• INITIATION OF THE INFECTIOUS PROCESS
• THE MECHANISMS THAT LEAD TO THE DEVELOPMENT OF SIGNS AND SYMPTOMS OF DISEASE.
CHARACTERISTICS OF BACTERIA THAT ARE PATHOGENS INCLUDE
• TRANSMISSIBILITY,
• ADHERENCE TO HOST CELLS,
• INVASION OF HOST CELLS AND TISSUES,
• TOXIGENICITY, AND
• ABILITY TO EVADE THE HOST'S IMMUNE SYSTEM.
 MANY INFECTIONS CAUSED BY BACTERIA THAT ARE COMMONLY CONSIDERED TO BE PATHOGENS ARE
INAPPARENT OR ASYMPTOMATIC.
DISEASE OCCURS IF THE BACTERIA OR IMMUNOLOGIC REACTIONS TO THEIR PRESENCE CAUSE
SUFFICIENT HARM TO THE PERSON.
•
TERMS FREQUENTLY USED IN DESCRIBING ASPECTS OF PATHOGENESIS ARE DEFINED IN THE GLOSSARY.
REFER TO THE GLOSSARY IN CHAPTER 8 FOR DEFINITIONS OF TERMS USED IN IMMUNOLOGY AND IN
DESCRIBING ASPECTS OF THE HOST'S RESPONSE TO INFECTION
•
INFECTION AND IMMUNITY INVOLVE INTERACTION BETWEEN THE ANIMAL BODY(HOST) AND INFECTING
INITIAL
PRIMARY INFECTION
INFECTION IN HOST
REINFECTION
SUBSEQUENT INFECTION BY THE SAME PARASITE
WHEN
SECONDARY INFECTION
A NEW PARASITE SETS UP IN A HOST WHOSE RESISTANCE IS LOWERED BY A
PREEXISTING INFECTIOUS DISEASE
WHEN
CROSS INFECTION
A PERSON ALREADY SUFFERING FROM A DISEASE A NEW INFECTION IS SET UP
FROM ANOTHER HOST
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CROSS
NOSOCOMIAL INFECTION
INFECTIONS IN HOSPITALS
PHYSICIAN
IATROGENIC INFECTIONS
INDUCED INFECTIONS
CLINICAL EFFECTS
INAPPARENT/SUBCLINICAL INFECTION
ARE NOT APPARENT
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SOURCES OF INFECTION
HUMANS
CARRIERS: IS A PERSON WHO HARBOURS THE PATHOGENIC
MICROORGANISMS WITHOUT SUFFERING FROM ANY ILL EFFECTS BECAUSE OF
IT
ANIMALS
ZOONOTIC INFECTIONS
INSECTS
SOIL AND WATER
FOOD
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METHODS OF TRANSMISSION OF
INFECTION
CONTACT
EXAMPLES: SEXUALLY TRANSMITTED DISEASES
INHALATION
EXAMPLES: RESPIRATORY ILLNESS
INGESTION
EXAMPLES: INTESTINAL INFECTIONS
EXAMPLES: HIV
INOCULATION
INSECTS
CONGENITAL
IATROGENIC
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INFECTIOUS
DISEASE
A DISEASE THAT
CAN BE PASSED •
FROM ORGANISM TO ORGANISM
CAUSED BY TINY ORGANISMS
CALLED PATHOGENS
•
Infectious Diseases
What is an infectious diseases??
Infectious disease is:
①
A group of common diseases
②
Caused by different pathogens
③
Possessing infectivity.
④
To form epidemic.
⑤
Infectious disease is a threat to the health of people.
Infectious Diseases
What is an infection??
Definition of infection
①
②
③
Complex process of interaction between pathogen and
human body
Infection is composed of three factors: pathogen, host
and environment
There are commensalisms and opportunistic infection
Factors Influencing Disease Transmission
Agent
Environment
• Infectivity
• Weather
• Pathogenicity
• Housing
• Virulence
• Geography
• Immunogenicity
• Occupational setting
• Antigenic stability
• Air quality
• Survival
• Food
• Age
Host
• Sex
• Genotype
• Behaviour
• Nutritional status
•Health status
Infectious Diseases
Factors Influencing Disease Transmission( Agent)
Pathogenicity
What does pathogenicity mean???
It means the ability of a microbiological agent to
induce disease
The pathogenicity of pathogen is related to :
1.
Invasiveness
2.
virulent
3.
Number of pathogen
4.
Mutation (variability)
Infectious Diseases
Factors Influencing Disease Transmission( Agent)
Infectivity:
 Ability
of agent to cause infection
 Number
 In
of infectious particles required
person-to-person transmission, secondary attack rate is a
measure of infectivity
Virulence :
Severity of the disease after infection occurs.
Measured by case fatality rate or proportion of clinical cases that
develop severe disease.
Infectious Diseases
Factors Influencing Disease Transmission( Agent)
IMMUNOGENICITY
ABILITY OF AN ORGANISM TO PRODUCE AN IMMUNE RESPONSE THAT PROVIDES

PROTECTION AGAINST REINFECTION WITH THE SAME OR SIMILAR AGENT
CAN BE LIFE LONG OR FOR LIMITED PERIODS

IMPORTANT INFORMATION FOR DEVELOPMENT OF VACCINES

Infectious Diseases
Barriers for Defense Against Infection:
1. Skin:

Prevents entry of infectious organisms, unless injured.

Severe burn patients who die are usually killed by infections. So much skin is
damaged they are very vulnerable to infections.
2. Mucus membrane:

Mucous is usually rich in enzymes that will kill many pathogens
3. Cilia:

These are hair-like structures lining the respiratory tract. They work to sweep
foreign particles out of the respiratory tract.

Damaged by smoking, leaving smokers more vulnerable to infections.
4. Coughing:

Helps remove foreign material from respiratory tract.
5. Personal Hygiene

Helps reduce the number of pathogenic organisms on the skin and other
surfaces of the body.
INCUBATION PERIOD
TIME BETWEEN EXPOSURE AND ONSET OF SYMPTOMS OR SIGNS OF INFECTION.
EACH DISEASE HAS TYPICAL INCUBATION PERIOD BUT VARIES WIDELY.
REQUIRES REPLICATION OF THE ORGANISM TO SOME THRESHOLD LEVEL FOR 
PRODUCING SYMPTOMS
IMMUNITY
THE TERM IMMUNITY REFERS TO THE RESISTANCE EXHIBITED BY THE HOST
TOWARDS INJURY CAUSED BY MICROORGANISMS
•
•
DIFFERENTIATE BETWEEN “SELF” AND “NONSELF” (SOMETHING FOREIGN), AND •
DESTROY THAT WHICH IS NONSELF. •
PRIMARY FUNCTIONS OF THE IMMUNE SYSTEM
IMMUNITY AGAINST INFECTIOUS DISEASES IS OF DIFFERENT TYPES:
•
A VACCINE IS DEFINED AS MATERIAL THAT CAN ARTIFICIALLY
INDUCE IMMUNITY TO AN INFECTIOUS DISEASE, USUALLY AFTER
INJECTION OR, IN SOME CASES, INGESTION OF THE MATERIAL
(E.G., ORAL POLIO VACCINE)
•
A PERSON IS DELIBERATELY EXPOSED TO A HARMLESS VERSION
OF A PATHOGEN (OR TOXIN), WHICH WILL STIMULATE THAT
PERSON’S IMMUNE SYSTEM TO PRODUCE PROTECTIVE
ANTIBODIES AND MEMORY CELLS ,BUT WILL NOT CAUSE
DISEASE IN THAT PERSON.
•
IN THIS MANNER, THE PERSON’S IMMUNE SYSTEM IS PRIMED TO
MOUNT A STRONG PROTECTIVE RESPONSE SHOULD THE ACTUAL
PATHOGEN (OR TOXIN) BE ENCOUNTERED IN THE FUTURE
•
ARTIFICIAL ACTIVE IMMUNITY:
DIFFERENCES BETWEEN ACTIVE AND
PASSIVE IMMUNITY
HERD IMMUNITY
•
REFERS TO THE OVERALL LEVEL OF IMMUNITY IN A COMMUNITY AND IS
RELEVANT IN THE CONTROL OF EPIDEMIC DISEASES
ANY
ANTIGENS:
SUBSTANCE WHICH WHEN INTRODUCED PARENTERALLY INTO THE BODY, STIMULATES
THE PRODUCTION OF AN ANTIBODY.
•
5TYPES: IGA,
•
ANTIBODY:
IGM, ,IGD. ,IGE. ,IGG

ALL ANTIBODIES ARE IN A CATEGORY OF PROTEINS CALLED IMMUNOGLOBULINS—
GLOBULAR GLYCOPROTEINS IN THE BLOOD THAT PARTICIPATE IN IMMUNE REACTIONS.
THE TERM ANTIBODIES IS USED TO REFER TO IMMUNOGLOBULINS WITH PARTICULAR
SPECIFICITY FOR AN ANTIGEN.

IN ADDITION TO BEING FOUND IN BLOOD, IMMUNOGLOBULINS ARE FOUND IN LYMPH,
TEARS, SALIVA, AND COLOSTRUM
ANTIBODIES FOUND IN THE BLOOD ARE CALLED HUMORAL OR CIRCULATING 
ANTIBODIES.
HOW ANTIBODIES PROTECT US FROM PATHOGENS
AND INFECTIOUS DISEASES
EXAMPLE 1. A PATHOGEN HAS ENTERED A PERSON’S BODY AND HAS STARTED PRODUCING
A TOXIN. THAT PERSON’S IMMUNE SYSTEM RESPONDS BY PRODUCING ANTIBODIES
AGAINST THE TOXIN; SUCH ANTIBODIES ARE CALLED ANTITOXINS. ONCE PRODUCED,
THE ANTITOXINS RECOGNIZE, BIND TO, AND NEUTRALIZE THE TOXIN MOLECULES, SO
THAT THEY CAN NO LONGER CAUSE HARM (I.E., THEY ARE NO LONGER TOXIC).
EXAMPLE 2. VIRUSES CAN ONLY BIND TO HOST CELLS THAT BEAR THE APPROPRIATE
RECEPTOR ON THEIR SURFACE. THE MOLECULE ON THE VIRUS THAT RECOGNIZES AND
BINDS TO THE RECEPTOR IS CALLED AN ADHESIN.. A PERSON HAS RECEIVED A VACCINE
CONTAINING AN STIMULATES THAT PERSON’S IMMUNE SYSTEM TO PRODUCE
ANTIBODIES AGAINST THE ADHESIN MOLECULES. AT SOME LATER DATE, SHOULD THAT
SAME VIRUS ENTER THE PERSON’S BODY, THOSE ANTIBODIES WILL ADHERE TO THE
ADHESIN MOLECULES, MAKING IT IMPOSSIBLE FOR THE VIRUS TO BIND TO HOST
CELLS. IF THE VIRUS IS UNABLE TO BIND TO THE APPROPRIATE HOST CELL, IT IS
UNABLE TO ENTER THE CELL, AND THE PERSON IS PROTECTED FROM INFECTION WITH
THAT VIRUS.
ANTIGEN ANTIBODY REACTIONS
•
EXAMPLES: AGGLUTINATION REACTION •
ALSO KNOWN AS SEROLOGICAL REACTIONS
ELISA
PRECIPITATION REACTIONS
COMPLEMENT REACTIONS
STRUCTURE AND FUNCTION OF IMMUNE SYSTEM
LYMPHORETICULAR CELLS CONSISTSS OF LYMPHOID AND RETICULAOENDOTHELIAL
COMPONENETS
•
LYMPHORETICULAR CELLS CONSISTS OF LYMPHOCYTES AND PLASMA CELLS ARE
CONCERNECD WITH THE SPECIFIC IMMUNE RESPONSE.
•
•
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CELLS OF IMMUNE SYSTEM
T LYMPHOCYTES (T CELLS)
B LYMPHOCYTES (B CELLS)
NK CELLS (A CATEGORY OF LYMPHOCYTES)
MACROPHAGES
•
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
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TWO TYPES OF IMMUNE RESPONSES:
HUMORAL OR ANTIBODY MEDIATED
ANTIBODIES ARE PRODUCED BY MACROPHAGES
CELL MEDIATED IMMUNE RESPONSE
IMMUNODEFICIENCY DISEASES
IF A PERSON’S IMMUNE SYSTEM IS NOT FUNCTIONING PROPERLY, THAT
PERSON IS SAID TO BE IMMUNOSUPPRESSED, IMMUNODEPRESSED, OR
IMMUNOCOMPROMISED.
•
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EXAMPLE
THYMIC HYPOPLASIA
IMMUNODEFICIENCY WITH SHORT-LIMBED DWARFISM
ACQUIRED IMMUNUDEFICIENCY DISEASE AIDS
•
HYPERSENSITIVITY
INJURIOUS CONSEQUENCES IN THE SENSITISED HOST, FOLLOWING CONTACT
WITH SPECIFIC ANTIGEN
•
•
Mantoux skin test. This test is performed by injecting 0.1 mL of
tuberculin or PPD intradermally and observing the results 48 to
72 hours later. If the person has been exposed to mycobacteria
in the past, redness and swelling will occur at the injection site;
this constitutes a positive TB skin test result. The diameter of
induration (the palpable raised hardened area)—not the area of
redness—is measured and the results are interpreted using
standardized criteria.
AUTOIMMUNITY
INJURY TO SELF
AN AUTOIMMUNE DISEASE RESULTS WHEN A PERSON’S IMMUNE SYSTEM NO LONGER
RECOGNIZES CERTAIN BODY TISSUES AS SELF AND ATTEMPTS TO DESTROY THOSE TISSUES
AS IF THEY WERE NONSELF OR FOREIGN.
•
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EXAMPLES:
AUTOIMMUNE HEMOLYTIC ANEMIAS
THYROTOXICOSIS
SLE
•
•
OF THE FOLLOWING,
WHICH IS THE LEAST LIKELY TO BE INVOLVED .1
SELF
ASSESSMENT
IN CMI?
A. ANTIBODIES
B. CYTOKINES
C. MACROPHAGES
D. T CELLS
2. IMMUNITY THAT DEVELOPS AS A RESULT OF AN ACTUAL INFECTION
IS CALLED:
A. ARTIFICIAL ACTIVE ACQUIRED IMMUNITY.
B. ARTIFICIAL PASSIVE ACQUIRED IMMUNITY.
C. NATURAL ACTIVE ACQUIRED IMMUNITY.
D. NATURAL PASSIVE ACQUIRED IMMUNITY
3.NATURAL PASSIVE ACQUIRED IMMUNITY WOULD RESULT FROM:
A. HAVING THE MEASLES.
B. INGESTING COLOSTRUM.
C. RECEIVING A GAMMA GLOBULIN INJECTION.
D. RECEIVING A VACCINE
4. WHICH OF THE FOLLOWING COULD BE AN EFFECT OF TYPE III
HYPERSENSITIVITY?
A. GLOMERULONEPHRITIS
B. RHEUMATOID ARTHRITIS
C. SLE
D. ALL OF THE ABOVE
5. ARTIFICIAL PASSIVE ACQUIRED IMMUNITY WOULD RESULT FROM:
A. HAVING THE MEASLES.
B. INGESTING COLOSTRUM.
C. RECEIVING A GAMMA GLOBULIN INJECTION.
D. RECEIVING A VACCINE.
6. THE VACCINES THAT ARE USED TO PROTECT PEOPLE FROM
DIPHTHERIA AND TETANUS ARE:
A. ANTITOXINS.
B. ATTENUATED VACCINES.
C. INACTIVATED VACCINES.
D. TOXOIDS.
7. ANTIBODIES ARE SECRETED BY:
A. BASOPHILS.
B. MACROPHAGES.
C. PLASMA CELLS.
D. T CELLS.
8. HUMORAL IMMUNITY INVOLVES ALL THE FOLLOWING
EXCEPT:
A. ANTIBODIES.
B. ANTIGENS.
C. NK CELLS.
D. PLASMA CELLS.