Host, Agent & Environment

Question 1

define Bacteria

Answer 1

Simple single cell
May replicate within and outside the human body, classified by shape.
Ex. Plague -Yersina pestis

Question 2

define Virus

Answer 2

Non cellular agent, nucleic acid fragments enclosed within a protein shell
Can only replicate within the host
Classified by type of nucleic acid 
Virus may develop resisitance
Ex. Varicella- Chickenpox
HPV- warts/cancer

Question 3

Fungi

Answer 3

2 types- mold (multiple cell) and yeast (single cell)
classified by location of infection- sytematic (true pathogen) or bodysurface infection
often live in free soil
Ex. trichophyton species- Tinea (athletes foot)

Question 4

Parasites - Protozoa

Answer 4

single cell
mostly live freely in aquatic env
ex. malaria , trichomoniasis
related to chemical, drying, and temperature

Question 5

Parasites- Helminths

Answer 5

large macroscopic worms

ex.tape worms, hook worms, trichinella

Question 6

Prions

Answer 6

agents cause spongiform changes in the brain
protein only
changes shape which disrupts brain protein function which interferes with neuron function
long incubation period

Question 7

Infection

Answer 7

Entry and establishment of a micro-organism within the body

Question 8

Types of infection (3)

Answer 8

Colonization
Asymptomatic
Symptomatic

Question 9

Colonization

Answer 9

infection type present on the surface of the body

organisms produce at a rate without producing identifiable evidence of any reaction in host

Question 10

Asymptomatic

Answer 10

aka inapparent/subclinical - org is multiplying and has measurable reaction but not clinically detectable

Question 11

Name the 5 Modes of transmission

Answer 11

Person-to-person contact
Food and water borne
Airborne
Vector-borne
Perinatal

Question 12

Person to person DIRECT

Answer 12

physical contact b/t infected and suscpetible
Ex. sexual transmission - mucous membrane to mucous membrane
Ex. skin to skin contact- Herpes

Question 13

Person to person INDIRECT

Answer 13

spread by 2 ways

1. body fluids-sneeze, cough, vomit
2. fomites- Objects - counter, doorknob, syringes

Question 14

Food and Water Borne

Answer 14

INDIRECT transmission - an ingestion of contaminated food. Extent of transmission affected by range of distribution of food and water
ex. hep A, Salmonella, E.Coli, campylobacter

Question 15

Airborne

Answer 15

inhalation of organism
Ex. Legoinlla, TB
avg. person inhales 8 organisms per min, most non pathogenic

Question 16

Vector borne

Answer 16

disease carried from host to host via insect

Ex. lyme, West nile, Malaria

Question 17

Perinatal

Answer 17

aka vertical transmission-
infection from mother to child 
1. in utero- placenta
2. during birth
2. post-partum- breast milk

Question 18

4 Descriptors of Infection

Answer 18

Infectivity
Pathogenicity
Virulence
Immunogenicity

Question 19

Infectivity

Answer 19

ability to cause infection

How likely is it that a person has an infection?

Question 20

Pathogenicity

Answer 20

ability for an organism to produce disease
ex. rabies(high) and polio (low)
How likely is a person with infection to develop symptomatic disease?

Question 21

Virulence

Answer 21

ability to cause SEVERE disease
Ex. smallpox(high) and common cold(low)
How likely is a person with infection to develop severe disease?

Question 22

Immunogenicity

Answer 22

ability of org to produce immune response after infection the provides protection from re-infection

can have immune response without protection

Question 23

Infectious dose

Answer 23

Amount of pathogen (number of organism copies) it takes to establish infection
E. coli - 106 to 108
Campylobacter – 500
M. tuberculosis – Less than 10

Question 24

Adaptations

Answer 24

Mechanism by which agent adapts to human host and environment – Genetic change

Question 25

3 Mechanism by which humans adapt to agents

Answer 25

Control measures
Immunity
Genetic change

Question 26

Zoonotic infection

Answer 26

Any disease or infection that is naturally transmissible from vertebrate animals to humans and vice-versa
60 percent were zoonotic pathogens

Question 27

Dead end host

Answer 27

A hostfromwhichinfectiousagentsarenot

transmittedtoothersusceptible hosts.

Question 28

3 Types of environmental influences

Answer 28

Natural environment – climate, season (Zika, flooding)
Man made environment – transportation, housing (homes in woods- lyme disease,airplanes increased global burden of infection)
Social system – social class, war, civil unrest, laws (stigma for std screening, antivaccers campaigns,wars result in refugees camps)