With over 800,000 tests run annually, TVMDL encounters many challenging cases. Our case study series will highlight these interesting cases to increase awareness among veterinary and diagnostic communities.
A 4-year-old, spayed female, German shepherd dog was diagnosed with anterior uveitis and treated with atropine drops, triple antibiotic drops, oral prednisone, and doxycycline. No improvement was noted in the right eye after extended therapy and the dog was referred to an ophthalmologist. The ophthalmologist confirmed chronic anterior uveitis with irreversible blindness OD and recommended enucleation with histopathology. The dog was otherwise clinically healthy. The affected eye was histologically diagnosed with severe, diffuse chronic fibrinopurulent to granulomatous endophthalmitis with intralesional fungi. The dog soon developed PU/PD and became azotemic. A urinalysis collected by cystocentesis revealed repeatable fungi. Urine culture yielded Aspergillus sp. Serology for systemic fungi and Aspergillus was negative.
Disseminated aspergillosis is caused by saprophytic fungi that are ubiquitous in the environment. The most commonly reported causative agents are A. terreus, A. deflectus, A. falvipes and A. fumigatus. Occasionally, mixed fungal infections with Aspergillus spp. and candidiasis are reported. The disease occurs worldwide. Disseminated aspergillosis is thought to occur after inhalation of spores and hematogenous spread. However, these cases often present with no clinical history of nasal or pulmonary involvement. Most cases of canine disseminated aspergillosis have occurred in German shepherd dogs, 2 to 8 years of age. As with any blood-borne pathogen, common sites of embolic dissemination of fungal organisms are the intervertebral discs, renal glomeruli and uveal tracts. Other parenchymal organs, muscles and long bones and the CNS may be affected. Nonspecific clinical signs include anorexia, weight loss, muscle wasting, pyrexia, weakness, lethargy and vomiting. Uveitis or endophthalmitis may be clinically apparent some months before generalized illness develops and thus may be important in early diagnosis.
Methods to detect Aspergillus include cytologic, cultural and histopathologic evaluations. An effective and simple diagnostic test involves examination of an aseptically collected urine sample for the presence of hyphal elements. Urinary tract Aspergillus infections are generally a consequence of hematogenous spread and are usually observed in immunocompromised hosts. Predisposing factors for canine aspergillosis may include a combination of optimal climatic conditions, an access to particular strains of Aspergillus, a subtle defect in mucosal immunity (IgA deficiency) that may have a genetic basis. Serologic tests are available but false negatives can occur, especially of the affected dog is immunodeficient and does not mount in adequate antibody response. Additional clinical evidence may be necessary for definitive diagnosis in some cases. Decreased levels of IgA, altered cell–mediated immunity, and changes in circulating serum complement levels confirm immunologic incompetence. Most dogs affected with disseminated aspergillosis are severely ill and the prognosis for recovery is grave. Although few dogs have responded to antifungal therapy, relapses have occurred after termination of therapy which resulted in death or euthanasia of the animal.
Reference: Day MJ. Canine Disseminated Aspergillosis in Infectious Diseases of the Dog and Cat, 4th ed. 2012, (pp. 662-666). Elsevier, St. Louis, MO.
To learn more about this case, contact Dr. Barbara Lewis, veterinary pathologist, at the College Station facility. For more information on tests and services offered by TVMDL, call 979.845.3414 or visit tvmdl.tamu.edu.