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Zoonotic Diseases
Bacterial Diseases - BLASTOMYCOSIS
SYNONYMS:
North American blastomycosis, Chicago disease, Gilchrist's disease.
ETIOLOGY:
Blastomyces dermatitidis, a dimorphic fungus existing in mycelial form in cultures
and as a budding yeast in the tissues of infected mammals.
GEOGRAPHIC DISTRIBUTION:
The disease has been observed in the United States, eastern Canada, Zaire, Tanzania,
South Africa, and Tunisia. Autochthonous cases may have occurred in some Latin
American countries.
THE DISEASE IN MAN:
The incubation period is not well known; it possibly extends to several weeks
or months. Blastomycosis is a chronic disease that principally affects the lungs.
The respiratory symptomatology initially resembles influenzas purulent or bloody
expectoration, weight loss, and cachexia, in addition to fever and cough, may
develop later. If the infection remains localized, it can become asymptomatic.
When it disseminates, it can cause subcutaneous abscesses as well as localized
infections in several organs. Death frequently results in cases of untreated disseminated
infection. The cutaneous form is commonly secondary to the pulmo-nary and is characterized
by an irregular-shaped, scabby ulcer that has raised borders and contains minute
abscesses. Lesions develop on exposed parts of the body.
THE DISEASE IN ANIMALS:
The highest incidence is observed in dogs around 2 years of age. The symptoms
consist of weight loss, chronic cough, dyspnea, cutaneous abscesses, fever, anorexia,
and sometimes blindness. The lesions localize in the lungs, lymph nodes, eyes,
skin, and joints and bones. Of 47 clinical cases recently described, 72% occurred
in large males. There were lesions of the respiratory tract in 85% of the cases.
SOURCE OF INFECTION AND MODE OF TRANSMISSION:
The reservoir is environmental, probably the soil, but the ecologic biotope has
not been determined. Transmission to man and to animals is effected by aerosols;
the fungal conidia are the infecting element. Persons at highest risk are those
having the most contact with the soil. Dogs most frequently infected are sporting
and hunting breeds.
ROLE OF ANIMALS IN THE EPIDEMIOLOGY OF THE DISEASE:
None. It is a disease common to man and animals. Cases of transmission from individual
to individual (man or animal) are not known.
DIAGNOSIS:
Diagnosis is based on direct microscopic examination of sputum and material from
lesions, on isolation of the agent in culture media, and on examination of histologic
preparations. B. dermatitidis grows well in Sabouraud's culture medium or other
adequate median it is most distinctive in its sprouting yeast form, and therefore
the inoculated medium should be incubated at 37oC, since at ambient temperature
the mycelial form of the fungus is obtained. B. dermatitidis in its yeast form
(in tissues or cultures at 37oC) is characterized by a single bud attached to
the parent cell by a wide base, from which it detaches when it has reached a size
similar to the parent cell. In contrast, Paracoccidioides brasiliensis, the agent
of paracoccidioidomycosis ("South American blastomycosis"), has multiple buds
in the yeast phase. Serologic tests in use are complement fixation and gel immunodiffusion;
the latter gives better results. It should be borne in mind that cross-reactions
with Histoplasma and Coccidioides may occur. At present, the intradermal test
is considered to have no diagnostic value.
TREATMENT: Humans.
Itraconazole, 100-200 mg/d orally, is now the therapy of choice for nonmeningeal
disease, with a response rate of over 70%. Amphotericin B is given for treatment
failures or cases with central nervous system involvement. Follow-up for relapse
should be regularly made for several years so that therapy may be resumed or another
drug instituted. Animals. Rare primary cutaneous disease may persist for months;
these lesions should be removed surgically since blastomycosis responds poorly
to therapy. Amphotericin B is considered the drug of choice, but treatment is
of little avail once the disease is disseminated. The combination of amphotericin
B and ketoconazole has been suggested to reduce the rate of relapse.
CONTROL:
As long as the ecologic biotope remains poorly defined, practical prevention methods
cannot be established.
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