Case Studies

The Nose Knows: An Unexpected Case of Cryptococcus in a Domestic Shorthair Cat.

Cryptococcus: Grey Moon


Cryptococcus is the most common fungal infection in domestic cats and can infect immune compromised and immune competent cats. The most likely route of infection is inhalation of the organisms.

By Isabel Salinas, DVM
and Michael Huber, DVM, MS
Diplomate American College of Veterinary Surgeons

1. Referral

Gray Moon, an indoor/outdoor 10 year old male neutered Domestic Shorthair cat, was referred to the Animal Specialty Group Surgery service by Animal Dermatology for surgical consultation of bilateral middle ear mechanical obstruction. Gray Moon was first evaluated by his primary care veterinarian in August for a 2 week history of listlessness and loss of appetite in addition to a 6-8 week preceding history of loss of hearing and increased sneezing with serous ocular and nasal discharge. He historically was treated for feline lower airway disease with albuterol puffs as needed. No improvement was noted in Gray Moon’s demeanor or clinical signs after a course of antibiotics, before referral to dermatology for aural evaluation.

Anesthetized video otoscopy was performed revealing discoloration/opacity and outward bulging of the left tympanic membrane with increased vasculature and a mildly tilted right tympanic membrane. Oral examination showed no trachea or oropharynx obstruction and normal tonsillar crypts. These findings were consistent with a middle ear mechanical obstruction such as a polyp (left > right). A ventral bulla osteotomy was recommended and a 2mg injection of dexamethasone SP was given. Per the owner’s temporary improvement of Grey Moon’s respiratory signs was noted with the injection.

2. Examination

On physical examination Grey Moon was bright and alert. Upper airway stertor with bilateral serous nasal and ocular discharge noted. Upper airway noise with no crackles or wheezes was appreciated on thoracic auscultation. His vital parameters were within normal limits and the remainder of his physical exam was unremarkable.

3. Diagnostics

Pre-surgical bloodwork was unremarkable while thoracic radiographs showed a bronchointerstitial pulmonary pattern consistent with chronic previous airway disease. A focal area of opacity was noted in the left caudal lung lobe, suspicious for either primary pulmonary neoplasia or a local inflammatory infiltrate.

Cryptococcus: Right lateral thoracic radiograph

Bulla and thoracic CT was recommended pre-operatively to fully evaluate the extent of the bilateral middle ear obstruction and further evaluate the pulmonary infiltrate. Pending results, the most severely affected aural canal would be surgically addressed. The contralateral side would be surgically addressed at a later date to reduce morbidity/mortality.

Cryptococcus: MRI3 head 2

4. Treatment + Procedures

CT scan of the head confirmed symmetrical exudate extending from the tympanic bullae to the opening of the horizontal ear canal bilaterally. Diffuse thickening of the tympanic bullae with punctate lucencies consistent with permeative lysis were also noted.

Thoracic CT scan revealed multiple soft tissue nodules distributed throughout the lungs with a severe surrounding patchy interstitial lung pattern. Medial retropharyngeal lymph nodes were bilaterally enlarged while mandibular lymph nodes were within normal limits.

Cryptococcus: MRI1The pulmonary, middle ear, and tympanic bullae changes all were most consistent with a suspect fungal, bacterial, or parasitic disease process with secondary and lesser considerations given to diffuse neoplasia. Cryptococcus serum titers and mandibular lymph node aspirates were submitted. Grey Moon was recovered from anesthesia uneventfully and was sent home on buprenorphine pending final laboratory findings.

5. Diagnosis

Cryptococcus serum antigen titers were strongly positive (≥1:32,768) while mandibular lymph node cytology revealed large and small Cryptococcus species with evidence of reactive lymphoid tissue.

Cryptococcus: Image-3

6. Discussion

Cryptococcus is a yeast species found worldwide with the ability to infect a variety of mammalian animals. Disease is more frequently encountered in Australia, British Columbia, and Southern California. It is the most common fungal infection in domestic cats and can infect immune compromised and immune competent cats. These infections are most often reported in middle to older aged animals (>8yrs). While there is no proven breed predilection, overrepresented breeds include Siamese, Burman, and Ragdoll cats. The most likely route of infection is inhalation of the organisms. While similar infecting species are often cultured from humans, cats, and dogs, it is in fact the least likely of the fungal organisms to result in zoonotic spread.

Cats are more often infected by Cryptococcus gattii with the predominant molecular subspecies VGIII (gattii). It has a wide genetic diversity and is reported in infectious cases throughout California. These species and subspecies distribution and infectious predilection are important as differences in pathogenicity and drug susceptibility have been documented which can subtly alter treatment approach.

Cryptococcus can be either locally invasive or disseminated systemically. If locally invasive it tends to penetrate the respiratory tract, specifically the nasal cavity. From there, systemic dissemination can include the CNS, ocular, lymphatic system, skin, and internal organs. The most common clinical symptoms in cats are nasal or ocular discharge. In all species, chronic malaise and progressive respiratory signs are often seen first. Infectious lesions can vary, from distinct gelatinous masses to multifocal granulomas/pyogranulomas.

Definitive diagnosis involves organism identification via cytology, histopathology +/- immunohistology. Serum or CSF latex agglutination is a highly specific and sensitive test that identifies cryptococcus antigen and is positive when titers are greater than 1:8.

Fluconazole, a fungistatic agent with minimal side effects and good tissue penetration, has become the primary choice of treatment in animals. If large fungal aggregates exist, then surgical debulking of the mass should be completed as medical therapy often has poor diffusion into affected tissue.

Treatment tends to be long term lasting months to the rest of the animal’s life before complete infection resolution is achieved. Serial serum antigen titers should be monitored to evaluate therapeutic efficacy. Antifungal medication should be administered at least 2 months post accomplishment of zero cryptococcal antigen titers. Prognosis is variable and depends largely on owner cooperation and compliance as months to years of therapy is required for treatment. Animals with neurologic signs generally have a more guarded prognosis, as do animals that are immunocompromised (FeLV +) or are extensively diseased.

7. Recovery

Grey Moon was started on oral fluconazole therapy and advised to follow up with Animal Specialty Group’s Internal Medicine service for continued treatment and care. The owner reports that Grey Moon is doing well at home with a definitive increase in energy.

Image of Domestic Shorthair is not Grey Moon

Animal Specialty Group

DVM, MS, Diplomate American College of Veterinary Surgeons

After Dr. Michael Huber received his Doctor of Veterinary Medicine degree in 1993 from Purdue University, he completed an internship at the University of Minnesota (in small animal medicine, surgery, and emergency medicine), followed by a three-year residency at Auburn University.