About
Infectious diseases are
diseases that are caused by
certain pathogens –
microorganisms (microbes)
also known as infectious
agents or, more commonly,
germs.
Infectious Disease
Viruses
They are usually contagious,
meaning that they can be
transmitted from one person
to another or from one species
of plant or animal to another
Bacteria
Worms
Infecting agents are transmitted
by:
The mechanisms by which they are
transmitted are:
 Physical contact with an
infected individual
 Contact with aerosolized droplets – these
droplets are spread by sneezing, coughing,
talking, kissing and singing.
 Liquids
 Food
 Eating contaminated food and drinking
contaminated water.
 Body Fluids
 Contact with bodily fluids
 Contaminated objects
 Contact with contaminated objects, for
example a coin passed from one person to
another – some diseases penetrate the
skin directly
 Airborne inhalation
 Vector – borne spread.
 Biological Vectors (more later)
 Mechanical Vectors (more later)
Infecting agents are transmitted
by:
The mechanisms by which they are
transmitted are:
 Physical contact with an
infected individual
 Contact with aerosolized droplets – these
droplets are spread by sneezing, coughing,
talking, kissing and singing.
 Liquids
 Food
 Eating contaminated food and drinking
contaminated water.
 Body Fluids
 Contact with bodily fluids
 Contaminated objects
 Contact with contaminated objects, for
example a coin passed from one person to
another – some diseases penetrate the
skin directly
 Airborne inhalation
 Vector – borne spread.
 Biological Vectors (more later)
 Mechanical Vectors (more later)
Transmission of infectious diseases may also involve a vector.
Vectors may be mechanical or biological:
Image: “Mosquito” by tanakawho on Flickr.
Transmission of infectious diseases may also involve a vector.
Vectors may be mechanical or biological:
An example of a
mechanical vector is a
housefly, which lands on
cow dung and then lands
on food, which is then
eaten. The bacteria travel
from the dung to the food
without ever actually
entering the body of the
fly.
Image: “Mosquito” by tanakawho on Flickr.
Transmission of infectious diseases may also involve a vector.
Vectors may be mechanical or biological:
An example of a
mechanical vector is a
housefly, which lands on
cow dung and then lands
on food, which is then
eaten. The bacteria travel
from the dung to the food
without ever actually
entering the body of the
fly.
A biological vector has the
pathogens within its body,
and delivers them to new
hosts in an active manner,
usually a bite.
Mosquitoes, ticks, fleas and
lice are examples of
biological vectors and are
often responsible for
serious blood-borne
diseases, such as malaria.
Image: “Mosquito” by tanakawho on Flickr.
Transmission of infectious diseases may also involve a vector.
Vectors may be mechanical or biological:
An example of a
mechanical vector is a
housefly, which lands on
cow dung and then lands
on food, which is then
eaten. The bacteria travel
from the dung to the food
without ever actually
entering the body of the
fly.
A biological vector has the
pathogens within its body,
and delivers them to new
hosts in an active manner,
usually a bite.
Mosquitoes, ticks, fleas and
lice are examples of
biological vectors and are
often responsible for
serious blood-borne
diseases, such as malaria.
A common strategy used to control vector borne infectious diseases is to
interrupt the life cycle of a pathogen by killing the vector.
Image: “Mosquito” by tanakawho on Flickr.
The study of disease in a population is called epidemiology.
In the case of infectious disease, epidemiology is used to
classify the type of disease outbreak:
Sporadic: occasional occurrence
Endemic: cases in a region are regular and often
Epidemic: unusually high number of cases in a region
Pandemic: global epidemic
The study of disease in a population is called epidemiology.
In the case of infectious disease, epidemiology is used to
classify the type of disease outbreak:
Sporadic: occasional occurrence
Endemic: cases in a region are regular and often
Epidemic: unusually high number of cases in a region
Pandemic: global epidemic
Transmission of an infectious disease depends on a
number of factors:
Virulence: the ability of a pathogen/infecting agent to
cause disease
The distance that is travelled by infected people
How contagious the disease is
The study of disease in a population is called epidemiology.
In the case of infectious disease, epidemiology is used to
classify the type of disease outbreak:
Sporadic: occasional occurrence
Endemic: cases in a region are regular and often
Epidemic: unusually high number of cases in a region
Pandemic: global epidemic
Transmission of an infectious disease depends on a
number of factors:
Virulence: the ability of a pathogen/infecting agent to
cause disease
The distance that is travelled by infected people
How contagious the disease is
Small-world Networks – how groups of people interact: a
small, relatively isolated group of infected people could
infect a large susceptible group of people even if there’s
very little interaction between the two groups
Testing for infectious Disease
Microbial Culture – growth medium is provided for a
specific agent, and a sample taken from potentially
diseased tissue or fluid is tested for the presence of an
infectious agent able to grow in that medium
Microscopy – can be a simple compound light
microscope or an advanced electron microscope
Biochemical Tests – used to test for infections like
strep throat
Molecular Diagnostics – used to test for infections
like tetanus
Testing for infectious Disease
Microbial Culture – growth medium is provided for a
specific agent, and a sample taken from potentially
diseased tissue or fluid is tested for the presence of an
infectious agent able to grow in that medium
Microscopy – can be a simple compound light
microscope or an advanced electron microscope
Biochemical Tests – used to test for infections like
strep throat
Molecular Diagnostics – used to test for infections
like tetanus
Clearance
Immune mechanisms kill or inactivate the
inoculums of the pathogen.
Antibodies and/or T lymphocytes mediate
immunity against infectious diseases by having
a direct effect on the pathogen
Neutralising viruses – they can no longer
enter cells to cause harm
Kill the infected cell so that the disease cannot
spread from this cell.
Testing for infectious Disease
Clearance
Microbial Culture – growth medium is provided for a
specific agent, and a sample taken from potentially
diseased tissue or fluid is tested for the presence of an
infectious agent able to grow in that medium
Microscopy – can be a simple compound light
microscope or an advanced electron microscope
Biochemical Tests – used to test for infections like
strep throat
Molecular Diagnostics – used to test for infections
like tetanus
Immune mechanisms kill or inactivate the
inoculums of the pathogen.
Antibodies and/or T lymphocytes mediate
immunity against infectious diseases by having
a direct effect on the pathogen
Neutralising viruses – they can no longer
enter cells to cause harm
Kill the infected cell so that the disease cannot
spread from this cell.
Immunity:
Resistance to infection may be acquired:
Following a disease
Asymptomatic (symptom free) carriage of the pathogen
Harbouring an organism with a similar structure –
cross-reacting
Vaccination
1
• Lower Respiratory Infections
2
• HIV/AIDS
3
• Diarrheal Diseases
4
• Tuberculosis (TB)
5
• Malaria
6
• Measles
7
• Pertussis
8
• Tetanus
9
• Meningitis
10
• Syphilis
Source: http://en.wikipedia.org/wiki/Infectious_disease