Download Infectious Disease

Infectious Diseases
Natural Emerging Dangers
Infectious Disease in the News
Avian flu and influenza vaccine shortage
West Nile outbreaks
Severe Acute Respiratory Syndrome
Polio eradication efforts
Anthrax in postal workers
Any current example can be used as teachable
moment about biology of infectious disease
What is an infectious disease?
Illness resulting when a foreign organism
lives in/on a person
Infection ≠ Infectious Disease
Factors involved
– Organism = Parasite or pathogen
– Human = Host
– Method of spread = Transmission
Parasite Factors
Cooperation is the rule; disease is rare
– Enlightened self-interest: If host dies, parasite dies
– Normal colonization with “smaller life”
Beneficial
– Bacteria growing in intestine (“gut flora”) make vitamin K
Unnoticed
– Mites in hair follicles
Characteristics related to ability to cause
disease: Virulence factors
– Avoid host control and allow growth
– Make products that damage host cells
– Cause host to damage itself as a result of responding
to infection
Host Factors
Barrier to infection
– Intact skin and mucous membranes
– Secretions
Response to infection
– Innate immunity: Non-specific and immediate,
includes phagocytes and neutrophils
– Adaptive immunity: Specific to organism,
includes antibodies and activated
lymphocytes
Transmission
Direct spread: by contact or airborne particles
from infected to uninfected (Contagious disease)
Food or environment-borne: water, food, or soil
contaminated by infected person and serve as
reservoir for spread
Zoonotic: infection transmitted to humans from
an animal host or reservoir
Mother-to-infant: shared blood circulation before
birth or exposure during delivery (Vertical )
Reasons for “Outbreaks”
Look to three major factors in infectious disease
– Parasite/Pathogen
New or new to population
Increased virulence due to genetic change or recombination
Drug resistance
– Host
Breakdown in defense (nutrition, infection, cancer, injury)
Genetic variation in immune response
– Transmission
Altered environment resulting in new exposures
New patterns of behavior (needle sharing, sex partners,
travel)
Detection of Outbreaks
Unusual pattern of disease detected by
public health monitors (sentinel
surveillance) or alert health care
professionals
– Higher than usual number of cases
– Unusually poor response to therapy
– New kind of disease
Determine disease epidemiology
Characteristics of sick individuals and
healthy individuals
– Age, race, sex, income, residence
– Travel, occupation, diet, medications
Determine factors more common in
disease group than healthy group (risk
factors)
Determine disease pathology
What organ systems are involved?
– Pathogens have characteristic patterns of infection
and damage (Imaging, biopsy, autopsy)
What damage has occurred?
– Histologic examination of affected tissues to identify
cell and tissue response (type and extent of
inflammation, fibrosis, cell death)
– Routine stains, immunochemistry or nucleic acid
hybridization in tissues to look for organisms
Laboratory Diagnosis
Culture
Antibody response
Antigen detection
Molecular diagnostics (hybridization,
nucleic acid amplification)
Unique problems presented by new or
“novel” pathogens: Require new or novel
tests.
Consensus PCR:
Typing Roche Line Probe Assay
Consensus PCR:
Typing Roche Line Probe Assay
Roche Strip: 27 Types
(Next Generation 36)
Outbreak Investigation
Determine what is being investigated
– Definition of a case
Initially based on clinical observations
– Rapid and easy to apply
– However limited accuracy and focus on most severe illness
Specific laboratory diagnosis improves accuracy of case
detection
– Requires optimal test and optimal sampling
Determine extent of problem
– How many cases and where are they?
– Noninvasive tests permit screening “healthy”
population, environment and animal hosts
Identify reservoirs of disease, atypical (mild) forms of disease
Intervention
Alter host
– Vaccination
– Change behaviors
Disrupt transmission
– Hand washing, sanitation of food and water
– Eliminate animal resevoirs (i.e. mosquito abatement)
or prevent contact (i.e. mosquito netting or repellant)
Eliminate pathogen
– Small pox is only example to date
– Polio eradication is underway
Web sites
www.cdc.gov
www.microbe.org