Page 1056 - Clinical Small Animal Internal Medicine

994 Section 9 Infectious Disease

time for dogs with CNS cryptococcosis in North America tachypnea, and/or exercise intolerance. Rarely, diffuse
VetBooks.ir was seven days (0–3680 days). pneumonia follows a more fulminant course, as reported
in immunocompromised humans.
A small percentage of infected dogs develop dissemi­
Public Health Implications nated infections. Sites of dissemination often include
Humans can develop cryptococcosis through environ­ osteoarticular sites, the CNS, skin, peripheral lymph
mental exposure. Notably, it is an important infection in nodes, eye, testes, prostate, and pericardium. Rarely,
people with AIDS. Direct transmission from animals to other sites, such as abdominal organs, are affected. Dogs
people has not been reported, but contaminated needle‐ with skin involvement may have ulcerated skin lesions
stick injuries may transmit the organism. Cryptococcus that drain serosanguinous fluid, or subcutaneous mass
grows on routine fungal laboratory media as a yeast, so is lesions. Neurologic signs result from fungal meningoen­
less likely to represent a hazard to laboratory personnel cephalitis and include obtundation, blindness, nystag­
than dimorphic fungi that grow as molds. mus, ataxia, placing deficits, circling, cervical pain,
tetraparesis, and seizures. Ocular manifestations include
chorioretinitis, uveitis, optic neuritis, and endophthal­
Coccidioidomycosis mitis. Pericarditis may lead to signs of right‐sided cardiac
failure, with development of ascites and pleural effusion.
Etiology/Pathophysiology
Coccidioides spp. (Coccidioides immitis and C. posa­ Diagnosis
dasii) are dimorphic fungi that exist in soil as chains of Thoracic radiographs in dogs with disseminated coc­
barrel‐shaped arthrospores. The arthrospores are aero­ cidioidomycosis are often unremarkable. The most
solized and inhaled by animal hosts. This may be fol­ common radiographic finding in dogs with pulmonary
lowed by localized pulmonary disease or dissemination coccidioidomycosis is tracheobronchial lymphadeno­
to the tracheobronchial lymph nodes and then other megaly. Although this may be the only finding, most
anatomic sites in the face of an inadequate immune dogs also have mild to moderate interstitial infiltrates.
response. Infections often follow a pattern of moist con­ Nodular interstitial, interstitial‐alveolar, bronchointer­
ditions (required for growth of Coccidioides spp. in the stitial infiltrates, and/or sternal lymphadenomegaly
soil), a dry period, then soil disruption, such as may may also be present. Dogs with pericarditis may have
occur with heavy rainfall, dust storms, or construction. cardiomegaly and pleural effusion, with hepatomegaly
After inhalation, arthrospores are phagocytosed by and decreased abdominal detail. Echocardiography in
alveolar macrophages. They then enlarge into a spherule these dogs may reveal thickening and mass lesions of
(8–100 μm in diameter). Hundreds of endospores the pericardium, pericardial and pleural effusion, and
develop within the spherule, which are released when cardiac tamponade.
the spherule ruptures. This is associated with a pyogran­ A diagnosis of coccidioidomycosis is typically con­
ulomatous inflammatory response. firmed using serology for antibodies to Coccidioides spp.,
because of the low sensitivity of cytology and the fact
Epidemiology and Signalment that culture is hazardous to laboratory personnel and
can have a long turnaround time. Cytologic examination
In the environment, Coccidioides spp. are distributed in of specimens from affected tissues or body fluids reveals
regions with arid soils, low elevations above sea level, and granulomatous or pyogranulomatous inflammation.
hot summers. Infections occur primarily in the south­ Occasionally, spherules can be identified as round, baso­
western United States, Mexico, and parts of Central and philic, double‐walled, crinkled structures (8–70 μm in
South America. In southwestern USA, highly endemic diameter) (Figure 109.5). Sometimes endospores (2–5 μm
regions include the south‐central valley of California in diameter) can be seen in association with ruptured
(“Valley Fever”) and Arizona. Latent infections occur in spherules.
dogs and these can reactivate after treatment with immu­ Most diagnostic laboratories detect antibodies to
nosuppressive drugs. Coccidioidomycosis is rare in cats. Coccidioides using gel immunodiffusion. False‐negative
serologic test results are rare in dogs with coccidioido­
mycosis. Antibody titers typically range from 1:2 to
History and Clinical Signs
1:256. Dogs with active infection may have titers as
Development of clinical signs often follows a subacute to low as 1:2, and healthy dogs in hyperendemic areas
chronic course. Many dogs continue to otherwise appear in Arizona have had titers as high as 1:16. As a result,
healthy, with occasional periods of inappetence. Clinical positive titers of 1:16 or lower should always be
signs of respiratory tract involvement include cough, interpreted in light of clinicopathologic abnormalities