Fungal disease

Question 1

What are the three main growth forms of fungi?

Answer 1

Yeast (unicellular), mould (multicellular-filamentous hyphae) & dimorphic fungi (both forms)

Question 2

How do fungi obtain nutrients?

Answer 2

Digest food externally & absorb nutrients through their cell walls

Question 3

What are the components of fungal cell walls?

Answer 3

Chitin & other polysaccharides

Question 4

How do fungi reproduce?

Answer 4

By spore formation, which can be asexual or sexual

Question 5

What is the predominant nature of most fungi?

Answer 5

Most fungi are saprophytic (live on dead organic material) though some cause opportunistic infections

Question 6

Do normal animals carry fungi on their skin?

Answer 6

Yes, animals harbour saprophytic fungi (yeasts & moulds)

Some are transient contaminants, while others (e.g. Malassezia yeasts) are part of normal flora

Question 7

What are transient contaminants?

Answer 7

Microorganisms temporarily present on animal’s skin, often from environment, but not part of normal flora

May cause disease under certain conditions

Question 8

What are dermatophytes?

Answer 8

Fungal pathogens that cause ringworm

Can be cultured from normal animals but are typically transient contaminants from environment & are never commensals

Question 9

How are fungi classified based on habitat?

Answer 9

Geophilic (soil/environment)

Zoophilic (on animals)

Anthropophilic (on humans)

Question 10

What are the three main mechanisms by which fungi cause disease?

Answer 10

Tissue invasion (mycosis) (most common)

Toxin production (mycotoxicosis)

Induction of hypersensitivity

Question 11

How can mycosis (tissue invasion) be classified & what tissues do they affect?

Answer 11

Question 12

What factors predispose an animal to mycosis (tissue invasion by fungi)?

Answer 12

Immunological deficits
Immunosuppression (including corticosteroids)
Immature or aging immune system
Malnutrition
Prolonged antibiotic use
High fungal spore exposure
Tissue trauma
Persistent moisture on skin surface

Question 13

What are the 2 most common superficial mycosis?

Answer 13

Dermatophytosis (caused by dermatophytes)

Dermatomycosis (caused by non-dermatophytic fungi)

Question 14

Describe dermatophytosis

Answer 14

Superficial mycosis caused by dermatophytes (Microsporum & Trichophyton spp.)

Invade keratinised structures (skin, hair, nails), are highly contagious, & have zoonotic potential

Commonly affected species:
- Cats, cattle, and horses

Question 15

Describe dermatomycosis

Answer 15

Superficial mycosis caused by non-dermatophytic fungi (e.g. Malassezia & Candida

Normal skin commensals that cause disease when they overgrow due to underlying condition

Infection is not contagious

Question 16

What is Malassezia dermatitis?

Answer 16

Very common dysbiosis of dogs (+- cats) often occurring secondary to other skin disease - affecting skin and ears

Type of dermatomycosis

Question 17

What is Candidiasis, and what does it cause?

Answer 17

Opportunistic dermatomycosis caused by Candida albicans in immunosuppressed animals

Can cause mycotic stomatitis (puppies, kittens, foals) & thrush (oesophagus/crop in young chickens)

Question 18

What are subcutaneous (deep) mycoses, and how do they develop?

Answer 18

Fungal infections that invade dermis or subcutaneous tissues, often following foreign body penetration that introduces environmental saprophyte

Cause chronic localised lesions (unless immunocompromised)

e.g. Sporotrichosis (Sporothrix schenkii)
- Zoonotic but rare in UK

Question 19

What is chromomycosis, and how does it differ from hyalohyphomycosis?

Answer 19

Chromomycosis is lesion caused by pigmented fungi, while hyalohyphomycosis is caused by non-pigmented fungi

(Pic is Chromomycosis)

Question 20

What is a mycetoma, and what are its two main types?

Answer 20

Organism forming granules/grains in lesions, associated with swelling & draining sinuses

Eumycotic mycetoma: organism is fungal

Actinomycotic mycetoma: organism is bacterial (e.g. Actinomyces, Nocardia)

Question 21

What are pseudomycetomas, and how do they differ from true mycetomas?

Answer 21

Resemble mycetomas but have different granule formation

Can be caused by dermatophytes (dermatophytic pseudomycetomas) or bacteria (bacterial pseudomycetomas)

Question 22

What is systemic mycosis?

Answer 22

Fungal infection that spreads throughout internal organs, usually via inhalation of fungal spores

Question 23

What is cryptococcosis and how is it transmitted?

Answer 23

Systemic fungal infection caused by Cryptococcus neoformans and C. gattii

Transmitted via inhalation of spores from contaminated dust (often pigeon droppings)

Infection starts in nasal cavity, then spreads to CNS via cribriform plate or through blood/lymph

Question 24

What species are affected by cryptococcosis, and what signs does it cause?

Answer 24

Cats: Respiratory, cutaneous, neural & ocular infections

Dogs: Disseminated disease with neural & ocular signs

Cattle (rare): Mastitis, nasal granulomas

Horses (rare): Nasal granulomas, sinusitis, cutaneous lesions, pneumonia, meningoencephalomyelitis, abortion

Question 25

What is mycotoxicosis, and what causes it?

Answer 25

Mycotoxicosis is poisoning caused by fungal mycotoxins present in contaminated crops, pasture, or stored feed Common fungi involved include Penicillium, Aspergillus (aflatoxicosis), Fusarium & Claviceps (ergotism)

Question 26

What are the effects of mycotoxicosis?

Answer 26

Mycotoxicosis can result from acute or chronic ingestion, leading to wide range of clinical signs depending on toxin In food-producing animals, mycotoxins can accumulate in tissues, posing risk of human exposure

Question 27

How do fungi induce hypersensitivity?

Answer 27

Fungal spores can act as allergens, causing chronic pulmonary disease in cattle/horses & conditions like recurrent airway obstruction (RAO) in horses

Question 28

Give examples of fungi that cause hypersensitivity in small animals

Answer 28

Malassezia hypersensitivity in dogs & cats, leading to skin conditions Saprophytic fungi can act as allergens, contributing to canine atopic dermatitis

Question 29

What are the three main pathological changes seen in fungal infections?

Answer 29

Acute suppurative inflammation Chronic inflammation (pyogranulomatous/ granulomatous) Necrosis

Question 30

What characterises acute suppurative inflammation in fungal infections?

Answer 30

It is a neutrophilic inflammation that can lead to micro-abscess formation with pus (suppuration)

Question 31

How do fungal infections lead to chronic inflammation and granuloma formation?

Answer 31

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

Question 32

What is necrosis in fungal infections, and what causes it?

Answer 32

Necrosis occurs when fungi invade blood vessels, leading to infarction (lack of blood supply), causing tissue death

Question 33

What are common clinical signs of superficial mycoses? | dermetatophytosis, malassezia, candida

Answer 33

Dermatophytosis: Alopecia, claw disease, papules Malassezia: Erythema, scaling, hair loss, otitis Candida: Ulcers, erosions with yellow/grey exudate.

Question 34

What are common clinical signs of subcutaneous mycoses?

Answer 34

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

Question 35

What are common clinical signs of systemic mycoses?

Answer 35

Granulomas, pyogranulomas, necrosis in affected organs & systemic illness

Question 36

What is Aspergillosis, and what causes it?

Answer 36

Fungal infection caused by Aspergillus spp., commonly A. fumigatus, a soil saprophyte with occasional pathogenic effects

Question 37

What are the main routes of Aspergillus infection, and what diseases do they cause?

Answer 37

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)

Question 38

What are the common diagnostic techniques for fungal infections?

Answer 38

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

Question 39

Give examples of direct microscopic examination methods for fungal infections

Answer 39

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 - e.g. Cryptococcus spp - see yeasts in CSF or aspirates/direct smears of cutaneous lesions/nasal exudate

Question 40

What samples are used for fungal culture?

Answer 40

Hair, dry skin scrapings & coat brushings (for dermatophytes) Tissue culture (from biopsy or post-mortem material) for subcutaneous/deep mycoses

Question 41

What medium is commonly used for fungal culture?

Answer 41

Sabouraud dextrose agar is used for most fungi, though some require specialized or enriched media

Question 42

How are fungi speciated in the lab?

Answer 42

Based on: Asexual spore type. Colony appearance. Features of vegetative hyphae

Question 43

What is histopathology used for in fungal diagnosis?

Answer 43

Primarily used for diagnosing subcutaneous & systemic fungal infections through biopsy or post-mortem material

Question 44

How does histopathology confirm fungal infections?

Answer 44

Demonstrates fungi within tissues, distinguishing infection from carriage or contamination

Question 45

What special stains are used in histopathology for fungi?

Answer 45

Periodic acid-Schiff (PAS) stain. Grocott-Gomori methenamine silver (GMS) stain

Question 46

What factors influence the clinical presentation of mycotoxicosis?

Answer 46

Type of mycotoxin produced Amount of toxin ingested & duration of exposure

Question 47

What is aflatoxicosis, what causes it, and what are its effects?

Answer 47

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

Question 48

What is ergotism, what causes it, and what are its effects?

Answer 48

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)

Question 49

What are the epidemiological features of mycotoxicosis?

Answer 49

Outbreaks usually seasonal & sporadic May be associated with certain batches of food

Question 50

What are the clinical signs of mycotoxicosis?

Answer 50

Often ill-defined e.g. Immunosuppression may present as increased susceptibility to infectious disease or higher rates of vaccination failure

Question 51

How is mycotoxicosis confirmed?

Answer 51

By demonstrating mycotoxins in feed or tissues of infected animals

Question 52

What are common hypersensitivity reactions to fungi?

Answer 52

Type 1 hypersensitivity to fungi/moulds can cause chronic pulmonary disease/recurrent airway obstruction, canine atopic dermatitis & Malassezia-associated pruritus

Question 53

What are the clinical signs of fungal hypersensitivity in the respiratory system & how is it diagnosed?

Answer 53

Chronic cough, nasal discharge & occasional respiratory distress Diagnosis based on history & physical examination

Question 54

What are the clinical signs and diagnostic methods for fungal hypersensitivity in the skin?

Answer 54

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