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Flashcards in Parasites Deck (38):
1

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

2

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

3

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

4

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

5

"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

6

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

7

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

8

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

9

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

10

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

11

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

12

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

13

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)

14

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

15

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

16

urinary and bladder disease; Africa
terminal spine egg; adult worms live in the veins that drain the bladder

granulomas and fibrosis in the bladder wall, hematuria, dysuria, increased urinary frequency, scarring, calcifications, bladder neck obstruction, bacterial UTIs, hydroureter, squamous cell carcinoma of the bladder

chronic infection in childhood and adolescence: growth impairment
severe disease: renal failure, inflammation in cervix, vagina (chronic pain and bleeding), increased HIV transmission

Dx: centrifuged urine examination, serology, ultrasound for hydronephrosis

Schistosoma haematobium

17

major cause of epilepsy in US cities bordering Mexico, high rates among Latin American immigrants (Mexico and Central America)

adult pork tapeworm infection is usually asymptomatic
proglottid segments break off the worm in the intestine, are excreted and release eggs in the environment; pigs ingest eggs; eggs release larvae that migrate to muscle, brain, eyes of pigs; larvae encyst in tissue and become cysticerci

humans serve as accidental hosts of larvae when they ingest eggs excreted by household contact with adult worm
larvae migrate to brain and encyst; cysticerci die and release antigens causing inflammation that results in seizures

Dx: ring-enhancing lesion on CT of the brain (dying cyst), MRI is more sensitive, confirmatory serology, brain biopsy usually not indicated

Taenia solium - Cysticercosis
Larval Pork Tapeworm Infection

18

Middle East, Africa, S America, western N America
definitive hosts are dogs, eggs are shed in feces
eggs are ingested by sheep, humans are accidental hosts when they ingest eggs that release larvae that migrate to the liver and form hydatid cysts (can also go to brain and lungs)

hydatid cysts cause mechanical obstruction or rupture to cause shock and anaphylaxis due to release of contents
liver cysts can cause hepatic enlargement, RUQ pain
lung cysts can cause chest pain, cough, dyspnea

Dx: Xray and serology

Echinococcosis
Echinococcus granulosus

19

pear shaped flagellated protozoan with 2 nuclei, 4 pairs of flagella, and a ventral sucking disc
worldwide distribution; zoonotic hosts (beavers)
outbreaks of diarrhea from drinking water in day care

ingestion of cysts that contain 2 trophozoites
water-borne, direct fecal-oral, food-borne
cysts are chlorine resistant; excystation follows exposure to gastric acid
trophozoites multiply by binary fission, adhere to enterocytes of the proximal small intestine

direct mucosal damage, secondary mucosal inflammation
asymptomatic, acute (steatorrhea and fat malabsorption) or chronic (failure to thrive in toddlers, growth and cognitive delays)

Dx: microscopic fecal examination, fecal antigen test, DFA, PCR, enterotest (string test), duodenal aspiration biopsy

Giardia duodenalis
Giardiasis

20

coccidian protozoan that infects gastric and respiratory epithelium; opportunistic pathogen of AIDs; water-borne outbreaks

humans swallow oocysts which are resistant to chlorine in recreational water or food
excystation in the small intestine releases sporozoites that invade the intestinal brush border membrane
sexual differentiation produces macro and microgametes that fuse to form zygotes and oocysts which are excreted in feces

intestinal villous blunting, mild inflammation, prolonged diarrhea and malnutrition
chronic diarrhea and wasting in immunocompromised patients

Dx: modified acid fast staining or fluorescent monoclonal antibody staining of fecal sample, enzyme immunoassay, PCR

Cryptosporidium parvum

21

food-borne parasite similar to cryptosporidium
outbreaks associated with contaminated food (raspberries)
chronic watery diarrhea in immunocompromised (AIDS)

Cyclospora cayetanensis

22

cause of amoebic dysentery; pseudopod-forming, non-flagellated amoeba; worldwide distribution
highest morbidity in Mexico, Central America, South America, India, Africa
peak seropositivity 5-9 years old, more severe in very young and very old and in malnourished people

ingest cysts in fecally contaminated food and water
excystation occurs in the intestine, trophozoites invade the mucosa and colonize the large intestine (flask-shaped colonic ulcers) causing bloody diarrhea
enter portal circulation and migrate to the liver, resulting in amoebic liver abscesses
hepatic amoebiasis is slowly progressive, more common in men, nonspecific febrile illness with RUQ pain, jaundice
parasite may migrate to lungs

Dx: microscopic exam (cannot distinguish species), PCR, fecal antigen detection, serology for liver abscesses

Entamoeba histolytica (pathogenic)
Entamoeba dispar (non-pathogenic)

23

amoeboflagellate
controversy over whether this is a true pathogen

Blastocystis hominis

24

endemic only in sub-Saharan Africa corresponding to Tsetse fly distribution

organism injected intradermally, divides at site of inoculation and forms chancre by lymphatic spread
Winterbottom's sign (posterior cervical lymphandenitis)
migrates from lymphatics to blood and avoids immune system with antigenic variation, travels to CNS

Gambian HAT (West and Central Africa): Winterbottom's sign, asymptomatic phase lasts for months or years, intermittent fever, headache, myalgias, malaise, weight loss, somnolence; develop severe headache, stupor, coma and death
Rhodesian HAT (East and Southern Africa) = zoonosis: more acute onset and rapid progression (months)

Dx: Giemsa staining of blood, lymph node aspirate, or CSF; CATT card test to detect antigen

Trypanosoma gambiense
Trypanosoma rhodesiense
African Trypanosomiasis "Sleeping Sickness"

25

zoonosis that is the major cause of heart disease found only in the Americas; seen in poor people living in rural areas; blood supply may be contaminated

transmitted by kissing bug (nocturnal feeder, liver in adobe), bug defecates in bites
autoinoculation by rubbing feces into wound or eye - chancre develops at site of inoculation
organism enters cells (macrophages); enters bloodstream, migrates to the CNS, heart, muscle, myenteric plexus of GIT

Acute: Romana sign (eyelid and periorbital edema, fever, LAD, hepatosplenomegaly, myocarditis)
Chronic: progressive myocardial destruction, dilated cardiomyopathy, megaesophagus, megacolon

Dx: acute - microscopy of blood/lymph or PCR; chronic - serology or PCR

Trypanosoma cruzi
Chagas Disease

26

Kala-azar
L. donovani: Eastern India, Bangladesh, East Africa
L. infantum: Middle East, Mediterranean, Southern Europe
L. chagasi: Central and South America
opportunistic pathogen in HIV

transmitted by sandflies, mammalian reservoirs (dogs)
inoculated into skin with sandfly bite, enter mononuclear phagocytes in skin, develop/multiply

high spiking fevers, hepatosplenomegaly, jaundice, pancytopenia, high concentration of serum protein and hypergammaglobulinemia

Dx: blood, lymph node biopsy, bone marrow aspirate; PCR, microscopic exam, culture; serology

Visceral Leishmaniasis
Leishmania donovani complex

27

Africa, Middle East, South/Central America
transmitted by sandflies
small red skin papule progresses to ulceration that can last for weeks to months before forming a scar

Dx: clinical; biopsy for microscopy and PCR

Cutaneous Leishmaniasis
Leishmania mexicana
Leishmania tropica
Leishmania major

28

only in Central/South America
results in erosive mucosal lesions (often in nose or oropharynx) that appear with or after initial cutaneous lesions
disfiguring and difficult to treat

Mucocutaneous Leishmaniasis
Leishmania braziliensis

29

intracellular protozoan
ubiquitous infection, zoonosis (cats, cattle, pigs)
causes CNS lesions in immunocompromised hosts and congenital abnormalities if a pregnant woman has a primary infection

Toxoplasma gondii

30

endemic in sub-Saharan Africa, central/South America, Middle East, Indian subcontinent, SE Asia, China, Oceania
vector = Anopheles mosquito
periodicity not usually seen

sporozoites are injected into host, invade hepatocytes, replicate asexually to form merozoites which rupture from hepatocytes and enter circulation to invade RBCs, replicate asexually in RBCs
some merozoites differentiate into male/female gametes that are ingested by mosquito and can form zygotes and oocysts that release sporozoites which migrate to mosquito salivary glands to be inoculated into host

medical emergency in children and nonimmune adults
uncomplicated: shaking chills, fever, sweating during defervescence
fatigue, headache, dry cough, myalgias, arthralgias, GI symptoms
complicated: cerebral malaria, severe anemia, hyoglycemia, ARDS, renal failure, circulatory failure, shock

Dx: microscopy with Giemsa stained thin or thick blood film; rapid diagnostic test

Malaria
Plasmodium falciparum

31

endemic in sub-Saharan Africa, central/South America, Middle East, Indian subcontinent, SE Asia, China, Oceania
not seen in W Africa, no Duffy antigen seen on RBCs
vector = Anopheles mosquito
tertian malaria

sporozoites are injected into host, invade hepatocytes (can enter dormant stage in liver forming hypnozoites), replicate asexually to form merozoites which rupture from hepatocytes and enter circulation to invade RBCs, replicate asexually in RBCs
some merozoites differentiate into male/female gametes that are ingested by mosquito and can form zygotes and oocysts that release sporozoites which migrate to mosquito salivary glands to be inoculated into host

uncomplicated: shaking chills, fever, sweating during defervescence
fatigue, headache, dry cough, myalgias, arthralgias, GI symptoms
may cause severe disease associated with splenomegaly and splenic rupture

Dx: microscopy with Giemsa stained thin or thick blood film; rapid diagnostic test

Malaria
Plasmodium vivax

32

endemic in sub-Saharan Africa, central/South America, Middle East, Indian subcontinent, SE Asia, China, Oceania
vector = Anopheles mosquito
tertian malaria

sporozoites are injected into host, invade hepatocytes (can enter dormant stage in liver forming hypnozoites), replicate asexually to form merozoites which rupture from hepatocytes and enter circulation to invade RBCs, replicate asexually in RBCs
some merozoites differentiate into male/female gametes that are ingested by mosquito and can form zygotes and oocysts that release sporozoites which migrate to mosquito salivary glands to be inoculated into host

uncomplicated: shaking chills, fever, sweating during defervescence
fatigue, headache, dry cough, myalgias, arthralgias, GI symptoms

Dx: microscopy with Giemsa stained thin or thick blood film; rapid diagnostic test

Malaria
Plasmodium ovale

33

endemic in sub-Saharan Africa, central/South America, Middle East, Indian subcontinent, SE Asia, China, Oceania
vector = Anopheles mosquito
quartan malaria

sporozoites are injected into host, invade hepatocytes, replicate asexually to form merozoites which rupture from hepatocytes and enter circulation to invade RBCs, replicate asexually in RBCs
some merozoites differentiate into male/female gametes that are ingested by mosquito and can form zygotes and oocysts that release sporozoites which migrate to mosquito salivary glands to be inoculated into host

uncomplicated: shaking chills, fever, sweating during defervescence
fatigue, headache, dry cough, myalgias, arthralgias, GI symptoms

Dx: microscopy with Giemsa stained thin or thick blood film; rapid diagnostic test

Malaria
Plasmodium malariae

34

single-celled protozoa that effects human RBCs
coastal southern New England, Wisconsin, Minnesota; sporadic in Europe

transmitted via tick bite, rarely transmitted in blood tranfusions
invade RBCs and replicates asexually causing RBC rupture

asymptomatic in 25% of adults and >50% of children
mild flu-like illness or severe disease is possible
fever, chills, sweats, headache, fatigue 1-6 weeks after bite
fever and possible mild hepatosplenomegaly
recovery takes up to 18 months
recovery occurs without treatment, complications in elderly and asplenics

Dx: exposure history, Giemsa stained smear, tetrads of merozoites is pathognomonic (Maltese cross); serology, PCR

Babesiosis
Babesia microti

35

Bolivia, Peru, Ecuador, Iran, Egypt
intermediate host = snails
transmission by consumption of infected vegetation (watercress)

acute: abdominal pain (RUQ), eosinophilia
chronic: destruction of liver parenchyma

dx: ultrasound, CT, serology
tx: anti-helminthic

Fascioliasis
Fasciola hepatica
Western Liver Fluke

36

China, Philippines
intermediate host = snail
transmission by eating infected crab or crayfish (shellfish)

chest pain, hemoptysis, cough, pulmonary infiltrates on CXR

dx: eggs in sputum or feces
tx: prazinquantel

Paragonimiasis
Paragonimus westermani
Lung Fluke

37

Alaska and Canada (native populations)
Great Lakes, Scandinavia

intermediate hosts: copepods, freshwater fish

vague abdominal pain, megaloblastic anemia (worm absorbs B12)

Diphyllobothriasis
Diphyllobothrium latum
Fish Tapeworm Infection

38

consumption of contaminated sushi
worm removed endoscopically

Anisakiasis