Fungal Disease - Clinical and Pathological Changes

Question 1

What are the mechanisms that fungi cause disease?

Answer 1

Tissue invasion - mycosis
Toxin production - Mycotoxicosis
Hypersensitivity

Question 2

Pathological changes in Mycoses

Answer 2

1. Acute suppurative inflammation
2. Chronic inflammation
3. Necrosis

Question 3

Acute suppurative inflammation

Answer 3

Predominantly neutrophilic inflammation
Purulent
May have microabsesses

Question 4

Chronic inflammation

Answer 4

Complex cell walls aren’t fully degraded when phagocytosed so cause chronic inflammation
* Pyogranulomatous or granulomatous
* Involves macrophages
* Fungal material released into tissues when phagocytes die - causes recruitment of macrophages + cytokines

Question 5

Necrosis

Answer 5

If fungi invade blood vessels it causes infarction and therefore tissue death

Question 6

Superficial mycoses examples

Answer 6

Dermatophytosis - ringworm
Dermatomycosis - malassezia, candida

Question 7

Dermatophytosis clinical signs

Answer 7

Affects keratinised structures
* Alopecia
* Claw disease
* Papules
* pustules

Question 8

Malassezia infection clinical signs

Answer 8

Erythema
Scale
Hair loss
Lichenification (if chronic)

Question 9

Candida infection clinical signs

Answer 9

Rare in small animals
Affects skin and mucosae
Ulcers/erosions covered with tenacious yellow/grey exudate

Question 10

Clinical signs of subcutaneous mycoses

Answer 10

Cutaneous papule or subcutaneous nodules
+/- ulceration
Most commonly on feet/limbs or head
Regional lymphadenopathy

Question 11

Clinical signs of systemic mycoses

Answer 11

Granulomas/pygranulomas/necrosis in organs
Systemic illness

Question 12

Manifestation of Aspergillosis

Answer 12

Common soil saprophyte with occasional pathogenic effects
* Inhalation
Local respiratory infections - birds
Guttural pouch mycoses - horses
Nasal aspergillosis - dolichocephalic dogs
* Local inoculation
Keratitis - horse
Mastitis - cattle
* Haematogenous spread from GIT
Mycotic placentitis/abortion - cattle

Question 13

Diagnostic Tests for Fungal infections

Answer 13

1. Direct microscopic examination
2. Fungal culture
3. Histopathology
4. PCR and Wood’s lamp
5. Latex agglutination
6. ELISA

Question 14

Direct microscopic examination

Answer 14

Hair pluck (Trichogram)
* For dermatophytosis
Cytology stained with diffquick
* Malassezia - direct/indirect impression smears or acetate tape strips
* Cryptococcus spp. - aspirates/direct smears of cutaneous lesions

Question 15

Fungal culture

Answer 15

Hair, dry skin scrapings/scale, coat brushings
For dermatophytes
Tissue culture (from biopsy or PM material)
For superficial/deep mycoses

Question 16

Which media is used for fungal culture?

Answer 16

Sabaurad dextrose agar
Incubation times/temps vary between fungi

Question 17

How can you speciate fungal culture?

Answer 17

• Asexual spore type
• Colony appearance
• Features of vegetative hyphae

Question 18

Histopathology

Answer 18

Generally used for subcut/systemic mycoses
Request special fungal stains
* E.g. Periodic acid-Schiff (PAS)
* E.g. Grocott-Gomori methenamine silver (GMS

Question 19

PCR and Wood’s lamp

Answer 19

For dermatophytosis

Question 20

What is the latex agglutination test used for?

Answer 20

Cryptococcal capsular antigen in serum/CSF/urine

Question 21

What is ELISA used for?

Answer 21

For Sporothrix schenkii antibodies

Question 22

What fungus causes Aflatoxicosis?

Answer 22

Aspergillus spp.

Question 23

Which crops have aspergillus spp?

Answer 23

Maize
Stored grain
Soybean

Question 24

Which species are affected by aflatoxicosis?

Answer 24

• Cattle
• Pigs
• Poultry
• Dogs
• Trout

Question 25

Clinical signs of aflatoxicosis

Answer 25

* Hepatotoxicity * Immunosuppression * Mutagenesis/teratogenesis of fetus * Ill-thrift

Question 26

What is ill-thrift?

Answer 26

When stock grow at a slower growth rate than expected

Question 27

What species causes ergotism?

Answer 27

Claviseps spp.

Question 28

Which crops are claviseps spp. found on?

Answer 28

Seedbeds of Ryegrass Other grasses Cereals

Question 29

Which species are affected by ergotism?

Answer 29

* Cattle * Pigs * Poultry * Deer * Sheep * Horses

Question 30

Clinical signs of ergotism

Answer 30

* Neurotoxicity * Perinatal deaths (lambs, calves)

Question 31

Diagnosis methods for mycotoxicosis

Answer 31

Epidemiological features * Outbreaks are usually seasonal * associated with certain batches of food Clinical signs * Often ill-defined Confirmation in feed or tissues of infected animals

Question 32

Clinical changes in induction of hypersensitivity

Answer 32

Depends on tissue type involved Mainly type 1 hypersensitivity to fungi/moulds in chronic pulmonary disease * Chronic cough * Nasal discharge * Occ resp distress Pruritus in atopic dermatitis Pruritus in malassezia mycoses