Yeast Pathologies

Animal Candidiasis

Pathology caused by the genus Candida, exerting its pathogenic action mainly on mucous membranes (1).

The animal species mainly affected are: bovines, pigs, poultry, etc. (1).

Bovine candidiasis

Candida species preferentially colonize mucous membranes; the most frequent conditions they produce are: soor of the digestive tract, pneumonias, abortions, mastitis and diarrhea (1).

Etiology

Different species of the genus Candida (24) — morphological scheme of various Candida spp.

Epidemiology

Predisposing factors are those previously mentioned in the generalities of systemic mycoses (1).

Clinical signs (1)

Acute yeast mastitis is characterized by:

• Mammary inflammation: affected quarter increased in volume, tense, and of gummy consistency.
• General disturbance and fever (42°C).

In this way the disease becomes chronic. In the acute phase secretion is scant, grey-yellowish, showing mucous clumps. In the chronic phase, milk returns and mucous floccules appear. (17) isolates Candida maltosa as the etiological agent of these chronic mastitis cases.

Spontaneous recovery takes place within three weeks.

(22) reports diarrhea in calves caused by Candida spp.

(14) has observed that “candidiasis” in other ruminants such as goats can cause abortions.

Diagnosis

Direct examination of samples reveals isolated yeasts, sometimes budding with short pseudohyphae bearing verticils of blastospores, which stain with Giemsa or Gram (24).

For isolation, Sabouraud dextrose with antibiotics but without actidione is used, since some species do not grow with this inhibitor. In media with tetrazolium salts, colony color is observed (24).

Colonies show rapid growth at 28°C, initially smooth and later rough (24).

Identification: by filamentation in inactivated serum at 37°C for 3–4 hours: C. albicans. Formation of chlamydospores and pseudomycelium. Sugar fermentation. Auxanogram. Urease test (24).

Treatment

• Etiological treatment: antifungals via canal route.
• Symptomatic treatment: anti-inflammatories, frequent milking (1).

Porcine candidiasis (1)

The pig is the animal that has the greatest quantity of yeasts per gram of feces (1).

Few Candida species are capable of being pathogenic. Candida infections in pigs are normally secondary and endogenous.

Candidiasis of the upper digestive tract is usually caused by C. albicans and infections of the lower digestive tract by C. krusei.

In artificially fed piglets, multiplication of Candida is predisposed, which causes:

• Vitamin deficiency.
• Reduction of defenses and secondary bacterial infections.

At the intestinal level the only observable finding is a pseudomembranous lining. In sows during the rearing period, diarrhea may occur.

Treatment

• Nystatin
• Amphotericin B
• Trichomycin

This treatment is not justified for economic reasons.

Avian candidiasis (1)

Notably C. albicans. Although it is also true that Candida albicans appears to be normally found in healthy crops according to (6), who isolates it from 80% of animals.

Soor: affects animals in the first three days of life (chickens, turkeys, waterfowl, partridges, etc.).

As a consequence of the pathogenic action of this organism, alterations occur in the mucous membranes of: tongue, pharynx and beak; with whitish crusty deposits, thickened and hemorrhagic mucosae. Diarrhea and weakness also appear.

Mortality during the first month of life can reach 100%.

Treatment

• Avoid predisposing factors.
• Vitamin supplementation.
• Symptomatic therapy.

TYPHLOHEPATITIS (1)

Avian candidiasis caused by C. albicans. In the affected organs, vegetative forms of yeast development appear, surrounded by macrophages.

All birds can be affected but especially turkeys. Contagion is oral.

Clinically there is adynamia and foul-smelling orange diarrhea.

The most notable lesions: alterations in the large intestine and liver exhibiting whitish foci with toothed edges; such foci can also be observed in the pancreas and kidneys.

No effective treatment is known.

In other animals such as cats and dogs, the most frequent isolations of Candida spp. are from otitis.

Cryptococcosis

Cryptococcus neoformans

Fungi of the genus Cryptococcus appear as spherical cells that reproduce by budding; they have the appearance of true yeasts (ascomycetes), but sexual forms have not been observed. Nevertheless, under certain culture conditions some elements of C. neoformans produce morphological structures suggesting these organisms should be placed in the class Basidiomycetes (8).

Microscopically they present yeast-like forms (3) with a thick capsule (7). Of the Cryptococcus species, only C. neoformans is considered pathogenic (19).

Infection frequently occurs by inhalation of yeasts (3, 8, 19).

It is pathogenic for bovines, dogs, cats, equines (3); (8) also cites humans and (7) goats.

The causative agent is frequently found in soil, often in bird droppings, without those birds being infected (3, 1); the microorganism colonizes the droppings after they are eliminated (3).

In dogs, cats and humans, nervous manifestations frequently occur, with other organs subsequently affected. In bovines it mainly presents as mastitis (3, 1).

In equines, nasal granuloma occurs that may extend to lungs and viscera (3). (8) refers to C. neoformans in goats, in which varied clinical signs are produced depending on localization and severity of infection; lesions observed in: trachea, nasal passages, skin, chronic hepatitis (7).

Diagnosis

Direct examination: of fresh preparations of cerebrospinal fluid or pus where yeast-like cells can be seen. Samples can also be emulsified in India ink or nigrosin, or stained with Gram (+) (3).

Isolation and culture: Blood agar and Sabouraud agar are used for culture (3); (7) uses Sabouraud Maltose agar with chloromycetin. Incubation at 37°C (7) or at 25 and 37°C for no more than one week (3, 7). Whitish to slightly yellowish colonies appear, moist and shiny, of mucous consistency (7). With continued incubation the color varies from cream to brownish (3). Most saprophytic strains of cryptococcus do not grow at 37°C (3).

Microscopically: characterized by the formation of blastospores of 4–7 microns and spheroidal budding cells of 5–20 microns (7).

Identification: by cultural and morphological characteristics of the fungus, presence of a large capsule (3); urease positive (+), which differentiates them from Candida spp., which do not produce it (3).

C. neoformans produces brown colonies on bird-seed agar; this medium containing Guizotia abyssinica is used as a selective medium for C. neoformans since it is the only cryptococcus that produces those brown colonies (3).

True yeast species of Saccharomyces can be distinguished from Cryptococcus by the presence of ascospores in the former (Ajello, L.; George, L.K.; Kaplan, W. and Kaufman, Laboratory Manual of Medical Mycology, Washington, U.S. Gov. Printing Office, 1963, cit. 4). Ascospores stain well with methylene blue (4). They can also be identified by sugar utilization and nitrate tests (3).

According to the Biomerieux catalogue for isolation and identification of Candida, the biochemical characteristics of C. neoformans are:

• Does not grow on Sabouraud Chloramphenicol Actidione, indicating sensitivity to Actidione.
• Does not ferment the following sugars: glucose, galactose, maltose, lactose, trehalose, raffinose.
• The “Auxanogram” is also used, in which C. neoformans behaves as follows: glucose, galactose, maltose and sucrose (+); lactose (−), trehalose and raffinose (+). This test demonstrates growth or inhibition of the fungus in the presence of the aforementioned sugars.

Animal inoculation techniques can also be used:

• Inoculation of 1 ml intraperitoneally in mice (3, 4, 7).
• Inoculation of 0.02 ml intracerebrally in mice (4). The inoculum is prepared by making a dense dilution of C. neoformans grown in Sabouraud in saline solution (3). Gelatinous masses form in the abdominal cavity associated with other lesions containing encapsulated cells (4, 7). Intracerebral inoculation causes death in 10 days. Rats and guinea pigs are much less sensitive (7).

Serology

The latex particle agglutination test is useful for identifying the microorganism’s antigens. Tube agglutination, complement fixation, IFI, among others can also be used (3).

TREATMENT (3)

• Amphotericin B
• Imidazole derivatives (promising).

Malassezia Pathologies

OTITIS: Malassezia

Species of this yeast genus are associated with the skin of humans and domestic animals. Yeasts formerly called Pityrosporum are now designated M. pachydermatis. This species exists as a commensal in oily areas of the skin and in the ears of dogs. It can also be isolated from cats’ ears. In some cases of external otitis these yeasts are present in greater numbers than usual; some veterinarians believe they may have etiological significance (3); they are indeed cited as causative agents of otitis in dogs (18, 9).

Others such as M. furfur cause: blepharitis, seborrhoea, dandruff, tinea versicolor in humans (3).

Microorganisms of the genus Malassezia are small budding cells with a bottle shape that reproduce by budding (3).

They can be observed in fresh preparations with 10% NaOH from clinical samples (3).

They are isolated from Sabouraud agar after two weeks of incubation at room temperature. If olive oil or coconut oil is added to the surface of the medium, growth is more abundant (3).

(23) has studied the response of M. pachydermatis to antifungals and obtained the following results: clotrimazole, ketoconazole, miconazole, nystatin. Ketoconazole proved to be the most suitable treatment for external otitis associated with M. pachydermatis.