Emerging Infectious Diseases - University of South...

1

Emerging Infectious DiseasesHSC4933

Emerging Infectious Diseases

Emerging Disease Trends

Presented by Christy Ottendorfer, PhD, MSPH

"The only way to keep your health is to eat what you

don't want, drink what you don't like,

and do what you'd rather not."

- Mark TwainHSC4933. Emerging Infectious Diseases

Learning Objectives

• Distinguish between viruses, bacteria & parasites

• Name 4 categories of emerging infectious diseases

• Name the components of the disease triangle

• Describe factors leading to emergence of infectious diseases

Emerging Infectious Diseases

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 the 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 & even in our

love.

- Hans Zinsser,1934 (quoted in Murphy 1994)

HSC4933. Emerging Infectious Diseases

Viruses

• Sub-microscopic agents

• Unable to grow or reproduce outside of a host cell

• Only DNA or RNA packaged into virions, which direct host cell to make more virus

• Infect all cellular life

• Cannot treat with antibiotics


Bacteria

• Unicellular organisms

with a wide range of

shapes

• Extremely diverse &

ubiquitous

• More than 5 x 1030

bacteria on earth, most

of world’s biomass

• Many susceptible to

antibiotics


Parasites

• Organism that lives on or in a host and gets its

food from or at the expense of its host

• Major human parasites belong to 2 kingdoms:

animals & protists

– Three main classes: protozoa, helminths, &

ectoparasites

• This course will focus on the worms & protozoa

• Helminths have long life spans, more complex

than bacteria & viruses

2

• Emerging infections: “…new, reemerging or drug-resistant infections

whose incidence in humans has increased within the past two decades

or whose incidence threatens to increase in the near future.” (A 1992,

Institute of Medicine)

• Health officials have recently warned: “Our ability to detect, contain,

and prevent emerging infectious diseases is in jeopardy.” (D. Satcher,

former dir. of the CDC)

©2010 Jones & Bartlett Publishers, LLC HSC4933. Emerging Infectious Diseases

Emerging Diseases

• EIDs are significant burden on global economies

& public health

• EID can be classified into several categories:

– Newly evolved strain of pathogen (MDR-TB)

– Pathogen entering human pop for 1st time

(HIV, SARS)

– Higher incidence known as “re-emerging”

(dengue)

– Unexplained syndromes


Scope of the Problem

• EID event: original case (or cluster)

representing an infectious disease emerging

in human populations for 1st time

• 335 events from 1940 – 2004

– 60% zoonoses

– 54% bacterial or rickettsial (esp. drug resistant)

– 23% vectorborne

• Peaked during 1980s


EID Event World Map

• Geographic origins of EID events from 1940 to 2004

• Map derived for EID events caused by all pathogen types

• Circles represent one degree grid cells. Area of circle is proportional to the number of events in the cell

1 2–3 4–5 6–7 8–11 Source: Global trends in emerging infectious

diseases. Nature, Vol 451 (2008)


Emerging & Reemerging

Diseases 1996-2007


Disease Triangle

• Need host, pathogen & environment to produce disease

• Multiple external factors can influence this cycle

– Reservoir

– Vectors

– Abiotic conditions (temp, rain)

– Culture & behavior

3

Factors Responsible for Emerging Infections

Table T02: Factors Responsible for Emerging Diseases


Demographics:

People Paradox• In 1999, population passed

6 billion– Expected to nearly double (to

11-12 billion) within 50 years!

• Urbanization: more people now live in cities vs rural areas for 1st time in human history

• Population explosion is unprecedented– Raises concerns about

carrying capacity of earth

– Heightened demandsfor energy, food & water

– Increased transmissionof infectious diseases!


Demographics Cont’d

• Population growth currently

slowing

– Influenced by fertility rates

– Family planning services

– Increased mortality due to

infectious diseases (especially

HIV/AIDS) & military conflicts

• Annual birth rates at 78 million

– 97% occur in the developing

world (middle to low-income

nations)

• Net gain of 3 people per

second (+ 260,000 per day)

Crowded street in China.

Urbanization and poverty combine to increase

infectious diseases.

©2010 Jones & Bartlett Publishers, LLC


Environmental Factors:

Climate, Temps & Weather

• Global Climate Changes:– 1990s warmest decade on record

– Human-induced climate change significantly increased

likelihood of European summer heatwave (2003)

– Increases in rainfall, particularly mid to high latitude

countries

– Parts of Asia and Africa, frequency & intensity of

droughts have increased

– Episodes of El Niño more frequent & intense since

mid-1970s

– Global emissions of carbon dioxide still increasingSource: Third Assessment Report

(2001) of the Intergovernmental

Panel on Climate Change (IPCC) HSC4933. Emerging Infectious Diseases

Ecological Factors

• Fig A. Zoonoses (relative risk of wildlife pathogens)

• Fig D. Vectorborne pathogen events (relative risk

due to abundance & diversity of insect vectors)

A. B.

C. D.

4

Microbial Evolution and Adaptation

• Resistance to antibiotics and antimicrobials is at a crisis level worldwide.

• The appearance of resistant bacteria is due to adaptation and selection (i.e.

Darwinian evolution), which is accelerated by misuse. Examples:

– Prescribing antibiotics (that only work against bacteria) for viral illness

(e.g., the flu or a cold)

– Failure of patient to complete drug regimen


Social/Behavioral Factors

• Travel– Circumnavigate the

globe in 24 hours compared to 1 year before air travel

– Infectious diseases travel well on airplanes (WNV, malaria)

– Travelers often unaware of disease risks, do not take appropriate precautions

• Globalization– Global transport of goods & people

– Geographic borders are NOT physical boundaries

– Interconnected global community allows for widespread (pandemic) transmission of infectious diseases


Travel


War, Refugees, & Diseases

Human Behavior and Attitudes

• Human Migration: about 190 million people live outside

their native countries.

– Internally displaced persons (IDPs) lack water,

shelter, food, and hygiene, all leading to increases in

infection

– Refugees transmit infectious diseases from their native

lands to those with whom they come in contact with in

new countries or in overcrowded refugee camps

• Complacency: Medical advances have led to the false

assumption that prevention and control are no longer

necessary. Examples of this are:

– Threatened resurgence of AIDS

– Lack of compliance with immunization regimens


Social/Behavioral Factors

• Hygiene (handwashing, barrier isolation &

universal precautions in hospitals)

– Have vs. Have Not countries

– Have Nots prone to increased transmission of

nosocomial acquired diseases

• High risk behaviors

• Unsafe sex (HIV, STDs)

• Drug Use (HIV & hepatitis)

5


Water & Sanitation Factors

• 884 million people lack access to improved water– Majority live in Africa

• 2.6 billion people lack access to improved sanitation– Majority live in Asia

• Each year, 1.8 million children under 5 years old die from water related diseases– 1 child every 20 seconds


Behavior + Poor Hygiene

• Improved health NOT guaranteed with access to improved water and sanitation facilities

• Hygienic behavior is extremely important to prevent diarrheal illness

• Hand washing with soap at critical times

– After defecating

– Before eating or preparing food

– After changing poopy diapers & before handling children

Societal Factors

• Increased use of day care

and preschools increases

childhood illness

• Increased population

of elderly means more residents in nursing

homes, which are a source of infection

• Globalization and centralization of the food

supply lead to widespread outbreaks of

foodborne illness

• Increased numbers tattooing and body

piercing, leading to infection©2010 Jones & Bartlett Publishers, LLC HSC4933. Emerging Infectious Diseases

Food Factors

• Mass production and preservation of foods

• Altered agricultural practices world-wide: farmers less diversified

• Contamination of product can result in large outbreaks

• Malnutrition & infection: 2 causal pathways

1. infection leads to malnutrition

2. malnutrition increases susceptibility to infections

• Difficult to resolve, pathways may occur concurrently


Summary

• Emerging Infectious Diseases are significant

threat to public health

– Most are dangerous pathogens, with high

morbidity & mortality rates

• Burden of infectious diseases remains high

& pathogens will continue to evolve

• Many factors contribute to EIDs

– Difficult to predict/control

• Challenges: How do we quickly detect a new

agent, respond, and treat/prevent the disease?

Emerging Infectious Diseases - University of South...

Documents

Transcript of Emerging Infectious Diseases - University of South...