12: Infectious Disease Flashcards
Infectious Disease Importance
- Significant cause of morbidity and mortality worldwide
- Associated with cancer (~10-15% cancers)
- Cause disease outbreaks in institutions
Epidemiologic Triangle
Used to explain etiology of infectious diseases. Three major factors in pathogenesis of disease: agent, host, and environment
Microbial Agents of Infectious Disease
- Bacteria
- Viruses and Rickettsia
- Mycoses
- Protozoa
- Helminths
- Arthropods
Bacteria
Once were leading killers, but now controlled by antibiotics. Remain significant causes of human illness. Emergence of antibiotic-resistant strains a growing concern.
Botulism, Cholera, Gonorrhea, Lyme Disease, Plague, Syphilis, Tetanus, TB, Typhoid Fever, Tularemia
BACTERIAL
Virus
Microorganism smaller than bacteria, which cannot grow or reproduce apart from living cell. Invades living cells and uses chemical machinery to replicate itself.
Rickettsial Agents
Gram negative bacteria that combines aspects of both bacteria and virus. Can reproduce only inside living cell. Organism can occur in cytoplasm of tissue cells or free in the gut of arthropods.
AIDS, Dengue Fever, Chickenpox, Hepatitis, Herpes, Measles, Mumps, Rabies, Rubella, West Nile, Ebola
VIRAL
Mycoses
Fungal Disease
- acts as a pathogen
- opportunistic mycoses (infect immunocompromised)
- Hospital-associated infections
- Community-acquired infections (Valley Fever)
Aspergillosis, Blastomycosis, Cryptococcosis, Histoplasmosis, Tinea Pedis
FUNGAL
Protozoa
Microscopic, one-cell organisms that can be free living or parasitic in nature. Able to multiply in humans, which contribute to their survival. Transmitted by fecal-oral route, via arthropod vector
Malaria, Amebiasis, Babesiosis, Leishamania, Cryptosporidiosis, Giardiasis
PROTOZOA
Leishmania Disease Presentation
- Cutaneous
- Mucocutaneous
- Visceral (Black Fever)
- No vaccines, use chemotherapies
Helminths
Large multicellular organism, either free living or parasitic. Typically found in tropical areas. Flatworms, Thorny-Headed Worms, or Roundworms.
Trichinellosis, Schistosomiasis
HELMINTHS
Alpers Syndrome, Creutzfeldt-Jakob Disease, Kuru, Fatal familial Insomnia, Transmissible Spongiform Encephalophathy
PRIONS
Arthropods
Act as insect vectors. Capable of transmitting bacteria, virus, and protozoa infections. Mosquitos, ticks, flies, mites
Infectivity
Capacity of agent to produce infection or disease. Measured by secondary attack rate. (new cases-initial cases)/(susceptible persons-initial cases) x 100
Pathogenicity
Capacity of agent to cause disease in infected host. Measured by proportion of individuals with clinically apparent disease. (ill+dead)/(infected) x 100
Virulence
Refers to severity of disease. Measured by proportion of total cases with overt infection divided by total number of infected cases. If fatal, use case fatality rate. (deaths)/(ill+infected) x 100
Toxigenicity
Capacity of agent to produce a toxin or poison.
Resistance
Ability of agent to survive adverse environmental conditions.
Antigenicity
Ability of agent to induce antibody production in host. Related to immunogenicity.
Host
Person who permits lodgment of infectious disease agent under natural conditions. Severity of infection will depend on host’s ability to fight off infectious agent. Nonspecific vs. Disease-Specific defense mechanisms
Nonspecific Defense Mechanisms
Body’s primary defense against disease.
Disease-Specific Defense Mechanisms
Immunity (resistance) against a particular agent. Active vs. Passive
Active Immunity
Administration of a microorganism to invoke an immunologic response that mimics the natural infection. Natural vs. Artificial
Natural, Active Immunity
Results from an infection by the agent.
Artificial, Active Immunity
Results from an injection with vaccine that stimulates antibody production in host.
Passive Immunity
Short-term immunity provided by a preformed antibody. Natural vs. Artificial
Natural, Passive Immunity
Preformed antibodies are passed to fetus during pregnancy and provide short-term immunity in newborn. Also breastfeeding.
Artificial, Passive Immunity
Preformed antibodies given to exposed individuals to prevent disease. Ex. Ebola
Environment
Domain external to host in which agent may exist, survive, or originate.
Reservoirs
Environment and animals can act as reservoir that fosters survival of infectious afents
Zoonoses
Infectious diseases that are potentially transmittable to humans by vertebrate animals.
Rabies, Plague, Cat Scratch Disease, Ebola, West Nile, Trichinosis
ZOONOSES
Direct Transmission
Spread of infection through person-person contact.
Portal of Exit
Site where infectious agents leave the body. Agent must exit in large enough quantities to survive in the environment and overcome the defenses at the portal of entry into the host.
Portal of Entry
Locus of access to the human body
Indirect Transmission
Spread of infection through intermediary source: vehicles, fomites, and vectors.
Vehicles
contaminated water, infected blood, food
Fomites
inanimate objects laden with disease-causing agents
Vectors
living insects or animals involved with transmission of disease agent
Inapparent Infection
No symptoms of infection present. Disease transmitted to unsuspecting hosts. Ex. Typhoid Mary
Incubation Period
Time interval between exposure and first signs and symptoms of disease. Provides clue to time and circumstance of exposure. Useful for determining etiologic agent.
Herd Immunity
Immunity of population, group, or community against infectious disease when large proportion of individuals are immune either through vaccinations or prior infection. Rubella requires 85-90%, Polio requires 80-86%
Generation TIme
Time interval between lodgment of infectious agent in host and maximal communicability of host. Can precede development of active symptoms. Useful for describing spread of infectious agents that have large proportions of subclinical cases. Applies to both inapparent and apparent cases of disease.
Colonization
Agents multiply on surface of body without invoking tissue or immune response.
Infestation
Presence of living infectious agent on body’s exterior surface, upon which a local reaction may be invoked.
Iceberg Concept of Infection
Active clinical disease accounts for only a small proportion of host’s infections and exposures to disease agents.
Attack Rate (AR)
Used when nature of disease is such that a population is observed for a short period of time. ill/(ill+well) x 100 during a time period
Secondary Attack Rate
Measure of contagiousness. Number of cases of infection that occur among contacts within the incubation period following exposure to a primary case in relation to the total number of exposed contacts. Useful in evaluating control measures. (new cases-initial cases)/(susceptible persons-initial cases) x 100
Initial Case
index case + coprimaries
Index Case
Case that first comes to the attention of public health authorities
Coprimaries
Cases related to index case so closely in time that they are considered to belong to the same generation of cases.
Case Fatality Rate (CFR)
Number of deaths caused by a disease among those who have the disease. (deaths due to disease)/(cases of disease) x 100
Basic Reproductive Rate (Ro)
Measure of infections produced on average by infected individual in early stages of an epidemic when virtually all contacts are susceptible. Used as a measure of transmissibility of infectious disease.
