Lecture 6: Class Nematodes PDF

Lecture six: Class Nematodes Dr. Eman Faisal Microbiology Department – College of Pharmacy Arab Academy for Science, Technology and Maritime Transport (AAST)  Nematodes (Round worms) (From Greek: nema, nematos = thread and...

Lecture six: Class Nematodes Dr. Eman Faisal Microbiology Department – College of Pharmacy Arab Academy for Science, Technology and Maritime Transport (AAST)  Nematodes (Round worms) (From Greek: nema, nematos = thread and ode = like) General features: Elongate, cylindrical, round or oval and tapering at both ends. Non-segmented, have well developed digestive tract. Sexes are separate and the male is shorter and more slender than female. Reproduction is usually sexual through the genital systems. Female worms may lay eggs (Oviparous) as trichuris worms or may give birth to larvae (Larviparous or viviparous) as in filarial worms. Males have curved posterior end while females have straight posterior end. Most nematodes are free-living in soil or in water. According to the habitat in human body, nematodes are classified into: Intestinal nematodes Tissue nematodes Have no intermediate host Requires intermediate host usually arthropod 1. Lymphatic Ascaris lumbricoides. a) Wuchereria bancrofti. Trichuris trichiura.(L.I) b) Brugia malayi. Enterobius vermicularis.(L.I) 2. Cutaneous : Hook worms. a) Onchocerca volvulus. Trichinella spiralis. b) loa- loa. Strongyloides stercoralis. c) Dracunculus medinensis. Nematodes molt: they periodically lay down a new cuticle and shed the old one.  Intestinal nematodes Ascaris lumbricoides (Giant intestinal round worm) Morphological characters: Ascaris is the largest of the common nematodes that infect humans. Adult worm: -Pink or yellow-white when fresh. -Cylindrical with tapering both ends. -Three fleshy lips; each lip has 2 minute sensory papillae. -Club-shaped esophagus. Male: About 20 cm long, have ventrally curved posterior end Female: About 25 cm long with straight posterior end Geohelminthic  Life cycle: After ingestion of the infective eggs, they hatch in the small intestine and the liberated rhabditiform larvae penetrate the intestinal wall, enter the circulatory system to the right side of the heart then to the lung. In the lung , the larvae remain for about 10 days , moulting twice (2nd & 3rd moults) then break into the alveoli to the bronchioles , bronchi, trachea, epiglottis to be swallowed and passed again to the small intestine. In the small intestine they moult for the fourth time (4th moult) and develop into mature worms then mating occurs and immature eggs pass in feaces about 3 months after infection. In suitable environmental conditions (shady soil, suitable temperature and humidity), rhabditiform larvae develop and moult for the first time (1st moult) inside the egg shells and become infective second-stage larvae (embryonated eggs) after around 2 weeks, so autoinfection is uncommon.  Ascaris lumbricoides Disease: Ascariasis. Geographical distribution: Worldwide , children are more frequently infected than adults. Host: -Definitive : Man. -Reservoir : None. -Intermediate : None. Habitat: Small intestine. Diagnostic stage: Both fertilized & unfertilized eggs are passed in feces of infected person, larva, adult worm. Infective stage: Larvated egg (Embryonated egg with the 2nd rahbditiform larva) Mode of infection: Ingestion of embryonated eggs in food, drink or from contaminated hands. Transplacental migration into a developing fetus is known.  Pathogenicity: Light infection is usually asymptomatic 1. Migration phase (Pulmonary phase): Larval migration through lungs causes a condition known as loeffler’s syndrome due to minute hemorrhages and eosinophilic infiltration. Fever, cough with blood stained sputum. Allergic manifestation as asthma and edema. 2. Intestinal Phase: a. Toxic effect : By product of living or dead worms produce allergic manifestation, nervous irritability, anorexia, loss of weight and dyspepsia. Worms produce a trypsin-inhibiting substance which interferes with protein digestion. Digestive disorders as nausea, vomiting diarrhea and abdominal discomfort. b. Traumatic effect (Phase of complication): During migration many worms get lost and accumulate in almost every organ of the body causing acute tissue reaction. When bacterial infections become superimposed death can result before the disease is diagnosed. Heavy infection results in intestinal obstruction, perforation and peritonitis. Prevention and control: Avoiding eating insufficiently cooked or washed food. Treatment of the infected cases to reduce egg output. Improving the hygienic habits (particularly in children). Sanitary disposal of excreta. Health education about the hazards and mode of infection of the parasite. Treatment: Mebendazole Albendazole : Single dose. In mixed infection, treat Ascaris first.  Enterobius Vermicularis (Pinworm or Threadworm or oxyuris) Enterobius vermicularis is the commonest nematode affecting humans (Children are particularly affected). Adult worm: -Whitish with dorsoventral cuticular expansions at the anterior end. - Double bulbed esophagus. Male: About 4 mm long - Ventrally curved posterior end. Female: About 1 cm long -Straight posterior end. Egg: -Shape: Oval, asymmetrical with flattened one side and convexed the other side. -Shell: Thick. Color: Translucent. Contents : Infective larva  Life cycle: After ingestion of the infective eggs, they hatch in the small intestine and the liberated rhabditiform larvae develop into mature worms on reaching into the large intestine. In the large intestine , mating occurs and the males usually die and the gravid female migrate to the rectum , pass out of the anus and lay their eggs on the perianal skin about one month after infection. The eggs are fully-embryonated and infective within few hours.  Pinworm infection Disease : Enterobiasis, oxyuriasis, thread worm infection. Geographical distribution : Worldwide , commonly in children. Host : -Definitive : Man. -Reservoir : None. - Intermediate: None. Habitat: Large intestine especially caecum and appendix. Diagnostic & Infective stage : Enterobius eggs. when laid are larvated and are immediately infective. Mode of infection: 1-Ingestion of eggs in food , drink or from contaminated hands. 2-External autoinfection by hand mouth infection. 3-Retroinfection when the eggs on the perianal skin hatch and the liberated larvae migrate back into the large intestine through the anus. 4-Inhalation of air-born eggs can also occur.  Irritation and pruritis ani at night (Nocturnal periodicity). Scratching may cause dermatitis and secondary bacterial infection. Nervous irritability, restlessness and insomnia. Nausea, vomiting, colic diarrhea alternating with constipation. Appendicitis. In female patients, worms may migrate to vagina, uterus, bladder and urethra causing irritation and inflammation. Appendicitis Diagnosis: Recovery of adult worms from anus at night or on the stool. Eggs are best obtained by swabbing the perianal region by : a. NIH swab. b. Scotch adhesive tape swab. Eggs may be recovered from urine in female patients. Prevention and Control: 1. Personal cleanliness. 2. Mass treatment. (The treatment should be for all members of the household)  Trichuris trichiura (Whip worm) Morphological characters: Adult worm : -Whip-like in shape. -Thin anterior part (about 60 % of the body length). -Thick posterior part (about 40 % of the body length). Male worms with a coiled posterior end. Female with a straight end. Eggs: -Shape : Barrel – shaped with polar plugs. -Shell : Thick. -Color : Yellowish – brown. -Contents : Unsegmented ovum cellular esophagus (unicellular glands surrounding esophageal tube ). Geohelminthic  Life cycle After ingestion of the embryonated eggs, they hatch in the small intestine and the liberated larvae penetrate the intestinal villi where they remain for about 1 week for their development. The larvae leave the small intestine and migrate to the large intestine where they develop into mature worms , then mating occurs and immature eggs pass in feces about 3 months after infection. Within about 3 weeks and in suitable environmental conditions (shady soil, suitable temperature and humidity), embryonic development occurs and infective first stage larvae are produced inside the egg shells.  Trichuris trichiura (Whip worm) Diseases : Trichuriasis , Whipworm infection. Geographical distribution : Worldwide, children are more frequently infected than adults. Host: -Definitive: Man. -Reservoir: None. -Intermediate: None. Habitat: Large intestine. Diagnostic stage: immature eggs in the feces of definitive host. Infective stage: Larvated eggs. Mode of infection: Ingestion of embryonated eggs in food , drink or from contaminated hands.  Trichuris trichiura Pathogenicity: (Whip worm) Depend on intensity and duration of infection. 1- Light infection: usually asymptomatic. 2- Moderate infection: Generalized abdominal pain, colic. Anorexia, nausea. Profuse mucus and bloody diarrhea. 3- Heavy infection: Anemia. Rectal prolapse. Intestinal perforation and peritonitis. Acute appendicitis. Diagnosis: Finding the eggs in the faces. Prevention and control as ascariasis.  HOOK WORMS ANCYLOSTOMA DUODENALE Morphological characters : ·Adult worm: -Grayish white when fresh. -Large buccal capsule provided with 2 pairs of ventral teeth A pair of dorsal plates. Club-shaped esophagus. Egg -Shape : Oval with bluntly rounded ends and has a clear space between the developing embryo and the shell. -Shell : Thin -Color : Transparent. -Contents : Segmented immature ovum (4-cell stage ). Life cycle: -After penertation of the filariform larvae through the skin , they enter the circulatory system to the right side of the heart then to the lung. -In the lung , the larvae break into the alveoli to the bronchioles , bronchi, Trachea, epiglottis to be swallowed and passed into the small intestine where they develop into mature worms after 2 moults (one during migratory phase and the other on reaching small intestine). -In the intestine , the worms attach to the mucosa by their mouth parts, the females deposit their eggs , and about 3 months after infection , immature eggs pass in feces (20,000 eggs by each female / day). -Within 2 days and in a moist, shady, warm soil, the rhabditiform larvae hatch from the eggs. -Within about 1 week and after 2 moults , the rhabditiform larvae develop into filariform larvae which penetrate the skin of a new host , thus the life cycle is continued. -The infection may also occurs by ingestion of filariform larvae which they develop (after 2 moults) into mature worms in the small intestine without migratory phase through the lung.  ANCYLOSTOMA DUODENALE Disease : Ancylostomiasis. Geographical distribution : Worldwide especially in tropical and subtropical areas including north of Africa , Asia , Meddle East and Mediterranean countries. Host : -Definitive : Man. -Reservoir : None. -Intermediate : None. Habitat : Small intestine. Infective stage : Filariform larva. Mode of infection : Penetration of filariform larvae through the skin or mucous membranes.  Pathogenesis and clinical picture: A-Cutaneous phase: Ground itch (due to larval penetration through the skin). B-Pulmonary phase: loeffler syndrome(due to larval migration through the lung) C-Intestinal phase: (due to presence of adult worms in the intestine) 1. Intermittent abdominal pain and distension (especially in children) 2. Nausea , vomiting and diarrhea with red to black stools. 3. Loss of appetite associated with craving to eat soil (pica). 4. Chronic infections produce iron deficiency anemia due to: Direct ingestion of blood by worms (single worm ingests about 0.15 ml blood / day ). Continuous blood loss from the previous sites of attachment , possibly as a result of anticoagulants secreted by the worms -Manifested by : Pallor, edema of the face and feet. Dyspnea on exertion , weakness and dizziness. Mental and physical retardation especially in children. 5-Eiosinophilia. Diagnosis : Clinical picture in an endemic area. CBC: Eosinophilia +anemia Finding the characteristic eggs in feces. Occasionally , finding the characteristic rhabditiform larvae in stool specimen stored at room temperature (without preservative)for more than 24 hours. Treatment : Mebendazole or Albendazol (as ascariasis) Correction of iron deficiency anemia by oral administration of iron Prevention and control : Personal protection by wearing protective clothes as footwear and gloves to prevent penetration of larvae through the skin. Treatment of infected cases to reduce egg output. Sanitary disposal of excreta. Health education about the hazards, mode of infection and the life cycle of the parasite.  Strongyloides stercoralis (Dwarf threadworm) Facultative opportunistic parasite Morphological characteristics: Adult worm: Rhabditoid esophagus. -Male (About 1 mm long). Ventrally curved, pointed tail. -Female parasitic: (About 2 mm long). Cylindrical esophagus. Straight, pointed tail. Egg: (Very rarely found in feces). -Shape: Oval. -Shell: Thin. -Color: Transparent. -Contents: Fully-developed rhabditiform larva. Mode of infection: 1. Penetration of the filariform larvae through the skin or mucous membranes. 2. Internal autoinfection where the rhabditiform larvae develop rapidly in the intestinal lumen into filariform larvae which penetrate the intestinal mucosa leading to internal autoinfection. 3. External autoinfection where the development of rhabditiform larvae into filariform larvae occurs on the perianal skin and the developed larvae penetrate the skin leading to external autoinfection  Strongyloidiasis Disease : Strongyloidiasis. Geographical distribution: Worldwide especially in tropical and subtropical areas including Africa Asia and South America. Host : -Definitive : Man -Reservoir : None, although some animals as dogs and monkeys may harbor the parasite but of no role in the transmission of infection to humans because the human transmission is essentially from person to person. -Intermediate : None. Habitat: Small intestine. Infective stage : Filariform larva THANK YOU