Infectious Diseases Flashcards
What is an infectious disease?
an illness due to a specific infectious agent or its toxic products that arises through transmission from an infected person, animal, or reservoir to a susceptible host, either directly or indirectly through an intermediate plant or animal host, vector, or inanimate environment
What are the 2 basic mechanisms of transmission of infectious agents?
- DIRECT TRANSMISSION from an infected host to a susceptible host
- INDIRECT TRANSMISSION to a vector IH that typically does not show clinical signs and then to a susceptible host
What are the 6 features of infectious diseases?
- dseases are caused by microorganisms
- a case may also be a risk factor (presence of an infected individual starts the spread)
- individuals may be immune
- a case may be a source without being recognizedas a case (no clinical signs)
- preventative measures usually have a scientific bases
- there is sometimes a need for urgency
What is infectivity? How is it calculated?
ability to invade a host
(# infected / # exposed to agent) x 100
What is pathogenicity? How is it calculated?
ability to induce disease
(# with clinical disease / # infected) x 100
What is virulence? How is it calculated?
ability to cause severe disease
(# severely ill / # with clinical disease) x 100
What are the most common infectious agents? Vectors?
- viruses
- bacteria
- parasites
- fungi
- prions
biting arthropods - mosquitos, ticks, lice, fleas, mites, blood sucking flies/bugs (midges, sandflies)
What are the 3 types of hosts of epidemiological importance?
- domestic animals/humans
- sympatric (exist in the same area, like rodents)
- wild
What is the epidemiological triad?
the idea that diseases result from the interactions between the HOST, AGENT, and ENVIRONMENT
(sometimes including a vector or intermediate hosts/reservoirs/carriers)
What are 2 common factors that determine the host susceptibility to and infectious agent?
- genetics
- immunological condition (stressed/well-nourished/vaccinated)
What drives pathogen life cycles? What conditions fvor survival and transmission of infectious agents?
modes of transmission and maintenance of infection (hosts, vectors, agents)
interactions among host, vectors, and the environment
JEV life cycle:
Trichinella life cycle:
Body surfaces as sites of horizontal infection and shedding of infectious agents:
How does vertical transmission occur?
transplacental transmission with direct contact through blood from mother results in birth of offspring with the infectous agent
What are the 2 modes of contact (horizontal) transmission?
- DIRECT - handshaking, bites, breeding, colostrum/milk
- INDIRECT - droplets from sneezing/coughing, fomites (needles, dirty boots, palpation gloves, milking equipment, transport trucks)
What are the 3 modes of vehicle (horizontal) transmission?
- AIRBORNE - dust particles, strong winds (influenza, PRRS, histoplasmosis)
- WATERBORNE - water troughs, streams, pools (Campylobacter, cholera, Giardia)
- FOODBORNE - contaminated food, “food poisoning,” under-cooked contaminated food
What are the 2 modes of vector (horizontal) transmission?
- MECHANICAL - present ON insect bodies, like on the feet and mouthparts (E. coli, salmonellosis, pink eye)
- BIOLGICAL - present IN insect bodies, like gut and salivary glands (Lyme disease, malaria)
What is the chain of infection? What affects the agent’s ability to cause infection, transmission, and host’s ability to be infected?
how the infection moves in a population from agent to host
AGENT - pathogenicity, infection dose, reservoir, source
TRANSMISSION - contact, common vehicle, airborne, vectors
HOST - individual host factors, non-specific resistance, specific immunity
What is the difference between infection and disease?
infection must include invasion of agent into host, multiplicaion of agent, and reaction of the host tissues to the agent +/- toxins, leading to inflammation and WBC reaction
disease is a disorder (so much of a host reaction) of the structure or function of the host, associated with clinical signs
You submit a sample for PCR test and it comes back positive. What do you actually know?
agent DNA/RNA is present —> don’t know if it’s alive or causing disease
What are the transmission time periods of infection and disease in the first patient?
INFECTION: latent period —> infectious period —-> extended period leading to carrier/reservoir status OR infection of a second susceptible host
DISEASE: incubation period —> clinical disease —> dead/suscpetiblility/immunity
What is propagative spread? What 3 types of cases are found?
spread of an infectious agent from one animal to another
- INDEX = first case identified
- PRIMARY = case that brings the infection into a population (can be the index)
- SECONDARY = infection from primary
(tertiary and onward)
What does maintenance of population-level infection depend on?
successful transmission to new host
- characteristics of infectious agents
- susceptibility of host
- population dynamics (size and density)
