Chapter 5 - Fungal disease Flashcards
What are the most commonly isolated dermatophytes in horses?
Trichophyton equinum
Also M. gypseum and T. mentagrophytes, M. equinum, M. canis. T. verrucosum
Which type of fungi produce masses of arthrospores on the surface of hair shafts, ectothrix or endothrix?
Ectothrix
With natural dermatophyte infections in horses, what is the incubation period?
1-6 weeks
Which is more important at preventing dermatophyte reinfection in horses, antibody or cell-mediated response?
Cell-mediated response
Which body sites are rarely affected by dermatophytosis in horses?
Mane and tail
Coronary bands
Which dermatophyte has been associated with pseudomycetomas in horses?
Trichophyton equinum
Name two lipid-dependant Malassezia species isolated from normal equine skin
other than M. pachydermatis
M. equina M. furfur M. globosa M. obtusa M. restricta M. slooffiae M. sympodialis
Which supplemented medium will facilitate growth of lipid-dependant and non lipid-dependant Malassezia?
Modified Dixon agar
White piedra (Trichosporon beigelii) has been described in horses; what are the clinical signs?
Whitish nodules and thickenings are seen along the hair shafts of the mane and tail resulting in splitting and breakages.
What is the treatment for white piedra (Trichosporon beigelii)?
Shaving off the hair is curative.
Do eumycotic mycetomas or phaeohyphomycosis lesions form grains?
Eumycotic mycetomas form grains, phaeohyphomycosis lesions do not
Are lesions usually solitary or multifocal in eumycotic mycetomas and phaeohyphomycosis?
Usually solitary with eumycotic mycetoma
Multifocal with phaeohypomycosis
Which histopathology stain is best to identify Pythium insidiosum?
Gomori methanamine silver (GMS); does not stain well with PAS
Why do linear arrangements of hard, dermal and s/c nodules form with sporotrichosis?
They follow the line of lymphatics draining the primary lesion in the cutaneolymphatic form
What is the treatment of choice for sporotrichosis?
Iodides e.g. sodium iodide IV and PO
What are the clinical signs of iodism (e.g. adverse effects of iodide therapy)?
Scaling Alopecia Depression Anorexia Fever Coughing Lacrimation Serous nasal discharge Salivation Nervousness Cardiovascular abnormalities
Cryptococcosis can cause nasal granulomas and cause which systemic clinical signs?
Rhinitis
Meningitis (CNS involvement)
What changes are evident on histopathology with cryptococcosis?
Cystic degeneration or vacuolation of the dermis and subcutis that is surprisingly acellular (like soap bubbles) or a nodular to diffuse, pyogranulomatous to granulomatous dermatitis and panniculitis containing multiple organisms
Which special stain can be used to identify Cryptococcus on histopathology?
Mayer mucicarmine (stains the mucinous capsule red)
What is the most reliable diagnostic test to identify Histoplasmosis farciminosi infection?
Demonstrating the organism in tissues on cytology or histopathology as it is difficult to culture
What is the antifungal action of nystatin and amphotericin B?
They bind with ergosterol in fungal cell membranes altering permeability (= death)
What is the antifungal action of azoles?
They inhibit the synthesis of ergosterol, triglyceride, phospholipid, chitin and oxidative and peroxidative enzymes
Which topical treatments can be used to treat dermatophytosis in horses?
Nystatin/amphotericin B
Azoles
Allylamines (e.g. terbinafine)
Azoles and allylamines; nystatin/amphotericin B are not effective
Which type of topical therapy is most effective at treating superficial mycoses in horses?
Rinses e.g. lime sulfur 2-5% and enilconazole 0.2%
Which fungal agent can cause nasal polyps and form sporangium (pl. sporangia)?
Rhinosporidium seeberi
Can people become infected with sporothrix schenckii from an infected horse?
No - transmission occurs with contact with an infected cat but not reported from horses
What is the causative agent of epizootic lymphangitis in horses?
Histoplasma capsulatum var farciminosum
What are differential diagnoses for epizootic lymphangitis in horses?
Ulcerative lymphangitis (Corynebacterium pseudotuberculosis)
Glanders (Burkholderia mallei)
Sporotrichosis
Are Malassezia found on cytology of normal skin from the intermammary and preputial fossa areas of horses?
Yes - cytology was more sensitive than culture (M equi, and M slooffiae)
Which body site has the greatest abundance of Malassezia species (based on culture)?
Ear canal (found in ~47% of samples)
Which Malassezia species have been found in the normal ear canal of horses?
M. nana
M. slooffiae
M. equi
How do you treat equine dermatophytosis?
Topical antifungal drugs (e.g. clotrimazole, miconazole and terbinafine) - systemic therapy is expensive and has yet-unproven efficacy and safety. Grooming implements and tack should be disinfected, and affected horses should be isolated. Correct predisposing factors (e.g. over-crowding).
Is Trichophyton bullosum zoophilic?
Yes - rarely isolated from horses
PCR-based methods for the identification of dermatophytes amplify what?
Intergenic spacer (ITS) regions
Name topical antifungal agents for treatment of dermatophytosis in horses
- 0.2% Enilconazole wash or spray used q3-4 days for four treatments
- Natamycin spray
- Miconazole with or without chlorhexidine
- 2% Lime sulfur whole body treatments weekly for 4-5 weeks
Which systemic antifungals can be given to horses?
Itraconazole (expensive) 5 mg/kg/day
Iodides (sodium and potassium iodide)
Which horses are more likely to have dermatophytosis?
Young, stressed animals or in geriatric horses with metabolic or endocrine diseases
Why can you see acanthocytes with dermatophytosis?
Can see severe exocytosis of neutrophils in the epidermis that release proteases and can trigger acantholysis
What should you do to the skin/hair before taking a sample for dermatophyte culture in horses?
The area should be treated with alcohol to decrease contamination by saprophytic fungi.
Why should you consider full body treatment even if lesions are focal?
Arthrospores may be present on the whole animal
Dermatophytosis is a self-limiting disease, how long does spontaneous resolution take?
3 months
What can be used to treat the environment for dermatophytes?
- 5% lime sulfur
- 5% sodium hypochlorite
- 0.2% enilconazole
Can depigmentation be seen with Malassezia dermatitis in horses?
Yes
Which fungi cause spherical, sharply circumscribed, firm, brown-black nodules of 2–3 cm in diameter in horses?
Chromoblastomycoses - Fonsecaea spp.
Name fungal causes of onychomycosis in horses
Scedosporium spp., Trichophyton spp. and Scopulariopsis brevicaulis, which invade the horn structures and cause damage
Name two subcutaneous mycoses that spread through the lymphatic system
Histoplasma capsulatum var. farciminosum
Sporothrix schenckii
How is Histoplasma capsulatum var. farciminosum spread?
- By direct contact with infected animals
- Fomites such as grooming equipment, bedding, tack (can survive for up to 10 weeks in the environment!)
- Biting flies of the genera Musca and Stomoxys
What are the four forms of Histoplasma capsulatum var. farciminosum infection?
- asymptomatic
- cutaneous
- conjunctival/ocular
- respiratory
What are the clinical signs of cutaneous histoplasmosis?
A granulomatous wound along a lymphatic vessel (mostly along the fore limbs, the chest wall, and the neck), which tends to ulcerate and/or discharge - heals with scarring.
What are the clinical signs of pythiosis?
Commonly localized to the limbs and ventral abdomen (Fig.4), usually contain yellowish gritty coral-like bodies known as ‘‘kunkers’’ and are intensely pruritic with mild to marked lymphadenopathy. In chronic infections (> 4 weeks duration), Pythium sp. may spread to the underlying bone and cause lameness.
Which other diseases can pythiosis look like?
Habronemiasis
Skin fungal infections caused by Conidiobolus and Basidiobolus spp.
Invasive SCC
What is the treatment of choice of pythiosis?
Surgical removal
What is the route of infection of Sporothrix schenckii?
Through damaged skin
How long is the incubation period of sporotrichosis in horses?
1–3 months
What are the clinical signs of sporotrichosis in horses?
Subcutaneous nodules which ulcerate and drain purulent discharges. Subsequently, fungi spread via the lymphatic vessels and secondary lesions appear along the regional lymphatics
What are the differentials for sporotrichosis in horses?
Ulcerative lymphagitis (i.e., Corynebacterium pseudotuberculosis) and Histoplasma capsulatum var. farciminosum infection
In sporotrichosis in horses, are there numerous or sparse oragnisms?
Sparse - need special staining e.g. PAS/GMS
How do you treat sporotrichosis in horses?
20% sodium iodide
What is the treatment of choice for coccidiodomycosis in horses?
Fluconazole
Can you use immunotherapy to treat pythiosis in horses?
Yes - made with secreted antigens and soluble mycelial antigens to encourage a cell-mediated immune response. Failure is typically seen in cases that have had the infection for more than 2 months.
What are the most common causes of phaehyphomycosis in the horse?
Alternaria alternaria, Bipolaris specifera and Cladosporium spp.
Where do you find lesions with zygomycosis?
- Conidiobolus lesions are found most commonly on the external nares and nasal passages.
- Basidiobolus lesions are more commonly found on the thorax, trunk, head and neck.
Which fungi are the most common causes of eumycotic mycetoma?
Pseudallescheria boydii (which produces white granules) Curvularia geniculata (which produces black granules).
