The development and use of polymerase chain reaction techniques to detect human Pneumocystis carinii and Toxoplasma gondii infection
A hemi-nested polymerase chain reaction (PCR) assay was developed to amplify a 125bp sequence of the large subunit of the mitochondrial rRNA gene oif Pneumocystis carinii. Its sensitivity was 590 organisms and was specific for P. carinii DNA. In the rat model, P. carinii infection may be characterised by infection within the lung with little or no spread of the organism within the blood. Negative Shield immunofluorescence assay and PCR results were obtained from 129/171 respiratory samples from patients with various forms of immunocompromise which may support the re-infection hypothesis for the mode of P. carinii infection. No difference was observed between Shield immunofluorescence assay and PCR results of 66 respiratory samples received from HIV/AIDS patients. However the PCR was found to be more sensitive in patients with low numbers of P. carinii such as patients with a form of immunocompromise other than HIV/AIDS; a significant difference was observed (p<0.001, McNemar test) from 87 respiratory samples of this patient group. In addition, five patients produced similar PCR results with less invasive samples suggesting that they might be useful in the routine diagnosis of P. carinii pneumonia (PCP). Differences have been observed in the clinical course of PCP in HIV/AIDS patients compared to those with some other forms of immunocompromise which may be due to strain variation, as suggested by differences observed between the sequences of isolates from patients of these two groups. T. gondii DNA was detected by a nested PCR assay in 2/99 (2%) respiratory samples from immunocompromised patients suggesting that toxoplasmosis should be considered in the differential diagnosis of pneumonia in this patient group.