Infection Microbial pathogenicity For MBBS 27 th Sept

Infection & Microbial pathogenicity For MBBS 27 th Sept, 2017 By: Dr Puneet Kumar Gupta Assistant Professor, Microbiology

Animal & Microorganisms relationship • Saprophytes – – Free living microbes Dead & Decaying matter Generally incapable of growth on living tissue Except: B. subtilis (opportunistic infection) • Parasites

Animal & Microorganisms relationship • Parasites – Microbes establish & multiply in host – Pathogen: Produce disease – Commensals: • Live in harmony with host without causing disease • Facultative pathogen: host resistance ↓ ↓

Definitions • Disease and Infectious Disease – 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

Entry of pathogen: • Infection: – Pathogen enter----establish ---multiply---invade Normal anatomical barrier—c/f---infectious ds – Lodgement & multiplication of pathogen in or on tissue of host – Infection----disease • Colonization – Pathogen enter—multiply—not invade/ds/elicit immune response

Classification of Infections • 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 infection vs. secondary infection – Primary Infection • An infection that develops in an otherwise healthy individual – Secondary Infection • An infection that develops in an individual who is already infected with a different pathogen

• Localized infection vs. systemic infection – Localized Infection • 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, subclinical, atypical, Latent infection – Clinical Infection • An infection with obvious observable or detectable symptoms – Subclinical/ in-apparent/Asymptomatic Infection • An infection with few or no obvious symptoms with active infection – Atypical Infection • No characteristic/typical manifestation – Latent infection • Infection—inactive or dormant latent/hidden form— ↓↓ host resistance---proliferation of pathogen----Disease

• 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

Definitions • The suffix “-emia” – A suffix meaning “presence of an infectious agent” • Bacteremia = Presence of infectious bacteria • Viremia = Presence of infectious virus • Fungemia = Presence of infectious fungus • Septicemia = Presence of an infectious agent in the bloodstream

Definitions • The suffix “-itis” – A suffix meaning “inflammation of” • Examples: – Pharyngitis = Inflammation of the pharynx – Endocarditis = Inflammation of the heart chambers – Gastroenteritis = Inflammation of the gastointestinal tract

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 • Noncommunicable Disease – A disease that is not transmitted from one individual to another

Definitions • Endemic Disease – A disease condition that is normally found in a certain percentage of a population • Epidemic Disease – A disease condition present in a greater than usual percentage of a specific population • Pandemic Disease – An epidemic affecting a large geographical area; often on a global scale

Source …. Reservoir § Source: § Person/Animal/Object from which a microorganism is transmitted to host § Reservoir: § Natural habitat in which organism multiply, live. § Maintain parasite in nature § Asymptomatic infection

Source …. Reservoir Infection Tetanus Source of infection Soil Reservoir Soil Hookworm Soil contaminated Man with larva Typhoid Contaminated water & Food Cases/carrier

Source &/or Reservoir • • Human Animal Insects Non living things

Human • Commonest source • Cases/Patients – On basis of symptoms • Subclinical infection • Clinical • Latent • Carriers

Carriers • Carriers – Person/animal harbour infectious agent in absence of clinical symptom & Shed organism from body via contact, air or secretions – Inadequate Treatment/Immune response ---incomplete elimination of organism – Less infectious than Cases BUT More Dangerous • Types: – Incubatory carrier: Measels, Mumps, Polio, Hepatitis B, Influenza, Diphtheria etc – Healthy carrier: Subclinical infection without suffering from overt disease converted into carrier eg. Polio, Diphtheria etc. – Convalescent carrier: Recovered from disease but still continue to harbour pathogen---shed from body

Carriers • Based on duration: – Temporary carrier: <6 months duration Healthy, incubatory, convalescent carrier – Chronic carrier: Indefinite period Hepatitis B, Typhoid, Gonorrhoea • Based on Source: – Contact carrier: acquire pathogen from patient – Paradoxical carrier: Acquire infection from another carrier

Source &/or Reservoir • Human • Animal: Zoonosis: Infection transmitted from animal to human Bacterial (Plague-Rat) Viral (Rabies-Dog) Protozoal (Toxoplasma-Cats) Helminthic (Hydatid disease-Dogs Fungal (Zoophilic Dermatophyte infection) • Insects • Non living things

Source &/or Reservoir • Human • Animal • Insects – – – Arthropod borne disease Mechanical vector Biological vector: multiply/development Extrinsic incubation period Transovarian/ Transstadial passage • Non living things – Soil & water – Food

Mode of transmission • Contact – Direct: STD – Indirect: Formite/ inaminate objects • Inhalational – Droplet >10µm – Droplet nuclei <10µm • Ingestion • Inoculation/ Percutaneous – Animal bite, Direct inoculation into tissue following injury – NSI, blood borne infections • Vector borne • Vertical

Mode of transmission • Vector borne – – – – Mechanical vector, Biological vector Mosquito Sandfly Ticks (hard, soft) Housefly Tsetse fly Louse cyclops • Vertical • Laboratory induced & Iatrogenic

Mode of transmission • Vertical – Transplacental: TORCH – During passage through birth canal: Gp B streptococcus, HIV, HBV, HCV • Laboratory induced & Iatrogenic

Mechanisms of Microbial Pathogenicity • Pathogenicity and Virulence – Pathogenicity • Ability of a microbe to cause disease • This term is often used to describe or compare species – Virulence • Degree of pathogenicity in a microorganism • This term is often used to describe or compare strains within a species

Virulence variations • Spontaneous • Induced ↓----Attenuation – – Passage in unfavourable conditions Repeated subculture artificial media Prolonged storage Growth in presence of inhibitors/high temperature ↑---Exaltation – Serial passage in susceptible host

Determinants of Virulence • Route of entry of pathogen – Cholera: oral ---ds Subcutaneous- no ds • Infective Dose/Inoculum – Low: (10 -500 organism) • • Shigella Cryptosporidium parvum EIEC C. jejuni – High (106 -108) • Salmonella • Vibrio cholera

Determinants of Virulence • Adhesions – Fimbriae or pilli – Biofilm – Non pilus adhesins • M protein (GAS) • Lipotechoic acid • Invasiveness: Ability of a pathogen to spread in host tissue after establishment – – – Staphylococcus/Streptococcal infections Antiphagocytic factors Capsule Cell wall proteins Cytotoxins

Determinants of Virulence • Intracellular survival Inhibition of Phagolysosomal fusion Legionella M. tuberculosis Resistance to lysosomal enzymes Salmonella Typhimurium Coxiella spp Leshimania M. leprae Adaptation to cytoplasmic replications Listeria Rickettsia – Facultative/Obligate intracellular

Determinants of Virulence • Toxins – Exotoxin – Endotoxin

Property Endotoxin Exotoxins Nature LPS Proteins Source Cell wall GN Secreted by G+ G-ve Released by Cell lysis Actively secreted to surrounding medium Heat stability Highly Stable Destroyed at 600 C M/A ↑IL-1, TNF Most enz mediated Effect Broad non specific Specific to particular tissue Tissue affinity No Yes Fatal dose Large Small Antigenicity Poorely immunogenic Highly Neutralization by Ab Ineffective Neutralised Used for vaccine No Toxoid form used

References • Textbook of Microbiology by Ananthanarayan & Paniker’s 10 th Edition • Essentials of Medical Microbiology by A S Sastry & Sandhya Bhat K, 1 st Edition

Thank you