Fungal Pathogens Flashcards
What is the most common vet fungal pathogen you will encounter
1 Malessezia
2nd most common = ringworm (dermatophytes)
What type of pathogen are fungi
- Opportunistic
In what animals are fungi infections common. why?
- Rare in mammals
o Yeast and Dermatophytes - Common in ectotherms (plant/insect/fish/reptile/amphibian)
o Most fungi grow best below body temp
Where are fungi acquired from? Give examples
- Commenasal (Candida/Malassezia) – disease when immunosuppressed
- Environmentally acquired (dimorphic fungi – Blastomyces)
o Disease due to exposure
o Geographically distributed
What are 3 pathogenic mechanisms of fungi
Pathogenesis
* Tissue invasion
* Toxin production
* Hypersensitivity (worsen asthma/H pneumonitis)
List 3 classifications of mycoses. Give examples.
Classification
* Cutaneous mycoses
o Dermatophytosis/candidiasis/malasseziosis
* SC mycoses
o Mucormycosis/entomophthoromycosis/sporotrichosis/mycotic mycetoma
* Systemic mycoses
o Blastomycosis/hhisstoplasmosis/coccidioidomyocosis/cryptococcosis
What are the 2 main genera of dermatophytes
DERMATOPHYTE (microsporum and trichophyton)
What are 2 main features of dermatophytes
- Use keratin for growth
- Produce asexual spored = arthrospores
o Resistant too disinfectants
o Infective agent
o Viable for 6-12 months
List 3 types of environments that dermatophytes can live in
- Geophilic: free living saprophytes in soil (Microsporum gypseum)
- Zoophiles: survive on animal skin
o Microsporum canis = cat
o Trichophyton mentagrophytes = rodent/hedgehog
o Trichophyton verrucosum = cattle - Anthropophile: survive on human host skin
How are dermatophytes transmitted
- Transmit:
o Between animals, animal to human, between humans, from soil
o Direct contact with infected hair/fomites/contaminated environment
o Mechanical vector = flea
o Infection depends on host state = immune state/skin condition
Young and old are more susceptible
What is the pre patent period of dermatophytes
- 1-3 weeks between infection and clinical signs
List the common dermatophytes affecting
- cat/dog
- horse
- ruminants
- pigs
- Common agents
o Cat/dog: Microsporum canis, Trichophyton mentagrophytes
o Horse: Trichophyton equinum, Trichophyton mentagrophytes
o Ruminant: Trichophyton verrucosum
o Pig: Microsporum nanum
What is the main dermatophyte affecting cats/dogs
- Microsporum canis Most common - >75% infections (M. gypsseum and T. mentagrophytes cause the rest)
What are the clinical signs of Microsporum canis
o Dog: circular to coalescing lesions
Claw infection = erythema/thickening/deformity
Nodular dermatophytosis (kerions) on muzzle/distal limb
o Cat: varied
Areas of alopecia with scale/crust
Dermatophytic mycetomas: focal/nodular/ulcer lesions +/- purulent fluid
Can be silent infection
What are the clinical signs of Trichophyton mentagrophytes
Trichophyton mentagrophytes
* Chronic infections
* Clinically:
o Dog: Alopecia/Crusting
Hyperpigmentation and ulcer on muzzle and periocular skin
o Cat: alopecia/scale/crust on paws/ear/nasal bridge
What are the clinical signs of Trichophyton equinum
Trichophyton equinum
* Clinically: raised circular lesions with alopecia/scale/crusting
* Can take a month for hair to grow back
What are the clinical signs of Trichophyton verrucosum
Trichophyton verrucosum
* Clinically: heavy grey crust/alopecia
* Resolve on own
What are the types of samples you should take to find dermatophytes
Sample Collection
* Best sample: pluck hair from the edge of the lesion
o Fungi are more likely to be at the base of the air
o Pluck damaged looking hair
* Scrape crust from edge of lesion
* Nail clipping
* Brushings (use now toothbrush and brush coat for several mins)
* Biopsy: kerion/mycetoma
* Wear gloved because many are zoonotic
List 4 ways to identify dermatophytes
- Woods UV lamp
- Trichogram: 10-20% KOH wet mount (KOH degrades scale/debris)
- Fungal Culture: best option
- Histo: periodic-acid Schiff/silver stain/IHC
What is Woods UV lamp for?
o Apple green fluorescence
o Microsporum canis
o But most don’t fluoresce
What is a trichogram mainly for? What samples do you use?
- Trichogram: 10-20% KOH wet mount (KOH degrades scale/debris)
o Hair/nail/crust
o Can show chain/clump of arthroconidia
What media is used for dermatophyte culture
- Fungal Culture: best option
o Derrmatophyte test media or Sabouraud Dextrose Agar
List 2 common stains for dermatophyte histo dx
- Histo: periodic-acid Schiff/silver stain/IHC
What is the treatment protocol for dermatophytes
- Healthy animals clear in 3 months
- Strongly recommend treatment for multi-animal household or if there is immunocompromised people
- Systemic and topical antifungals with environmental decontamination
Provide examples of systemic and topical antifungals
- Topical: lime sulphur/enilconazole
- Systemic: Itraconazole
How to environmentally decontaminate after dermatophytes
- Enviro: 1:10 bleach and high heat on bedding
o Vacuum and steam clean carpet
o Throw out leashed/collars/grooming supplies
Provide 3 common yeast pathogens (genus)
YEAST: candida/Malassezia/cryptococcus
Where is candida found
Candida
* Common in environment
* Infections caused by resident organisms
What is the disease manifestation of candida infection in birds, horses, dogs, cattle
- Clinically
o Bird: crop mycosis
o Horse: foot thrush/metritis/vaginitis/stomach ulcer
o Dog: otitis
o Cattle: mastitis
When does fungal disease occur?
- immunosuppressed
- exposure to large inoculums
What are the main pathogenesis of fungal infection
- tissue invasion = mycosis
toxin production = mycotoxicosis
hypersensitivity
What are the phases of dimorphic fungi and when does it occur
yeast - 35-37C
W
mold/mycelial - <25
What are some examples of dimorphic fungi
Blastomyces dermatitidis/Coccidioides immitis/Histoplasma capsulatum/Sporothrix schenckii
What are the most common species of dermatophytes that affect dogs and cats
Microsporum canis
Trichophyton mentagrrophytes
Microsporum gypseum
What is the most common yeast species that infects dogs
Malassza pachyderrmatis
Describe what type of birds Avian Crop Thrush affect and what are the common clinical signs and gross features
o Young birds most susceptible
o Can affect a large proportion of the flock
o Clinically: non specific
Poor growth/rough feathers
o Gross: raised focal thickening on crop mucosa
Describe what the risk factors are for Avian Crop Thrush and what are the common treatments
o Risk factors: abx or anti-parasitic
Malnutrition
Secondary immunosuppression (virus/stress)
o Treat: separate affected bird
Correct environment
Use antifungal: nystatin
Where is Malassezia pachydermatis found?
- Found in skin of mammals and birds normally – sebaceous glands
- Uses lipid for growth
What are the clinical signs of Malassezia pachydermatis? What are the risk factors?
- Clinically: otitis and dermatitis in dogs
o Erythema/pruritis/alopecia/scale/greasy exudate
o If severe: lichenification/hyperpigmentation
o Superficial infection in warm/moist anatomic sites - Risk factors: long ears/hairy ears
How to treat Malassezia pachydermatis
- Treat: topical therapy
o Control underlying condition: allergy/endocrinopathy
Where is cryptococcus found and how is it transmitted?
Cryptococcus
* C. neoformans = pigeon poop
* C. gattii = on Eucalyptus trees
* Infect via inhalation of spores
* No zoonoses from contact with the infected animal
What is the most common systemic mycosis of cats
Cryptococcus
Most common systemic mycosis of cats – all ages but young is most risk
What is the incubation period and clinical signs of cryptococcus infection in cats
- Incubation period: 2-13 months (travel history is important)
- Clinically: cats with nasal granulomas
o Sneeze/mucopurulent nasal discharge
o Fluctuant subcutaneous swelling on nose bridge
o Can have neuro signs: depression/seizure/circling/head pressing
o Koala with resp infection - Hematogenous spread: LN/eye/skin/bone/joint/CNS
How to treat cryptococcus infection in cats
- Treat: combo of Azole antifungal (fluconazole) and amphotericin B
o Surgical excision of infected tissue
o Long term follow up
What is the disease type and clinical signs of cryptococcus infection in dogs
- Less common, mainly young/active dogs
- Disseminated disease: multi-organ (nasal cavity/lung/LN/internal organ/eye/CNS)
o Skin/bone/joint involvement is less common = marker for severe disease - Clinically: non specific (weight loss/lethargy/inappetence
o Rhinosinusitis: epistaxis/sneeze/mucopurulent nasal discharge
o Neuro: stumbling/paralysis/ataxia/seizure
What type of diagnostics do you use for diagnosis of yeast? What samples do you use for each?
Sample Collection and Dx
* Cytology: exudate/impression smear/tape impression/skin scrape/biopsy/CSF
* Culture (candida/Malassezia – not cryptococcus)
* Serology (serum or CSF)
* PCR
What are the general features of Aspergillus
- Rapidly growing
- Ubiquitous in environment
- Pigmented colonies – blue – yellow – black
- Uncommon and sporadic infections – affect resp
- Very small spores – can reach the end of bronchial tree in lungs
What are the disease manifestations of aspergillus infection in cows, horses, dogs, and birds
- Clinically:
o Cow: mycotic abortion/mastitis
o Horse: guttural pouch mycosis
o Dog: nasal aspergillosis
o Bird: brooder pneumonia/air sacculitis
What is the most common species of aspergillus
- Species: most common (90-95%) = A. fumigatus
What species of aspergillus is associated with aflatoxicosis
o A. flavus = aflatoxicosis
What causes brooder pneumonia and what are the gross features
aspergillus
- Brooder pneumonia: young chicken
o Large exposure of spores – associated with dirty environment
o Gross: nodules in lungs and air sac
What causes brooder pneumonia/aspergillosis is mature birds and what are the gross features
- Aspergillosis: mature birds
o Inhale spores
o Clinically: dyspnea/emaciation
o Gross: nodules in lung
o Penguins susceptible
What is the causative agent of guttoral pouch mycosis
o A. fumigatus
What is the clinical manifestation of guttoral pouch mycosis
o Unliteral disease
o Clinically: epistaxis/laryngeal hemiplegia/facial nerve dysfunction (Horner’s syndrome)
o Invade neurological/vascular structures
How to diagnose and treat guttoral pouch mycosis? What is the prognosis
o Diagnose: clinical signs and endoscopic examination – high case rate fatality (1/3 – exsanguinate due to erosion of carotid artery)
o Treat: topical antifungals via intro-nasal tube
What is the clinical presentation of mycotic abortion in cows? What are the gross features?
- Mycotic abortion: sporadic
o 6-9 months into pregnancy
o Poor quality feed associated
o Gross: Blood transmit to placenta = ringworm like lesions of fetus
Thickened placenta with necrotic cotyledons
What are the clinical signs of nasal aspergillosis? What is the causative agent?
- Nasal Aspergillosis
o Clinically: mucopurulent nasal discharge/epistaxis/sneeze/exophthalmos/mass or ulcer in pterygopalatine fossa
o A. fumigatus makes osteolytic toxins = destroy turbinate’s/cribiform plate
How to diagnose and treat Nasal Aspergillosis
o Dx based on PE and rhinoscopy
o Treat: topical antifungal as nasal infusion
What are the clinical signs of disseminated aspergillosis in dogs/cats? How do you treat?
- Disseminated Aspergillosis
o Anorexia/weight loss/spine pain/lameness/cough
o Treat: systemic antifungals
What type of diagnostics do you use for diagnosis of aspergillus? What samples do you use for each?
- Cytology: aspirate/body fluid/impression smear/brush samples
- Histopath: lung/nodules/nasal biopsy/fetal abomasal contents/placental tissue
- Culture: scraping/fungal plaque
Where do you find the 4 types of dimorphic fungi? What type of environment are they found in?
Blastomyces dermatitidis
* Acidic soil (near water/warm/wet/sandy/organic matter)
* Location: Mississippi/Ohio river/St. Lawrance river/SK/Winnipeg/Great lakes/QC
Coccidioides immitis
* Alkaline soil of low elevation desert/hot – seasonal disease (cycle of moist period > dry period > soil disruption)
* Location: Arizona/California/Mexico/SA
Histoplasma capsulatum
* 22-29C soil, nitrogenous with decaying vegetation – intestinal tract of bats/bird (high N)
* Location: Mississippi/Ohio river/St. Lawrance river/AB/SK/ON/QC/New Brunswick
Sporothrix schenckii
* Worldwide but tropical to temperate in old wood/roses thorn/moss/soil
How are the 4 types of dimorphic fungi transmitted?
Blastomyces dermatitidis
Coccidioides immitis
Histoplasma capsulatum
* Transmit: inhale
Sporothrix schenckii
* Transmit: traumatic inoculation
What species do each of the 4 types of dimorphic fungi affect?
Blastomyces dermatitidis
* Species: dog/cat
o Mainly young/large breed (sport breed/hounds)
o Dogs = 10x more susceptible than people = sentinel for human exposure
Coccidioides immitis
* Species: dog/cat/horse
o Young large breed dog
o Travel history is important
o Cats = less common
Histoplasma capsulatum
* Species: dog/cat/horse
o Animals <4yo = more severe
Sporothrix schenckii
* Species: dog/cat/horse/cattle/pig/people
o Zoonotic – *contact with infected animal lesions/discharge (scratch/bite)
What is the incubation period, pathogenesis, and clinical signs of Blastomyces dermatitidis
- Incubation = 5-12 weeks
- Clinically: resp infection
o Varied signs
o Non specific: fever/lethargy/anorexia/weight loss
o Dyspnea/cough/lymphadenopathy/ocular lesions/cutaneous lesions/lameness/neuro
o If previously given abx – fever will be non-responsive to abx - Pathogenesis: inhale > mycelium turn into yeast > pyogranulomatous response > hematogenous spread to skin/eye/bone/repro/LN/CNS
How to treat Blastomyces dermatitidis
- Tx: long term systemic antifungals (4-6months) – Amphotericin B/Itraconazole
What are the pathogenesis, and clinical signs of Coccidioides immitis in dogs
- Clinically: resp and bone infection/disseminated infection = ‘Valley fever”
o Non specific: intermittent fever/lethargy/anorexia/weight loss
o Depends on site of infection – can be subclinical
Cough/lameness/SC lesion/lymphadenopathy/ocular lesion/neuro - Pathogenesis: inhale > mycelium turn into large spherules containing lots of endospores > hematogenous spread to body tissues
How to you treat Coccidioides immitis
- Treat: long term systemic antifungals (amphotericin B/fluconazole/itrazonazole)
What are the clinical signs of Coccidioides immitis in cats
o Cats = less common – cutaneous disease (draining skin lesions/SC granuloma/abscess)
Fever/anorexia/weight loss/resp signs/lameness/ocular problem/neuro sign
What are the clinical signs of Histoplasma capsulatum
in cats
- Clinically: resp and bone infection/disseminated infection
o Cat: non-specific
Lethargy/weight loss/anorexia/weak/fever
Resp signs/icterus/ocular signs/lymphadenopathy/cutaneous lesion/lameness
What are the clinical signs of Histoplasma capsulatum
in dogs
o Dog: non-specific + diarrhea
Lethargy/weight loss/anorexia/weak/fever/pallor/icterus
Resp signs: dyspnea/tachypnea/cough/nasal discharge
* Pulmonary histoplasmosis may be self-limiting
Lymphadenopathy/hepatosplenomegaly/kameness/skin/nodules/ocular/neuro signs
Preference for intestines = melena/tenesmus/hematochezia/dyschezia/vomit
What is the pathogenesis and treatment of Histoplasma capsulatum
- Pathogenesis: inhale > mycelium turn into yeast > yeast associated with phagocytes
- Treat: always treat to prevent disseminated infection
o Antifungal: long term systemic (amphotericin B/ketoconazole/itrazonazole)
What are the clinical signs and treatment of Sporothrix schenckii
- Clinically: SC nodules – lymphocutaneous disease
o Without treatment a disseminated diseases can occur - Treat: itraconazole/amphotericin B/Na or K iodine
What type of diagnostics do you use for diagnosis of dimorphic fungi? What samples do you use for each?
Sample collection + Dx
* Cytology: aspirate/impression smear/exudate
* Serology: urine/serum/CSF
* PCR: EDTA whole blood/TTW/BAL/CSF/aspirate
* Histopath: biopsy
* Culture not recommended – zoonotic risk
What are 3 different manifestations of opportunistic fungal pathogens? Provide examples of each
- Low virulence – depend on low host defence/traumatic inoculation
- Mycetoma: granulomatous SC nodules
- Mucormycosis: inhale spores or traumatic inoculation
o Mycetoma – like granulomas
o Ex.
Mucor/Rhizopus/Absidia/Mortierella spp. - Phaeohyphomycosis: mycetoma-like mass
o Ex. Alternaria/Cladosporum/Curvularia spp.
What is Pythium insidiosum? What is the disease complex that it forms
- Oomycete: not true fungi but form fungi-like hyphae in tissue
- Phythiosis: lesions similar to mycetomas (similar to mucormycosis)
What is the clinical manifestation of Pythium insidiosum in horses, dogs, cats
- Horse: cutaneous infection
- Dog: cutaneous and SC GI infection
- Cat: sinus infection
Where is Pythium insidiosum found?
- Location: tropical/subtropical region
