Intro to Microbial Disease and Diagnosis Flashcards
What are Koch’s postulates to establish an agent as the cause of infectious disease?
-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
what are examples of constitutional symptoms?
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)
what are examples of physical signs and symptoms?
-skin rashes (exanthema)
-buccal lesions (enanthema)
-sores
-vesicular rashes
-warts
-nodules
-pustules
what is the chain of infection
microorgansim>reservoir>port of exit>modes of transport>port of entry>susceptible host
airborne transmission
infectious agents are carried in the air via aerosols
respiratory transmission
-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
formite transmission
-inanimate objects that are contaminated with an infectious agent
-usually nonporous hard surfaces that infectious agents stay on until they are disinfected
direct contact transmission
-direct physical contact like touching, hugging, kissing, sex
-also spread from sharing food, cups, utensils
blood-borne transmission
-occur from the introduction of a pathogen via blood transfusion
-organ transplant also known risk
trans-cutaneous (vector) transmission
occurs when a living organism carries a disease pathogen and passes it to another living organism; vector not harmed or infected
enteric (fecal-oral) transmission
-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
vertical (maternal-fetal) transmission
-passed from mother to child either in utero, during vaginal birth, or perinatally
how can the chain of infection be broken
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))
what are the 7 techniques of diagnosing microbial disease in vitro?
-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
-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
direct visualization
-plaque assay to determine the presence of virus
-can be challenging and slow; may take 7 days or more to yield useful info
culture
detection of bacterial or viral antigens
antigen tests
typically look for antibodies (ELISA and western blot) but can look for T cells as well (ELISpot)
detection of host immune response
-demonstrates the presence of a specific pathogen
-can determine the amount of infectious agent present
-can determine presence of specific mutations
detection of genomes
what test is widely used for detection of changes in host cells?
-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
what needs to be considered to determine how good a diagnostic test is?
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)
generally, the more rapid the test….
the greater the margin of error
