Clinical and pathological changes seen in fungal infections

What are the major tissue reactions seen with fungal infections?

1. Acute suppurative inflammation + micro-abscess formation

2. Chronic inflammation -( pyogranulomatous or granulomatous)

3. Necrosis - if fungi invade blood vessels we see infarction and tissue death

what kind of inflam is seen in acute fungal infections

(Predominantly neutrophilic inflammation)

what happens in chronic inflam in fungal infection

• The complex molecules of fungal walls do not fully degrade when phagocytosed, so not totally removed by acute inflammation

• → fungal material released into tissues when phagocytes die → recruitment of additional macrophages to remove debris → Activated → produce chemokines and cytokines → recruit more macrophages

• Repeated cycles → granulomatous inflammatory response

Well-demarcated fungal granuloma

• fungal organisms in middle

How might an animal present with dermatophytosis?

-alopecia, claw disease, papules and pustules

How might an animal present with Malassezia infection?

§Erythema, scale, hair loss, lichenification with chronicity. Also involved in otitis

What would be seen in candida infection?

§Very rare in small animals

§Affects skin, mucosae

§Ulcers/erosions covered with tenacious yellow/grey exudate

What would be seen in subcutaneous (deep) mycoses?

•Present as cutaneous papules or s/c nodules +/- ulceration, discharging tracts

•Usually due to traumatic implantation of fungus - most commonly on feet/limbs or head

•Regional lymphadenopathy common

•Occasionally disseminate to other organs

What will be seen in systemic mycoses?

•Granulomas/pyogranulomas/necrosis in organs affected - can affect any organ system

•causes systemic illness

Describe Aspergillosis

-A common soil saprophyte with occasional pathogenic effects

-A fungal that can show more than one manifestation of tissue invasion such as through inhalation, local inoculation and haematogenous spread from Gi tract

Describe inhalation route of aspergillus

-Most common

§Local respiratory infection, esp birds

§Guttural pouch mycosis (horses)

§Nasal aspergillosis (dolicocephalic dogs)

Describe local inoculation route of aspergillus

-Ocassional

§Keratitis (horse)

§Mastitis (cattle - via contaminated intra-mammary tubes)

Describe haematogenous spread from GI tract of aspergillus

§Mycotic placentitis/abortion (cattle)

How does mycotic placentitis manifest?

Causes necrosis of placenta and abortion

How will mycotic abortion present?

Hyperkeratotic skin lesions on aborted foetus

What are the diagnostic tests for mycoses?

-Direct microscopic examination

-fungal culture

-histopathology

-Other test: PCR and Wood’s lamp for dermatophytosis, Latex agglutination test for cryptococcal capsular antigen in serum/CSF/urine, ELISA for Sporothrix schenkii antibodies

Describe direct microscope examination?

• Examine hair plucks/scale: For dermatophytosis     

• Cytology stained e.g. with Diff Quick such as

  • Malassezia - stained direct/indirect impression smears or acetate tape strips

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

Describe fungal culture

• hair, dry skin scrapings/scale, coat brushings - for dermatophytes

• tissue culture (from biopsy or PM material) - for subcutaneous/deep mycoses

• Sabauraud dextrose agar for most; some require specialised/enriched media

• Incubation times/temps vary between fungi

• potential for false +ve results due to carriage/contamination

• Can speciate based on

  • Asexual spore type

  • Colony appearance

  • Features of vegetative hyphae

Describe histopathology

§Generally used for subcutaneous/systemic infections - on biopsy or PM material

§Histological demonstration of fungi within tissues confirms infection, c.f. carriage/contamination - occasionally used for dermatophytes

§Request special fungal stains,

what stains for fungi for histopathology

e.g. Periodic acid-Schiff (PAS), Grocott-Gomori methenamine silver (GMS)

what other tests can be done for fungi

PCR and Wood’s lamp for dermatophytosis – see later teaching

Latex agglutination test for cryptococcal capsular antigen in serum/CSF/urine

ELISA for Sporothrix schenkii antibodies

Give 2 examples of mycotoxicosis

-Aflatoxicosis (aflatoxins)

-Ergotism (ergotamine)

What are the clinical findings of aflatoxicosis?

-hepatotoxicity

-immunosuppression

mutagenesis/teratogenesis,

ill-thrift

what fungus causes aflatoxicosis and what doe sit affect

• aspergillus

• grown on grain so affects animals consuming grain

  • cattle, pigs, poultry, dogs, trout

What are the clinical findings of Ergotism?

Neurotoxicity and perinatal deaths in lambs and calves

what fungus causes ergotism and what doe sit affect

Claviseps sp

seedheads of ryegrass/other grasses/cereals

• grown on grain seed heads → cattle pigs, poultry, deer, sheep horses

what does the severity and recovery of mycotoxicosis depend on

Severity depends on amount of toxin ingested

Recovery rate depends on duration of exposure

What are the epidemiological feature of mycotoxicosis/

Outbreaks, usually seasonal and sporadic, +/- associated with certain batches of food

how to confirm mycotoxicosis

-To confirm must find mycotoxin in feed of concern as clinical signs often just present as immunosuppression

what type of hypersensitivity is it usually

type 1

What are the clinical changes seen with hypersensitivity fungal induced disease?

• fungi/moulds in chronic pulmonary disease/recurrent airway obstruction

  • causes chronic cough, nasal discharge, occ resp distress

• environmental fungi/moulds in canine atopic dermatitis

  • causes pruritus

• skin Malassezia

  • causes pruritus

what can be done for induction of hypersensitivity due to fungi

Once clinical investigations have shown potential allergy to exist, IgE serology or intradermal testing can be carried out if want to investigate causal allergens

what is the main clinical effect of fungal disease

tissue mycosis

• less commonly mycotoxicosis and fungal hypersensitivity