nematodes affecting large intestine Flashcards
How are nematodes classified based on their habitat? Provide specific examples of nematodes found in each category.
Nematodes are classified based on habitat into intestinal and extraintestinal types. Intestinal nematodes include those found in the small intestine (Ascaris, Strongyloides, Hookworm) and large intestine (Enterobius vermicularis, Trichiuris). Extraintestinal nematodes, such as Trichinella spiralis, are found in muscle tissue.
What is Trichuriasis, and what are the distinguishing characteristics of Trichuris trichiura? Where in the human body does this parasite establish itself?
Trichuriasis is an infection caused by the nematode Trichuris trichiura, also known as the whipworm. It is named due to its whip-like appearance, with a thick posterior end and a long, thin head. The worm is typically 3-5 cm long, with males being smaller than females. It primarily infects the cecum, appendix, colon, and rectum.
What is the reproductive capacity of Trichuris trichiura, and how do its eggs develop in the environment before becoming infectious?
A female Trichuris trichiura produces 3,000-10,000 eggs per day. The eggs are barrel-shaped with a polar plug at each end and develop into the infective first-stage larvae in 2-4 weeks under warm and damp conditions. Some eggs can remain dormant in the soil for up to 5 years and stay infectious for at least 1-2 years.
Why are children between 3-9 years old more frequently infected with Trichuris trichiura than adults?
Children are more susceptible to Trichuris trichiura infection because they are more likely to ingest contaminated soil while playing. Additionally, they may have poorer hygiene practices, such as inadequate handwashing before eating, which increases their risk of exposure to infective eggs.
Describe the complete life cycle of Trichuris trichiura, starting from egg excretion in feces to adult maturation in the human host.
Unembryonated eggs are passed in the feces and develop in the soil into infective eggs in 15-30 days. After ingestion through contaminated soil or food, the eggs hatch in the small intestine, and the larvae attach to the intestinal villi for nourishment. They migrate to the cecum, molt four times, and develop into adults. The adult worms embed their anterior portions into the colonic mucosa and begin oviposition (egg-laying) after 60-70 days. The life span of an adult worm is about one year.
What are the gastrointestinal symptoms of a heavy Trichuris trichiura infection, and what complications can arise from severe infestations?
In heavy infections, symptoms include abdominal pain, distention, bloody or mucus-filled diarrhea, and tenesmus (a feeling of incomplete defecation). Severe infections can lead to rectal prolapse, where embedded worms cause inflammation and edema, making the rectal tissue protrude. Additionally, damage to the intestinal mucosa can lead to bacterial infections, anemia, growth retardation, and nutritional deficiencies.
How is a Trichuris trichiura infection diagnosed microscopically, and what are the identifying characteristics of its eggs?
Trichuris trichiura infection is diagnosed through stool microscopy, where characteristic barrel-shaped eggs with a polar plug at each end are identified. These eggs may appear yellow to brown due to bile staining, and their colorless plugs help in their microscopic recognition.
What are the recommended treatments for Trichuris trichiura infection, and how do they work?
The primary treatments for Trichuris trichiura infection are Albendazole and Mebendazole. These anthelmintic drugs work by inhibiting microtubule formation in the parasite’s cells, leading to energy depletion, immobilization, and eventual death of the worm.
What measures should be taken to prevent Trichuris trichiura infection, particularly in high-risk areas?
Preventive measures include proper handwashing, avoiding ingestion of soil, using clean water sources, washing and cooking vegetables grown in manure-fertilized soil, and improving sanitation to prevent fecal contamination of the environment.
What are the defining physical characteristics of Enterobius vermicularis (pinworm), and how does its reproductive behavior differ from other nematodes?
Enterobius vermicularis is a small, white, threadlike worm. Female worms are 8-13 mm long and have a long, pin-shaped posterior end. Unlike other nematodes, gravid female pinworms migrate nocturnally to the perianal region to lay eggs, leading to intense itching and easy transmission.
Explain the life cycle of Enterobius vermicularis, including how transmission occurs and where the larvae develop in the host.
Eggs are deposited at night around the perianal area by gravid females. Transmission occurs through ingestion of contaminated hands, surfaces, or airborne eggs. Once ingested, larvae hatch in the small intestine, mature in the colon, and mate. Males die after mating, while females migrate to the anus to lay eggs. Some larvae can migrate back into the intestines (retroinfection), prolonging the infection.
What are the different modes of transmission of Enterobius vermicularis, and how does retroinfection contribute to sustained infection?
Pinworm transmission occurs through direct anus-to-mouth contact via contaminated fingers, contact with contaminated surfaces (clothing, bed linens, bathroom fixtures), or inhalation of airborne eggs. Retroinfection occurs when newly hatched larvae from the anus migrate back into the intestines, increasing the worm burden and ensuring continued infestation.
What are the primary symptoms of Enterobius vermicularis infection, and why is perianal itching worse at night?
The main symptom of pinworm infection is intense perianal itching, particularly at night when female worms lay their eggs. This itching leads to scratching, which can result in secondary bacterial infections and contamination of hands, promoting further transmission.
How is Enterobius vermicularis infection diagnosed, and what is the ‘Scotch tape test’ used for?
Diagnosis is made using the ‘Scotch tape test,’ where a piece of clear adhesive tape is pressed against the perianal skin in the morning before bathing or defecation. The tape is then examined under a microscope for the presence of pinworm eggs, which are flattened on one side and ovoid in shape.
What are the recommended treatments for Enterobius vermicularis infection, and how do these medications function?
Mebendazole and Albendazole are used to treat pinworm infections. These drugs disrupt the worm’s ATP production, causing energy depletion and leading to worm paralysis and death.
What hygiene practices should be followed to prevent Enterobius vermicularis infections, particularly in households with young children?
Preventive measures include bathing in the morning to remove eggs, washing hands frequently, trimming fingernails, discouraging nail-biting, washing bed linens and underwear frequently, and ensuring proper cleaning of contaminated surfaces. Since pinworm eggs are sensitive to sunlight, opening blinds during the day can also help reduce contamination.
