By Stan Deresinski, MD, FACP, FIDSA
Clinical Professor of Medicine, Stanford University
Dr. Deresinski reports no financial relationships relevant to this field of study.
SYNOPSIS: Blastomycosis occurs in western Canada and in the United States well outside the known endemic area, but it is due to Blastomyces helicus, not Blastomyces dermatitidis.
SOURCE: Schwartz IS, Wiederhold NP, Hanson KE, et al. Blastomyces helicus, a new dimorphic fungus causing fatal pulmonary and systemic disease in humans and animals in western Canada and United States. Clin Infect Dis 2018; doi: 10.1093/cid/ciy483. [Epub ahead of print].
Schwartz and colleagues described 10 blastomycosis cases in humans and five in animals (including two dogs and two cats) that were acquired in the western regions of the continental United States and Canada. However, the cases were not caused by Blastomyces dermatitidis, but instead by Blastomyces helicus. The human cases appeared to have been acquired in Alberta, Saskatchewan, Texas, Utah, Nebraska, and Northern California. Clinical information was available for seven of the human cases, with six of these occurring in immunocompromised patients. The authors recounted an instructive case that had been reported from Stanford University in 2017 that described a California snake farmer who had trapped and fed small mammals and who developed fatal pulmonary infection with dissemination shortly after undergoing liver transplantation.1
The most frequent sites from which the fungus was isolated in the patients, in decreasing order of frequency, were blood, bronchoalveolar lavage fluid, cerebrospinal fluid, pleural fluid, bone marrow, liver, sputum, and lung tissue. On histopathological examination, the organisms appeared as small budding yeast cells, although hyphae also were seen in lung tissue in one case. A B. dermatitidis DNA probe was positive in all three cases in which it was applied, while one patient had a positive urinary Histoplasma antigen test. A Blastomyces galactomannan antigen test was positive in a cat. On culture, the organism exhibited yeast-like growth at 35°C on potato dextrose agar, and the cells were pleomorphic and variably sized. Mycelial growth was notable for the absence of conidia, which usually are present (and said to resemble “lollipops”) in B. dermatitidis, and the presence of helically coiled hyphae (hence, the name B. helicus), especially on media with low concentrations of carbohydrates with incubation at 25°C.
Outcomes were known for six of the human cases. The infection was fatal in four of these, three of whom received antifungal therapy. Both survivors received such therapy. One animal was known to have received treatment with fluconazole and survived.
This report describes the occurrence of blastomycosis due to B. helicus in regions of North America outside those known to be endemic for B. dermatitidis infection. On histopathological examination, the yeasts that are observed may be mistaken not only for the latter (although the occasional observation of short yeast chains is somewhat distinctive), but also for Histoplasma capsulatum. Furthermore, DNA probes for B. dermatitidis and urinary antigen tests for this organism and H. capsulatum also may be positive in the presence of B. helicus infection. In culture, the lack of conidia as well as the presence of coiled hyphae are distinctive.
The infections were disseminated frequently, with two involving the central nervous system. Most patients with disseminated B. dermatitidis infection do not have underlying immunocompromise identified, while most cases in this short series occurred in immunocompromised patients.
In addition, none of the patients were described as having skin lesions, which is a frequent finding in patients with disseminated B. dermatitidis infection.
B. helicus infections are not as new as one might suspect. Instead, this story represents an example of the general effects of changing nomenclature, something that has become a Tower of Babel for clinicians. When first reported, this organism was called Emmonsia helicus. More recently, E. helicus has been included, along with several other Emmonsia, in the genus Blastomyces. The Stanford case involving a snake farmer with a liver transplant mentioned earlier was reported in 2017 by Kappagoda et al as a case of infection due to Emmonsia sp.
- Kappagoda S, Adams JY, Luo R, et al. Fatal Emmonsia sp. infection and fungemia after orthotopic liver transplantation. Emerg Infect Dis 2017;23:346-349.