Parasites Flashcards
only soil transmitted helminth that parasitizes the colon
subtropics/tropics
unembryonated eggs passed in stool, embryonate in soil, ingested with contaminated foods, eggs hatch in GIT, larvae enter columnar epithelium of colon, sexually differentiate and mate in GIT
adult worms cause inflammation at attachment site in colon causing syndrome similar to IBD
Trichuris colitis
Trichuris dysentary syndrome
Rectal prolapse
Dx: microscopy of feces, foot-ball shaped eggs with 2 polar end plugs
Trichuris trichiura
whipworm
most prevalent parasitic infection in developing countries; hardy eggs are ubiquitous in urban and rural areas
adult worms live in small intestine; eggs can survive harsh conditions for years (thick coat); embryonate and develop in soil with moisture and shade; ingested eggs release larvae that invade intestinal mucosa, enter portal circulation and lungs (ascend bronchial tree), are coughed up and swallowed into the GIT
larval migration elicits peripheral eosinophilia, Loeffler’s pneumonitis (transitory infiltrates on CXR)
migration causes asthma life symptoms
chronic intestinal infection causes growth impairment and IQ deficits
heavy worm burden causes intestinal obstruction and hepatobiliary ascariasis; major cause of surgical abdomen, confused with appendicitis
Dx: microscopic exam of feces; adult worms apparent after migration through nasopharynx or rectum
Ascaris lumbricoides
giant round worm
one of the most common helminth infections in the US and Europe
the vast majority of puppies harbor the worms
adult worms shed eggs which are found in sandboxes and playgounds; accidental ingestion by children
ingested eggs release larvae that invade viscera (liver, lungs, brain) or the eye; larvae do not develop into adults in humans (no eggs)
Visceral larva migrans (toddlers): pneumonitis, hepatitis, eosinophilia, hypergammaglobulinemia, seizures
Ocular larva migrans (older children): strabismus with larval tracts on retina
Dx: VLM with ELISA and OLM by pediatric ophthalmologist
Toxocara canis
large intestinal dog roundworm
highest prevalance in sub-Saharan Africa, SE Asia, Brazil, Central America
leading cause of anemia in children and women of reproductive age
high worm burdens in children and adults
larvae penetrate skin (feet, hands, abdomen, buttocks) and enter small lymphatics/venules, migrate to the right heart and pulmonary capillary bed, ascend bronchial tree, swallowed into GIT, mature in small intestine, adults attach to mucosa and submucosa and rupture capillaries to ingest blood, eggs are expelled in feces
adult worms cause blood loss in the intestinal lumen
iron deficiency anemia, protein malnutrition, impaired cognition, fatigue
Dx: microscopic exam of feces for eggs
Necator americanus
Ancylostoma duodenale
Hookworm
“creeping eruption” is a skin condition caused by larval invasion of dog and cat hookworms; common on beaches in the tropics and Gulf Coast
Ancylostoma caninum
Ancylostoma braziliense
Cutaneous Larva Migrans
one of the most common helminths in temperate climates, not a severe condition
adult worms live in the colon, females migrate nocturnally out of the anus and lay eggs while crawling on perianal skin; self-infection when eggs re swallowed by hand to mouth contact or when eggs are aerosolized and deposited on contaminated surfaces and ingested
larvae are released in the GIT and migrate to the colon
often asymptomatic, eggs may cause perianal pruritus, secondary bacterial infection from scratching
adult worms may enter the female GU tract and cause vulvovaginitis
anorexia, irritability, abdominal pain
Dx: scotch tape test on the perianal area in the morning, microsccopic examination
Enterobius vermicularis
Pinworm
tropics/subtropics, Appalachia, immigrants from SE Asia and Latin America
helminth capable of replication within the host
can result in hyperinfection in immunocompromised patients
larvae invade the skin and travel the afferent circulation to the lungs, coughed up and swallowed into GIT
only adult female worms parasitize the human intestine, live in the intestinal epithelium and produce eggs by parthenogenesis
eggs hatch in the intestine, larvae can be seen in feces
autoinfection - individuals can harbor the parasite for decades
often asymptomatic but can cause diarrhea, abdominal pain, Loeffler’s pneumontis, larva currens (perianal rash), eosinophilia
hyperinfection: thousands of adult female worms in the intestine; bacteremia and meningitis - life threatening
associated with steroid treatment, hematologic malignancy, malnutrition, HTLV-1
HIV does not appear to be a risk factor
severe diarrhea, abdominal pain/distension
Dx: examination of multiple stool samples, fecal sample on blood agar (tracks of bacterial colonies), serologic test
Stronglyoides stercoralis
Threadworm
worldwide zoonotic infection caused by ingesting larvae from uncooked wild meat (pork or bear meat)
Now uncommon in N. America, nativa variant is seen in Inuit populations
ingest meat with encysted larvae which survive gastric acid and invade intestinal mucosa, adult worms release new larvae that migrate to striated muscle where they encyst and remain viable for years
triad: myalgias, edema, eosinophilia
light infection - few symptoms
heavy infection - intestinal phase (diarrhea, abdominal pain, vomiting), muscle phase (muscle pain, peri-orbital and facial edema, high eosinophilia)
CPK and LDH are elevated
Dx: clinical suspicion, dietary history; muscle biospy/ELISA confirm
Trichinella spiralis
most common fiarial infection worldwide
sub-Saharan Africa, Egypt, India, Haiti, Guyanas, Brazil
adult worms live in the lymphatics (inguinal) and look like angel hair pasta; adult females produce microfilariae that circulate lymph and blood at night
microfilariae are ingested by mosquito, develop, and can infect new host with mosquito bite
progression to clinical disease may take years
children are usually infected but asymptomatic, first signs in adolescence (adenolymphangitis and fever)
lymphatic obstruction, lymphedema, hydrocele, connective tissue proliferation (elephantiasis) which can partially be prevented by preventing secondary bacterial infection
tropical pulmonary eosinophilia = nocturnal cough and wheezing
Dx: microfilariae on blood film, detection of antigen; blood collected at night; filarial dancing sign on ultrasound of inguinal lymph node
Wuchereria bancrofti
Lymphatic filariasis
Central and West Africa; seen among returning Peace Corps volunteers and other long-term expatriates
Adult worm lives in subcutaneous tissue, females excrete microfiliae into the blood which have diurenal periodicity
vector = flies
migrating or episodic angioedema, Calabar swellings, pruritus
fever, arthralgia, headaches
adults worms may migrate across the conjunctiva
Dx: examine blood for microfiliae
Loa Loa
African Eye Worm
major infectious cause of adult blindness
Central and West Africa, Central America
vector = blackfly that breeds along rivers
adult worms live coiled within subcutaneous nodules on the pelvic girdle (Africa) or head (Latin America)
female worms produce microfilariae in the skin underlying connective tissues and lymphatics not blood
blackflies ingest microfilariae from the blood, develop into larvae that are transmitted to another host
intense pruritus and depigmentation of skin, chronic infection causes orange peel consistency
loss of skin elasticity leads to hanging skin folds
lymphadenopathy
ocular manfestations secondary to punctuate opacities in the anterior chamber of the eye, accumulate resulting in sclerosing keratitis that blocks light (can take decades to develop)
Dx: skin snips and microscopy
Onchocerca volvulus
River Blindness
almost eradicated except for foci in South Sudan, Ethiopia, Chad, and Mali (fewer than 200 cases)
adult worms live in subcutaneous tissues of lower extremities
female worm creates a blister, prolapses uterus to discharge newborn larvae upon contact with water
larvae ingested by water-borne crustaceans (copepods)
humans are infected by swallowing untreated drinking water, larvae penetrate the intestine and travel to the lower extremities
blister and ulcer (can cause disability); secondary bacterial infection and cellulitis
Dx: clinical diagnosis
worms removed by winding around a stick
Dracunulus medinensis
Guinea worm
China, Korea, Thailand
adult flukes live in intrahepatic bile ducts and produce eggs that are deposited in fresh water
eggs are ingested by snails releasing cercariae which swim in fresh water, penetrate the flesh of fish and encyst
humans eat raw fish, cysts excyst in the duodenum and mature into adults that migrate through the sphincter of Oddi and ascend the common bile duct
acute: fever, abominal pain, tender liver, eosinophilia
chronic: hepatomegaly, weight loss, recurrent ascending cholangitis, cholangiocarcinoma
Dx: microscopic fecal exam for eggs, abdominal ultrasound, cystic dilatation of bile duct
Clonorchis sinensis
Chinese Liver Fluke
cercariae in fresh water directly penetrate skin, larvae inter afferent circulation and migrate through lungs to efferent circulation
differentiate sexually into male:female pairs
after mating females produces eggs
adult worms cause minimum pathology
eggs induce granulomas and fibrosis
Schistosomiasis
intestinal and biliary disease
only schistosomiasis endemic in the Americas
adult worms live in mesenteric venules of the intestine
peak worm burdens in adolescents and young adults
chronic infection is associated with physical and intellectual growth impairment
acute: Katayama fever 4-8 weeks after exposure (maturation of infecting worm) causes fever, chills, cough, headache, LAD, hepatospenomegaly, eosinophilia
chronic: progressive illness, fibrosis of liver and intestine from granulomatous reaction; fatigue, abdominal pain, bloody diarrhea, hepatomegaly, portal hypertension, esophageal varices
Dx: fecal examination or rectal biopsy for eggs
Schistosoma mansoni
