Nematodes --General information Department of Medical Parasitology

Classification and Species Nematodes are multicellular animals belong to Phylum Nemathelminthes, Class Nematoda The number of nematode species is estimated at half a million, most of them are “free-living” types Few are best known in the parasitic realm, 35 species are reported human parasitic

Common human nematodes: Ascaris lumbricoides Ancylostoma duodenale Necator americanus (hookworm) Trichuris trichiura (whipworm) Enterobius vermicularis (pinworm) Wuchereria bancrofti Brugia malayi (filaria ) Trichinella spiralis Strongyloides stercoralis, etc. Classification and Species

Characteristics of Nematodes Elongated, cylindrical unsegmented worms; bilaterally symmetrical; taper towards their anterior and posterior ends

Characteristics of Nematodes Range in length from a few millimeters to many centimeters Nematodes: relative size

Characteristics of Nematodes Dioecious. The female adult is bigger than the male adult, the tail of male adult is curled or expends out to form a bursa, but the terminate of female adult is straight and slender

cuticle digestive tract lateral cord reproductive organs hypodermis Characteristics of Nematodes Pseudocoelom Body wall consists of three layers: cuticle, hypodermis and an inner layer of muscle cells musculature

The arrangement of the somatic muscles is of value in the systematic grouping of nematodes polymyarian holomyarian meromyarian Ascaris Hookworm Whipworm

Complete digestive tract Characteristics of Nematodes mouth opening or buccal cavity esophagusintestinerectumanus

testis seminal vesicle vas deferens ejaculatory duct ovary oviduct uterus Characteristics of Nematodes Reproductive system Male -- single tube type Female -- double tube type vagina malefemale

Life Cycle Mode ： egg → larva → adult ♀♂ Under favorable conditions larvae undergo molts four times Two types of life cycle Direct life-cycle: soil-transmitted nematodes (most) e.g. Ascaris / Hookworm / Enterobius Indirect life-cycle: bio-transmitted nematodes e.g. Filaria / Trichinella

Ascaris lumbricoides (Roundworm)

Introduction The largest and most common of the intestinal helminthes More than 1 billion of the world’s population are infected Result in ascariasis, a disease of warm climates and poor sanitation May be acquired through ingestion of egg- contaminated food by the host Eggs may become airborne and be inhaled and swallowed in dry, windy climates

Morphology -- Adult Similar to earthworm, cylindric fusiform body, cross veins and a pair of lateral lines on the body surface Light brown or pink in color, white when fixed with formalin as the sample Male to 31cm, female to 30cm

A mouth opening lies at the anterior end with three lips, finely teeth at the lumen edge The male possesses a curved tail with copulatory spicules spicules

Morphology -- Egg Elliptic in shape, yellow in color Thick egg shell, rough protein membrane outside Fertilized eggs and unfertilized eggs fertilized eggunfertilized egg protein membrane

shell Shell--three layers: outer layer--embryo membrane middle layer--chitinous layer inner layer--lipid layer / ascaroside layer protein membrane chitinous layerlipid layer embryo membrane Fertilized eggs: broadly oval, a embryo cell inside, 45~75×35~50 μm, new-moon shaped space at each end embryo cell new-moon shaped space

Unfertilized eggs: narrow oval, contain mainly a mass of refractile granules (a oocyte and many yolk cells), 88~94 × 39~44 μm refractile granules

Infective stage egg larva

Life cycle

infective stage Development of ova in soil

(temperature, moisture, oxygen) unembryonated eggs infective eggs 25 ℃ 10-15d enclosed larva has undergone its first molt

Development in human body Eggs ingested and hatched Larvae penetrate intestine wall Migrate via bloodstream Liver Heart Lung Alveoli of lungs Bronchi Trachea Pharynx (swallowed) Larvae mature and mate in intestine Eggs in feces

Characteristics of life cycle Human is the only host (direct life cycle) The location of adult: Small intestine Infective stage: infective eggs Larvae migration in body: liver, heart, lung (circulatory system); alveoli, bronchi, trachea, pharynx (respiratory system); esophagus, stomach, small intestine (digestive system) Nutrition: the semidigested food of host

Pathogenesis Pathogenesis caused by Ascaris infections is attributed to The host immune response Effects of larval migration Mechanical effects of the adults Nutritional deficiencies due to the presence of the adult worms

Clinical features Both migrating larvae and adult worms of A. lumbricoides can cause pathological changes and symptoms Damage of migrating larvae Damage of adult worms

Damage of migrating larvae Bronchial asthma Transient eosinophilia allergic reaction Angioneurotic edema Pneumonitis Bronchospasm a dry or productive cough, wheezing fever mechanical damage

Damage of adult worms If the worm burden is small, infections with worms may be asymptomatic. Clinical manifestations may result from a heavier worm load in the intestinal lumen Malnutrition and Growth retardation Allergic reaction Syndrome of Ascariasis Chinese leek

Malnutrition and Growth retardation In children ( ﹤ 5), ascariasis may cause severe malnutrition and growth retardation related to the worm burden Clinical symptoms include anepithymia, nausea, diarrhea, coprostasis,vague navel abdominal pains, weight loss, lassitude Allergic reaction Allergic manifestations include urticaria, itch, conjunctivitis, angioneurotic edema

Syndrome of Ascariasis Syndrome of ascariasis may be severe An adult may migrate to the appendix, bile duct or pancreatic duct, and cause obstruction and inflammation of the organs. Biliary ascariasis is the most common (abdominal pain, gallstone, gallbladder rupture, peritonitis or liver abscess) Large numbers of adults cause mechanical obstruction of the intestine Intestinal intussusception or perforation

Biliary ascariasis The most common complication, 64% The most common complication, 64% Symptoms: Symptoms: Right upper abdominal pain, sudden onset, a very strong intensity; nausea, vomiting and extremal nervous Right upper abdominal pain, sudden onset, a very strong intensity; nausea, vomiting and extremal nervousComplications

Mechanical ileus The usual site of obstruct: ileocecal region The usual site of obstruct: ileocecal regionSymptoms: Start suddenly with vomiting and colicky, recurring abdominal pain Start suddenly with vomiting and colicky, recurring abdominal painComplications

Intestinal perforationComplications

Laboratory Diagnosis Microscopic identification of eggs collected in stool is the method of choice. The eggs are most easily seen on a direct wet smear Detection of adult in feces

Ascariasis is most prevalent in the area with warmer climates, moister and poor sanitation Epidemiology

Treatment and prevention Albendazole / Mebendazole Sanitary disposal of feces Pay attention to personal hygiene and eating habits

Questions 1. What are the reasons why Ascariasis is one of the most common parasitic diseases? 2. If you ingested the eggs of A.lumbricoides, will you acquire the infection certainly? 3. How to diagnose the infection of Ascariasis ?