Yeast-like fungi

FUNGI

Candidosis

Sour Crop - Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

• Candidia albicans is the most important species
  • C. tropicalis and C. pelliculosa are other important species

• World wide distribution

• Usually an endogenous mycoses

• Noramlly present on skin, vagina and in the GI tract

• Immunocompromised animals may show symptoms

• Usually lesions on mucous membranes and at mucocutaneous junctions

• Many species have been implicated in bovine mastitis

• C. albicans has been isolated in porcine stomach ulcers

• C. rugosa has been implicated in pyometra in mares

• Infection of the crop, oesophagus and mouth occur in poultry and other birds leading to sour crop
  • White-grey lesions in mouth which adhere loosly to the mucous membrane
  • Crop wall may be thickened
  • Crop wall may be covered by a yellow-white necrotic material
  • Underlying tissue is inflammed

• Causes thrush in humans

• C. albicans causes metritis and vaginitis in mares and genital candidiosis in stallions (and bulls)

• Skin scrapings in 20% KOH for microscopy

• Diphtheritic membranes, pus and fluids can be examined by Lactophenol Cotton Blue and stained by Gram or Methylene Blue stain

• Gram positive, oval, thin-walled budding cells with hyphal fragments

• Grow on Blood agar and Sabouraud's Dextrose agar producing soft, creamy colonies in 24-48 hours

• Grossly:
  • Exudative, papular, pustular to ulcerative dermatitis
  • Stomatitis and otitis externa may develop

• Microscopically:
  • Spongiotic neutrophilic pustular inflammation
  • Parakeratosis
  • Ulcerations
  • Superficial exudate containing organisms

• Candida spp. in candidiasis

Cryptococcosis

• Over 19 species
  • C. neoformans only major pathogen

• Worldwide

• Occurs in high concentrations in pigeon droppings (high creatinine concentration)
  • The pigeon is not infected
  • C. neoformis colonise the droppings after they have been excreted
  • Also found in fruit, milk and soil

• Exogenous, inhaled infection which is generally sporadic (non-contageous)
  • Can also be absorbed via skin penetration and ingestion

• May be a primary pathogen or opportunistic

• Targets the respiratory system
  • Including the paranasal sinuses
  • Also can be systemic, cutaneous, visceral, skeletal or ocular

• Causes sporadic mastitis in cattle
  • Can spread within the herd

• Affects the CNS of dogs and cats
  • Paranasal sinuses and pharynx can be infected with dissemination to the CNS and other tissues
    • E.g. Lungs, kidneys and joints
  • Also causes subcutaneous granulomas
  • The tip of the nose is a common site of infection in cats
    • See here

• Causes myxoma-like lesions of the lung and lip in horses

• Causes cryptococcal meningitis in humans

• Also affects dolphins, foxes, ferrets, monkeys, birds, cheetahs and guinea-pigs

• Large yeast with capsule seen using India ink stain

• Stains with PAS (Periodic acis Schiff)

• Gram positive

• Grows on blood agar and Sabouraud's Dextrose agar forming white, granular colonies which become slimy, mucoid and turn cream/brown within a week

• Species identified by carbohydrate assimilation tests

• Antigen and antibody should be tested for as antibody formed by the body is soon overwhelmed and neutralised by abundent polysaccharide antigen from the capsule, in active, systemic infections
  • Latex agglutination for antigen, complement fixation, ELISA and IFAT can be used

Geotrichosis

• G. candidum

• Rare

• Two forms: the yeast-like (glaborous) and fluffy

• Affects a wide range of species

• Usually diagnosed post-mortem

• Affects the mucous membranes, udder, bronchi and lungs

• Usually mild, causing suppurative granulomas

• Can be recovered from otitis externa infections in dogs

• Organisms appear as rectangular or spherical arthrospores on wet mounts
  • Thick walled, non-budding, gram positive

• Grow on Sabouraud's Dextrose agar
  • Membranous colonies
  • Does not grow well on blood agar

Malassezia pachydermidis

Malassezia pachydermidis - Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

• Caused by Malassezia pachydermatis

• Normally present in oily areas on the external ear canal and skin in dogs
  • Some strains have been recovered from the ear canal of cats

• Bottle-shaped, small budding cells, non-mycelial

• Gram stain shows purple yeast cells with a very wide base

• Grow on Sabouraud's Dextrose agar in 2 weeks of incubation at room temperature

• Greenish discolouration on blood agar

• Clinical disease may cause yeast to proliferate and cause infection
• Grossly:
  • Regional lesions: muzzle, ears, interdigital, perianal
  • Or generalised disease
  • Erythematous, hyperpigmented, lichenified and scaly lesions with alopecia
• Microscopically:
  • hyperkeratosis, parakeratosis
  • Spongiotic pustular dermatitis
  • Acanthosis
  • Organisms are usually present, minimum 3-5 yeasts per high-power field must be found to imply cause of disease

• Malassezia pachydermis in malassezia dermatitis

Rhodotorula

• Rhodotorula minuta and R. rubra

• Canine ear infections

• Equine uterus

• Seldom seen in animal infections

Torulopsis glabrata

• Commensal in animals and is found in the soil

• Implicated in cases of:
  • Pyelonephritis, pneumonia, septicaemia and meningitis (humans)
  • Mastitis and abortion in cattle
  • Systemic infection of monkeys and dogs

Trichosporonosis

• Found in soil

• Deuteromycetes yeast

• Trichosporonosis beigelii
  • Implicated in feline nasal granuloma, skin infections in horses and monkeys, mastitis in cattle and sheep and in feline bladder infections

• T. capitum implicated in bovine mastitis

Further Links

• Mycotic skin infections - Pathology

• Antifungal Drugs