Investigation of dogs as a reservoir of Penicillium marneffei in northern Thailand

SummaryBackgroundPenicillium marneffei is a dimorphic pathogenic fungus endemic in Southeast Asia that usually causes disseminated disease, mainly in immunocompromised individuals, especially those with HIV infection. Untreated cases are usually fatal. The only known natural reservoir exists in bamboo rats and there is no firm evidence that these animals are involved in direct transmission to humans. The risk of infection is not restricted to those living in endemic areas; HIV-infected individuals who travel to Southeast Asia have also become infected by P. marneffei. Hence, there must exist sources to which even tourists are exposed on a short-term basis.Design and methodsPenicillium is known to infect dogs and this animal is common in the streets and temple areas of Chiang Mai, where there is one of the highest incidences of P. marneffei infection in the world. Dogs have not been well studied as a possible reservoir. To investigate this possibility, we took nasal swabs from 83 outdoor dogs and performed culture and nested polymerase chain reaction (PCR) to detect P. marneffei.ResultsWe found that approximately 13% of nasal swabs from dogs in Chiang Mai, Thailand were positive when tested by two different PCR methods, but culture results were negative. Sequencing the products from both PCR reactions showed 100% identity with P. marneffei, whereas no other known fungi shared both sequences.ConclusionsOur results suggest that dogs might be an animal reservoir for P. marneffei in northern Thailand. This observation should be confirmed by additional studies

Low Effective Dispersal of Asexual Genotypes in Heterogeneous Landscapes by the Endemic Pathogen Penicillium marneffei

Long-distance dispersal in microbial eukaryotes has been shown to result in the establishment of populations on continental and global scales. Such “ubiquitous dispersal” has been claimed to be a general feature of microbial eukaryotes, homogenising populations over large scales. However, the unprecedented sampling of opportunistic infectious pathogens created by the global AIDS pandemic has revealed that a number of important species exhibit geographic endemicity despite long-distance migration via aerially dispersed spores. One mechanism that might tend to drive such endemicity in the face of aerial dispersal is the evolution of niche-adapted genotypes when sexual reproduction is rare. Dispersal of such asexual physiological “species” will be restricted when natural habitats are heterogeneous, as a consequence of reduced adaptive variation. Using the HIV-associated endemic fungus Penicillium marneffei as our model, we measured the distribution of genetic variation over a variety of spatial scales in two host species, humans and bamboo rats. Our results show that, despite widespread aerial dispersal, isolates of P. marneffei show extensive spatial genetic structure in both host species at local and country-wide scales. We show that the evolution of the P. marneffei genome is overwhelmingly clonal, and that this is perhaps the most asexual fungus yet found. We show that clusters of genotypes are specific to discrete ecological zones and argue that asexuality has led to the evolution of niche-adapted genotypes, and is driving endemicity, by reducing this pathogen's potential to diversify in nature

Environmental detection of Penicillium marneffei and growth in soil microcosms in competition with Talaromyces stipitatus

Accepted versio

Penicillium marneffei Infection and Recent Advances in the Epidemiology and Molecular Biology Aspects

Penicillium marneffei infection is an important emerging public health problem, especially among patients infected with human immunodeficiency virus in the areas of endemicity in southeast Asia, India, and China. Within these regions, P. marneffei infection is regarded as an AIDS-defining illness, and the severity of the disease depends on the immunological status of the infected individual. Early diagnosis by serologic and molecular assay-based methods have been developed and are proving to be important in diagnosing infection. The occurrence of natural reservoirs and the molecular epidemiology of P. marneffei have been studied; however, the natural history and mode of transmission of the organism remain unclear. Soil exposure, especially during the rainy season, has been suggested to be a critical risk factor. Using a highly discriminatory molecular technique, multilocus microsatellite typing, to characterize this fungus, several isolates from bamboo rats and humans were shown to share identical multilocus genotypes. These data suggest either that transmission of P. marneffei may occur from rodents to humans or that rodents and humans are coinfected from common environmental sources. These putative natural cycles of P. marneffei infection need further investigation. Studies on the fungal genetics of P. marneffei have been focused on the characterization of genetic determinants that may play important roles in asexual development, mycelial-to-yeast phase transition, and the expression of antigenic determinants. Molecular studies have identified several genes involved in germination, hyphal development, conidiogenesis, and yeast cell polarity. A number of functionally important genes, such as the malate synthase- and catalase-peroxidase protein-encoding genes, have been identified as being upregulated in the yeast phase. Future investigations pertaining to the roles of these genes in host-fungus interactions may provide the key knowledge to understanding the pathogenicity of P. marneffei

Corneal Chromoblastomycosis Caused by Fonsecaea pedrosoi

Purpose: To report 2 unusual cases of fungal keratitis due to Fonsecaea pedrosoi. Methods: Two patients were diagnosed with Fonsecaea pedrosoi keratitis. Their files were reviewed for predisposing factors, clinical characteristics, microbiological study, treatment, and outcome. Results: Two consecutive patients presented with brownish pigmented corneal ulcers in their eyes after sustaining eye trauma from vegetative matter. In both cases, corneal scrapings were collected for microscopic examination and culture. Dematiaceous hyphae were seen on the smears, and dark pigmented colonies grew on the culture media, identified as F. pedrosoi. Both patients were treated and cured with combined topical antifungal agents and oral itraconazole. The first patient required an amniotic membrane patch, while the second received an intracameral amphotericin B injection. Conclusions: Pigmented infiltrates can be an important diagnostic clue, but a microscopic evaluation and culture are required to obtain an accurate diagnosis of Fonsecaea keratitis. The prompt diagnosis and combined antifungal treatment can prevent morbidity associated with this fungal infection

Corneal Phaeohyphomycosis Caused by Bipolaris hawaiiensis

Purpose: To report a rare case of keratitis infected by Bipolaris hawaiiensis. Methods: A patient who was diagnosed as fungal keratitis caused by B. hawaiiensis was retrospectively reviewed for history, clinical characteristics, risk factors, laboratory findings, treatments, and outcomes. Results: A 63-year-old man with a history of trauma and saw dust in the left eye presented with a corneal ulcer. Eye examination revealed whitish infiltration with a feathery edge and small brownish deposits in the anterior stroma of the left cornea. Numerous septate hyphal fragments were detected in a corneal specimen, and nucleotide sequence analysis identified B. hawaiiensis. Treatment was started with 5% natamycin eyedrops and oral itraconazole. Subsequently, a corneal plaque developed which did not respond to medication and debridement. The patient underwent therapeutic penetrating keratoplasty. Conclusions: B. hawaiiensis is a rare cause of corneal phaeohyphomycosis. A brownish pigmented infiltration is an important diagnostic clue, however microbiologic studies are required to obtain a definite diagnosis. Although antifungal medication and debridement are the mainstay of most corneal fungal infection, therapeutic penetrating keratoplasty can prevent morbidity related to this fungal infection

Ocular Basidiobolomycosis: A Case Report

Background: Ocular basidiobolomycosis is an unusual infection caused by fungus of the order Entomophthorales. This fungus has been previously reported as a common cause of skin, subcutaneous, and gastrointestinal tract infection. The fungus isolation and its typical characteristics are clues for diagnosis of this uncommon pathogen. Case Report: A 47-year-old male patient with nodular scleritis in the left eye after an eye injury from sawdust was treated as bacterial scleritis. The lesion improved with early surgical drainage and antibacterial therapy; then, he was discharged from the hospital. Thereafter, the patient was re-admitted due to progression of infectious scleritis with keratitis and orbital cellulitis. Surgical abscess drainage was performed again. The microbiological study demonstrated Basidiobolus ranarum. The patient was treated with topical ketoconazole, subconjunctival fluconazole injection, and oral itraconazole with partial response to the treatment. However, the patient eventually denied any further treatment and did not return for follow-up. Conclusions: B. ranarum is a rare pathogen of ocular infection in which a definite diagnosis requires isolation of the causative organism. Delay in diagnosis and appropriate treatment can lead to extension of the infection and poor outcomes

Ocular Basidiobolomycosis: A Case Report

Background: Ocular basidiobolomycosis is an unusual infection caused by fungus of the order Entomophthorales. This fungus has been previously reported as a common cause of skin, subcutaneous, and gastrointestinal tract infection. The fungus isolation and its typical characteristics are clues for diagnosis of this uncommon pathogen. Case Report: A 47-year-old male patient with nodular scleritis in the left eye after an eye injury from sawdust was treated as bacterial scleritis. The lesion improved with early surgical drainage and antibacterial therapy; then, he was discharged from the hospital. Thereafter, the patient was re-admitted due to progression of infectious scleritis with keratitis and orbital cellulitis. Surgical abscess drainage was performed again. The microbiological study demonstrated Basidiobolus ranarum. The patient was treated with topical ketoconazole, subconjunctival fluconazole injection, and oral itraconazole with partial response to the treatment. However, the patient eventually denied any further treatment and did not return for follow-up. Conclusions: B. ranarum is a rare pathogen of ocular infection in which a definite diagnosis requires isolation of the causative organism. Delay in diagnosis and appropriate treatment can lead to extension of the infection and poor outcomes