Clinical and pathological changes seen in fungal infections Flashcards
What are the three main pathological changes seen in fungal infections?
Acute suppurative inflammation
Chronic inflammation (pyogranulomatous/ granulomatous)
Necrosis
What characterises acute suppurative inflammation in fungal infections?
It is a neutrophilic inflammation that can lead to micro-abscess formation with pus (suppuration)
How do fungal infections lead to chronic inflammation and granuloma formation?
Fungal cell walls are complex & not fully degraded by neutrophils
When phagocytes die, fungal material is released, recruiting macrophages, which produce chemokines & cytokines to recruit more macrophages
This repetitive cycle results in granuloma formation
Granulomas consist mainly of macrophages, while pyogranulomas contain both macrophages & neutrophils
What is necrosis in fungal infections, and what causes it?
Necrosis occurs when fungi invade blood vessels, leading to infarction (lack of blood supply), causing tissue death
What are common clinical signs of superficial mycoses?
Dermatophytosis: Alopecia, claw disease, papules
Malassezia: Erythema, scaling, hair loss, otitis
Candida: Ulcers, erosions with yellow/grey exudate.
What are common clinical signs of subcutaneous mycoses?
Cutaneous papules, subcutaneous nodules, ulceration, discharging tracts & regional lymphadenopathy
Usually due to traumatic implantation of fungus - most commonly on feet/limbs or head
- Occasionally disseminate to other organs
What are common clinical signs of systemic mycoses?
Granulomas, pyogranulomas, necrosis in affected organs & systemic illness
What is Aspergillosis, and what causes it?
Fungal infection caused by Aspergillus spp., commonly A. fumigatus, a soil saprophyte with occasional pathogenic effects
What are the main routes of Aspergillus infection, and what diseases do they cause?
Inhalation (most common):
- Local respiratory infection (esp. birds)
- Guttural pouch mycosis (horses)
- Nasal aspergillosis (dolichocephalic dogs)
Local inoculation (rare):
- Keratitis (horses)
- Mastitis (cattle, via contaminated intra-mammary tubes)
Haematogenous spread from GI tract:
- Mycotic placentitis/abortion (cattle)
What are the common diagnostic techniques for fungal infections?
Direct microscopic examination
Fungal culture
Histopathology
Other tests
- PCR & Wood’s lamp for dermatophytosis
- Latex agglutination test for cryptococcal capsular antigen in serum/CSF/urine
- ELISA for Sporothrix schenkii antibodies
Give examples of direct microscopic examination methods for fungal infections
Examine hair plucks/scale
- e.g. for dermatophytosis
Cytology stained (e.g. with Diff Quick):
- e.g.: Malassezia - stained direct/indirect impression smears or acetate tape strips
What samples are used for fungal culture?
Hair, dry skin scrapings & coat brushings (for dermatophytes)
Tissue culture (from biopsy or post-mortem material) for subcutaneous/deep mycoses
What medium is commonly used for fungal culture?
Sabouraud dextrose agar is used for most fungi, though some require specialized or enriched media
How are fungi speciated in the lab?
Based on:
Asexual spore type.
Colony appearance.
Features of vegetative hyphae
What is histopathology used for in fungal diagnosis?
Primarily used for diagnosing subcutaneous & systemic fungal infections through biopsy or post-mortem material
How does histopathology confirm fungal infections?
Demonstrates fungi within tissues, distinguishing infection from carriage or contamination
What special stains are used in histopathology for fungi?
Periodic acid-Schiff (PAS) stain.
Grocott-Gomori methenamine silver (GMS) stain
What factors influence the clinical presentation of mycotoxicosis?
Type of mycotoxin produced
Amount of toxin ingested & duration of exposure
What is aflatoxicosis, what causes it, and what are its effects?
Caused by aflatoxins from Aspergillus spp., found in maize, stored grain & soybean
Affects cattle, pigs, poultry, dogs & trout
Causes hepatotoxicity, immunosuppression, mutagenesis/teratogenesis & ill-thrift (slow growth)
What is ergotism, what causes it, and what are its effects?
Caused by ergotamine toxins from Claviceps spp., found in ryegrass & other grasses/cereals
Affects cattle, pigs, poultry, deer, sheep & horses
Causes neurotoxicity & perinatal deaths (lambs, calves)
What are the epidemiological features of mycotoxicosis?
Outbreaks usually seasonal & sporadic
May be associated with certain batches of food
What are the clinical signs of mycotoxicosis?
Often ill-defined
e.g. Immunosuppression may present as increased susceptibility to infectious disease or higher rates of vaccination failure
How is mycotoxicosis confirmed?
By demonstrating mycotoxins in feed or tissues of infected animals
What are common hypersensitivity reactions to fungi?
Type 1 hypersensitivity to fungi/moulds can cause chronic pulmonary disease/recurrent airway obstruction, canine atopic dermatitis & Malassezia-associated pruritus
What are the clinical signs of fungal hypersensitivity in the respiratory system?
Chronic cough, nasal discharge & occasional respiratory distress
What are the clinical signs and diagnostic methods for fungal hypersensitivity in the skin?
Pruritus, often associated with environmental fungi in canine atopic dermatitis & Malassezia
Diagnosis can be confirmed using IgE serology or intradermal testing to investigate causal allergens
