Detection of Coccidioides posadasii from xerophytic environments in Venezuela reveals risk of naturally acquired coccidioidomycosis infections

Abstract

A wide range of mammals are susceptible to infection by the fungal species Coccidioides immitis and C. posadasii. In humans, 60% of infections are asymptomatic; however, certain patients may develop a severe and deep systemic mycosis called coccidioidomycosis. Genetic analysis suggests that the majority of clinical isolates recovered from South America are C. posadasii; however, little is known about the prevalence, species distribution, and ecological factors that favor the occurrence of this pathogen in those areas. By using a combined quantitative polymerase chain reaction (qPCR)-based approach and mycobiome amplicon sequencing, we provide evidence that at least two genotypes of C. posadasii are found in the xerophytic environment in Venezuela. We detected a 3806-fold range in the amount of Coccidioides DNA when comparing among the sampled locations, which indicates that human exposure risk is variable, and is one critical factor for disease manifestation. We identified fungal communities that are correlated with a higher prevalence of C. posadasii, suggesting that a combination of specific microbes and a xeric microenvironment may favor the growth of Coccidioides in certain locations. Moreover, we discuss the use of a combinatorial approach, using both qPCR and deep-sequencing methods to assess and monitor fungal pathogen burden at outbreak sources.

Population Structure and Genetic Diversity among Isolates of Coccidioides posadasii in Venezuela and Surrounding Regions

“…Notably, skin test surveys using coccidioidin in Latin American communities revealed positive intradermic test rates of 44% and 46% in the Chaco region of Paraguay and the Lara State of Venezuela, respectively (26, 31). Additionally, environmental molecular detection of Coccidioides posadasii in Venezuela suggests a high prevalence of the organism in the soil (32). The actual occurrence of coccidioidomycosis remains unclear; as fewer than 1,000 total coccidioidomycosis cases have been reported over the last century in South and Central America (19, 26).…”

Strong population structure in Venezuelan populations ofCoccidioides posadasii

“…Epidemiological studies show that coccidioidomycosis in South America is mostly caused by C. posadasii (19, 61, 64). Molecular analyses of soil DNA revealed that Coccidioides is common in xeric environments of Venezuela: all sampled sites (N = 15) were positive for Coccidioides; and sequencing of one of the ribosomal Internal Transcribed Spacers (ITS2) suggested that all the environmental samples from the region are, indeed, C. posadasii (33). Nonetheless, the sample of genotypes was diverse and encompassed multiple ITS2 haplotypes.…”

“…Additionally, environmental molecular detection of Coccidioides spp. in Venezuela suggests a high prevalence of C. posadasii in the soil (33). The actual occurrence of coccidioidomycosis remains unclear; as fewer than 1,000 total coccidioidomycosis cases have been reported over the last century in South and Central America (19, 26).…”

Re-drawing the Maps for Endemic Mycoses

“…Coccidioidomycosis (Valley Fever) is caused by two epidemiologically and genetically diverse species, C. immitis and C. posadasii [ 34 , 114 – 120 ]. C. immitis was first discovered in 1892 in Buenos Aires and misidentified as a protozoan; years later, it was correctly identified as a fungus [ 34 , 121 – 124 ].…”