Communicable diseases such as flu, AIDS and SARS can become worldwide epidemics, killing millions. Containing such diseases is often seen as a medical problem, to be solved in a laboratory. But human factors such as war, poverty and politics can be just as important in determining how far and fast a disease will spread.

When public health officials wrestle with halting the spread of communicable diseases, they must also wrestle at the same time with poverty.

That's because more than half the people on Earth live in poverty, existing on less than $2 (US) per day.

Stewart Parkinson, Population Services International

Also, poverty and disease are linked in a vicious cycle, says Stewart Parkinson, of Population Services International, which works to improve health in developing countries. “A person with very little money can't necessarily choose where they live. They might have to live in a slum with open sewers. So they're much more susceptible to infection.

Often because they get repeated infections, their immune systems just get destroyed so they are much more susceptible to further infections. It's a condition where everything mounts together to create a perfect storm, and being poor means you cannot weather that storm.”

Dr. Joxel Garcia, Pan American Health Organization

In poor areas, health care efforts often fail, said Dr. Joxel Garcia, deputy director of the Pan American Health Organization due to lack of resources, “If you don't have primary care, if you don't have nurses in public health, if you don't have doctors, if you don't have the infrastructure to create systems related to health, then you cannot sustain the approach.”

Dr. Garcia says war also spreads disease because it often creates large populations of refugees. “And they're moving from one town to another, or one country to another (and) they may bring with them some prevalence of disease that may not be a disease that is present in that other country.”

Mr. Parkinson adds, “It's also probably no coincidence that the great Spanish flu epidemic of 1918 was associated with troop movements in Europe and especially afflicted the United States because that was the time of the U.S. involvement in the war, and the troop movements back and forth created a great vector for infection.”

The epidemic itself killed more people than died in the entire war -- an estimated 20 to 40 million people died from the epidemic.

Where there are soldiers and conflict, there are also prostitutes and rape. This has led to a rapid spread of AIDS in many war-torn African countries, say public health officials.

Dr. Joseph Malone, US Navy

Conflict impacts disease in other ways, too, said Dr. Joseph Malone, director of the U.S. Navy's program to track emerging global infections. “Basic services such as clean water, availability of food, are threatened when there's substantial conflict and generally the health care infrastructure and availability of medicines is generally reduced whenever there's conflict and even any supplies that might be available can be diverted to non-helpful uses.”

Sometimes politics can also interfere with combating disease. He says publicizing the crisis could mean a decline in tourism. “Many countries suffering from AIDS, for instance, don't want to publicize that there is a prevalence of HIV because they are afraid it will affect tourism, and therefore affect national revenue. So there are all kinds of considerations that mitigate against good public health and these are driven by political considerations and not health considerations.”

Mr. Parkinson says the impact of not acknowledging the crisis can be profound. “ If you don't acknowledge it, you don't tackle it. If you don't tackle it, it spreads.”

Local politics and corruption sometimes undermines efforts to fight disease. For example, The Global Fund to Fight Aids, Tuberculosis and Malaria, created by the Group of 8, the world's richest nations, recently suspended financial aid to Uganda when evidence surfaced that grant money was being mismanaged by a government agency.

Uganda has received $45 million, of $201 million, earmarked for the country over a two-year period. Health officials warn that the world is overdue for a deadly flu pandemic, similar to that of 1918. If that should happen, public health agencies will have to deal not only with medical issues, but also with the triple threat of poverty, war and politics.