Nematodes, Round Worms Flashcards
General characteristics
Cylindrical, tapered at both ends, cuticle (cellular material and nuclei without separate membranes), moves side to side
Cryptobiosis: able to suspend life processes completely when unfavorable conditions, can survive extremes
Sexual dimorphism, cream-white color, mouth surrounded by 3 lips, muscular pharynx
Ascaris lumbricoides
Intestinal round worms
Characteristics: infection 1-5 years, eggs must remain outside body 2-3 weeks to become infective, temperate/tropical areas, rural SE USA, feces in soil or vegetables enters human cycle
Life cycle:
1. Feces contaminated raw vegetables most common source of eggs, swallowed, second stage larvae hatch in SI
2. Penetrates intestinal wall, hepatic portal, liver parenchyma, becomes third stage larva over 1-2 weeks
3. Re-enters circulation to access lungs via heart, larvae migrate up lungs, bronchi etc, third stage larvae swallowed
4. 2 months in SI to reach adult, full length 3 months, feeds on chyme, female produces 200k eggs/day 1-2 years
Infection/symptoms: Ascariasis, ingestion of large amounts of eggs, similar to PNA, “asthma attacks after visiting poor places”, low infections asymptomatic, moderate flatulance and smelly loose stool, heavy bowel obstruction fever mailase abdominal distension/vomiting/tenderness, maintain position by constant movement, can severely alter nutrition status
Treatment: Mebendazole
Wuchereria bancrofti
Elephantiasis
Characteristics: Central America Madagascar Nile delta (humid areas, microfilariae (eggs become elongated and wormlike, adapted for migration through vascular system, sheathed, can live a long time
Life cycle:
1. Infected culcine or anopheline mosquitoes transmit third stage larvaeduring blood meal, larvae crawl onto skin
2. Crawl into wound, enters lymphatics to afferent nodes
3. One year to complete dev, females give birth to microfilariae that live 1.5 years
4. Microfilariae move to peripheral circulation at night to encounter mosquito
5. Move to central during daytime and activities, ingested during blood meal
6. Worm penetrates mosquito intestine, enters hemocoel, migrates to flight wing muscles in thorax, penetrate muscle fibers and grow third stage larva
7. Migrates into hemocoel and take up residence in biting mouth, 2 weeks for dev in mosquito
Infection/symptoms:
Elephantiasis: proportional to degree of infection, begins with fevers and chills, subsides 2-5 days, lymphangitis commonly affects limbs begins proximal and moves distal, lymph vessels distended and tender, once enlarged stays, males enlarged gentalia, not inevitable, swelling due to lymphatic blockage, skin hardens from edema with wart like elevations
Tropical pulmonary eosinophilia: immunological reaction infection (Ig specific serum), paroxysmal non productive cough, wheezing, wt loss, lymphadenopathy, low grade fever
Treatment: Diethlcarbamazine or Ivermectin
Trichinella spiralis
Trichinellosis (adult intestinal worm) or Trichinosis (eggs)
Characteristics: lacks host specificity, eating raw undercooked pork, salvation cycle (pigs/rats in temperate zones, polar bears), domestic cycle (rats/pigs fed undercooked scraps
Life cycle:
Enteral phase
1. Ingestion of infected undercooked park that contains first stage larvae in skeletal muscle, parasite freed from host tissue by digestive enzymes
2. Larvae penetrates multiple columnar epithelial cells in SI at same time intramuscular parasite (shish kabob), molts 4x in 28hr
3. Adult molt 30hr post infection in SI, female sheds first stage larvae 5-6 days post infection
4. Newborn have stylet to penetrate SI, enter blood vessel or lacteal
Parenteral phase
1. First stage larvae enter general circulation and distribute throughout body, larvae use esophageal stylet to burrow through tissue to muscle
2. Muscle cell converted to nurse cell over 9 days, day 12 nurse cell providing nutrition and removing wastes, larvae nurse cell complex by day 20
3. Viable for years, transmission by carnivores and scavengers
Infection/symptoms: proportional to # of larvae penetrating muscle cell, fever eosinophilia peak 3-4 weeks, IgE, muscle inflammation 12-20 day peak
Classic trichinosis: circumorbital edema (swelling around lid of eyes), visual disturbance, CNS symptoms, prolonged severe diarrhea
Treatment: corticosteroids and Mebendazole/Albendazole
