PharmD Program: Nematodes Lecture

Nematodes

• Cylindrical, elongated, smooth, and unsegmented body with a complete digestive system
• Body is tapered to a pointed posterior end and a rounded anterior end
• No circulatory or respiratory systems
• All are unisexual, with females usually larger than males

Classification of Nematodes

• Classified into two main categories according to their primary location:
  • Intestinal nematodes
  • Tissue nematodes

Ascaris lumbricoides (Giant Intestinal Roundworm)

• Disease: Ascariasis
• Habitat: Small intestine of man
• Definite host (DH): Man
• Infective stage (IS): Embryonated egg (ingestion)
• Diagnostic stage (DS): Worm or egg
• Worm reaches up to 35 cm in length, the largest nematode of humans
• Worldwide distribution, with highest prevalence in tropical and subtropical regions, and areas with inadequate sanitation

Pathogenesis and Clinical Picture of Ascaris lumbricoides

• Pulmonary phase:
  • Larval migration through lungs causes Loeffler's syndrome
  • Characterized by fever, asthmatic cough, dyspnea, wheezes, and blood-tinged sputum
• Intestinal phase:
  • Light infection: Asymptomatic
  • Heavy infection: Nausea, vomiting, diarrhea, colic, and weight loss
  • Allergic reaction: Bronchial asthma and urticaria

Complications of Ascaris lumbricoides

• Intestinal obstruction due to worm mass
• Adult worms have the tendency of wandering habit if irritated by fever, drugs, or anesthetics
• Wandering single worm can cause:
  • Migration up and down to be expelled from mouth or anus
  • Passage through intestinal orifices (e.g., bile duct, pancreatic duct, appendix)
  • Perforation of the alimentary canal, leading to peritonitis

Diagnosis of Ascaris lumbricoides

• Clinical diagnosis: Non-specific symptoms
• Laboratory diagnosis:
  • Stool examination for egg (fertilized and unfertilized)
  • Sputum examination: In pulmonary phase for larvae
  • Blood examination: Eosinophilia

Treatment of Ascaris lumbricoides

• Albendazole (Bendax) or mebendazole (Vermox)

Prevention and Control of Ascaris lumbricoides

• Treatment of infected population
• Environmental sanitation (clean water supply and safe sewage disposal)
• Health education (hand washing before meals and washing raw vegetables)
• Avoid using human excreta as fertilizers before exposure to sunlight or raising temperature to 51°C
• Fly control

Enterobius vermicularis (Pinworm)

• Disease: Enterobiasis
• Habitat: Large intestine
• Definite host (DH): Man
• Infective stage (IS): Larvated egg (ingestion)
• Diagnostic stage (DS): Worm in feces or egg on perianal folds
• Adult female: 8-10 mm in length, adult male: 1-5 mm in length

Egg Description of Enterobius vermicularis

• Size: 50-60 um x 20-32 um
• Shape: Elongate-oval and slightly flattened on one side (D-shaped)
• Shell: Thick double-walled shell
• Color: Colorless
• Content: Mature larva

Mode of Infection of Enterobius vermicularis

• Ingestion or inhalation of larvated egg
• Autoinfection (external) occurs when the host scratches the perianal area and transfers the eggs from the fingers to the mouth
• Retroinfection (internal autoinfection)
• Transmission between hosts (heteroinfection) occurs when another human handles or touches contaminated items

Pathogenesis and Clinical Picture of Enterobius vermicularis

• Irritation and pruritis of anus, especially at night
• Nervous irritability, restlessness, and insomnia
• Intestinal pain (inflammation of intestinal mucosa)
• Appendicitis (worms present in the appendix)
• In female patients: the worm may reach the urether, urinary bladder, vagina, and cause urethritis, nocturnal enuresis, and vaginitis

Diagnosis of Enterobius vermicularis

• Clinical diagnosis: Children with pruritis anus
• Laboratory diagnosis:
  • Recovery of adult worm: Crawling from anus at night or in stool
  • Recovery of egg (D-shaped) by:
    • Stool examination (5% of cases)
    • Swabbing of perianal area (in early morning before defecation)
    • Urine examination (for female patients, eggs)

Treatment of Enterobius vermicularis

• Oral: Flubendazole (Fluvermal) or mebendazole (Vermox)
• Topical: 1% white precipitate mercury ointment at night on the anus region to kill the females and relieve itching and avoid secondary bacterial infection

Prevention and Control of Enterobius vermicularis

• Mass treatment
• Hand washing before meals and after defecation
• Finger nails should be kept short
• Underwear, nightwear, and bed linen must be changed and boiled
• Unwashed clothes should be exposed to sunlight to destroy eggs
• Toilet seats must be washed with disinfectants

Ancylostoma duodenale (Old World Hookworm) and Necator americanus (New World Hookworm)

• Disease: Ancylostomiasis
• Habitat: Small intestine of man
• Definite host (DH): Man
• Infective stage (IS): 3rd stage filariform larva L3 (skin penetration)
• Diagnostic stage (DS): Egg (female lays 30,000 eggs)

Adult Worm of Ancylostoma duodenale

• Size: Male 10 mm, female 15 mm
• Head slightly bent in relation to the rest of the body (hook-like)
• Buccal capsule contains teeth

Pathogenesis and Clinical Picture of Ancylostoma duodenale

• Skin invasion: Itchy papule, edema, and erythema (ground itch)
• Pulmonary migration: Loeffler's syndrome
• Intestinal attachment: Nausea, vomiting, diarrhea, epigastric pain, and bloody stool (due to laceration of intestinal mucosa)
• Polyphagia, puffy face, swollen feet, and general edema (due to malabsorption of protein and hypoproteinemia)
• Mental and physical growth retardation in children due to anemia
• Hookworm anemia: Due to sucking of blood by the worm and bleeding at the site of attachment