Roundworms and Segmented Worms - Veterinary Medicine PDF

Study programme: VETERINARY MEDICINE 1 Year, 2d Semester VF/AF/VM-U31 LIFE SCIENCES II ZOOLOGY AND LABORATORY ANIMALS Phylum. Roundworms (Nematoda) Phylum. Segmented worms (Annelida)  Phylum. Roundworms (Nematoda)...

Study programme: VETERINARY MEDICINE 1 Year, 2d Semester VF/AF/VM-U31 LIFE SCIENCES II ZOOLOGY AND LABORATORY ANIMALS Phylum. Roundworms (Nematoda) Phylum. Segmented worms (Annelida)  Phylum. Roundworms (Nematoda) Six intestinal nematodes commonly infect humans: Enterobius vermicularis (pinworm), Trichuris trichiura (whipworm), Ascaris lumbricoides (large roundworm), Necator americanus and Ancylostoma duodenale (hookworms), and Strongyloides stercoralis. Together, they infect more than 25% of all humans, producing embarrassment, discomfort, malnutrition, anemia, and occasionally death. 2 http://www.ulac.lt/ligos/A/askaridoze  Body Plans All intestinal nematodes have cylindrical, tapered bodies covered with a tough, acellular cuticle. Sandwiched between this integument and the body cavity are layers of muscle, longitudinal nerve trunks, and an excretory system. A tubular alimentary tract consisting of a mouth, esophagus, midgut, and anus runs from the anterior to the posterior extremity. Highly developed reproductive organs fill the remainder of the body cavity. The sexes are separate; the male worm is generally smaller than its male. 3  Body Cavities The nematodes are triploblastic. They show bilateral symmetry. Their body is unsegmented. They are pseudocoelomate. The body cavity is called pseudocoel. It is derived from the hollow space, the blastocoel. Blastocoel is formed in blastula stage during embryological development. So their coelom is not formed form mesoderm. Pseudocoel has a large number of vacuolated cells (cells with vacuoles). These cells are filled with a protein — rich fluid. This fluid produces high hydrostatic pressure (pressure due to fluid). 4  Phylum. Roundworms (Nematoda) They have different sizes. Nematoda may be microscopic or some nematodes having up to one meter length. They have tube like digestive system. It is in the form an alimentary canal with two openings. Mouth is present at anterior end and anus is present at the posterior end. A fluid filled space is present between the body wall and the alimentary canal. So it forms tube within tube” type structure in nematods. The digestive system of parasitic forms is simple. The excretory system consists of excretory canal. These canals run longitudinally and unite at the anterior end to form a single canal. This canal open outside through an excretory pore on the ventral surface. 5 https://thesoilhuggersjourney.wordpress.com/2014/09/15/soil-life-series-pick-a-phylum-nematodes/ 6  Phylum. Roundworms (Nematoda) There is a nerve ring around the pharynx. It gives rise to dorsal, ventral and lateral nerve cords. These nerves run throughout the length of the body of worm. Their sense organs are in the form of sensory papilla. It is present on the lips at the anterior end. Locomotion takes place by muscles. These muscles contract and relax and produce undulating waves. These muscles are arranged in four bands. Two are dorso-lateral and two are ventro-lateral. The circular muscles are absent. So, they can bend only dorso-ventrally. Reproduction: The sexes are separate. The female gonads are ovaries and these produce eggs. The male gonads are testes and these produce sperms. A larval stage is present during their life cycle. 7  SPECIES. ASCARIS (ASCARIS LUMBRICOIDES) Ascariasis is a disease caused by the parasitic roundworm Ascaris lumbricoides. Ascaris lumbricoides, a short-lived worm (6-18 months), is the largest and most common of the intestinal helminths. Measuring 15 to 45 cm in length, it dwarfs its fellow gut roundworms and brings an unexpected richness to our mental image of a parasite. Its firm, creamy cuticle and more pointed extremities differentiate it from the common earthworm, which it otherwise resembles in both size and external morphology. The male is slightly smaller than the female and possesses a curved tail with copulatory spicules. The female passes 200 000 eggs daily, whether or not she is fertilized. Eggs are elliptical, measure 35 by 55 μm, and have a rough, mammillated, albuminous coat over their chitinous shells. These eggs are highly resistant to environmental conditions and may remain viable for up to 6 years in mild climates. 8 Ascaris lumbricoides. A. Structure of fertile and infertile egg. B. Fertilized egg in stool. C. Adult female worm. (B, Reproduced with permission from Connor DH, Chandler FW, Schwartz DQ, et al: Pathology of Infectious Diseases. Stamford, CT: Appleton & Lange, 1997.) Citation: Intestinal Nematodes, Ryan KJ. Sherris Medical Microbiology, 7e; 2017. Available at: https://accessmedicine.mhmedical.com/content.aspx?sectionid=176089727&bookid=2268&jumpsectionid=176089805&Resultclick=2 Acces sed: February 17, 2020 Copyright © 2020 McGraw-Hill Education. All rights reserved 9 ANTERIOR END OF ASCARIS 10  Species. Ascaris (Ascaris lumbricoides) 11 http://tacbio.weebly.com/giant-roundworm-humans.html  Species. Ascaris (Ascaris lumbricoides) 12 https://www.biologydiscussion.com/zoology/practicals/structure-of-ascaris-with-diagram-zoology/60589  ASCARIS FEMALE Female worm is longer and stouter than males measuring 25-49 cms in length and 5mm in diameter. The tail (posterior end ) is straight and blunt. The female genital aperture , or vulva is located mid ventrally at about 1/3 the length from mouth. The anus is present a little in front of the tail end. Egg laying capacity of Ascaris is very high. It lays about 2,00,000 per day. 13 13 ASCARIS FEMALE - ANATOMY 14  15 http://teaslaboratoriuligamocda.blogspot.com/2012_01_01_archive.html  MALE The male worm measure 12-23 cms in length and 3-4 mm in diameter. The tail (posterior end) is curved ventrally in the form of a hook , with a conical tip. On the ventral side of the tail region occurs a single aperture , the cloacal aperture, through which , the male and female reproductive systems open to the side. Cloacal aperture also contains a pair of copulatory spicules which are equal in length. 16 Ascaris lumbricoides life cycle. [Redrawn from Centers for Disease Control and Prevention (CDC).] Citation: Intestinal Nematodes, Ryan KJ. Sherris Medical Microbiology, 7e; 2017. Available at: https://accessmedicine.mhmedical.com/content.aspx?sectionid=176089727&bookid=2268&jumpsectionid=176089805&Resultclick=2 Acces sed: February 17, 2020 Copyright © 2020 McGraw-Hill Education. All rights reserved 17  LIFE CYCLE The adult ascarids live high in the small intestine, where they actively maintain their position not by burrowing into the mucosa, but rather by sheer strength of muscular activity, swimming against the stream of stool to avoid being expelled. The eggs are deposited into the intestinal lumen and passed in the feces. The eggs must embryonate in soil, usually for a minimum of 3 weeks, before becoming infectious. The eggs of Ascaris must be ingested, ends after ingestion. Once they hatch in the intestines, Ascaris larvae penetrate the intestinal mucosa and invade the portal venules. They are carried to the liver, where they are still small enough to squeeze through that organ’s capillaries and exit in the hepatic vein. They are then carried to the right side of the heart and subsequently pumped out to the lung. In the course of this migration, the larvae increase in size. By the time they reach the pulmonary capillaries, they are too large to pass through to the left side of the heart. Finding their route blocked, they rupture into the alveolar spaces, are coughed up, and subsequently swallowed. After regaining access to the upper intestine, they complete their maturation and mate. Their reasons for making this circuitous journey are unknown, although the high oxygen tension in the alveoli may provide a growth advantage. Ascaris lumbricoides life cycle. [Redrawn from Centers for Disease Control and Prevention (CDC).] Citation: Intestinal Nematodes, Ryan KJ. Sherris Medical Microbiology, 7e; 2017. Available at: https://accessmedicine.mhmedical.com/content.aspx?sectionid=176089727&bookid=2268&jumpsectionid=176089805&Resultclick=2 Acces sed: February 17, 2020 Copyright © 2020 McGraw-Hill Education. All rights reserved 18  SPECIES. PINWORM (ENTEROBIUS VERMICULARIS ) Pinworm infection, also known as enterobiasis, is a human parasitic disease caused by the pinworm. The adult female pinworm is 10 mm long, cream colored, with a sharply pointed tail; such characteristics have given rise to the common name pinworm, or threadworm. Running longitudinally down both sides of the body are small ridges that widen anteriorly to fin-like alae. The male is smaller (3 mm) and possesses a ventrally curved tail and copulatory spicule. The clear, thin-shelled, ovoid eggs are flattened on one side and measure 25 by 50 μm. 19  LIFE CYCLE Enterobius has the simplest life cycle of the intestinal nematodes. The adult worms lie attached to the mucosa of the cecum, where the male inseminates the female. As her period of gravidity draws to a close, the female migrates down the colon, slips unobserved through the anal canal in the dark of the night, and deposits as many as 20 000 sticky eggs on the host’s perianal skin, bedclothes, and linens. The eggs are near maturity at the time of deposition and become infectious shortly thereafter. Handling of bedclothes or scratching of the perianal area to relieve the associated itching results in adhesion of the eggs to the fingers and fingernails; subsequently the eggs are ingested during eating or thumb sucking. Alternatively, the eggs may be shaken into the air (eg, during making of the bed), inhaled, and swallowed. The eggs subsequently hatch in the upper intestine, and the larvae migrate to the cecum, maturing to adults and mating in the process. The entire adult-to-adult cycle is completed in 2 weeks. Enterobius vermicularis life cycle. [Redrawn from Centers for Disease Control and Prevention (CDC).] Citation: Intestinal Nematodes, Ryan KJ. Sherris Medical Microbiology, 7e; 2017. Available at: https://accessmedicine.mhmedical.com/content.aspx?sectionid=176089727&bookid=2268&jumpsectionid=176089745&Resultclick=2 Acces sed: February 17, 2020 Copyright © 2020 McGraw-Hill Education. All rights reserved 20 Enterobius vermicularis. A. Egg structure. B. Structure of adult female pinworm. C. Embryonated egg recovered from stool. (C, Reproduced with permission from Connor DH, Chandler FW, Schwartz DQ, et al: Pathology of Infectious Diseases. Stamford, CT: Appleton & Lange, 1997.) Citation: Intestinal Nematodes, Ryan KJ. Sherris Medical Microbiology, 7e; 2017. Available at: https://accessmedicine.mhmedical.com/content.aspx?sectionid=176089727&bookid=2268&jumpsectionid=176089745&Resultclick=2 Acces sed: February 17, 2020 Copyright © 2020 McGraw-Hill Education. All rights reserved 21 Enterobius vermicularis life cycle. [Redrawn from Centers for Disease Control and Prevention (CDC).] Citation: Intestinal Nematodes, Ryan KJ. Sherris Medical Microbiology, 7e; 2017. Available at: https://accessmedicine.mhmedical.com/content.aspx?sectionid=176089727&bookid=2268&jumpsectionid=176089745&Resultclick=2 Acces sed: February 17, 2020 Copyright © 2020 McGraw-Hill Education. All rights reserved 22 Species. Trichina (Trichinella spiralis) Trichinosis (or trichinellosis) is caused worldwide by Trichinella spiralis and related Trichinella species. The disease is spread by ingestion of undercooked meat, most commonly pork in areas where pigs feed on garbage. When infected raw meat is ingested, Trichinella larvae are freed from cyst walls by gastric acid and pass into the small intestine. The larvae then invade intestinal epithelial cells, develop into adults, and the adults release infective larvae. Females are 2.2 mm in length; males 1.2 mm. The life span in the small bowel is about 4 weeks. After 1 week, the females release larvae image that migrate to striated muscles where they encyst image. These parasites travel to skeletal muscle via the bloodstream. They invade muscle cells, enlarge, and form cysts. These larvae may be viable for years. Pigs and other animals become infected by eating infected uncooked food scraps or other animals, such as rats. 23  Trichinella spiralis. Life cycle. Top: Blue arrow on left shows ingestion of meat (muscle) containing encysted Trichinella larva. Adult worms form in intestine and produce larvae that enter bloodstream and encyst in human muscle. Bottom: Red circular arrow describes the natural cycle in which Trichinella circulates between pigs and various carnivores such as bears. (Source: Public Health Image Library, Centers for Disease Control and Prevention.) Citation: Nematodes, Levinson W, Chin-Hong P, Joyce EA, Nussbaum J, Schwartz B. Review of Medical Microbiology & Immunology: A Guide to Clinical Infectious Diseases, 15e; 2018. Available at: https://accessmedicine.mhmedical.com/content.aspx?sectionid=187695301&bookid=2381&jumpsectionid=208186166&Resultclick=2 Accessed: February 17, 2020 Copyright © 2020 McGraw-Hill Education. All rights reserved 24 Trichinella larva in tongue muscle of a rat 25  Phylum. Segmented worms (Annelida) earthworm Body metamerically segmented; symmetry bilateral Body wall with outer circular and inner longitudinal muscle layers; outer transparent moist cuticle secreted by epithelium Chitinous setae, setae absent in leeches Coelom well developed and divided by septa, except leeches; coelomic fluid supplies turgidity and functions as hydrostatic skeleton 26 INTERNAL STRUCTURE OF AN EARTHWORM 27 INTERNAL STRUCTURE OF AN EARTHWORM Blood system closed and segmentally arranged; respiratory pigments (hemoglobin, hemerythrin or chlorocruorin) often present; amebocytes in blood plasma. Digestive system complete and not metamerically arranged. Respiratory gas exchange through skin 28  INTERNAL STRUCTURE OF AN EARTHWORM 29 https://en.wikipedia.org/wiki/Earthworm Circulatory system Earthworms have a dual circulatory system in which both the coelomic fluid and a closed circulatory system carry the food, waste, and respiratory gases. The closed circulatory system has five main blood vessels: the dorsal (top) vessel, which runs above the digestive tract; the ventral (bottom) vessel, which runs below the digestive tract; the subneural vessel, which runs below the ventral nerve cord; and two lateroneural vessels on either side of the nerve cord. 30  Excretory system Excretory system typically a pair of nephridia (or metanephridia) for each metamere 31  Nervous system Nervous system with double ventral nerve cords and a pair of ganglia with lateral nerves in each metamere; brain a pair of dorsal cerebral ganglia with connectives to cord Sensory system of tactile organs, taste buds, statocysts (in some), photoreceptor cell and eyes with lense (in some) 32 Earthworms are hermaphrodites where each earthworm contains both male and female sex organs. The male and female sex organs can produce sperm and egg respectively in each earthworm. Although earthworms are hermaphrodites, most need a mate to reproduce. During mating, two worms line up inverted from each other so sperm can be exchanged. The earthworms each have two male openings and two sperm receptacles, which take in the sperm from another mate. The earthworms have a pair of ovaries that produce eggs. The clitellum will form a slime tube around it, which will fill with an albuminous fluid. The earthworm will move forward out of the slime tube. As the earthworm passes through the slime tube, the tube will pass over the female pore picking up eggs. The tube will continue to move down the earthworm and pass over the male pore called the spermatheca which has the stored sperm called the spermatozoa. The eggs will fertilize and the slime tube will close off as the worm moves completely out of the tube. The slime tube will form an “egg cocoon” and be put into the soil. The fertilized eggs will develop and become young worms. Pamatyti viso dydžio vaizdą 33  Reproduction Pamatyti viso dydžio vaizdą Hermaphroditic; larvae, if present are trochophore type; asexual reproduction by budding in some; spiral cleavage and mosaic development 34  Phylum. Roundworms (Nematoda) Phylum. Segmented worms (Annelida) External structure Digestive system Circulation system Respiratory system Nervous system Excretion system Reproductive system Life cycle 35 Review questions: 1. Describe the phylum of Roundworms (Nematoda). 2. What are the differences between male and female Ascaris (Ascaris lumbricoides)? 3. Describe the structure and the life cycle of Ascaris (Ascaris lumbricoides)? 4. Describe the structure and the life cycle of Pinworms (Enterobius vermicularis) 5. Describe the structure and the life cycle of Trichina worm (Trichinella spiralis). 6. Describe the phylum of Segmented worms (Annelida). 7. Describe the structure and the life cycle of Earthworms. 36