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Fungal Disease - Aspergillosis

Introduction

Aspergillosis is found worldwide and in almost all domestic animals and birds as well as in many wild species.

It is primarily a respiratory infection that may become generalized; however tissue predilection varies among species.

The most common forms are pulmonary infections in poultry and other birds, mycotic abortion in cattle, guttural pouch mycosis in horses, and infections of the nasal and Para nasal tissues, intervertebral sites, and kidneys of dogs.

Pulmonary and intestinal forms have been described in domestic cats.

Etiology

Aspergillosis is caused by several Aspergillus sp., especially Aspergillus fumigatuas and A.terreus.

A.niger, A.nidulans, A.viridinutans, A.flavus, and A.felis are being recognized more commonly as molecular techniques for identification are being increasingly used

Clinical findings and lesions

Ruminants

Aspergillosis may be asymptomatic, appear in a broncho pulmonary form, cause mastitis, or cause placentitis and abortion. Mycotic pneumonia may be rapidly fatal.

Sings include pyrexia, rapid, shallow, stertorous respiration nasal discharge, and a moist cough. The lungs are firm, heavy; and mottled and do not collapse.

In sub-acute to chronic mycotic pneumonia, the lungs contain multiple discrete granulomas, and the disease grossly resembles tuberculosis.

In absence of pneumonia, infected cows generally have no signs except for abortion; dead fetus is aborted at 6-9 months gestation, and the fetal membranes are retained. Lesions are found in the uterus, fetal membrane and often the fetal skin.

In the uterus, the inter caruncular areas are grossly thickened, leathery, dark red to tan, and contain elevated or eroded foci covered by a yellow-gray adherent pseudo membrane. Maternal caruncles are dark red to brow, and the adherent fetal cotyledons are markedly thickened.

Cutaneous lesions in aborted fetuses consist of soft, red to gray, elevated, discrete foci that resemble ringworm.

Horses

Epistaxis and dysphagia are common complications of gutturomycosis.

The infected guttural pouch is characterized by a necrotizing inflammation and is thickened, hemorrhagic, and covered by a friable pseudo membrane. Mycotic rhinitis characterized by dyspnea and nasal discharge has also been described.

Aspergillosis can be a rapidly fatal disease associated with diffuse pulmonary invasion. In these cases, acute enteritis is often a predisposing factor.

The colitis is thought to result in a profound neutropenia that decreases the immune competence of the host, followed by invasion of Aspergillus from disrupted intestinal mucosa.

Loco motor and visual disturbances, including blindness, may occur when the infection spreads to the brain and optic nerve.

Dogs

Aspergillosis is typically localized to the nasal cavity or para nasal sinuses and is usually caused by infection with fumigates.

Nasal aspergillosis is seen mainly in dolichocephalic breeds; it begins in the posterior region of the ventral maxilla turbinate with signs of lethargy, nasal pain, laceration of the nares, sneezing, unilateral or bilateral sanguine purulent nasal discharge, frontal sinus osteomyelitis and epistaxis.

Gross lesions- Mucosa of the nasal and para nasal sinuses may be covered by a layer of necrotic material and white to gray-white fungal growth.

Disseminated disease in dogs is seen most often in German Shepherds and usually involves A.terreus and A.deflectus.

The clinical signs of disseminate aspergillosis may include lethargy, lameness, anorexia, weight loss, pyrexia, hematuria, urinary incontinence, generalized lymphadenopathy, and neurologic deficits.

Lesions are frequently found in the kidneys, spleen, and vertebrae. Disco spondylitis is common.

Diagnosis

Radiograph in dogs with nasal aspergillosis may show generalized radiolucency of the nasal chambers secondary to turbinate tissue destruction.

Frontal sinus osteomyelitis is seen up to 80% of the dogs.

Visualization of fungal plaques by rhinoscopy together with serology and either mycologic or radiographic evidence of disease is often how a diagnosis is made.

A diagnosis based on culture results alone is not appropriate. Because aspergillus are ubiquitous and can be isolated from the nasal cavity of healthy dogs. Positive culture results should be supported by demonstration of narrow, hyaline, separate, ranching hyphae within lesions or by serological tests.

The agar-gel double-diffusion test for serum antibody is reliable technique for diagnosis; improved sensitivity may be possible with techniques such as ELISA. Immunofluorescent procedures can be used to identify hyphae in tissue sections.

Treatment

Treatment

In chronic cases of canine nasal aspergillosis, surgical excision and curettage have been used with 10% iodine flushes instilled through a surgically exposed open nasal cavity.

Enilconazole, 10 mg/kg, instilled b.i.d for 7-14 days tubes implanted surgically into the frontal sinuses, has also been used with a rate of 80-90%. For administration, the stock solution of enilconazole (100 mg/kg) mixed with an equal volume of water or saline immediately before use, and this dose is divided equally between nasal tubes.

Because the drug has a bad taste profuse salivation and inappetance may occur. Systemically administered drug have included thiabendazole (10-20 mg/kg, b.i.d), ketoconazole (5-10 mg/kg, b.i.d), and fluconazole (2.5-5 mg/kg, b.i.d), itraconazole (5 mg/kg, b.i.d) have been with success rate of 70%.

Historic therapies include the following

Bovines

No clinical symptoms have been observed in the dam before or after abortion and no treatment has ever been given to affected animals.

As far as known, cows which abort fungus-infected fetuses may calve normally on the next occasion, but this may not always be so. At present the spontaneous "recovery" of the dam is assumed to follow the regeneration of the uterine wall.

Treatment of hay with fungicides during hay making in order to reduce subsequent mould growth might also help.

Horses

Surgical exposure and curettage have been used to do guttural myotomy for treatment. Topical natamycin and oral potassium iodide have been reported effective in Aspergillus infection. Recently, Itraconazole 3 mg/kg, b.i.d given for 84-120 days report effective in equine Aspergillus rhinitis.


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