Infection
DEEPA BABINASST PROF, MICROBIOLOGY, TMC
Infection Infection -The lodgement and
multiplication of a microbe in or on the tissues of a host.
Disease Any deviation from a condition of good health and well-being
Infectious Disease A disease condition caused by the presence or growth of infectious microorganisms or parasites
Range of relationships
Saprophytes – Free living microbessubsisting on dead or decaying organicmatter.Parasites – Microbes establishing andmultiplying themselves in hosts.Commensals – Microbes living in completeharmony with host without causing any harm tothem.Pathogens Microbes capable of causing diseasein host.
Predisposing Factors to Microbial Pathogenicity
–Pathogenicity • The ability of a microbe to cause disease.This
term is often used to describe or compare species
–Virulence • The degree of pathogenicity in a
microorganism .This term is often used to describe or compare strains within a species
• Exaltation-Enhancement of virulence• Attenuation-Reduction of virulence
Classification of infection• Acute infection vs. Chronic infection –Acute Infection •An infection characterized by sudden
onset, rapid progression, and often with severe symptoms
–Chronic Infection •An infection characterized by delayed
onset and slow progression
Primary vs. Secondary infection –Primary Infection • Intial infection that develops in an
healthy individual– Secondary Infection
•An infection that develops in an individual who is already infected with a different pathogen
-ReinfectionSubsequent infection with the same
pathogen in same host
Localized vs. Systemic infection
–Localized Infection (focal)•An infection that is restricted to a
specific location or region within the body of the host
–Systemic Infection •An infection that has spread to several
regions or areas in the body of the host
Clinical vs. subclinical infection
–Clinical Infection • An infection with obvious observable or
detectable symptoms
–Subclinical Infection • An infection with few or no obvious
symptoms
Atypical infection• Typical clinical features of particular
infection is not present
ENDO vs EXO• Endogenous – disease originates
within the body. Ex: metabolic disorders, congenital abnormalities, tumors.• Exogenous – disease originates
outside the body. Ex: chemical agents, electrical shock, trauma.
Nosocomial infection-
–Cross infection-Already suffering from disease and acquire new disease from another host or another external sources–Nosocomial infection-
–Hospital acquired infection
–Iatrogenic infection-• Physician induced infection during
therapeutic or investigative procedures
Latent & Opportunistic infection
–Latent infection-• After following an infection the pathogen remain in
tissues in a hidden or latent form which produce clinical disease when the host resistance is lowered.
• Opportunistic infection–An infection caused by microorganisms that are
commonly found in the host’s environment. This term is often used to refer to infections caused by organisms in the normal flora
Causing an Infection• In order for disease to occur and spread from
one individual to another, certain conditions must be met.
• If any one condition is not met, the transmission of the disease will not happen.
• Pathogens are everywhere and preventing their transmission is a continuous process.
Introduction of a flora
•Portal of Entry• Susceptible Host• Causative Agent• Reservoir• Portal of Exit• Mode of Transmission
6 Links to the Chain of Infection
SOURCES OF INFECTIONHuman Beings • Animals• Patients• CarriersHealthyConvalescentTemporaryChronicContactParadoxical
• Zoonosis• ReservoirInsects• Mechanical• Biological
Soil & Water Food,Formites
Carriers• Carrier/Human cases–An individual who carries an infectious
agent without manifesting symptoms, yet who can transmit the agent to another individual- Healthy carrier–Convalescent carrier-Individual who
recovered from infectious disease but continous to harbour the pathogen
CARRIERS• Temporary –harbor the pathogen for
short time(days,weeks)• Chronic - harbor the pathogen for long
time(months years,life)• Contact –Acquires the pathogen from a
patient • Paradoxical- Acquires the pathogen from
another carrier
•Animal Vectors •An animal (nonhuman) that can transmit an infectious agent to humans •Two types: mechanical and biological
–Biological animal vectors: The infectious agent must incubate in the animal host as part of the agent’s developmental cycle; eg, the transmission of malaria by infected mosquitoes –Mechanical animal vectors: The infectious agent is physically transmitted by the animal vector, but the agent does not incubate or grow in the animal; eg, the transmission of bacteria sticking to the feet of flies
METHODS OF TRANSMISSIONOF INFECTION
• Contact-Direct/ Indirect-5Fs• Congenital-• Inhalation• Ingestion• Inoculation• Insects• Iatrogenic• Lab Acquired
Factors predisposing to Microbial Pathogenicity1.Adhesion –Adhesins 2. Invasiveness3.Toxigenicity-Exotoxins ,Endotoxins4.Plasmids5. Enzyme production IgA ,proteases6.Bacteriophages7.Communicability8. Bacterial appendages9.Infecting dose-MID AND MLD
Exotoxins Vs Endotoxins
• Protein• Heat Labile• Secreted by cells. Diffuse• out• Separable by filtration• Enzymatic action• Specific effect• Specific tissue affinity• Active in small qty• Highly antigenic• Action neutralized by Ab• Both G + &G –• Eg:Botulinum,Tetanus,Diphtheri
a
• LipoPolysaccharide• Heat Stable• Part of cell wall. No
diffusion• Obtained only by cell lysis• No Enzymatic action• Effect nonspecific• Not specific• Active in large doses• Weakly antigenic• Antibody does not• Gram negative
Generalized Stages of Infection 1. Entry of Pathogen –Portal of Entry
2. Colonization –Usually at the site of entry
3. Incubation Period –Asymptomatic period –Between the initial contact with the microbe and the appearance of the first symptoms
Prodromal Symptoms –Initial Symptoms
5. Invasive period –Increasing Severity of Symptoms –Fever –Inflammation and Swelling –Tissue Damage –Infection May Spread to Other Sites
Epidemiological terms
• ENDEMIC-Disease constantly present in particular area• EPIDEMIC-spreads rapidly, involves many
persons in an area at a time• Eg-meningococcal meningitis, Influenza• PANDEMIC-spreads many areas in world
involves large no with in short period-Cholera,Enterovirus
DEFINITIONS Epidemiology The study of the transmission of disease Communicable Disease –A disease that can be transmitted from one
individual to another • Contagious Disease • A communicable disease that is easily spread from
one individual to another • Non communicable Disease -A disease that is not
transmitted from one individual to another
TYPES OF INFECTIOUS DISEASES• Bacteremia• Common occurrencewhile brushing, chewing Septicemia•Circulation,multiplication
, formation of toxins with high swinging fever
• Pyemia –• Septicemia by pyogenicorganisms. Produces
multiple abscesses in internal organs.