Chapter 18 19 Blanks Chapter 18 Pathogenic microbes What is an infectious disease 04 14 2015 Disease a disturbance in normal functioning of an organism o Infectious disease caused by a microbe and can be transmitted from host to host o Influenza HIV hepatitis B Zoonotic diseases infectious diseases of infectious diseases of animals that can cause disease when transmitted to humans o Rabies West Nile fever a human cannot give another human rabies o Pathogens microbes frequently associated with disease production o Pathogenesis mechanism a microbe uses to cause the disease state o Infection replication of a pathogen in or on its host may or may not cause disease symptoms so it doesn t necessarily mean sickness Not all pathogens have the same ability to cause disease o Primary pathogens produce disease readily in a healthy host o Opportunistic Pathogens generally only cause disease when displaced to an unusual site or when he host has a weakened immune system means they are immuno compromised Virulence measure of the severity of disease a pathogen can induce o Pathogens can weaken over time or show different virulence levels due to genetic differences Attenuated strains show decreased virulence May be useful for vaccine development Avirulent strains can no longer cause disease Carrier individual infected with a pathogenic microbe who never exhibits overt signs or symptoms of the disease asymptomatic o The asymptomatic host may still be able to transmit the microbe to others o A famous carrier case was Mary Mallon aka Typhoid Mary The Transmission of Infectious Diseases How are infectious diseases transmitted Routes of transmission o Transmission spread of an infectious agent from one host to another o Contact May also occur from a pathogen s natural source reservoir to a host Direct physical contact between infected and susceptible individual object is often a fomite inanimate object o Fecal oral o Respiratory aerosol o Vector borne transmitted via another species e g mosquitoes carrying malaria parasites to humans sexual transmission Zoonotic transfers Pathogen moves from its natural reservoir host to a human o humans are often dead end hosts where the pathogen isn t o Epidemiology study of patterns of disease in populations o morbidity rate rate of disease in a population o mortality rate death rate of disease o ultimate goal is to know as much as possible about how infectious diseases spread to be better equipped to prevent them In the United Sates the Centers for Disease Control and Prevention CDC is the federal epidemiology body The World Health Orginazation WHO is a global epidemiology center Patterns of infectious disease o Endemic disease habitually always present in the population often results in cyclical patterns of increased and decreased incidence not present at the same levels at all times Rabies to North American foxes bats etc Incidence rates may change with the season o Epidemic incidence of a disease rises significantly above the normally expected value o Outbreak unexpected cluster in a short time in a localized population o o Pandemic A global epidemic H1N1 Spanish flu of 1918 plague smallpox cholera AIDS Types of epidemics o Common source epidemics a single source to which the population is exposed Food poisoning rapid increase in incidence with a rapid decrease o Propogated epidemic infection passing from one host to another often results when an infected individual is introduced into a susceptible population chickenpox typically exhibits a gradual increase in incidence over time 04 14 2015 The Evolution of New Pathogens How do new infectious diseases arise Encountering a new population o Emerging or re emerging diseases may occur when a pathogen encounters a new population Transfer of simian immunodeficiency virus SIV into humans as HIV is an example HIV 1 has evolved into several genetically distinct subtypes clades Encountering a new population o Lyme disease Caused by the bacterium Borrelia burgdorferi Normally resides in deer and mice Can be transmitted to humans through the black legged tick lxodes scapularis a vector organism Induces a characteristic bulls eye rash in early stages Began appearing in the U S in the mid 1970 s in Old Lyme Connecticut Quickly spread through the U S as human developments spread into wooded areas Increased interactions between humans and the bacteria laden tick vectors Microbes becoming more virulent Some things that were previously harmless can gain characteristics that make them virulent An example of this is o Pathogenic E coli We have E coli in our intestines and it doesn t harm us Why does some E coli become dangerous Acquisition of virulence factor genes via horizontal gene transfer E coli O157 H7 produces a toxin derived from Shigella species This toxin allows it to destroy host hells by shutting down protein production making this strain much more dangerous o Methicillin resistant Staphylococcus aureus MRSA Again S aureus is very common in us and on us In 1961 first reports of MRSA began Since the 1990 s MRSA infection rates have drastically increased from locker rooms wrestling mats and contact sports Selective pressures of antibiotic overuse have led to acquisition of resistance traits against the drugs a normal microbe becomes significantly more dangerous more virulent to humans as strains able to resist elimination drugs are selected Chapter 19 Introduction Immunity is important to life around us We are constantly under assault from microbes in us on us and We must have systems in place to provide defense against this assault which compromise immunity Immunity can be split into two parts o Innate non specific o Adaptive specific Immunity Innate immune defenses Provide a first line against microbes Usually recognize biochemical differences between microbes and host cells This will hopefully prevent foreign cells from being able to take up residence and start reproducing Adaptive immune defense While microbes can be recognized as foreign this system can t discern the precise identity of the microbe o It simply responds to an entire group of similar microbes in the same manner o It is therefore nonspecific in the nature of its responses Found only in vertebrates Works with innate responses to achieve a stronger level of defense o However it recognizes specific pathogens rather than broad classes of microbes o The response is mediated by molecules cells or substances that bind to specific pathogens After initial