As part of their coursework for the Human Ecology course, first years in Columbia's Sustainable Development Ph.D. program (and a few select students from the SIPA Masters programs) were asked to put together reviews of recently active areas of the broad environment/development literature. Anna Tompsett, the course's TA and sometimes guest blogger on FE, has asked the students permission to share them with us, so over the next two weeks we'll be posting them, starting with today's on disease and development. Enjoy!
Disease and Development: Some Notable Recent Findings
One of the most formidable impediments to sustainable development in low-income countries is disease. In an attempt to offer a rough sketch of the current state of research in this realm, we canvassed the past year’s worth of issues of three major journals—Nature, Lancet, and the New England Journal of Medicine—and picked out six articles that we found particularly relevant to disease, development, and global health policy.
We were especially interested in health issues that rate among the World Health Organization’s leading causes of death and global burden of disease in developing countries. (Global burden of disease measures years of healthy life lost to disability as well as death.) We selected studies based on the number of people that could benefit from the findings, out-of-sample validity (in the case of experimental studies), socioeconomic aspects, and potential policy implications.
It’s no surprise that several of the studies deal with malaria and HIV, two of the top five killers in low-income countries. Two focus on the preventive aspect of disease control—one testing a promising malaria vaccine and another exploring a new use for antiretroviral HIV drugs. Two other articles—one on malaria mosquito genes and the other surveying evidence from cholera pandemics—deal with the phylogeny of vectors of transmission. The remaining two are policy-focused, one looking at the impact of disease in youth around the world (including regional, income and gender gaps) and the other at equity in maternal care interventions. This is appropriate, given that youth, poverty, and gender equity are key development issues in low-income countries. They are also, of course, intertwined. And if certain theorists are right, studies that point the way toward improved health conditions might ultimately help address these broader development concerns as well.
One of the most noteworthy global health articles of the past year comes from a November 2011 issue of the New England Journal of Medicine, which published the results of the world’s first large-scale trial of a malaria vaccine, financed by the Bill & Melinda Gates Foundation. The vaccine contains an engineered protein that blocks the parasite's ability to infect the liver and mature there. Data from 6,000 children in seven African countries show an efficacy rate of 55.8% (97.5% CI, 50.6 to 60.4) in the 14 months after the first dose of vaccine. The efficacy rate for severe malaria was 47.3% (95% CI, 22.4 to 64.2). While more study is needed, the results are remarkable given that there has never been a successful vaccine against a parasite. One drawback of the treatment is that it is likely to be more expensive than other preventive methods, such as insecticide-treated bed nets, which also offer partial protection.
In a second fascinating malaria study, from the May 2011 Nature, Windbichler et al. explore the potential of a quite different means of malaria control. Past research has suggested the idea of genetically manipulating malaria mosquitos so that they can’t serve as vectors for the disease. The problem is how to propagate lab-altered genes in the wild. This paper tests a way to do just that. The researchers show how a “selfish” synthetic homing endonuclease gene can work its way into half of a mosquito population in just a handful of generations of the malaria mosquito Anopheles gambiae. This new mechanism could represent a step from the genetic engineering of individuals to the genetic engineering of populations.
(It’s worth briefly noting here a third article from the October 2011 PNAS by Adjalley et al. [a team that includes our colleague Geoff] that attacks malaria transmission from yet another angle: the potential for antimalarial drugs to inhibit transmission from infected humans back to mosquitos.)
Moving back to clinical trials, an August 2011 New England Journal of Medicine article by Cohen et al. shows the potential for early antiretroviral drugs (ARVs), used to treat the HIV-infected, to also cut transmission rates. Across nine countries, the researchers studied 1,763 couples (97% of them heterosexual) in which one partner was HIV-1–positive and the other HIV-1–negative. ARVs were administered to the infected partners even though they were not showing actual symptoms of AIDS and therefore would not normally have been treated. After six years, the results showed that only 28 individuals were infected by their respective partner. Of those, only one occurred in the early-treatment group. If these types of results are borne out by future studies, the policy impacts could be profound.
Cholera is not one of the WHO’s top ten causes of death, and it was all but eliminated in developed countries over a century ago. Yet recent outbreaks in Zimbabwe and Haiti serve as a reminder of the threat it poses in crowded regions with water and sanitation problems. In the September 2011 Nature, Mutreja et al. make an interesting contribution to our understanding of cholera’s evolution and spread by tracing how the seventh (and current) pandemic has spread from the Bay of Bengal in at least three independent yet overlapping waves. They also identify multiple events in which the disease has been transmitted across continents. Particularly timely in light of the recent confirmation that cholera was introduced to Haiti by Nepalese UN peacekeepers, these findings shed light on the mechanisms by which diseases long vanquished in the industrialized world continue to evolve and spread around the globe.
Such regional disparities are reinforced by a June 2011 study in Lancet, in which Gore et al. use data from the WHO’s global burden of disease reports to focus specifically on disease in young people, aged 10 to 24. This group, which comprises 27% of the world’s population and is concentrated in developing countries, has received less attention because it is assumed to be healthy. But it has outsize implications for future generations’ health and socioeconomic outcomes. The study’s most interesting findings highlight regional disparities and gender gaps in disease burden. Not surprisingly, it’s far more prevalent in low-income regions, led by Africa, whose youth lose two to five times as many healthy life-years as those in high-income countries. By far the leading cause worldwide is neuropsychiatric disorders (45%), followed distantly by injuries (11%) and infectious and parasitic diseases (10%). Among the most affected groups are girls aged 15 to 19, who lose 12-15% more healthy life-years than boys of the same age across regions. In all, the study finds that youth aged 10 to 24 account for 15.5 percent of the total worldwide disease burden, making a convincing case that young people’s health issues merit more attention in public health policy.
Another macro-scale study in Lancet comes from Barros et al. (2012) who track progress toward attaining Millennium Development Goals four (reduce child mortality) and five (improve maternal health) in 54 countries. Whereas many studies focus on inequalities between countries in access to maternal and child health services, this one looks at inequality within countries. The findings could be informative to policy-makers looking at where to direct resources. For instance, it finds that an average of 84% of women in the richest quintile of each country have access to skilled birth attendants, compared to just 32% in the poorest quintile. Among the countries studied, higher inequality was found in Chad, Nigeria, Somalia, Ethiopia, Lagos, and Niger. Of particular relevance to policy-makers, services provided through community-based interventions were more equitably accessed than those provided at health facilities.
Sophie H Adjalley et al., “Quantitative assessment of Plasmodium falciparum sexual development reveals potent transmission-blocking activity by methylene blue,” Proceedings of the National Academy of Sciences 2011; 108 (47): E1214–E1223
Aluísio JD Barros et al., “Equity in maternal, newborn, and child health interventions in Countdown to 2015: a retrospective review of survey data from 54 countries”, Lancet 2012; 379: 1225–1233
Myron S. Cohen et al. for the HPTN 052 Study Team, “Prevention of HIV-1 Infection with Early Antiretroviral Therapy.” N Engl J Med 2011; 365: 493-505
Fiona M Gore et al., “Global burden of disease in young people aged 10–24 years: a systematic analysis.” Lancet 2011; 377: 2093–2102
Ankur Mutreja et al., “Evidence for several waves of global transmission in the seventh cholera pandemic,” Nature 2011; 477: 462-65
The RTS, S Clinical Trials Partnership, “First Results of Phase 3 Trial of RTS,S/AS01 Malaria Vaccine in African Children,” N. Engl. J. Med. 2011; 365: 1863-1875
Nikolia Windbichler et al., “A synthetic homing endonuclease-based gene drive system in the human malaria mosquito,” Nature 2011; 473: 212-215