Health workers fighting the Ebola epidemic that swept West Africa several years ago waited days, even a week, for the results of laboratory tests to detect the deadly virus. But in an Ebola outbreak that began in early April in the Democratic Republic of the Congo (DRC), this waiting time has shrunk to hours — thanks to a genetic test that was developed in response to the 2014-2016 West African epidemic.
Researchers and health officials credit the faster tests with helping to contain the spread of Ebola in the DRC, by allowing those infected to be isolated and their contacts traced promptly. And should sparks from this outbreak light new fires in neighbouring countries, the nimbler test could help to avert a repeat of the devastating West African epidemic.
The test involves a small machine called the GeneXpert, which is widely used across Africa to diagnose tuberculosis. The DRC’s government has made the GeneXpert its primary method of testing for Ebola in the current outbreak.
"Labs have been set up with two to three days' notice in new transmission zones, whereas in West Africa it took months and months to get facilities up and running," says Mark Perkins, head of laboratory networks for the World Health Organization (WHO) Health Emergencies Programme. "It's a remarkable change."
One of the biggest lessons of the West African epidemic — in which around 29,000 people were infected and 11,000 died in Sierra Leone, Guinea and Liberia — was the need to diagnose cases of Ebola more quickly. Better lab tests could have averted 30–70% of cases and saved thousands of lives and billions of dollars, according to a May 2018 report by the Foundation for Innovative New Diagnostics in Geneva, Switzerland.
Most Ebola lab diagnostics detect genetic sequences that are specific to the virus in blood, serum and other bodily fluids. During the West African epidemic, these manual tests required highly trained scientists working in sophisticated, highly secure labs that were often far from outbreak zones.
In the DRC, by contrast, the same tests are being performed more rapidly, nearer to transmisson zones and in an automated manner by GeneXpert. The machine uses custom cartridges for different diseases and was developed for resource-poor settings. In response to the 2014–16 epidemic, the firm developed a cartridge, Xpert Ebola, to test for the Zaire strain of Ebola, which is behind the current DRC outbreak. The turnaround time from taking a sample to receiving a diagnosis in the outbreak is usually a matter of hours or at most a day, Perkins says.
The DRC outbreak, which is mainly centered in remote regions of Équateur Province in the north west of the country, is still relatively small, with 38 lab-confirmed cases, 14 probable cases, and 14 suspected. As of 9 June, 28 of those people had died (See 'Rapid Response').
Health officials are cautiously optimistic that the outbreak can be quickly stopped. But the WHO is still worried that the virus could spread across the DRC and Central Africa. Some cases may have gone undetected, which could lead to resurgences of the disease. And for the first time in the DRC, cases have occurred in an urban area: Mbandaka, a city of more than a million people and a major travel hub.
Should further regional outbreaks occur, GeneExpert machines will continue to be a big help, officials say. There are already around 150 of the machines in DRC and several hundred in nearby countries for testing for tuberculosis and other diseases. By swapping in Xpert Ebola cartridges, a large Ebola testing network could be quickly created, says Perkins.
That's provided that there are enough Ebola test cartridges. No countries have purchased stockpiles of Xpert Ebola cartridges, and the DRC had none when the outbreak started, says Iain Sharp-Paul, a marketing director at Cepheid, the Sunnyvale, California company that makes the machines . It shipped 3,600 Xpert Ebola cartridges to the DRC in less than two days after being alerted to the outbreak, and a further 4,000 cartridges are on their way.
Faster field tests
Other Ebola diagnostics are also being field-tested in the DRC outbreak. Public health officials are keen to have access to screening tests, which, unlike GeneXpert, do not require electricity or refrigeration and can be distributed to affected areas in large numbers to get on-the-spot results within minutes. These tests work by detecting Ebola proteins using the same analytical technique as over-the-counter pregnancy tests.
Researcher plan to evaluate two such tests in the DRC outbreak. One is the OraQuick Ebola Rapid Antigen Test made by medical device company OraSure Technologies in Bethlehem, Pennsylvania. OraQuick has been approved by the WHO for emergency use in testing patients' blood samples — as well as the oral fluids of corpses — for the Zaire strain of the virus. Also being tried out is a more-experimental test, QuickNavi-Ebola, produced by diagnostic company Denka Seiken in Tokyo. Oraquick has sent 2,000 tests to DRC, and Denka Seiken 1,500.
Outbreak responders aim to use the tests to investigate suspect deaths reported in remote and difficult-to-access regions, says Perkins. This will help confirm tests carried out by GeneXpert and provide a better idea of the tests' performance. Lack of field data has been a barrier to the adoption of such tests.
Thanks to lessons learned from the West African outbreak, "a new paradigm for Ebola virus detection and diagnosis is taking shape", says Mara Jana Broadhurst, an Ebola diagnostics expert at Stanford University in California. "It is critical that this process is guided by careful field studies."
Nature 558, 172 (2018)