In an era when the marvels of modern medicine continue to inspire and awe, focusing on the threat to health posed by microorganisms might seem somewhat anachronistic. It shouldn’t. Arguably among humankind’s oldest foes, pathogenic microorganisms are far from being defeated. Despite dramatic advances during the twentieth century in the fight against infectious diseases that have led to notable successes – none more spectacular than the global eradication of smallpox – pathogenic microorganisms continue to exert a huge toll, both in terms of mortality and morbidity.
Even though only a small fraction of the virtually countless number of microorganisms cause disease in humans, the WHO estimated that infectious diseases caused 14.7 million deaths in 2001, accounting for 26% of global mortality. Infectious diseases are still the leading cause of death in low-income countries. Interestingly, five diseases account for nearly 80% of the total global infectious disease burden. These include: AIDS, tuberculosis (TB), malaria, diarrhoeal disease, and respiratory infections.
Infectious diseases also leave a horrific legacy of severe and permanent disability and deformity – impaired childhood growth and cognitive development, mental retardation, blindness, and disfigurement, to list a few. Too often, these are the consequences of neglected diseases – diseases confined largely to the poorest and remotest parts of the world, although the sequelae of bacterial meningitis and the measles virus can be equally devastating and are still observed in many developed countries. Interestingly, links between infectious agents and various types of cancer have blurred the distinction between infectious and non-infectious diseases. The International Agency for Research on Cancer has determined that infections with several specific viruses, bacteria and parasites increase the risk of cancers of the cervix, liver, urinary bladder and stomach and can also cause acute leukaemia.
To date, smallpox remains the only infectious disease affecting humans to have been completely eradicated across the globe. Hopes of eradicating other diseases such as polio have yet to be realized, though significant progress has been made. Much of the success against infectious diseases can be attributed to three main pillars: 1) basic public health measures such as improved hygiene, sanitation and housing; 2) the development of antimicrobial drugs; and 3) the expansion of vaccination and disease surveillance programmes. These three areas still comprise the basis of contemporary approaches against infectious diseases, though significant obstacles and challenges remain.
“Infectious agents take advantage of every opportunity to multiply, mutate, migrate, adapt to new hosts, and evolve to resist drugs” – WHO
Emerging antimicrobial resistance is a major concern across the globe and has even prompted speculation of a ‘post-antibiotic era’. AIDS continues to have a devastating impact in sub-Saharan Africa and the goal of universal access to antiretroviral treatment is yet to be met. Multidrug resistant TB is on the increase in many countries and the exponential rise in international travel has exacerbated fears about a new global influenza epidemic. There is growing worry that climate change could facilitate the spread of vector borne and waterborne infectious diseases. Several infectious diseases have already spread to new continents. For example, West Nile fever is now firmly established in North America. In addition, conflict and natural disasters provide fertile conditions for the spread of infectious diseases, while rising economic inequality hinders efforts at controlling many of the most preventable infectious diseases. Despite the worrying trends described above, all is not lost. The possibility of a vaccine for malaria is inching ever closer to becoming a reality and new compounds are being developed to address drug resistance and neglected diseases, often as a result of public-private initiatives and social responsibility programmes by big pharma.
The fight against infectious diseases may not be glamorous or represent the lure of massive profits. Nevertheless, there is absolutely no room for complacency. As the WHO has cautioned, “The world must never relax its guard against a microscopic adversary that changes and adapts so rapidly and has the advantages of stealth and surprise on its side.”1 Healthcare practitioners, policy makers and governments would do well to take these words to heed.
 World Health Organization Communicable Diseases 2002: Global defence against the infectious disease threat. Geneva: 2003.
 World Health Organization. The global burden of disease: 2004 update. 2004. Retrieved 02/05/2012 from www.who.int/healthinfo/global_burden_disease/2004_report_update/en/index.html
 Global Polio Eradication Initiative. 2012. Retrieved 02/05/2012 from www.polioeradication.org
 Shuman E.K. Global climate change and infectious diseases. N Engl J Med 2010; 362:1061-1063.