Analyses of pediatric isolates of Cryptococcus neoformans from South Africa

Abstract

Compared to the incidence in adults, cryptococcosis is inexplicably rare among children, even in sub-Saharan Africa, which has the highest prevalence of coinfection with HIV and Cryptococcus neoformans. To explore any mycological basis for this age-related difference in the incidence of cryptococcosis, we investigated isolates of C. neoformans recovered from pediatric and adult patients during a 2-year period in South Africa. From reports to the Group for Enteric, Respiratory, and Meningeal Disease Surveillance in South Africa (GERMS-SA), we reviewed all cases of cryptococcosis in 2005 and 2006. We analyzed one isolate of C. neoformans from each of 82 pediatric patients (<15 years of age) and determined the multilocus sequence type (ST), mating type, ploidy, and allelic profile. This sample included isolates of all three molecular types of serotype A or C. neoformans var. grubii (molecular types VNI, VNII, and VNB) and one AD hybrid. Seventy-seven (94%) of the strains possessed the MATα mating type allele, and five were MATa. Seventy-five (91%) were haploid, and seven were diploid. A total of 24 different STs were identified. The ratios of each mating type and the proportion of haploids were comparable to those for the isolates that were obtained from 86 adult patients during the same period. Notably, the most prevalent pediatric ST was significantly associated with male patients. Overall, these pediatric isolates exhibited high genotypic diversity. They included a relatively large percentage of diploids and the rarely reported MATa mating type.

FIG. 1.

Pediatric isolates from the Republic of South Africa (RSA) were analyzed using Bayesian concordance analysis (3). The nuclear DNA sequence data were obtained from 10 unlinked loci: CAP10, GPD1, IGS1, ISC1, LAC1, MPD1, PLB1, SOD1, TEF1, and TOP1 (see Table S1 in the supplemental material). The 31 strains represented in this Bayesian primary concordance tree include one strain of each of the 24 pediatric sequence types and seven reference strains. The pediatric isolates are clustered in distinct clades that represent the three molecular types of serotype A (VNI, VNII, and VNB). The reference strains are the sequenced VNIV molecular type of serotype D (JEC21), which served as the outgroup, and reference strains for VNI (WM148) and VNII (WM626, MMRL2472, MMRL1246, MMRL1305, MMRL1310, and MMRL1320). The VNB genotypes were identified from separate Bayesian inference analyses (56) that included several VNB reference strains (bt63, bt85, bt88, and bt89).