16: Testing for Infectious Diseases Flashcards
What is difference between dermatomycosis and dermatophytosis?
Mycosis = any fungus, phytosis = ringworm
What are the requirements to culture a virus?
Functional virus particle, stable outside host, virus transport medium, cell line supports replication and monolayer on plastic
What are three viruses that are stable outside the host?
Parvovirus, calicivirus, cowpox
What is the cytopathic effect?
Cellular toxicity due to virus replication
What are the disadvantages or trying to culture a virus?
Takes 2-3 weeks, need specialist facilities
Which clinical sample do you take for parvo?
Faeces
Which clinical sample do you take for cowpox?
Skin lesion
How do you confirm virus presence has cause aggultination?
Haemagglutination inhibition - add antiserum
What is a polyclonal antibody?
To different epitopes
What is a monoclonal antibody?
Single epitope by single clone of B cell
What clinical sample for in-house FeLV test?
Blood, saliva, tears
How do in-house FeLV kits work?
Rapid immunomigration (RIM) or ELISA
How do in-house parvo kits work?
ELISA
What is a disadvantage of PCR?
False +ve due to contamination
How sensitive is PCR?
Very
WHat may cause a false negative on PCR?
Intermittent shedding
How long do materal antibodies last?
6-8 weeks, some up to 6 months
Which Ig is present in early infection?
IgM
What -fold rise in titre is significant?
4-fold
Which antibody rises after IgM?
IgG
Which test can you do to test titre of antibody?
Virus neutralisation (last dilution that prevents plaque formation)
Which cat viruses do you use PCR to detect?
herpes, chlamydia, calicivirus
Which cat viruses do you use virus isolation to detect?
calicivirus, herpesvirus
Is FeLV a virus antigen test or antibody test?
virus antigen
Is FIV a virus antigen test or antibody test?
antibody
How do you confirm an FIV positive test?
IF, PCR, Western blotting
What do you do if you get an FeLV positive?
Retest in 12 weeks
if FeLV is negative on a blood test, what other test can you try?
Bone marrow PCR
Why is virus isolation of coronavirus very difficult?
Virus very fragile
Why is PCR for FIP a diagnostic challenge?
Can’t differentiate between FIP and feline enteric coronavirus
What can you test in the pleural/peritoneal effusion for FIP?
Antibody titre and PCR
When is antibody titre and PCR for FIP diagnostic?
If positive margin of error is high
What can cause false -ve on a virus test?
Strain variation
What can cause false -ve on a antibody test?
Antigen excess
What can cause false +ve on an antibody test?
Cross reactive antibodies, anti-mouse antibodies in cats, anti-cell culture antibodies
What can cause a false -ve for a bacterial disease?
Antibiotic treatment
Which samples can you use a blood culture for?
Blood, CSF, synovial
How long can you keep urine in boric acid for culture?
72 hours
How long can anaerobic cultures survive in air?
20 mins
What temperature should you keep an anaerobic sample?
Cool, but not refrigerated
Where is E Coli pathogenic?
Conjunctivitis, otitis externa
What are the two ways of testing for antibiotic sensitivity?
Broth dilution MIC or agar gel disc diffusion
What are two limitations of sensitivity testing?
You can only test aerobic bacteria, and in vivo tissue penetration varies
Why are characteristics of mycobacteria?
Gram +ve, acid fast
Why organs can mycobacteria infect?
Systemic or cutaneous
Why is intradermal tuberculin testing not recommended in cats?
inconsistent, infrequent
or transient reactions
Where do you perform the BCG test in dogs?
Inner surface of pinna
When can you get a false +ve for BCG in dogs?
cross-reactivity
with other bacterial species
Why is serology for mycobacterial disease unreliable?
antibodies to mycobacteria crossreact with
bacteria, fungi and protozoa
How do you diagnose mycobacterial disease?
Bacterial isolation from smear and tissue or stain
What technique can you use for mycobacterial speciation?
PCR
Which species mainly causes ringworm?
Microsporum canis
Which species are important ringworm carriers?
Asymptomatic cats
Which brush can you use to get a fungal culture?
Mackenzie
How should you store a sample for ringworm identification?
Non-airtight container
Which culture mediums can you use for ringworm?
Sabouraud’s agar or dermatophyte test medium
How long does culture from Sabouraud’s agar take?
3-4 weeks
How long does culture from dermatophyte test medium take?
5-7 days
What’s the problem with dermatophyte test medium?
False negative, difficult identification
What other commensal does Malassezia have a symbiotic relationship with?
Staphylococci
How common is malassezia in cats?
Rare
What predisposes to candida?
Prolonged antibiotic treatment,
immunodeficiency and immunosupression
How do you submit swabs for yeast culture?
Bacterial transport medium
What’s a problem with cello tape preparations?
Difficult to stain
How many organisms per 400x field are significant for impression smears?
1 or more
How many organisms per 400x field are significant for ear swabs?
Over 10
Which species causes nasal aspergillosis?
A fumigatus
How can you test for aspergillus antigen?
Serum or ELISA
What’s the problem with agar gel immunodiffusion for aspergillus serology?
False positives
What’s the problem with nasal flush and fungal culture for aspergillus diagnosis?
Often -ve
Which species gets crytococcus neoformans?
Cats in USA
Which organs does crytococcus neoformans infect?
CNS, respiratory tract, skin, eye
What’s one problem with cryptococcus neoformans diagnosis?
Zoonosis
How can you diagnose cryptococcosis?
Culture, serology (agglutination, ELISA), cytology, histo
Which antigen do you look for to diagnose cryptococcosis?
Capsular antigen
