Infectious diseases

Infectious diseases

1. Definition

   • Infectious disease
     • -disease caused by infectious agents(bacterium, virus, protozoan, fungus) -can be passed to other host
   • Infection
     • -occurs when the infectious agent enter the body and start reproduction -may or may not lead disease
     • Pathogen
       • -a type of infectious agent can cause disease
     • Host
       • -an organism infected by another organism
     • Virulence
       • the relative ability of an agent can cause rapid and severe disease in a host
   • Prevalence
     • -number of cases at a given time -expressed as a percent at a given time =product of incidence x duration of disease(long duration:hepatitis B)
   • Contamination
     • The presence of an infectious agent on different kinds of material/substances(e.g. water, a body surface, clothes)
   • Disease
     • -a pathological condition -characterized by signs and symptoms
   • Immunogenicity
     • The ability of an organism to produce immune response after an infection: -providing protection against a similar or the same organism(e.g. infectious agents)
   • Vector of infection
     • an insect or any living carriers:transport an infectious agent from an infected individual/its wastes to other susceptible individuals/food/surroundings.
   • Reservoir
     • any person,animal, arthropod, plant, soil or substance or combination of these:allow an infectious agent to live and multiplies. -an infectious agent are transmittable to other susceptible(natural habitat)
   • Imapparent infection
     • -no detectable clinical symptoms -can be documented by :    1.isolation of a pathogen,     2. detection of it component(DNA)    3. produce a specific immune response in                 person(asymptomatic)
   • Incidence
     • 1.number of new cases in a given time period 2.expressed as percent infected per year/number per person time of observation
   • Special terms
     • Nosocomial
       • 1. an infection originating in a patient while in a hospital 2. not related to the patient's primary condition-e.g. infection of surgical wound, hepatitis B, urinary tract infection
       • Opportunistic infections
         • infection by organisms -take opportunity provided by a defect in host defense -organism infect the host and cause disease. 
     • Eradication
       • -aims to termination of all transmission of infection(extermination of the infectious agent) -absolute process(an all or non phenomenon)
       • Elimination
         • It is used to describe eradication of a disease(e.g. measles/polio) from a large geographic  region.
     • Reproductive rate
       • It describes the potential for an infectious disease to spread. Influential factors: 1.probability of transmission 2.frequency of population contact 3.virulence of the organism 4.population immune proportion 5.duration of infection

2. Causes

   • Genetic
   • Biological
   • Physical
   • Environment
   • Chemical

3. Early history

   • 1.Smallpox-trigger epidemic in ancient Greece and Egypt 2.Plague-coinfect with measles and smallpox  3.Syphilis- spreadly rapidly through europe in 1490s and cause high mortality

4. Koch's Postulates(a particular agent can cause a specific disease)

   • 1. specific agent must be associated with every case of the disease. 2. the agent can be isolated from a diseased host and grown in culture 3. the culture-grown agent is introduced into a healthy species must cause the same disease 4.the same agent must be again isolated from the infected host

5. Caused by infectious disease agents

   • 1.microbes/microorganisms -bacteria -viruses -protozoa -fungi -Helminths(animals)
   • MOA for induceing disease
     • 1.production of poisons(enzymes or toxins) 2.direct invasion and destruction 3.trigger immune responsed

6. Phases

   • Incubation period
     • Time between infection and apparent of symptoms
     • Prodromal period
       • mild,non specific symptoms that signal onset of some disease
       • Clinical phase
         • a person experiences typical signs and symptoms
         • Decline phase
           • subsidence of symptoms
           • Recovery phase
             • symptoms have disappeared -tissue heal -body remains strength

7. Classifications

   • By duration
     • 1. Acute 2.Chronic 3.Latent -characterized by periods of no symptoms between outbreaks of illness
   • By location
     • 1. Local- confined to a specific area of body 2. Systemic- infects most of the body with pathogens distributed widely in tissues
   • By Timing
     • 1. Primary:initial infection in a healthy person 2. Secondary:infection that occurs in a person weakened by a primary infection
   • Clinical
     • 1. Diarrheal diseases 2. Respiratory diseases 3. Central nervous system infection 4. Cardiovascular infection 5.Sepsis
   • Microbiological
     • 1. Bacterial 2. Viral 3. Fungal 4. Parasitic 5. Prion
   • Transmission
     • 1. Contact(direct/indirect) 2. Food/water borne 3. Airborne 4. Vecter borne 5. Perinatal:occurs during pregnancy
   • Reservoir
     • 1. Human:HIV, HBV 2. Animals: Rabies 3. Soil 4. Water:Pseudomonas aeruginosa

8. The severe level

   • Endemic
     • The constant of a disease or infectious agent within a given geographic area
   • Pandemic
     • an worldwide epidemic affect high proportion of global population
   • Epidemic
     • The occurrence of a disease/illnesses excess of what may be expected on the basis of past experience for a given population

9. Transmission

   • 1.air 2.contaminated food/water 3. body fluids 4.Direct contact 5.animal vectors
   • Reducing spreading
     • 1.Vaccines 2.Antimicrobial drugs 3.Good personal hygiene 4.Protection against vectors 5.Quarantine