Parasitic and Other Uncommon Infections
Core concepts
Recognize the major parasitic syndromes: malaria (Plasmodium falciparum-artemisinin-based combination therapy; P. vivax/ovale-chloroquine plus primaquine after G6PD testing), babesiosis (azithromycin + atovaquone for mild; clindamycin + quinine for severe), toxoplasmosis (pyrimethamine + sulfadiazine + leucovorin), giardiasis (tinidazole or metronidazole), amebiasis (metronidazole plus paromomycin or iodoquinol for luminal cysts), strongyloidiasis (ivermectin; hyperinfection in HTLV-1 or steroid use), and leishmaniasis (liposomal amphotericin B).
Must-know syndromes
Cerebral malaria (IV artesunate), severe malaria (IV artesunate), toxoplasma encephalitis in AIDS (ring-enhancing lesions), Chagas disease (benznidazole or nifurtimox), and schistosomiasis (praziquantel).
Traps
Primaquine and tafenoquine require G6PD testing-hemolysis risk. Artesunate can cause delayed hemolysis-monitor after treatment. Strongyloides hyperinfection can present with gram-negative sepsis in a steroid-treated patient-screen at-risk patients with serology. Amebic liver abscess does not require drainage unless superinfected.
Worked rule of thumb
For a returning traveler with fever and ring-enhancing brain lesions plus HIV, think toxoplasmosis and treat empirically with pyrimethamine + sulfadiazine + leucovorin; if no response in 2 weeks, biopsy for CNS lymphoma.