CHAPTER 1 –PUBLIC HEALTH

INFECTIOUS DISEASE

1. An infectious disease is a clinically evident disease of humans or animals

that damages or injures the host so as to impair host function, and results

from the presence and activity of one or more pathogenic microbial agents,

including viruses, bacteria, fungi, protozoa, multi-cellular parasites, and

aberrant proteins

It is a disease caused by a microorganism that is potentially transferable to

new individuals. 

Example: HIV, Malaria

2. A communicable disease is an infectious disease that readily spreads from

person to person, and is easily caught from an infected person.

Example: a cold or chicken pox

3. A non communicable disease an infectious disease (i.e., with a

microorganism etiology) that is not typically spread from person to person.

The distinction, not spread from person to person, is important since it

implies not only that:

i. individuals carrying the disease are not likely to spread the

disease to others

ii. whatever led to the infection in such an individual likely did not

include person to person contact

Example : Cancer, Asthma, Heart Disease

DISEASE CAUSED BY CONTAMINATION

1. Waterborne Disease

Waterborne diseases are caused by pathogenic microorganisms

which are directly transmitted when contaminated fresh water is

consumed.

Waterborne disease can be caused by protozoa, viruses, or bacteria,

many of which are intestinal parasites

Water borne diseases spread by contamination of drinking water

systems with the urine and feces of infected animal or people.

This is likely to occur where public and private drinking water systems

get their water from surface waters (rain, creeks, rivers, lakes

etc.), which can be contaminated by infected animals or people.

Runoff from landfills, septic fields, sewer pipes, residential or industrial

developments can also sometimes contaminate surface water.

Example of Waterborne Disease

1. Diarrhea

is caused by a bacterial, viral, or parasitic infection.

Diarrhea may be accompanied by cramping, abdominal pain, nausea, an

urgent need to use the bathroom, or loss of bowel control. Some infections

that cause diarrhea can also cause a fever and chills or bloody stools.

2. Cholera

Cholera occurs because of the bacteria present in water contaminated

by incorrect sanitation, or in improperly cooked fish, especially

shellfish

Cholera is transmitted through feces contaminated with the bacterium.

The contamination normally appears when sewage water is released

into the waterways, affecting the drinking water, fish and food washed

in the water. In normal conditions it doesn't spread from person to

person, but this is possible in poor sanitary conditions.

Common symptoms include severe diarrhea abdominal cramps, fever

and vomiting.

If not treated immediately, the dehydration can cause death through

circulatory volume shock in just a few hours.

Cholera can be prevented by respecting a number of sanitary rules

3. Typhoid Fever

is caused by the infection with a bacterium called Salmonella typhi. It

is very common, as it is transmitted by water or food contaminated

with feces from infected people.

symptoms including a high fever, slowly rising from 39 to 40 degrees

Celsius (103 to 104 degrees Fahrenheit), chills, bradycardia (low pulse

rate) and weakness

Typhoid fever can be dangerous, and if untreated, it has a mortality

rate between 10 and 30%.

A vaccine is available and it is highly recommended for anyone

traveling to regions where typhoid fever is common.

4. Dysentery

Dysentery is characterized by a severe inflammation of the intestines,

affecting the body in a significant measure. Dysentery used to be a

common disease in the past centuries, but it is becoming less common

today.

Pathogen agent : Shigellosis, caused by Shigella bacteria, an

amoeba called Entamoeba histolytica that transmitted by

contaminated water

The usual sign of epidemic dysentery is blood appearing in the feces,

associated with diarrhea, abdominal cramps, fever and rectal pain.

Sepsis and kidney failure may occur in more severe cases.

Prevention

Clean water is a pre-requisite for reducing the spread of water-borne diseases

It is well recognized that the prevalence of water-borne diseases can

be greatly reduced by provision of clean drinking water and safe

disposal of feces

Water is disinfected to kill any pathogens that may be present in the

water supply and to prevent them from growing again in the

distribution systems

Disinfection is then used to prevent the growth of pathogenic

organisms and to protect public health and the choice of the disinfect

depends upon the individual water quality and water supply system.

Without disinfection, the risk from waterborne disease is increased.

The two most common methods to kill microorganisms in the water

supply are: oxidation with chemicals such as chlorine, chlorine dioxide

or ozone, and irradiation with Ultra-Violet (UV) radiation

2. Food borne Disease

is any illness resulting from the consumption of contaminated food,

pathogenic bacteria, viruses, or parasites that contaminate food,

rather than chemical or natural toxins.

Cause by improper handling, preparation, or food storage.

More than 250 different food borne diseases have been described. 

Most of these diseases are infections, caused by a variety of bacteria,

viruses, and parasites that can be food borne

Common food borne disease

1. Campylobacter

is a bacterial pathogen that causes fever, diarrhea, and abdominal

cramps. 

It is the most commonly identified bacterial cause of diarrheal illness

in the world. 

These bacteria live in the intestines of healthy birds, and most raw

poultry meat has Campylobacter on it. 

Eating undercooked chicken or other food that has been contaminated

with juices dripping from raw chicken is the most frequent source of

this infection. 

2. Salmonella

is also a bacterium that is widespread in the intestines of birds, reptiles

and mammals. 

It can spread to humans via a variety of different foods of animal

origin. 

The illness it causes, salmonellosis, typically includes fever, diarrhea

and abdominal cramps. 

In persons with poor underlying health or weakened immune systems,

it can invade the bloodstream and cause life-threatening infections. 

3. E. coli

is a bacterial pathogen that has a reservoir in cattle and other similar

animals. 

Human illness typically follows consumption of food or water that has

been contaminated with microscopic amounts of cow feces. 

The illness it causes is often a severe and bloody diarrhea and painful

abdominal cramps, without much fever.  

In 3% to 5% of cases, a complication called hemolytic uremic

syndrome (HUS) can occur several weeks after the initial symptoms. 

This severe complication includes temporary anemia, profuse bleeding,

and kidney failure. 

Prevention

1. Keep clean

• Wash your hands before handling food and often during food preparation

• Wash your hands after going to the toilet

• Wash and sanitize all surfaces and equipment used for food preparation

• Protect kitchen areas and food from insects, pests and other animals

2. Separate raw and cooked

• Separate raw meat, poultry and seafood from other foods

• Use separate equipment and utensils such as knives and cutting boards for

handling raw foods

• Store food in containers to avoid contact between raw and prepared foods

3. Cook thoroughly

• Cook food thoroughly, especially meat, poultry, eggs and seafood

• Bring foods like soups and stews to boiling to make sure that they have

reached 70°C. For meat and poultry, make sure thatjuices are clear, not pink.

Ideally, use a thermometer

Reheat cooked food thoroughly

4. Keep food at safe temperatures

• Do not leave cooked food at room temperature for more than 2 hours

• Refrigerate promptly all cooked and perishable food (preferably below 5°C)

• Keep cooked food piping hot (more than 60°C) prior to serving

• Do not store food too long even in the refrigerator

• Do not thaw frozen food at room temperature

5. Use safe water and raw materials

• Use safe water or treat it to make it safe

• Select fresh and wholesome foods

• Choose foods processed for safety, such as pasteurized milk

• Wash fruits and vegetables, especially if eaten raw

• Do not use food beyond its expiry date

3. Vector Disease

Occur in infectious microbes such as viruses, bacteria, parasite, etc

that present in a vector.

Mosquito, birds, rat, insects and all others pests that transfer diseases are

referred to as a vector.

The vector picks up the disease organism from an infected host, an

animal or a human, and transmits it either to an intermediary host or

directly to the human host.

The transfer happens directly by bites, or infestation of tissues, or

indirectly through disease transmission.

Example of Vector Disease

No Vector Disease

1. Aedes Mosquito Chikungunya

Dengue Virus

West Nile Virus

Yellow Fever

2. Anopheles Mosquito Malaria

3. Bird Avian influenza (Bird flu)

4. Rats Leptospirosis

Plague (via Fleas)

Leishmaniasis (via Sand Fly)

Symptom of disease

1.Dengue

Dengue is transmitted by the bite of an Aedes mosquito infected with any

one of the four dengue viruses. It occurs in tropical and sub-tropical areas of

the world. Symptoms appear 3—14 days after the infective bite.

Dengue fever is a febrile illness that affects infants, young children and

adults.

Symptoms range from a mild fever, to incapacitating high fever, with severe

headache, pain behind the eyes, muscle and joint pain, and rash. There are

no specific antiviral medicines for dengue. It is important to maintain

hydration. Use of acetylsalicylic acid (e.g. aspirin) and non steroidal anti-

inflammatory drugs (e.g. Ibuprofen) is not recommended.

Dengue haemorrhagic fever (fever, abdominal pain, vomiting, bleeding) is a

potentially lethal complication, affecting mainly children. Early clinical

diagnosis and careful clinical management by experienced physicians and

nurses increase survival of patients

In January 2009, reported there are 5000 cases of dengue.

2. Malaria

Malaria is a major disease in the tropics and subtropics. Each year, it is

estimated that more than 225 million cases of malaria, killing around 781 000

people according to WHO. Historical records suggest that the disease has

infected human since the beginning of mankind.

When a person is infected, he or she will suffer symptoms including fever,

chills, headache, muscle pain, sweating or vomiting. Severe cases will

progress to coma and death. These symptoms normally appear between 10

to 15 days after being bitten by the Anopheles mosquito. The disease can

also be transmitted from a mother to her unborn baby and by blood

transfusions.

3. Bird Flu

Bird flu or avian influenza is a highly contagious disease which can cause

sickness and death especially in domesticated birds like chickens, geese,

ducks and turkeys.

Bird flu is caused by avian influenza (AI) virus which normally only infects

birds, less commonly pigs and rarely horses, seals, whales, humans and other

animals.  There are many subtypes of AI virus. 

The subtype H5N1 currently circulating among birds worldwide was first

detected in 1997.  Since 2003 has spread among many countries in Asia and

Europe causing heavy mortalities in poultry flocks and wild birds.  Over 200

million poultry and birds have died or were killed since 1997 due to this virus.

The H5N1 virus is also capable of causing disease in humans under certain

circumstances.

Malaysia has been free from bird flu until August 2004 when cases were

detected for the first time, in Kelantan.  The disease was promptly eradicated

and Malaysia’s disease-free status was reinstated on 5 January 2005. 

Isolated cases are again reported exactly one year later, in Kuala Lumpur

which is being eradicated.

This disease can spread by migration birds and movement of infected bird

Birds get infected when they come into contact with these, with dead birds

and with contaminated feed and water, equipments, vehicles and other

objects. Virus is shed in feces, saliva and nasal secretions of infected birds.

Avian influenza viruses do not usually infect humans but people can contract

the disease through close contact with infected poultry and the feces.  Only

140 human cases reported, mostly in South East Asia (Vietnam, Thailand,

Indonesia, Cambodia and China) with over 70 deaths, despite widespread

outbreaks in poultry and wild birds.

4. Leptospirosis

Leptospirosis is a most common zoonotic disease caused by Leptospira

Interrogans bacterium, which affects both humans and animals. It is

transmitted through contaminated fresh water, food or soil which is

swallowed or comes in contact with broken skin, eyes and mucous

membranes.

This Leptospira spreads through infected animal’s urine and contagious while

it is moist.

Rats, mice and voles known to be primary hosts while dogs, deer, rabbits,

cows, sheeps, and certain marine mammals are possible carrier and known to

be secondary hosts.

This biphasic disease normally begins with flu-like symptoms such as fever,

chills and intense headache. It will then cause meningitis, renal failure and

liver damage that cause jaundice.

Disease Transmission

NON COMMUNICABLE DISEASE

1. Lead

Lead accounts for most of the cases of pediatric heavy metal poisoning

(Roberts 1999).

It is a very soft metal and was used in pipes, drains, and soldering materials

for many years.

Millions of homes built before 1940 still contain lead (e.g., in painted

surfaces), leading to chronic exposure from weathering, flaking, chalking, and

dust.

Every year, industry produces about 2.5 million tons of lead throughout the

world.

Most of this lead is used for batteries. The remainder is used for cable

coverings, plumbing, ammunition, and fuel additives. Other uses are as paint

pigments and in PVC plastics, x-ray shielding, crystal glass production, and

pesticides.

Since lead is chemically very similar to calcium, it is handled by the body as if

it were calcium. Thus the first place to which it is transported is to the plasma

and the membrane sites in soft tissues. It is then distributed to the other sites

where calcium plays an important role, most notably in the teeth of

developing children and in bone at all ages.

Target organs are the bones, brain, blood, kidneys, and thyroid gland

2. Mercury

Mercury is generated naturally in the environment from the degassing of the

earth's crust, from volcanic emissions.

It exists in three forms: elemental mercury and organic and inorganic

mercury.

Mining operations, chloralkali plants, and paper industries are significant

producers of mercury (Goyer 1996).

Atmospheric mercury is dispersed across the globe by winds and returns to

the earth in rainfall, accumulating in aquatic food chains and fish in lakes

(Clarkson 1990).

Mercury compounds were added to paint as a fungicide until 1990. T

These compounds are now banned; however, old paint supplies and surfaces

painted with these old supplies still exist.

Mercury continues to be used in thermometers, thermostats, and dental

amalgam. (Many researchers suspect dental amalgam as being a possible

source of mercury toxicity [Omura et al. 1996; O'Brien 2001].)

Medicines, such as mercurochrome and merthiolate, are still available.

Algaecides and childhood vaccines are also potential sources.

Inhalation is the most frequent cause of exposure to mercury. The organic

form is readily absorbed in the gastrointestinal tract (90-100%); lesser but

still significant amounts of inorganic mercury are absorbed in the

gastrointestinal tract (7-15%).

Target organs are the brain and kidneys.

3. Insecticide

Pesticides are designed to kill "pests", but some pesticides can also cause

health effects in people. The likelihood of developing health effects depends

on the type of pesticide and other chemicals that are in the product you are

using, as well as the amount you are exposed to and how long or often you

are exposed.

Most often, pesticides affect the nervous system (system in your body that

controls your nerves and muscles).

Some health effects from pesticide exposure may occur right away, as you

are being exposed. Some symptoms may occur several hours after exposure.

Other effects may not be noticed for years, for example cancer.

Pesticides can enter your body during mixing, applying, or clean-up

operations. There are generally three ways a chemical or material can enter

the body:

o through the skin (dermal),

o through the lungs (inhalation), or

o by mouth (ingestion).

In general, the risk of illness increases as the concentration (strength) of the

pesticide, and duration (length) of exposure increases. "How much" and "how

long" is necessary to cause illness will depend on the exact type of pesticide

4. Asbestos

Asbestos is the name given to a group of naturally occurring minerals used in

certain products, such as building materials and vehicle brakes, to resist heat

and corrosion. Asbestos includes chrysotile, amosite, crocidolite, tremolite

asbestos, anthophyllite asbestos, actinolite asbestos, and any of these

materials that have been chemically treated and/or altered.

The inhalation of asbestos fibers by workers can cause serious diseases of

the lungs and other organs that may not appear until years after the

exposure has occurred.

For instance, asbestosis can cause a buildup of scar-like tissue in the lungs

and result in loss of lung function that often progresses to disability and

death.

Asbestos fibers associated with these health risks are too small to be seen

with the naked eye, and smokers are at higher risk of developing some

asbestos-related diseases

Employee exposure to asbestos must not exceed 0.1 fiber per cubic

centimeter (f/cc) of air, averaged over an 8-hour work shift. Short-term

exposure must also be limited to not more than 1 f/cc, averaged over

30 minutes. Rotation of employees to achieve compliance with either

permissible exposure limit (PEL) is prohibited.

5. Cadmium

Cadmium is a byproduct of the mining and smelting of lead and zinc

It is used in nickel-cadmium batteries, PVC plastics, and paint pigments.

It can be found in soils because insecticides, fungicides, sludge, and

commercial fertilizers that use cadmium are used in agriculture.

Cadmium may be found in reservoirs containing shellfish.

Cigarettes also contain cadmium. Lesser-known sources of exposure are

dental alloys, electroplating, motor oil, and exhaust.

Inhalation accounts for 15-50% of absorption through the respiratory system;

2-7% of ingested cadmium is absorbed in the gastrointestinal system. Target

organs are the liver, placenta, kidneys, lungs, brain, and bones.

6. Nitrate

Nitrates and nitrites are chemicals that can be found naturally in our

environment. Two of earth’s most common elements, nitrogen and oxygen,

combine to form these nitrogen-containing compounds. Nitrates are essential

(needed) nutrients for plants to grow. Nitrates can be found in the air, soils,

surface waters and ground water

The main exposure route to nitrates is by eating vegetables and preserved

meats (70%). The remainder of the nitrate in a typical diet comes from

drinking nitrate-contaminated water (about 21%)

Exposure to nitrates and nitrites are not usually an immediate (acute) health

threat. When you eat or drink nitrates, they are absorbed from the small

intestine (gut) into the blood. Nitrates then enter the large intestine from the

blood.

If certain, normal conditions exist in the intestine, such as a low pH, the

nitrate is simply processed and removed as waste without any harmful

effects.

However, under other conditions, such as a high pH in the intestine, the

nitrate will be changed into nitrite. This nitrite is then reabsorbed into the

blood where it will react with the blood’s hemoglobin iron to form

methemoglobin.

The hemoglobin in our blood carries (transports) oxygen throughout our

body.

The condition where the nitrite reacts with the iron and hemoglobin is known

as methemoglobinemia (often called “blue baby syndrome”).

Unlike hemoglobin that carries oxygen throughout our body, methemoglobin

is unable to transport oxygen.

A person who has methemoglobinemia can lack the proper oxygen levels

needed for the body to function correctly. One of the signs of

methemoglobinemia is cyanosis (turning a blue color).

7. Particular Matter

Particular matter is the sum of all solid and liquid particles suspended in air,

many of which are hazardous. This complex mixture contains for instance

dust, pollen, soot, smoke, and liquid droplets

Particles are either directly emitted into the air by sources such as

combustion processes and windblown dust, or formed in the atmosphere by

transformation of emitted gases such as SO2.

In long-term exposure to current ambient particulate matter concentrations

may affect the lungs of both children and adults and may reduce life

expectancy by a few months, mainly in subjects with pre-existing heart and

lung diseases.

Fine particles are more dangerous than coarse particles. Apart from the size

of the particles, other specific physical, chemical, and biological

characteristics that can influence harmful health effects include the presence

of metals, PAHs, other organic components, or certain toxins.

When particulate matter is combined with other air pollutants, the individual

effects of each pollutant are cumulated. In certain cases, especially for

combinations of particulate matter with ozone or allergens, effects were

shown to be even greater than the sum of the individual effects.

Certain groups of people are more susceptible to suffer health effects due to

ambient particulate matter. These include elderly people, children, people

with a pre-existing heart and lung disease, asthmatics, and socially

disadvantaged and poorly educated populations.

8. Dioxin

Dioxins are a group of chemically-related compounds that are persistent

environmental pollutants.

Dioxins are found throughout the world in the environment and they

accumulate in the food chain, mainly in the fatty tissue of animals.

More than 90% of human exposure is through food, mainly meat and dairy

products, fish and shellfish. Many national authorities have programmes in

place to monitor the food supply.

Dioxins are highly toxic and can cause reproductive and developmental

problems, damage the immune system, interfere with hormones and also

cause cancer.

Short-term exposure of humans to high levels of dioxins may result in skin

lesions, such as chloracne and patchy darkening of the skin, and altered liver

function.

Long-term exposure is linked to impairment of the immune system, the

developing nervous system, the endocrine system and reproductive

functions. Chronic exposure of animals to dioxins has resulted in several

types of cancer.

No Type of Heavy

Metal

Source/Exposure Organ Target/

Disease

1. Lead Used in pipes, drains, and

soldering materials for

many years.

Exposure from

weathering, flaking,

chalking, and dust.

Used for batteries.

The remainder is used for

cable coverings,

plumbing, ammunition,

and fuel additives.

Other uses are as paint

pigments and in PVC

plastics, x-ray shielding,

Transport to

soft tissues

Target organs

are the bones,

brain, blood,

kidneys, and

thyroid gland

crystal glass production,

and pesticides.

2. Mercury generated naturally in the

environment from the

degassing of the earth's

crust, from volcanic

emissions

Mining operations,

chloralkali plants, and

paper industries are

significant producers of

mercury

Used in paint,

thermometer medicine

and medical equipment

Expose by inhalation

Target organ:

brain and

kidney.

3. Insecticide From pesticide

enter body during mixing,

applying, or clean-up

agriculture operations

affect the

nervous system

4. Asbestos used in certain products,

such as building materials

and vehicle brake

cause serious

diseases of the

lungs and other

organs

5. Cadmium byproduct of the mining

and smelting of lead and

zinc

used in nickel-cadmium

batteries, PVC plastics,

and paint pigments.

Effect liver,

placenta,

kidneys, lungs,

brain, and

bones.

Absorb in

can be found in soils

because insecticides,

fungicides, sludge, and

commercial fertilizers that

use cadmium are used in

agriculture.

Cadmium may be found in

reservoirs containing

shellfish

Cigarette

respiratory

system and

gastrointestinal

system

6. Nitrate is by eating vegetables

and preserved meats

from drinking nitrate-

contaminated water

baby blue

syndrome

lack of oxygen

7. Particular Matter From dust, pollen, soot,

smoke, and liquid droplets

emitted into the air by

sources such as

combustion processes

heart and lung

disease

High risk to

elderly people,

children, people

with a pre-

existing heart

and lung

disease,

asthmatics, and

socially

disadvantage

8. Dioxin a group of chemically-

related compounds that

are persistent

environmental pollutants.

cause

reproductive

and

developmental

problems,

exposure is through food,

mainly meat and dairy

products, fish and

shellfish.

damage the

immune system,

interfere with

hormones

also cause

cancer.