Human-Microbe Interactions: Principles of Disease Transmission PDF

NURS 236: Human-microbe interactions Principles of disease and transmission 1  Learning objective (part 1) To recall predisposing factors for disease To explain the stages of disease To explore the variety of reservoirs of infection...

NURS 236: Human-microbe interactions Principles of disease and transmission 1  Learning objective (part 1) To recall predisposing factors for disease To explain the stages of disease To explore the variety of reservoirs of infection To contrast methods of disease transmission and examples of each 2  Patterns of disease Predisposing factors – Any factor that would increase a host’s ability to be infected or alter how a disease progresses – Examples Gender – UTIs, pneumonia, meningitis Genetic background – sickle-cell anemia and malaria Climate – environmental survival of MO Weather, nutrition, fatigue, age, environment, lifestyle, occupation, etc. p. 410 3  Patterns of disease Stages of disease – Can link to stages of MO growth – Different MOs May vary in the length of each period Whether the host is infectious at each stage Fig. 14.5 Tortora et al., 2013 4  Patterns of disease Incubation period – Initial infection to first symptoms Prodromal period – Early, mild symptoms – Relatively short, may not be present in all diseases (virulence attack) Fig. 14.5 Tortora et al., 2013 5  Patterns of disease Period of illness – Most severe signs and symptoms; major immune response Period of decline – Symptoms decrease; susceptibility to secondary infections Fig. 14.5 Tortora et al., 2013 6  Patterns of disease Period of convalescence – Return to normal/homeostasis Fig. 14.5 Tortora et al., 2013 7  Discussion: How do the stages of microbial growth compare to the different stages of disease? 8  Spread of infection: Reservoirs Reservoirs – Source of a disease-causing MO 3 major groups – Humans – Animals – Nonliving 9  Spread of infection: Reservoirs Humans – Symptomatic – Asymptomatic Carriers (E.g., hospital staff with MRSA) During incubation or period of convalescence stages of disease – Example organisms STIs Streptococcal infections 10  Spread of infection: Reservoirs Animals – Zoonoses Diseases that are transferred from animals to humans – Many different routes Direct contact with an infected animal or its feces Animal contaminated water, food (pets), animal products, hides Can also be transmitted by arthropod vectors 11  Table 14.2 Tortora et al., 2013 12  Spread of infection: Reservoirs Nonliving – Environmental sources of infection Soil – Fungi, nematodes, Clostridium tetani, C. botulinum Water – Protozoa, some helminths Food – Food poisoning, such as salmonellosis 13  Spread of infection: Transmission 3 modes: contact, vehicles, vectors Contact – Direct contact Physical contact between source and host (touching, kissing, etc.) Common cold, influenza, hepatitis A, measles, STIs Prevent via protective equipment 14  Spread of infection: Transmission Contact (continued) – Indirect contact Physical contact from source to host via a nonliving object HIV or hepatitis B in contaminated syringes, organisms living in hospital environment Prevention by maintaining a clean environment – Droplet Contact with aerosolized liquid that contains MOs (< 1 m) Influenza, whooping cough Prevention through good hygiene practices 15  Spread of infection: Transmission Vehicle transmission – Disease transmitted by a medium – Water E.g., fecal contamination leading to cholera or leptospirosis – Food Such as poor cooking, storage or preparation conditions leading to food poisoning or tapeworms – Air Similar to droplet contact, but larger distances Airborne MOs or dust particles leading to tuberculosis or fungal infections 16  Spread of infection: Transmission Vectors – MO is transmitted between hosts by another organism (typically an insect) – Mechanical Passive transport by insect from vector’s body to food Typhoid fever or shigellosis on fly feet – Biological More active and complex Some phase of MO life cycle (growth/reproductive) occurs in vector Malaria – Plasmodium faciparum 17 Vector organisms Table 14.3 18 Tortora et al., 2013  Learning Objectives( Part 2) To be able to explain pathology, etiology, infection and disease To recognize the difference between normal and transient microbiota To understand the different types of symbiosis To be aware of where in the body normal flora are present or absent To recall the impact of opportunistic pathogens 19  Important terms Pathology – Scientific study of disease Etiology – Cause of a particular disease (e.g., a particular MO) Pathogenesis – Steps in progression of a disease Infection – Pathogenic MO enters a host and begins to grow Disease – Change in host’s state of health that is associated with an infection 20  MOs on the human body Many environments on/in the human body – Microbiomes – Influenced by many factors (chapter 6) Differences between: – Normal microbiota MOs that are normally found on our body – Transient microbiota MOs that live on/in our body for a period of time and then leave – Can also be differences between individuals Image from Wikimedia Commons 21 Example human MOs Table 14.1 22 Tortora et al., 2013  MOs on the human body Different relationships with these MOs – Different types of symbiosis +/O +/+ +/- Relationships can change with conditions (Ch. 6) – Opportunistic pathogens (E.g., Candida albicans, Clostridium difficile) Fig. 14.2 23 Tortora et al., 2013  Learning objectives (part 3) To know all that there is to know about nosocomial infections To recognize the causes of emergent infectious diseases and some examples 24  Nosocomial infections Infection acquired during a hospital or other health-care associated visit – Growing frequency Interaction between 3 factors Fig. 14.5 25 Tortora et al., 2013  Nosocomial infections MOs in hospital environment – Common environment for MOs that alter health – Resistances to cleaning agents, antibiotics Table 14.4 26 Tortora et al., 2013  Nosocomial infections Compromised host – Many body structures prevent illness These can be broken (open wounds, skin, or mucous membranes) or weakened (immune system) Table 14.5 27 Tortora et al., 2013  Nosocomial infections Chain of transmisssion – Mostly through direct and indirect contact transmission (hospital staff) Moving between different patients, shared patients Control of nosocomial infections – Handwashing – lead by example – Identify sources/causes and resolve any problems – Watch for patterns → epidemiology 28  Think-pair-share Identify the 3 factors that results in nosocomial infections and 2 strategies that could be used to combat these. Have each strategy address different factors. 29  Emerging infectious disease Disease that either appears for the first time or changes in a manner that either potentially or actually increases its incidence Many causes/factors influence “emergence” 30  Emerging infectious disease: factors Factors – New disease Zoonotics – humans never exposed before (HIV) New to an area - international travel a major concern (smallpox in N. America, West Nile virus) – Genetic Acquisition of a new traint – Antibiotic resistance (MRSA), strain mixing (Influenza), Toxin production (E. coli O157:H7) – Environmental Movement of MO, reservoir, or vector to a new area – Climate change leading to changes in malaria, Hantavirus regions – More on p. 418 31 Emerging infectious diseases: examples Table 14.6 32 Tortora et al., 2013  Sample question Identify an emerging infectious disease and explain why that particular disease may be classified that way 33