Page 203 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

Microbiology ` microbiology—Parasitology Microbiology ` microbiology—Parasitology SEcTioN ii 159

Nematodes (roundworms)
orgaNism Disease traNsmissioN treatmeNt
Intestinal
Enterobius vermicularis Causes anal pruritus (diagnosed by seeing Fecal-oral. Bendazoles (bendy
(pinworm) egg A via the tape test). worms), pyrantel
pamoate.
Ascaris lumbricoides May cause obstruction at ileocecal Fecal-oral; knobby-coated, Bendazoles.
(giant roundworm) valve, biliary obstruction, intestinal oval eggs seen in feces
perforation, migrates from nose/mouth. under microscope B .
Strongyloides GI (eg, duodenitis), pulmonary (eg, dry Larvae in soil penetrate skin; Ivermectin or
stercoralis cough, hemoptysis), and cutaneous (eg, rhabditiform larvae seen in bendazoles.
(threadworm) pruritus) symptoms. Hyperinfection feces under microscope.
syndrome caused by autoinfection
(larvae enter bloodstream).
Ancylostoma spp, Cause microcytic anemia by sucking Larvae penetrate skin. Bendazoles or pyrantel
Necator americanus blood from intestinal wall. pamoate.
(hookworms) Cutaneous larva migrans—pruritic,
serpiginous rash C from walking
barefoot on contaminated beach.
Trichinella spiralis Larvae enter bloodstream, encyst in Undercooked meat (especially Bendazoles.
striated muscle D Ž myositis. pork); fecal-oral (less likely).
Trichinosis—fever, vomiting, nausea,
periorbital edema, myalgia.
Trichuris trichiura Often asymptomatic; loose stools, Fecal-oral. Bendazoles.
(whipworm) anemia, rectal prolapse in children.
Tissue
Toxocara canis Visceral larva migrans—nematodes Fecal-oral. Bendazoles.
migrate to blood through intestinal wall
Ž inflammation affecting liver, eyes
(visual impairment, blindness), CNS
(seizures, coma), heart (myocarditis).

Onchocerca volvulus Skin changes, loss of elastic fibers, river Female black fly. Ivermectin (ivermectin
blindness (black skin nodules, “black for river blindness).
sight”); allergic reaction possible.
Loa loa Swelling in skin, worm in conjunctiva. Deer fly, horse fly, mango fly. Diethylcarbamazine.
Wuchereria bancrofti Lymphatic filariasis (elephantiasis)— Female mosquito. Diethylcarbamazine.
worms invade lymph nodes.
Ž inflammation Ž lymphedema E ;
symptom onset after 9 mo–1 yr.
A B C D E

FAS1_2019_03-Microbiology.indd 159 11/14/19 12:21 PM