(FORTUNE Magazine) – THE BACKGROUND Avian flu, SARS, HIV/AIDS, and other diseases have the potential to wipe out entire populations. But early detection and quick response are tough in many developing countries, where more than 12 million people die annually from infectious diseases. Often the only way to get word of a deadly epidemic from a remote area to health officials is by mail, which can take months.

THE SOLUTION A techie, a social entrepreneur, and a former government official teamed up to launch Voxiva, a real-time epidemic-tracking system for isolated places with little or no technology. It can be accessed through the Web, cellphones, landlines, and even radio. Health-care workers access the network with passwords and punch in their reports, which instantly go to an online database. Health authorities analyze the reports and respond, confirming diagnoses or sending word that supplies are on the way. India purchased Voxiva to track the spread of disease after the tsunami, Rwanda is using it for HIV, and Indonesia has started a pilot program to help speed up reporting of avian flu.

Co-founder and president Paul Meyer learned about wiring the developing world when he created an electronic refugee database in West Africa. Health expert Pamela Johnson, another founder, worked for the United Nations and the U.S. Agency for International Development. Anand Narasimhan, the third founding partner, was chief technologist for a messaging service. Their shared goals: saving the world and providing returns for investors.

THE PAYOFF After five years the Washington-based firm has nearly 100 employees and offices in the U.S., Peru, and India. Not all clients are government agencies. The Institute for OneWorld Health, a nonprofit pharmaceutical company, is using Voxiva to test a new drug for the sand-fly-borne disease leishmaniasis. And private medical clinics operating in far-flung low-tech places use it for collecting patient data.

The cost varies. Voxiva ties its fees to the number of people who will access the system and the time it takes to design and implement a project. The company also charges for tech support and maintenance. Though privately held Voxiva won't disclose revenue, company officials say it's growing by double-digit percentages each year. "We think we could be a $40 million company in four years," Meyer says.

THE OPPORTUNITY Tracking epidemics is just one emerging business. There is rising demand for long-distance learning systems (via phone or PC) that sharpen field workers' skills, and for systems that link big-city specialists with remote areas. "Quick and easy to implement, that's the way to do it," says Meyer. —Michal Lev-Ram