Chapter 1 : A Guide to Human Helminths - CORE Guide To Human Helminths Cl [Isabel Coombs, D. W. T. Crompton] on blog.quintoapp.com *FREE* shipping on qualifying offers. Three hundred and forty one species of helminth, which have been found in association with humans, are listed in this book. Helminthic therapy Parasitic worms have been used as a medical treatment for various diseases, particularly those involving an overactive immune response. One study suggests a link between the rising rates of metabolic syndrome in the developed worlds and the largely successful efforts of Westerners to eliminate intestinal parasites. The work suggests eosinophils a type of white blood cell in fat tissue play an important role in preventing insulin resistance by secreting interleukin 4, which in turn switches macrophages into "alternative activation". Alternatively-activated macrophages are important to maintaining glucose homeostasis i. Helminth infection causes an increase in eosinophils. In the study, the authors fed rodents a high-fat diet to induce metabolic syndrome, and then injected them with helminths. Although sparse in blood of persons in developed countries, eosinophils are often elevated in individuals in rural developing countries where intestinal parasitism is prevalent and metabolic syndrome rare. We speculate that eosinophils may have evolved to optimize metabolic homeostasis during chronic infections by ubiquitous intestinal parasitesâ. Such soil is often characterized by moist and warm conditions. Therefore, the risk of using contaminated wastewater and sludge in agricultural fields is a real problem, especially in poor countries, where this practice is prevalent. Helminth eggs are resistant to various environmental conditions due to the composition of the egg shell. Each helminth egg species has 3 to 4 layers with different physical and chemical characteristics: In feces, fecal sludge and sewage sludge they can even remain viable for several years. Fertilized eggs and unfertilized eggs can exist side by side. Unfertilized eggs are identifiable under the microscope by their elongated shape. No larvae can hatch from these kinds of eggs. Therefore, unfertilized eggs do not pose a danger to human health. In the case of Ascaris lumbricoides giant roundworm, which has been considered the most resistant and common helminth type, fertilized eggs deposited in soil are resistant to desiccation but are, at this stage of development, very sensitive to environmental temperatures: This larva has the ability to get out of the egg, hatch in the small intestine and migrate to different organs. These infective larvae or "infective eggs" may remain viable in soil for two years or longer. These conventional wastewater treatment processes do not inactivate the helminth ova but only removes them from the wastewater and moves them to the sewage sludge. In particular, the number of viable Ascaris eggs is often taken as an indicator organism for all helminth eggs in treatment processes as they are very common in many parts of the world and relatively easy to identify under the microscope. However, the exact inactivation characteristics may vary for different types of helminth eggs. The detection of viable helminth eggs in samples of wastewater, sludge or fresh feces as a diagnostic tool for the infection helminthiasis is not straight forward. In fact, many laboratories in developing countries lack the right equipment or skilled staff required to do so. An important step in the analytical methods is usually the concentration of the eggs in the sample, especially in the case of wastewater samples. A concentration step may not be required in samples of dried feces, e. Human stool samples[ edit ] For medical purposes, the exact number of helminth eggs is less important and therefore most diagnoses are made simply by identifying the appearance of the worm or eggs in feces. Due to the large quantity of eggs laid, physicians can diagnose using only one or two fecal smears. Eggs per gram is a laboratory test that determines the number of eggs per gram of feces in patients suspected of having a parasitological infection, such as schistosomiasis. Page 1
Chapter 2 : Helminths, Soil-Transmitted - Chapter 3 - Yellow Book Travelers' Health CDC Book: A guide to human helminths. blog.quintoapp.com + pp. ref Abstract: This book represents an enormous act of scholarship. Its pages of text are packed with snippets of information regarding the species of helminth "which have been found in association with humans". Figure Generalized life cycle of flukes. All cycles involve snails as intermediate hosts. Hermaphroditic flukes - Clonorchis sinensis, Fasiolopsis buski, Paragonimys westermani, and Heterophytes heterpphyes. Metacercaria are infective for humans. Flukes have a well-developed alimentary canal with a muscular pharynx and esophagus. The intestine is usually a branched tube secondary and tertiary branches may be present consisting of a single layer of epithelial cells. The main branches may end blindly or open into an excretory vesicle. The excretory vesicle also accepts the two main lateral collecting ducts of the excretory system, which is of a protonephridial type with flame cells. A flame cell is a hollow, terminal excretory cell that contains a beating flamelike group of cilia. These cells, anchored in the parenchyma, direct tissue filtrate through canals into the two main collecting ducts. Except for the blood flukes, trematodes are hermaphroditic, having both male and female reproductive organs in the same individual. The male organ consists usually of two testes with accessory glands and ducts leading to a cirrus, or penis equivalent, that extends into the common genital atrium. The female gonad consists of a single ovary with a seminal receptacle and vitellaria, or yolk glands, that connect with the oviduct as it expands into an ootype. The tubular uterus extends from the ootype and opens into the genital atrium. Both self- and cross-fertilization occur. The components of the egg are assembled in the ootype. Eggs pass through the uterus into the genital atrium and exit ventrally through the genital pore. Fluke eggs, except for those of schistosomes, are operculated have a lid. The blood flukes or schistosomes are the only bisexual flukes that infect humans Fig. Although the sexes are separate, the general body structure is the same as that of hermaphroditic flukes. Within the definitive host, the male and female worms inhabit the lumen of blood vessels and are found in close physical association. The female lies within a tegumental fold, the gynecophoral canal, on the ventral surface of the male. The medically important flukes belong to the taxonomic category Digenea. This group of flukes has a developmental cycle requiring at least two hosts, one being a snail intermediate host. Depending on the species, other intermediate hosts may be involved to perpetuate the larval form that infects the definitive human host. Flukes go through several larval stages, each with a specific name, before reaching adulthood. Taking into account variations among species see Fig. Eggs are passed in the feces, urine, or sputum of humans and reach an aquatic environment. The eggs hatch, releasing ciliated larvae, or miracidia, which either penetrate or are eaten by a snail intermediate host. In rare instances land snails may serve as intermediate hosts. A saclike sporocyst or redia stage develops from a miracidium within the tissues of the snail. The sporocyst gives rise either to rediae or to a daughter sporocyst stage. In turn, from the redia or daughter sporocyst, cercariae develop asexually and migrate out of the snail tissues to the external environment, which is usually aquatic. The cercariae, which may possess a tail for swimming, develop further in one of three ways. They either penetrate the definitive host and transform directly into adults, or penetrate a second intermediate host and develop as encysted metacercariae, or they encyst on a substrate, such as vegetation, and develop there as metacercariae. When a metacercarial cyst is ingested, digestion of the cyst liberates an immature fluke that migrates to a specific organ site and develops into an adult worm. Tapeworms Cestodes As members of the platyhelminths, the cestodes, or tapeworms, possess many basic structural characteristics of flukes, but also show striking differences. Figure shows the general features of the structure and development of tapeworms. Figure Structure of tapeworms. Atlas of Medical Helminthology and Protozoology. Churchill Livingstone, Edinburgh,, with permission. Whereas flukes are flattened and generally leaf-shaped, adult tapeworms are flattened, elongated, and consist of segments called proglottids. Tapeworms vary in length from 2 to 3 mm to 10 m, and may have three to several thousand segments. Anatomically, cestodes are divided into a scolex, or head, which bears the organs of attachment, a neck that is the region of segment proliferation, and a chain of proglottids called the strobila. The strobila elongates as new proglottids form in the neck region. The segments nearest the neck are immature Page 2
sex organs not fully developed and those more posterior are mature. The terminal segments are gravid, with the egg-filled uterus as the most prominent feature. Externally, the scolex is characterized by holdfast organs. Depending on the species, these organs consist of a rostellum, bothria, or acetabula. A rostellum is a retractable, conelike structure that is located on the anterior end of the scolex, and in some species is armed with hooks. Bothria are long, narrow, weakly muscular grooves that are characteristic of the pseudophyllidean tapeworms. Acetabula suckers like those of digenetic trematodes are characteristic of cyclophyllidean tapeworms. Differential features of pseudophyllidean and cyclophyllidean tapeworms are listed in Table Most human tapeworms are cyclophyllideans. Table Differences between Pseudophyllidean and Cyclophyllidean Tapeworms. A characteristic feature of adult tapeworm is the absence of an alimentary canal, which is intriguing since all of these adult worms inhabit the small intestine. The lack of an alimentary tract means that substances enter the tapeworm across the tegument. This structure is well adapted for transport functions, since it is covered with numerous microvilli resembling those lining the lumen of the mammalian intestine. The excretory system is of the flame cell type. Cestodes are hermaphroditic, each proglottid possessing male and female reproductive systems similar to those of digenetic flukes. However, tapeworms differ from flukes in the mechanism of egg deposition. Eggs of pseudophyllidean tapeworms exit through a uterine pore in the center of the ventral surface rather than through a genital atrium, as in flukes. In cyclophyllidean tapeworms, the female system includes a uterus without a uterine pore Fig. Thus, the cyclophyllidean eggs are released only when the tapeworms shed gravid proglottids into the intestine. Some proglottids disintegrate, releasing eggs that are voided in the feces, whereas other proglottids are passed intact. The eggs of pseudophyllidean tapeworms are operculated, but those of cyclophyllidean species are not. Eggs of all tapeworms, however, contain at some stage of development an embryo or oncosphere. The oncosphere of pseudophyllidean tapeworms is ciliated externally and is called a coracidium. The coracidium develops into a procercoid stage in its micro-crustacean first immediate host and then into a plerocercoid larva in its next intermediate host which is a vertebrate. The plerocercoid larva develops into an adult worm in the definitive final host. The oncosphere of cyclophyllidean tapeworms, depending on the species, develops into a cysticercus larva, cysticercoid larva, coenurus larva, or hydatid larva cyst in specific intermediate hosts. These larvae, in turn, become adults in the definitive host. Figure illustrates these larval forms and representative life cycles. Generalized life cycle of tapeworms. Hymenolepsis nana, Hdiminuta, Taenia saginata, T solium, Diphyllobothrium latum, Dipylidium craninum. Cysticercus larva in cow and pig; procercoid larva in copepod, plerocercoid sparganum more Roundworms Nematodes Figure shows the structure of nematodes. In contrast to platyhelminths, nematodes are cylindrical rather than flattened; hence the common name roundworm. The body wall is composed of an outer cuticle that has a noncellular, chemically complex structure, a thin hypodermis, and musculature. The cuticle in some species has longitudinal ridges called alae. The bursa, a flaplike extension of the cuticle on the posterior end of some species of male nematodes, is used to grasp the female during copulation. Figure Structure of nematodes. Transverse sections through the midregion of the female worm C and through the esophageal region D. Modified from Lee DL: The Physiology of Nematodes. Oliver and Boyd, Edinburgh,, with permission. The cellular hypodermis bulges into the body cavity or pseudocoelom to form four longitudinal cordsâ a dorsal, a ventral, and two lateral cordsâ which may be seen on the surface as lateral lines. Nuclei of the hypodermis are located in the region of the cords. The somatic musculature lying beneath the hypodermis is a single layer of smooth muscle cells. When viewed in cross-section, this layer can be seen to be separated into four zones by the hypodermal cords. The musculature is innervated by extensions of muscle cells to nerve trunks running anteriorly and posteriorly from ganglion cells that ring the midportion of the esophagus. The space between the muscle layer and viscera is the pseudocoelom, which lacks a mesothelium lining. This cavity contains fluid and two to six fixed cells celomocytes which are usually associated with the longitudinal cords. The function of these cells is unknown. The alimentary canal of roundworms is complete, with both mouth and anus. The mouth is surrounded by lips bearing sensory papillae bristles. The esophagus, a conspicuous feature of nematodes, is a muscular structure that pumps food into the intestine; it differs in shape in different species. The intestine is a tubular structure composed of a single layer of columnar cells possessing prominent microvilli on their luminal surface. The excretory system of some Page 3
nematodes consists of an excretory gland and a pore located ventrally in the mid-esophageal region. Page 4
Chapter 3 : A guide to human helminths. A guide providing a classification list for all the species of helminths known to be associated with humans. It establishes the valid names for species of human helminth and gives additional information on hosts, distribution and other features in an accessible, tabular format. Advanced Search Abstract Geohelminth infections and allergic disease are major public health problems and there is evidence in developing countries that they are associated. Although there is an extensive literature of the relationship between geohelminth infections and allergy, there is little consensus on whether the association is causal and if so, whether geohelminth infections may increase or decrease the risk of allergy. An explanation for the conflicting findings of epidemiological studies is that geohelminths decrease the risk of allergy in areas of high infection prevalence and increase the risk of allergy in areas of low prevalence. Chronic geohelminth infections are inversely associated with allergy and anthelmintic treatment may increase the prevalence of allergy. In this paper, we review studies that have investigated the relationship between geohelminths and allergy; discuss the relevance of prevalence and timing of geohelminth infections and propose a conceptual model to define relevant scientific questions in future human and animal studies. Introduction Geohelminth also known as intestinal helminth or soil-transmitted helminth infections and allergic disease both cause significant morbidity worldwide. Geohelminths are primarily a health problem of resource-poor developing countries, whereas allergic diseases are recognized as increasingly important in resource-rich developed countries. However, the epidemiology of allergic diseases appears to be changing in developing countriesâ particularly in populations undergoing urbanizationâ where the frequency of allergy may be increasing very fast. Geohelminths Geohelminth infections include Ascaris lumbricoides, Trichuris trichiura and hookworm Ancylostoma duodenale and Necator americanus. These infections have a worldwide distribution being present in almost all geographic and climatic regions, except for those with extremes of cold or heat where survival of infectious stages in the environment is impossible. Prevalences tend to be highest in warm, moist climates and are closely correlated with poor environmental hygiene in particular, a lack of adequate excreta disposal and lack of access to health services. The estimated global prevalences of A. Ascariasis and hookworm undergo a phase of larval migration through the lungs, whereas trichuriasis has a purely enteric life cycle. Infections with ascariasis and trichuriasis peak in prevalence and intensity between 5 and 15 years of age in endemic areas and there is a decline in both epidemiological parameters in adulthood. Epidemiological observations have provided evidence that geohelminth infections and another important helminth infection, schistosomiasis, may affect the risk of the development of allergy. Allergic diseases are an important cause of morbidity in developed countries where they are the commonest cause of chronic disease in childhood. Allergic diseases are caused by a complex interaction between host genetics and environmental factors. Because the prevalence of allergy appears to have increased dramatically over the previous four decades, 13 it is likely that changes in environmental exposures underlie such temporal trends. Important environmental exposures that have been associated with the risk of allergy include high-level exposure to allergens, 14 exposure to pets 15 and farm animals, 14 socio-economic level, 16 nutritional status 14 and life-style factors such as diet 14 and smoking. This hypothesis proposes that reduced exposures to childhood infections increase the risk of allergy. Acute infections include primary infections and repeated or intermittent infections without a period of continuous infection between infection episodes and may result from infrequent or short exposures and affect generally visitors and expatriates in endemic areas. Clinical allergic reactions appear to be rare among individuals with chronic infections i. Consistent with the acute and chronic clinical phenotypes observed in helminth-infected individuals, observations from epidemiological studies that have examined the relationship between helminth infections and allergy have provided evidence for both allergy-enhancing and allergy-suppressant effects of geohelminths in different populations. For example, a nested caseâ control study in a highly endemic area in Ethiopia provided evidence that hookworm infection was inversely associated with symptoms of wheeze, but that trichuriasis was positively associated with allergen skin test reactivity. The latter possibility has significant public health implications that concurrent Page 5
geohelminth infections may affect the development or clinical course of allergic diseases such as asthma. The major part of the evidence for an association between geohelminths and allergy, presented below, has been generated by epidemiological cross-sectional studies that have recognized weakness for the inference of causality i. Geohelminths and allergen skin test reactivity Epidemiological studies have shown an inverse relationship between geohelminth infection and allergen skin test reactivity, 4, 23 with evidence of a doseâ response relationship and reduced risk of atopy for greater geohelminth parasite burdens. Geohelminths and asthma Several studies have investigated the relationship between asthma symptoms and geohelminth infections and results are inconsistent. The prevalence of atopic dermatitis was found to be lower in rural areas when compared with urban areas of Ethiopia, 28 but risk was unrelated to geohelminth infection. Chapter 4 : A Guide to Human Helminths Revista do Instituto de Medicina Tropical de SÃ o Paulo Parasitic helminths occur all over the world, in all continents, in all climatic zones, in animals, and in humans as well. We know helminths living only in and circulating (directly or indirectly. Chapter 5 : A Guide to Human Helminths Guide to human helminths cl Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. If you continue browsing the site, you agree to the use of cookies on this website. Chapter 6 : helminthic therapy for treatment of allergy, asthma and autoimmune disease A Guide to Human Helminths I. COOMBS D.W.T. CROMPTON A Guide to Human Helminths. Revista Do Instituto De Medicina Tropical De SÃ o Paulo, 34(4), https. Chapter 7 : View of A Guide to Human Helminths Adapted from The Guide to Human Helminths. Whipworm can be found all over the world, including Europe and North America, where it is most frequent in rural areas of the southeast. Chapter 8 : - NLM Catalog Result Topics: Medicine (General), R, Medicine, R, DOAJ:Medicine (General), DOAJ:Health Sciences, Arctic medicine. Tropical medicine, RC Chapter 9 : Parasitic worm - Wikipedia Helminth is a general term meaning worm. The helminths are invertebrates characterized by elongated, flat or round bodies. In medically oriented schemes the flatworms or platyhelminths (platy from the Greek root meaning "flat") include flukes and tapeworms. Page 6