Ebola Test Development Continues, Despite Declines in Cases

Despite declines in current cases in Africa, interest remains high for development and validation for a rapid, point-of-care diagnostic test for Ebola. The federal government is funding test development, researchers are publishing results of proof-of-principle and field validation studies, and companies are continuing the process of securing regulatory approval for rapid tests.

In late September, OraSure Technologies (Bethlehem, Penn.) announced it received $7.2 million of continued funding from the Biomedical Advanced Research Development Authority for "clinical and regulatory activities" necessary to secure U.S. Food and Drug Administration (FDA) approval for its OraQuick Ebola Rapid Antigen test, which previously received emergency use authorization (EUA) from the FDA. The company simultaneously announced the U.S. Centers for Disease Control and Prevention is purchasing an additional $1.5 million worth of the test for further field testing. The antigen-based, fingerstick test is read visually and does not require refrigeration or instrumentation, making the test potentially, much more widely available than the current polymerase-chain reaction-based testing.

Expanded Purpose for Existing EUA Assays
The polymerase chain reaction- (PCR-) based assays currently granted EUA were intended for use with blood samples. However, recent evidence suggests the first case of transmission of the virus through the semen of survivors following extended periods after active infection.

"The potential for sexual transmission of Ebola in West Africa has become a critical concern and the urgent need to screen survivors for the presence of Ebola virus RNA in semen has been realized," writes James Pettitt, from the National Institutes of Health, in a Sept. 15 paper published in the Journal of Infectious Diseases. The small study found that the EUA PCR assays perform equally well using semen instead of originally intended whole blood and plasma samples.

The researchers assessed the performance of the Ebola Zaire (EZ1) real-time- (RT-) PCR (TaqMan) assay using six seminal fluid samples spiked with live Ebola virus and six spiked whole blood samples. The EZ1 and Major Groove Binder quantitative RT-PCR assays were "demonstrably suitable," the authors say, and could be used to begin epidemiological studies of long-term survivors. They add that, in the future, determining the assays' performance for urine and saliva would also be "desirable."

New Test Development Continues
While expanded use of existing PCR-based assays is necessary, extensive efforts are underway to bring a rapid, POC Ebola test to the clinical setting.

"Accurate rapid diagnostic tests, particularly those that can be completed at the point of care, could move the timing and place of diagnosis closer to the community in which a patient with suspected Ebola virus disease is first seen, halting transmission chains and allowing better allocation of scarce health care resources," writes Nahid Bhadelia, from Boston University, in an editorial published online June 26 in The Lancet.

In the same issue of The Lancet, researchers present the field validation results of the Corgenix (Colorado) ReEBOV Antigen Rapid Test kit. The dipstick immunoassay, which received World Health Organization and FDA EUA, had 100 percent sensitivity and 92 percent specificity in both POC and reference laboratory testing in adults and children with suspected Ebola in Sierra Leone (Feb. 3 to Feb. 20, 2015).

Testing was performed on samples of plasma or whole blood (collected by either fingerstick or venipuncture) and two independent readers scored results. Results were compared to clinical real-time PCR results (altona Diagnostics GmbH; Germany) tested in a Public Health England field reference laboratory. Additionally, the rapid diagnostic and PCR testing was performed on 284 specimens collected from many clinical sites throughout the country.

"We found that it was feasible to perform the test in the restricted so-called red zone; that inter-operator agreement at the point of care was high; [and] that results of POC fingerstick testing were consistent with the results of the rapid diagnostic test performed on venipuncture blood samples," writes senior author Nira Pollock, M.D., from Partners In Health (Boston). "These findings suggest that the test could have had an immediate effect on patient care and infection control in our facilities by reliably detecting patients with cycle threshold values of up to 26.3, all of whom would be expected to be highly infectious."

Takeaway: Despite waning attention being paid to the Ebola outbreak, academic researchers, industry, and the government remain committed to development and validation of a rapid, point-of-care Ebola virus assay.