Ch207 - Cryptococcosis Flashcards
What is cryptococcosis?
Cryptococcosis is a systemic fungal infection found worldwide that affects various mammalian species, including dogs and cats.
What is cryptococcus
A dimorphic fungus that exists in a filamentous form in the environment and as an encapsulated budding yeast in the host.
What species of cryptococcus are normally responsible for infections in dogs, cats and humans
Cryptococcus neoformans and Cryptococcus gattii
Cryptococcus organisms had been divided into five serotypes - what are these and what were the divisions based on?
(A, B, C, D, and AD) based on antibody response to capsular polysaccharide
How are animals infected with cryptococcus?
- Desiccated yeast cells or basidiospores in the environment are inhaled
- These are primarily deposited into the upper respiratory tract
- This initial colonization will result in cryptococcal rhinitis in some dogs and cats
- No clinical signs noted in some exposed individuals.
In some cases the cryptococcus yeast undergoes haematogenous dissemination to which organs?
CNS, eyes, lymph nodes, and skin to establish a disseminated infection
Why is the polysaccharide capsule of cryptococcus an important virulence factor?
- It inhibits phagocytosis,
- depletes complement
- inhibits the cell-mediated immune response by shifting the host adaptive immune response from a Th1 to a Th2 type response
- Organisms can also evade the host cell-mediated immune system by altering the cell membrane composition and structure
Does cryptococcus require individuals to be immune-compromised?
- It is usually diagnosed in seemingly immunocompetent individuals
- Cats concurrently infected with FeLV or FIV may have more severe clinical signs or be slower to respond to treatment
How long does it take clinical signs to develop?
Clinical signs can develop between 2 months and 1 year after exposure.
Are cats or dogs more commonly affected?
Cats are more commonly affected than dogs.
What are the most commonly infected breeds of cat in Australia?
Siamese, Birman, and Ragdoll - this has not been noted in the US
What is the typical clinical presentation of cryptococcus in cats?
- Chronic progressive URT infection with sneezing and mucopurulent to haemaorrhagic nasal discharge
- 50% cats have nasal swelling or ulcerated cutanseous nasal lesions
- 50% cats have ulcerative draining sub/cutaneous nodules
- 1/3 cats have chorioretinitis and optic neuritis (strongly associated with CNS involvement)
- 20% cats neurological signs
- Less commonly: Lameness (osteomyelitis) and lower respritary signs (pleural effusion)
Cryptococcus most commomly affected which breeds of dog in Australis and the US?
Australia: Great dane, GSD, Doberman pinscher
US: American cocker spaniel
What age are most dogs diagnosed with cryptococcosis?
<4years
Are dogs or cats more likely to have disseminated disease with cryptococcosis?
Dogs
What percentage of dogs with cryptococcosis have multiple organ systems involved?
80%
What clinical signs do dogs with cryptococcosis present with?
- Non specific signs predominate: lethargy, weight loss, hyporexia
- 75% dogs exhibit neurological sifns that corrolate with lesion localisation (seizure, ataxia, blindness)
- URT signs - sneezing and nasal discharge
- Lymphadenomegaly, ulcerated skin lesions, GI signs
- Ocular signs - granulomatous chorioretinitis
- Lameness (osteomyelitis)
- Lower resp signs very rare
- 50% dogs had subclinical disease - only diagnosed at necropsy
What is this ocular lesion in a Doberman Pinscher diagnosed with nasal and central nervous system cryptococcosis?
granulomatous chorioretinitis
What are CSF findings in dogs and cats who have CNS involvement with cryptococcosis?
- Elevated protein and leukocyte concentrations
- Cytology: mononuclear and neutrophilic inflammation
- Cryptococcal organisms are observed in up to 90% of infected dogs.
- Note - CSF collection can result in acute increases in intracranial pressure + clinical decompensation; CSF should not be pursued unless a diagnosis cannot be achieved in other ways
What does the image show
Impression smear specimen demonstrating the appearance of stained cryptococcal yeast organisms surrounded by a large, non-staining capsule.
Although pulmonary cryptococcosis is rare, what would thoracic radiographs show?
Interstitial to alveolar pattern or nodular infiltrates. Occasionally, pleural effusion or tracheobronchial lymphadenomegaly.
What does CT if the nasal cavity in animals with cryptococcal rhinitis show?
Soft tissue mass with evidence of rhinosinusitis and lysis of the nasal bones or cribriform plate
Typical MRI findings in dogs and cats with cryptococcosis with CNS involvement
- contrast-enhancing mass lesions that are T2W hyperintense and T1W hypointense
- May have evidence of edema with surrounding T2 hyperintensity
What is the standard for diagnosis cryptococcosis?
- Cytologic or histologic identification of Cryptococcus yeasts.
- Obtained from nasal swabs, impression smears of ulcerated cutaneous lesions, aspirates of mass lesions, cavitary effusions, or bodily fluids
