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.