Page 1533 - Small Animal Internal Medicine, 6th Edition

CHAPTER 97 Polysystemic Mycotic Infections 1505

been the drug of choice for the treatment of blastomycosis COCCIDIOIDOMYCOSIS
(see Table 97.2). Dogs should be treated with 5 mg/kg/day Etiology and Epidemiology
VetBooks.ir twice daily for the first 5 days and then 5 mg/kg once daily. Coccidioides immitis is a dimorphic fungus found deep in
Treatment should be continued for 60 to 90 days or for 4
weeks beyond resolution of measurable disease (i.e., thoracic
fall, and high environmental temperatures, including the
radiographic abnormalities or skin lesions). A bioequiva- sandy alkaline soils in regions with low elevation, low rain-
lence study showed that generic intraconazole was not bio- southwestern United States, California, Mexico, Central
equivalent to the approved product but was close enough to America, and South America. In the United States coccidi-
be used clinically (Mawby et al., 2014). In contrast, one oidomycosis is diagnosed most frequently in California,
source of compounded itraconazole was not suitable for use. Arizona, New Mexico, Utah, Nevada, and southwest Texas.
Fluconazole can also be used and may be effective for CNS, Coccidioides posadasii has also been proven in some regions
ocular, and urinary system blastomycosis. In one retrospec- that are endemic for C. immitis (Brown et al., 2013; Luna-
tive study, overall responses to fluconazole or itraconazole in Isaac et al., 2014). The environmental mycelial phase pro-
dogs with blastomycosis were similar. However, dogs treated duces arthrospores (2-4 µm wide, 3-10 µm long) that enter
with fluconazole had a higher mortality rate in the first 2 the vertebrate host by inhalation or wound contamination.
weeks of therapy, suggesting differences between the drugs Large numbers of arthrospores return to the surface after
in early efficacy (Mazepa et al., 2011). periods of rainfall and are dispersed by the wind; the preva-
Relapses occur in 20% to 25% of treated dogs. When they lence of coccidioidomycosis increases in the years after a
occur, a complete course of therapy should be reinstituted. high rainfall. Most cases of feline coccidioidomycosis are
Posterior segment ocular disease responds well to itracon- diagnosed between December and May. In one study of dogs
azole, but anterior uveitis and endophthalmitis often require residing in an endemic area (Arizona), the cumulative prob-
enucleation of the affected eye. In dogs with ocular blasto- ability of infection (evidenced by seroconversion) by 2 years
mycosis resulting in euthanasia or enucleation of the affected of age was 28%, and the cumulative probability of clinical
eye, differences in the presence of the organism was not infection by 2 years of age was 6% (Shubitz et al., 2005). In
noted between treated and untreated dogs (Hendrix et al., another recent study that included 41 dogs with coccidioi-
2004). In one study of 23 cats with blastomycosis, successful domycosis and 79 control dogs, younger age, digging behav-
results were reported for two cats treated with amphotericin ior, and travel to Arizona or the California central valley
B and ketoconazole, one cat treated with amputation, and were associated with infection (Gayzel et al., 2017).
one cat treated with potassium iodide. In a more recent study Inhaled arthrospores induce neutrophilic inflamma-
of eight cats, two cats treated with itraconazole and one cat tion followed by infiltrates of histiocytes, lymphocytes, and
treated with fluconazole had clinical resolution of their plasma cells. The lymphocytic infiltrates associated with
disease (Gilor et al., 2006). infection sites are predominantly T cells. Infection is cleared
After treatment, decreases in B. dermatitidis serum anti- if cell-mediated immune responses are normal; most people,
body levels are variable. In contrast, in one study of 46 dogs, and cats exposed to the organism are subclinically
treated dogs, urine antigen concentrations decreased with affected. The organism disseminates to mediastinal and
treatment and so may be of benefit for monitoring therapy tracheobronchial lymph nodes, bones and joints, visceral
with clinical and radiographic parameters (Spector et al., organs (liver, spleen, kidneys), heart and pericardium, testi-
2008). cles, eyes, brain, and spinal cord of some individuals. Spher-
ules (20-200 µm in diameter) containing endospores (see
Zoonotic Aspects and Prevention Table 97.1) form in tissues of infected hosts. Endospores are
Genetic analyses have confirmed three haplotypes of B. der- released by cleavage and produce new spherules. Respiratory
matitidis that are common to both dogs and humans (Ander- signs and signs of disseminated disease occur 1 to 3 weeks
son et al., 2013). Direct zoonotic transmission from infected and 4 months after exposure, respectively.
animals is unlikely because the yeast phase is not as infec-
tious as the mycelial phase. One veterinarian was infected Clinical Features
after material from a pulmonary aspirate from an infected Clinical disease in dogs is most common in young, male,
dog was injected intramuscularly, and another developed large-breed dogs. Dogs that are allowed to roam or walk in
disease after being bitten by an infected dog. The mycelial the desert in endemic areas, particularly if they also exhibit
phase develops at temperatures lower than body tempera- digging behavior are most likely to be exposed. Approxi-
ture; positive cultures and contaminated bandages are infec- mately 90% of clinically affected dogs have lameness with
tious. Multiple reports have been made of canine and human swollen, painful bones or joints. Cough, dyspnea, anorexia,
blastomycosis that developed from the same environmental weakness, weight loss, lymphadenopathy, clinical signs of
exposure. Decreasing potential for exposure by avoiding ocular inflammation, and diarrhea are other presenting
lakes and creeks in endemic areas is the only way to prevent complaints. Crackles, wheezes, or muffled lung sounds
the disease. A vaccine made of a genetically engineered live- from pleural effusion are common. Restrictive pericardi-
attenuated strain of B. dermatitidis shows promise for use in tis presenting with evidence of right heart failure, such as
dogs (Wüthrich M et al., 2011). hepatomegaly, pleural effusion, and ascites, can also occur.