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Lecture #1-2 Introduction to Microbial Pathogens Fig 20.1. Community water supply in a developing country Recent microbes in the news • • • • • • • Severe acute respiratory syndrome (SARS) West Nile virus Viral or bacterial meningitis Human immunodeficiency virus (HIV) Tuberculosis (drug resistant) Cholera and Malaria Bovine sphongiform encephalitis (Madcow disease) • Salmonella Microbial infection and pathogenesis Types of microbes - Bacteria, fungi and protozoa - Viruses, viroids, prions Pathogenesis - interactions of molecular events in replication of a microbe and host responses that can result in disease Figs 1.5, 1.7, 1.9 Figs 1.10 and 1.11 Microbial infection + immune response = pathogenesis • Patterns of infection or disease . acute - short-lived . persistent - continuous . latent - reoccurs . subclinical - carrier state, no symptoms Table 20.1 Common terms in epidemiology Unifying concepts for replication and pathogenesis Microbe structure (eg. morphology, genome type and size, species or variant) • determines how it interacts with . host or host cells to replicate • . the host immune response • Knowledge of the interaction of microbe with cells provides insights into: • clinical manifestations of infections and • how to control or interfere with these Impact of viruses • Many discovered in the last 20 years • Viral infections cause estimated 50% of all absenteeism from work and school • Bacteriophages affect drug resistance and molecular biology eg. restriction enzymes and reverse transcriptase for cloning • Study as tools to explore biological processes Three things all microbes must do –1 –2 –3 - Make more progeny - Spread and transmission - Evade host defenses • Outcomes of these determine • pathogenesis Fig 20.1 Spread of pathogens How do these microbes spread? • • • • • • • Severe acute respiratory syndrome (SARS) West Nile virus Viral or bacterial meningitis Human immunodeficiency virus (HIV) Tuberculosis (drug resistant) Cholera and Malaria Bovine sphongiform encephalitis (Madcow disease) • Salmonella Reservoirs of infectious agents • Carriers (asymptomatic or subclinical) • Zoonotic diseases • Environmental Fig. 20.01a Reservoirs harbor potentially pathogenic microbes Transmission • Modes of transmission to humans - human to human - animal to human - insect to human • Infection can be localized or systemic - replicates, remains in local area of entry - replicates, spreads by viremia to other sites Fig. 20.01b Modes of transmission of microbes Modes of transmission to or from a host Sites of microbe entry or shedding – Respiratory (secretions, aerosols) – Oral/enteric (food, water) – Urogenital (sexually transmitted) – Vectors (insects, needles, animals) – Contaminated tissues or body products Fig. 20.01c Portals of entry Some specific modes of virus transmission Skin infections - for most, skin lesions not significant means of transmission - exceptions are HSV in genital herpes, chicken pox from shingles, small pox in dried crusts- infectious for months, up to a year Respiratory tract infections - transmission in air depends on coughing, sneezing or infected secretions Figure 20.3 Air bourne transmission Some specific modes of virus transmission (cont.) Semen • - HIV - much less for CMV, hepatitis B - Human milk or colostrum • - CMV, HTLV by mother to child • - not a major transmission mode for • hepatitis B, encephalitis viruses, mumps, rubella Some specific modes of virus transmission (cont.) Salivary secretions • - EBV, rabies - rare possibility for CMV, hepB - Gastroenteric transmission • • • stools eg. enteric virus, poliovirus, rotavirus, hepatitis A - childcare centers, institutions, military camps - contaminated water from poor waste disposal - urine is not a major means of transmission Host factors that affect susceptibility • • • • • • age of host underlying physiological conditions malnutrition genetic determinants gender environmental conditions • others eg. stress, personal behavior Trends in disease • Reduction and eradication of disease • Emerging diseases Epidemiology • The study of factors that influence disease frequency and distribution Fig. 20.08 National and worldwide surveillance of infectious diseases is critical Fig 20.9 Child with smallpox, an eradicated disease (polio, bubonic plague) Fig. 20.09 Fig 20.10 World Map of Emerging Diseases Nosocomial infections Figure 20.11 Fig. 20.12 Nosocomial infections • Hospital acquired disease • Hospitals are reservoirs of infectious agents • Hospitals enable transmission of infectious agents • How to prevent nosocomial infections ? Reservoirs • • • • Other patients Hospital environment Health care workers Patient’s own normal flora What procedures are used in dentistry? Survival strategies of microbes • • • • Gain entry into host Multiply at local site Find suitable niche Overcome or subvert host defenses - outrun - antigenic change - hide in host - mimic host component - inactivate/down-regulate host response ? Questions to consider • • • • • • • • What is the clinical disease manifestation? What microbe(s) causes the disease(s)? How does the microbe enter or leave the host? What is the target tissue(s) and means of replication? Is there damage from replication or immune response? What are the disease patterns? What are the controls, preventions or therapies? Specific distinguishing features