Enhanced detection of Rift Valley fever virus using molecular assays on whole blood samples.

BACKGROUND

Rift Valley fever (RVF) is an emerging arthropod-borne zoonoses of global agricultural and public health importance. In December 2006, an RVF outbreak was recognized in Kenya which led to the deployment of international response laboratory teams to the area.

OBJECTIVES

A field laboratory was operated in Malindi, Kenya to provide safe sample handling and molecular testing for RVF virus (RVFV) as well as selected other pathogens for differential diagnosis.

STUDY DESIGN

Safe sample handling was carried out using a negative pressure flexible film isolator (glovebox) and commercial reagents to inactivate clinical specimens and purify nucleic acid. Whole blood was routinely used for diagnostic testing although paired plasma samples were also tested in select cases. Subsequently, human macrophages were tested in vitro for their susceptibility to RVFV.

RESULTS

The field laboratory received samples from 33 individuals and a definite laboratory diagnosis was provided in 16 of these cases. Using molecular diagnostic techniques, RVFV was more consistently detected in whole blood than in plasma samples most likely due to association of RVFV with blood cells. Subsequent in vitro studies identified macrophages as a target cell for RVFV replication.

CONCLUSIONS

RVFV appears to replicate in blood cells such as macrophages. Thus, the sensitivity of molecular diagnostic testing is improved if whole blood is used as the clinical specimen rather than plasma or serum.