Penicillium marneffei in Humans and Rodents | CDC EID

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Volume 17, Number 2–February 2011
Research
Common Reservoirs for Penicillium marneffei Infection in Humans and Rodents, China
Cunwei Cao, Ling Liang, Wenjuan Wang, Hong Luo, Shaobiao Huang, Donghua Liu, Jianping Xu, Daniel A. Henk, and Matthew C. Fisher

Author affiliations: The First Affiliated Hospital of Guangxi Medical University, Nanning, People's Republic of China (C. Cao, L. Liang, W. Wang, H. Luo, D. Liu); The Fourth Hospital of Nanning, Nanning (S. Huang); McMaster University, Hamilton, Ontario, Canada (J. Xu); and Imperial College, London, UK (D.A. Henk, M.C. Fisher)

Suggested citation for this article

Abstract

Human penicilliosis marneffei is an emerging infectious disease caused by the fungus Penicillium marneffei. High prevalence of infection among bamboo rats of the genera Rhizomys and Cannomys suggest that these rodents are a key facet of the P. marneffei life cycle. We trapped bamboo rats during June 2004–July 2005 across Guangxi Province, China, and demonstrated 100% prevalence of infection. Multilocus genotypes show that P. marneffei isolates from humans are similar to those infecting rats and are in some cases identical. Comparison of our dataset with genotypes recovered from sites across Southeast Asia shows that the overriding component of genetic structure in P. marneffei is spatial, with humans containing a greater diversity of genotypes than rodents. Humans and bamboo rats are sampling an as-yet undiscovered common reservoir of infection, or bamboo rats are a vector for human infections by acting as amplifiers of infectious dispersal stages.

Penicillium marneffei is the only pathogenic species of Penicillium within this grouping of >270 species. This unique feature is due to the ability of P. marneffei to exhibit temperature-dependent dimorphic growth as an intracellular macrophage-associated fission yeast at 37°C. Before the HIV pandemic in Asia during the early 1990s, human penicilliosis was an exceedingly rare infection (1). Since then, however, this mycosis has become widely recognized as a co-infection in patients with HIV/AIDS, with an incidence that rivals that seen for Cryptocococcus neoformans and Mycobacterium tuberculosis (1). The organism is endemic across a narrow band of tropical Southeast Asia, with human- and rodent-associated infections occurring in northeast India, Thailand, the Guangxi region of China, Vietnam, Taiwan, and Hong Kong (2–4). Within these regions, P. marneffei has emerged as a major threat to public health; in Guangxi Province alone, ≈16% patients with AIDS are infected with the pathogen, and >100 new cases are reported from The First Affiliated Hospital of Guangxi Medical University per year (C. Cao, unpub. data). Although unproven, humans are assumed to become infected by inhaling aerosolized infectious conidia originating from thus far unidentified environmental sources (1).

Despite the growing cost of this infection to human health across this region, the reservoir for human infections remains enigmatic. One clue to the potential source of infection is that P. marneffei maintains a close association with rodent species, particularly bamboo rats. Across Thailand and Vietnam, P. marneffei is commonly recovered from species of Cannomys and Rhizomys bamboo rats, with prevalences of infection approaching 100%. The type isolate of the pathogen was identified from a sample from an infected Rhizomys sinensis rat in 1956 (5). The observation that P. marneffei is the only species of Penicillium to have evolved a pathogenic lifestyle strengthens the hypothesis that small mammals are an obligate phase in the life cycle of P. marneffei.

As with other dimorphic fungal pathogens that infect rodents, such as Coccidioides spp., infection in bamboo rats is assumed to lend a selective benefit by creating a nutrient-rich patch for sporulation and widespread aerosol-dispersal after the eventual death of the host (6). However, identifying penicilliosis infections in rodents as the ultimate sources of penicilliosis infections in humans requires, as a first step, a demonstration that the genotypes of sylvatic and human-associated isolates are similar or identical.

To this end, we ascertained the sylvatic prevalence of infection by trapping hoary bamboo rats (Rhizomys pruinosis) from across a region to which the infection is endemic, Guangxi Province in southern China, a region in which the observed case-rate for human penicilliosis marneffei is rapidly increasing (1,2). From these rodents, P. marneffei was isolated and genotyped by using a panel of highly polymorphic microsatellite loci. We also collected a panel of isolates from human infections across this region and then compared the distribution of genetic diversity within and between bamboo rats and humans across Guangxi and, more widely, Southeast Asia. These analyses were then used to identify the distribution of genetic diversity within and between hosts, identifying its major hierarchical components and identifying common genotypic features.

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Penicillium marneffei in Humans and Rodents | CDC EID


Suggested Citation for this Article
Cao C, Liang L, Wang W, Luo H, Huang S, Liu D, et al. Common reservoirs for Penicillium marneffei infection in humans and rodents, China. Emerg Infect Dis [serial on the Internet]. 2011 Feb [date cited]. http://www.cdc.gov/EID/content/17/2/209.htm


DOI: 10.3201/eid1702.100718


Comments to the Authors
Please use the form below to submit correspondence to the authors or contact them at the following address:

Ling Liang, Department of Dermatology, First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi Province, 530021, People's Republic of China; email: gxmull@163.com