Diagnosis of Penicillium marneffei infection by quantitation of urinary antigen by using an enzyme immunoassay.

Penicillium marneffei is a major cause of opportunistic infection in patients with AIDS in north and northeastern Thailand. A method for the quantitation of P. marneffei antigen in urine was developed by using fluorescein isothiocyanate-labelled purified rabbit hyperimmune immunoglobulin G in an enzyme-linked immunosorbent assay. This method was evaluated with 33 patients with culture-proven penicilliosis and 300 controls (52 healthy subjects, 248 hospitalized patients without penicilliosis) from the same area in which penicilliosis is endemic. Urinary antigen was found in all 33 (100%) patients with penicilliosis, with a median titer of 1:20,480. With undiluted samples, 67 (27%) of 248 hospital patients and 3 (6%) of 52 healthy controls were reactive. At a cutoff titer of 1:40, the urine antigen detection assay had a diagnostic sensitivity of 97% and specificity of 98% (positive predictive value, 84%; negative predictive value, 99.7%). This test offers a valuable and rapid method for the diagnosis of penicilliosis in patients with AIDS and could be a useful addition to conventional diagnostic methods in areas in which penicilliosis is endemic.

Semi-quantitative measurement of Plasmodium falciparum antigen PfHRP2 in blood and plasma.

Plasmodium falciparum histidine rich protein 2 (PfHRP2) antigen was measured semi-quantitatively in whole blood, plasma, and supernatants and red blood cells of cultures in vitro using the dipstick ParaSight-F test and also by a quantitative antigen-capture enzyme-linked immunosorbent assay (ELISA). In vitro, PfHRP2 was secreted mainly during the second half of the asexual cycle with a marked rise during schizont development and rupture. The total PfHRP2 secreted before schizogony corresponded to approximately 4% of that contained in the red blood cells. In samples from 55 patients with acute falciparum malaria, the level of detection by ELISA corresponded to parasitaemias of 100/microL for whole blood and 1600/microL for separated plasma. Whole blood PfHRP2 levels were correlated significantly with admission parasitaemia (r = 0.76, P < 0.0001) and the stage of parasite development (r = 0.43, P < 0.01). Although whole blood PfHRP2 concentrations were higher in severe malaria, plasma concentrations of PfHRP2 were considerably higher in severe malaria (median titre 1:320, range zero to 1:1280) than in uncomplicated malaria (median titre 1:5, range zero to 1:80; P < 0.0001). The ratio of whole blood to plasma PfHRP2 was lower in severe than in uncomplicated malaria (median 4, range 0.25 to 256, versus 64, range 4 to 1280; P < 0.0001). With plasma samples the intensity of colour change on the dipstick correlated well with more precise measurement of optical density in the ELISA (r = 0.88, P < 0.0001). These results suggest that measurement of PfHRP2 in plasma could provide an alternative approach to the assessment of the parasite biomass, and thus prognosis, in severe malaria, and that this could be done simply by using the currently available dipsticks.

Immunological analysis of Opisthorchis and Clonorchis antigens.

Immunoreactive components of Opisthorchis viverrini and Clonorchis sinensis were analysed by enzyme-linked immunosorbent assay (ELISA), radioimmunoprecipitation and immunoblotting. Somatic extracts from these two liver flukes as well as from other related parasites, together with the metabolic products, were tested for their reactivities with sera from patients with opisthorchiasis and clonorchiasis. A significant cross-reactivity in the ELISA was noted between Opisthorchis and Clonorchis. Immunoblotting and radioimmunoprecipitation analyses showed that the 89-kD protein which was previously shown to be a predominant metabolic product of O. viverrini reacted with sera from both groups of patients. However, an antigen with a molecular weight of 16 kD, apparently a predominant somatic component, appeared to be specific for O. viverrini.