Animal Disease: Yeast Infections

Yeasts

• These are eukaryotic, unicellular, round or oval organisms with unicellular budding features
• Asexual reproduction happens via blastoconidia (also referred to as buds or daughter cells)
• Pseudohyphae or true hyphae could form
• Teleomorphs can be either ascomycetes or basidiomycetes

General Information About Yeasts

• They are found in the environment, mostly in plants and plant materials
• These organisms can occur as commensals on the skin or mucous membrane of animals
• They cause opportunistic infections: exogenous if derived from the environment; endogenous if resulting from overgrowth of commensals

Yeasts of Importance in Animal Disease

• Candida spp. (Candida albicans)
• Cryptococcus neoformans
• Malassezia pachydermatis
• Macrorhabdus ornithogaster (formerly 'megabacteria') – 'going light’
• Trichosporon beigelli
• Geotrichum candidum

Candida Species

• Candida albicans are the most implicated animal disease that do not have a sexual stage, from the genus with more than 200 species
• This species produces thick-walled resting cells – chlamydospores (chlamydoconidia)

Candida albicans - Characteristics

• Microscopic traits include oval, budding yeast-like cells, pseudohyphae
• Cultural traits include soft, creamy, convex colonies when cultured for 24-48 hours at 30°C
• Antigenic specificity is dependent on polysaccharide and glycoprotein content
• Grows aerobically when incubated at 37°C on media such as SDA
• It exhibits polymorphism in the form of pseudohyphae or hyphae
• Can produce thick-walled, resting cells (chlamydospores/chlamydoconidia)

Candida albicans - Habitat

• Present worldwide on plant materials
• Commonly found in the digestive and urogenital tracts of animals and humans

Candida albicans - Pathogenesis and Pathogenicity

• Organisms have surface integrin-like molecules that allow adhesion to matrix proteins
• Surface structures can bind fibrinogen and complement components
• Proteases and phospholipases production can aid tissue invasion
• They have phenotype switching and biofilm formation that help in evasion of host defence mechanisms

Candida albicans - Predisposing factors

• Defects in CMI
• Concurrent diseases
• Disturbance of normal flora due to prolonged antibiotic therapy
• Damage to the mucosa from indwelling catheters
• Poor nutrition and stress
• The affected mucosa is thickened and often hyperemic

Clinical Infections from Candida albicans

• Lead to opportunistic infections associated with immunosuppression or antibiotic therapy
• Can cause "thrush" in birds, exhibiting whitish, circular patches in the mouth, crop, proventriculus and gizzard that may slough off and ulcerate
• Cause systemic candidiasis in cattle, pigs, dogs and cats that results in pseudomembrane on tongue, esophagus and stomach
• Lead to Gastro-esophageal ulceration in pigs and foals

Fungal infections in clinical situations in animals:

• Mycotic stomatitis in pups, kittens, and foals
• Gastro-esophageal ulcerations in pigs and foals
• Bovine abortion and mastitis
• Pyometra, urocystitis and pyothorax in cats
• Reduce fertility, abortion and mastitis in cows
• Ocular lesions in Cats and horses
• Rumenitis in Calves
• Disseminated dss in dogs, cats, pigs and calves
• Enteritis, cutaneous lesions in Dogs
• Thrust of the esophagus or crop in Chickens
• Cloacal and vent infections in Geese and turkeys

Common clinical conditions to note in certain species:

• Pups, kittens, and foals can develop Mycotic stomatitis
• Pigs, foals, and calves can develop Gastro-esophageal ulcers
• Calves can develop Rumenitis
• Dogs can develop Enteritis, cutaneous lesions
• Chickens can develop thrust of the esophagus or crop
• Geese, turkeys can develop Cloacal and vent infections
• Cows can develop reduced fertility, abortion, and mastitis
• Mares can develop Pyometra
• Cats can develop Urocystitis, pyothorax
• Cats and horses can develop Ocular lesions
• Dogs, cats, pigs and calves can develop dissseminated disease

###Diagnostic steps for fungal infection

• Biopsy or PM tissue and milk samples for culture and histoptahology
• Use of tissue sections stained by PAS or methenamine silver methods to reveal budding yeast cells or hyphae
• Culture, aerobic at 37°C for 2-5 days in SDA with or w/o cyclohexamide
• Observation of Colonial appearance on CHROMagar Candida
• Molecular techniques usage

Infections in humans: Candidiasis(Candida albicans)

• Widespread and common yeast infections
• Budding cells that also form enlongated pseudohyphae and true hyphae
• Infections can be short, superficial irritations to overwhelming, fatal systemic diseases
• They form off-white colonies
• Are normal flora of the mouth, genitalia, large intestine and the skin (20%)

Additional Details About Candida albicans

• Account for 80% of nosocomial fungal infections, and 30% of all deaths from nosocomial infections
• The infection known as "thrush" forms a thick white layer of growth in the mouth and throat
• Vulvovaginal yeast infections causes painful inflammatory condition with ulceration and discharge
• Cutaneous candidiasis develops in moist areas of the skin or in burn patients

Additional information

• With lab tests, presumptive diagnosis if budding yeast cells and pseudohyphae are found
• Presumptive diagnosis made if budding yeast cells and pseudohyphae are found; germ tube on selective, differential media
• Use topical antifungals like amphotericin B and fluconazole

Cryptococcus neoformans species characteristics

• Over 30 species known
• Leads to opprotunistic infections
• Round to oval cells, 3.5-8um
• Thick mucopolysaccharide capsule
• Diagnosed with India ink

Cryptococcus neoformans Varieties

• Cryptococcus neoformans var. grubii (serotype A) as well as neoformans D and gatii
• Has capsular antigens A,B,C,D

Cryptococcus neoformans Usual Habitat

• C. neoformans var. neoformans; C. neoformans var var. grubii in pigeon and bird droppings
• C. neoformans var.gatii in red gum trees (Eucalyptus spp.) in Australia
• Pigeons with microorganism may excrete for months without symptoms