parasites Flashcards
all helminths are
animals –> metozoans (complex structure, multicellular, and eukaryotic)
helminths 2 phyla
playhelminths (cestodes and trematodes) and nematodes
cestodes are tapeworms
trematodes are flukes
nematodes are roundworms
true or false:
- helminths live for years
- helminths multiply within host
1 - true
2 - do NOT multiply in host (a few exceptions); need to leave body to continue lifecycles
fasciolopsis buski is a …
trematode (fluke)
trematodes
flukes
flat, leaf shaped worms with 2 muscular suckers and a blind loop intestinal tract (regurgitates)
hermaphroditic (except scistosomes)
require intermediate host (snails/clams)
fasciolopsis buski
a trematode you acquire by eating encysted larva in aquatic vegetation (like water chestnuts)
develops in small intestine for 3 months –> eggs in stool
*can be asymptomatic OR diarrhea, fever, abd pain, ulcers, and hemorrhage
treat with praziquantel
what parasite encysts in water vegetation (water chestnuts/clams)?
fasciolopsis buski (a trematode)
cestodes
tapeworms
flat, ribbon like composed of proglottid segments which contain reproductive organs
have suckers with hooks on scolex (head) to attach to intestinal lining
has NO digestive tract – food absorbed through soft body
which cestode does not have hooks to attach to intestines?
D. latum
which group contains the taenia?
cestodes
taenia lifecycle
cystic larvae in striated muscle of animals
cooking meat destroys the cysts so transmission occurs with undercooked meat
you have to ingest the EGGS fo rinfections; tapeworm itself is not infections so ingesting an adult just results in you passing eggs in stool which THEN are infectious for next victim
to be infected by taenia you have to ingest
the eggs
taenia solium
tapeworm acquired by eating larvae in pork
ingestion of larvae –> adult in intestines
ingestion of eggs in food/water/or self (hand to mouth) –> cysticercosis
after ingestion the oncosphere penetrates intestinal wall, circulates in tissues, and develops into a cysticercus (fluid filled bladder containing the scolex of larval form –> usually head to brain, muscle, and eyes
can cause neurocysticercosis
neurocysticercosis
taenia solium eggs were ingested and cysticersi implant in brain
presents with headache, seizure, deficit, death to hydrocephalus
single lesion can resemble cancer –> tissue biopsy is only sure diagnosis
treat with albendazole or praziquantel and corticosteroids
treat cestodes with
albendazole
praziquantel
+/- corticosteroids
taenia saginatum
a cestode (tapeworm) acquire by eating larvae in undercooked beef; few symptoms; can grow to 10 m!!!
diphyllobathrium latum (d latum)
a cestode (tapeworm) acquire by eating fish larvae causes B12 deficiency
e granulosus
a cestode (tapeworm) tiny tapeworm in dog bowel larvae infect human if they ingest dog poop worm doesnt grow in humans but can produce eggs/proglottids in stool
can you tell the difference between taenia eggs in feces?
no but you can tell difference between proglottid segments
nematodes
roundworms
nonsegmented smooth with tapered ends, nonpigmented, with flexible outer coatings (cuticle) and muscular layer underneath
has nervous, digestive, renal, and reproductive organs
under positive pressure (filled with fluid; pressure is >atm)
hydrostatic skeleton for shape and movement
3 ways to transmit nematode round worms
eating eggs in fecal contaminated food/water
direct penetration through skin
eating infected food
type of nematode that can cause death and mortality?
intestinal nematodes
intestinal nematodes cause
stunted growth, reduced, physical activity, lower cognitive performance and low school attendance in children
determinant of nematode symptoms is
the number of nematodes
three characteristics of pathogenic nematodes
Smooth borders, Even shapes with tapered ends, Not pigmented
nematode symptoms
GI - Abdominal discomfort, Bloating, diarrhea, perianal itching, Malabsorption
Pulmonary – Pneumonitis, Transient infiltrates – migrate through the lungs, wheeze
Skin
• Cutaneous larva migrans Worms get lost and can’t penetrate the subcutaneous tissue so they just move around until they die or you treat it
• Hives (both hookworm and Strongyloides)IgE reaction to the worm causes generalize allergic reaction when invading into mucosa
Nutrition/Hematologic - Fatigue due to iron deficiency (hookworm), Vitamin A/Zinc deficiency, & Protein losses
cutaneous larva migrans
nematode Worms get lost and can’t penetrate the subcutaneous tissue so they just move around until they die or you treat it
helminths and poverty
a vicious cycle
Anemia (esp. hookworm) Reduced work output, Impaired cognitive ability, and Decreased school attendance
This leads to… poverty – contributes to poor levels of sanitation/education and more helminth infections
Strongyloides and Hookworm lifecycle?
SKIN –> LUNGS –> GUT
ascaris lifecycle?
gut –> liver –> lungs –> gut
when ascaris is in lungs it causes
igE
pulmonary eosinophilia
ascaris
most common helminth; largest nematode (up to 40 cm) One female can lay up to 200,000 eggs/day
Worms will crawl out if the host is anaesthetized or has a fever
Life Cycle
• Eggs in soil (remain infective for years) embryonated eggs ingested larvae hatch and molt in bowel migrate in the blood to the lungs (PULMONARY EOSINOPHILS – loefflers syndrome) ascend airways to glottis and are swallowed become adults in GI tract and cause obstruction, malnutrition, infection, can also obstruct biliary/pancreatic ducts lays up to 200,000 eggs which are pooped out and continue cycle
Clinical Manifestations
• Most patients: asymptomatic
• GI: abdominal discomfort, Intestinal obstruction, Biliary/pancreatic obstruction (aberrant migration)
• Pulmonary: Löeffler’s syndrome (transient pulmonary infiltrates, dyspnea, dry cough, occasional fever, and eosinophilia)
Diagnosis
• Will not find eggs until 2-3 months after pulmonary symptoms occur – sputum may have Charcot-Leyden crystals
• After 2-3 months, easy to find eggs since females make 200,000/day
Treatment
• Pulmonary disease: self-limited
• GI disease: single dose therapy of Mebendazole or Albendazole
loeffler syndrome
caused by ascaris nematode
transient pulmonary infiltrates, dyspnea, dry cough, occasional fever, and eosinophilia
hookworm
Sucks blood A major cause of anemia worldwide (most prevalent in warm/humid areas)
Infection by one of 2 species: Ancylostoma duodenale and Necator americanus
Most risk: Children, pregnant/lactating women, women who menstruate heavily
Life Cycle
• Eggs pooped out and larvae develop in soil sit on grass penetrate skin and enter bloodstream larvae go to heart, lung capillaries, and alveolar spaces get coughed up and swallowed mature in the small intestine and can live up to 9 yrs-> eggs pooped and cycle continues
Necator americanus
Cutting plates
• 0.2-0.4 inches long
• 5-10,000 eggs/day
• Drinks .03 mL/worm/day Need 25 worms to lose 1 ml blood/day
Teeth
• 0.3-0.5 inches long
• 10-30,000 eggs/day
• Drinks 0.15 ml/worm/d 5 worms cause 1 ml blood/day loss
• Secrete anticoagulants so more blood is lost
which helminth secretes anticoagulant?
Ancylostoma duodenale - a hookworm
hookworm symptoms
- Abd pain, wheezing, dsypnea, dry cough (usually a few days to weeks after infection)
- Urticarial rash
- Fatigue due to iron deficiency anemia (chronic)
- If sensitized à papulovesicular dermatitis at entry site “ground itch”
- If worms migrate laterally à cutaneous larvae migrans (especially dog and cat hookworms, as late as 2-8 wks after exposure to A. braziliense)
hookworms and pregnancy
- Hookworm anemia in pregnancy causes: IUGR, Low birth weight/Stunting
- Antenatal antihelminthics increase maternal hemoglobin and Infant birth weight/survival
hookworm treatment
• Mebendazole x3 or Albendazole once
trichuriasis
whip worm
4cm long nematode; both intracellular and extracellular
Hair-like part contains the head(goes into epithelium); Wider posterior section has reproductive organs(protrudes into GI lumen)
Eggs take 2-4 weeks in soil to become infective;2-3 months to mature in humans
Make 0-20,000 eggs/day – Eggs have bipolar plugs.
Fecal oral lifecycle
• Eggs are ingested, larvae hatch and migrate to caecum where they mature
• Large # worms can cause colitis mimicking IBD– abdominal pain and diarrhea
Symptoms à
• Usually asymptomatic
• In heavy infections (because adults live primarily in cecum):
o Loose and frequent stools with mucus, Tenesmus (the feeling one has to constantly defecate), blood
o In heavily infected children: rectal prolapse
Treatment: ivermectin, mebendazole, or albendazole (1-3 days depending on severity)
o Strongyloides stercoralis
Has both free living and parasitic forms
Causes autoinfection/problems in immunosuppressed
Infection can last decades
Symptomatic: Diarrhea, abdominal pain, nausea, vomiting
LARVAE are shed in stool (not eggs)
• RABDITIFORM LARVAE ARE EXCRETED IN STOOL can either become free living adults, auto infect or become filariform larvae
• Free living produce eggs, rabditiform hatch and become infective filarform larvae penetrate skin
• Autoinfection: rabditiform larvae in large intestine become filariform larve, penetrate intestinal mucosa or perianal skin and follow infective cycle
• Cycle filariform larvae enter circulatory system, go to lungs/alveolar spaces coughed and swallowed into small intestine to become adults adult female deposits eggs in intestinal mucosa hatch and migrate to lumen as rabditiform larvae excreted or autoinfection
Strongyloides Hyperinfection syndrome
• Immunocompromised state
• Large burden of parasites
• GI: Nausea, vomiting, abd. pain, diarrhea, many erosions due to millions of larvae in intestinal mucosa
• Pulmonary: diffuse infiltrates, wheezing, dyspnea, cough with hemorrhage, pneumonitis, and edema
• Neurologic: gram negative polymicrobial meningitis
• Systemic: fever, hypotension àgram negative sepsis
Clinical clues – abdominal discomfort, wheezing, eosinophilia
Diagnosis
• Stool o/p isn’t good due to : low worm burden, low/irregular egg production, and uneven distribution
• So…multiple stools on multiple days (time from infection to shedding of larvae is 3-5 weeks)
• Examination for larvae on duodenal aspirate via endoscopy
Treatment Ivermectin, Albendazole, or Thiabendazole
nematode from eating raw freshwater fish in se asia
o Paracapillaries (Capillaria) philippinens –
o Paracapillaries (Capillaria) philippinens –
Like Strongyloides, can autoinfect
Symptoms:
• Often initially asymptomatic watery diarrhea, abdominal pain, and often death
• Over time develop: Borborygmus, Abdominal pain, Watery diarrhea
If not treated over weeks to months get large electrolyte losses and dehydration which can lead to death
Pathogenesis:
• Eat infected raw fish
• Larvae released into intestine Grow to adults which burrow in mucosa
• Female worms lay eggs (oviparous); Some female worms are larviparous into stool
• Some larvae burrow into the intestinal lining and develop into adults
• Over time the worm burden increases (from a few to thousands) and symptoms progress
Diagnosis: stool o/p (eggs similar to Trichuris)
Treatment: 10 d course albendazole + supportive Rx (IVF, replete electrolytes, etc.)
helminth prevalent most in temperate areas
o Pinworm (Enterobius vermicularis)
o Pinworm (Enterobius vermicularis)
common in TEMPERATE areas
Kids>adults; causes peri-anal ITCHING
Humans are the only host –> fecal/oral transmission
Diagnosis early am, before showering or defecating, ”Scotch tape test” tape side down on slide
• Stool O/Ps not very helpful
Treatment = Mebendazole, pyrantel pamoate, or ivermectin
• Treat all members of households and repeat in two weeks to prevent reinfection
• Careful trimming of fingernails, handwashing, washing of bedclothes to rid house of eggs
• Polyparasitism
o In areas where helminth infections are common, usually people are infected with MULTIPLE helminth species
signs indicating you to consider intestinal nematodes
o Consider in cases of unexplained abdominal pain, nutritional deficiencies, rash, or eosinophilia in immigrant or traveler.
diagnostic plan for nematodes
stool O&P (OVA & PARASITE) x 3 , plus Strongyloides serology
o Would empirically treat immigrants (and long-term travelers) with ivermectin prior to immunosuppression to prevent possibility of Strongyloides hyperinfetion.
nonsegmented roundworms?
nematodes
