17. Emerging Infections

Question 1

Definition: Emerging infectious diseases

Answer 1

infections that have recently appeared within a population or

those whose incidence or geographic range is rapidly increasing or threatens to increase in the near future.

Question 2

Pathway to Emerging Diseases

Answer 2

Pathogen introduced into vulnerable population

• 3 types if pathogens are introduced:

1. Previously undetected/unknown infectious agents (SARS)
2. Known agents spreading to new geographic locations or new populations (Lyme Disease)
3. Re-emergence of agents whose incidence had significantly declined in the past, but are now increasing (Measles)

Pathogen has the ability to spread from person to person and cause disease

Emerging disease may arise (usually with events)

Question 3

Factors Promoting Emergence/Re-emergence

Answer 3

1. Increased Susceptibility of the Human Host

• AIDS, cancer, other immunocompromising conditions
• Aging
• Nutritional deficiencies
• Chronic disease

2. Changes in Infectivity & Virulence of Pathogens

• Genetic changes in pathogens
• Antibiotic resistance
  
  • Used both therapeutically & prophylactically in humans
  • Used for growth promotion in animals

3. Increased Exposure to Infectious Agents

• Crowding and population growth
  
  • Accelerated growth began in the latter half of the 19th century. At the end of the 20th century, dramatic growth of large urban populations, but the necessary sanitary infrastructure to support this growth did not keep pace
• Speed and ease of travel
  
  • Can travel from one part of the globe to another during the incubation period of many infectious diseases
  • Facilitates the spread from one area to another. e.g. air travel effectively spreads new strains of influenza from one continent to another
• Changes in the Food Industry
  
  • Food is grown, processed, and delivered globally
  • Rise of agribusiness has created extremely large farm and processing facilities, cross contamination
• Changes in human behavior (sex, drug use, nutrition, health care)
• Increased contact with animals
• Climate change:
  
  • Global warming. increasing vector populations. in emergency situations, crowding in shelters and contaminated water sources
• Ecosystem changes (deforestation)
• Expansion of human populations into previously uninhabited areas. e.g. increasing lyme cases (could result from Tick hosts and ticks increasing geographic range; Longer seasonal activity; Increased human exposure)

Question 4

Severe Acute Respiratory Syndrome (SARS)

Answer 4

Example of a new, unknown infection

severe respiratory illness caused by a coronavirus (SARS-CoV) 冠状病毒

FIRST REPORTED in February in 2003 in China

Spread across the globe to 29 countries in North America, South America, Europe & Asia

Outbreak lasted 6 months; there have been no cases of SARS since 2004

Question 5

Zika Virus Disease

Answer 5

Example of an emerging disease that is NEW and SPREADING TO NEW GEOGRAPHIC LOCATIONS

Transmitted primarily through the bite of an infected mosquito

Zika virus was first discovered in 1947 (in Zika Forest in Uganda)

Prior to 2007, only 14 cases of Zika virus had been documented (Africa, Southeast Asia, Pacific Islands)

Question 6

Avian Influenza (Bird Flu) e.g. H5N1

Answer 6

Some types of avian influenza will not cause illness in birds while others can cause severe illness and death

Avian influenza can spread very quickly through bird flocks

Avian influenza viruses rarely infect people and cannot be spread easily from person to person

Sporadic infections of people have occurred, often causing severe disease and death (mortality high)

If avian flu mutated and was able to be transmitted easily from person to person, this could cause a pandemic