Stanford Assistant Professor of Medicine Marcella Alsan had always wondered why the mineral-rich African continent — with so many natural resources, diverse climates and arable land — remains so poor.

She launched into extensive research while working on her PhD in economics and has now come up with an intriguing theory: A pesky parasite prevented many precolonial Africans from adopting progressive agricultural methods, a phenomenon that still impacts parts of the continent today.

The tsetse fly has plagued Africa for centuries — having sent millions of people into the confusing stupor of sleeping sickness, while killing the cows and other livestock needed to plough their fields and feed their families.

Alsan writes in a paper published in The American Economic Review that the tsetse fly, which today is found only in Africa, drove precolonial Africans to use slaves instead of domesticated animals for agriculture. This limited their crop yields and the ability to transport goods.

“Communicable disease has often been explored as a cause of Africa’s underdevelopment,” writes Alsan, who is the only infectious-disease trained economist in the United States and a core faculty member of the Center for Health Policy/Center for Primary Care and Outcomes Research.

“Although the literature has investigated the role of human pathogens on economic performance, it is largely silent on the impact of veterinary disease,” she notes. “This is peculiar, given the role that livestock played in agriculture and as a form of transport throughout history.”

The economic impact caused by the parasite of the trypanosome vector is estimated to be as much as $4 billion a year. The Food and Agricultural Organization estimates 37 African countries are affected by the tsetse fly and that its trypanosomosis kills around 3 million livestock per year.

The World Health Organization reports that the sleeping sickness delivered by the tsetse bite in humans is hard to diagnose and treat. Some 60 million people were once at risk with an estimated 300,000 new cases each year.

Sleeping sickness causes headaches, fatigue and weight loss; confusion and personality disorders occur as the illness progresses. If left untreated, people typically die after several years of infection.

Fortunately, sustained control efforts have reduced the number of new cases, dropping below 10,000 annual cases annual for the first time in 50 years in 2009. This is in part to an eradication effort using radiation sterilization techniques adopted by the International Atomic Energy Agency.

But the lingering economic impact from the tsetse has been monumental.

For her research, Alsan used geospatial-mapping software to mine data gathered by missionaries and anthropologists in the 1800s. She found that farming methods used in other developing regions of the world — such as the agricultural revolution in England — were not widely adopted in Africa.

“Livestock were really important for development in many places, such as Europe and North America and in some parts of Africa like the highlands of Ethiopia,” Alsan said in an interview. “They pulled plows and carried carts, their manure was used for fertilizer. They helped transport people and goods across land.”

She found that ethnic groups inhabiting tsetse-prone African regions were less likely to use domesticated animals to plow their fields, turning instead to the slash-and-burn technique still used in many parts of the continent today.

The same people were also less likely to be politically centralized, due to lack of transportation by livestock, and had a lower population density.

“These correlations are not found in the tropics outside of Africa, where the fly does not exist,” she writes. “The evidence suggests current economic performance is affected by the tsetse through the channel of precolonial political centralization.”

The FAO estimates that the tsetse fly infects nearly 10 million square kilometers in sub-Saharan Africa. Much of this large area is fertile but left uncultivated, a so-called green desert not used by humans and cattle. Most of the tsetse-infected countries are poor, debt-ridden and underdeveloped.

And this is what triggered Alsan’s interest in the tsetse fly: How its deadly bite has altered the socioeconomic impact of a continent.

“I am an infectious disease doctor, so part of my work is looking at neglected infectious diseases much like this one,” she said. “And it is

incredibly important to shine light on issues that are Africa-specific and therefore may not garner as much attention as those economic and medical issues that affect wealthier regions of the world.” 

Alsan, who sees patients at the Stanford University Medical Center and is an investigator at the VA Palo Alto Health Care Systems, is now launching work in India, Ghana and the San Francisco Bay Area. She hopes to better understand how socioeconomic and health disparities interact, and the important role that history plays in understanding those interactions.

An aspirin a day may keep heart attacks and cancer away, according to new recommendations by a medical panel. But that doesn’t mean everyone should run to the drugstore without talking to his or her doctor first.

The U.S. Preventive Services Task Force, an independent panel of medical experts from around the nation, said Monday that taking aspirin can help 50- to 59-year-olds who are at increased risk of cardiovascular disease prevent heart attacks and strokes.

The panel also said that taking aspirin for at least five to 10 years could help prevent colorectal cancer. Individuals 60 to 69 may also benefit from aspirin, but the benefit is smaller than in people 50 to 59.

Because heart attacks are caused by blood clots in the arteries, aspirin can help prevent heart attacks and strokes that are caused by these clots.

It is the first time the task force has included both the evidence on preventing cardiovascular disease and colorectal cancer in developing recommendations on aspirin use in patients at high risk of cardiovascular disease.

Stanford Professor of Medicine Douglas K. Owens, a member of the task force, cautioned the new recommendations come with a caveat: a daily dose of aspirin can cause stomach and brain bleeds. People with stomach and liver problems, bleeding disorders or who are taking blood thinners, are at greater risk of experiencing the side effects of aspirin.

And, he emphasized, the new recommendations are for older adults and those with substantially elevated risk of cardiovascular disease.

Douglas K. Owens

“It is nuanced,” said Owens, director of the Center for Health Policy/Center for Primary Care and Outcomes Research. “Our recommendation applies to people who are at increased risk of heart disease and who do not have increased risk of bleeding complications.

He added that those risk assessments by physicians are extremely important.

The task force, an independent panel of experts in prevention and primary care appointed by the Department of Health and Human Services, said a “pragmatic approach” consistent with the evidence is to prescribe 81mg per day, or one baby aspirin, which is the most commonly prescribed dose.

“Each person has only one decision to make — whether or not to take aspirin for prevention,” said Owens. “To help individuals and their clinicians make this decision, the task force integrated the evidence about the use of aspirin to prevent cardiovascular disease and colorectal cancer into one recommendation on the use of aspirin.”

But the task for also concluded that it doesn’t have enough to current evidence to assess the balance of benefits and harms of aspirin use in adults younger than age 50 and those older than 70.

The draft guidelines, which are open for public comment on the task force website, have provoked criticism by some cardiologists and physicians who are concerned that healthy Americans who start taking aspirin on a daily basis could expose themselves to the drug’s negative side effects, such as stomach bleeding and hemorrhagic strokes.

And the Food and Drug Administration wrote last year that it had reviewed studies on the use of aspirin for primary prevention of a heart attack “and did not find sufficient support for the use of aspirin.” The agency did say, however, it was awaiting results of additional clinical trials.

Owens said that while the FDA looked at aspirin to prevent an initial heart attack or stroke, “the task force looked at evidence for the broader benefits of aspirin to reduce heart attacks, strokes and colorectal cancer.”

In addition, Owens said, the evidence review for the task force included a wide variety of research, including meta-analyses, which may not have been included in the FDA review. The task force commissioned three systematic reviews, he said, as well as a sophisticated modeling study to help integrate the evidence about cardiovascular disease and cancer.

So what’s the bottom line? Consult your physician.

Because, as task force vice chair Dr. Kirsten Bibbins-Domingo said, “Taking aspirin is easy, but deciding whether or not to take aspirin for prevention is complex.”

Listen to Owens' interview on NPR's Morning Edition.

Stanford health policy expert Karen Eggleston has been appointed as a senior fellow at the Freeman Spogli Institute for International Studies (FSI), effective Sept. 1, 2015, on a continuing term.

Eggleston, who leads the Asia Health Policy Program at Stanford’s Walter H. Shorenstein Asia Pacific Research Center (APARC), is a recognized authority on comparative health policy and the economics of the demographic transition in Asia, especially China.

“FSI is delighted that Karen’s impressive scholarship and strong program leadership has earned her a promotion to the position of senior fellow,” FSI director Michael McFaul said. “It’s a well-deserved honor and the institute looks forward to working with her for many years to come.”

Trained as an economist, Eggleston first came to Stanford as a center fellow in 2007 to lead a program on Asian health policy in comparative perspective. Since then, the program has grown into an innovative hub of research, training and policy outreach.

Eggleston’s new appointment also carries membership in the University’s Academic Council and status as a principal investigator for research projects. Her research areas include population aging, healthcare productivity (“value for money”), insurance and payment incentives, and health system governance. Currently, she is leading a comparative study of “value for money” in diabetes care, with patient-level data from Japan, Hong Kong, Taiwan and China.

“Karen has been a pioneering force at our center, and in the area of Asia health policy,” said Gi-Wook Shin, director of Shorenstein APARC. “Her strong record of scholarly accomplishment has enriched the intellectual life at Stanford, and we look forward to continuing to support her research and teaching endeavors.”

Eggleston has led many crosscutting initiatives at Stanford including the organization of multiple international conferences in the United States and abroad. This past year, she co-organized a conference on China’s health reforms and primary care, held at the Stanford Center at Peking University.

She has testified on China’s health system before a U.S. congressional commission, and in 2014, spoke at the Jackson Hole Symposium of the Federal Reserve Bank.

Eggleston teaches students through Stanford’s East Asian Studies program and is an active author/editor of books and publications, including a special issue of the Journal of the Economics of Ageing (2014) focused on the economic implications of population aging in China and India. She expects to release two edited volumes through Shorenstein APARC’s publishing program shortly.

Eggleston is also a faculty research fellow at the National Bureau of Economic Research as well as affiliated with Stanford’s Center for Health Policy / Center for Primary Care and Outcomes Research.

Dr. Jay Bhattacharya, a professor of Medicine and a CHP/PCOR core faculty member, speaks about the Center on the Demography and Economics of Health and Aging (CDEHA). He discusses how the center's research promotes a better understanding of the health needs of aging populations around the world.  As societies age, it is important for people and governments to understand how to cope with the economic and health consequences of having a larger elderly population.  CDEHA's Japanese Future Elderly Model simulates changes in the aging population of Japan and helps researchers understand what changes healthcare and governments can make to prepare for aging populations.