Assessing the virulence of Cryptococcus neoformans causing meningitis in HIV infected and uninfected patients in Vietnam

Abstract

We previously observed a substantial burden of cryptococcal meningitis in Vietnam atypically arising in individuals who are uninfected with human immunodeficiency virus (HIV). This disease was associated with a single genotype of Cryptococcus neoformans (sequence type [ST]5), which was significantly less common in HIV-infected individuals. Aiming to compare the phenotypic characteristics of ST5 and non-ST5 C. neoformans, we selected 30 representative Vietnamese isolates and compared their in vitro pathogenic potential and in vivo virulence. ST5 and non-ST5 organisms exhibited comparable characteristics with respect to in vitro virulence markers including melanin production, replication at 37°C, and growth in cerebrospinal fluid. However, the ST5 isolates had significantly increased variability in cellular and capsular sizing compared with non-ST5 organisms (P < .001). Counterintuitively, mice infected with ST5 isolates had significantly longer survival with lower fungal burdens at day 7 than non-ST5 isolates. Notably, ST5 isolates induced significantly greater initial inflammatory responses than non-ST5 strains, measured by TNF-α concentrations (P < .001). Despite being generally less virulent in the mouse model, we hypothesize that the significant within strain variation seen in ST5 isolates in the tested phenotypes may represent an evolutionary advantage enabling adaptation to novel niches including apparently immunocompetent human hosts.

Associations between Cryptococcus Genotypes, Phenotypes, and Clinical Parameters of Human Disease: A Review

“…On the other hand, ST5 HIV-infected patients from the African COAT trial were associated with reduced mortality in both humans and mice [ 114 ]. In agreement, a study using Vietnam clinical isolates found that ST5 is not associated with greater mortality in a mouse inhalation model [ 131 ].…”

“…C. neoformans VNI ST5 strains can cause infections in both HIV-infected and HIV-negative patients and are found in China, Vietnam, South America, Thailand, Korea, Laos, and USA [ 106 , 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 ]. In China and Vietnam, cryptococcosis is predominately caused by ST5 strains [ 116 , 119 , 121 , 123 , 124 , 133 ].…”

The interplay of phenotype and genotype inCryptococcus neoformansdisease

“…Interestingly, the four isolates that exhibited both 'small' and 'large' phenotypes all resulted in patient death [70]. Additionally, Thanh et al showed clinical isolates able to infect immunocompetent patients displayed a significant increase in within-strain variation with regard to capsule and cell size [83]. These studies provide support to the idea that phenotypic heterogeneity within a population may contribute to host adaptation, which may subsequently impact patient survival.…”

“…Recent studies have begun to investigate the correlation between human disease progression and C. neoformans cell surface changes using clinical data and virulence factor analysis of clinical isolates [81][82][83][84][85][86][87][88]. Several studies observed a significant correlation between capsule size and strain virulence [81][82][83]. Clancy et al observed strains that produced smaller in vivo capsule size in mice were also more likely to have a higher lethal dose for 50% of mice (LD 50 ) [82].…”

“…The phenotypic analysis of clinical isolates has largely focused on easy to measure virulence phenotypes such as in vitro capsule enlargement and/or shedding, melanin synthesis, growth at 37 • C, urease activity, and phospholipase activity [77,85]. Several studies did not find a direct link between patient outcome and the virulence factors tested, especially with the use of in vitro assays [81][82][83][84][86][87][88]. Overall, these studies did highlight the high level of virulence factor heterogeneity between clinical isolates and the lack of association between a single virulence phenotype in determining disease outcome.…”