Evaluation of targets for Strongyloides genus specific molecular diagnosis in experimental strongyloidiasis

Strongyloides venezuelensis has been used in different experimental studies, such as those aimed at the evaluation of diagnostic techniques for human strongyloidiasis, mainly the molecular diagnosis. In this study, three regions (genus, 18S and 28S targets) of Strongyloides ribosomal DNA were evaluated for the molecular diagnosis of experimental strongyloidiasis. Rats were infected subcutaneously with 400 or 4000 S. venezuelensis infective larvae (400iL3 and 4000iL3), and kept for 35 days. Fecal samples were collected daily to count eggs per gram of feces (EPG) and to perform the polymerase chain reaction (PCR). Egg count started on the 5th day post-infection (pi) and ended on days 33 and 34 pi, in 400iL3 and 4000iL3 groups, respectively. Based in EPG, fecal samples were selected from days 2, 5, 8, 11, 15, 23 and 35 pi for DNA extraction; PCR (genus, 18S and 28S); and sequencing. The PCR-28S products showed higher values of identity (95-100%) in the database with the Strongyloides sequences. Therefore, it is possible to reinforce the application of PCR-28S in the diagnosis of experimental and human strongyloidiasis.

Altitude and human disturbance are associated with helminth diversity in an endangered primate, Procolobus gordonorum

Gastrointestinal parasites colonizing the mammalian gut influence the host immune system and health. Parasite infections, mainly helminths, have been studied intensively in both humans and non-human animals, but relatively rarely within a conservation framework. The Udzungwa red colobus monkey (Procolobus gordonorum) is an endangered endemic primate species living in the Udzungwa Mountains of Tanzania, a global biodiversity hotspot. Since this endemic primate species is highly sensitive to human disturbance, here we investigate whether habitat type (driven by natural and human-induced factors) is associated with helminth diversity. Using standard flotation and sedimentation techniques, we analyzed 251 fecal samples belonging to 25 social groups from four different forest blocks within the Udzungwa Mountains. Five parasitic helminth taxa were recovered from Udzungwa red colobus, including Trichuris sp., Strongyloides fulleborni, S. stercoralis, a strongylid nematode and Colobenterobius sp. We used Generalized Linear Mixed Models to explore the contribution of habitat type, altitude and fecal glucocorticoid levels (as biomarkers of stress) in predicting gut parasite variation. Although some parasites (e.g., Trichuris sp.) infected more than 50% of individuals, compared to others (e.g., Colobenterobius sp.) that infected less than 3%, both parasite richness and prevalence did not differ significantly across forests, even when controlling for seasonality. Stress hormone levels also did not predict variation in parasite richness, while altitude could explain it resulting in lower richness at lower altitudes. Because human activities causing disturbance are concentrated mainly at lower altitudes, we suggest that protection of primate forest habitat preserves natural diversity at both macro- and microscales, and that the importance of the latter should not be underestimated.

Comparative transcriptomics gives insights into the evolution of parasitism in Strongyloides nematodes at the genus, subclade and species level

Strongyloides spp., gastrointestinal nematode parasites of humans and other animals, have genetically identical parasitic and free-living adult life cycle stages. This is an almost unique feature amongst nematodes and comparison of these two stages can provide insights into the genetic basis and evolution of Strongyloides nematode parasitism. Here, we present RNAseq data for S. venezuelensis, a parasite of rodents, and identify genes that are differentially expressed in parasitic and free-living life cycle stages. Comparison of these data with analogous RNAseq data for three other Strongyloides spp., has identified key protein-coding gene families with a putative role in parasitism including WAGO-like Argonautes (at the genus level) and speckle-type POZ-like coding genes (S. venezuelensis-S. papillosus phylogenetic subclade level). Diverse gene families are uniquely upregulated in the parasitic stage of all four Strongyloides species, including a distinct upregulation of genes encoding cytochrome P450 in S. venezuelensis, suggesting some diversification of the molecular tools used in the parasitic life cycle stage among individual species. Together, our results identify key gene families with a putative role in Strongyloides parasitism or features of the parasitic life cycle stage, and deepen our understanding of parasitism evolution among Strongyloides species.

The genomic basis of parasitism in the Strongyloides clade of nematodes

Soil-transmitted nematodes, including the Strongyloides genus, cause one of the most prevalent neglected tropical diseases. Here we compare the genomes of four Strongyloides species, including the human pathogen Strongyloides stercoralis, and their close relatives that are facultatively parasitic (Parastrongyloides trichosuri) and free-living (Rhabditophanes sp. KR3021). A significant paralogous expansion of key gene families--families encoding astacin-like and SCP/TAPS proteins--is associated with the evolution of parasitism in this clade. Exploiting the unique Strongyloides life cycle, we compare the transcriptomes of the parasitic and free-living stages and find that these same gene families are upregulated in the parasitic stages, underscoring their role in nematode parasitism.

Dexamethasone reduces bronchial wall remodeling during pulmonary migration of Strongyloides venezuelensis larvae in rats

Strongyloidiasis is an intestinal parasitosis with an obligatory pulmonary cycle. A Th2-type immune response is induced and amplifies the cellular response through the secretion of inflammatory mediators. Although this response has been described as being similar to asthma, airway remodeling during pulmonary migration of larvae has not yet been established. The aim of this study was to identify the occurrence of airway remodeling during Strongyloides venezuelensis (S. v.) infection and to determine the ability of dexamethasone treatment to interfere with the mechanisms involved in this process. Rats were inoculated with 9,000 S. v. larvae, treated with dexamethasone (2 mg/kg) and killed at 1, 3, 5, 7, 14 and 21 days. Morphological and morphometric analyzes with routine stains and immunohistochemistry were conducted, and some inflammatory mediators were evaluated using ELISA. Goblet cell hyperplasia and increased bronchiolar thickness, characterized by edema, neovascularization, inflammatory infiltrate, collagen deposition and enlargement of the smooth muscle cell layer were observed. VEGF, IL1-β and IL-4 levels were elevated throughout the course of the infection. The morphological findings and the immunomodulatory response to the infection were drastically reduced in dexamethasone-treated rats. The pulmonary migration of S. venezuelensis larvae produced a transitory, but significant amount of airway remodeling with a slight residual bronchiolar fibrosis. The exact mechanisms involved in this process require further study.

Progress in the molecular biology of malaria and the immunology of nematode infections

Japan is one of a small number of countries to have successfully controlled or eliminated major parasitic diseases, including malaria, filariasis, schistosomiasis and enteric parasitoses. Of particular importance in this success was a close collaboration between primary research and public health efforts. Many Japanese researchers continue to study malaria, particularly the areas of genetics and immunology, and this should contribute to global parasite eradication strategies. Furthermore, studies of immunoregulation of nematode infection using the interleukin-18 pathway, most of which have been conducted in Japan, are helping to improve researchers' understanding of human immune mechanisms and host-parasite interactions.

Strongyloides hyper-infection causing life-threatening gastrointestinal bleeding

A 55-year old male patient was diagnosed with strongy-loides hyper-infection with stool analysis and intestinal biopsy shortly after his chemotherapy for myeloma. He was commenced on albendazole anthelmintic therapy. After initiation of the treatment he suffered life-threatening gastrointestinal (GI) bleeding. Repeated endoscopies showed diffuse multi-focal intestinal bleeding. The patient required huge amounts of red blood cells and plasma transfusions and correction of haemostasis with recombinant activated factor VII. Abdominal aorto-angiography showed numerous micro-aneurysms (‘berry aneurysms’) in the superior and inferior mesenteric arteries’ territories. While the biopsy taken prior to the treatment with albendazole did not show evidence of vasculitis, the biopsy taken after initiation of therapy revealed leukoclastic aggregations around the vessels. These findings suggest that, in addition to direct destruction of the mucosa, vasculitis could be an important additive factor causing the massive GI bleeding during the anthelmintic treatment. This might result from substances released by the worms that have been killed with anthelmintic therapy. Current guidelines advise steroids to be tapered and stopped in case of systematic parasitic infections as they might reduce immunity and precipitate parasitic hyper-infection. In our opinion, steroid therapy might be of value in the management of strongyloides hyper-infection related vasculitis, in addition to the anthelmintic treatment. Indeed, steroid therapy of vasculitis with other means of supportive care resulted in cessation of the bleeding and recovery of the patient.

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.

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.

Coinfection of Schistosoma mansoni and Strongyloides stercoralis in a Patient with Variceal Bleeding

We report a case of hepatosplenic schistosomiasis with portal hypertension and variceal bleeding in an immigrant patient from Egypt, coinfected with Strongyloides stercoralis. The diagnosis was based on the following: (a) identification of Schistosoma mansoni ova in the stools and colonic biopsy specimens, (b) portal hypertension and esophageal varices with normal liver function and the absence of hepatic cirrhosis stigmata, (c) history of migration from an endemic area and (d) ultrasonographic findings of spleen and liver enlargement, fibrosed portal tracts, and normal lobular architecture of liver parenchyma. Hepatosplenic schistosomiasis should be suspected in any patient from an endemic area who has splenomegaly, portal hypertension, and esophageal varices bleeding in the absence of stigmata of liver cirrhosis and hepatic insufficiency. Coinfection with S. stercoralis could be attributed to common epidemiological features of the parasites and the patient's habits.

[Strongyloidiasis im Moscow region]

The paper presents two cases of infection with Strongyloides stercoralis (in a 13-year-old boy and in a 93-year-old female), occurred in the Moscow Region, which is indicative of the resurgence of stronglyoidiasis in the Moscow Region. Although the likelihood of this infection in this region is little, nevertheless, strongyloidiasis should be borne in mind in examining patients who are not leaving for well-known endemic areas if they have an allergic reaction of unclear etiology, eosinophilia, and digestive disorders. In these cases, the syndromic-and-empiric approach to justifying and performing chemotherapy is recommended due to the inadequate efficiency of parasitological methods for diagnosing strongyloidiasis at the low rate of invasion. These cases are indicative of the rather low virulence of Moscow strains, but at the same time of their capacity for autoinvasion and accordingly for the long-term infection of patients without recurrent infections.

Adult worms of the rodent intestinal nematode, Strongyloides venezuelensis, successfully invade chick intestinal mucosa

In order to study the mucosal invasion of a rodent intestinal nematode in bird intestine, chicks were infected with the intestinal nematode of rodents, Strongyloides venezuelensis, by subcutaneous larva inoculation and adult worm implantation. No evidence was obtained for larvae reaching the lungs or the intestine after infective larva inoculation. Adult worms implanted in the small intestine invaded the mucosa and remained there at least for 24 h, whereas those implanted in the caecum were trapped by mucus, and did not invade the mucosa. Mucosal invasion of adult worms in the small intestine was confirmed by histological examination. The number of adult worms in the intestinal mucosal tissue dropped rapidly within the first 24 h, which was associated with infiltrating granulocytes around the worms. The present study suggests that S. venezuelensis adult worms are able to invade the intestinal tissue of chicks, which do not belong to the vertebrate class of its normal definitive host, but that they are eliminated rapidly by mucosal defense system of the bird.

Secreted adhesion molecules of Strongyloides venezuelensis are produced by oesophageal glands and are components of the wall of tunnels constructed by adult worms in the host intestinal mucosa

The parasitic female of Strongyloides venezuelensis keeps invading the epithelial layer of the host intestinal mucosa. Upon invasion, it adheres to the surface of the intestinal epithelial cells with adhesion molecules secreted from the mouth. It has been demonstrated that S. venezuelensis are expelled from the intestine because mucosal mast cells inhibit the attachment of adult worms to the mucosal surface. In the present study, we generated specific antibodies against secreted adhesion molecules to investigate their function in vivo, because these molecules have been demonstrated only in vitro in spite of the importance in the infection processes. A mouse monoclonal antibody specific to S. venezuelensis adhesion molecules inhibited the attachment of adult worms to plastic dishes and the binding of adhesion molecules to rat intestinal epithelial cells. Immunohistochemical study revealed that adhesion molecules were produced by oesophageal glands and were continuously secreted in vivo to line the wall of the tunnels formed by adult worms in the intestinal mucosa. Our findings indicate that adhesion molecules play essential roles in the infection processes of S. venezuelensis in the host intestine.

Persistent infection with Strongyloides venezuelensis in the Mongolian gerbil (Meriones unguiculatus)

To examine the fate of Strongyloides venezuelensis. Mongolian gerbils (Meriones unguicalatus) were orally infected with 1,000 L3 larvae per animal. Altogether, 50 gerbils divided into 5 groups of 10 each were monitored for a period of 570 days to document the kinetics of faecal egg output, adults worm population, morphological development, fecundity, and hematological changes including peripheral blood eosinophilia. This study chronicled a life long parasitism of S. venezuelensis in the gerbil host, and showed that S. venezuelensis infection was quite stable throughout the course of infection and the worms maintained their normal development as evidenced by their body dimension. A progressive loss of body condition of the infected gerbils was observed as the level of infection advanced. However, no detectable pathological changes were observed in the gastrointestinal tract. The present findings indicate that an immunocompetent host, such as the Mongolian gerbil, can serve as a life long carrier model of S. venezuelensis if the worms are not expelled within 570 days after infection.

Strongyloides venezuelensis: longitudinal distribution of adult worms in the host intestine is influenced by mucosal sulfated carbohydrates

Mechanisms for the longitudinal distribution of parasitic females of Strongyloides venezuelensis in the host intestine were investigated in mice. Adult worms were mostly recovered from the anterior-most one-third of the small intestine throughout the infection after infective larvae inoculation. Surgically implanted adult worms established well in the small intestinal mucosa, either in the duodenum or in the ileum, whereas a few worms could establish in the large intestine. Implanted worms in the small intestine remained where they were implanted until expelled. Mucosal mast cells were induced in the whole small intestine after the worm implantation. In the large intestine, a considerable number of adult worms settled in the mucosa of mutant mice, whose goblet cell mucins were undersulfated because of a mutation in sulfate-activating enzymes. In these mice, the degree of sulfation of goblet cell mucins in the large intestine was significantly reduced to the level of normal small intestine goblet cell mucins. Our results suggest that sulfated glycoconjugates, either from mucosal mast cells or goblet cells, have important effects on the longitudinal distribution of parasitic females of S. venezuelensis.

A role of mast cell glycosaminoglycans for the immunological expulsion of intestinal nematode, Strongyloides venezuelensis

We examined effects of mast cell glycosaminoglycans on the establishment of the intestinal nematode, Strongyloides venezuelensis, in the mouse small intestine. When intestinal mastocytosis occurred, surgically implanted adult worms could not invade and establish in the intestinal mucosa. In mast cell-deficient W/Wv mice, inhibition of adult worm invasion was not evident as compared with littermate +/+ control mice. Mucosal mastocytosis and inhibition of S. venezuelensis adult worm mucosal invasion was tightly correlated. To determine effector molecules for the invasion inhibition, adult worms were implanted with various sulfated carbohydrates including mast cell glycosaminoglycans. Among sulfated carbohydrates tested, chondroitin sulfate (ChS)-A, ChS-E, heparin, and dextran sulfate inhibited invasion of adult worms into intestinal mucosa in vivo. No significant inhibition was observed with ChS-C, desulfated chondroitin, and dextran. ChS-E, heparin, and dextran sulfate inhibited adhesion of S. venezuelensis adult worms to plastic surfaces in vitro. Furthermore, binding of intestinal epithelial cells to adhesion substances of S. venezuelensis, which have been implicated in mucosal invasion, was inhibited by ChS-E, heparin, and dextran sulfate. Because adult worms of S. venezuelensis were actively moving in the intestinal mucosa, probably exiting and reentering during infection, the possible expulsion mechanism for S. venezuelensis is inhibition by mast cell glycosaminoglycans of attachment and subsequent invasion of adult worms into intestinal epithelium.

A method of decontaminating Strongyloides venezuelensis larvae for the study of strongyloidiasis in germ-free and conventional mice

To study the possible influence of intestinal micro-organisms on the course of strongyloidiasis in mice, a method was developed to obtain axenic infective larvae of Strongyloides venezuelensis. Cultured larvae from conventional mice were treated with sodium hypochlorite 0.25% for 10 min, washed in distilled water and then exposed to various combinations of antibiotics for 30 or 60 min. Success was achieved with a combination of penicillin 180 mg/L and ceftazidime 1 mg/ml. Decontamination of the larvae was determined by aerobic and anaerobic culture and by inoculation into gnotobiotic mice. Viability was established by subcutaneous inoculation of larvae into germ-free and conventional mice. Preliminary results showed that gnotobiotic mice were more susceptible than conventional mice to infection with axenic S. venezuelensis larvae as judged by faecal egg excretion, recovery of worms in the small intestine and histopathological examination of the duodenal mucosa. These results suggest that the normal intestinal flora protects the host against experimental infection with S. venezuelensis.

Hypolipemia associated with the wasting condition of rabbits infected with Strongyloides papillosus

Rabbits develop a wasting condition in the intestinal stage of Strongyloides papillosus infection. Serum inflammatory cytokine and lipid profiles were investigated in five rabbits infected with S. papillosus and five uninfected pair-fed controls to ascertain whether the disease is inflammatory cytokine-mediated cachexia. Tumor necrosis factor alpha (TNF alpha) was detected in one infected animal at Day 7 after infection. Interleukin (IL)-1 was detected in three infected, and one control, animals at Day 28. IL-6 remained unchanged in both the groups. Infected animals developed hypolipemia, including hypotriglyceridemia in the intestinal stage of infection. Control animals lost body weight in the same manner as the infected animals, but had elevated cholesterols and phospholipids with normal triglyceride concentrations. The results suggested that the wasting condition has no association with cachexia induced by TNF alpha. IL-1 or IL-6, and that hepatic function for lipid synthesis is affected during the intestinal stage of S. papillosus infection.

Experimental studies with Stronglyloides papillosus in goats

Unusual clinical and pathological observations in the field in goats and sheep suffering from Strongyloides papillosus infection prompted experimental work on this parasite. Goats were infected percutaneously with either single or multiple, low or high levels of S. papillosus. Young goats up to 12 months of age were found to be the most susceptible. Some animals, however, showed substantial resistance to infective doses. Clinical signs included transient diarrhoea, misshapen, elongated faecal pellets terminally, dehydration, anorexia, cachexia, gnashing of teeth, foaming at the mouth, anaemia and nervous signs such as ataxia, a wide-based stance, stupor and nystagmus. A 'pushing syndrome' was seen in 22% of the animals. The pathological changes are described and included enteritis, status spongiosus in the brain, hepatosis leading to rupture of the liver, nephrosis, pulmonary oedema, interstitial pneumonia and pneumonia. About 6% of the goats died acutely from fatal hepatic rupture. The development of an acquired immunity was determined. The immunity elicited an allergic skin reaction at the application site of larvae or injection sites of larval metabolites. This immunity, however, could be breached by large doses of larvae. The most profound clinicopathological changes induced by the parasites were an anaemia (most pronounced in the young goats) and hypophosphataemia. Trace element analyses provided evidence of Cu, Mn and possibly Se deficiencies in some goats.

Effects of in vitro culture methods on morphological development and infectivity of Strongyloides venezuelensis filariform larvae

The effects of in vitro culture methods on morphological development and infectivity of Strongyloides venezuelensis filariform larvae (L3) to rats were investigated. A significantly higher body length was observed in L3 from filter paper culture (597.3 +/- 32.2 microns) than those in fecal (509.9 +/- 35.0 microns) and nutrient broth culture (503.3 +/- 31.0 microns) (P < 0.05). Larval infectivity was assessed by exposing rats to 1,000 L3 from each culture and worms were recovered from the lungs and small intestines. Recovery rate of these worms did not show any significant difference. A significantly greater body length of adults was recorded in those corresponding to the L3 harvested from filter paper (2,777.5 +/- 204.4 microns) and nutrient broth culture (2,732.5 +/- 169.8 microns) than those corresponding to the L3 obtained from fecal culture (2,600.5 +/- 172.4 microns) (P < 0.05). Although worm fecundity and EPG counts differed among culture methods but worm burdens and course of infection did not. These findings suggest that the methods of cultures have a significant effect on the morphological development of the larvae to the L3 stage, but do not influence the infectivity to rats.

A freeze-fracture and deep-etch study of the cuticle and hypodermis of infective larvae of Strongyloides venezuelensis (Nematoda)

The body walls of infective 3rd-stage larvae of S. venezuelensis were studied by routine transmission electron microscopy, ruthenium red cytochemistry, quick-freeze, freeze-fracture and deep-etch techniques. In routine thin sections the cuticle is formed by 5 layers: epicuticle, cortical, medial, fibrous and basal. The epicuticle showed a trilaminate appearance and a surface coat stained with ruthenium red. Specimens submitted to freeze-fracture were frequently sectioned along the body wall at the level of the hypodermis, showing the E and P fracture faces of the outer and inner hypodermal membranes. In replicas of fractures submitted to etching, the external surface of the nematode was exposed, revealing particles and fine strands of fibrous elements, and was sometimes covered by a well organized structure with a crystalline pattern. At the level of the cortical, medial and basal layers, interconnecting fibrous and globous structures were seen. The fibrous layer was formed by parallel bars of thick fibrous elements. The cytoskeleton of the hypodermis and muscle cells also became evident with this technique.

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.

Development of the free-living stages of Hyostrongylus rubidus and Oesophagostomum spp. at different temperatures and humidities

Faeces containing a mixture of Hyostrongylus rubidus and Oesophagostomum spp. eggs were mixed with vermiculite and water and set up at combinations of different relative humidities (65.5%, 79.5% 90.0%, and 100%) and temperatures (5 degrees C, 10 degrees C, 15 degrees C, 20 degrees C, and 25 degrees C) in order to study the rate of egg hatching and larval development. The study established that the development from egg to infective larva showed similar patterns for the two parasites. Optimum development and survival was in the temperature range from 15 degrees C to 20 degrees C and at humidities from 79.5 to 95.5%.

Wasting condition under normal cardiac rhythms in rabbits following Strongyloides papillosus infection

Pathogenicity of Strongyloides papillosus to rabbits was investigated by monitoring of food intake, body weight and electrocardiogram. No abnormalities were observed in rabbits infected with 10(4) infective larvae (L3)/kg. Rabbits given 10(5) L3/kg exhibited anorexia after the establishment of patent infections. Four of them died on Days 19-33 having lost 32-44% of initial body weight. The other one animal regained appetite and body weight as fecal egg output decreased. Cardiac rhythms remained normal even in the emaciation state. In lethal cases, cardiac activities finally disappeared through escape beats preceded by sinus arrhythmia as in a fasted control. These results suggest that heavy S. papillosus infection produces a wasting condition in rabbits resulting from anorexia under normal cardiac functions.

Parasitic females of Strongyloides papillosus as a pathogenetic stage for sudden cardiac death in infected lambs

The present study was aimed at elucidating the responsibility of parasitic females for sudden cardiac death following Strongyloides papillosus infection in calves. A preliminary experiment demonstrated a percutaneous infection with S. papillosus infective larvae to cause sudden cardiac death in lambs as in calves, indicating lambs could serve as a model to study fatal stronglyloidiasis in calves. Parasitic females of S. papillosus were inoculated into the duodenum of lambs. Lambs given live worms developed continuous sinus tachycardia immediately after inoculation, and died of sudden cardiac arrest by ventricular fibrillation through a phase of the disease identical to the case of percutaneous larval infection. The lambs had high fecal egg counts at the time of death. Inoculation of homogenized worms did not produce fatal arrhythmias. These results demonstrate that live parasitic females of S. papillosus in the small intestine are responsible for cardiac dysfunction regardless of the presence or absence of migratory larvae.

Strongyloides venezuelensis infections in mice

The course and intensity of Strongyloides venezuelensis infection as compared with S. ratti infection were investigated in BALB/c mice. The mice were found to be much more susceptible to infection with S. venezuelensis than S. ratti. The majority of worms inoculated were recovered from the lungs and subsequently from the small intestines, suggesting that their migratory route via the lungs to the small intestine was comparable to that of S. stercoralis in humans. Spontaneous expulsion of worms occurred by about 10 days after infection, which was the same as that of S. ratti. Different infectivities, as assessed by faecal egg excretion, age, sex and strain of mouse were observed in mice infected with S. venezuelensis, as well as in those infected with S. ratti. A striking immunity was acquired following a primary exposure to S. venezuelensis. Mice infected with S. venezuelensis are considered to provide as useful a model as those infected with S. ratti for the study of human strongyloidiasis.

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.

Cryopreservation of first-stage and infective third-stage larvae of Strongyloides stercoralis

Infective third-stage larvae of Strongyloides stercoralis were frozen over liquid nitrogen and remained infective to dogs when thawed. Successful cryopreservation depended on a 30-60-min incubation in a cryoprotectant (10% DMSO and 10% dextran) before freezing and thawing the frozen larvae into RPMI. First-stage larvae could also be frozen by this method. Thawed first-stage larvae remained viable and continued their development to third-stage larvae, which were shown to be infective to dogs.

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.

Differential responses of Duroc, Hampshire, and crossbred pigs to a superimposed experimental infection with the intestinal threadworm, Strongyloides ransomi

In both spring and fall, 12 Duroc, 12 Hampshire, and 12 Duroc times Hampshire F1 weanling pigs all reared under the same management were fed in pens of 3 to slaughter weights. Three Duroc and 4 Hampshire boars, essentially unrelated within breed, were used in sampling the breeds. Swine herd management allowed pig infection with Strongyloides ransomi and Ascaris suum, but neither clinical nor subclinical parasitism was evident in the herd. Pigs were percutaneously exposed by pens within breed and season, half to none (control) and half to 3,000,000 (exposed) S. ransomi infective larvae, Breed, treatment, and seasons were prominent sources of variation in pig response. Breeds failed to respond alike to parasitism in respect to experimental periods and exposure levels. This interaction response (P smaller than 0.01) showed that S. ransomi egg production increased rapidly for all breed groups but decreased quicker and greater in Durocs, slowest and least in Hampshires, with cross breds intermediate in these respects. The 2.0830 for mean of log A. suum EPG from exposed Durocs was near double that of control Durocs but the mean for exposed Hampshires was less than half that for controls; crossbreds tended to be intermediate in this respect. Daily gains of 0.70 and 0.73 for Durocs and crossbreds were similar (P greater than 0.10) but averaged 11.7% more (P smaller than 0.05) than the 0.64 kg for Hampshires and gains by control pigs were 20.6% above (P greater than 0.01) that of exposed pigs. Exposed pigs required more feed per kg of gain (P greater than 0.05) than control pigs (3.60 vs. 3.33 kg). Comparison of relative gains and feed efficiences of control and exposed pigs among and within breed groups supported the position that a superimposed exposure of 3,000,000 S. ransomi larvae was more severe for Hampshires, intermediate for crossbreds, and least severe for Durocs.

The effect of ageing on the metabolism of the infective larvae of Strongyloides ratti Sandground, 1925

The infective larvae ofS. rattihad a high Qo2(9·8 μl/mg dry weight/h at 20 °C). Their R.Q. was 0·74 indicating that lipid was the main metabolite.

As the infective larvae aged there was an exponential decrease in their infectivity and a corresponding decrease with age in the Qo2rate of activity and rate of substrate utilization. The R.Q. of fresh and aged larvae was the same showing that there was no change in the substrate being utilized.

The infective larvae ofS. ratticontained 25% lipid 3% glycogen and 0·25% free sugars (dry weight). The free sugars consisted of glucose and trehalose in approximately equal amounts. Both lipid and glycogen decreased as the larvae aged.

Analyses showed all the normal lipid components to be present, the major lipid fraction detected was free fatty acid. As the larvae aged there was a big decrease in the amounts of triglyceride and free fatty acid. There was, however, no difference in the amounts of cholesterol or in the phospholipid composition of fresh and aged larvae.

The fatty-acid composition of the larvae was analysed; 68% of the total fatty acids were unsaturated and the major fatty acid was C18:1. As the larvae aged, the fatty acids were not all catabolized at the same rate; the acid C18:1was the most heavily catabolized decreasing by 75% in 8 days, whilst C20:1decreased by only half this amount in the same time.

The distribution of lipid and glycogen was investigated histochemically. Lipid droplets were confined to the posterior two-thirds of the infective larvae and occurred in the lateral lines, non-contractile parts of the muscles and in the cells of the intestine. As the larvae aged the lipid in the body wall and lateral lines disappeared first. Dark granules, possibly excretory products, accumulated in old larvae. Glycogen was found in the lateral lines throughout the length of the larva.

I should like to thank Dr P. Tate for his constant advice and encouragement. This work was carried out during the tenure of a Medical Research Council scholarship.