Answer to Case 642

Answer to theParasite Case of the Week 642:Plasmodiumsp. infection with relatively high (1%) parasitemia; differential diagnosis includes mixedP. falciparum/P. malariaeinfection andP. knowlesiinfection. Recommend nucleic acid amplification testing for definitive identification.PCR testing confirmed that this wasP. knowlesiinfection!This interesting case highlights the difficulty in diagnosingP. knowlesiinfection, given that many of its key morphologic features in humans overlap with those ofP. falciparumandP. malariae. LikeP. falciparum,high parasitemias may be observed, and thin delicate rings - occasionally with double chromatin dots ( " headphone " forms) and applique forms - may be seen. Conversely, all stages ofP. knowlesi are commonly seen in peripheral blood, unlike most cases of P. falciparum, so that late stage trophozoites and schizonts are also seen. Many of these later stage forms resemble those ofP. malariae,such as " band form " late stage trophozoites. Of note, P. malariaedoes not reach high levels of parasitemia (1% would be unexpectedly high).Given this complexity, PCR confirmation is important for understanding the nature of infection and guiding therapy.
Source: Creepy Dreadful Wonderful Parasites - Category: Parasitology Source Type: blogs