Major Infectious Diseases

Since the publication of the second edition of Disease Control Priorities in 2006, we have experienced some of the most substantial progress in infectious disease–caused mortality and morbidity. The number of annual deaths attributable to human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS) declined 50 percent between 2004 and 2015, thanks to an unprecedented expansion of life-saving antiretroviral therapy to over 18 million people (UNAIDS 2016); since 2006, mother-to-child transmission of HIV has been reduced to low levels, even in generalized epidemic settings (AVERT 2017). Similarly, fewer children and adults die from malaria, diarrheal diseases, and lower respiratory infections. Two infectious diseases are close to eradication: polio and dracunculiasis (Guinea worm disease).

 

This third edition of the Disease Control Priorities (DCP3) comes at a pivotal moment for infectious disease control and research. Its chapters clearly demonstrate that, despite the remarkable progress, infectious diseases remain a major threat to health worldwide—particularly in South Asia and Sub-Saharan Africa—but that an increasing range of highly cost effective interventions is available.

 

As this volume amply illustrates, innovations in the prevention, diagnosis, and treatment of infectious diseases have been impressive. They include preexposure prophylaxis (PrEP) to prevent HIV infection, new forms of computer-based education for clinicians to manage sexually transmitted infections, HPV vaccines to prevent cervical cancer, and a cure for hepatitis C. The new attention to viral hepatitis in this volume is most welcome, as greatly improved control is now technically feasible—although the history of tuberculosis illustrates that a cure alone is insufficient to bring a disease under control. Much of the progress is due to political and technical leadership, greatly increased funding, and improved delivery of interventions through health systems and other sectors. Community engagement is the key to success in many cases; a community buy-in to very simple, non-technological prevention mechanisms was instrumental in the sharp decline in dracunculiasis cases, from 130,000 in 2000 to only 22 in 2015 and 0 cases at the time of writing in 2017. However, dogs, which act as alternative hosts for the worm, present a threat to total eradication and remind us of the importance of a “One Health” approach. 

 

At the same time, several epidemics and new pathogens have emerged, including the swine flu (H1N1) pandemic; the Middle East Respiratory Syndrome (MERS); the largest Ebola outbreak ever known in the West African region where it had never caused an outbreak; and an epidemic of Zika and associated neurological disorders. In particular, the collective failure to respond to the Ebola outbreak in a timely and coordinated fashion before it spiraled out of control—infecting over 28,000 people and causing over 11,000 deaths—was a wake-up call for the world. The disastrous impact of the Ebola epidemic prompted an urgent rethinking of how governments, nongovernmental organizations, and international organizations can better work to contain emerging disease threats in an increasingly interconnected world.

 

It is, however, noteworthy that almost as many people in the three Ebola-affected West African countries died from the disease’s disruption on increasing mortality from HIV/AIDS, tuberculosis, and malaria as from Ebola itself (Parpia and others 2016). These three diseases, as well as diarrheal diseases and lower respiratory infections, continue to exact a heavy burden, particularly in Sub-Saharan Africa, where infectious diseases remain the leading cause of death. In 2015, over 1.8 million people worldwide died from tuberculosis (including 0.4 million among people with HIV) (WHO 2017); 1.1 million people from AIDS (UNAIDS 2016); and an estimated 429,000 people died from malaria (WHO 2016). In spite of real achievements in improved access to HIV treatment, over 2 million new infections occur each year, with hardly any decline in new infections over the past five years, and several subpopulations continue to be heavily affected. A critical review of current HIV strategies may be needed to achieve the United Nations goals of ending the AIDS epidemic. Lower respiratory infections remain a major persistent cause of death in children.

 

Many of these infectious diseases have sophisticated vaccines, diagnostics, and therapeutics available, but political, economic, and social factors limit the extent to which populations can benefit. Furthermore, in a world of growing resistance to antimicrobials and drug-resistant infections, we need to continue to develop innovations in biomedicine. We also need to improve incentives for rational antibiotic use, antimicrobial stewardship, and increased acceptance of the importance of prevention to avoid infection.

 

The global health agenda is an increasingly crowded space, and the cost-effectiveness of interventions is under growing scrutiny. While there is more information than ever regarding the cost-effectiveness of different interventions in a growing spectrum of contexts, hard choices remain in terms of allocating scarce funding to infectious diseases, especially in light of the complexities of fragile health systems, comorbidities with other infections and NCDs, structural factors that can undermine disease prevention, and treatment programs. One particularly valuable facet of DCP3 is that it demonstrates that some of the most effective steps we can take to reduce the burden of infections are not necessarily expensive, as exemplified by the low cost per disability-adjusted life year averted of condoms for female sex workers or insecticide-treated bednets. Often, the key is not just more, but smarter, investment, for example, better integration of services, strong community engagement, and targeted interventions based on the population most in need in specific locations. In addition to cost-effectiveness, key questions are whether people will accept and use the interventions, whether the interventions are affordable and work in various parts of the real world, and what the best way is to deliver them.

 

If we are to reach the ambitious targets under the Sustainable Development Goals, we must focus not only on delivery of innovation but also on “innovation of delivery.” One example might be new systems of community-based treatment for tuberculosis to minimize transmission in health care settings. DCP3 helps us to think about improving health care delivery models through its unique focus on packages of interventions, and on the interrelationships among different kinds of interventions, at both the policy level and in terms of the outcomes across populations.

 

DCP3 is to be lauded for its focus on equity, recognizing that cost-effective intervention is not costeffective if the financial burden falls on the poor. With this DCP3 volume on major infectious diseases, we have a highly pragmatic addition to the literature that will help policy makers across the world make smarter decisions to improve health sustainably and equitably in the ongoing fight against infectious disease threats, old and new.

 

Peter Piot, PhD

Director, London School of Hygiene & Tropical Medicine

London, United Kingdom

 

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