiced in variety of parasitic infections. On the other hand parasites or parasite antigens have also been considered for immunotherapy against other diseases such as cancer, asthma and multiple sclerosis. In this paper immunotherapy against common parasitic infections, and also immunotherapy of cancer, asthma and multiple sclerosis with parasites or parasite antigens have been reviewed.

Helminth Therapy for MS

In the last 50 years, environmental factors such as helminth infections have been proposed to explain why autoimmunity is less prevalent in the developing world; this proposal has been termed the hygiene or old friends hypothesis. The epidemiology of MS shows an inverse correlation with helminth infections. Positive effects of helminths in animal models of MS and observational studies in people with MS naturally infected with helminths suggest that those organisms can act as immune regulators and led to clinical trials of helminth therapy. The goal of helminth therapy is to introduce parasitic organisms into people with MS in a controlled and predictable fashion, and to prevent immune-mediated disease without increasing the risk of pathology with high parasite load. This chapter focuses on intestinal worms as they are the current choice as a therapeutic strategy in a number of autoimmune diseases, including MS. Here we review current data regarding the rationale and the current state of research in the field of helminth therapies in MS.

The hookworm pharmacopoeia for inflammatory diseases

In the developed world, declining prevalence of parasitic infections correlates with increased incidence of allergic and autoimmune disorders. Current treatments for these chronic inflammatory conditions have little to no effect on their prevalence and are referred to as "controllers" rather than cures. There has been limited success in therapeutically targeting allergic and autoimmune pathways, leaving an unmet need for development of effective anti-inflammatories. We discuss the benefit of hookworm infections and the parasite's ability to condition the immune system to prevent allergic asthma and inflammatory bowel diseases. We then examine the immunomodulatory properties of selected hookworm-derived proteins in these two models of inflammation. While hookworm protein therapy has yet to be fully exploited, the identification of these proteins and the mechanisms by which they skew the immune system will provide new avenues for controlling and optimally reversing key pathological processes important in allergic and inflammatory bowel diseases.

Parasites or cohabitants: cruel omnipresent usurpers or creative "éminences grises"?

This paper presents many types of interplays between parasites and the host, showing the history of parasites, the effects of parasites on the outcome of wars, invasions, migrations, and on the development of numerous regions of the globe, and the impact of parasitic diseases on the society and on the course of human evolution. It also emphasizes the pressing need to change the look at the parasitism phenomenon, proposing that the term “cohabitant” is more accurate than parasite, because every living being, from bacteria to mammals, is a consortium of living beings in the pangenome. Even the term parasitology should be replaced by cohabitology because there is no parasite alone and host alone: both together compose a new adaptive system: the parasitized-host or the cohabitant-cohabited being. It also suggests switching the old paradigm based on attrition and destruction, to a new one founded on adaptation and living together.

Helminthic therapy: using worms to treat immune-mediated disease

There is an epidemic of immune-mediated disease in highly-developed industrialized countries. Such diseases, like inflammatory bowel disease, multiple sclerosis and asthma increase in prevalence as populations adopt modern hygienic practices. These practices prevent exposure to parasitic worms (helminths). Epidemiologic studies suggest that people who carry helminths have less immune-mediated disease. Mice colonized with helminths are protected from disease in models of colitis, encephalitis, Type 1 diabetes and asthma. Clinical trials show that exposure to helminths reduce disease activity in patients with ulcerative colitis or Crohn's disease. This chapter reviews some of the work showing that colonization with helminths alters immune responses, against dysregulated inflammation. These helminth-host immune interactions have potentially important implications for the treatment of immune-mediated diseases.

Reduced helminth burden increases allergen skin sensitization but not clinical allergy: a randomized, double-blind, placebo-controlled trial in Vietnam

BACKGROUND

Observational evidence suggests that infection with helminths protects against allergic disease and allergen skin sensitization. It is postulated that such effects are mediated by helminth-induced cytokine responses, in particular IL-10.

OBJECTIVE

We tested this hypothesis in a rural area of central Vietnam where hookworm infection is endemic.

METHODS

One thousand five hundred and sixty-six schoolchildren aged 6-17 were randomly allocated to receive either anti-helminthic therapy or a placebo at 0, 3, 6, and 9 months. We compared changes in the prevalence of exercise-induced bronchoconstriction, allergen skin sensitization, flexural eczema on skin examination, questionnaire-reported allergic disease (wheeze and rhinitis symptoms), and immunological parameters (hookworm-induced IFN-gamma, IL-5, IL-10) between 0 and 12 months.

RESULTS

One thousand four hundred and eighty-seven children (95% of these randomized) completed the study. The most common helminth infections were hookworm (65%) and Ascaris lumbricoides (7%). There was no effect of the therapy on the primary outcome, exercise-induced bronchoconstriction (within-participant mean percent fall in peak flow from baseline after anti-helminthic treatment 2.25 (SD 7.3) vs. placebo 2.19 (SD 7.8, P=0.9), or on the prevalence of questionnaire-reported wheeze [adjusted odds ratio (OR)=1.16, 95% confidence interval (CI) 0.35-3.82, P=0.8] and rhinitis (adjusted OR=1.39, 0.89-2.15, P=0.1), or flexural dermatitis on skin examination (adjusted OR=1.15, 0.39-3.45, P=0.8). However, anti-helminthic therapy was associated with a significantly higher allergen skin sensitization risk (adjusted OR=1.31, 1.02-1.67, P=0.03). This effect was particularly strong for children infected with A. lumbricoides at baseline (adjusted OR=4.90, 1.48-16.19, P=0.009). Allergen skin sensitization was inversely related to hookworm-specific IL-10 at baseline (adjusted OR=0.76, 0.59-0.99, P=0.04). No cytokine tested, including IL-10, changed significantly after the anti-helminthic therapy compared with the placebo.

CONCLUSION

A significant reduction in worm burden over a 12-month period in helminth-infected children increases the risk of allergen skin sensitization but not of clinical allergic disease. The effect on skin sensitization could not be fully explained by any of the immunological parameters tested.

The mucosal cellular response to infection with Ancylostoma ceylanicum

Although hookworms are known to stimulate inflammatory responses in the intestinal mucosa of their hosts, there is little quantitative data on this aspect of infection. Here we report the results of experiments conducted in hamsters infected with Ancylostoma ceylanicum. Infection resulted in a marked increase in goblet cells in the intestinal mucosa, which was dependent on the number of adult worms present and was sustained as long as worms persisted (over 63 days) but returned to baseline levels within 7 days of the removal of worms by treatment with ivermectin. Increased mast cell responses were also recorded. Levels were again dependent on the intensity of worm burdens and lasted as long as 63 days after infection. When worms were eliminated, mast cell numbers took over 2 weeks to return to normal. Paneth cell numbers fell soon after infection, the degree of reduction being dependent on the worm burden. After clearance of worms, Paneth cell numbers returned to normal within a week, but then rebounded and numbers rose to higher levels than those in control naïve animals. The time course of the response was similar whether animals experienced a chronic low-intensity infection without loss of worms or a higher intensity infection during the course of which worm burdens were gradually reduced. Clearly, A. ceylanicum was able to induce a marked inflammatory response in its host's intestine which was sustained for over 9 weeks after infection, and which hamsters appeared able to tolerate well. Our data draw attention to the resilience of hookworms which, unlike many other nematodes, are able to survive for many weeks in a highly inflamed intestinal tract.

Vaccines against blood-feeding nematodes of humans and livestock

This paper summarises the progress towards vaccine development against the major blood-feeding nematodes of man and livestock, the hookworms and Haemonchus contortus, respectively. The impact of the diseases and the drivers for vaccine development are summarized as well as the anticipated impact of the host immune response on vaccine design. The performance requirements are discussed and progress towards these objectives using defined larval and adult antigens, many of these being shared between species. Specific examples include the Ancylostoma secreted proteins and homologues in Haemonchus as well as proteases used for digestion of the blood meal. This discussion shows that many of the major vaccine candidates are shared between these blood-feeding species, not only those from the blood-feeding stages but also those expressed by infective L3s in the early stages of infection. Challenges for the future include: exploiting the expanding genome information for antigen discovery, use of different recombinant protein expression systems, formulation with new adjuvants, and novel methods of field testing vaccine efficacy.

Helminths as governors of immune-mediated inflammation

Immune-mediated diseases (e.g. inflammatory bowel disease, asthma, multiple sclerosis and autoimmune diabetes) are increasing in prevalence and emerge as populations adopt meticulously hygienic lifestyles. This change in lifestyles precludes exposure to helminths (parasitic worms). Loss of natural helminth exposure removes a previously universal Th2 and regulatory immune biasing imparted by these organisms. Helminths protect animals from developing immune-mediated diseases (colitis, reactive airway disease, encephalitis and diabetes). Clinical trials show that exposure to helminths can reduce disease activity in patients with ulcerative colitis or Crohn's disease. This paper summarises work by multiple groups demonstrating that colonization with helminths alters immune reactivity and protects against disease from dysregulated inflammation.

Intestinal allergy expels hookworms: seeing is believing

It is unclear how immunity limits hookworm infection. Australian researchers, using capsule and conventional gastrointestinal endoscopy in volunteers inoculated with Necator americanus, have reported that virtually all larvae reach the intestine within six weeks. Unlike the neutral response surrounding resident hookworms, newly arrived adults provoke an eosinophilic enteropathy. This allergic reaction curtails the attachment of hookworms and accompanies the passage of additional worms as they are expelled from the proximal small intestine.

Allergy controls the population density of Necator americanus in the small intestine

BACKGROUND & AIMS

Nearly 700 million people remain infected with hookworms. Although allergy is intuitively linked to immunity against helminths, few positive examples have been characterized. Larval migration through the lungs has been considered the likely interface at which hookworm attrition occurs. As part of a study evaluating a potential role for hookworms in the modulation of human autoimmunity, we examined parasite migration and intestinal colonization.

METHODS

Capsule and conventional endoscopies supplemented the evaluation of healthy volunteers and Crohn's disease patients recently inoculated with larvae of the human hookworm Necator americanus. Two healthy volunteers with a previously established and stable hookworm infection were inoculated with 50 larvae and had serial capsule endoscopies performed.

RESULTS

Eosinophilic enteritis developed in all subjects after the initial inoculation. Newly inoculated larvae in the 2 subjects with an established infection reliably reached the intestine within 4 weeks. Thereafter, the colony diminished to the host's constitutive status quo because mostly immature worms failed to attach. The intensity of the eosinophilic response correlated negatively with the time available for hookworms to feed and positively with hookworm attrition.

CONCLUSIONS

Necator larval migration to the intestine is uncontested. We propose that allergic inflammation purposefully degrades the hookworm's bite, causing premature detachment, restricted feeding, and expulsion. This novel biological dynamic suggests a new paradigm of hookworm resistance.

Consequences of concurrent Ascaridia galli and Escherichia coli infections in chickens

Three experiments were carried out to examine the consequences of concurrent infections with Ascaridia galli and Escherichia coli in chickens raised for table egg production. Characteristic pathological lesions including airsacculitis, peritonitis and/or polyserositis were seen in all groups infected with E. coli. Furthermore, a trend for increased mortality rates was observed in groups infected with both organisms which, however, could not be confirmed statistically. The mean worm burden was significantly lower in combined infection groups compared to groups infected only with A. galli. It was also shown that combined infections of E. coli and A. galli had an added significant negative impact on weight gain.

The innate allergenicity of helminth parasites

Helminth parasites are well known to induce an immune response in their hosts characterised by elevated IgE, peripheral blood or local tissue eosinophilia, and in some cases, intestinal mastocytosis. This immunological response has a strong T-helper 2 (Th2) cytokine bias and is reminiscent of the immunological constellation found in allergic diseases. However, the molecular forces driving the Th2 response to helminth parasites are still not understood. By using the human hookworm parasite Necator americanus as an example, the authors of the current article propose that in the course of its life cycle, this parasite becomes innately allergenic through the secretion of a molecular array designed to promote tissue migration and homing, feeding and survival against immunological attack. This complex array comprises proteases, lectins and other classes of molecules. Subsequent immunological and physiological events seemingly protect the host from both the allergic sequelae of exposure to environmental allergens and, moreover, from the parasite itself.

Parasite role reversal: worms on trial

Asthma has reached epidemic proportions globally. This has been attributed by many to improved hygiene. The frequent failure of conventional pharmaceuticals to manage the disease has led to the introduction of parasites as a potential alternative therapy for asthma and other immunological diseases. In this article, we briefly review the immunological rationale underpinning therapeutic parasitic infection, describe recently initiated trials, and highlight potential risks and benefits of introducing parasites into patient cohorts.

The assessment of hookworm calreticulin as a potential vaccine for necatoriasis

A vaccine against the human hookworm Necator americanus is urgently required to reduce hookworm-induced morbidity in endemic areas. In the present study, recombinant hookworm calreticulin, a nominated vaccine candidate, has been tested in mice. Mice given calreticulin had 43-49% fewer worms in their lungs, compared to non-vaccinated controls, following challenge infection with infective hookworm larvae. These levels of protection were achieved in the absence of adjuvant following intraperitoneal administration of three doses of 15 microg antigen. Antigen was also encapsulated in PLG microparticles. Encapsulated calreticulin elicited higher levels of anti-calreticulin IgG1 than free antigen but failed to induce protective immunity. The protection induced by free calreticulin was associated with low levels of serum IgE and moderate lung eosinophilia whilst administration of calreticulin-loaded microparticles was associated with high levels of serum IgE and higher lung eosinophil activity, suggesting that the classical Th2 phenotype may not always be associated with protective immunity, albeit in experimental necatoriasis.

Immunobiology of hookworm infection

Hookworms infect almost one billion people and are a major cause of iron-deficiency anaemia in developing countries of the tropics. Despite their prevalence and the morbidity they cause, little is known about the immune response to this complex eukaryotic parasite. Recent publications have shed light on the human cellular immune responses to hookworms, as well as mechanisms that hookworms utilize to skew the immune response in its favour. Unlike most other human helminth infections, neither age- nor exposure-related immunity develops in the majority of infected people. A vaccine is therefore a highly desirable goal. To this end, gene sequencing efforts have resulted in the deposition of more than 10,000 hookworm cDNA sequences in the public domain, providing a molecular snapshot of this intriguing parasite and providing novel tools for the development of new control strategies. Significant progress has been made in the development of anti-hookworm recombinant vaccines, and clinical trials are expected to begin in the near future.

Human hookworm infection in the 21st century

The scientific study of human hookworm infection began at the dawn of the twentieth century. In recent years, there have been dramatic improvements in our understanding of many aspects of this globally widespread parasite. This chapter reviews recent advances in our understanding in the biology, immunology, epidemiology, public health significance and control of hookworm, and to look forward to the study of this important parasite in the 21st century. Advances in molecular biology has lead to the identification of a variety of new molecules from hookworms, which have importance either in the molecular pathogenesis of hookworm infection or in the host-parasite relationship; some are also promising vaccine targets. At present, relatively little is known about the immune responses to hookworm infection, although it has recently been speculated that hookworm and other helminths may modulate specific immune responses to other pathogens and vaccines. Our epidemiological understanding of hookworm has improved through the development of mathematical models of transmission dynamics, which coupled with decades of field research across multiple epidemiological settings, have shown that certain population characteristics can now be recognised as common to the epidemiology, population biology and control of hookworm and other helminth species. Recent recognition of the subtle, but significant, impact of hookworm on health and education, together with the simplicity, safety, low cost and efficacy of chemotherapy has spurred international efforts to control the morbidity due to infection. Large-scale treatment programmes are currently underway, ideally supported by health education and integrated with the provision of improved water and sanitation. There are also on-going efforts to develop novel anthelmintic drugs and anti-hookworm vaccines.

Dirt, worms and atopic dermatitis

The past three decades have witnessed a marked rise in the prevalence of atopic diseases in industrialized countries and urban centres in less developed regions. This has led to an intense search for aetiological factors that may explain such a pattern. Epidemiological and immunological data suggest the eradication of nonparasitic and endoparasitic infections as possible aetiological elements. This has been formulated as the 'hygiene hypothesis', linking a reduced frequency of childhood infections with allergy. So far, most work in this area has focused on asthma. The potential relationship between endoparasites and atopic dermatitis has received much less attention. This paper reviews the scientific literature on the links between atopic dermatitis and endoparasites. At present, there is no clear evidence for a direct relationship between the two. This may be due to the overall small number of studies and insufficient methodological rigour in the existing body of research.

Could control of soil-transmitted helminthic infection influence the HIV/AIDS pandemic

In May 2001, the World Health Assembly (WHA) estimated that two billion people were infected by soil-transmitted helminths (S-THs) and schistosomiasis, worldwide. The WHA urged member states to recognise that there can be synergy between public health control programmes for S-THs, schistosomiasis and other diseases. This is particularly relevant to the new dimension created by the HIV/AIDS epidemics in the same impoverished communities and countries where helminthiasis is hyperendemic. Immunological adaptation between humans and parasitic helminths has developed during evolution. Review of 109 research papers, 76% (83/109) of which, were published between 1995 and February 2002, revealed increasing evidence that this relationship may have created an opportunity for more rapid infection by the human immunodeficiency virus (HIV), as well as quicker progression to AIDS. Moreover, the efficacy of some vaccines against HIV is likely to be impaired by chronic helminthiasis. For this, there is strong, indirect evidence. There is an urgent need for parasitologists, epidemiologists, immunologists and virologists to undertake comprehensive, transdisciplinary research. On the other hand, there is no current evidence that immunosuppression by HIV facilitates helminthic infection. The situation in regard to strongyloidiasis, however, is not yet clear.

The effect of concurrent infections with Pasteurella multocida and Ascaridia galli on free range chickens

Pasteurella multocida and Ascaridia galli are observed with high prevalences in free range chickens in Denmark, but the impact is unknown. A study was carried out to examine the interaction between A. galli and P. multocida in chickens and the impact on production. Five groups, each with 20 18-week-old Lohmann Brown chickens were infected. Group 1 was orally infected with 1000+/-50 embryonated A. galli eggs. Group 2 received 10(4) cfu P. multocida intratracheally. Group 3 was infected with A. galli and subsequently with P. multocida. Group 4 was infected with P. multocida followed by A. galli. Group 5 was the control. The study ran for 11 weeks where clinical manifestations, weight gain and egg production were recorded. Excretion of P. multocida was determined on individual basis and blood smears were made for differential counts. At the end of the study pathological lesions and the number of adult worms, larvae and eggs in the faeces were recorded. The birds were more severely affected when infected with both pathogens compared to single infections with A. galli or P. multocida, respectively. A lower weight gain and egg production was observed with dual infections. A. galli infection followed by a secondary P. multocida infection resulted in more birds with pathological lesions and continued P. multocida excretion. In conclusion a negative interaction between A. galli and P. multocida was observed and it is postulated that free range chickens are at higher risk of being subjected to outbreaks of fowl cholera when they are infected with A. galli.

The effect of Plasmodium gallinaceum on a challenge infection with Ascaridia galli in chickens

The effect of a primary infection with the haemoparasite Plasmodium gallinaceum on the establishment of a challenge infection with the nematode Ascaridia galli in chickens was studied. Four groups were infected as follows. Group 1: inoculated intravenously with 10(6) P. gallinaceum-infected erythrocytes on day 0; group 2: orally infected with 500 embryonated A. galli eggs on day 10; group 3: infected with P. gallinaceum on day 0 and A. galli on day 10; and group 3: non-infected control birds. The results of this investigation demonstrates that a primary infection with P. gallinaceum in chickens alters the course of a subsequent infection with A. galli. Thus, an antagonistic effect was seen in which the malaria infection caused a significant reduction on the establishment of the nematode in concurrently infected animals.

Vaccination with neutrophil inhibitory factor reduces the fecundity of the hookworm Ancylostoma ceylanicum

Neutrophil inhibitory factor (NIF), a protein isolated from hookworms of the genus Ancylostoma, inhibits CD11b/18-dependent leucocyte function, binding to the I domain of CD11b. Historically, NIF was serendipitously isolated from whole worm extracts during a search for novel antihaemostatic agents, and little is known of its source or biological significance to the parasite. NIF has also been identified as a possible hookworm vaccine candidate. Ancylostoma ceylanicum recombinant NIF, expressed in its active form in Pichia pastoris, was purified and its functional activity confirmed using neutrophil adhesion assays and confirmatory immunoassay. Recombinant NIF was subsequently used in vaccination trials in the A. ceylanicum-hamster model system for human hookworm infection. Vaccinated and challenged animals were not protected in terms of worm burden or haematocrit values, despite the presence of high levels of specific antibody against NIF. However, adult worms resident in vaccinated animals showed a significant reduction in fecundity (85.8% by day 21 postinfection), indicating a degree of protection against subsequent transmission by vaccination. These data indicate that targeted vaccination with recombinant subunit material, derived from a known and effective immune suppressant secreted by the parasite, may offer partial protection against the transmission of hookworm infection. Furthermore, we can also report that a biological activity characteristic of NIF is detectable in the secretions of A. ceylanicum using two complementary bioassays. Complete neutralization of this secreted activity by vaccination in combination with other vaccine candidates may result in improved protection against A. ceylanicum infection.