UNDERSTANDING DISEASES

COMMUNICABLE DISEASES

Some Important Terms

MORBIDITY

• Ratio of persons infected with the disease to those who are not infected in a population

MORTALITY

• Number of death in a population

Projected causes of Death

Some Important Terms

EPIDEMIC

• “outbreak”; disease affects greater than usual number of cases in a particular region, usually occurring within a relatively short period

PANDEMIC

• Disease occurs in epidemic proportions in many countries simultaneously

The Chain of Infection

The Chain of Infection

1. Infectious Agent – PATHOGEN• Microbial organisms which has an ability to

cause a disease

a. Algae

b. Bacteria

c. Fungi

d. Protozoa

e. Viruses

Ex. Infectious disease – Dengue fever

Pathogen - Flavivirus

The Chain of Infection

Characteristics of pathogens which enables it to cause an infection:

a. Virulence – ability to grow & multiply

b. Invasiveness – ability to enter the tissue

c. Pathogenicity – ability to cause a disease

*Infection *Infection – colonization by a pathogen; when a pathogen lands or enters a person’s body & remains there

The Chain of Infection

2. Reservoir – where a microorganism normally lives & reproduces

*Carriers – *Carriers – an organism that is infected by a pathogen but does not necessarily have the infectious disease caused by that pathogen

The Chain of InfectionTypes of Carriers:

a. Passive Carrier – carries the pathogen without ever having had the disease

b. Incubatory Carrier – is capable of transmitting a pathogen during the incubation period

c. Convalescent Carrier – harbors & can transmit a particular pathogen while recovering from an infectious disease (convalescent period)

d. Active Carrier – have completely recovered from the disease but continue to harbor the pathogen indefinitely

The Chain of Infection

3. Portal of Exit• route of escape of the pathogen from

the reservoir• Body orifices (mouth, nose, anus),

secretions, skin through insect bitesEx. Flu – mucus secretions

Hepatitis A – stoolSARS – droplets from sneezing

The Chain of Infection

4. Mode of transmission• The way the pathogen gets from the

reservoir to the new hosta. Contact – indirect & directb. Airborne – pathogen stays in the air,

common air sourcec. Droplets – from sneezing, coughing; bloodd. Vehicular – contaminated inanimate

objects e. Vectors – biting insects/arachnids

Dengue Mosquito

Aedes aegypti

The Chain of Infection

5. Portal of Entry

• Route through which the pathogen enters its new host

• Body orifices, breaks in the skin (open wounds); skin through bites

6. Susceptible Host

• A person who can get sick when exposed to a disease-causing pathogen

• Humans with low immunity or resistance

The Chain of Infection

INFECTIOUS AGENT

RESER-VOIR

PORTAL

OF EXIT

MODE OF

TRANS-MISSION

PORTAL

OF ENTRY

SUSCEPTIBLE HOST

Plasmodium falciparum

(malaria)

Salmonella typhi

(typhoid fever)

Blood – liver cell

Gall bladder

Skin – mosquito bite

Rectum – feces

Vectors - mosquito

Contact

Vehicular

Skin – mosquito bite

Mouth –food

Humans especially those with low immunity

Humans exposed to contaminated sources of food