Comparative detection of Plasmodium vivax and Plasmodium falciparum DNA in saliva and urine samples from symptomatic malaria patients in a low endemic area

BACKGROUND: Definite diagnosis of malaria relies on microscopy detection of blood stages of parasites in peripheral blood and requires blood sample collection. The nested PCR method has shown to be more sensitive and superior to microscopy in detecting co-infections of Plasmodium species in circulation while Plasmodium falciparum DNA can be identified in urine and saliva specimens of patients, albeit at a lower sensitivity. METHODS: Matched blood, saliva and urine samples were collected from 100 microscopy-positive and 20 microscopy-negative febrile patients who attended a malaria clinic in Tak Province, northwestern Thailand for nested PCR analysis targeting the small subunit ribosomal RNA gene of human malaria. Both P. falciparum and Plasmodium vivax have been known to circulate at a comparable rate in the study area. RESULTS: Comparing with microscopy results, nested PCR of saliva samples had a sensitivity of 74.1% for P. falciparum detection and 84% for P. vivax detection while 44.4% and 34.0% of the corresponding values were observed for urine samples. Both nested PCR results of saliva and urine samples had a specificity of 100% for identification of P. falciparum and P. vivax when compared with nested PCR results from blood. Co-infections of both species were found in four, 26 and 8 patients by microscopy and nested PCR of blood and saliva samples, respectively. Although the positive rates of nested PCR of saliva samples for P. falciparum increased with parasite density, no tendency occurred in results from nested PCR of saliva samples for P. vivax as well as those of urine samples. CONCLUSIONS: Saliva and urine samples could be alternative noninvasive sources of DNA for molecular detection of both P. falciparum and P. vivax. Further improvement of the detection method will offer an opportunity to use these samples for diagnosis of malaria.