Fungal Disease Flashcards
Panfungal PCR reliability when performed on cytological specimens
Sens 67%; Spec 73%
(86% if considering slides with only abundant fungi)
able to provide classication to the genus level
Risk of amplification of contaminant fungal DNA, so should not be used as standalone diagnostic. Interpret along with morphology of fungi on slide.
Sporothrix schneckii - clinical signs, significance, diagnosis, treatment
Saprophytic fungi found in warm/humid climates including northern Aust
Infection of cats and dogs occurs through traumatic innoculation but zoonotic spread from cats to humans without skin break is reported and considered high risk.
Cats are more susceptible to infection and thought to facilitate spread of disease
In tissue the organism turns into a yeast. Disease development depends on route of infection and host immune factors (can be just in skin or respiratory tract but disseminated disease also reported in up to 50% of cats).
Cutaneous lesions on head/nose form draining sinuses. Up to 80% of cats have multiple lesions (either from spread during grooming or due to disseminated disease)
Dx based on culture of tissue is best combined with morphologic features of fungi on cytol/histo
Cytology has 80% sensitivity, while histopathology is lower
Ability to identify the fungal elements in dogs is reduced compared to cats.
Treatment is with itraconoazole, usually require 4-6 months. Fluconazole is less effective and Amphotericin reserved for very severe cases.
Pathogenesis of Cryptococcus
Yeast in env are opportunistic pathogens in immunocompetent hosts.
Evade immuine clearance due to thickpolysaccharide capsule that inhibits complement and phagocytosis. Can also survive and replicate in macs.
Produces factors that inhibit T cell function, and humoral immune response to capsular antigens is ineffective. Causes pyogranulomatous inflammation
Typically cause local nasal disease in cats but can invade locally to CNS or disseminate heterogeneously. Disseminated dz and CNS involvement more common in dogs
Diagnostic Tests for Cryptococcus with Sens/Spec and pros/cons
Cytology - highly sensitive in cats (less so in dogs). Specific (though can get carrier state)
Culture - recommended as allows sensitivity testing particularly in dogs. More sensitive than cytol/histo, again can have false +
Ag detection (capsular ag shed into ECF)
LCAT - >90% sens and spec (varies by lab slightly), false + in carrier state usually <1:200, false - in localised disease
IMMY - newer cage side lateral flow test for Ag.
2 recent JVIM studies
First showed sens and spec of 95% but used LCAT as gold standard (not demonstration of org) and smallish numbers
2nd study used internist diagnosis reported 100% positive agreement and 92% negative aggreement.
Sustained positive after clearance, flase neg eith C. laurentii
Should be confirming results with direct demonstration of organisms on cytol/histo
Treatment for Cryptococcus
Fluconazole greter efficacy than itraconazole in most isolates.
Severe/disseminated disease or CNS involvement use Amophtericin B +/- 5-flucytosine
Addition of GCS to cases with CNS disease had improved outcome
Comparative studies with new antifungals lacking. But Posaconazole has good CNS penetration
Cats should not recieve voriconazole as they are more likely to develop AEs (azotaemia, weight loss, lethargy)
Potential presentations of systemic aspergillosis
Young GSD - overrepresented
PUO, lethargy, ataxia, weakness in HLs, hyperaesthesia, PUPD, cough
Discospondylitis
Splenitis
Pyelonephritis
Inflammatory CNS disease
Diagnostic Tests for Systemic Aspergillosis with Sens/Spec and pros/cons
Fungal hyphae demonstration on cytology/histo in lesion - prone to false - due to low levels of fungi
Culture - 75% sensitivity, approx 50% positive in urine. allows sensitivity testing (though takes a long time)
NB: false + due to env ubiquity so must have consistent clinical findings. PCR may be required for speciation
Antibody testing not useful
Galactomannan serum antigen is sensitive and specific for disseminated disease.
May get false + with some other fungal infection or recent plasmalyte administration. False negatives in localised disease.
May be negative if atypical fungal infection
PCR - poorly studied thus far so cannot evaluate sens/spec but likely useful in speciation.
Pneumocystis - case, pathogenesis, Dx and Tx
Fungal saprophyte, behaves more like protozoa
Diseases associated with host immunodeficiency - predilaection for Min Dachy with Ig deficiencies
Also in CKCS.
Replicates in alveoli and prevents gas exchange resulting in chronic inflammatory disease
Dx based on presence on BAL
newer qPCR available - only considered true positive if present at high levels (requiring fewer PCR cycles to identify). Cutoffs for clinical relevance not well established.
Tx with TMS or other antiprotozoal drugs
