Chapter 32: Helminths Flashcards
Which nematodes are acquired by ingesting their eggs?
Ascaris, lumbricoides, Trichuris trichiura, and Enterobius vermicularis
What two nematodes are acquired by breaking through the skin?
Necator americanus and Strongyloides stercoralis = penetrates the feet.
What nematodes is acquired by ingesting larvae?
Trichinella spiralis = found in undercooked pork
What do Ascaris lumbricoides, Necator americanus, and Strongyloides stercoralis have in common?
They all pass into the lungs as one point in time through their life cycle before being coughed up and swallowed to mature within the intestines.
Describe the Ascaris lumbricoides life cycle?
Ascaris egg is ingested
larvae emerge in small intestines
Larvae penetrate intestine wall and travel to lung
Larvae grow in lung, then coughed up and swallowed
Larvae in intestines for second time
Larvae fully mature to adults and get excreted
Describe the Necator americanus life cycle?
Soil eggs hatch and release larvae > filariform larvae
Flariform penetrate between toes of human
Flariform travels directly to lung
Lung larvae grow and are coughed up and swallowed
Larvae reach intestine for first time
Larvae mature to adults and get excreted
What are the possible Strongyloides stercoralis life cycles?
There are three possible cycles = autoinfection, direct and indirect
Direct = flariform larvae penetrate human foot
flariform larvae travels to lung
lung larvae grow and are coughed up and swallowed
Larvea reach intestine for first time
Larvae mature into adults and produce larvae, not eggs
Then the larvae pass out in stool
Indirect = Same uptake but leads to eventual sexual reproduction of adults after development to produce eggs that will mature to flariform larvae
Autoinfection = does NOT have uptake from foot
A current infection pass larvae from lungs to intestines
The larvae then reinvades the intestinal walls
They do not leave out in stool
Ascaris lumbricoides have a range of severity from asymptomatic to a severe infection. As the worm grows it can block different passages. What can it block and what can it lead to?
These worms can invade the bile ducts, gallbladder, appendix, and liver. The more obvious infection of the intestines can easily lead to blockage of the food from passing through the GI tract. Due to the inhabitation of the intestines diagnosis is based on eggs in stool.
What are the main differences between Necator americanus and Ancylostoma duodenale?
They are both hook worms that enter the body but,
Necator moves directly from foot to lung and Ancylostoma moves to intestines before lung.
Hook worms present like many intestinal worms but can develop iron deficiency anemia. What is the cause of the loss of iron in infections with this type of organism?
Hook works tend to feed on the blood of the host causing a blood loss = iron loss.
What are some symptoms a host presents due to a hook worm going through its cell cycle?
The site of entry for a hook worm = itchy rash = foot
intestines = diarrhea and ab pain
lungs = cough and infiltrates
eosinophilia
Strongyloides stercolarlis present like many worms except for the fact that it causes vomiting and abdominal bloating not just pain. Why should you not this patient some sort of prednisone?
Prednisone is an immunosuppresive drug and any drugs like that can cause the worm to spread and invade during filariform larvae stage. The worms can pass back into intestinal walls, lungs, or other organs. This can lead to pneumonia, COPD, ARDS, and multi-organ failure.
Unlike other worms, Trichinella spiralis moves from intestines to what types of tissue?
After maturation in the intestines the worms tend to invade muscle tissue. This includes skeletal muscles causing muscle aches and fever. The worms can even invade areas like the heart and brain which are usually fatal.
What is usually found high in serum with a Trichinella spiralis infection?
Eosinophils and creatinine phosphokinase a skeletal muscle enzyme released with their degradation.
Eating what tasty treat causes Trichinella spiralis?
BACON and other pork products that are not cooked properly
What are some characteristics that set Trichuris trichiura and Enterobius vermicularis apart from the other worms that infect the intestines and cause diarrhea?
These two worms are not “hookworms” and do not have a filariform larvae stage. The Worms actually don’t leave the intestines at all like the other worms meaning there is no invasion on the lungs to cause cough or infiltrates. Also because there is no leaving the intestines, the eosinophil level is held normal.
What is the general life cycle of Trichuris trichiura and Enterobius vermicularis?
Eggs incubate in moist soil and cover whats in the soil
Humans ingest a food that is contaminated w/ eggs
Eggs hatch in the GI and migrate to cecum/ascending
The larvae mature to adults and lay eggs
they produce 1000s a day.
Trichuris passes them in stool to be incubated in soil
Enterobius eggs are placed on the perinium to hatch
this causes itching which reinfects host or others
What is the scotch tape test?
Gross. That’s what it is.
It is when a person takes a piece of tape and places it over the perianal area and microscopically can see eggs of Enterobius vermicularis.
How are blood and tissue nematodes transmitted to a human host?
They require an arthropod vector and when the animal bites the human it transmit the worm.
Describe some major differences between life cycle of the intestinal worms and blood and tissue worms?
The intestinal worms all required of their cycles to be in the intestines and in the lungs. The blood and tissue worms are found as adults in the lymph tissue and have live births of offspring that burrow through tissue into the blood stream and other organs.
These blood and tissue words are from the family Filarioidae = filariae with offspring called microfilariae
What bacteria live within the filarioidae worms to aid in their infectivity?
Wolbachia is the bacteria that lives within these worms and they are similar to Rickettsia. Killing these bacteria can actually lead destruction of the worms.
This bacteria from the dead worms + microfilariae cause allergic reactions inside infected patients.
Describe the species, vector and associated symptoms of the colloquial “river blindness”.
This is an infection of Onchocerca volvulus passed by black flies especially where they breed near water in Africa and Central and South America. This infection leads to microfilariae that migrate through dermis and connective tissue to create pruritic skin rashes with darkened pigmentation. Thin can thicken to create intraepithelial granulomas = lizard skin.
The reason for blindness is due to invasion of the cornea which can be seen with a lamp examination.
What are the two organisms associated with Elephantiasis and how does it occur?
Wachereria bancrofti (pacific islands and africa) and Brugia malayi (SE Asia) are known to cause this disease by clogging up the lymphatic system with dead worms. The worms are injected by mosquitos that lead to microfilariae and adult filariae in the lymph vessels and nodes. This can cause febrile events and enlarged lymph nodes that can have fibrous tissue form around the dead worms. The fibrous tissue leads to swelling of lymph nodes of the lower extremities, legs and genitals. This will also be paired with thickening and scaly skin production over the areas of swelling.
How and when do you tests for elephantiasis?
The main test is to look at blood draws at night time for the presence of worms in the sample. For an unknown reason the worms tend to be mobile in the blood stream at this time.
