Page 1538 - Small Animal Internal Medicine, 6th Edition

1510 PART XIV Infectious Diseases

Treatment should continue for at least 1 to 2 months past
resolution of clinical disease. Serum and CSF LA antigen
VetBooks.ir titers can diminish with therapy and have been used to
monitor response. Antigen titers fail to decrease in some
animals without clinical evidence of disease, suggesting per-
sistence of the organism in tissues.
Zoonotic Aspects and Prevention
People and animals can have the same environmental expo-
sure to Cryptococcus spp., but zoonotic transfer from contact
with infected animals is unlikely. Prevention is achieved by
decreasing potential for exposure.

HISTOPLASMOSIS

Etiology and Epidemiology
Histoplasma capsulatum is a saprophytic dimorphic fungus
found in the soil in all regions with tropical and subtropical
climates; histoplasmosis is diagnosed most frequently in the
Mississippi, Missouri, and Ohio River valleys and in the mid-
Atlantic states. The organism is considered endemic in 31 of
the 48 contiguous United States. The organism has also been FIG 97.6
associated with disease in dogs in some other countries. The Histoplasma capsulatum (2-4 µm in diameter) in
microconidia (2-4 µm) and macroconidia (5-18 µm) of the mononuclear cells. (Courtesy Dr. Dennis Macy, College of
mycelial phase are found in the environment. In the vertebrate Veterinary Medicine and Biomedical Sciences, Colorado
host, the 2- to 4-µm yeast phase is found in the cytoplasm State University.)
of mononuclear phagocytes (see Fig. 97.6 and Table 97.1).
Histoplasma capsulatum is concentrated most heavily in
soil contaminated with bird or bat excrement. Point sources
for infection are found in endemic areas; two dogs and 20 Physical examination abnormalities often include de -
people developed pulmonary histoplasmosis after removing pression, increased bronchovesicular sounds, respiratory
a tree that had served as a bird roost (Ward et al., 1979). wheezes, fever, evidence of diarrhea, pale mucous mem-
Subclinical infections are common in dogs. Dogs in endemic branes, hepatomegaly, splenomegaly, icterus, ascites, and
areas are commonly exposed, but the prevalence of disease intraabdominal lymph node enlargement. Airway obstruc-
is low. Immunosuppression may predispose to clinical infec- tion from massive hilar lymphadenopathy occurs in some
tion in dogs and cats. In one study of 30 cats, 11 cats were dogs. Lameness from bone infection or polyarthritis, periph-
housed strictly indoors with potted plants (5 cats) or unfin- eral lymphadenopathy, chorioretinitis, CNS disease, and skin
ished basements (6 cats) being the possible sources of infec- disease occur occasionally. Subcutaneous nodules rarely
tion (Reinhart et al., 2012). drain or ulcerate and are less common than in dogs with
Infection is by ingestion or inhalation of microconidia cryptococcosis or blastomycosis.
from the environment. The organism is engulfed by mono- Infected cats are either normal or develop disseminated
nuclear phagocytes, transformed to the yeast phase, and disease. Most clinically affected cats are younger than 4
transported throughout the body in the blood and lymph. years, and some are co-infected with feline leukemia virus.
Granulomatous inflammation results in persistently infected Depression, weight loss, anorexia, lameness, and dyspnea are
organs and clinical signs of disease. Disseminated disease is common presenting complaints. Weight loss can be severe
common in cats. and develop in as little as 2 weeks. Fever, pale mucous mem-
branes, abnormal lung sounds, oral erosions or ulcers, periph-
Clinical Features eral or visceral lymphadenopathy, icterus, soft tissue swelling
Most dogs with histoplasmosis are outdoor sporting breeds around osseous lesions, hepatomegaly, skin nodules, and,
younger than 7 years. Subclinical infection, pulmonary rarely, splenomegaly are physical examination abnormali-
infection, and disseminated infection are recognized most ties potentially consistent with histoplasmosis. Disseminated
frequently. Most affected dogs are presented for evaluation of disease has a grave prognosis in cats. Osseous histoplasmo-
anorexia, fever, depression, weight loss, cough, dyspnea, or sis is most common in bones of the appendicular skeleton
diarrhea. Large-bowel diarrhea is most common, but small- distal to the stifle or elbow joints, and one or more limbs
bowel diarrhea, mixed-bowel diarrhea, and protein-losing can be involved. Feline ocular histoplasmosis manifests with
enteropathy occur in some. conjunctivitis, chorioretinitis, retinal detachment, or optic