Overview of disease agents and other issues

Overview on:
Disease agents, vectors and
transmission of infectious,
communicable,
emerging diseases,
Sterilization, disinfection
antisepsis and
decontamination
Dr. Zakir Hossain Habib
Principal Scientific Officer (Associate Professor)
Head Department of Microbiology
Institute of Epidemiology,Disease Control & Research
(IEDCR)

Communicable diseases
 A communicable disease is an illness due to a
specific infectious (biological) agent or its toxic
products capable of being directly or indirectly
transmitted from:
-man to man
-animal to man
- animal to animal or
-from the environment (through air, water,
food, etc..) to man.

 Non-communicable disease:
A disease that can NOT be spread from person to
person. Ex: cancer, heart disease, cirrhosis, etc.

Bacteria
Viruses
Fungi
Protozoa
Helminths
Algae
Prions
(proteinaceous infectious agents)
Infectious Agents

Common Pathogens:
Viruses, Bacteria, Fungi & Protozoa
 Virus: smallest simplest life form. Not alive, and cause upper
respiratory infections and many other type of diseases.
 Bacteria: simple one-celled organisms. They are everywhere.
Not all bacteria is bad.
 Fungi: more complex than bacteria, but cannot make their own
food. Thrive in warm, moist environments.
 Protozoa: one celled, animal like organisms.

Usually…
The poor hygiene
behaviors promote the
transmission of
infectious diseases
The fecal-oral and
respiratory routes are
the most common
sources of transmission

CD- Modes of transmission
 Direct
 Skin-skin: Herpes type 1
 Through breast milK: HIV
 Blood-borne or sexual – HIV, Hepatitis B,C
 Inhalation – Tuberculosis, influenza, anthrax
 Food-borne – E.coli, Salmonella,
 Contaminated water- Cholera, rotavirus, Hepatitis A
 Indirect
 Vector-borne- malaria, trypanosomiasis
 Fomites
 Zoonotic diseases – animal handling and feeding
practices (Mad cow disease, Avian Influenza)

Some Pathogens that Cross the Placenta

Disease is the result of
forces within a dynamic
system consisting of:
agent of infection
host
environment
Epidemiologic Triad

Agent
Host
Environment
• Age
• Sex
• Genotype
• Behaviour
• Nutritional status
• Health status
• Infectivity
• Pathogenicity
• Virulence
• Immunogenicity
• Antigenic stability
• Survival
• Weather
• Housing
• Geography
• Occupational setting
• Air quality
• Food
(www)
Factors Influencing Disease
Transmission

Terminologies related to communicable diseases…
-Infection
 Infection is the entry and development or multiplication of an
infectious agent in the body of man or animals.
 An infection does not always cause illness.
 There are several levels of infection (Gradients of infection):
 Colonization (S. aureus in skin and normal nasopharynx)
 Subclinical or inapparent infection (polio)
 Latent infection (virus of herpes simplex)
 Manifest or clinical infection

Contamination
 The presence of an infectious agent on a body
surface, on or in clothes, beddings, toys, surgical
instruments or dressings, or other articles or
substances including water and food

Infestation
 It is the lodgment, development and reproduction of
arthropods on the surface of the body or in the
clothing, e.g. lice, itch mite.
 This term could be also used to describe the invasion
of the gut by parasitic worms, e.g. ascariasis.

Contagious disease
 A contagious disease is the one that is transmitted
through contact.
 Examples include scabies, trachoma, STD and
leprosy.

Vectors
A host that carries a
pathogen without injury
to itself and spreads
the pathogen to
susceptible organisms
(asymptomatic carriers of
pathogens)

Reservoir Any person, animal, arthropod, plant,
soil, or substance, or a combination of
these
…… in which an infectious agent
normally lives and multiplies
….. on which it depends primarily for
survival, and where it reproduces itself in
such a manner that it can be transmitted
to a susceptible host.
It is the natural habitat of the infectious
agent.

Nosocomial
infection
or
Hospital
Acquired
infection
(HAI)
Nosocomial infection is an
infection originating in a
patient while in a hospital or
another health care facility.
It has to be a new disorder
unrelated to the patient’s
primary condition.
Examples include infection
of surgical wounds, hepatitis
B and urinary tract infetions.

Opportunistic
infection This is infection by organisms
that take the opportunity
provided by a defect in host
defense (e.g. immunity) to
infect the host and thus cause
disease.
For example, opportunistic
infections are very common in
AIDS. Organisms include
Herpes simplex,
cytomegalovirus, M.
tuberculosis….

Incubation
period
 Time from exposure to
development of disease.
 In other words, the time
interval between invasion
by an infectious agent and
the appearance of the first
sign or symptom of the
disease in question.

Dynamics of disease Transmission
(Chain of Infection)
Source or Reservoir Modes of transmission Susceptible host
I II III

Cases
 A case is defined as “a person in the population or
study group identified as having the particular
disease, health disorder, or condition under
investigation”

Carriers
 It occurs either due to inadequate treatment or immune
response, the disease agent is not completely eliminated,
leading to a carrier state.
 It is “an infected person or animal that harbors a specific
infectious agent in the absence of (visible) clinical disease
 They serves as a potential source of infection to others.

Common
Communicable
Diseases
The common cold is a
respiratory infection caused by
over 200 different viruses.
Symptoms include congestion,
sore throat and cough. It can
be spread through direct and
indirect contact.
Prevention techniques include
hand washing and avoiding
contact with infected persons.

Influenza, more commonly called “flu”, is a respiratory
infection caused by several groups of viruses.
Symptoms include high fever, fatigue, muscle and joint
aches. It is spread through direct contact with
infected people and water droplets in the air from
coughs and sneezes.

Tuberculosis
 2 billion people infected with microbes that cause TB.
 Not everyone develops active disease
 A person is infected every second globally
 22 countries account for 80% of TB cases.
 >50% cases in Asia,
 28% in Africa

Tuberculosis and HIV
 A third of those living with HIV are co-infected with TB
 Most common opportunistic infection in Africa
 70% of TB patients are co-infected with HIV in some
countries in Africa

Malaria
 Every year, 500 million people become severely ill with
malaria
 >1 million people die of malaria every year.
 40% of the world’s population is at risk of malaria.
 Malaria is the 9th leading cause of death in LICs and MICs

Neglected diseases
 Cause over 500,000 deaths annually.
 Include the following
 Helminthic infections
 Hookworm (Ascaris, trichuris), lymphatic filariasis,
onchocerciasis, schistosomiasis, dracunculiasis
 Protozoan infections
 Leishmaniasis, African trypanosomiasis, Chagas disease
 Bacterial infections
 Leprosy, trachoma, buruli ulcer

Sexually
Transmitted
Diseases
Chlamydia
Gonorrhea
Genital Herpes
Syphilis
HIV/AIDS

International boundaries are disappearing
 Borders are not very effective at stopping
communicable diseases.
 With increasing globalization
 Other global issues affect or are affected by
communicable diseases.
 climate change
 migration
 Change in biodiversity

Prevention  Ways to prevent Infectious
Disease
– Getting enough sleep, avoiding
alcohol/cigarettes, and eating a
healthy diet.
– Getting vaccines when
available.
– Staying away from disease
carrying animals or food/water
that is dirty.

Emerging
&
Re-emerging
Infectious Diseases

Which killed more people: WWI (1914-1918) or
the Influenza Epidemic of 1918?
 World War I (1914 – 1918) death toll:
 8-10 million worldwide
 1918 Influenza Epidemic death toll:
 40 million worldwide

Influenza
“There was a little bird
its name was Enza.
I opened the window
and in-flu-enza.”

Infectious
Disease-
Trends
Receded in Western
countries 20th century
Urban sanitation, improved
housing, personal hygiene,
antisepsis & vaccination
Antibiotics further
suppressed morbidity &
mortality

Infectious Disease- Trends
 Since last quarter of 20th century- New &
Resurgent infectious diseases
 Unusually large number- Rotavirus,
Cryptosporidiosis, HIV/AIDS, Hantaviraus,
Lyme disease, Legionellosis,
Hepatitis C……

?
AIDS
Avian Influenza
Ebola
Marburg
Cholera
Rift Valley Fever
Typhoid
Tuberculosis
Leptospirosis
Malaria
Chikungunya
Dengue
JE
Antimicrobial resistance
UP
Guinea worm Smallpox
Yaws
Poliomyelitis
Measles
Leprosy
Neonatal tetanus
DOWN
Infectious Diseases: A World in Transition

Definition
 Emerging infectious disease
Newly identified & previously unknown infectious
agents that cause public health problems either locally
or internationally

Definition
 Re-emerging infectious disease
Infectious agents that have been known for some time,
had fallen to such low levels that they were no longer
considered public health problems & are now showing
upward trends in incidence or prevalence worldwide

Factors Contributing To Emergence
AGENT
 Evolution of pathogenic infectious agents
(microbial adaptation & change)
 Development of resistance to drugs
 Resistance of vectors to pesticides

Factors Contributing To Emergence
HOST
 Human demographic change (inhabiting new areas)
 Human behaviour (sexual & drug use)
 Human susceptibility to infection
(Immunosuppression)
 Poverty & social inequality

Factors
Contributing
To
Emergence
ENVIRONMENT
Climate & changing ecosystems
Economic development & Land use
(urbanization, deforestation)
Technology & industry (food
processing & handling)
International travel & commerce
Breakdown of public health measure
(war, unrest, overcrowding)

Transmission
of Infectious
Agent from
Animals to
Humans
>2/3rd emerging infections originate
from animals- wild & domestic
Animal displacement in search of
food after deforestation/ climate
change (Lassa fever)
Humans themselves penetrate/
modify unpopulated regions- come
closer to animal reservoirs/ vectors
(Yellow fever, Malaria)
Global warming- spread of Malaria,
Dengue, Leishmaniasis, Filariasis

Poverty, Neglect & Weakening of
Health Infrastructure
 Poor populations- major reservoir & source of
continued transmission
 Poverty- Malnutrition- Severe infectious disease
cycle
 Unsafe sexual practices (HIV, Gonorrhoea, Syphilis)
 Poor prioritization of health funds,
 Misplaced in curative rather than preventive
infrastructure,

Uncontrolled
Urbanization
&
Population
Displacement
Growth of densely populated
cities- substandard housing,
unsafe water, poor sanitation,
overcrowding, indoor air
pollution (>10% preventable
ill health)
Problem of refugees &
displaced persons

Antimicrobial
Drug
Resistance
Dr. KANUPRIYA CHATURVEDI
Causes:
Wrong prescribing
practices
non-adherence by
patients
Use of anti-infective
drugs in animals & plants

HUMAN
ANIMALS
ENVIRONMENT
VECTORS
Population
Growth
Mega-cities
Migration
Exploitation
Pollution
Climate change
Vector
proliferation
Vector
resistance
Transmission
Antibiotics
Intensive farming
Food
production

Examples of recent emerging diseases
Source: NATURE; Vol 430; July 2004;
www.nature.com/nature

CONTD.  Zoonoses- 1,415 microbes are
infectious for human
Of these, 868 (61%) considered
zoonotic
70% of newly recognized
pathogens are zoonoses

Emerging Zoonoses: Human-animal
interface
Marburg virus
Hantavirus Pulmonary Syndrome
Ebola virus
Borrelia burgdorferi: Lyme Deer tick (Ixodes
scapularis)
Mostomys rodent: Lassa fever
Avian influenza virus Bats: Nipah virus

SARS: The First Emerging Infectious
Disease Of The 21st Century
SARS Cases
19 February to 5 July 2003
China (5326)
Singapore (206)
Hong Kong (1755)
Viet Nam (63)
Europe:
10 countries (38)
Thailand (9)
Brazil (3)
Malaysia (5)
South Africa (
Canada (243)
USA (72)
Colombia (1)
Kuwait (1)
South Africa (1)
Korea Rep. (3)
Macao (1)
Philippines (14)
Indonesia (2)
Mongolia (9)
India (3)
Australia (5)
New Zealand (1)
Taiwan (698)
Mongolia (9)
Russian Fed. (1)
Total: 8,439 cases, 812 deaths,
30 countries in 7-8 months
Source: www.who.int.csr/sars
No infectious disease has spread so fast and far as SARS did in 2003

CONTD.
Dr. KANUPRIYA CHATURVEDI
High level commitment is
crucial for rapid containment
WHO can play a critical role in
catalyzing international
cooperation and support
Global partnerships & rapid
sharing of data/information
enhances preparedness and
response

Examples
of Re-
Emerging
Infectious
Diseases
Diphtheria- Early
1990s epidemic in
Eastern
Europe(1980- 1%
cases; 1994- 90%
cases)
Cholera- 100%
increase
worldwide in 1998
(new strain eltor,
0139)
Human Plague- India (1994)
after 15-30 years absence.
Dengue/ DHF- Over past 40
years, 20-fold increase to
nearly 0.5 million (between
1990-98)

Key
Tasks in
Dealing
with
Emerging
Diseases
 Surveillance at national, regional, global level
 epidemiological,
 laboratory
 ecological
 anthropological
 Investigation and early control measures
 Implement prevention measures
 behavioural, political, environmental
 Monitoring, evaluation

 Sterilization,
 Disinfection,
 Antisepsis
 and Decontamination

Sterilization
and
disinfection
 Historical background •
 The scientific use of disinfection
and sterilization methods originated
more than 100 years ago •
 Ignatz Semmelweis (1816-1865)
 Joseph Lister (1827-1912)
 Important pioneers for the
promotion of infection control

Principles
of
sterilization
and
disinfection
 Sterilization - destruction of ALL
forms of life, including the
bacterial spores, viruses, prions –
 No degrees of sterilization: an all-
or-nothing process - physical or
chemical methods

Disinfection
Eliminates most pathogens but not
necessarily all types of microbes.
Disinfection reduces the level of
microbial contamination.
Chemical disinfection does not kill
spores, unlike chemical
sterilization.
Some common laboratory
disinfectants include 10% bleach,
70% ethanol,

Descending
order of
resistance to
germicidal
chemicals
Bacterial
spores
Bacillus subtilis, Cl. sporogenes
Mycobacteria M. tuberculosis, M. bovis
Non-lipid or
small viruses
Poliovirus, Rhinovirus, Coxackie
virus
Fungi Trichophyton spp. Cryptococcus
spp., Candida spp.
Vegetative
bacteria
Pseudomonas, Staphylococcus
aureus
Lipid or
medium size
virus
Herpes simplex virus, CMV,
Hepatitis B, Hepatititis C

Overview of disease agents and other issues

Antisepsis
 Antisepsis is the application of a liquid
antimicrobial chemical to skin or living tissue to
inhibit or destroy microorganisms.
 It includes swabbing an injection site on a person
or animal and hand washing with germicidal
solutions.

Disinfection
Decontamination- removal
of microorganisms
contaminating an object
-Sanitisation-removal of
microbes that pose a threat
to the public health, food
industry, water conditioning
Sanitizer-an agent, usually a
detergent, that reduces the
numbers of bacteria to a safe
level

Aseptic techniques-
prevent microbial
contamination of materials
or wounds
antisepsis-disinfection of
living tissues(e.g., in a
wound),achieved through
the use of antiseptics
-antiseptics are applied (do
not kill spores) to reduce or
eliminate the number of
bacteria from the skin

Factors
that
influence
the
degree of
killing
Types of organisms
Number of organisms
Concentration of disinfecting agent
Presence of organic material (e.g., serum,
blood)
Nature (composition) of surface to be
disinfected
Contact time
Temperature
pH
Biofilms
Compatibility of disinfectants and sterilants

 Prions can withstand temp.
exceeding 121C for several
hours while immersed in
acid or basic solutions

Non criticial materials
Semicriticial materials
Criticial materials
Medical materials are categorized
into tree device classifications:

High-level disinfectants
 Activity against bacterial spores
Intermediate-level disinfectants
 -Tuberculocidal activity but not sporocidal
Low-level disinfectants
 -A wide range of activity against microorganisms but no
sporocidal or tuberculocidal activity

DISINFECTION
Physical methods
• Heat
• moist heat
• dry heat
• Pasterisation
• boiling
• Filtration
• Radiaton

Dry heat
 -requires much longer
exposure times and higher
temperatures than moist heat
 -2 hours at 160Cin dry air
ovens or
 -30 min. at 180C
 Application:sterilization for
heat-stable substances that are
not penetrated by moist heat,
such as oils; for glasswear or
surgical instruments

Boiling and pasteurisation achieve
disinfection but not sterilisation (do
not eliminates spores)!!!
boiling
-kills most microorganisms in 10
min. at 100C
-Tyndallisation-an exposure of
100°C for 20 minutes on 3
successive days; sporicidal

Pasteurisation
 -do not kill spores
 -LTH(low temperature holding) batch method-63-65C for
30min.
 -) -135C for 1-2 sec.
 UHT(ultra-high temperature
 -HTST(high temperature short time)flash method- 72C for
15 sec.
 Application: in the food industry, eliminating food-born
pathogens without affecting the taste (e.g. UHT milk)

Filtration
of liquid
-the membrane filters composed of plastic
polymers or cellulose esters containing
pores of certain size
-pore size of:
•0,45 and 0,80 μm-most bacteria, yeasts
and molds
•0,22 μm-for criticial sterilizing, e.g.
parenteral solutions
•0,01 μm-for retaining small viruses
Application: parenteral solutions (serum),
vitamins, vaccines and antibiotic solutions

Filtration of air
-Filters remove microorganisms larger than 0,3μm
-the high efficiency participate air (HEPA) filters
Application: In laboratory hoods and in rooms of
immunocompromised patients

Radiation
 -used in two forms: ionizing and nonionizing
 ionizing radiation
 -gamma rays or electron beams
 -short wavelenght and high energy
 Application: for the medical industry: the sterilization of
disposable supplies (syringes, bandages, catheters and
gloves)

Radiation
(nonionizing)
-in the form of ultraviolet rays
(UV)(280-200 nm)
-long wavelenght and low energy
-poor penetrabilty
-the use is limited
Application: to reduce airborn
pathogens
(surgical theaters, filling equipment)

Chemical agents
 Alcohols
 Aldehydes
 Halogens
 Phenols
 Surfactants
 Heavy metals
 Dyes
 Gases (ethylene oxide, oxidants)

Alcohols -ethanol 70%,isopropanol 70%, propanol
60%
-inactivate microorganisms by denaturing
proteins
-wide spectrum againts bacteria and fungi
but not sporocidal!
-tuberculocidal and virucidal for most
viruses (15 min.)
-the most effective concentrations are
between 60%-90% (water is needed in
chemical reactions)
Application: surgical and hygienic
disinfectio nof the skin and hands

Halogens(chlorine,
iodine,and their
derivatives)
Øchlorine
-denatures proteins by oxidative effects
after dissolution with water of chloride ions
-used in the form of hypochlorite(e.g. liquid
sodium hypochlorite -household bleach)
-broad-spectrum activity, sporocidal
required the long exposure time
-corrosive
Application:disinfection of water and
swimming pool, cleaning and washing
products

Iodine (2 forms)
 Tincture (alcohol and iodine)
 Iodophores (iodine and surfactants)
- bactericidal, not sporocidal
 -less irritant than pure iodine
 Application:as aniseptics, disinfection of skin and
small wounds

Phenols
-today, chemically substituted
 -denaturate proteins
 -irritate the skin, corrosive
 -broad-spectrum, but not sporocidal, not virucidal
 Application: widely used, disinfectionof hospital,
institutional, and household enviroment (soaps)

Sterilization
methods
Physical methods
•Moist heat in autoclaves
•Dry-heat in ovens
•Gamma irradiaton
•Filtration
üChemical agents
•Ethylene oxide
•Glutaraldehye (high concentration)

Disinfection
methods
 Chemical
agents
 Alcohols
 Aldehydes
 Halogens
 Phenols
 Surfactants
 Heavy metals
 Dyes
 Oxidants
Physical
methods
 Boiling and
pasteurisation
 Ultraviolet
radiation

Overview of disease agents and other issues

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