Card Set Information
What is epidemiology?
Essentially the study of transmission and proliferation of disease and its application to control disease
What factors affect the successful transmission of a microorganism
1. Number of microorganisms shed
most of shed microorganisms die, with few reaching potential hosts alive ∴ more shedding increases the chance of reaching a fresh host
2. Microorganism stability in the environment
thermostability and resistance to drying increase stability (Clostridial endospores, cysts)
decreased stability creates reliance on close contact, vector, or food/water contamination for infection
3. Efficiency of infection (# needed to cause infection)
varies between organism (10
spp) and route of infection (10 gonococci in urethra vs 1000s gonococci in the oropharynx)
4. Genetic factors in microorganisms
: some strains are more readily transmitted than others
5. Utilizing host responses to benefit the microorganism
Coughing and sneezing can increase fluid secretions and make transmission more efficient
Diarrhea is a highly effective spreading mechanism
How are the most common infections spread?
How is humidity related to transmission from the respiratory tract?
Ill-ventilated rooms are more humid, favoring survival of suspended microorganisms
Air-conditioned rooms tend to be dry which impair mucociliary activity
What are the VERY BASIC 3 steps in fecal-oral spread
Poor public health and hygiene
Fecal microbes appear in water and food
Susceptible individuals are infected
What are the two methods of venereal transmission w/ organisms and description?
Purulent (pus-like) discharge
N. gonorrhoeae, Chlamydia trachomatis
induce discharge to carry organisms over epithelial surfaces easily for transmission
Mucosal sores (ulcers)
: herpes simplex virus
cold sores are sites that contain virus particles
What are the social factors that facilitate STDs?
An increased number of sexual partners per person
Decline of belief that sexual activity is sinful
Knowledge that STDs are treatable and pregnancy is avoidable
***favor of the pill over mechanical barriers for contraception
What are examples of infectious agents of the oropharynx?
streptococci and tubercle bacilli
during respiratory tract infections
paramyxovirus, herpes simplex virus, cytomegalovirus, and human herpesvirus type 6
infect the salivary glands
What are the two methods of transmission from the skin? Which is more common? Example microorganisms?
Direct contact/contaminated fingers is much more common than release into environment
Can include staphylococci and human papillomaviruses
What organisms can be shed in human milk?
HIV, cytomegalovirus (CMV), human T-cell lymphotropic virus (HTLV1)
What are the two main paths for transmission from blood?
Needles (transfusion, drug use, etc)
What is vertical transmission? Horizontal? Importance of each?
: from parents to offspring via sperm, ovum, placenta, milk, or blood
Only important in small, isolated, communities since there are only a few affected individuals per lifecycle
: from individual to individual
Cause quick spread amongst populations
What are the most important vectors? Examples of devastating diseases caused by vectors w/ organism.
Insects, ticks, and mites (the bloodsuckers)
spread by fleas of rats caused the plague
Rickettsia typhi, Rickettsia prowazekii
spread by lice caused typhus
mosquito causes malaria
Aquatic molluscs are necessary intermediate hosts for....?
Schistosomes (blood flukes)
Describe the major infections from domestic pets
: (from dogs) caused by roundworms (
) that can be transmitted from dogs OR cats. Can cause blindness and rheumatic, neurologic, or asthmatic symptoms
: (from cats) caused by protozoan
which affects brain, lung, heart, eyes, or liver