Module 7: Novel and Emerging Diseases Originating in Developing Countries

Introduction

In the past, there have been many examples of new and virulent pathogens invading an immunologically naïve population and causing a devastating epidemic. Historic literature dating back hundreds of years demonstrates the terror that unknown pathogens can create. In the cases of the Plague or the Spanish flu of 1918, fear can spread as quickly as the disease.(1) In an age in which new technology helps us understand and investigate new and emerging diseases, disease surveillance is imperative in preventing future pandemics. Surveillance of novel diseases improves our knowledge of the disease, facilitating prompt implementation of control measures. Emerging infections are defined as those that have not previously occurred in human hosts, have occurred in humans before but only infected small/isolated populations, or have occurred throughout time but have only recently been recognized as distinct diseases.(2) Emerging diseases are often borne of environmental changes, natural evolution of the pathogen, antibiotic resistance, vector resistance to pesticides, and decreasing vaccination rates that can lead to a resurgence of previously controlled or eliminated diseases.(3) Antibiotic resistance is a huge problem in the global fight against tuberculosis, and has become an issue when treating infections in developed countries as well. The figure below demonstrates how antibiotic resistance occurs.

Description: http://images.medicinenet.com/images/Government/geneTransfer.gif

 

 

 

 

 

 

 

http://www.medicinenet.com/antibiotic_resistance/page3.htm

Categories of Priority Pathogens

The CDC has created a system for classifying emerging pathogens. Priority pathogens and biological agents have been divided into three categories – Category A, Category B, and Category C – based on their potential to cause widespread public health emergencies.(4)

Category A pathogens are the highest priority pathogens. According to the CDC, their surveillance is considered the most important due to the following characteristics:(5)

Category A Agents/Diseases include:(6)

Category B pathogens are the second highest priority for public health agencies. The CDC says that Category B pathogens:(7)

Category B agents and pathogens include:(8)

Category C agents are emerging pathogens that can be altered in the laboratory to be effective biological weapons in the future because they possess the following traits:(9)

Category C agents include:(10)

This module presents three novel or emerging diseases that are of particular public health importance and require continued surveillance. All three of these examples are zoonotic infections. According to the CDC, approximately 75% of emerging infectious diseases and 60% of all pathogens that infect humans have originated in animals.(11)

Influenza (Category C Pathogen)

Influenza is a virus that requires constant surveillance because it is forever evolving and creating new strains. The RNA virus evolves in two ways – antigenic drift and antigenic shift – that change the virus’ primary surface antigens (hemagglutinin [HA] and neuraminidase [NA]). HA and NA surface antigens are important because they allow the influenza virus to both infiltrate and leave host cells.(12) Influenza often goes by different names, such as H5N1 or H1N1, as these correspond to the type of HA and NA antigens expressed by the virus.

Description: http://micro.magnet.fsu.edu/cells/viruses/images/influenzafigure1.jpg

An influenza virus molecule (http://micro.magnet.fsu.edu/cells/viruses/influenzavirus.html)

The changing of antigens helps the virus evade an immune system that has learned (naturally or artificially via vaccination) how to respond to prior strains.(13) Antigenic drift (in Influenza types A and B) occurs during the virus’ replication process in host cells, when translation and transcription errors result in minor alterations in the surface antigens of the virus.(14) Antigenic shift, on the other hand, which occurs in Influenza A, takes place when gene segments mix (gene re-assortment) because multiple strains of different origins infect the same host cell, causing major changes in antigens.(15) Antigenic shift has the potential to create entirely new viruses that humans are underprepared to deal with. Genetic re-assortment can occur when multiple types of the influenza virus infect one animal, which serves as a “mixing vessel” that churns out novel strains of influenza.(16) Charts that explain antigenic shift and drift are included below. Surveillance of novel strains of influenza is critical in creating vaccinations to prevent future pandemics. Influenza’s main reservoirs are birds (avian type), pigs (swine type), and humans. Data collection about influenza strains including their ancestors, virulence, and ability to transmit between people is pertinent to global health security.(17)

Description: http://upload.wikimedia.org/wikipedia/commons/thumb/5/5e/AntigenicShift_HiRes_vector.svg/300px-AntigenicShift_HiRes_vector.svg.pngDescription: http://www.globalsecurity.org/security/ops/images/antigenic-drift.jpg

http://www.globalsecurity.org/security/ops/hsc-scen-3_flu-antigenic.htm

Ebola (Category A Pathogen)

Description: http://students.cis.uab.edu/sajayi11/ebola_1.jpg

 

 

 

 

 

 

 

 

 

http://foxfromzim.files.wordpress.com/2010/05/ebola.jpg

First recognized in 1976, Ebola hemorrhagic fever is a virulent RNA virus that infects humans and non-human primates. Ebola virus can cause fever, headache, sore throat, weakness, diarrhea, stomach pain, and internal and external bleeding.(18) Ebola is in need of further surveillance because it is thought to be zoonotic, yet its natural reservoir is unknown.(19) This is troubling because without an idea of how the disease enters the population, we cannot efficiently prevent outbreaks. Transmission, which occurs mostly in hospitals, is possible between humans via blood or secretions and contaminated fomites.(20) Surveillance and correct diagnosis are important in preventing transmission. Prevention, however, remains challenging because some symptoms manifest in ways that do not distinguish Ebola from common infections. Because of its very high case fatality rate (50-90%) and the rarity with which it is found, Ebola is difficult to diagnose, and is often considered a potential biological weapon, making its surveillance an even greater priority for developed nations.(21)

Nipah Virus (Category C Pathogen)

The Nipah virus is an emerging virus that causes the rapid onset of acute encephalitis and (in some cases) respiratory illness. Its case fatality rate can be as high as 33% to 75%.(22) Symptoms include fever, headache, dizziness, and loss of consciousness. Some survivors (20%) have long-lasting neurological problems.(23) The first reported outbreaks in 1998 were in Malaysia and Singapore. The virus primarily infected men in the pig/pork industry, indicating the possibility of pig to human transmission of the virus.(24) The virus has been implicated in many outbreaks since that time in Bangladesh and India.(25)

Description: http://3.bp.blogspot.com/-0jq--sA5g5Y/Tn3AmkeeF7I/AAAAAAAACIw/WcVHZPRcS2M/s1600/Pteropus+tonganus.jpg

The natural reservoir of the Nipah virus was recently discovered to be the Pteropus genus fruit bat. Transmission between bat and humans often occurs when the bat contaminates date palm syrup that is not boiled before it is consumed by villagers.(26) Surveillance of the Nipah virus is important for implementation of control efforts, and in tracking changes in the disease. Some countries are watching changing behavior of fruit bats in hopes of predicting future epidemics.(27) Recent investigations into other novel diseases have focused on bats as potential reservoirs, as they were in the case of Nipah virus.

Go To Module 8: Organizations Working to Enhance Surveillance in Developing Countries >>

Footnotes

(1) Hellerman, C. (2009, April 30). Scientists dig for lessons from past pandemics. Retrieved May 30, 2012.

(2) Biological Sciences Curriculum Study. (2007). Understanding Emerging and Re-emerging Infectious Diseases [NIH Curriculum Supplement Series [Internet]]. Retrieved May 30, 2012, from National Institutes of Health (US).

(3) Ibid.

(4) Biodefense and Emerging Infectious Diseases. (2012, February 27). Category A, B, and C Priority Pathogens. Retrieved May 30, 2012, from National Institute of Allergy and Infectious Diseases.

(5) Emergency Preparedness and Response. (n.d.). Bioterrorism Agents/Diseases. Retrieved May 30, 2012, from Centers for Disease Control and Prevention.

(6) Ibid.

(7) Ibid.

(8) Biodefense and Emerging Infectious Diseases. (2012, February 27). Category A, B, and C Priority Pathogens. Retrieved May 30, 2012, from National Institute of Allergy and Infectious Diseases.

(9) Emergency Preparedness and Response. (n.d.). Bioterrorism Agents/Diseases. Retrieved May 30, 2012, from Centers for Disease Control and Prevention.

(10) Biodefense and Emerging Infectious Diseases. (2012, February 27). Category A, B, and C Priority Pathogens. Retrieved May 30, 2012, from National Institute of Allergy and Infectious Diseases.

(11)National Center for Emerging and Zoonotic Infectious Diseases. (2012, May 17). Retrieved May 30, 2012, from Centers for Disease Control and Prevention.

(12) Webster, R. G. (1998, July). Influenza: An Emerging Disease. Retrieved May 30, 2012, from Emerging Infectious Diseases Journal, CDC.

(13)Influenza Viruses. (2005, November 18). Retrieved May 30, 2012, from Centers for Disease Control and Prevention.

(14) Webster, R. G. (1998, July). Influenza: An Emerging Disease. Retrieved May 30, 2012, from Emerging Infectious Diseases Journal, CDC.

(15)Influenza Viruses. (2005, November 18). Retrieved May 30, 2012, from Centers for Disease Control and Prevention.

(16) Webster, R. G. (1998, July). Influenza: An Emerging Disease. Retrieved May 30, 2012, from Emerging Infectious Diseases Journal, CDC.

(17)Influenza Viruses. (2005, November 18). Retrieved May 30, 2012, from Centers for Disease Control and Prevention.

(18)Ebola Hemorrhagic Fever Information Packet. (2009). Retrieved May 30, 2012, from Centers for Disease Control and Prevention.

(19) Ibid.

(20) Ibid.

(21) Weapons of Mass Destruction (WMD). (2011). Ebola Haemorrhagic Fever. Retrieved May 30, 2012, from GlobalSecurity.org.

(22)Nipah Virus Infection. (2007, November 9). Retrieved May 30, 2012, from The Center for Food Security and Public Health, Iowa State University.

(23)Nipah Virus. (2009, July). Retrieved May 30, 2012, from World Health Organization.

(24)Nipah Virus Infection. (2007, November 9). Retrieved May 30, 2012, from The Center for Food Security and Public Health, Iowa State University.

(25) Ibid.

(26)Nipah Virus. (2009, July). Retrieved May 30, 2012, from World Health Organization.

(27) Ibid.