Oculosystemic pneumocystosis in 2 sibling Chihuahuas

Abstract

Sibling female and male Chihuahuas were evaluated for a 9-month history of tachypnea that failed to respond to fenbendazole, doxycycline, amoxicillin-clavulanate, and prednisone. Physical examination identified tachypnea, hyperpnea, and harsh bronchovesicular lung sounds. Fundic examination disclosed diffuse chorioretinitis, manifested as multifocal chorioretinal granulomas in the female dog and occasional chorioretinal scars in the male dog. Thoracic radiographs indicated moderate to severe interstitial to broncho-interstitial infiltrates in both dogs. Serum and urine antigen and antibody testing in the female dog failed to identify infectious agents, but cytologic assessment of hepatic lymph node, liver, and splenic aspirates identified Pneumocystis trophozoites. Infection was confirmed in both dogs by 28S rRNA PCR sequencing from multiple tissue samples. The female dog responded well to trimethoprim-sulfamethoxazole, but the male dog was euthanized because of liver failure, presumably related to antimicrobial treatment.

Keywords: fundic examination; infectious disease; ophthalmology.

FIGURE 1

Color fundus photograph of the right eye of dog 1 on the day of admission. Multifocal maroon to cream‐colored, well‐delineated, subtly raised, circular areas are visible throughout the tapetal and non‐tapetal fundus. The optic nerve head, retinal and choroidal vasculature appear normal. The apparent tapetal hyperreflectivity in this image is a photographic artifact. The ophthalmic diagnosis was multifocal, highly localized, chronic active chorioretinitis OU.

FIGURE 2

Ultrasound imaging on dog 1 on the day of admission demonstrating severe nephrocalcinosis.

FIGURE 3

Cytologic findings from aspiration of the peri‐hepatic lymph node from dog 1 (×50); (Wright Giemsa staining). Many individualized and aggregated Pneumocystis organisms (black arrows) are present alongside macrophages containing intracytoplasmic organisms (black arrowheads).

FIGURE 4

Color fundus photograph of the right eye of dog 1 10 days after initiating antibiotic and anti‐inflammatory treatment. Note that, relative to Figure 1, the multifocal chorioretinal lesions throughout the tapetal and non‐tapetal fundus are better circumscribed, no longer appeared raised, and are darker, suggestive of resolving inflammation and early development of chorioretinal scars. The optic nerve head, and retinal and choroidal vasculature remain normal.

FIGURE 5

Color fundus photograph of the right eye of dog 2 at initial presentation. Note the two dark, well‐circumscribed, non‐raised circular lesions in the far nasal tapetal periphery (black arrows). Each was surrounded by a narrow zone of tapetal hyper‐reflectivity, although this finding is not evident in the more ventral lesion in this photograph because of the angle of illumination. Both lesions were considered to be chorioretinal scars consistent with focal areas of resolved chorioretinitis. The general tapetal reflectivity, optic nerve head, and retinal and choroidal vasculature of the right eye were normal. No abnormalities were detected in the left eye.

FIGURE 6

Right lateral (A) and dorsoventral (B) thoracic radiographs of dog 2 identified a diffuse homogenous moderate interstitial pulmonary pattern and increased soft tissue opacity in the perihilar region suspicious for hilar lymphadenopathy.

FIGURE 7

Postmortem appearance of the lungs and trachea of dog 2. The lungs were diffusely firm and failed to collapse. The pleura was diffusely covered by pale tan to white, firm plaques, and nodules. Multifocal, firm, white nodules (granulomas) expanded the pulmonary parenchyma.

FIGURE 8

Phylogenetic tree based on portions of the 28S LSU sequences of various members of the Pneumocystis genus including samples from 2 sibling Chihuahuas with oculosystemic pneumocystosis. Pneumocystis murina sequence was used as an outgroup. The tree was constructed using the Maximum Likelihood Method. Bootstrap values shown at the main nodes represent the probabilities based on 1000 replicates. ST, sequence type.