Download Infectious Disease Cycle

Community Health and
Infectious Diseases
社區健康與傳染病
K.N. Leung 梁國南
Department of Biochemistry, and Food and
Nutritional Sciences Programme ,CUHK
香港中文大學生化系、食品及營養科學課程
Lecture Outline
 Concepts of Health and Disease
 Human Pathogens and Infections
 Prevention of Infectious Diseases

Microbial Control and Public Health
 Emerging and Reemerging
Infectious Diseases
WHO Definition of Health
“Health is a state of complete
physical, mental and social
well-being, and not merely the
absence of disease and
infirmity.”
Community Health
 the participation of the community
in health care programs.
“A healthy community is one that embraces
the belief that health is more than merely an
absence of disease.
A healthy community includes those elements
that enable people to maintain a high quality
of life and productivity.”
- Department of Health, USA
Definition of Disease
(1) Dis-ease: opposite of ease,
when something is wrong with a
bodily function.
(2) “An impairment of health due
to an interruption, cessation or
disorder of body functions.”
Mother is the First
Microbiology Instructor!
Antonie van Leeuwenhoek (1632-1723)
“Father of Microbiology”
Founders of Microbiology and Modern Medicine
Louis Pasteur (1822-1895)
Robert Koch (1843-1910)
Types of Disease
Infectious vs. Non-infectious
Infectious disease  a disease caused by a
pathogenic microorganism
Communicable disease  an infectious disease that
is transmissible from one human to another,
either directly or indirectly
Contagious disease  a communicable disease that
is easily transmitted from one person to another
The World’s Most Common Causes of Death
from Infectious Diseases
Tetanus
2.50%
Hepatitis B
Measles
Malaria
Tuberculosis
5%
4% Others
26%
7%
Respiratory
Infections
(3.9 million)
9%
11%
18% AIDS
17.50% Diarrheal diseases
Data from The World Health Report 2002
Infection  invasion of the body tissues
by living organisms
Types of Infection
Acute vs. Chronic
Latent vs. Persistent
Clinical vs. Subclinical
Hospital-acquired vs. Community-acquired
Causes of Infectious Disease
PATHOGENS IN OUR ENVIRONMENT
Viruses
Bacteria
Fungi
Protozoa
Parasitic worms
Most micro-organisms are harmless,
only a few are pathogenic
Typical Structure of a Virus
Envelope proteins
(often as receptors
for host cell)
Lipid envelope
derived from host
cell membrane
Capsid
protein
Viral nucleic
acid (double or
single-stranded)
Nucleoprotein
20-300 nm in diameter
Typical Structure of a Bacterium
Flagellum
(confers motility)
Capsule (mainly
polysaccharides)
Cell wall
Pili (adhere
to host cell
surface)
Circular DNA
genome
Cell membrane
Plasmids (DNA that
code for toxin
production or
antibiotic resistance)
Different Types of Bacteria
Streptococcus that
causes sore throats
Legionella pneumophila that
causes Legionnaire’s disease
Campylobacter jejuni that
causes food poisoning
FACTORS AFFECTING THE EXTENT &
SEVERITY OF AN INFECTION

Factors related to micro-organisms:
e.g. Dose, Pathogenicity, Route of entry

Intrinsic host factors:
e.g. Age, Sex, Immune competence,
Genetic makeup, Previous infections,
Nutritional & emotional states

Extrinsic factors:
e.g. Infections in community,
Hygiene & sanitation, Medication used,
Environmental pollution
ROUTES OF ENTRY
OF INFECTIOUS ORGANISMS
 Through the skin or mucus membrane
1) by direct close contact:
e.g. Venereal disease (花柳病);
AIDS (愛滋病)
2) by contamination of abrasions and wounds:
e.g. Rabies (狂犬病); Tetanus (破傷風)
3) by inoculation:
insect bite – Malaria (瘧疾);
syringe – serum hepatitis (血清性肝炎)
ROUTES OF ENTRY
OF INFECTIOUS ORGANISMS
 By ingestion of contaminated food and water:
e.g. Cholera (霍亂);
Infective hepatitis (傳染性肝炎)
 By inhalation of dust and aerosols-borne
pathogens:
e.g. Influenza (流行性感冒);
Tuberculosis (肺結核)
SARS (嚴重急性呼吸道症候群)
The Human Immune System 人體的免疫系統
骨髓
幹細胞
病毒
細菌
真菌
寄生蟲
癌細胞
花粉
Lymphocytes 淋巴細胞
B cells: ~10-15% of blood lymphocytes
T cells: ~70-80% of blood lymphocytes
Phagocytes 吞噬細胞
Include Macrophages & Granulocytes
Immune Mechanisms
Innate (Non-specific) Immunity
Acquired (Specific) Immunity
Resistance not improved
by repeated antigen exposure
Without memory
Fast response
Resistance improved
by repeated antigen exposure
With memory
Slow response
Physical barriers:
Skin, Mucus membrane
Biochemical factors: Complement,
Humoral Immunity:
(B cells + Antibodies)
Acute phase proteins, Lysozyme
Chemical barriers:
Acid in stomach, Mucus in saliva
Cellular factors: Phagocytes,
NK cells, Eosinophils
Cell-mediated Immunity:
(T cells + Accessory cells
+ Cytokines)
Normal Resistance to Microbial Infection
Epithelium
Bac
teri
um
Ba
ct
er
iu
m
First barriers to infection
Physical
Mechanical
Chemical/Biochemical
Normal flora
sIgA
Intraepithelial lymphocytes
Invading microbe (Inflammatory stimulus)
Second line of defense
Macrophages
Subepithelial lymphocytes
Dendritic cells
Innate
immunity
Adaptive
Immunity
T cells
Antibodies
Inflammatory
mediators
Reinforcement
Infectious Disease:
Dynamic Interaction and Balance of Various Factors
HOST
PATHOGEN
ENVIRONMENT
Chain of Infection (Infectious Disease Cycle)
The pathogen
Exit from host
Reservoir
(Source of pathogen)
Susceptibility of
the host
Mode of transmission
Prevention of Infectious Diseases
 breaking the chain of infection
 Isolation and Quarantine
- remove the source of infection
 Increase host resistance
- vaccination and immunopotentiation
 Modify environment
- improve sanitation, eradication of vectors
Isolation and Quarantine
 Separation of ill infected patients in hospitals
(Isolation) or infected suspects in their homes,
or in community-based facilities (Quarantine)
 Voluntary basis or mandatory to protect
public’s health
Invention of Vaccination
Variolation in Ancient China
Variolation introduced to Europe (1721)
by Lady Mary Montagu
From Variolation to Vaccination (1796)
Edward Jenner: “Father of Immunology”
Discovery of smallpox vaccine
Vaccination against smallpox in 1796
Eradication of smallpox in 1979
Principle of Vaccination
Vaccination
Antibody titer
Toxoid
1st Exposure
Natural
infection
Primary
Antibody
Response
Toxin
2nd Exposure
Memory cell
formation
Time
Secondary
Antibody
Response
STRATEGIES FOR VACCINATION
Killed
Organism
Natural
Infectious
Agent
Live
Attenuated
Organism
Protein subunits
DNA for
Protective
Antigens
Recombinant
proteins
Protective
Antigens
Synthetic
Peptides
VACCINES CURRENTLY
AVAILABLE FOR HUMANS
Live attenuated
Polio (小兒痲痺)
Measles (痲疹), Mumps (痄腮)
& Rubella (德國痲疹) (MMR)
BCG (TB肺癆)
Subunit
Hepatitis B (乙型肝炎)
Haemophilus B
(流感杆菌性腦膜炎)
Inactivated
Influenza (流感),
Rabies (狂犬病)
Hepatitis A (甲型肝炎)
Cholera (霍亂)
Pertussis (百日咳)
Toxoid
Tetanus (破傷風)
Diphtheria (白喉)
Newly Developed Vaccines
Conjugate vaccine for
Haemophilus influenzae
type b (Hib)
Oral vaccine for
Rotavirus
Bacterial Meningitis
Viral Gastroenteritis
Microbial Control Methods
Physical Agents:
Dry heat (incineration) and moist heat
(autoclaving and Pasteurization)
Radiation (gamma irradiation and UV irradiation)
Chemical Agents:
Gases (ethylene oxide, beta-propiolactone)
Disinfectants and antiseptics
(alcohols, chlorine compounds)
Mechanical Removal Methods:
Filtration and sanitization
Disinfectants Commonly Used in Hospitals
 60 - 90% Alcohols (Ethanol, Isopropanol)
 Chlorine compounds (Halazone, Hypochlorite)
 Glutaraldehyde
 Iodine and iodophors
 Phenolic compounds (Lysol, Cresol)
 Quaternary Ammonium Compounds
Action of Antibiotics
Inhibit protein
synthesis:
Tetracycline
Erythromycin
Chloramphenicol
Inhibit nucleic
acid synthesis:
Nalidixic acid
Rifampicin
Inhibit synthesis of
essential metabolites:
Sulfonamide
Inhibit cell
wall synthesis:
Penicillins
Cephalosporins
Change cell
membrane
permeability:
Polymyxin
Antibiotic Resistance Mechanisms
Antibiotics are
broken down
by enzymes
Antibiotics are
removed from
cell via pumps
Antibiotic
Altered receptor
sites do not allow
antibiotics to fit
Decreased cell membrane
permeability does not
allow antibiotics to enter
Personal Protection Against
Infectious Diseases
 Wash hands frequently
 Wear cap, gloves and gowns
 Wear face masks (N95/Surgical)
 Cook and store foods properly
 Observe healthy lifestyles
 Stay up-to-date on immunizations
Strategies to Improve Public Health
 Better cooperation between the public and
private health sectors
 Maintain and improve vector control programs
 Increase monitoring and surveillance programs
 Promote education of the public for community
health matters
 Increase research in public health and
infectious diseases
Major Public Health Agencies
International
Local (HKSAR)
Hospital
Authority
醫管局
Department of
Health
衛生署
Centre for Health
Protection
衛生防護中心
World Health
Organization
世界衛生組織
Centres for Disease
Control and Prevention,
USA
美國疾病控制
及預防中心
Surveillance &
Epidemiology Branch
監察及流行病學
處部
Food and
Environmental
Hygiene
Department
食物及環境
衛生署
“New viruses and drug-resistant
bacteria are reversing human
victories over infectious diseases”
Time
Sept. 12, 1994
Dengue Fever (登革熱)
An acute viral disease caused by infection
with dengue virus which is transmitted
through mosquito bites
Sept. 2002 : First local cases
detected in Hong Kong
The Human Immunodeficiency Virus (HIV)
人體免疫缺陷病毒
HIV-1 major cause of AIDS
HIV-2  less harmful
What is AIDS ?
 AIDS is a transmissible disease caused by
infection with HIV which impairs or
destroys the body’s immune system.
 Death may result from wasting syndromes,
opportunistic infections and cancers
 Transmitted by (1) sexual contact
(2) blood-borne and (3) maternal route
Global Summary of HIV/AIDS Epidemic
No. of cases
People living with HIV/AIDS
39.4 million
New HIV infection in 2004
4.9 million
Deaths due to HIV/AIDS in 2004
3.1 million
Cumulative AIDS deaths since 1980s
~34 million
From the Joint United Nations Programme on HIV/AIDS (UNAIDS)
- Figures in December 2004
Structure of HIV
gp120
gp41
ss RNA
Protease
Reverse transcriptase
What Causes The Immune System to
Collapse in AIDS?
Direct killing of HIV-infected CD4+ T cells
or indirect lysis of uninfected CD4+ T cells
Life-threatening
immune suppression
What is Avian Influenza (Bird Flu) (禽流感)?
 An infectious disease of birds caused by
certain type A flu virus
 Infected birds shed virus in saliva,
nasal secretions and feces
 Mainly infect birds but occasionally
affect humans
 Can cause high fever, chest infection,
respiratory and multi-organ failure and
death in humans
The Influenza Viruses (A, B, C)
 Types A and B viruses  cause widespread
outbreaks in humans
 Type C viruses  cause only mild upper
respiratory tract infection in humans
 Type A viruses can infect several animal species,
including birds, pigs, horses, seals and whales
 Type B and C viruses do not affect domestic animals
Influenza A Virus (甲型流感病毒)
病毒基因
血凝素
Hemagglutinin
(H1 – H15)
Segmented
RNA
神經氨酸酵素
Neuraminidase
(N1 – N9)
膜蛋白
Matrix protein
Human Infection with Flu and Avian Flu Viruses
Virus strain Year
Location
Effects
Human Flu
H1N1
H2N2
H3N2
H1N1
1918
1957
1968
1977
Spain?
Asia
Hong Kong
Russian
40 - 50 million deaths
> 1 million deaths
Virus still circulating
Virus still circulating
Avian Flu
H5N1
1997
Hong Kong
H9N2
1999
H7N7
2003
Highly pathogenic for birds
& humans
Hong Kong Mild infection in humans
Not highly pathogenic in birds
Netherlands Highly pathogenic for bird
Emergence of “new” influenza viruses
by genetic recombination?
Human flu virus
(XX)
XY
New flu virus
(XY)
Pig
(Blender)
Avian flu virus
(YY)
Human
Severe Acute Respiratory Syndrome
(SARS) 嚴重急性呼吸道症候群
Worldwide Cases
8,098 probable cases
& 774 deaths
(By Dec. 2004
Source: CDC)
What is SARS?
 A highly contagious and sometimes fatal respiratory infection
 First appeared in China in Nov. 2002, then spread to
> 30 countries
 Causative agent (SARS-CoV) was identified in late March 2003
 Transmitted mainly by close person-to-person contact via
respiratory droplets or via air-borne route (?)
 Incubation period  ranged from 2 to 11 days
 Symptoms include high fever (>38.0°C >24 h), chills,
body aches, dry cough, breathing difficulties;
Diarrhea is seen in ~10 - 20% patients;
Most patients develop pneumonia
SARS-CoV Virus (沙士冠狀病毒)
病毒基因
RNA
膜蛋白
Membrane
protein
刺蛋白
Spike Protein
Treatment and Prevention of SARS
 No specific treatment for SARS
 Anti-viral drugs:
(a) inhibit virus entry to target cells
(b) block virus-induced cell fusion
(c) inhibit virus replication
 Immunosuppressants (e.g. corticosteroids)
 Development of SARS vaccines
Know More About
Communicable Diseases

www.info.gov.hk/dh/diseases/CD/CD_index.html
www.who.int/vaccines-diseases/
THE END
Thank you for your attention!