Abstract:
Real-time reverse transcription polymerase chain reaction (real-time RT-PCR), histopathology, and
immunohistochemical labeling (IHC) were performed on liver specimens from 380 naturally infected cattle and sheep
necropsied during the 2010 Rift Valley fever (RVF) epidemic in South Africa. Sensitivity (Se) and specificity (Sp) of realtime
RT-PCR, histopathology, and IHC were estimated in a latent-class model using a Bayesian framework. The Se and Sp of
real-time RT-PCR were estimated as 97.4% (95% confidence interval [CI] = 95.2–98.8%) and 71.7% (95% CI = 65–77.9%)
respectively. The Se and Sp of histopathology were estimated as 94.6% (95% CI = 91–97.2%) and 92.3% (95% CI = 87.6–
95.8%), respectively. The Se and Sp of IHC were estimated as 97.6% (95% CI = 93.9–99.8%) and 99.4% (95% CI = 96.9–
100%), respectively. Decreased Sp of real-time RT-PCR was ascribed to cross-contamination of samples. Stratified analysis
of the data suggested variations in test accuracy with fetuses and severely autolyzed specimens. The Sp of histopathology in
fetuses (83%) was 9.3% lower than the sample population (92.3%). The Se of IHC decreased from 97.6% to 81.5% in the
presence of severe autolysis. The diagnostic Se and Sp of histopathology was higher than expected, confirming the value
of routine postmortem examinations and histopathology of liver specimens. Aborted fetuses, however, should be screened
using a variety of tests in areas endemic for RVF, and results from severely autolyzed specimens should be interpreted with
caution. The most feasible testing option for countries lacking suitably equipped laboratories seems to be routine histology in
combination with IHC.
