Nematoda Revise PDF

General data Nematodes are the first group that had been successful in adapting to terrestrial habitats. Although many species are parasitic on plants and animals, nematodes are extremely abundant...

General data Nematodes are the first group that had been successful in adapting to terrestrial habitats. Although many species are parasitic on plants and animals, nematodes are extremely abundant in soil. Size – from millimeters to mote than a meter. Nematodes were once classified with a very large cluster of animals grouped together on the basis of their overall worm-like appearance, simple structure of the internal organs, and the lack of features such as cilia and a well-defined head. It is quite likely that the simple body plan of nematodes has resulted from reduction and simplification of ancestral organisms. Current studies indicate that nematodes are closer to the arthropods than to other worms. According to the modern classification, nematodes belong to a newly recognized group, Ecdysozoa. The most notable characteristic shared by ecdysozoans is a three-layered cuticle, which is periodically molted as the animal grows. This process nytimes.com of molting is called ecdysis and gives the group its name. Coelom and pseudocoelom Flatworms do not possess coelom (body cavity). Nematodes have body cavity between a single mesodermal layer and the endoderm (the gut). This cavity is called pseudocoelom. Segmented worms have real coelom - cavity bordered by two mesodermal layers. Several decades ago, one of the prevailing theories for the evolution of the bilateral animals was based on the morphology of their body cavities (coelomate hypothesis). According to this hypothesis, the evolutionary line must be flatworms—roundworms—segmented worms. Now we know that’s not true. The new science molecular phylogenetics has proved that the coelomate hypothesis has to be abandoned. Now we know that in the pseudocoelom, one of the mesodermal layers was lost secondarily. www.docstoc.com Animal phylogeny http://biology-forums.com Nematodes are protostome animals, as all other worms, Arthropoda and Mollusca. dream-prophecy.blogspot.com Protostomes - the blastopore becomes the mouth. Deuterostomes - the blastopore becomes the anus.  Body www.uic.edu structure of nematodes Cross section Acellular covering - the cuticle. The pseudocoelom is full of liquid and acts as hydrostatic skeleton. Move by contracting muscles. Two openings of the digestive tract – mouth and anus. There are several lips arranged circularly around the oral opening. Some nematodes have wide stoma with teeth. Excretory system – two lateral ducts that run longitudinally down either side of the body. Nervous system - a dorsal and ventral never cord. No circulatory or respiratory systems. asm.wku.edu Sexual dimorphism- females are larger; males have a "hooked" posterior end and a pair of copulatory spicules. Soil-transmitted helminths The soil-transmitted nematodes are also called geohelminths. They are intestinal parasites transmitted primarily through contaminated soil. Their life cycles are direct - no intermediate hosts. The parasitic infection occurs through fecal contamination of soil, foodstuffs and water supplies. mdpi.com The adult forms are essentially parasites of humans, but also infect domesticated mammals. The larvae undergo tissue-migratory stages during which they invade vital organs. Thus, the symptoms can be both local and systemic. Ascaris That is the largest nematode parasitizing the human intestine; adult females: 20 to 35 cm; adult male: 15 to 30 cm. lumbricoides Geographic distribution: the most common human helminthic infection; worldwide distribution; highest prevalence in tropical and subtropical regions, and areas with inadequate sanitation. Geohelminth (soil transmitted helminth); the eggs mature in soil. Infective stage – the eggs. Eggs in the feces  Ascariasis Diagnosis – by finding eggs in the feces; worms can appear in vomit or stool; worms may leave the body through the nose or mouth. High worm number may cause severe abdominal pain, vomiting, intestinal disfunction, shortness of breath, skin rash, and weight loss. Very massive infections can lead to perforation of the intestine. Migrating worms may cause blockage of the biliary tract, appendicitis, uncommon form of pneumonia, Heavy infections in children may cause stunted growth via malnutrition. Surgical complications of Ascaris lumbricoides infestation: A prospective, observational study at a teaching hospital in Butare, Rwanda. Kazigo et al, 2020 Ascaris – life cycle Adult worms live in the lumen of the small intestine. A female may produce 200,000 eggs per day, which are passed with the feces. Fertile eggs embryonate and become infective after several weeks. The eggs are swallowed, the larvae hatch, invade the intestinal mucosa, and are carried via circulation to the lungs. The larvae mature in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed. Upon reaching the small intestine, they develop into adult worms. Between 2 and 3 months are required from ingestion of the infective eggs to new egg production. Adult worms can live 1 to 2 years. Trichiurus trichiura Trichuris trichiura (or Trichocephalus trichiuris) infects human large intestine. It is commonly known as the whipworm. (whipworm) Narrow anterior esophageal part and shorter and thicker posterior part; threaded through the mucosa; attach to the host through their slender anterior end and feed on tissue secretions. Females are larger than males; approximately 35–50 mm long compared to 30– 45 mm. The females have a bluntly round posterior end compared to their male counterparts with a coiled posterior end. The eggs are barrel-shaped and brown, with bipolar protuberances. Male Female chegg.com ruby.fgcu.edu wikipedia.org Trichiurus trichiura – life cycle Eggs are deposited from human feces to soil. After two to three weeks, they become embryonated and infective. These are ingested and hatch in the human small intestine. This is the location of growth and molting. The infective larvae penetrate the villi and continue to develop in the small intestine. The young worms move to the cecum and penetrate the mucosa. There, they complete development to adult worms. The period from ingestion of eggs to mature worms is three months. The female begins to lay eggs after three months of maturity. Worms can live up to five years. Disease: frequent painful passage of stool that contains a mixture of mucus, water, and blood; rectal prolapse can occur. Heavy infection in children can lead to severe anemia, nature.com growth retardation, and impaired cognitive development.  Strongyloides stercoralis microbenotes.com Strongyloides stercoralis is a tiny nematode that lives in the intestines of humans and a number of other animals. Female worms, only 2.5mm long, move through the lining of the small intestine and produce eggs, which hatch within hours. The larvae pass out into the outside world in the stool, and can survive for some time as free-living nematodes, even reproducing through several generations. Sooner or later, infective parasitic larvae develop, which have only to come in contact with the skin of a potential host to continue their parasitic life cycle. People acquire Strongyloides stercoralis when they come in contact with soil or fecal matter that contains the Disease: Most people infected with Strongyloides do not infective larvae. know they are infected. If they do feel sick the most About half a millimeter long, these larvae can penetrate common symptoms are: abdominal pain, dry cough, bare skin and move through the body quickly, arriving in throat irritation; itchy, red rash that occurs where the the intestine within a couple of days. worm entered the skin All parasitic larvae mature to female worms and Rarely, severe forms of the disease can occur. These forms reproduce without the contribution of a male. (There are of the disease are more common in people who are on males in the free-living soil stages.) corticosteroids or other immunosuppressive therapies.  Strongyloides – life cycle in details Adult free-living female S. stercoralis alongside a smaller rhabditiform larva. Note the developing eggs in the adult female. cdc.gov  It is found in humans, cats and dogs. Ancylostoma duodenale and Necator americanus are the two Ancylostoma human hookworm species that are normally discussed together as the cause of hookworm infection. duodenale Adult males (a) are 8-11 mm long; females arе 10-13 mm. Hookworms attach to capillary beds in the small intestine; they suck blood resulting in anemia. (Old World Hookworms are a major cause of chronic anemia and growth stunting in children in the tropics. hookworm) The standard method for diagnosing the presence of hookworm is by identifying hookworm eggs in a stool sample. Two large teeth fused at their bases. A parasitichookworm pair of small teeth in the depths of the buccal capsule. Ancylostoma – life cycle Eggs are passed in the stool, and under favorable conditions, larvae hatch in 1 to 2 days. The released rhabditiform larvae grow in the feces and/or the soil, and after 5 to 10 days (and two molts) they become filariform (third- stage) larvae that are infective. These larvae can survive 3 to 4 weeks in favorable conditions. The larvae can penetrate the skin and are carried through the blood vessels to the heart and then to the lungs. They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed. The larvae reach the small intestine, where they reside and mature into adults. Adult worms attach to the intestinal wall with resultant blood loss by the host. Most adult worms are eliminated in 1 to 2 years, but the longevity may reach several years. Enterobius It is not typical geohelminth – the eggs mature outside the body – onto the skin around the anus. The eggs are both infective and diagnostic stage. They are transparent and slightly asymmetric. vermicularis Size - adult females: 8 to 13 mm, adult male: 2 to 5 mm. (pinworm) Geographic distribution: worldwide, with infections more frequent in school- or preschool- children and in crowded conditions. Enterobiasis appears to be more common in temperate than tropical countries. It is the most common helminthic infection in the regions with high sanitation. www.dpd.cdc.gov Enterobius vermicularis – life cycle Eggs are deposited on perianal folds. Self-infection occurs by transferring infective eggs to the mouth with hands. Person-to-person transmission can also occur. Enterobiasis may also be acquired through surfaces in the environment that are contaminated with pinworm eggs. Some small number of eggs may become airborne and inhaled. These would be swallowed and follow the same development as ingested eggs. The larvae hatch in the small intestine and the adults establish themselves in the colon. The time from ingestion to new egg production is about one month. Life span - about two months. Gravid females migrate nocturnally outside the anus and oviposit while crawling on the skin of the perianal area. The larvae inside the eggs develop in 4 to 6 hours. Phylum Nematoda Tissue nematodes and filaria Department of Biology, Medical University of Sofia Human nematodes which are not geohelminths Tissue nematodes – they remain within tissues, not in cavities; they neither release eggs nor larvae into the blood, but they are not transmitted via blood sucking insects. EXAMPLES: Trichinella spiralis Dracunculus. Filarian nematodes (filaria) – their larvae are called microfilariae; they are transmitted via blood sucking insects. EXAMPLES: Wuchereria bancrofti Onchocerca volvulus Loa loa.  Trichinella Nematodes of the genus Trichinella cause trichinellosis. T. spiralis is the most important to humans due to its worldwide distribution and spiralis high pathogenicity. Females are nealy 2 mm in length; males 1 mm. Geographic distribution: worldwide. Trichinella spiralis is most common in parts of Europe and the North America. Adult, female Larva between muscle fibers male bioweb.uwlax.edu female Trichinella spiralis – life cycle Trichinellosis is caused by the ingestion of undercooked meat containing encysted larvae. In the stomach, the larvae are released from the cysts and invade the intestinal mucosa where they develop into adult worms. The life span in the small intestine is about four weeks. After 1 week, the females release larvae that migrate to striated muscles where they encyst. Diagnosis is usually made based on clinical symptoms and is confirmed by immunological methods or identification of encysted larvae in biopsy specimens. All stages in one host: Adult worms and encysted larvae develop within a single vertebrate host. Hence, the same animal serves as a definitive host and potential intermediate host. A new host is required to start a new the life cycle. The domestic cycle most often involved pigs and rodents, but other domestic animals such as horses can be involved. In the sylvatic cycle, the range of infected animals is great, but animals most often associated as sources of human infection are bear, moose and wild boar. Herbivores, such as horses, sheep, or goats, can be infected by accidental presence of animal waste in their food. https://youtu.be/6zyaapwWPcs How herbivores can be infected by trichinellosis Trichinellosis One week after the infection, the females release larvae. The life span of adult worms in the small intestine is about four weeks. The first symptoms are gastrointestinal, usually occurring 1–2 days after infection. These symptoms include the following: diarrhea, vomiting, abdominal pain. The classic symptoms occur within 2 weeks after eating contaminated meat and can last up to 8 weeks: muscle pain, fever, swelling of the face, particularly the eyes. Although rare, death can occur in severe cases. For mild infections, most symptoms go away within a few months. Shutterstock.com Diagnosis is based on clinical symptoms and is confirmed by immunological methods or identification of encysted larvae in biopsy specimens. Encapsulated larvae in muscle tissue  Trichinella spiralis is an intracellular parasite as both a Trichinella modifies the gene expression in host cells. larva and an adult. Parasite signals secreted around the nurse cell results in The larva modifies somea skeletal muscle cells turning them reprogramming of host gene expression, reflected in loss of into nurse cells and can reside there for the life span of the muscle-specific proteins, over-expression of collagen, and the host. Adult worms occupy cells in columnar epithelium, development of a circulatory rete. living there as intramulticellular parasites. The newborn As result of signals from parasite to host and from host to larva is the only extracellular stage, living free in the parasite, the host develops long-lasting immunity to circulation. reinfection. This may confer advantages both for the parasite, as well as the host, because strong immune responses should reduce competition with other parasitic worms. Nurse cells in muscle biopsy (A) Cellular infiltrates; (B) collagen capsule of the nurse cell; (C) intersected larva. Epidemiology, Diagnosis, Treatment, and Control of Trichinellosis. Gottstein et al, 2009.trichinella.org Dracunculus Causes dracunculiasis (guinea worm disease). Geographic distribution: now restricted to rural, isolated areas in a narrow belt of African countries. medinensis Humans are the principal definitive host, dogs, cats and other animals can be definitive hosts. (guinea worm) The small crustacean copepod Cyclops is the intermediate host. The females to 80 cm long; in contrast, the longest recorded male Guinea worm is only 4 cm. There is no vaccine or medicine for the disease, however community-based interventions, such as teaching people to filter drinking water, have led to significant reductions in recent years wikipedia.org Dracunculus medinensis larvae. Dracunculus – life cycle Humans become infected by drinking unfiltered water containing copepods which are infected with larvae. Alternatively, people and animals might be infected by eating aquatic that have swallowed infected copepods and might carry Guinea worm larvae. The larvae penetrate the host stomach and intestinal wall and enter the abdominal cavity. After maturation into adults and copulation, the male worms die and the females (length: 70 to 120 cm) migrate in the subcutaneous tissues towards the skin surface. Approximately one year after infection, the female worm induces a blister on the skin. Most often, the blister is on the foot, but other locations are possible. The blister eventually ruptures. Contact with water relaxes the pain. When this lesion comes into contact with water, the female worm emerges and releases larvae. If they are ingested by a copepod, after two weeks (and two molts) they develop into infective larvae. Carter Center  The female induces a painful blister. After rupture of the blister, the worm emerges as a whitish filament in the center of a painful ulcer. (The, Atlanta, Georgia). plpnemweb.ucdavis.edu Guinea worm disease is not usually fatal, but people suffering from it become “non-functional” for weeks and months. In addition to the pain of the blister, removing the worm is also very painful. Furthermore, without proper care the wound often becomes infected by bacteria. A guinea worm extraction procedure on a child in Ghana. Mary Glenshaw/CDC VIDEO https://youtu.be/oCB1A2gFvuU  W. bancrofti causes lymphatic filariasis, called elephantiasis. Lymphatic filariasis impairs the lymphatic Wuchereria system and can lead to the abnormal enlargement of body parts, causing pain, severe disability and bancrofti social stigma. It is more common in tropical regions. It is almost absent in Europe and North. (thread-like The parasite is carried from person to person by mosquitoes in tropical and subtropical regions. worm) The infection is usually asymptomatic. Some people can develop lymphedema, swelling in the legs, but sometimes also in the arms, genitalia and breasts. Diagnosis - by larvae in blood sample. Getty Images Wuchereria – life cycle Mosquitoes are intermediate hosts. During a blood meal, an infected mosquito introduces third- stage filarial larvae onto the skin of the human (definitive host), where they penetrate into the bite wound. They develop in adults that commonly reside in the lymphatics. The female worms are 8-10 cm, the males are about 4 cm. Adults produce microfilariae. They migrate into lymph and blood channels moving actively. During the day time, these larvae live in the large deep- seated blood vessels but during night they migrate to the peripheral blood vessels (to be available for mosquitoes). Female mosquitoes ingest microfilariae during a blood meal. There the microfilariae develop into first-stage larvae and subsequently into third-stage infective larvae. The parasite does not multiply within its intermediate host, the mosquito. Wuchereria – The microfilaria is about 0.2 мм in length. At the surface there are protective cover and flattened epidermal cells. microfilaria Between the organs, there are columns of cytoplasm with multiple nuclei. healthjade.net  Loa loa is a thread-like worm that lives under the skin in the subcutaneous Loa loa fat causing loiasis. Because it is often spotted migrating in the eye (under the conjunctiva), it is known as the eye worm. Adult Loa loa male is about 34 mm long; the female is 40–70 mm long. Loa loa migrates in the subcutaneous layer. When it stops moving, the surrounding tissue develops Calabar swelling (a localized angioedema and erythema usually on the extremities). This often occurs in joints, which are its usual stopping points. Diagnosis is made by analyzing blood under a microscope to find the microfilariae. wikimedia.org Loa – microfilaria in blood www.proprofs.com Loa loa – life cycle The female gives birth to living microfilariae inside the skin. The microfilariae travel in peripheral blood during daytime, but during the night they reside in the lungs. When a noninfected deer fly takes a blood meal from an infected human, it ingests microfilariae. The microfilariae lose their sheaths and develop into first stage and eventually into third stage (infective) filarial larvae in two weeks. They invade another human during the next blood meal. The third stage larvae are transferred from the fly's mouth to the skin. They burrow into the bite wound and enter the subcutaneous layer where they mature into adults in one year. Loa loa adults live up to 17 years. Loa loa migrates in the subcutaneous layer. Calabar swellings, named for the Nigerian town where they were first recorded, may be several inches in diameter. They form as a result of immune reaction to the metabolic products of the worms or to dead worms. These swellings can occur anywhere, but are more frequently seen on the limbs, especially the forearms. sciencedirect.com Chrysops (deer fly) missoulabutterflyhouse.org Onchocerca volvulus The disease is called river blindness because the black fly lives and breeds near fast- flowing streams and rivers and the infection can result in blindness. www.icp.ucl.ac.be Distribution - in both the Old and New World, but about 95% of all cases are in Africa. In addition to visual impairment, onchocerciasis causes skin disease, including nodules under the skin or debilitating itching. The parasite is transmitted by blackflies, genus Simulium. wikipedia.org During a blood meal, an infected blackfly introduces third-stage filarial larvae onto the skin, where they penetrate into the bite wound. In subcutaneous tissues the larvae develop into adult filariae, which commonly reside in nodules in subcutaneous connective tissues. Adults can live in the nodules for 15 years. Some nodules may contain numerous male and female worms. Females are 3-5 cm long, males are 2-4 cm. In the nodules, the females are capable of producing microfilariae for approximately 9 years. The microfilariae (220-360 µm) have a life span that may reach 2 years. They are occasionally found in peripheral blood, urine, and sputum but are typically found in the skin and in the lymphatics of connective tissues. A blackfly ingests the microfilariae during a blood meal. The microfilariae develop into first-stage larvae and subsequently into third-stage infective larvae. They can infect another human when the fly takes a blood meal.  parasite.org.au Onchocerca – cross sections of adults in nodule section. Microfilariae are visible in adult pasties. The Nobel prize for medicine in 2015 was given for the discovery of a combination of substances for treatment and prevention of river blindness. Their research led to the creation of Ivermectin. Human infections with non typical nematodes Sometimes, humans are infected by nematodes typical for animals integrated in human society – pets or pests. EXAMPLES  Subcutaneous migration of the animal hookworms (genus Ancylostoma) could lead to cutaneous larva migrans (CLM) in man.  Toxocara is found in dogs and cats. In humans, Toxocara be seen the liver, lungs or eyes. They can cause serious problems like difficulty breathing or loss of vision.  Dirofilaria (dog heartworm), is a filarial worm transmitted by mosquitoes. In humans it is found in the lungs and under the skin  Gnathostoma species have a prominent cephalic bulb and body spines. They use associated with carnivorous mammal as definitive hosts. Gnathostomiasis is a food-borne zoonosis of public health significance.  Angiostrongylus (the rat lungworm) in humans can cause meningitis and other neurolrgical symptoms. It is endemic in south Asia, Pacific islands, Australia, China and Caribbean islands. Most cases are in Hawaii. How the nematodes behave in non-typical hosts When the nematodes infect occasional non-typical hosts, their larvae are unable to mature to adult worms, but can provoke diseases. The larvae migrate to various tissues (skin, lungs, liver, brain) causing mechanical injuries and inflammation. That process is known as LARVA MIGRANS. In most cases, the cutaneous migrating larvae are immature forms of non-human species that belong to genus Ancylostoma (cat or dog hookworms). Cutaneous larva migrans Eosinophil s attack nematode larva.  Most frequently, humans are infected by Genus Toxocara (T. canis, T. cati) ingesting toxocara eggs. When the eggs hatch, larvae penetrate the intestinal wall, and move by the circulation to a variety of tissues (liver, heart, lungs, brain, muscle, eyes). In rare cases, humans are infected by eating undercooked meat of birds and mammals that contain larvae. After migration in human tissues, the larvae do not undergo any further development. They can cause local reactions and mechanical damage. Sometimes, migration to the central nervous system (neural larva migrans) can cause eosinophilic meningoencephalitis. According to different studies, between 30% and 100% of dogs younger than 6 months ate infected with toxocara. For cats the degree of toxocara infection is 25%. The infection in dogs and cats can be transmitted also via placenta and mother milk. Genus Dirofilaria That genus includes filarial nematodes, which are usually associated with carnivore hosts. They are transmitted by mosquitoes. Human dirofilariasis is generally divided into pulmonary dirofilariasis (D. immitis) and subcutaneous dirofilariasis (D. repens, D. tenuis, and others). DO NOT LEARN THE SPECIES NAMES.  Concurrent subcutaneous and ocular infections with Dirofilaria repens in a Polish patient: a case report in the light of epidemiological data. Szostakowska et al, 2022 Dog heart. Subcutaneous and ocular infections with Dirofilaria immitis is commonly called Dirofilaria. the "heartworm"; however, adults often reside in lung arteries damaging the lung vessels and tissues. Extraintestinal hookworm in humans Some hookworms typical for cats and dogs (Ancylostoma caninum, A. braziliense, Uncinaria stenocephala) can infect humans. After penetration of human skin, the larvae do not reach the intestines but stay under the skin. The situation is known as CUTANEOUS LARVA MIGRANS. The sand on the beach is a very probable source of that infection. Ancylostoma caninum. CDC Gnathostoma Most human infections are caused by G. spinigerum. In animal definitive hosts, adult worms reside in tumor- like structures in the gastric wall. Humans become infected by eating raw or undercooked meat of second intermediate or paratenic hosts (in which development does not occur) containing larvae. These larvae migrate in various tissues and may develop into immature adults but never achieve reproductive maturity; they may range in size from 2 mm to about 2 cm depending on the species and the extent of development image. Whether humans can become infected by drinking water that contains infected copepods is not clear.  The intermediate hosts of Angiostrongylus are land slugs, land snails and freshwater snails. Angiostrongylus Natural definitive hosts are domestic dogs, rats and various other carnivores. In rats and dogs, adult worms inhabit pulmonary arteries. In human, larvae do not mature and usually are found in the brain. Angiostrongylus vasorum Angiostrongylus vasorum Bayer animal Health® wormsandgermsblog.com