Intestinal Nematodes PDF

2.2.2 Intestinal Nematodes Thursday, October 17, 2024  Learning Objectives Recognize the names of pathogens associated with characteristic diseases Recognize the morphology Remember the key features of the life c...

2.2.2 Intestinal Nematodes Thursday, October 17, 2024  Learning Objectives Recognize the names of pathogens associated with characteristic diseases Recognize the morphology Remember the key features of the life cycles (i.e., how do the parasite get from one host to the next?) Remember the main mechanisms of disease (i.e., how does damage to the host occur?) Lab diagnosis of parasitic disease (stages of parasite seen in clinical samples & how to differentiate from non-pathogenic types) Aktive Grotesk Aktive Grotesk Aktive Grotesk Aktive Grote sk Aktive Grote sk  Helminthic Diseases of the Digestive System Aktive Grotesk Aktive Grotesk Aktive Grotesk Aktive Grote sk Aktive Grote sk Figure Relative incidence of helminth infections worldwide.  Intestinal Helminths General Characteristics: Multicellular Complex life cycles Most species have both male and female species Many ways of transmission Symptoms vary Aktive Grotesk Aktive Grotesk Aktive Grotesk Aktive Grote sk Aktive Grote sk  Lesson 2.2.2 5 Helminths General properties: 3 forms to their life cycles: Ovum (Ova) – laid by adult worm Larva – hatches from the ovum Immature adult form Found in the intermediate host Adult worm – this stage found in the definitive host  Lesson 2.2.2 6 Mode of Transmission Fecal-oral route, may involved: Arthropods (vectors) Intermediate hosts (pigs, cows, sheep, bats, birds) before it infects humans 1) Ingestion Ova ingested, then adult worm develops in intestines (Humans are definitive, no intermediate host) Ova ingested, larvae develop in intestines (Humans not definitive) Larvae ingested from eating meat from intermediate host, develop into adult in humans (Human definitive) 2) Penetration Eggs excreted into feces → hatch into larvae → larvae penetrates skin of humans  Lesson 2.2.2 7 Classification of Helminths 3 Groups 1) Nematodes – Round Worms 2) Cestodes – Tape worms 3) Trematodes – Flukes  Lesson 2.2.2 8 Nematodes (Round worms) General characteristics: Unsegmented round worms Pointed at each end Has both male and female species Female usually larger than male Many different life cycles Different sizes (from 0.5 mm to many cm)  Lesson 2.2.2 9 Common Nematodes Species are many but following cause infections Species Mode of transmission Ascaris lumbricoides Ingestion of ova Enterobious vermicularis Ingestion of ova Trichuris trichuria Ingestion of ova Toxocara canis Ingestion of ova Necatar americanus Penetration of skin by larvae Strongyloides stercoralis Penetration of skin by larvae Ancylostoma duodenale Penetration of skin by larvae Trichinella spiralis Ingestion of larvae in infected meat  Lesson 2.2.2 10 1. Ascaris lumbricoides (Large intestinal roundworms) Causes ascariasis Lives in human intestines Transmitted by ingesting Ascaris eggs Treatment is medendazole Figure above shows Female and Male Adult Ascaris. Female is larger than male, 15-30 cm long, has a waist. Male has curved tail.  Lesson 2.2.2 11 1. Ascaris lumbricoides (Large intestinal roundworms) Ova – 3 forms seen 1) Fertilized ova – measure 60-70 um (length) and 40-50 um (wide). Has thick brown cell covered with dense irregular layer of albumin. 2) Decorticated ova – has lost albumin layer 3) Unfertilized egg – cannot cause infections, longer and narrower  Lesson 2.2.2 12 1. Ascaris lumbricoides (Large intestinal roundworms) Ova in feces or inside adult worms. Sometimes adult worms seen in vomit or lung biopsy. Note Infective stage and Diagnostic stage.  Lesson 2.2.2 13 1. Ascaris lumbricoides (Large intestinal roundworms) Condition is called Ascariasis Pathogenicity: Seen worldwide lots of people infected Symptoms depend on the parasite load Symptoms include – Eosinophilia Vomiting and abdominal pain Allergic reactions Pneumonitis Obstruction of intestine, bile ducts, and trachea  Lesson 2.2.2 14 2. Enterobius vermicularis (Pinworms) Causative agent – Enterobius vermicularis Definitive host: Humans Transmitted by ingesting Enterobius eggs Treatment with pyrantel pamoate or mebendazole  Lesson 2.2.2 15 2. Enterobius vermicularis (Pinworms) Life cycle  Lesson 2.2.2 16 2. Enterobius vermicularis (Pinworms) Diagnostic Stage Gravid female migrates to perianal region to lay eggs Method of Diagnosis Recover eggs from the perianal region with a cellophane tape preparation.  Lesson 2.2.2 17 2. Enterobius vermicularis (Pinworms) Disease condition – Enterobiasis, pinworm infection. Major Symptoms Approximately 1/3 of all cases are asymptomatic Other symptoms are associated with the nocturnal migration of the gravid female from the anus to lay her eggs. Slight irritation to intestinal mucosa, mild nausea or vomiting, loss of sleep, irritability, severe perianal itching; eggs get on hands during scratching.  Lesson 2.2.2 18 3. Trichuris trichuria (Whipworm) Human infected by ingestion of the ova in contaminated food and water. Eggs found in soil / water → eaten by human → larvae hatch in small intestine → Adult lives in colon. Morphology – adult worm is not normally seen. Ova are barrel or tray shaped with mucous plug at each end (50 um length) Lab Diagnosis – ova are seen in feces Pathogenicity – asymptomatic most, sometimes obstruction with a heavy infection  Lesson 2.2.2 19 3. Trichuris trichuria (Whipworm)  Lesson 2.2.2 20 3. Trichuris trichuria (Whipworm) Disease condition – Trichuriasis, whipworm infection Major Symptoms Slight infection is usually asymptomatic Heavy infection Bloody or mucoid diarrhea, weight loss and weakness, abdominal pain and tenderness, rectal prolapse in children, intestinal obstruction  Lesson 2.2.2 21 4. Hookworms Larvae in soil hatched from eggs shed in feces Larvae bore through skin; migrate to intestine Treated with mebendazole  Lesson 2.2.2 22 4. Hookworms Two types Ancylostoma duodenale Necator americanus Similar life cycles, similar ova Differentiated by the mouth piece structure of adult worms A. duodenale – has 4 teeth N. americanus – cutting plates no teeth Adult worm – female larger than male Larvae seen in old feces, sometimes Ova – thin smooth colorless shell with 4 lobes  Lesson 2.2.2 23 4. Life cycle of Hook worms  Lesson 2.2.2 24 4. Hookworms Pathogenicity Itching at site of penetration Allergic reactions – movement of larvae Pneumonitis Secondary bacterial infections Anemia due to blood loss, B12 deficiency – blood suckers Lab diagnosis – detect ova in feces, adult not normally seen  Lesson 2.2.2 25 5. Strongyloides stercoralis (threadworm) Lab diagnosis – ova not seen in feces, as ova hatch into larvae inside the intestines Diagnostic method = Wet prep Motile filariform larvae in wet prep of fresh feces  Lesson 2.2.2 26 5. Life cycle of Strongyloides stercoralis (threadworm)  Lesson 2.2.2 27 5. Strongyloides stercoralis (threadworm) Disease condition – Strongyloidiasis, threadworm infection Major symptoms Skin – raised, itchy red blotches at the site of larval penetration Migration of larvae – primary symptoms are in lungs, bronchial pneumonia Intestinal – abdominal pain, diarrhea and constipation, vomiting, weight loss, variable anemia, eosinophilia Has caused death in immunosuppressed persons due to heavy autoinfection and larval migration  Lesson 2.2.2 28 Nematodes (roundworms) in tissues Trichinella spiralis Toxocara canis / Toxocara catis  Lesson 2.2.2 29 6. Trichinella spiralis Humans infected by ingesting meat containing encysted larvae The larvae hatch into adult worm in intestine Adult worm produces more larvae move through blood into muscle Methods of diagnosis: Histology – encysted larvae seen in tissue biopsy Serology – Antibodies in serum Radiology – cysts can be seen in x-ray Hematology – eosinophilia, larvae seen in blood when migrating  Lesson 2.2.2 30 6. Trichinella spiralis Disease condition – Trichinosis Larvae encyst in muscles of humans and other mammals Transmitted by ingesting larvae in undercooked meat Treated with mebendazole to kill adult worms  Lesson 2.2.2 31 6. Trichinella spiralis Found in both domestic and wild (sylvatic) animals Humans are accidental host Humans ingest the larvae in undercooked meat from these animals  Lesson 2.2.2 32 6. Trichinella spiralis Disease condition – Trichinosis or trichinellosis Method of diagnosis – identification of encysted larvae in biopsied muscle, serologic testing. Major symptoms: Intestinal phase – nausea, vomiting, abdominal pain, diarrhea, headache, and fever Migration phase – fever (104oF), blurred vision, edema of the face and eyes, cough, pleural pains, eosinophilia, death can occur at this phase Muscular phase – acute local inflammation with edema of the musculature.  Lesson 2.2.2 33 7. Toxocara canis Wrongly called dog tapeworm, however this is a roundworm Humans are accidental hosts Ova ingested by humans, hatches into larvae, larvae searches for place to develop into adult, it searches blood and lymphatics (visceral larval migration) Larvae settles in eye, brain Diagnosis – ova, larvae not detected in humans Diagnosis made on lesions on the eye, brain and serology  Lesson 2.2.2 34 7. Toxocara canis Thank You