1. Definition:
Communicable diseases are caused by pathogens
passed from one human to another.
Pathogens are viral, bacterial, parasitic and fungal.
Methods of transmission include mucus, blood,
breath, saliva and sexual contact.
Contaminated surfaces, such as doorknobs,
counter tops and playground equipment, provide a
medium for passing disease from one human to
another.

2. Various categorizations of means of transmission

3.  Direct transmission refers to direct contact such as
touching, biting, kissing, or sexual intercourse, or the
direct projection of droplet spray into the eye, nose, or
mouth during sneezing, coughing, spitting, singing, or
talking.
This projection usually is limited to a distance of 1 meter or
less.
Examples of direct contact transmission include rabies and
sexually transmitted HIV (human immunodeficiency virus).
Direct projection is responsible for transmission of diseases
such as measles and influenza.

4. Indirect transmission may occur through a vehicle or an
arthropod vector.
The causative agent may or may not multiply or develop
in or on the vehicle. Examples of possible vehicles
include water, food, biological products, or contaminated
articles (such as syringe needles).
Water-and foodborne diseases have the potential for
causing outbreaks involving thousands of persons.
However, sharing of needles by injection drug users
remains an important factor in the AIDS (acquired
immunodeficiency syndrome) epidemic.

5. Some infectious agents can be spread through the air
over long distances. Airborne spread requires that
infectious particles are small enough to be suspended in
the air and inhaled by the recipient.
Tuberculosis and histoplasmosis are bacterial and fungal
diseases spread in this fashion.
Airborne transmission could also be used to disseminate
agents of biological warfare or bioterrorism. Anthrax and
smallpox have been considered among the most likely
biological weapons.

6. Hepatitis
Hepatitis is a viral infection of the liver.
The three types of hepatitis are hepatitis A, hepatitis B
and hepatitis C.
The most prevalent of the three types worldwide is the
hepatitis B virus, with about 350 million people infected in
2005. Hepatitis causes inflammation of the liver that can
lead to life-threatening conditions, such as cirrhosis and
liver failure.

7. PERTUSSIS (Whooping Cough)
Whooping cough, or pertussis, is a highly communicable
disease that affects all ages.
The symptoms of whooping cough include respiratory
infection, runny nose, low-grade fever and a mild cough
that progresses to an uncontrollable cough with a high-
pitched whoop.

8. Ebola
 Ebola, previously known as Ebola hemorrhagic fever, is a rare and deadly disease caused by
infection with one of the Ebola virus strains. Ebola can cause disease in humans and
nonhuman primates (monkeys, gorillas, and chimpanzees).
 Ebola is caused by infection with a virus of the family Filoviridae genus Ebolavirus. There are
five identified Ebola virus species, four of which are known to cause disease in humans: Ebola
virus (Zaire ebolavirus); Sudan virus (Sudan ebolavirus); Taï Forest virus (Taï Forest ebolavirus,
formerly Côte d’Ivoire ebolavirus); and Bundibugyo virus (Bundibugyo ebolavirus). The fifth,
Reston virus (Reston ebolavirus), has caused disease in nonhuman primates, but not in
humans.
 Ebola viruses are found in several African countries. Ebola was first discovered in 1976 near
the Ebola River in what is now the Democratic Republic of the Congo. Since then, outbreaks
have appeared sporadically in Africa.
 The natural reservoir host of Ebola virus remains unknown. However, on the basis of evidence
and the nature of similar viruses, researchers believe that the virus is animal-borne and that
bats are the most likely reservoir. Four of the five virus strains occur in an animal host native to
Africa.

9. Communicable diseases associated
with natural disasters
Waterborne diseases
 Diarrheal disease outbreaks can occur following
contamination of drinking-water, and have been
reported following flooding and related displacement.
The risk of diarrheal disease outbreaks following
natural disasters is higher in developing than in
developed countries.

10. Waterborne diseases
Hepatitis A and E :
Are also transmitted by the fecal–oral route, in association
with lack of access to safe water and sanitation. Hepatitis
A is endemic in most developing countries, and children
are exposed and develop immunity at an early age. As a
result, the risk of large outbreaks is usually low in these
settings. In endemic areas, hepatitis E outbreaks
frequently follow heavy rains and floods; it is generally a
mild, self-limited illness, but in pregnant women case-
fatality rates can be up to 25% .

11. Waterborne diseases
Leptospirosis is a zoonotic bacterial disease that is
transmitted through contact of the skin and mucous
membranes with water, damp vegetation, or mud
contaminated with rodent urine. Infected rodents shed
large amounts of leptospirosis in their urine. Flooding
facilitates the spread of the organism due to the
proliferation of rodents and the proximity of rodents to
humans on shared high ground.