Intro to Microbial Disease and Diagnosis

Question 1

What are Koch’s postulates to establish an agent as the cause of infectious disease?

Answer 1

-agent must be associated with disease state, but not normal
-must be isolated in pure culture
-pure culture must be able to induce disease in an appropriate model
-same agent must be re-isolated from model system

Question 2

what are examples of constitutional symptoms?

Answer 2

headache
fever
malaise (ill feeling)
rhinitis (runny nose)
coryza (stuffy nose, sneezing, cough)
myalgia (muscle aches)
arthralgia (joint aches)
parotitis (swelling of salivary glands)
jaundice (yellowing of skin, white of eyes)

Question 3

what are examples of physical signs and symptoms?

Answer 3

-skin rashes (exanthema)
-buccal lesions (enanthema)
-sores
-vesicular rashes
-warts
-nodules
-pustules

Question 4

what is the chain of infection

Answer 4

microorgansim>reservoir>port of exit>modes of transport>port of entry>susceptible host

Question 5

airborne transmission

Answer 5

infectious agents are carried in the air via aerosols

Question 6

respiratory transmission

Answer 6

-infectious agents are carried from an infected person’s nose or mouth via coughing, sneezing, or through saliva and mucus
-requires close but not direct contact

Question 7

formite transmission

Answer 7

-inanimate objects that are contaminated with an infectious agent
-usually nonporous hard surfaces that infectious agents stay on until they are disinfected

Question 8

direct contact transmission

Answer 8

-direct physical contact like touching, hugging, kissing, sex
-also spread from sharing food, cups, utensils

Question 9

blood-borne transmission

Answer 9

-occur from the introduction of a pathogen via blood transfusion
-organ transplant also known risk

Question 10

trans-cutaneous (vector) transmission

Answer 10

occurs when a living organism carries a disease pathogen and passes it to another living organism; vector not harmed or infected

Question 11

enteric (fecal-oral) transmission

Answer 11

-infectious agents that are spread from the feces of infected individual to the mouth of another individual
-most cases of food or waterborne illness
-frequently caused by poor sanitation or hygiene

Question 12

vertical (maternal-fetal) transmission

Answer 12

-passed from mother to child either in utero, during vaginal birth, or perinatally

Question 13

how can the chain of infection be broken

Answer 13

1) eliminating reservoirs (drain diseased ponds; reduce HIV viral load in infected patients)
2) disrupting transmission (disinfecting surfaces, wearing masks, condom use)
3) reducing numbers of susceptible hosts (immunization, drug prophylaxis (HIV Prep))

Question 14

what are the 7 techniques of diagnosing microbial disease in vitro?

Answer 14

-direct visualization of organisms
-culture organisms in vitro (gold standard)
-detect antigens
-detect host immune response
-detect activity of specific enzymes
-detect genomes (RTPCR)
-detect cellular changes likely due to presence of organism

Question 15

-method of choice for diagnosing parasitic diseases
-look for parasites in blood ova or stool
-relatively easy for parasites and worms due to size
-harder for bacteria
-virus detection required electron microscopy

Answer 15

direct visualization

Question 16

-plaque assay to determine the presence of virus
-can be challenging and slow; may take 7 days or more to yield useful info

Answer 16

culture

Question 17

detection of bacterial or viral antigens

Answer 17

antigen tests

Question 18

typically look for antibodies (ELISA and western blot) but can look for T cells as well (ELISpot)

Answer 18

detection of host immune response

Question 19

-demonstrates the presence of a specific pathogen
-can determine the amount of infectious agent present
-can determine presence of specific mutations

Answer 19

detection of genomes

Question 20

what test is widely used for detection of changes in host cells?

Answer 20

-Papanicolaou stain (Pap test)
-examines cervicovaginal squamous epithelial cells
-abnormal cells may indicate cervical dysplasia
-increased nucleus/cytoplasm ratio associated with HPV disease and cancer

Question 21

what needs to be considered to determine how good a diagnostic test is?

Answer 21

1) sensitivity (how many true positives)
2) specificity (can it discriminate against false positives)
3) positive predictive value (how likely is a patient with a positive result to be a true positive)
4) negative predictive value (how likely is a patient with a negative result to be a true negative)

Question 22

generally, the more rapid the test….

Answer 22

the greater the margin of error