learn about Infectious diseases

1. INFECTIOUS DISEASES IN
HUMANS AND PREVENTIVE MEASURE
BIOLOGY ASSIGNMENT

2. What are infectiousdiseases?
• Infectious diseases are caused by microorganisms such as
viruses, bacteria, fungi or parasites.
• Microorganisms that cause disease are collectively called
pathogens.
• Pathogens cause disease either by disrupting the bodies normal
processes and/or stimulating the immune system to produce a
defensive response, resulting in high fever, inflammation? and
other symptoms.
• Infectious diseases can be spread from one person to another,
for example through contact with bodily fluids, by aerosols
(through coughing and sneezing), or via a vector, for example a
mosquito.

3. What causes an infectiousdisease?
• Bacteria. These one-cell organisms are responsible for
illnesses, such as strep throat, urinary tract infections and
tuberculosis.
• Viruses. Even smaller than bacteria, viruses cause a multitude
of diseases — ranging from the common cold to AIDS.
• Fungi. Many skin diseases, such as ringworm and athlete's
foot, are caused by fungi. Other types of fungi can infect your
lungs or nervous system.
• Parasites. Malaria is caused by a tiny parasite that is
transmitted by a mosquito bite. Other parasites may be
transmitted to humans from animal.

4. Bacteria
• Bacteria are single-celled microorganisms.
• They come in many shapes including ball-,
rod- and spiral-shaped.
• Most bacteria are not harmful and some are
actually beneficial. Less than one per cent of
bacteria will actually make you ill.
• Infectious bacteria can grow, divide and
spread in the body, leading to infectious
disease.
• Some infectious bacteria give off toxins
which can make some diseases more severe.
• Spread by aerosols.
• Spread by surface and skin contact.
• Spread through body fluids, such as blood
and saliva.

5. Viruses
• Viruses are tiny infectious agents that
replicate only in the living cells of
other organisms.
• They can infect all types of life forms,
from animals to plants and bacteria to
amoebae.
• From plant to plant by insects that
feed on plant sap.
• From animal to animal by blood-
sucking insects.
• Spread by not washing hands after
going to the toilet
• Spread by sexual contact.
• Spread by exposure to infected blood.

6. Fungi
• Fungi are microorganisms characterised by cell
walls made from a substance called chitin.
• Most fungi are harmless to humans and some are
edible.
• Other fungi can be infectious and may lead to life-
threatening diseases.
• Fungi reproduce by releasing spores that can be
picked up by direct contact or even inhaled.
• Fungal infections often affect the lungs, skin or
nails. Some infections may also penetrate the body
to affect organs and cause whole-body infections.
• Athlete’s foot: itching, scaling or cracking of the
skin
• Ringworm: reddish, itchy, scaly rash usually on the
skin and scalp
• Thrush: caused by the fungus Candida albicans
which can infect the mouth, vagina, stomach and
urinary tract.

7. Parasites
• Parasites are organisms that live in or on another organism
and benefit by getting nutrients at the expense of their
host.
• Parasites can be found in many different body sites, for
example in the blood, liver, digestive system, brain and even
the eyes.
• Roundworms: these are nematode worms that can get into
humans by ingestion, directly penetrating the skin or
through insect bites.
• Protozoa: these are single-celled parasites. Many are
delivered by biting insects or are ingested with
contaminated water or food. They invade or eat host cells,
or swim around the bloodstream and quickly reproduce by
copying themselves.
• Tapeworms: these are flatworms whose heads hook on to
the intestinal wall of their host. Their larvae? migrate to
other parts of the body. They can live in the host for
decades.
• Flukes: blood flukes are flatworms that are caught through
contact with contaminated water. Blood fluke larvae are
released from infected snails into freshwater. Liver flukes
can be found in raw or undercooked fish or water plants and
can live in the body of the host for decades.

8. Directcontact
An easy way to catch most infectious diseases
is by coming in contact with a person or
animal who has the infection. Three ways
infectious diseases can be spread through
direct contact are:
• Person to person. A common way for
infectious diseases to spread is through the
direct transfer of bacteria, viruses or other
germs from one person to another. This can
occur when an individual with the bacterium
or virus touches, coughs on or kisses
someone who isn't infected.
• These germs can also spread through the
exchange of body fluids from sexual contact
or a blood transfusion. The person who
passes the germ may have no symptoms of
the disease, but may simply be a carrier.

9. • Animal to person. Being bitten or scratched by an infected animal
— even a pet — can make you sick and, in extreme circumstances,
can be fatal. Handling animal waste can be hazardous, too. For
example, you can acquire a toxoplasmosis infection by scooping
your cat's litter box.
• Mother to unborn child. A pregnant woman may pass germs that
cause infectious diseases to her unborn baby. Some germs can pass
through the placenta. Germs in the vagina can be transmitted to the
baby during birth.

10. Indirect contact
• Disease-causing organisms also can
be passed by indirect contact. Many
germs can linger on an inanimate
object, such as a table top,
doorknob or faucet handle.
• When you touch a doorknob
handled by someone ill with the flu
or a cold, for example, you can pick
up the germs he or she left behind.
If you then touch your eyes, mouth
or nose before washing your hands,
you may become infected.

11. Insect bites
• Some germs rely on insect carriers
— such as mosquitoes, fleas, lice
or ticks — to move from host to
host. These carriers are known as
vectors.
• Mosquitoes can carry the malaria
parasite or West Nile virus, and
deer ticks may carry the bacterium
that causes Lyme disease.

12. Food contamination
• Another way disease-causing germs can infect you is
through contaminated food and water. This mechanism of
transmission allows germs to be spread to many people
through a single source. E. coli, for example, is a
bacterium present in or on certain foods — such as
undercooked hamburger or unpasteurized fruit juice.

13. Prevention
Infectious agents can enter your
body through:
• Skin contact or injuries
• Inhalation of airborne germs
• Ingestion of contaminated food
or water
• Tick or mosquito bites
• Sexual contact

14. Follow these tips to decrease your risk of infecting
yourself or others:
• Wash your hands. This is especially important
before and after preparing food, before eating
and after using the toilet. And try not to touch
your eyes, nose or mouth with your hands, as
that's a common way germs enter the body.
• Get vaccinated. Immunization can drastically
reduce your chances of contracting many
diseases. Make sure to keep up to date on your
recommended vaccinations, as well as your
children's.
• Stay home. Don't go to work if you are
vomiting, have diarhea or are running a fever.
Don't send your child to school if he or she has
these signs and symptoms, either.

15. • Prepare food safely. Keep counters and other
kitchen surfaces clean when preparing meals. Cook
foods to the proper temperature using a food
thermometer to check for doneness. For ground
meats, that means at least 160 F (71 C), for poultry,
165 F (74 C), and for most other meat, at least 145 F
(63 C). In addition, promptly refrigerate leftovers
— don't let cooked foods remain at room
temperature for extended periods of time.
• Practice safe sex. Always use condoms if you or
your partner has a history of sexually transmitted
infections or high-risk behaviour.
• Don't share personal items. Use your own
toothbrush, comb and razor. Avoid sharing
drinking glasses or dining utensils.
• Travel wisely. If you're traveling out of the
country, talk to your doctor about any special
vaccinations you may need.

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