DIAGNOSTIC TESTS are an integral part of the health care system in developed countries. When we’re sick, we assume our doctors will order lab tests to help them figure out the problem.
But people in developing countries can’t count on such tests being available. In limited-resource settings there are many barriers to using them, not least of which is cost.
A number of academic researchers and nonprofit organizations are taking on the challenge of developing high-performance, affordable diagnostics that can withstand the harsh conditions—such as tropical climates and unreliable sources of electricity and clean water—often found in developing countries and other limited-resource settings. Such technologies might even pull double duty and help lower health care costs in developed countries, too.
“If you look at the first-world health care system, it’s just too expensive,” says George M. Whitesides, a chemistry professor at Harvard University. “We need better ways of anticipating disease, of forestalling it, of getting to the problem before it becomes something that consumes enormous resources.”
It’s a common misconception that diagnostics don’t need to perform as well in the developing world as they do in the developed world, says Mark D. Perkins, a physician and the chief scientific officer at the Foundation for Innovative New Diagnostics, in Geneva. If anything, the quality of diagnostics in developing countries needs to be even better than those in developed countries, he says.
“In the developed world you have all kinds of redundant systems. You’re negative by test one, so you get test two. You have a couple of physicians who evaluate the results and consider your clinical picture,” Perkins says. “In the developing world you don’t have these redundancies. What you need is to give exactly the kind of information that the health worker needs to act upon.”
For the developing world, infectious diseases, especially HIV/AIDS, tuberculosis, and malaria, top the list of priorities for which better, more practical, and affordable diagnostics would do a world of good.
Making diagnostic devices as simple as possible is a major push. Bernhard Weigl, leader of the diagnostic development group at the Seattle-based nonprofit Program for Appropriate Technologies in Health (PATH), wants to make diagnostics for limited-resource settings instrument-free, even with tests that have traditionally required instruments, such as those based on nucleic acid amplification.
“The only assays that really have made an impact so far in low-resource settings are devices or assays that don’t require instruments,” Weigl says. He has been to many labs in developing countries where instruments are in unusable condition. “The only assays that are being used regularly are things like strip kits, where you just buy the kit and run it,” he says.
Such tests tend to be lateral-flow immunoassays in which health care providers use paper strips to detect antibodies that a patient generates in response to infection by a pathogen. Although such tests work well for a low cost, they may not be sensitive enough for diagnosing some diseases, where a test that detects the pathogen rather than antibodies in the patient would be preferred.
An alternative to immunoassays is nucleic acid assays that detect the pathogen itself. “There still aren’t very many practical nucleic acid assays that could be used in low-resource settings,” Weigl says. “A lot of Western scientists are trying to develop integrated, simplified versions of nucleic acid assays, such as microfluidic assays, but you still end up with an instrument and a disposable.”
Weigl and his coworkers at PATH are working on instrument-free ways of amplifying and detecting pathogenic nucleic acids from patients. Instead of the temperature-cycling instrument normally required to amplify nucleic acids by the polymerase chain reaction (PCR), they use exothermic reactions, with reagents similar to those found in camping hand warmers, to provide the heat needed. “Even something as complex as nucleic acid amplification assays—we think there are ways to do without instruments,” he says.
TO KEEP such a test instrument-free, Weigl and his colleagues are working on two different methods for detecting the amplified nucleic acids. It may be possible to visually detect a positive amplification reaction that results in a turbid solution, whereas a negative reaction would be signaled by a clear solution. An alternative is to label the amplified nucleic acids with immunoreagents and detect them with a strip test.
Not everyone is convinced that instrument-free is the way to go. Paul Yager, a bioengineering professor at the University of Washington, Seattle, thinks that, although it’s a worthy goal, expecting all assays for use in developing countries to be instrument-free is an oversimplification.
“You want the assays to work where they’re needed,” Yager says. “You minimize the power requirements, you minimize the weight, you minimize the complexity, you minimize the cost. But if it needs an instrument, it needs an instrument.”
Yager contends that an instrument is almost always necessary for quantitative measurements. “The human eye is okay at comparative things—for example, looking at color changes to determine pH and things like that from a strip. That’s pretty much the limit of what the human eye can do, and not everything can be converted into that format,” he says. “I’m a firm believer in the use of instrumentation, just the simplest and most easily available instrumentation possible.”
Yager heads a project to develop a diagnostic system, called the DxBox, to be used for infectious-disease monitoring in limited-resource settings. The project is funded by the Bill & Melinda Gates Foundation as part of its Grand Challenges in Global Health initiative. To develop the DxBox, Yager’s group is collaborating with Patrick S. Stayton at Washington; scientists at the Redmond, Wash.-based microfluidics company Micronics; the diagnostics company Nanogen, in San Diego; and PATH.
The DxBox reduces the power requirements for PCR by simply shuttling the sample back and forth between heated zones in the instrument, rather than repeatedly heating and cooling a single part of the instrument. Such an approach has the added advantage of speeding up the analysis because you no longer need to wait for the temperature to cycle.
ALTHOUGH THE targets for such an instrument are users in the developing world, Yager’s work garners interest from Western labs as well. “One of the first questions I get is ‘How soon can I get it in my lab?’ and then ‘How soon can I get many of them?’ They want a rack of them,” Yager says. “There’s a lot of interest in having a rapid PCR turnaround time.”
As part of the DxBox project, the team set a goal of distinguishing six diseases that are common in the developing world and involve a rapid-onset fever and other undifferentiated symptoms. The pathogens associated with the diseases include three RNA viruses, the malaria parasite Plasmodium falciparum, and two bacteria.
“There isn’t a single place we’ve gone for user-needs assessments where they want all six of those or where the doctors believe that panel is the right one. They all want their own subset, and some of them want a few other things,” Yager says. “Clearly, the long-range plan is to tailor the disposable to have the diseases that are endemic to a particular region.”
Yager notes, however, that preliminary measurements in Kenya show that even the experts don’t always know what diseases lurk in a particular region. “We found far more diseases present than people thought, and frequently patients are coinfected with as many as three of the panel pathogens,” he says. “Capabilities like the ones we can provide with this panel are going to teach people that people are sicker than they thought and in different ways than they thought.”
The DxBox project is approaching the end of its five-year course. Yager’s team is testing prototype instruments and expects them to be ready for clinical testing within 15 months.
Although Yager declines to predict the cost of the DxBox, he does say surveys in India, Brazil, and Kenya suggest that the potential users of DxBox in those regions will be able to afford it.
Another initiative sponsored by the Gates Foundation is the CD4 Initiative, run by Imperial College London. The initiative was launched in 2005 with an initial award of $8.6 million and a goal of developing a low-cost, instrument-free test for measuring CD4 T cells in HIV/AIDS patients. CD4 T-cell counts are used to determine whether antiretroviral therapy is needed and how well it is working.
“We really wanted to take a new approach,” says Steven Reid, project manager for the CD4 Initiative. “We didn’t want to simply make existing technologies smaller or put them in a smaller box.”
Three of six original subcontractors supported by the initiative are still in the running: Beckman Coulter, in Miami; Zyomyx, in Hayward, Calif.; and the Macfarlane Burnet Institute for Medical Research & Public Health, in Melbourne, Australia.
The Burnet Institute’s test is based on traditional lateral-flow technology, such as that used in home pregnancy tests, but the other two incorporate novel technology. The Beckman Coulter assay allows visual identification of CD4 cells from whole blood. A blood sample is placed onto a slide loaded with CD4-capture reagents, and lines appear at different spots on the slide depending on the number of CD4 cells in the sample. Zyomyx’ assay uses CD4-binding reagents to pull CD4 cells from a blood sample and transfer them to a volumetric region of the device where the volume of the cells can be read from the height of a dark line, similar to how a thermometer is read.
The three projects are scheduled to undergo independent evaluation this month in London, Reid says, with clinical trials slated to begin at the end of the year. The first round of trials will take place in developed countries, to be followed next year with trials in the developing world. “We figure if we can’t get it to work in the developed world, it’s unlikely to work in the developing world,” Reid says.
The initiative is covering all the R&D costs for the new tests. As a condition of the Gates funding, “the test has to be sold pretty much at cost in the developing world,” Reid says. “There’s a very small margin.”
With so much emphasis on cost, science might seem to take a backseat, but that emphasis leads to what Whitesides considers to be some of the most interesting problems in analysis. “How do we provide actionable, useful information at the lowest possible cost?” he asks. “You think about materials and problems in a different way, and you may be more likely to come up with a new idea than if you follow well-established conventional pathways.”
Whitesides is using everyday objects to attack the problem of diagnostics in limited-resource settings. For example, his group demonstrated that they could separate blood plasma from human whole blood by using a hand-cranked egg beater as a centrifuge (Lab Chip 2008, 8, 2032). They also propose to combine camera cell phones with paper-based diagnostics to detect assay results and transmit them to off-site experts for interpretation (Anal. Chem. 2008, 80, 3699).
Most recently, his group showed that they can make complex microfluidic devices by layering paper with double-sided waterproof adhesive tape (Proc. Natl. Acad. Sci. USA 2008, 105, 19606). The layers are patterned to channel fluid flow within and between layers of paper. Holes in the tape permit fluid to move between layers. These devices provide the capability of performing multiple assays with a single sample.
“People don’t want to run 10 different tests on someone to find out what’s there. They want to have one,” Whitesides says. “You put one drop of blood or one drop of urine on the device, and you get a bunch of different results simultaneously.”
IN THE FUTURE, the focus may shift from detecting infectious diseases to monitoring endocrine diseases, such as diabetes. Whitesides’ three-dimensional paper microfluidic devices could provide a way to do quantitative, low-cost glucose testing.
Whitesides has started a nonprofit organization called Diagnostics for All (DFA) to develop the paper microfluidic devices. The first multiplexed test will be a panel test for liver function.
“In the first world we monitor liver function pretty rigorously as people go onto new medication,” Whitesides says. “In the developing world there just isn’t a way of doing this. We’re developing a panel of tests that will be useful for generically diagnosing liver injury.”
Harvard is licensing the paper microfluidic technology to DFA on a nonroyalty basis. DFA will develop the technology and license it to others in the developed world for applications beyond use in the developing world. The royalty stream will fund DFA’s activities. “We’re trying to develop a system by which this activity becomes self-supporting,” Whitesides says.
The goal is not to make these diagnostic tests free but to make them affordable. Ultimately, even in the developing world, somebody has to make money from it, Whitesides says. “If these things are useful, they should be able to pay for themselves,” he says. “Philanthropic institutions should be in the business of getting stuff started but not of paying for it forever.”