FINALS MICP

• Nematodes


  • The adult forms can reside in the gastrointestinal tract, blood, lymphatic system or subcutaneous tissues
  • The immature (larval) states can cause disease through their infection of various body tissues
• Ascaris lumbricoides


  Large Intestinal Roundworm
• The most frequent helminthic infection is Ascaris lumbricoides
• In the pediatric population, an incidence of 20–60% has been documented
• When an adult worm emerges from the anus, mouth, or nose, a diagnosis is frequently made
• These worms can grow to be quite enormous in the intestinal tract, reaching lengths of up to 30 cm (about 1 foot)
• They ingest partially digested food
• Geographic distribution


  • Worldwide in areas with warm, moist climates
  • Most common in tropical and subtropical areas where sanitation and hygiene are poor
• Ascaris lumbricoides life cycle

  1. Eggs (up to 200,000) per day are excreted in a person's feces

  2. In unsanitary conditions, the eggs are consumed by another person

  3. Eggs hatch in upper intestine into small wormlike larvae that enter the bloodstream and then the lungs

  4. They migrate into the throat and are swallowed there

  5. In the intestines, the larvae mature into egg-laying adults
• Ascariasis


  • The tiny larvae in the lungs may cause some pulmonary symptoms
  • Excessive numbers can clog the intestine, bile duct, or pancreatic duct and potentially perforation; impair growth in children via malnutrition
  • Migrating adult worms may cause symptomatic occlusion of the biliary tract, appendicitis, or nasopharyngeal expulsion, particularly in infections involving a single female worm
  • Although the worms do not usually cause severe symptoms, their presence can be distressing
  • The most dramatic consequences of infection is derived from adult worm migrations. Worms have been known to leave the body of a small child through the umbilicus (navel) and to escape through a sleeping person's nostrils
  • Other symptoms such as cough are due to migration of the worms through the body
• Diagnosis is based on a microscopic examination of feces for eggs
• Ascaris lumbricoides


  Very large (adult females: 20 to 35 cm; adult males: 15 to 30 cm) nematodes (roundworms) that parasitize the human intestine
• A. lumbricoides is the primary species involved in human infections globally, but Ascaris derived from pigs (often referred to as A. suum) may also infect humans. These two parasites are very closely related, and hybrids have been identified; thus, their status as distinct, reproductively isolated species is a contentious topic.
• Hosts for Ascaris


  • Humans
  • Swine
• Natural infections with A. lumbricoides sometimes occur in monkeys and apes
• Occasionally, Ascaris sp. eggs may be found in dog feces. This does not indicate true infection but instead spurious passage of eggs following coprophagy.
• Anthelminthic medications


  Drugs that rid the body of parasitic worms
• Albendazole, mebendazole, and pyrantel pamoate are the drugs of choice for treatment of Ascaris infections, regardless of the species of worm
• Infections are generally treated for 1-3 days. Drugs are effective and have few side effects.
• Prevention of ascariasis


  1. Avoid ingesting soil that may be contaminated with human or pig feces, including where human fecal matter ("night soil"), wastewater, or pig manure is used to fertilize crops

  2. Wash your hands with soap and water before handling food

  3. Wash your hands with soap and water after touching or handling pigs, cleaning pig pens, or handling pig manure

  4. Teach children the importance of washing hands to prevent infection

  5. Supervise children around pigs, ensuring that they do not put unwashed hands in their mouths

  6. Wash, peel, or cook all raw vegetables and fruits before eating, particularly those that have been grown in soil that has been fertilized with manure

  7. Not defecating outdoors

  8. Effective sewage disposal systems
• Enterobius vermicularis


  Pinworm, Seatworm
• The people most likely to be infected with pinworm are children under 18, people who take care of infected children and people who are institutionalized. In these groups, the prevalence can reach 50%.
• Humans are the only species that can transfer this parasite
• Household pets like dogs and cats cannot become infected with human pinworms
• Pinworm eggs can survive in the indoor environment for 2 to 3 weeks
• Pinworm infections


  • More common within families with school-aged children
  • More common in primary caregivers of infected children
  • More common in institutionalized children
• Geographic distribution of Enterobius vermicularis


  Worldwide, with infections occurring most frequently in school- or preschool-children and in crowded conditions
• Transmission of Enterobius vermicularis

  1. By ingesting pinworm eggs either directly or indirectly

  2. These eggs are deposited around the anus by the worm and can be carried to common surfaces such as hands, toys, bedding, clothing, and toilet seats

  3. By putting anyone's contaminated hands (including one's own) around the mouth area or putting one's mouth on common contaminated surfaces, a person can ingest pinworm eggs and become infected with the pinworm parasite

  4. Since pinworm eggs are so small, it is possible to ingest them while breathing

  5. Incubation period: 1 to 2 months or longer for the adult gravid female to mature in the small intestine. Once mature, the adult female worm migrates to the colon and lays eggs around the anus at night, when many of their hosts are asleep
• Pinworm infection (Enterobiasis)


  • Most common clinical manifestation is itchy anal region
  • When the infection is heavy, there can be a secondary bacterial infection due to the irritation and scratching of the anal area
  • Often the patient will complain of teeth grinding, and insomnia due to disturbed sleep, or even abdominal pain or appendicitis
  • Infection of the female genital tract has been well reported
• Enterobius vermicularis


  • Human pinworm due to the female's long, pointed tail
  • Also known as "seatworm"
• Enterobius gregorii, has been described and reported from humans in Europe, Africa, and Asia. However, further morphologic and molecular evidence suggests E. gregorii likely represents an immature form of E. vermicularis.
• The rat pinworm, Syphacia obvelata, has also very rarely been reported infecting humans.
• Rarely, eggs may become airborne & be inhaled & swallowed. Retroinfection, or the migration of newly hatched larvae from anal skin back into rectum, may occur but the frequency with which this happens is unknown.
• Hosts for Enterobius vermicularis


  • Humans are considered the only host
  • Occasional infections have been reported in captive chimpanzees
• Clinical presentation of Enterobiasis

  • Frequently asymptomatic
  • Most typical symptoms: perianal pruritus, especially at night, which may lead to excoriations & bacterial superinfection
  • Occasionally, invasion of the female genital tract with vulvovaginitis and pelvic or peritoneal granulomas can occur
  • Other symptoms include, teeth grinding, enuresia, insomnia, anorexia, irritability, and abdominal pain, which can mimic appendicitis
  • E. vermicularis larvae are often found within the appendix on appendectomy, but the role of this nematode in appendicitis remains controversial
  • Very rare instances of eosinophilic colitis associated with E. vermicularis larvae have been reported
• Diagnosis of Enterobiasis


  1. Look for the worms in the perianal region 2 to 3 hours after the infected person is asleep

  2. Touch the perianal skin with transparent tape to collect possible pinworm eggs around the anus first thing in the morning. Examine the tape under a microscope. Repeat for 3 consecutive mornings

  3. Analyze samples from under fingernails under a microscope. An infected person who has scratched the anal area may have picked up some pinworm eggs under the nails

  4. Examining stool samples is not recommended as pinworm eggs and worms are often sparse in stool

  5. Serologic tests are not available for diagnosing pinworm infections
• Medications for pinworm treatment

  Mebendazole, pyrantel pamoate, or albendazole
• Any of these drugs are given in one dose initially, and then another single dose of the same drug two weeks later. The medication does not reliably kill pinworm eggs. Therefore, the second dose is to prevent re-infection by adult worms that hatch from any eggs not killed by the first treatment.
• Repeated infections should be treated by same method as the first infection.
• In households where more than one member is infected or where repeated, symptomatic infections occur, it is recommended that all household members be treated at the same time. In institutions, mass and simultaneous treatment, repeated in 2 weeks, can be effective.