Parasitic Nematodes Exercise 7 PDF

Parasitic Nematodes Exercise 7 Zool 115 Department of Biological Sciences Objectives At the end of this lesson, students must be able to: 1. Describe the general morphology of Phylum Nematoda, 2. Classify and differentiate the characteristic features of roundworms, and 3. Identify rep...

Parasitic Nematodes Exercise 7 Zool 115 Department of Biological Sciences Objectives At the end of this lesson, students must be able to: 1. Describe the general morphology of Phylum Nematoda, 2. Classify and differentiate the characteristic features of roundworms, and 3. Identify representative species of roundworms and define their structures. Phylum Nematoda Phylum Nematoda Phylum Nematoda Characteristics: More developed than Platyhelminthes Possess a definite body cavity (pseudocoelomate) Alimentary canal is complete Dioecious The head may have a buccal capsule with teeth or cutting plates Either oviparous or larviparous Phylum Nematoda Phylum Nematoda Characteristics: “nema” meaning “thread” most nematodes are free-living forms, found in soil and water There are an estimated 500,000 species of nematodes. Phylum Nematoda Adult Worm: Shape: elongated, cylindrical, unsegmented worms with tapering ends; unsegmented without any appendages Size: 5mm (hookworm) – 1 meter (Dracunculus); Male is generally smaller than female and its posterior end is curved or coiled ventrally. Phylum Nematoda Adult Worm: Symmetry: Body is bilaterally symmetrical (one plane) while head is radially symmetrical (multiple plane) Body wall: tough acellular cuticle (outer layer) longitudinal muscles (inner layer) Locomotion: move by contraction of the longitudinal muscles Phylum Nematoda Phylum Nematoda Male reproductive system : consists of a long-convoluted tube that can be differentiated into testes, vas deferens, seminal vesicle, and ejaculatory duct accessory copulatory organs: copulatory bursa with two spicules gubernaculum - an elevation of cloaca that guides the spicule during copulation Phylum Nematoda Female reproductive system : Consists of two (common) or one convoluted tube. Each tube is differentiated into an ovary, oviduct, seminal receptacle, and uterus Phylum Nematoda Nervous system : consists of circular nerve ring (brain) Six longitudinal nerve trunks (one dorsal, one ventral, and four lateral). Some species possess sensory structures like sensory papilla and phasmid (chemoreception organs) over the cuticle Phylum Nematoda Excretory system : It is also rudimentary. Various ways of waste disposal are: ‒ Through anus ‒ Excretion of nitrogenous waste in the form of ammonia through the body wall ‒ In some species, an H-shaped canal along each side of the body regulates nutrients and waste content ‒ In a few other species, an excretory gland is situated near the esophagus. Phylum Nematoda Characteristics Class Adenophora Class Secernentea Sensory pouches Absent Present (phasmids) Esophagus Modified with the presence of: Normal appearance Gland cells (stichocytes) or Reserve organ (trophosome) Excretory organs Without lateral canals With lateral canals Caudal papillae Absent Present Infective form to the First stage larva (Trichinella) or Third stage larva or definitive host embryonated eggs (Trichuris) embryonated eggs Phylum Nematoda Phylum Nematoda Classification based on whether they lay egg or larva: 1. Oviparous – following fertilization the female worms produce eggs that take some time to hatch out to form larvae in the environment. Hookworm, Ascaris spp., Trichuris spp., Enterobius spp. 2. Viviparous - Female worms directly give birth to larvae; there is no egg stage. Filarial worm, Trichinella spp., Dracunculus spp. 3. Ovoviviparous - Female worms lay eggs containing larvae that immediately hatch out. Strongyloides spp. Phylum Nematoda Developmental Stages: Modes of infection: 1. Adult worm By ingestion of: 2. Egg stage Eggs 3. Four larval stage (L1 – L4) Larvae within intermediate host 4. Molting – shedding of the cuticle Encysted larvae in muscle By penetration of skin By blood-sucking insects By inhalation of dust containing eggs Phylum Nematoda Class Adenophorea/ Enoplea Trichinella spiralis Cause Trichinellosis/ Trichinosis First detected by James Paget and Richard Owen (1835) from a cadaver muscle Prevalent in pork-eating countries like Europe, South America, and North America including the USA. Pig – optimum host and principal reservoir Man – accidental host Infective form – First stage (L1) larvae Pathogenesis Laboratory Diagnosis Direct slide technique and H and E stain Serology (antibody detection)— ELISA, CIEP Bachman intradermal test - Intradermal injection of Bachman antigen (prepared from Trichinella larva obtained from rabbit muscle) Animal inoculation in rats Trichinella cysts within human muscle tissue (hematoxylin and eosin stain) Class Adenophorea/ Enoplea Trichuris trichiura Also called Whipworm First described by Linnaeus in 1771 Resides in the large intestine of man (cecum and appendix) Worldwide in distribution mainly in warm and moist climate Children are commonly affected Pathogenesis In people with heavy infections: Adult female worm gets buried in the large intestinal mucosa that leads to: Mechanical distortion Allergic response by the host: Increased numbers of macrophages infiltrates the lamina propria that produce tumor necrosis factor Common manifestations include: Abdominal pain, anorexia, etc. Trichuris dysentery syndrome bloody or mucoid diarrhea resembling inflammatory bowel disease Iron deficiency anemia due to blood loss Recurrent rectal prolapse (due to heavy worm load in the rectum and malnutrition) Growth retardation and impaired cognitive function Class Adenophorea/ Enoplea Laboratory Diagnosis Stool examination — detects barrel- shaped eggs with mucus plugs at the ends level of egg output is high (approximately 200 eggs/g of feces per worm pair), microscopic examination of a single fecal smear is sufficient for diagnosis of symptomatic cases Whip-shaped adult worms of 3–5 cm long, are occasionally seen on proctoscopy Class Secernentea/ Chromadorea Enterobius vermicularis Pinworm or Threadworm First described by Leuckart in 1865 Remains attached to the large intestine by their mouth end Around 209 million people are infected Factors promoting infection:  Overcrowding and impaired hygiene Poor personal care (nail biting and inadequate hand washing) Humans – only host Infective form – embryonated eggs Pathogenesis Asymptomatic Symptomatic patients: Female, children, young adult Cardinal symptoms – perianal pruritus often worse at night due to the nocturnal migration of the female worm Excoriation of the perianal skin Abdominal pain and weight loss Laboratory Diagnosis Cellophane Tape Method Eggs – detected by the application of clear cellulose acetate tape to the perianal region (morning) NIH Swab Method devised in the National Institute of Health consists of a glass rod attached to a cellophane tape by a rubber band cellophane part of the glass rod is rolled over the perineal and perianal skin area to collect the sample Class Secernentea / Chromadorea Ascaris lumbricoides Largest nematode parasitizing the human intestine Askaris – intestinal worm; Lumbricus – resembling with common earthworm Commonly known as Roundworm Cosmopolitan in distribution Clay soils – most favorable development of Ascaris egg Children – the most important disseminator of the disease Class Secernentea / Chromadorea Ascaris lumbricoides Adult worms: Female – 20-35 cm; longer than males; Posterior end is straight and pointed; Vulva is situated at the junction of anterior and middle third of the body (this portion is narrower) – vulvar waist Male – 15-31cm; Posterior end is curved and pointed with two spicules Life span – 1-2 years Class Secernentea / Chromadorea Ascaris lumbricoides Larva: Four stages – L1 to L4 Eggs (2 types of eggs liberated): Fertilized Egg o Decorticated egg – fertilized egg may lose the thick mamillated albuminous coat Unfertilized Egg Life Cycle of Ascaris lumbricoides Migratory Phase: Eggs hatch to liberate L2 larvae in the duodenum L2 larvae molt once (L3) and penetrate the intestine reach the right side of the heart via portal circulation and finally enter the lungs via pulmonary capillaries L3 larvae mature and molt to form L4 –break up into the alveoli, migrate via bronchi, trachea, and pharynx, and finally swallowed to reach the intestine Intestinal Phase: L4 larvae undergo final molt and develop into adults in the small intestine Adults become sexually mature, fertilize and female worms start laying eggs – over 200,000 eggs per day Development in soil: Rhabditiform larvae (L1) – produced inside the eggs then molt to produce L2 larvae Embryonated eggs – survive for as long as 15 years (highly resistant) Pathogenesis Treatment Affect due to migrating Albendazole, Mebendazole larva Alternate drugs – ivermectin Pulmonary symptoms and nitazoxanide Eosinophilic pneumonia (Loeffler’s syndrome) In pregnancy, pyrantel pamoate is safe Affect due to adult worm Asymptomatic Malnutrition and growth retardation Intestinal complications Extraintestinal complications Allergic manifestation Laboratory Diagnosis Detection of the parasite: Egg detection(stool examination) – fertilized and unfertilized eggs Adult worm detection—X-ray (Trolley car lines), USG and Barium meal of GIT Larva detection (sputum/gastric aspirate) Serology (antibody detection) — ELISA, IFA, IHA test Other findings such as eosinophilia and Charcot Leyden crystals in sputum and stool Class Secernentea Wuchereria bancrofti Sushruta – first describe elephantiasis Microfilaria – first discovered by Demarquay (1863) in hydrocele fluid from a patient in Cuba Wucherer (1868) – detected microfilaria in urine; Lewis (1872) – in blood Bancroft – first to describe the female worm (1877); Bourne – discovered adult male worm (1888) Manson – described the periodicity of the microfilaria and the role of insect vectors (1899) Class Secernentea Wuchereria bancrofti Most widely distributed filarial parasite of humans (110 million) Found throughout the tropics and subtropics with highest prevalence in Asia (India-5%, China) and Subsaharan Africa (8%) and other places like Pacific Islands, areas of South America, and the Caribbean basin Definitive host – Man Intermediate Host – Mosquito (Culex quinquefasciatus is the principal vector worldwide); Rarely Anopheles (rural Africa) or Aedes (Pacific Island) can serve as a vector. Class Secernentea Wuchereria bancrofti Adult worms: Male – smaller; corkscrew like tail and presence of two spicules (helps in copulation) at posterior end Female – viviparous Both adult male and female remain coiled together Larva: Four larval stage Microfilaria – first stage Filariform – third stage larva; infective form to humans Pathogenesis Chronic Filiariasis It develops 10–15 years after infection. Chronic host immune response against the dead worm leads to enhanced granuloma, thrombi formation and fibrosis of the lymph vessels leading to severe lymphatic obstruction and pedal edema Class Secernentea Dracunculus medinensis Causes Guinea worm disease or dracunculiasis Currently, dracunculiasis is limited to few countries in Sub-Saharan Africa such as Sudan (the highest burden), Ghana, Mali, and Niger. Definitive host – Man Intermediate host – Copepods (Cyclops) Infective form – Third stage filariform larvae Man gets infection by drinking fresh water from stagnant pools containing minute freshwater crustaceans (Cyclops) infected with L3 larvae. Life cycle of Dracunculus medinensis Development in Man: Cyclops are digested in stomach releasing the L3 larvae. They penetrate the wall of the small intestine and migrate through the thoracic musculature. Gravid female worms migrate throughout the body, and ultimately reach the skin, particularly over the ankles, feet, and lower legs. When skin comes in contact with water, the female worm (1 meter long) induces a local blister that eventually ruptures. Large numbers of L1 larvae are released into the water Development in Cyclops: The motile free-swimming L1 larvae infect Cyclops. They molt twice to form L3 larvae which are infective to man over a period of 2 weeks. Class Secernentea Loa loa African eye worm First reported in West Indies in 1770 In 1895, Argyll-Robertson described the adult worm from the subcutaneous swelling of the eye of a woman residing in Calabar from West Africa (Calabar Swelling) Restricted to the rain forests of West and Central Africa. Class Secernentea Loa loa Vector – female Chrysops species (deerflies, mango flies, red flies or tabanid flies) Adult worms (females, 50–70 mm long and 0.5 mm wide; males, 30–35 mm long and 0.3 mm wide) live in subcutaneous tissues. Infective (L3) larvae are transmitted by the bite of female Chrysops species during the blood meals in the daytime