Intestinal Nematodes Anatomy

Enterobius Vermicularis (Pinworm)

• Habitat: Upper small intestine, mature in 5-6 weeks without migration
• Size: Males 2-5 mm long, 0.3 mm in diameter; females 8-13 mm long, up to 0.6 mm in diameter
• Inhabit: Caecum, appendix, and adjacent portions of the ascending colon
• Female worms migrate out of the anus to lay eggs, usually at night, due to drop in host body temperature
• Eggs embryonate and become infective within 6 hours of deposition
• Infectivity: Up to 2 weeks in cool, humid climates; 2 days in warm, dry conditions

Pathology and Pathogenesis

• Migration of worms out of the GIT to the anus causes local perianal irritation and pruritus
• Scratching leads to contamination of fingers, especially under fingernails, contributing to autoinfection
• Finger sucking and nail biting may be sources of recurrent infection in children
• Spread within families is common
• Most cases are asymptomatic; common symptom is perianal pruritus, especially at night
• Irritability and fatigue from loss of sleep occur, but the infection is relatively benign

Diagnosis and Treatment

• Diagnosis: Recognition of dead adult worms or characteristic ova in a stool O&P test
• Scotch tape or cellophane tape method is the most successful diagnostic method
• Treatment: Mebendazole (100 mg), albendazole (400 mg), repeated after 14 days, with a cure rate of >90%

Ascaris Lumbricoides (Ascariasis)

• Largest nematode infecting humans, with females 25-40 cm long and males 15-30 cm long
• Soil-transmitted infection, with over 1.4 billion people infected worldwide
• Most infections are subclinical; more severe complications occur in children who tend to suffer from the highest worm burdens
• Eggs can survive in the absence of oxygen, live for 2 years at 5-10º C, and be unaffected by desiccation for 2-3 weeks

Life Cycle

• No intermediate host is required
• Intestinal nematodes have cylindrical bodies covered with a tough, acellular cuticle
• The sexes are separate; the male worm is generally smaller than the female, which can produce thousands of eggs
• Female worms produce 200,000 eggs per day, which are passed in the feces and are infectious after about 1 month in the soil

Pathology and Pathogenesis

• Adult worms affect the nutrition status of the host, leading to malnutrition
• Digestive and respiratory organs of the worm float inside the body cavity, possessing a toxic fluid known as ascaron
• Allergic reactions seen in infected individuals are due to this toxin
• If present in high numbers, adult worms may cause mechanical obstruction of the bowel and bile and pancreatic ducts
• Larvae migrating through lungs induce an inflammatory response (pneumonitis)

Diagnosis and Treatment

• Diagnosis: Microscopic examination of stool specimens, recognizing fertilized and unfertilized eggs
• Occasionally, an adult worm is passed via rectum
• Larvae may be detected in sputum
• Eosinophilia may be present, especially during the larval migration through the lungs
• Plain X-ray of the abdomen may reveal a mass of worms
• Serology: Useful for diagnosis
• Treatment: Albendazole and mebendazole are effective therapies for ascariasis; reevaluation of infected individuals is recommended following therapy

Explore the anatomy of intestinal nematodes, focusing on their cylindrical bodies, tough cuticle, muscle layers, nerve trunks, alimentary tract, and reproductive systems. Learn about the unique features of Enterobius vermicularis.