Infectious disease is one of the few genuine adventures left in the world. The dragons are all dead and the lance grows rusty in the chimney corner. ... About the only sporting proposition that remains unimpaired by the relentless domestication of a once free-living human species is the war against those ferocious little fellow creatures, which lurk in dark corners and stalk us in the bodies of rats, mice and all kinds of domestic animals; which fly and crawl with the insects, and waylay us in our food and drink and even in our love.
— Hans Zinsser
Rats, Lice and History (1935)
According to the National Institute of Allergy and Infectious Diseases (NIAID), infectious diseases remain a worldwide problem and leading causes of death for the following reasons:
1) emergence of new infectious diseases, examples HIV/AIDS, severe acute respiratory syndrome (SARS), Lyme borreliosis (Lyme disease)
2) re-emergence of old infectious diseases, examples, dengue, tuberculosis (TB), malaria
3) persistence of intractable infectious diseases, examples, Guillain-Barre syndrome (GBS), sexually transmitted diseases, Hepatitis B.
Emerging infectious diseases or more aptly, newly recognized diseases, and re-emerging infectious diseases, also known as previously recognized diseases have significantly increased in the last two decades. These infections include “deliberately emerging diseases,” namely, bioterrorism like anthrax.
Emerging diseases are not unique to modern life, but have appeared as notable epidemics, e.g., the Black Death (plague), smallpox, cholera, throughout recorded history. The common denominator among these emerging diseases over the ages is probably a set of circumstances that in combination contributed to or created the arrival of disease in abundance. In today’s complex world, a variety of factors continue to provide ample opportunities for disease emergence, and with international travel, present a case for the “perfect microbial storm.”
In addition to the increasing globalization with people, animals, and products traversing the world, other factors that give impetus to emerging and re-emerging diseases are: climate changes, war and civil unrest, poverty, urbanization, decreased vaccination compliance, and indiscriminate use of antimicrobials and pesticides among others. Also, impinging wildlife and the commingling of multiple species, particularly under stressful conditions, has facilitated the extended range of hosts of pathogens and promoted species jump.
About 60% of emerging human pathogens are zoonotic, meaning acquired from animals, and more than 70% of those are from wildlife. The zoonotic source is not limited to animal contact but more often arises from consumption of infected meat or animal products such as unpasteurized dairy products. Of major concern are vector-borne (e.g., ticks, mosquitoes) infections that can be transmitted from wildlife to domestic animals and to humans. Extremely large populations of deer in the eastern U.S. (for instance, Missouri) are a considerable factor in the emergence of new tick-borne diseases such as STARI, the putative etiological agent being the bacterium, Borrelia lonestari.
Virulence traits can also evolve resulting in wider transmission and altered pathogenicity. Gene mutation acted upon by natural selection, recombination, and other evolutionary forces serve to further variation in the genetic constitution of potential pathogens. High mutation rates are especially notable in viruses because of their relatively small genomes and short generation times.
Emerging and re-emerging diseases have been and probably will always be a challenge to human survival. To mitigate the “perfect microbial storm,” strategies are needed to increase and integrate disease surveillance systems from the local level to global networks. For instance, the U.S. Centers for Disease Control and Prevention (CDC) has initiated a program assigning veterinarians with human public health experience to international agencies and hotspots around the world. Monitoring and response activities to areas of concern should greatly impact the prevention of disease emergence.
References and Read-more-about-it:
1. Kuehn BM. Human, animal, ecosystem health all key to curbing emerging infectious diseases. JAMA. 2010 Jan 13; 303(2):117-8, 124.
2. Morens DM, Folkers GK, Fauci AS. Emerging infections: a perpetual challenge. Lancet Infect Dis. 2008 Nov; 8(11):710-9.
3. Cutler SJ, Fooks AR, van der Poel WH. Public health threat of new, reemerging, and neglected zoonoses in the industrialized world. Emerg Infect Dis. 2010 Jan;16(1):1-7.
4. Murphy FA. Emerging zoonoses: the challenge for public health and biodefense. Prev Vet Med. 2008 Sep 15;86(3-4):216-23.
5. Jones KE, Patel NG, Levy MA, Storeygard A, Balk D, Gittleman JL, Daszak P. Global trends in emerging infectious diseases. Nature. 2008 Feb 21;451(7181):990-3.
6. Lutz D. Emerging tick-borne diseases: a domestic ecological mystery. Washington University in St. Louis, Newsroom. Available at: http://news.wustl.edu/news/Pages/20343.aspx . Accessed April 8, 2010.
7. Emerging and Re-emerging Infectious Diseases. National Institute of Allergy and Infectious Diseases. Available at: http://www.niaid.nih.gov/topics/emerging/pages/introduction.aspx . Accessed April 8, 2010.