module05 epi part2

8/10/2019 Module05 Epi Part2

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Communicable Disease Concepts

Dona Schneider, PhD, MPH, FACE

Definitions

A communicable disease is one that can be

transmitted from one human to another orfrom

animals to humans

Many, but not all are reportable diseases Measles is reportable

Head colds are not

Definitions

A zoonosis is a type of communicable disease

that is transmissible from a vertebrate animal to

man. Normally it is a disease of animals

Zoonoses

Rabies

Plague

West Nile Virus

Eastern Equine

Encephalitis

Brucellosis

Anthrax

Trichinosis

Rocky Mountain

Spotted Fever

Lyme Disease

Typhus

Leptospirosis

Q Fever

Tularemia

Hantavirus


Epidemiologic Triad Agent, host, environment

Chain of Infection

Modes of Transmission

Characteristics of Infectious Agents

Infectivity, pathogenicity, virulence

Spectrum of Disease

Herd Immunity

Terminology: Incubation, Latency, and Infectious Periods

Levels of Disease

Endemic, Epidemic, Cluster, Pandemic

Epidemiologic Triad

AGENT

HOST ENVIRONMENT


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Definition: Agent

A microorganism,

chemical, nutritive

element or physical

factor whose

presence or absence

is essential for a

particular disease or

condition to occur

Types of Agents

Bacteria

Virus

Protozoa

Parasite

Fungi

Diet deficiency

Diet excess

Radiation

Chemicals

endogenous

exogenous

Heat, cold

Genetic traits

Stress

Host Factors

Age, sex, ethnic group, nutritional status,

socioeconomic status

Host Factors

Personal behaviors: smoking, diet, drinking,

sexual practices, exercise

Host Factors

Immunization status: vaccinated or

unvaccinated

Host Factors

Physiologic states: pregnancy, puberty,

fatigue, immunocompromised, pre-

existing disease


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Environmental Factors

Physical Weather, climate and geology


Biological - Sources of food, water, and air;

presence of vectors, flora and fauna


Social and cultural - Density, crowding,

adequate housing, war, sanitation,

availability of health care


Epidemiologic Triad

Agent, host, environment

Chain of Infection Modes of Transmission



Spectrum of Disease

Herd Immunity


Levels of Disease

Endemic, Epidemic, Cluster, Pandemic

Chain of InfectionChain of Infection

Agent leaves the reservoir/host

Portal of exit

Mode of transmission

Portal of entry

Infects the new susceptible host


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Chain of Infection

Reservoir - the natural habitat in which an

agent lives, grows and multiplies

Human - persons with symptomatic illness,

or may be inapparent or chronic carriers

Animal- cows, pigs, sheep, raccoons, bats,

dogs, cats, birds, rodents, etc.

Environmental - plants, water, soil

Chain of Infection

Portal of Exit- path by which an agentleaves its human or animal source host

Respiratory tract

Urine

Feces

Conjunctiva

Skin lesions

Percutaneous

Placental

Examples of Portal of Exit

Respiratory

Tuberculosis

Diphtheria

Pneumonia

Influenza

Measles

Chicken Pox

Smallpox

Mumps


Fecal (Alvine diseases)

Typhoid fever

Hepatitis

Shigellosis

Salmonellosis

Cholera

Amebic Dysentery

Giardiasis


Skin Lesions

Syphilis

Gonorrhea

Herpes

Smallpox

HIV

Chlamydia


Epidemiologic Triad


Chain of Infection




Spectrum of Disease

Herd Immunity


Levels of Disease

Endemic, Epidemic, Cluster Pandemic


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Chain of Infection

Modes of Transmission the way inwhich the agent is transferred to a new

host

Direct Direct contact

Droplet spread

Indirect Air borne

Vehicle borne

Vector borne

Examples of Direct Transmission

Direct contact kissing, skinto skin contact and sexualintercourse. Also refers to

direct contact with plants orsoil harboring infectiousagents

Droplet spread spray byshort range aerosol, largedroplets from coughingsneezing, talking or singing

Examples of Indirect Transmission

Air borne Microbes,

particles of droplet nuclei and

dust suspend in the air

Vehicle borne food, water,

blood, tissues, organs and

fomites

Vector borne Diseasetransmission by a

nonvertebrate host

Fomites

Inanimate objects capable of transferringinfectious material

Examples: bedding, toys, doorknobs,combs, clothing, drinking glasses,cooking utensils, pencils, straws, or

surgical instruments

Vector Borne Transmission

Agent is carried by a live non-human

carrier (vector)

Most vectors are arthropods (insects)

such as mosquitoes, flies, ticks or fleas,

but they may be animals

Vector-borne transmission may be

mechanical and/or biological

Vector borne Diseases

Malaria

Yellow Fever

WNV

Plague

Typhus

Tularemia

Lyme

Rabies

Salmonellosis

EEE

Filariasis

RMSF

Erlichiosis

Dengue Fever

Hantavirus

Sleeping Sickness


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Mechanical Vector borne Transmission

The vector is contaminated through

mechanical means

Example: The fly lands on Shigella-contaminated items,carries the agent on its legs, antennae, etc. to a new

location

Mechanical Vector borne Transmission

There is no multiplication of the agent within

the vector

Biological Vector borne Transmission

The agent undergoes

part of its life cycle

within the vector,

multiplying or

undergoing

physiologic change

Examples of Biological Transmission

Malaria Life Cycle WNV Life Cycle


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Other Examples Include

Rabies Lassa Fever

Hanta Virus

Back to the Chain of Infection

Chain of Infection

Portal of Entry- the route the agent uses to

get into the new host

Respiratory tract

Ingestion

Dermal

Blood borne Mucous membranes

Infection of a New Host Depends on

Characteristics of the Agent Infectivity, pathogenicity, virulence

Herd Immunity Ability of the agent to reach a susceptible host

Spectrum of Disease Host reaction to the disease

Dose

Immunologic status

Incubation, latency, and infectious periods

Characteristics of the InfectiousAgent

Infectivity ability of an organism to

invade and infect a host

Pathogenicity ability to cause disease

Virulence ability to cause serious

complications and/or death

Herd Immunity

The decreased

possibility of a group

or community

developing an

epidemic because

there is a specific

level of immunity or

resistance to that

disease in the

population


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Herd Immunity

Immunized persons act as a barrier to

spread

The entire population does not have to be

immunized to prevent the occurrence of anepidemic

Spectrum of Disease

The progress of a disease with no intervention:

Exposure Pathological changes

Clinical illness Symptoms

Recovery, Disability or Death

Terminology

Incubation period

Time between infection and the onset of

clinical illness

Latencyperiod

Time between infection and when the

individual becomes infectious to others

Infectious period

Time during which the infectious agent may beshed (host need not be symptomatic)

Example: Measles

Incubation period 13-18 days

Latency period 6-7 days*

Infectious period 6-9 days*

*An individual becomes infectious and stays

infectious BEFORE they have clinical

disease

More About the Incubation Period

Each infectious disease has a characteristic

incubation period dependent upon:

Portal of entry

Dosage of the agent

Immune response of the host

Rate of growth of the agent in the host

Food borne Disease

Incubation Periods

Intoxications shorter

incubation periods,

upper gastrointestinal

symptoms

Infections longer

incubation periods,

typically lower

gastrointestinal

symptoms


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Example Staphylococcus aureus

to 8 hours, usually 2 to 4 hours

Causes severe nausea, vomiting, cramps,

often diarrhea

No significant fever; body temperature

often drops

INTOXICATION

Example - Salmonella

6 to 72 hours, usually 12 to 36 hours

Causes gastroenteritis with cramping,

diarrhea, abdominal tenderness,vomiting, and fever

The diarrhea is usually watery, but maycontain blood or mucus

INFECTION

Example Plague (zoonosis)

In 1-6 days after aninfected flea bite, thesubject getslymphadenopathy

The bite getsgangrenous andnecrotic turningblack

The resultant infection

causes septicemiaand death

As it rages through a population

Plague can change to a more virulent form and

enter the lungs

Victims cough up blood-spotted mucus and then

graduate to coughing bloody froth

The cough spreads the PNEUMONIC PLAGUE

through airborne droplets (no longer a zoonosis)

Plague took a hefty toll over the

centuries

13th Century Europe

25 million died

1855-96 China/India

12 million died

1910-11 Manchuria

60,000 died ofpneumonicplague

Remember This?

Ring around the rosies,

A pocket full of posies,

Ashes, ashes!

A Tchoo, A Tchoo!

We all fall down.


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Bubonic plague suspected in

NYC visitors

Friday, November 8, 2002 Posted: 12:14 PM EST(1714 GMT)

NEW YORK (CNN) -- A New Mexico couple who

traveled to New York have been hospitalized with

what is believed to be the first case of bubonic

plague in the city in a century, said health officials.

In Contrast, Tuberculosis is a slow

plague

TB has killed more people than any other disease

in history

In 1800, one out of every three people died from

the "white plague

King Tutankhamen (1340 BCE)

Cardinal Richelieu (1640)

Robert Louis Stevenson (1894)

Eleanor Roosevelt (1962)

billions of others and

The Entire Bronte Family

Mother Bronte

Reverend Bronte

Maria

Elizabeth

Branwell

Emily

Ann

Charlotte

1821

Carrier chronic infection

1825

1825

1948

1848 (Wuthering Heights)

1849 (Agnes Grey)

1855 (Jane Eyre)

Tuberculosis Today

Approximately 1.86billion people world-wide are infected withTB, including Nelson Mandela

Desmond Tutu

Tina Turner

Tom Jones

One person dies of TBevery 15 seconds WHO 2003


Epidemiologic Triad


Chain of Infection




Spectrum of Disease

Herd Immunity


Levels of Disease Endemic, Epidemic, Cluster, Pandemic


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Levels of Disease

Endemic

A disease or condition persists within a

certain geographical area

The baseline or expected level of diseasein a community

Does not reflect the preferred level of

disease, which is zero

Levels of Disease

Epidemic orOutbreak

When the level of disease rises

significantly above the normal endemiclevel

Endemic vs. Epidemic

0

5

10

15

20

25

30

TIME

CASES

Epidemic

Endemic

Types of Epidemics

Levels of Disease

Cluster An aggregation of cases that are more than

expected

Clusters may be based on space (geographical

area) or time

A cluster may or may not be an outbreak

Levels of Disease

Pandemic

A widespread epidemic, usually affecting several

countries or continents affecting large numbers

of people and sometimes the entire globe


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A pandemic occurs because

Entire populations are

susceptible

There are no effectivetreatments for the

outbreak

Ever Heard This?

I had a little bird

Its name was Enza

I opened up the

window

And in-flu-Enza

1918

Influenza is Serious

Hippocrates

documented the first

influenza pandemic in

412 BCE

Since 1580, there have

been 31 influenza

pandemics recorded

Where Does It Come From?

Type A influenza viruses infect birds, pigs,

horses and humans

A novel virus is created

When an intermediate host (pig) is infected by

both human and bird strains at the same time

or

When an avian strain jumps the species

barrier, moving from chickens or ducks tohumans

It started at Fort Riley

On Saturday, March 9, 1918, a threateningblack sky forecast the coming of asignificant dust storm. The dust,combining with the ash of burningmanure, kicked up a stinging, stinkingyellow haze. The sun was said to havegone dead black in Kansas that day.

PBS Influenza 1918

Our soldiers shipped out

They carried the virus

to the trenches of

Europe where it

mutated into a killer

They brought it home

again, where it killed

hundreds of

thousands almost

instantly


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My Grandma died of influenza

People would suddenly develop the flu on their

way to work and die within hours (Henig,

1998) Patients "died struggling to clear their airways

of a blood-tinged froth that sometimes gushed

from their nose and mouth" (Starr, 1976)

The world was in shock

It happened so fast

that we ran out of

coffins

1918-1919 Influenza Pandemic

Was the most rapid and devastating epidemic

in recorded history

1/2the worlds population was infected and

40 million people died

The strain was incredibly virulent

Mortality was so great that the average life

span in the United States was depressed by

10 years

A Perspective on Communicable

Disease U.S. and Global Statistics

Prevalence isthe the number of

existing cases (old

and new)

Incidence is thenumber of new cases

(usually on an annual

or seasonal basis)

192-0SARS (2003)

81-1Measles

6,755-5Pertussis

>10,000 cultured

specimens

-1,765Influenza

12,942-2,460Tuberculosis

-31 million4,487Asthma

-24 million119,000COPD

179,400-160,288Lung Cancer

U.S.

Incidence

U.S.

Prevalence

U.S.

Mortality

Disease

(2000)

-

-

-

-

150 million

1.86 BILLION

600 million

-

Global

Prevalence

8,098774SARS

(1 Nov 2002 to 30 July 03)

40 million777,000Measles

43.1 million400,000Pertussis

>100 million

(5 M severe)

500,000Influenza

-180,000Asthma

10.2 million2.7 millionTuberculosis

-3 millionCOPD

248.3 million4.1 millionLower respiratory

infections

Global

Incidence

Global

Mortality

Disease

(2000)


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Questions?

Lunch

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