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Sarah - Equine > Chapter 5 - Fungal disease > Flashcards

Chapter 5 - Fungal disease Flashcards

1
Q

What are the most commonly isolated dermatophytes in horses?

A

Trichophyton equinum

Also M. gypseum and T. mentagrophytes, M. equinum, M. canis. T. verrucosum

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2
Q

Which type of fungi produce masses of arthrospores on the surface of hair shafts, ectothrix or endothrix?

A

Ectothrix

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3
Q

With natural dermatophyte infections in horses, what is the incubation period?

A

1-6 weeks

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4
Q

Which is more important at preventing dermatophyte reinfection in horses, antibody or cell-mediated response?

A

Cell-mediated response

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5
Q

Which body sites are rarely affected by dermatophytosis in horses?

A

Mane and tail

Coronary bands

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6
Q

Which dermatophyte has been associated with pseudomycetomas in horses?

A

Trichophyton equinum

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7
Q

Name two lipid-dependant Malassezia species isolated from normal equine skin
other than M. pachydermatis

A 
M. equina
M. furfur
M. globosa
M. obtusa
M. restricta
M. slooffiae
M. sympodialis
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8
Q

Which supplemented medium will facilitate growth of lipid-dependant and non lipid-dependant Malassezia?

A

Modified Dixon agar

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9
Q

White piedra (Trichosporon beigelii) has been described in horses; what are the clinical signs?

A

Whitish nodules and thickenings are seen along the hair shafts of the mane and tail resulting in splitting and breakages.

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10
Q

What is the treatment for white piedra (Trichosporon beigelii)?

A

Shaving off the hair is curative.

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11
Q

Do eumycotic mycetomas or phaeohyphomycosis lesions form grains?

A

Eumycotic mycetomas form grains, phaeohyphomycosis lesions do not

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12
Q

Are lesions usually solitary or multifocal in eumycotic mycetomas and phaeohyphomycosis?

A

Usually solitary with eumycotic mycetoma

Multifocal with phaeohypomycosis

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13
Q

Which histopathology stain is best to identify Pythium insidiosum?

A

Gomori methanamine silver (GMS); does not stain well with PAS

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14
Q

Why do linear arrangements of hard, dermal and s/c nodules form with sporotrichosis?

A

They follow the line of lymphatics draining the primary lesion in the cutaneolymphatic form

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15
Q

What is the treatment of choice for sporotrichosis?

A

Iodides e.g. sodium iodide IV and PO

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16
Q

What are the clinical signs of iodism (e.g. adverse effects of iodide therapy)?

A 
Scaling
Alopecia
Depression
Anorexia
Fever
Coughing
Lacrimation
Serous nasal discharge
Salivation
Nervousness
Cardiovascular abnormalities
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17
Q

Cryptococcosis can cause nasal granulomas and cause which systemic clinical signs?

A

Rhinitis

Meningitis (CNS involvement)

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18
Q

What changes are evident on histopathology with cryptococcosis?

A

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

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19
Q

Which special stain can be used to identify Cryptococcus on histopathology?

A

Mayer mucicarmine (stains the mucinous capsule red)

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20
Q

What is the most reliable diagnostic test to identify Histoplasmosis farciminosi infection?

A

Demonstrating the organism in tissues on cytology or histopathology as it is difficult to culture

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21
Q

What is the antifungal action of nystatin and amphotericin B?

A

They bind with ergosterol in fungal cell membranes altering permeability (= death)

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22
Q

What is the antifungal action of azoles?

A

They inhibit the synthesis of ergosterol, triglyceride, phospholipid, chitin and oxidative and peroxidative enzymes

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23
Q

Which topical treatments can be used to treat dermatophytosis in horses?
Nystatin/amphotericin B
Azoles
Allylamines (e.g. terbinafine)

A

Azoles and allylamines; nystatin/amphotericin B are not effective

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24
Q

Which type of topical therapy is most effective at treating superficial mycoses in horses?

A

Rinses e.g. lime sulfur 2-5% and enilconazole 0.2%

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25
Q

Which fungal agent can cause nasal polyps and form sporangium (pl. sporangia)?

A

Rhinosporidium seeberi

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26
Q

Can people become infected with sporothrix schenckii from an infected horse?

A

No - transmission occurs with contact with an infected cat but not reported from horses

27
Q

What is the causative agent of epizootic lymphangitis in horses?

A

Histoplasma capsulatum var farciminosum

28
Q

What are differential diagnoses for epizootic lymphangitis in horses?

A

Ulcerative lymphangitis (Corynebacterium pseudotuberculosis)
Glanders (Burkholderia mallei)
Sporotrichosis

29
Q

Are Malassezia found on cytology of normal skin from the intermammary and preputial fossa areas of horses?

A

Yes - cytology was more sensitive than culture (M equi, and M slooffiae)

30
Q

Which body site has the greatest abundance of Malassezia species (based on culture)?

A

Ear canal (found in ~47% of samples)

31
Q

Which Malassezia species have been found in the normal ear canal of horses?

A

M. nana
M. slooffiae
M. equi

32
Q

How do you treat equine dermatophytosis?

A

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).

33
Q

Is Trichophyton bullosum zoophilic?

A

Yes - rarely isolated from horses

34
Q

PCR-based methods for the identification of dermatophytes amplify what?

A

Intergenic spacer (ITS) regions

35
Q

Name topical antifungal agents for treatment of dermatophytosis in horses

A
  • 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
36
Q

Which systemic antifungals can be given to horses?

A

Itraconazole (expensive) 5 mg/kg/day

Iodides (sodium and potassium iodide)

37
Q

Which horses are more likely to have dermatophytosis?

A

Young, stressed animals or in geriatric horses with metabolic or endocrine diseases

38
Q

Why can you see acanthocytes with dermatophytosis?

A

Can see severe exocytosis of neutrophils in the epidermis that release proteases and can trigger acantholysis

39
Q

What should you do to the skin/hair before taking a sample for dermatophyte culture in horses?

A

The area should be treated with alcohol to decrease contamination by saprophytic fungi.

40
Q

Why should you consider full body treatment even if lesions are focal?

A

Arthrospores may be present on the whole animal

41
Q

Dermatophytosis is a self-limiting disease, how long does spontaneous resolution take?

A

3 months

42
Q

What can be used to treat the environment for dermatophytes?

A
  • 5% lime sulfur
  • 5% sodium hypochlorite
  • 0.2% enilconazole
43
Q

Can depigmentation be seen with Malassezia dermatitis in horses?

A

Yes

44
Q

Which fungi cause spherical, sharply circumscribed, firm, brown-black nodules of 2–3 cm in diameter in horses?

A

Chromoblastomycoses - Fonsecaea spp.

45
Q

Name fungal causes of onychomycosis in horses

A

Scedosporium spp., Trichophyton spp. and Scopulariopsis brevicaulis, which invade the horn structures and cause damage

46
Q

Name two subcutaneous mycoses that spread through the lymphatic system

A

Histoplasma capsulatum var. farciminosum

Sporothrix schenckii

47
Q

How is Histoplasma capsulatum var. farciminosum spread?

A
  • 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
48
Q

What are the four forms of Histoplasma capsulatum var. farciminosum infection?

A
  1. asymptomatic
  2. cutaneous
  3. conjunctival/ocular
  4. respiratory
49
Q

What are the clinical signs of cutaneous histoplasmosis?

A

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.

50
Q

What are the clinical signs of pythiosis?

A

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.

51
Q

Which other diseases can pythiosis look like?

A

Habronemiasis
Skin fungal infections caused by Conidiobolus and Basidiobolus spp.
Invasive SCC

52
Q

What is the treatment of choice of pythiosis?

A

Surgical removal

53
Q

What is the route of infection of Sporothrix schenckii?

A

Through damaged skin

54
Q

How long is the incubation period of sporotrichosis in horses?

A

1–3 months

55
Q

What are the clinical signs of sporotrichosis in horses?

A

Subcutaneous nodules which ulcerate and drain purulent discharges. Subsequently, fungi spread via the lymphatic vessels and secondary lesions appear along the regional lymphatics

56
Q

What are the differentials for sporotrichosis in horses?

A

Ulcerative lymphagitis (i.e., Corynebacterium pseudotuberculosis) and Histoplasma capsulatum var. farciminosum infection

57
Q

In sporotrichosis in horses, are there numerous or sparse oragnisms?

A

Sparse - need special staining e.g. PAS/GMS

58
Q

How do you treat sporotrichosis in horses?

A

20% sodium iodide

59
Q

What is the treatment of choice for coccidiodomycosis in horses?

A

Fluconazole

60
Q

Can you use immunotherapy to treat pythiosis in horses?

A

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.

61
Q

What are the most common causes of phaehyphomycosis in the horse?

A

Alternaria alternaria, Bipolaris specifera and Cladosporium spp.

62
Q

Where do you find lesions with zygomycosis?

A
  • 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.
63
Q

Which fungi are the most common causes of eumycotic mycetoma?

A 
Pseudallescheria boydii (which produces white granules) 
Curvularia geniculata (which produces black granules).

Sarah - Equine (13 decks)

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