What you need to know: gram-negative rod that causes cat-scratch disease. It gets into the body through a cat scratch or bite and is taken up by macrophages.

What to expect on the exam: a patient with cat exposure, fever, malaise, and regional lymphadenopathy. That is Bartonella until proven otherwise.

What you need to know: a dimorphic fungus found in soil, moss, wood, and plants. It enters through a skin puncture.

What to expect on the exam: a gardener/outdoor worker with a single skin nodule that spreads into more nodules along lymphatics. The phrase they want you to think of is nodular lymphangitis.

What you need to know: an obligate intracellular protozoan spread by the sand fly. It lives inside macrophages.

What to expect on the exam: one of three patterns.
Cutaneous = skin ulcer.
Mucocutaneous = destructive lesions of mucosa.
Visceral = fever + splenomegaly + anemia.
If they mention sand fly + macrophages, they want Leishmania.

What you need to know: a nonenveloped DNA virus that infects erythroid precursor cells.

What to expect on the exam: the big giveaway is slapped-cheek rash in a child. The higher-yield complication stem is aplastic crisis in someone with underlying hematologic disease, or hydrops fetalis in pregnancy.

What you need to know: a protozoan parasite spread by the Ixodes tick. It infects RBCs and causes hemolysis.

What to expect on the exam: fever, fatigue, anemia, and a smear showing either ring forms or the Maltese cross. If they say Ixodes + hemolysis + Maltese cross, the answer is Babesia.