Download Chapter 7 - Communicable Diseases

Chapter 7
Communicable
Diseases
Slideshow developed by:
Richard C. Krejci, Ph.D.
Professor of Public Health
Columbia College of SC
3.2.16
Key Questions…
• What is the burden of disease caused by
communicable diseases?
• What Public Health Tools are available to
address the burden of communicable diseases?
• How can barriers against disease address the
burden of communicable diseases?
Communicable Disease
• How can the process of immunization be used to
address the burden of communicable diseases?
• How can screening and case finding address the
burden of communicable diseases?
• How can Public Health efforts maximize
effectiveness of treatment and prevent
resistance?
• How can Public Health strategies eliminate
specific communicable diseases?
Communicable Disease
• What options are available for control of
HIV/AIDS?
• What options are available for control of
influenza?
• What options are available for control of rabies
(zoonotic disease)?
Scenarios
Communicable Diseases (TB)
As a health advisor to a worldwide HIV/AIDS
foundation, you are asked to advise on ways to
address the HIV and growing TB epidemic. You are
asked to do some long range thinking and to come up
with a list of potential approaches to control the
epidemic or at least reduce the development of
tuberculosis, which now threatens to become a
widespread consequence of the epidemic. The first
recommendation you make is forget about eradicating
HIV/AIDS. How did you come to that conclusion?
What Is the Burden of Disease
Caused by Communicable Diseases?
• Communicable disease may be caused by a
wide variety of organisms, such as bacteria,
viruses, or parasites
• For many centuries, communicable diseases
were the leading cause of death and disability
among all ages, but especially among the young
and the old
– May cause great epidemics
– Can also become endemic and become routine
causes of death
What Is the Burden of Disease
Caused by Communicable Diseases?
• Public health and medical interventions have
and will continue to have major impacts on the
burden of communicable diseases
– Last half of 1900s saw a brief respite due to medical
efforts to treat infections and public health efforts to
prevent or eradicate infections
– The early 2000s have seen the return of infections
that were previously under control, as well as the
emergence of new diseases
Koch’s Postulates: Four Conditions
to Establish Contributory Cause
1. The organism must be shown to be present in
every case of the disease by isolation of the
organism
2. The organism must not be found in cases of
other disease
3. Once isolated, the organism must be capable of
replicating the disease in an experimental
animal
4. The organism must be recoverable
from the animal
Robert Koch
What Factors Affect the Ease With Which
a Communicable Disease Is Transmitted?
• Three factors have major impacts on transmission:
1. Route of transmission
• Anatomical and physical methods for transmission from
person to person and from animal species to humans
2. Asymptomatic transmission
• Ability to transmit the disease while humans or animals
are free of symptoms
What Factors Affect the Ease With Which
a Communicable Disease Is Transmitted?
3. Reproduction ratio (R0)
• The number of new cases one individual with the
disease generates on average over the course of its
reproductive period
• Measure of inherent transmissibility
• Depends heavily on the route of transmission as well
as the presence or absence of asymptomatic
transmission
What are Some of the Common Methods
of Transmission of Human Disease?
Data from Timmreck T.C., An Introduction to Epidemiology 3rd Edition Jones and Bartlett, Sudbury Mass 2002 p. 34.
Table 7-1
pg.139
Burden of Communicable Disease
• Epidemics throughout history
– Bubonic plague
– High maternal and childhood mortality
• Great advances 2nd half of 20th century
– Polio, Small Pox, Measles
– Bacterial resistance to antibiotics
• 21st Century - TB is beginning to return
– New diseases such as Lyme, West Nile
– Cases of malaria are still present
– Expecting influenza pandemics
– The Ebola epidemic in West Africa
Key Concepts
• Infectious Disease
• Communicable Disease
– Person to person
– Animal to person
– Physical Environment (fomites) to person
• Infections
– Microorganisms
• Immunizations
– Inactive vs live
– Passive vs herd
Available Public Health Tools
•
•
•
•
Barrier protections
Screening and case finding
Treatment and contract treatment
Maximize treatments to prevent resistance
– early intervention
– vaccinations
How Can Barriers Against Disease Be
Used to Address the Burden?
• Insecticide-impregnated bed nets decrease the
rate of malaria transmission
• Condoms prevent sexually transmitted diseases
• Masks reduce the spread of disease in
healthcare institutions
• Isolation and quarantine are used to separate
individuals with disease from the healthy
population to prevent exposure
How Can Immunizations Be Used to
Address the Burden?
• Immunizations strengthen the immune system to
prevent or control disease
– Passive immunity—inject antibodies into an individual
for short-term protection
– Inactivated vaccines—dead organisms injected into
patient to build immunity
– Live vaccines—attenuated organisms used to stimulate
cell-mediated immunity and create long-term protection
• Immunizations create herd immunity
How Can Screening and Case Finding
Be Used to Address the Burden?
• Screening controls the spread of many infections
– HIV, STDs, tuberculosis, syphilis
• Screening for communicable disease has been
linked with case finding
– Confidential interviewing of those diagnosed with the
disease and asking for their recent close physical or
sexual contacts
– Key to the control of syphilis and TB both before and
after the availability of effective treatment
How Can Treatment of Those Diagnosed
and Their Contacts Help to Address the
Burden of Communicable Disease?
• Treatment of symptomatic disease may in and of
itself reduce the risk of transmission
– Reduces infectivity
• Epidemiological treatment—treatment of
contacts
– Effective in controlling the number of individuals with
the disease
– Used with sexual partners of patients with STDs
How Can Public Health Efforts Maximize
Effectiveness of Treatment and
Prevent Resistance?
1. Drug resistance occurs due to overuse of
prescribed antibiotics, over-the-counter sales of
antibiotics, and widespread use of antibiotics in
agricultural animals
2. Directly observed therapy (DOT) can be
effective treatment, even in the presence of drug
resistance
– DOT ensures complete adherence to treatment by
observing individuals taking treatment at certain
intervals
What are the Characteristics of a Disease
that Make Eradication Possible?
1. No animal reservoir
2. Short persistence in environment
3. Absence of long-term carrier state
4. The disease produces long-term immunity
5. Vaccination produces long-term immunity
6. Herd immunity protects those who are susceptible
7. Easily identified disease
8. Effective postexposure vaccination
Eradication of Human Diseases:
What Makes it Possible?
Smallpox
Polio
Measles
Disease is limited
to humans, i.e.,
no animal
reservoir?
Yes
Yes
Yes
Limited persistence
in the
environment?
Yes
Yes
Yes
Absence of long
term carrier state?
Yes
Yes—Absent, but
may occur in
immune
compromised
individuals
Yes—Absent, but may
occur in immune
compromised
individuals
Eradication of Human Diseases:
What Makes it Possible?
Smallpox
Polio
Measles
Long-term
immunity results
from infection?
Yes
Yes—But may not
be sustained in
Immune
Compromised
individuals
Yes—But may not be
sustained in immune
Compromised
individuals
Vaccination
confers long-term
immunity?
Yes
Yes—But may not be
sustained in immune
compromised
Individuals
Virus used for
production of the
live vaccine can
produce polio-like
illness and has
potential to revert
back to "wild type
infection"
Yes—But may not be
sustained in immune
Compromised
individuals
Eradication of Human Diseases:
What Makes it Possible?
Smallpox
Polio
Measles
Herd immunity
prevents
perpetuation of an
epidemic?
Yes
Yes
Yes
Easily-diagnosed
disease?
Yes—Disease
easily identified
Yes/No
Disease relatively
easy to identify, but
large number of
asymptomatic
infections
No
Disease may be
confused with other
diseases by those
unfamiliar with
measles
Vaccination
effective post
exposure?
Yes
Postexposure
Vaccination
effective
No
Post-exposure
vaccination not
effective
No
Post-exposure
vaccination not
effective
Potential for Eradication of HIV &
AIDS
HIV & AIDS
Disease is limited to humans, i.e., no
animal reservoir?
No—Animal reservoirs exist
Limited persistence in the
environment?
No—May persist on contaminated needles long
enough for transmission
Absence of long-term carrier state?
No—Carrier state is routine
Long-term immunity results from
infection?
Effective long-term immunity does not usually occur
Table 7.3
Potential for Eradication of HIV &
AIDS
HIV & AIDS
Vaccination confers long-term
immunity?
Herd immunity prevents
perpetuation of an epidemic?
No—None currently available and will be difficult
to achieve
No—Large number of previously-infected
individuals increases the risk to the
uninfected
Easily-diagnosed disease?
No—Requires testing
Vaccination effective postexposure?
No—None currently available
Modes and Chance of Transmission of
HIV and Existing Interventions
Route of Transmission
Estimated
Transmission
Rate per
Exposure
Blood transfusion
Contaminated
blood over 90%
chance of
transmission;
pooling of blood
dramatically
increases infection
rate
Blood and blood
products, such as
pooled blood
products previously
used in U.S. by
hemophiliacs
Potential Interventions
Screening of blood to
detect HIV early
Use of individual’s
own blood for
surgery
Modes and Chance of Transmission of
HIV and Existing Interventions
Route of Transmission
Estimated
Transmission
Rate per
Exposure
Sexual contact
Range from 0.1% to
10% with unprotected
receptive anal
intercourse posing
highest risk.
Vaginal male to female
greater than female to
male.
Circumcision reduces
risk by half.
Other sexually
transmitted diseases
may increase risk.
Anal higher than vaginal,
which is much higher than
oral
Potential Interventions
Latex condom
Circumcision
Abstinence
Serial monogamy reduces
spread compared to two or
more concurrent partners
Modes and Chance of Transmission of
HIV and Existing Interventions
Route of Transmission Estimated
Transmission Rate
per Exposure
Mother–to–child
transmission
15 to 40% Higher in
developing countries
Highest rate of
transmission at time of
vaginal delivery
Potential Interventions
Cesarean delivery
Drug treatment during
pregnancy and at time of
delivery for mother and child
Modes and Chance of Transmission of
HIV and Existing Interventions
Route of Transmission
Breast-feeding
Estimated
Transmission
Rate per
Exposure
Very low per exposure,
but up to 25% over year
or more of breast
feeding
Potential Interventions
Continuation of drug
treatment reduces, but does
not eliminate transmission
Modes and Chance of Transmission of
HIV and Existing Interventions
Route of Transmission Estimated
Potential Interventions
Transmission Rate
per Exposure
Less than 0.5% of HIV
positive needle sticks
Health care occupational risk result in transmission
Needle stick
exposures:
Post-exposure treatment with
drugs established as effective
prevention
Modes and Chance of Transmission of
HIV and Existing Interventions
Route of Transmission
Injection drug use
Estimated
Transmission Rate
per Exposure
Less than 1% per
episode of needle
sharing
Potential Interventions
Needle exchange
programs
What Options Are Available for the
Control of HIV/AIDS?
• Currently, we are unable to eradicate HIV/AIDS
like we have eradicated smallpox
• However, we are able to reduce the load of virus
through drug treatment and preventing the
transmission of the disease through a variety of
public health interventions
– Potential interventions depend upon the route of
transmission being considered
Mode and Chances of Transmission of
HIV and Existing Interventions
Route of
transmission
Estimated transmission
rate per exposure
Potential interventions
Blood transfusion
Blood and blood
products, such as
pooled blood products
previously used
in US by
hemophiliacs
Contaminated blood over 90%
chance of transmission with
infected blood;
pooling of blood dramatically
increases infection risk
Screening of blood to
detect HIV early
Use of individual’s own
blood for surgery
Sexual contact—anal
higher than vaginal,
which is much higher
than oral
Range from 0.1% to 10% per
Latex condom
contact with unprotected
Circumcision
receptive anal intercourse
Abstinence
posing highest risk
Serial monogamy reduces
Vaginal male to female greater spread compared to two or
than female to male
more concurrent partners
Circumcision reduces risk by
half
Other sexually transmitted
diseases
may
increase
riskPandemic. Population Bulletin 2002: 57(3).
Data from Population Reference
Bureau.
Facing
the HIV/AIDS
Mode and Chances of Transmission of
HIV and Existing Interventions
Route of transmission
Estimated transmission
rate per exposure
Potential interventions
Mother-to-child
transmission
15% to 40% higher in
developing countries
Highest rate of transmission
at time of vaginal delivery
Cesarean delivery
Drug treatment during
pregnancy and at time of
delivery for mother and
child
Breastfeeding
Very low per exposure, but
up to 25% over year or more
of breastfeeding
Continuation of drug
treatment reduces, but
does not eliminate,
transmission
Needlestick exposures
Less than 0.5% of HIVHealthcare occupational positive
risk
needlesticks result in
transmission
Postexposure treatment
with drugs established as
effective prevention
Injection drug use
Needle exchange program
Less than 1% per episode of
needle sharing
Data from Population Reference Bureau. Facing the HIV/AIDS Pandemic. Population Bulletin 2002: 57(3).
Table 7-4 p. 145
What Options Are Available for the
Control of Influenza?
• Influenza A continues to mutate, creating new
types against which previous infections and
vaccinations have little or no impact
– New live and attenuated vaccines are needed each
year
• Medications to treat influenza and modestly
shorten the course of the disease have been
developed
– Temporarily slows the spread of new strains to provide
more time to develop vaccines to target it
– However, widespread use has already lead to
resistance
How are Viruses Named? (WHO)
1. The antigenic type (e.g., A, B, C)
2. The host of origin (e.g., swine, equine, chicken, etc. For
human-origin viruses, no host of origin designation is
given.)
3. Geographical origin (e.g., Denver, Taiwan, etc.)
4. Strain number (e.g., 15, 7, etc.)
5. Year of isolation (e.g., 57, 2009, etc.)
6. For influenza A viruses, the hemagglutinin and
neuraminidase antigen description in parentheses (e.g.,
(H1N1), (H5N1)
Examples:
A/duck/Alberta/35/76 (H1N1) for a virus from duck origin
A/Perth/16/2009 (H3N2) for a virus from human origin
Pandemic Influenza
• Influenza A
• 1918
– Mortality over 50 million
• Immunization
– Inactivated virus
– Attenuated (live vaccines) are gaining popularity
• Recent advances in medications
– Shorten term and severity of symptoms
Three Types of Influenza
Viruses
• Type A, B, and C – based on antigen produced
• A and B are seasonal and the cause the most
serious symptoms
– A (H1N1), A (H3N2), and influenza B are included in
the annual flu vaccine
– New type of H1N1 caused the 2009 nation-wide
pandemic
• Type A
– 29 subtypes with different strains under each subtype.
Animal Bites and Rabies
• Dogs are responsible for about 80% of animal bite
injuries (quarantined for 10 day period of time).
• Bacteria can enter through bite wound.
• Cat bites have higher rate of infection.
• Ferrets are especially likely to bite.
• Children and older people are at greater risk.
• Wildlife bites pose the greatest rabies risk
– Raccoons, bats, skunks, foxes, and coyotes
80%
Rabies
• Spread through saliva by bite or lick
• Consider rabies if:
– Animal attacked without provocation
– Animal was behaving strangely
– High-risk species
• Report animal bites to police or animal control.
• Animal control should capture or confine for
observation
Recognizing an Animal Bite
•
•
•
•
Puncture wound
Tissue/skin crushed
Open wound on fingers, knuckles, or hand
Animal is often present and must be captured or
killed to confirm condition
Rabies
•
•
•
•
•
4000 year old communicable disease
20-60 day incubation period
Viral infection
Damages the CNS and leads to death
Multicomponent vaccination strategy for
humans is very effective
What Options Are Available for the
Control of Rabies?
• A multicomponent vaccination strategy has been
very successful in preventing the development of
rabies in humans
– Vaccines are administered to individuals who are bitten
by suspicious species of wild animals
– U.S. law requires that all dogs and cats are vaccinated
– The recent development of an effective oral vaccine
that is administered to wildlife through baits is thought
to be reducing the number of infected animals
Summary
• HIV/AIDS, Influenza A, and Rabies are diverse
viral infections
• All require multiple interventions
• Close collaboration between public health and
health care providers.
• Prevention and control strategies continue to
evolve with time.
The End
Slide show was developed by:
Richard C. Krejci, Ph.D.
Professor of Public Health
Columbia College of SC
All Rights Reserved
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• PBS: Rx for Survival (there are 15 video clips
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