Class Nematoda – Roundworms
- Cylindrical, elongated, unsegmented worms
- Complete digestive tract, sexes separate
- Transmitted by ingestion or tissue invasion
Classification
- Biohelminths: Trichinella spiralis, Enterobius vermicularis
- Geohelminths: Ascaris lumbricoides, Trichuris trichiura
Trichinella spiralis
Disease
- Trichinosis / Trichinellosis
Morphology
- Male: 1.5 × 0.04 mm, ventrally curved posterior end, two lobular caudal appendages
- Female: 3.5 × 0.06 mm, blunt posterior end, single ovary, vulva in anterior fifth
- Long, narrow digestive tract in both
Life Cycle
- Same host acts as definitive and intermediate host
- Infection via undercooked pork
- Larvae released in upper small intestine → invade intestinal mucosa
- Males fertilize females and are expelled
- Females release larvae into mucosa/lymphatics → bloodstream via thoracic duct
- Larvae pass liver & lungs → encyst in striated muscles only
- Development completed in 4–16 weeks
Symptoms
- Intestinal phase: abdominal pain, diarrhea, nausea, vomiting
- Parenteral phase: fever, myalgia, muscle tenderness
- Muscle swelling, stiffness, hypertrophy
- Severe cases → myocarditis
Enterobius vermicularis
Disease
- Enterobiasis (pinworm)
Morphology
- Female: 8–13 mm, anterior alar expansions, esophageal bulb, long pointed tail
- Male: 2–5 mm, curved tail, single spicule (rarely seen)
Host: Humans only
Life Cycle
- Adults live in cecum/adjacent intestine
- Gravid females migrate to perianal region at night
- Eggs mature outside body (clothes, bedding)
- Eggs ingested → larvae hatch in duodenum
- Maturation in jejunum & ileum
- Life cycle: 4–6 weeks
Symptoms
- Often asymptomatic
- Perianal/perineal itching
- Secondary bacterial infection from scratching
- Possible vulvitis/vaginal infection in females