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- beingInfectious Disease A disease condition caused by the presence or growth of infectious microorganisms or parasites
Range of relationshipsSaprophytes – 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 -Reinfection Subsequent 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.
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 TRANSMISSION OF INFECTION• Contact-Direct/ Indirect-5Fs• Congenital-• Inhalation• Ingestion• Inoculation• Insects• Iatrogenic• Lab Acquired
Factors predisposing to Microbial Pathogenicity1.Adhesion –Adhesins2. Invasiveness3.Toxigenicity-Exotoxins ,Endotoxins4.Plasmids5. Enzyme production IgA ,proteases6.Bacteriophages7.Communicability8. Bacterial appendages9.Infecting dose-MID AND MLD
Exotoxins Vs Endotoxins • LipoPolysaccharide• Protein• Heat Labile • Heat Stable• Secreted by cells. Diffuse • Part of cell wall. No• out diffusion• Separable by filtration • Obtained only by cell lysis• Enzymatic action • No Enzymatic action• Specific effect • Effect nonspecific• Specific tissue affinity• Active in small qty • Not specific• Highly antigenic • Active in large doses• Action neutralized by Ab • Weakly antigenic• Both G + &G – • Antibody does not• Eg:Botulinum,Tetanus,Diphth eria • Gram negative
Generalized Stages of Infection1. Entry of Pathogen–Portal of Entry2. Colonization–Usually at the site of entry3. Incubation Period–Asymptomatic period–Between the initial contact with the microbeand the appearance of the first symptoms
Prodromal Symptoms–Initial Symptoms5. 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 • Pyemia –• Common occurrence • Septicemia by pyogenicwhile brushing, chewing organisms. Produces Septicemia multiple abscesses in•Circulation,multiplication internal organs. , formation of toxins with high swinging fever
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