Parasitology: Intestinal Nematodes

A vocabulary set covering the morphology, life cycles, and clinical features of major intestinal nematodes including whipworms, hookworms, pinworms, and roundworms.

Nematodes

Also known as roundworms, these are thread-like (nema, thread), elongated, cylindrical, unsegmented organisms with bilateral symmetry and a complete digestive tract (mouth to anus).

Dioecious

A characteristic of nematodes where there are separate male and female worms; males are generally smaller with copulatory spicules, while females are larger.

Cuticle

A tough, noncellular layer that covers the body of a nematode and is periodically molted.

Trichuris trichiura

Commonly known as whipworm, this nematode has a whip-like shape with a thin, thread-like anterior end that embeds in intestinal mucosa and a thicker posterior end.

Bipolar plugs

Characteristic mucoid plugs found at both ends of the barrel-shaped, brownish eggs of Trichuris trichiura that measure approximately $50 \times 20\,\mu\text{m}$.

Trichuris dysentery syndrome

A clinical condition resulting from heavy whipworm infection, characterized by chronic bloody diarrhea, anemia, and growth retardation in children.

Rectal prolapse

A severe clinical sign of Trichuriasis that can occur in pediatric cases with heavy infections.

Ancylostoma duodenale

Known as the Old World hookworm, it possesses two pairs of teeth in its buccal capsule for attachment and blood feeding.

Necator americanus

Known as the New World hookworm, it is characterized by dorsal and ventral cutting plates in its buccal capsule.

Copulatory bursa

A fan-shaped or umbrella-like expansion at the posterior end of male hookworms, supported by bursal rays, used for attachment to the female during copulation.

Rhabditiform larvae

The first stage of hookworm larvae that hatches from eggs in warm, moist soil within $1$ to $2$ days and feeds on bacteria and debris.

Filariform larvae

The infective, non-feeding stage of hookworms that can survive up to $6$ weeks and enters the human host by penetrating the skin.

Ground itch

A pruritic papule or vesicle that occurs at the site of skin penetration by hookworm filariform larvae.

Enterobius vermicularis

Commonly known as pinworm, these small, white, thread-like worms reside in the caecum and appendix and are the most frequent nematode infection in children.

Cervical alae

A pair of winglike expansions found at the anterior end of both male and female Enterobius vermicularis.

Scotch tape test

A diagnostic procedure for pinworm where cellophane tape is pressed on the perianal skin in the morning to collect eggs for microscopic visualization.

Autoinfection

A process in Enterobiasis where individuals reinfect themselves by scratching the perianal area and transferring eggs from fingernails to the mouth.

Ascaris lumbricoides

The largest intestinal nematode infecting humans; females can reach $20-35\,\text{cm}$ in length and produce up to $200,000$ eggs per day.

Löffler’s syndrome

A pulmonary condition featuring fever, cough, wheezing, and eosinophilia, caused by the migration of Ascaris larvae through the lungs.

Treatment for Intestinal Nematodes

The drug of choice for most intestinal nematodes is albendazole or mebendazole.

Life Cycle of Nematodes

The life cycle generally includes eggs, larval stages, and adult stages, often with several molts during development.

Eggs of Nematodes

Typically have a characteristic shape and size, often specific to the species; may be important for diagnosis.

Juvenile Stage

This is the larval form that develops after the egg hatches; different species may have different juvenile stages.

Molt

The process where nematodes shed their cuticle, allowing for growth; occurs multiple times during development.

Symptoms of Nematode Infection

Common symptoms may include abdominal pain, diarrhea, fatigue, and anemia, depending on the species.

Diagnostic Techniques

Methods such as stool examination, serologic tests, and imaging may be used to diagnose nematode infections.

Preventive Measures

Preventive measures include proper sanitation, access to clean water, and educating communities about hygiene.

Public Health Impact

Nematode infections can lead to significant health problems, especially in children, affecting growth and development.

Transmission Routes

Nematodes may be transmitted through contaminated food, water, or soil, as well as via skin penetration or direct contact.

Immune Response to Nematodes

The human immune system reacts to nematode infections by mounting a Th2 immune response, involving antibodies and eosinophils.

Anthelmintic Treatment

Drugs such as albendazole and mebendazole are commonly prescribed to treat nematode infections by targeting adult worms.

Epidemiology of Nematodes

Nematodes are prevalent in tropical and subtropical regions, often affecting populations in poverty with limited healthcare access.