Enteric pathogens induce tissue tolerance and prevent neuronal loss from subsequent infections

The enteric nervous system (ENS) controls several intestinal functions including motility and nutrient handling, which can be disrupted by infection-induced neuropathies or neuronal cell death. We investigated possible tolerance mechanisms preventing neuronal loss and disruption in gut motility after pathogen exposure. We found that following enteric infections, muscularis macrophages (MMs) acquire a tissue-protective phenotype that prevents neuronal loss, dysmotility, and maintains energy balance during subsequent challenge with unrelated pathogens. Bacteria-induced neuroprotection relied on activation of gut-projecting sympathetic neurons and signaling via β2-adrenergic receptors (β2AR) on MMs. In contrast, helminth-mediated neuroprotection was dependent on T cells and systemic production of interleukin (IL)-4 and IL-13 by eosinophils, which induced arginase-expressing MMs that prevented neuronal loss from an unrelated infection located in a different intestinal region. Collectively, these data suggest that distinct enteric pathogens trigger a state of disease or tissue tolerance that preserves ENS number and functionality.

Gene silencing and sex determination by programmed DNA elimination in parasitic nematodes

Maintenance of genome integrity is essential. However, programmed DNA elimination removes specific DNA sequences from the genome during development. DNA elimination occurs in unicellular ciliates and diverse metazoa ranging from nematodes to vertebrates. Two distinct groups of nematodes use DNA elimination to silence germline-expressed genes in the soma (ascarids) or for sex determination (Strongyloides spp.). Data suggest that DNA elimination likely evolved independently in these nematodes. Recent studies indicate that differential CENP-A deposition within chromosomes defines which sequences are retained and lost during Ascaris DNA elimination. Additional studies are needed to determine the distribution, functions, and mechanisms of DNA elimination in nematodes.

Evaluation of gastrointestinal transit after infection with different loads of Strongyloides venezuelensis in rats

The aim was to correlate the gastrointestinal transit profile in rats, evaluated by a biomagnetic technique, in response to infection with different loads of Strongyloides venezuelensis. Eggs per gram, intestinal number of worms and fecundity, and also gastric emptying time, cecum arrival time, small intestinal transit time and stool weight were determined. Assessments occurred at 0 (control), 3, 6, 9, 12, 15, 18 and 21 days post infection (dpi) with three infective loads (400, 2000, and 10,000 L). Gastric emptying was faster (p=0.0001) and the intestinal transit was significantly slower (p=0.001) during the infection time course. Also, linear mixed-effects models showed significantly changes in small intestinal transit after three parasite load over time. Cecum arrival was not influenced by infection time course or parasite load. As indirect effect, stool weight decreased accompanied a strong oviposition peak at 9 dpi in 400 L and 2000 L. In several motor function instances, neuromuscular dysfunction persists after mucosal inflammation has decreased. Our approach could be very helpful to evaluate gastrointestinal motor abnormalities in vivo after parasite infection. Despite parasitological data progressively decreased after 15 dpi, small intestinal transit worse over time and according to burden.

Notch2 signaling in mast cell development and distribution in the intestine

Notch signaling controls cell-fate specification events in various types of blood cells, and it further regulates the function of particular blood cells. Recent studies have identified the role of Notch signaling as a determinant of mast cell fate from bone marrow progenitors and mast cell maturation towards mucosal type rather than connective tissue type. Furthermore, Notch2 has functional properties for immune defense against Strongyloides venezuelensis through properly distributing intestinal mast cells. The goal of this chapter is to provide the researchers with the comprehensive protocols to examine the functions of Notch signaling in mast cells both in vitro and in vivo.

Strongyloidiasis--an insight into its global prevalence and management

BACKGROUND

Strongyloides stercoralis, an intestinal parasitic nematode, infects more than 100 million people worldwide. Strongyloides are unique in their ability to exist as a free-living and autoinfective cycle. Strongyloidiasis can occur without any symptoms or as a potentially fatal hyperinfection or disseminated infection. The most common risk factors for these complications are immunosuppression caused by corticosteroids and infection with human T-lymphotropic virus or human immunodeficiency virus. Even though the diagnosis of strongyloidiasis is improved by advanced instrumentation techniques in isolated and complicated cases of hyperinfection or dissemination, efficient guidelines for screening the population in epidemiological surveys are lacking.

METHODOLOGY AND RESULTS

In this review, we have discussed various conventional methods for the diagnosis and management of this disease, with an emphasis on recently developed molecular and serological methods that could be implemented to establish guidelines for precise diagnosis of infection in patients and screening in epidemiological surveys. A comprehensive analysis of various cases reported worldwide from different endemic and nonendemic foci of the disease for the last 40 years was evaluated in an effort to delineate the global prevalence of this disease. We also updated the current knowledge of the various clinical spectrum of this parasitic disease, with an emphasis on newer molecular diagnostic methods, treatment, and management of cases in immunosuppressed patients.

CONCLUSION

Strongyloidiasis is considered a neglected tropical disease and is probably an underdiagnosed parasitic disease due to its low parasitic load and uncertain clinical symptoms. Increased infectivity rates in many developed countries and nonendemic regions nearing those in the most prevalent endemic regions of this parasite and the increasing transmission potential to immigrants, travelers, and immunosuppressed populations are indications for initiating an integrated approach towards prompt diagnosis and control of this parasitic disease.

Effects of infection intensity with Strongyloides papillosus and albendazole treatment on development of oxidative/nitrosative stress in sheep

The objective of this study was to estimate and evaluate oxidative/nitrosative stress parameters in sheep infected with Strongyloides papillosus and after antihelminthic treatment with albendazole (ABZ). This parasite, especially during development stages can seriously damage parenchaematous organs during migration within the host. The presence of parasites leads to increased productions of reactive oxygen species (ROS) and reactive nitrogen species (RNS). It is also well known that certain drugs can be very harmful for the delicate oxidant-antioxidant equilibrium, provoking oxidative stress during their biotransformation. ABZ is a broad spectrum antihelminthic drug, frequently used in veterinary medicine for therapy of parasitic infections. The current research was performed on female Württemberg sheep (n=48). The distribution of parasites in sheep was evaluated using the native smear coprological technique, by sedimentation and flotation methods, revealing the presence of S. papillosus. The degree of infection intensity per sheep was quantitatively established by the method of McMaster, the animals having been divided into three groups according to the intensity of infection; mild, moderate and high. The control group consisted of sheep negative to the parasites. After determining the type of parasite infection, the sheep were treated with ABZ, per orally, in single doses of 5mg/kg per body weight. Sampling of feces for parasitological and blood for biochemical assaying was performed on the 0 and 21st day after treatment with ABZ. The oxidative stress parameters were measured for catalase activity (CAT), the red cell membrane damage by level of malondialdehyde (MDA), while carbonyl and thiol plasma protein group concentrations were used as indicators of the degree of protein oxidative modification. The activity of Cu,Zn-superoxide dismutase (SOD) and relative distribution of lactate dehydrogenase (LDH(1)-LDH(5)) activity were determined electrophoretically. The distribution of LDH isoenzymes in sheep moderately and highly infected with S. papillosus revealed that the parasite induced damage to the myocardial (LDH(2)), lung (LDH(3)) and liver cells (LDH(5)) in infected animals, while ABZ treatment only damaged liver cells (LDH(5)). The MDA concentration revealed that lipid peroxidation increased both in the presence of parasites and the antihelminthic formulation tested (p<0.001) when compared to the control sheep, while the increase of carbonyl concentration (p<0.001), as well as the observed decrease of thiol concentration (p<0.001) indicated significant oxidative damage of plasma proteins in experimental sheep, when compared to the control animals. Our results indicate that S. papillosus induces oxidative/nitrosative stress in sheep. The antihelminthic treatment with ABZ further promotes the disbalance of oxidative-antioxidative equilibrium in all tested sheep.

Migratory route of Strongyloides venezuelensis in Lewis rats: comparison of histological analyses and PCR

Strongyloides venezuelensis is a parasitic nematode that has been used as a model to study human and animal strongyloidiasis. In this study, we compared the sensitivity between traditional methodologies and PCR assay to characterize the dynamics of S. venezuelensis infection and its migration route in Lewis rats subcutaneously infected with 4000 L3. The dynamics of the infection was determined by counting the number of eggs and by detecting parasite deoxyribonucleic acid in faeces samples. Both techniques similarly detected the infection at day 6 after larvae inoculation. However, PCR performed with the genus primer showed higher sensitivity during the recovery phase. Histological analysis and PCR assay were then used to follow parasite tissue migration. S. venezuelensis migration route included the muscular fibers below the skin, the pulmonary alveoli and the small intestine vilosities. The sensitivity of these two techniques to detect parasite's presence in these tissues was statistically similar.

The free-living generation of the nematode Strongyloides papillosus undergoes sexual reproduction

The nematode genus Strongyloides consists of parasites that live as parthenogenetic females in the small intestines of their hosts. They can also form a facultative free-living generation with males and females. Recently, research on Strongyloides cellular and molecular biology has concentrated on Strongyloides ratti and Strongyloides stercoralis. We propose that the related nematode Strongyloides papillosus, a common parasite of ruminants, is well suited for comparative and evolutionary studies and we show that it is phylogentically basal to S. ratti and S. stercoralis. Based on cytological observations several reports have proposed that Strongyloides males do not contribute genetically to the next generation, leaving open the question of why males still exist. In contrast, the only study employing molecular markers showed that S. ratti males do pass on genetic material. Here, we demonstrate that in S. papillosus males also contribute molecular genetic markers to the next generation. This is interesting for two reasons. First, it shows that S. papillosus is amenable to genetic analysis and second, it indicates that sexual reproduction is more common in Strongyloides than previously assumed.

The biology and genomics of Strongyloides

Parasitic nematodes are widespread and important pathogens of humans and other animals. The parasitic nematodes Strongyloides have an unusual life cycle in which there is a facultative free-living generation in addition to the obligate parasitic generation. The genomes of many species of parasitic nematodes, including Strongyloides ratti and Strongyloides stercoralis, have been investigated, principally by expressed sequence tag (EST) analyses. These have discovered very many genes from these parasites but, in so doing, have also revealed how different these species are from each other and from other organisms. Understanding the role and function of these newly discovered genes is now the challenge, made more difficult by the parasitic lifestyle. The genomic information available for parasitic nematodes is allowing new approaches for the control of parasitic nematodes to be considered.

Infection of naïve, free-living brushtail possums (Trichosurus vulpecula) with the nematode parasite Parastrongyloides trichosuri and its subsequent spread

Despite the importance of spatial processes in host-parasite interactions, parasite dispersal has been the subject of few experimental studies. Introduced marsupial common brushtail possums (Trichosurus vulpecula) are a major environmental and agricultural pest in New Zealand. Parastrongyloides trichosuri, an intestinal rhabdiasoid nematode parasite specific to possums, is being evaluated as a self-disseminating delivery system for engineered fertility control vaccines. This study addressed whether an artificial infection could be established in a naïve, free-living possum population, by measuring the post-release dynamics of possum-parasite interactions at the release site, and by following the spread of the parasite into surrounding possum populations. Infection was established efficiently by applying infective larvae to the skin of possums on a single occasion. All experimentally infected possums recaptured 3 weeks after infection had parasite eggs in their faeces. Over the subsequent 2.5 years, infection spread steadily over an area of about 6000 ha. Infection persisted at the original release site for the 3.5 years of the study and at a nearby site infected by natural spread for more than 3 years. Seasonal changes in faecal egg counts were similar at the two sites. The rapid establishment of the parasite and its spread provide additional support for its ongoing development as a vaccine delivery system.

Parastrongyloides trichosuri, a nematode parasite of mammals that is uniquely suited to genetic analysis

Commonly studied nematode parasites have not proven amenable to simple genetic analyses and this has significantly reduced the available research options. We introduce here a nematode parasite of mammals, Parastrongyloides trichosuri, which has features uniquely suited for genetic analysis. This parasite has the capacity to undergo multiple reproductive cycles as a free-living worm and thereby amplify the numbers of its infective L3s in faeces. Culture conditions are presented that permit facile laboratory maintenance of this worm for >90 free-living life cycles (to date) without the need for re-entry into a permissive host. Even after long maintenance as a free-living worm, culture conditions can be manipulated to favour development of infective L3 worms, which remain able to successfully infect their marsupial hosts. The switch to infective L3 development is triggered by a secreted factor contained in culture medium conditioned by multiple generations of free-living worm culture. It is simple to perform single pair crosses with P. trichosuri to carry out Mendelian genetics in the laboratory and this has been done multiple times with sibling pairs to generate highly inbred lines. Lines of worms can readily be cryopreserved and recovered. Over 7000 expressed sequence tags have been produced from cDNAs at different life cycle stages and used to identify single nucleotide polymorphisms and microsatellites as genetic markers. Free-living worms live only a few days on average while the patency of parasitic infections can last for several months. Since we show this is not the result of re-infection, we conclude that parasitic worms have a lifespan capacity at least 20-30 times longer than their free-living counterparts. We discuss how it should be possible to exploit these unique features of P. trichosuri as a model for future studies that explore the genetic basis of longevity and parasitism.

Successive changes in tissue migration capacity of developing larvae of an intestinal nematode, Strongyloides venezuelensis

Infective larvae of an intestinal nematode, Strongyloides venezuelensis, enter rodent hosts percutaneously, and migrate through connective tissues and lungs. Then they arrive at the small intestine, where they reach maturity. It is not known how S. venezuelensis larvae develop during tissue migration. Here we demonstrate that tissue invasion ability of S. venezuelensis larvae changes drastically during tissue migration, and that the changes are associated with stage-specific protein expression. Infective larvae, connective tissue larvae, lung larvae, and mucosal larvae were used to infect mice by various infection methods, including percutaneous, subcutaneous, oral, and intraduodenal inoculation. Among different migration stages, only infective larvae penetrated mouse skin. Larvae, once inside the host, quickly lost skin penetration ability, which was associated with the disappearance of an infective larva-specific metalloprotease. Migrating larvae had connective tissue migration ability until in the lungs, where larvae became able to settle down in the intestinal mucosa. Lung larvae and mucosal larvae were capable of producing and secreting adhesion molecules.

Migration of Strongyloides venezuelensis in Rats after Oral Inoculation of Free-Living Infective Larvae

Strongyloides venezuelensis (SVZ) infection was chronologically monitored in 85 Sprague-Dawley rats (SDR), which were orally inoculated with approximately 1,000 infective larvae. In order to describe the characteristics of migrating larvae (MLS) in various visceral organs (the liver, lung, cardiac blood, and small intestine), 5 SDR were sacrificed at 20 min, 45 min, 1 hr, 2 hr, 3 hr, 4 hr, 8 hr, 12 hr, 16 hr, 48 hr, 72 hr, 96 hr, 120 hr, 144 hr, 168 hr and 192 hr post inoculation (PI). MLS were recovered from the liver and blood 20 and 45 min PI and measured 788 +/- 26 microm and 846 +/- 40 microm in length, respectively. MLS were first observed in the lung tissue 45 min PI and measured 925 +/- 38 microm on the average. In the trachea, MLS measuring 849 +/- 75 microm appeared 3 to 96 hrs PI. Adult worms (AWS) measuring 1,926 +/- 521 microm to 2,956 +/- 159 microm in length were observed in the small intestine from 120 hr PI. The worms appeared to mature more than 168 hr PI and attained the average maximum length of 2,420 +/- 532 microm. At 3 hr PI focal hyperemic and necrotic lesions were evidently observed in the liver and lung, together with eosinophilic infiltration in the stomach, liver, and lung. The parasites were histologically detectable in the lung tissues but were very difficult to find in the liver and the epithelial layer of small intestine. These data demonstrate that SVZ parasites take 20 min to reach the liver via the stomach and only three hours to reach the trachea through the same route. The development from eggs to adults takes 168 hr in the SDR model.

Enhanced protection against the migratory phase, but defective protection against the intestinal phase of Strongyloides venezuelensis infection in cotton rats, Sigmodon hispidus

The protective capacity of the cotton rat, Sigmodon hispidus, against the migratory and intestinal phases of Strongyloides venezuelensis infection was examined. After subcutaneous infection with infective larvae (L(3)), adult worm recovery rates from male and female animals on Day 71 were only 0.10% and 0.06% of initial dose, respectively. To determine whether this enhanced protection was expressed during the migratory phase or the intestinal phase, larval recovery from the lungs of cotton rat was evaluated 3 days after subcutaneous L(3) infection. The larval recovery rate was only 0.5% of initial dose and about 40-fold lower than that from control mice. Protection in the intestine was also evaluated after intraduodenal implantation of adult worms. About 30% of implanted worms became established and worm burden remained constant until Day 28. Despite a high worm burden on Day 28, EPG was about 25-fold lower than the peak count. To evaluate expulsive capacity and monitor the cellular responses in the intestine of cotton rats, adult Nippostrongylus brasiliensis worms were implanted in addition to S. venezuelensis. Cotton rats were unable to expel adult S. venezuelensis worms, even after 21 days of observation. Although the number of mucosal mast cells increased significantly, the intraepithelial migration of mast cells was not observed. In contrast, N. brasiliensis was expelled by Day 6 in association with goblet cell hyperplasia. These results suggest that in cotton rats, the defective intestinal protection against adult S. venezuelensis worms results from dysfunction of mucosal mast cells.

Sex determination in the parasitic nematode Strongyloides ratti

The parasitic nematode Strongyloides ratti reproduces by both parthenogenesis and sexual reproduction, but its genetics are poorly understood. Cytological evidence suggests that sex determination is an XX/XO system. To investigate this genetically, we isolated a number of sex-linked DNA markers. One of these markers, Sr-mvP1, was shown to be single copy and present at a higher dose in free-living females than in free-living males. The inheritance of two alleles of Sr-mvP1 by RFLP analysis was consistent with XX female and XO male genotypes. Analysis of the results of sexual reproduction demonstrated that all progeny inherit the single paternal X chromosome and one of the two maternal X chromosomes. Therefore, all stages of the S. ratti life cycle, with the exception of the free-living males, are XX and genetically female. These findings are considered in relation to previous analyses of S. ratti and to other known sex determination systems.

Demonstration of chymotryptic and tryptic activities in mast cells of rodents: comparison of 17 species of the family Muridae

On the basis of studies in laboratory rats, mast cells were originally classified into two subgroups, namely, mucosal mast cells (MMCs), which contained chymase, and connective tissue mast cells (CTMCs), which contained both tryptase and chymase. This classification has been applied to other animal species, despite the fact that the MMCs and CTMCs of such species sometimes consist of mixed populations of mast cells in terms of tryptase and chymase constitution. This report describes the protease constitution of mast cells in 17 species of nine genera (Acomys, Apodemus, Cricetulus, Meriones, Millardia, Mus, Rattus, Sigmodon and Vandeleuria) of the family Muridae. MMCs with negative tryptase activity were detected only in the intestinal mucosa of six subspecies of Mus musculus, two Rattus spp. and Vandeleuria oleacea, and only Apodemus sylvaticus possessed CTMCs with no tryptase activity. Since mast cells conforming to the conventional classification were observed only in three of the nine genera examined, we propose that mast cells of rodents of the family Muridae should be classified by their protease constitution rather than by their location.

Seasonal infection pattern of gastrointestinal nematodes of beef cattle in Minas Gerais State--Brazil

Tracer calves were used to assess the seasonality of infections of gastrointestinal parasites in beef cattle extensively raised at a farm in the State of Minas Gerais, Brazil. Tracer calves acquired infections during all months of the year, however, highest worm burdens were observed in the rainy season. The following nematode species were recovered from tracer calves: Cooperia punctata, C. spatulata, C. pectinata, Haemonchus similis, H. placei, Oesophagostomum radiatum, Trichostrongylus colubriformis, T. axei, Bunostomum phlebotomum and Trichuris discolor. Cooperia was most prevalent, representing 74.4% of the total of all nematodes recovered. This was followed by Haemonchus 19.2%, Oesophagostomum 4.5%, Trichostrongylus, Trichuris and Bunostomum, represented less than 1% of the total. Thirty Nellore cows with calves were used to evaluate the dynamics of the infections. The cows were the principal source of contamination to pasture and to infection of suckling calves during the pre-weaning period, and probably, also contributed to increased infection of weaned calves at the beginning of the rainy season. Strongyloides was the first infection observed in the calves. The peak egg count was observed in the 2nd month, however, all Strongyloides egg counts became negative in the 7th month. Strongylate nematode egg counts were low in calves from the 3rd month of age onward, and increased gradually until calves were 1 year old. A gradual reduction then occurred until the end of the trial. From the 3rd month onward Cooperia and Haemonchus infective larvae (L3) were most prevalent in fecal cultures. Fecal cultures after the 4th month also resulted in recoveries of Oesophagostomum, Trichostrongylus, and Bunostomum L3. Cooperia was the predominant genus in fecal cultures until the calves were 9 months old. After the calves were 9 and 12 months of age, L3 of Cooperia and Oesophagostomum, respectively decreased in prevalence. Trichostrongylus and Bunostomum L3 were only minimally present in the fecal cultures at this time.

[Strongyloidosis. II. Clinical manifestations]

Clinical manifestations of chronic, uncomplicated and severe, complicated disseminated strongyloidosis of a patient infected with Strongyloides stercoralis are shown. Cutaneous, gastrointestinal, hepatobiliary, pulmonary, rheumatic, neurological, psychiatric symptoms, as well as those of genitourinary, and cardiovascular systems and other clinical manifestations are discussed.

Massive experimental infection with Strongyloides venezuelensis in rats and absence of sudden death

Ten rats were divided into five groups, A - E, to determine the larval dose-effect of infection with Strongyloides venezuelensis (SVZ). The rat groups were exposed to SVZ infective larvae as follow: (A) 100, (B) 1,000, (C) 10,000, (D) 100,000 and (E) 1,000,000. The eight rats in Groups A - D survived the infection. Rats exposed to the higher doses of larvae had the higher egg per gram counts (EPG), but more rapid reduction in EPG counts. The four rats in Groups C and D had EPG counts greater than 10,000 EPG during days 7 - 21 after infection. Maximum EPG values in Group C were 85,400 and 106,600; those in Group D were 134,000 and 346,000. The two rats in Group E showed severe itching and bleeding on their digital pads at the time of infection. They became listless thereafter and died with hemorrhagic pneumonia at 4 days after infection. The sudden death that has been demonstrated in calves infected with massive doses of S. papillosus was not observed in SVZ-infected rats.

Migration route of Strongyloides venezuelensis in rodents

Infective larvae of Strongyloides venezuelensis were injected into the medial aspect of the thigh of Wistar rats and ddy mice to investigate their distribution within their hosts with the passage of time. The parasite migrated subcutaneously or intramuscularly towards the upper body and gradually arrived in the lung from 45 h post infection (p.i.) in rats and from 42 h p.i. in mice. After the larvae passed through the trachea, they first appeared in the small intestine at 60 h p.i., probably via the oesophagus and stomach. In comparison to the rats, more larvae were recovered from the mice at all times, and a higher concentration of larval localization was observed in the mice. The present study has established a good model of larval migration of S. venezuelensis in rodents, with the migration route apparently different from of Strongyloides ratti, another species found in rodents.

Sensory neuroanatomy of a skin-penetrating nematode parasite: Strongyloides stercoralis. I. Amphidial neurons

The Strongyloides stercoralis infective larva resumes feeding and development on receipt of signals, presumably chemical, from a host. Only two of the anterior sense organs of this larva are open to the external environment. These large, paired goblet-shaped sensilla, known as amphids, are presumably, therefore, the only chemoreceptors. Using three-dimensional reconstructions made from serial electron micrographs, amphidial structure was investigated. In each amphid, cilialike dendritic processes of 11 neurons extend nearly to the amphidial pore; a twelfth terminates at the base of the amphidial channel, behind an array of lateral projections on the other processes. A specialized dendritic process leaves the amphidial channel and forms a complex of lamellae that interdigitate with lamellae of the amphidial sheath cell. This "lamellar cell" is similar to one of the "wing cells" or possibly the "finger cell" of Caenorhabditis elegans. Each of the 13 amphidial neurons was traced to its cell body. Ten neurons, including the lamellar cell, connect to cell bodies in the lateral ganglion, posterior to the nerve ring. The positions of these cell bodies were similar to those of the amphidial cell bodies in C.elegans. Therefore, they were named by using C. elegans nomenclature. Three other amphidial processes connect to cell bodies anterior to the nerve ring; these have no homologs in C. elegans. A map allowing identification of the amphidial cell bodies in the living worm was prepared. Consequently, laser ablation studies can be conducted to determine which neurons are involved in the infective process.

Pathogenesis of human strongyloidiasis: autopsy and quantitative parasitological analysis

The distribution of pathologic lesions and the parasite burden of major organs were studied in seven patients with disseminated strongyloidiasis who were autopsied at the University of Texas Medical Branch (Galveston, TX). All patients were immunosuppressed and had additional bacterial, viral, and fungal infections; six patients had received cortisone therapy and one patient had AIDS. High Strongyloides burdens were noted in untreated patients or in those with a short period of treatment. The proximal small intestine and the lungs showed the heaviest parasite burden, with large numbers of filariform larvae found in both locations. The lungs showed persistence of larvae in all patients, in the absence of intestinal or extraintestinal infection; this suggests that the respiratory cycle may be more resistant to therapy than the intestinal cycle. In the intestines, filariform larvae were seen at all levels, but higher burdens were seen in the upper as compared to lower small intestine, and larvae were more concentrated in the proximal jejunum than in the duodenum. Autoinfection (i.e., filariform larval penetration) occurred more prominently in the distal small and proximal large intestine than in the distal colon. Most filariform larvae were found in the intestinal lymphatics and were highly concentrated in mesenteric and retroperitoneal lymph nodes; conversely, larvae were not found in the spleen and were found in very low density in the liver. These findings, in concert, suggest that during autoinfection in humans, the Stronglyloides larvae transverse lymphatics to the thoracic duct, then pursue a lymphohematogenous dissemination to the lungs where they penetrate the air spaces and ascend through the airways to reach the gut.

Long-lasting parasitism of Strongyloides venezuelensis in Mongolian gerbils (Meriones unguiculatus)

Mongolian gerbils (Meriones unguiculatus) were infected with 100, 1,000 and 10,000 Strongyloides venezuelensis infective larvae (L3) to determine the duration of fecal egg output. Eggs per gram of feces (EPG) were counted chronologically, and adult worms in the small intestine were recovered on 100 days after infection. Changes of EPG in Mongolian gerbils infected with 10,000 L3 also were observed for 450 days. EPG was stable for each dose after the peak value noted 9 or 10 days after the infection. The EPG and number of worms recovered were dependent on the dose. The high EPG value continued for 450 days. These results demonstrate that Mongolian gerbils allowed a long-lasting parasitism of S. venezuelensis. Strongyloides venezuelensis-Mongolian gerbil systems may be useful for parasitological study of S. venezuelensis.

Parasitic diseases. Other roundworms. Trichuris, hookworm, and Strongyloides

Trichuriasis may be asymptomatic or, in heavy infection, lead to profuse, bloody diarrhea and rectal prolapse. Diagnosis is made by finding the distinctive barrel shaped eggs in the stool or in the heavily infested patient, by anoscopy and identification of worms attached to reddened and ulcerated rectal mucosa. Mebendazole is the drug of choice in treatment. Capillariasis, a parasitic infection encountered mainly in the Philippine Islands, is of interest in that the eggs may be confused with the eggs of trichuris. Hookworm disease is generally asymptomatic, but in heavy infection, leads to iron deficiency and hypochromic, microcytic anemia. Diagnosis is made by finding the characteristic hookworm eggs on a examination of a direct fecal film. Accidental invasion of humans by dog and cat hookworm leads to cutaneous larva migrans, also known as "creeping eruption." Human hookworm is treated most effectively with mebendazole, while the rash produced by creeping eruption responds to topical thiabendazole. Strongyloides is fairly common in rural areas of the southeastern United States and may be seen in the urban setting among inmates of mental institutions, prisons, and in immigrants who formerly resided in endemic tropical regions. Because of its remarkable capacity for dissemination of larvae throughout the body, this parasite is now recognized as a serious problem for the patient who is immunocompromised. Diagnosis is made by finding larvae in the stool or by the Enterotest. All infected patients should be treated with thiabendazole. I consider the issue on Drugs For Parasitic Infections, published annually or biannually by The Medical Letter on Drugs and Therapeutics, to be the single best source of information on the treatment of parasitic diseases for primary care physicians.

A basis to extend the proof of migration routes of immature parasites inside hosts: estimated time of arrival of Nippostrongylus brasiliensis and Strongyloides ratti in the gut of the rat

The time taken for larvae of Nippostrongylus brasiliensis and a homogonic strain of Strongyloides ratti to complete their migration from the skin surface to the small intestine of the rat was estimated by a new method in which a mirror image of arrival times was created by counting mature parasites at day 8 (N. brasiliensis) or day 5 (S. ratti) in the intestines of rats that had received a single pulse of morantel tartrate by stomach tube at different times starting 10 h after skin application of exact doses of infective larvae. It was confirmed that the effect of the drug was confined to parasites in the gut, so that the kinetics of migration were unperturbed. The persistence of the anthelmintic effect in the gut was shown by independent assays to be less than 8 h for both species. The time-course of arrival calculated from drug pulse data corrected for persistent effects was compared with direct counts of larvae arriving in the intestines of rats not dosed with anthelmintic. Both methods agreed in all respects for N. brasiliensis, whereas the estimates for direct counts of S. ratti, lagged 15-17 h behind those from drug-treated rats. In the discussion it is argued that the anthelmintic method provides a more correct picture for S. ratti and, on this basis, rates and synchrony of migration of the two species are compared. The role of these data as part of a proof of migration routes is explained.

An extended proof of migration routes of immature parasites inside hosts: pathways of Nippostrongylus brasiliensis and Strongyloides ratti in the rat are mutually exclusive

Rigorous proofs applicable to the routes of migration of Strongyloides ratti and Nippostrongylus brasiliensis skin-penetrating juveniles inside the rat are extended. By applying the inequality principle (Tindall & Wilson, 1988) it was confirmed with a probability of error of 1 in 10(10) that N. brasiliensis larvae applied to the skin passed through the lungs on their way to the intestine. Taking the analysis further, migrating larvae of S. ratti or N. brasiliensis were extracted from the nose or lungs, respectively, of donor rats and transferred to recipients by stomach tube to assay their ability to colonize the intestine. Results showed that (a) changes undergone by each parasite in its proven, specific transit site were essential before larvae could establish in the intestines of recipients, (b) these changes could be monitored by morphological criteria, and [corrected] (c) these changes were not completed until larvae had been in the nose or lung for a significant period. It follows from (c) that anywhere in the body of the host, termed a 'nursery', that supports a substantial amount of this mandatory development must be detectable by the conventional procedure of sampling at autopsy. Conversely, absence of parasites judged by sampling at autopsy is positive proof that a site is not a nursery when sampling is timed in relation to reliable estimates of overall kinetics (Tindall & Wilson, 1990), and with control information on the efficiency of sampling. Comparative data from sampling at autopsy using the same extraction techniques for both species met these criteria: they demonstrated that no part of the head of the rat was a nursery for N. brasiliensis, and that the lung did not serve in this capacity for S. ratti.(ABSTRACT TRUNCATED AT 250 WORDS)

Strongyloides stercoralis: identification of a protease that facilitates penetration of skin by the infective larvae

Host invasion and tissue migration of several helminths have been linked to the expression and release of parasite-derived proteases. One of the most remarkable examples of tissue migration is that of larvae of the nematode parasite Strongyloides stercoralis, which can move through tissue at speeds of up to 10 cm per hour. We have shown the Strongyloides L3 larvae secrete a potent histolytic metalloprotease to facilitate their rapid migration. This protease has elastase activity and catalyzes the degradation of a model of dermal extracellular matrix. The importance of this enzyme in the pathogenesis of strongyloidiasis is underscored by the observation that invasion by larvae of skin in vitro is prevented by metalloprotease inhibitors. These results substantiate the role of proteases as virulence factors in strongyloidiasis, as well as other related parasitic infections, and suggest new approaches to therapy.

The acquirement of growth ability for third-stage larvae of Strongyloides ratti during the head-passage in the rat

The role of larval passage through the head in the course of the migration of Strongyloides ratti in rats was investigated. Third-stage larvae (L3) recovered from various portions of donor rats were re-injected into the skin, cranial cavity and small intestine of recipient rats to check their ability for further growth. Cultured L3 (L3c) and the L3 recovered from the skin of donor rats (L3s) did not survive in the small intestine after intestinal inoculation. However, intestinal inoculation of L3 recovered from the head of donor rats (L3h) revealed growth to the adult stage. Cultured L3 injected into the cranial cavity of rats also became adult worms in the small intestine. L3 incubated in the cranial cavity for more than 24 h could grow in the small intestine of the recipient rats. These experiments suggest that S. ratti L3 acquire their ability to mature in the small intestine during their migration through the head of rats.

Radiolabeling of infective third-stage larvae of Strongyloides stercoralis by feeding [75 Se]selenomethionine-labeled Escherichia coli to first- and second-stage larvae

A technique is described for radiolabeling Strongyloides stercoralis larvae with [75Se]selenomethionine. Cultures of an auxotrophic methionine-dependent stain of Escherichia coli were grown in a medium containing Dulbecco's modified Eagle's medium supplemented with 5% nutrient broth, amino acids, and [75Se]selenomethionine. When the 75Se-labeled bacterial populations were in the stationary phase of growth, cultures were harvested and the bacteria dispersed on agar plates to serve as food for S. stercoralis larvae. Use of nondividing bacteria is important for successful labeling because the isotope is not diluted by cell division and death of larvae attributable to overgrowth by bacteria is prevented. First-stage S. stercoralis larvae were recovered from feces of infected dogs and reared in humid air at 30 C on agar plates seeded with bacteria. After 7 days, infective third-stage larvae were harvested. The mean specific activity of 6 different batches of larvae ranged from 75 to 330 counts per min/larva with 91.8 +/- 9.5% of the population labeled sufficiently to produce an autoradiographic focus during a practicable, 6-wk period of exposure. Labeled infective larvae penetrated the skin of 10-day-old puppies and migrated to the small intestine, where the developed to adulthood.

Strongyloides stercoralis: is there a canonical migratory route through the host?

It is generally accepted that the skin-penetrating larvae of Strongyloides stercoralis travel from the skin to the intestinal habitat of the adult stage by an obligatory migratory route that includes the blood, lungs, trachea, and upper gastrointestinal tract in sequence (the pulmonary route). It is assumed, furthermore, that following autoinfective invasion of the bowel wall, S. stercoralis larvae follow this same route to return to the small intestine where they mature. We reexamined the parasite's migratory behavior using a canine isolate of S. stercoralis, specific-pathogen-free pups, radiolabeled larvae, and compressed tissue autoradiography. Compartmental analysis of the number of larvae found in the organ sets examined revealed no reason to reject the simple idea that the pulmonary route was just one of several possible pathways to the duodenum. This was true whether the larvae began their journey in the subcutaneous tissue of the inguinal area or in the distal part of the ileum. Direct sampling of the larvae traversing the trachea indicated that the number of larvae reaching the duodenum by way of the presumptive pulmonary route was insufficient to account for the estimated absolute number actually found there.

Strongyloides stercoralis: loss of ability to disseminate after repeated passage in laboratory beagles

A strain of Strongyloides stercoralis originally isolated from a south-east Asian patient and maintained by passage in monkeys for four years was introduced into parasite-free laboratory-reared beagles. After the second passage in these dogs, the prepatent period shortened from an average of 12-14 d to 8-9 d. Up to the third generation, immunosuppressive treatment of the dogs with oral corticosteroids caused hyperinfection with dissemination, albeit limited, to extra-intestinal organs. From the fourth generation onward, neither hyperinfection nor extra-intestinal migration could be induced even by higher doses of corticosteroids. These observations suggest that the biological behaviour of populations of S. stercoralis can alter as they pass from host to host. Such changes may account, at least in part, for the diverse clinical manifestations of strongyloidiasis.

Criteria for a proof of migration routes of immature parasites inside hosts exemplified by studies of Strongyloides ratti in the rat

The first rigorous proof applicable to the migration pathway of an infective juvenile macroparasite inside its host is presented. Third-stage larvae of a homogonic strain of Strongyloides ratti applied in exact doses of less than 20 to the skin of the flank of young rats were recovered 16-40 h later in the naso-frontal part of the head. The peak proportion of the dose (po) recovered between 20 and 25 h in this site had a mean value of 0.316 +/- 0.021 in 48 animals. In 40 other rats infected simultaneously the mean proportion of the dose (pf) that reached the small intestine was at least 0.837 +/- 0.013. Proof resides in verification of the inequality po + pf greater than 1. With appropriate statistical tests the excess of the sum of the means of these two proportions over unity is shown to have a probability of occurring by chance of 1 in 3.5 x 10(6). Thus it is effectively certain that the naso-frontal portion of the head is part of at least one pathway taken by this parasite on its way from the skin to the intestine of its host. By suitable protection of the infection site it was confirmed that migration to the head was achieved by an internal route and not as a result of grooming. Larvae were recovered from the cranium in the same rats over the period 15-40 h, but the peak proportion of the dose occurred at 20 h, and po + pf less than 1 in this location. Whether the cranium is also part of the pathway is therefore still undecided. The significance of this novel analysis in the general context of in-host migration of infective stages is discussed and it is concluded, following its application to data sets from other authors, that the only cases in which proof can be demonstrated are the anterior skull of the rat for S. ratti (present data) and the lung of the same host for Nippostrongylus brasiliensis (Twohy, 1956).

Electron microscopical studies of Strongyloides ratti infective larvae: loss of the surface coat during skin penetration

Previous indications using radiolabelled larvae that Strongyloides ratti free-living infective larvae lose a surface coat during penetration of the skin were further investigated by transmission electron microscopy of the cuticle of S. ratti infective larvae in the free-living stage, after penetration of mouse skin, and after migration to the lungs. These studies demonstrated the presence of a faint electron-dense surface coat external to the epicuticle on free-living worms which was absent from larvae recovered from the skin and lungs. When free-living infective larvae were incubated in 10% CO2 at 37 C and then examined with phase-contrast microscopy, worms were observed in the process of losing this coat. These observations confirm the hypothesis that S. ratti infective larvae lose a surface coat during penetration of the skin.

Studies of the effect of contralateral versus ipselateral challenge of rats primed on one side with Strongyloides ratti

The initial pathway of skin penetrating larvae of Strongyloides ratti inside the host is not systemic and could well involve local components of the lymphatic system. The experiments described were an attempt to detect an effect on immunity depending on whether larvae of a challenge infection were committed to a pathway through heavily primed or lightly primed lymph nodes. Female rats were immunised by subcutaneous injection into the right forearm of 10,000 [corrected] heat killed, or 1000 live, third stage larvae of S. ratti. Animals given living parasites were placed on a diet containing 0.1 or 0.2% thiabendazole 48h or 36h after infection. Challenge infections of less than 100 larvae ('exact' doses) were applied on day 21 to either the right or left flank and, similarly, to controls that had received the anthelmintic but not the priming infection. Heat killed parasites elicited no response at all. Priming with live larvae stimulated a significant immunity (16% and 37% depression in 2 experiments), but there was no difference between rats whose challenge was on the same side as the priming dose and those which had the contralateral treatment. The significance of these results to theories of pathfinding in general, and to practical immunology, is discussed.

Elucidation of Strongyloides stercoralis by bacterial-colony displacement

Two cases of unsuspected Strongyloides stercoralis infection were elucidated by the displacement of bacterial colonies on primary plating media. Observation of primary plates inoculated for the diagnosis of bacterial pneumonia or gastroenteritis revealed that normal flora colonies had been moved and were aligned in a pathway, or track. This unusual colony alignment prompted us to request a stool for the examination of parasites, and S. stercoralis was found. It was concluded that the parasite is capable of motility on agar surfaces, resulting in the displacement of bacterial colonies that make up the normal flora.

The effect of method of infection on the pathway of juvenile Strongyloides ratti in the host

Subcutaneous injection of the larvae is the almost universally adopted means of initiating experimental infections of skin-invading roundworms but, so far, the possibility that this procedure introduces artefacts of one kind or another has not been critically studied. Experiments described in this paper were used to compare the effect of (a) injection and (b) skin application, of a small, precisely counted ('exact') dose of larvae. Results with two strains of S. ratti showed that the same proportion of the dose developed to adults in the intestines of rats irrespective of the method. With the same exact dose technique it has been shown that milk-borne infection of the pups of lactating rats is not an artefact produced by injection. Large doses (mean 4000) of larvae of the homogonic strain of S. ratti carrying a radioactive label of 75Se were tracked in their migration to the mammary gland following injection or skin application at two different sites on the right-hand side of nursing mother rats. The broad conclusion of earlier work in this laboratory using injection, that larvae move by a local route and not a systemic one, was supported by the results. The detailed distribution of the label and of unlabelled worms of the heterogonic strain in families was, however, different for the two methods, indicating that subtle variations in pathway can be brought about by the use of injection. If migration involves the lymphatic system, then the interpretation of immunological experiments in terms of lymphatic anatomy must take account of such procedural effects. The extent to which these results contribute to theories of migration in Strongyloides ratti is discussed.

Intestinal nematode infections

This article discusses strongyloidiasis, hookworm infection, trichostrongyliasis, ascariasis, trichuriasis (whipworm infection), and enterobiasis (pinworm infection). For each infection, the author describes the organism, the epidemiology and geographic distribution, symptomatology and pathogenesis, and diagnosis and treatment.

Unsuspected strongyloides coexisting with adenocarcinoma of the lung

The findings in an unsuspected case of Strongyloides stercoralis infestation coexisting with adenocarcinoma of the lung are presented. The diagnosis of adenocarcinoma was confirmed histologically by lung biopsies; the parasitic infection was initially diagnosed by sputum cytology and then by bronchial washings. A stool specimen submitted to the microbiology laboratory confirmed the diagnosis of S. stercoralis infection. This case again suggests the possibility that neoplastic disease may play a role similar to that of immunosuppression in creating an immune deficiency, thus increasing the susceptibility to infectious diseases.

Loss of surface coat by Strongyloides ratti infective larvae during skin penetration: evidence using larvae radiolabelled with 67gallium

The optimal conditions for labelling infective larvae of Strongyloides ratti with 67gallium citrate were determined. Radiolabelled larvae were injected s.c. into normal and previously infected rats. The distribution of radioactivity in these animals was compared with that in rats infected subcutaneously with a similar dose of free 67Ga by using a gamma camera linked to a computer system. Whereas free 67Ga was distributed throughout the body and excreted via the hepatobiliary system, the bulk of radioactivity in rats injected with radiolabelled larvae remained at the injection sites. Direct microscopical examination of these sites, however, revealed only minimal numbers of worms. When rats were infected percutaneously with radiolabelled larvae, it was found that most radioactivity remained at the surface, despite penetration of worms. When infective larvae were exposed to CO2 in vitro and examined carefully by light microscopy, loss of an outer coat was observed. It was concluded that infective larvae lose an outer coat on skin penetration.

Immunobiology of strongyloidiasis

Strongyloides stercoralis causes a usually silent infection that, under certain conditions of altered host-parasite balance, may become a severe, often fatal, disseminated disease. Patients, as well as experimental animals, develop specific humoral and cellular responses to the tissue-invading stage of the parasite, the filariform larvae. These responses, however, while potentially useful for diagnostic purposes, appear to be of little importance in determining the course of the disease. It is suggested that local intestinal factors may play a central role in the control of autoinfection. Until these questions are resolved and more accurate diagnostic methods are devised, preventive therapy in all patients from endemic areas that must undergo immunosuppressive therapy is advised.