RESUMO
Histoplasma capsulatum has a worldwide distribution but is particularly concentrated in the midwestern United States and throughout Central and South America. Genetic differences between isolates resident in separate parts of the world have been reported, but the relationship between the isolates and the level of migration between different endemic foci has not been clear. In this study we used multilocus genotypes based on amplified polymorphic loci and one microsatellite to quantify the level of genetic differentiation occurring between North and South American populations of H. capsulatum. Significant genetic differentiation occurred between isolates obtained from Indiana and Alabama, and a marked division was seen between the Indiana population and the Class 1 isolates from St. Louis. Strong genetic differentiation occurred between the two North American populations and the Colombian population. This study supports the separation of North and South American H. capsulatum into different species, which has been proposed under the phylogenetic species concept.
Assuntos
Histoplasma/classificação , Polimorfismo de Nucleotídeo Único , Marcadores Genéticos , Genótipo , Histoplasma/genética , Histoplasmose/microbiologia , Humanos , Repetições de Microssatélites , América do Norte , América do Sul , Especificidade da EspécieRESUMO
Long-distance population dispersal leaves its characteristic signature in genomes, namely, reduced diversity and increased linkage between genetic markers. This signature enables historical patterns of range expansion to be traced. Herein, we use microsatellite loci from the human pathogen Coccidioides immitis to show that genetic diversity in this fungus is geographically partitioned throughout North America. In contrast, analyses of South American C. immitis show that this population is genetically depauperate and was founded from a single North American population centered in Texas. Variances of allele distributions show that South American C. immitis have undergone rapid population growth, consistent with an epidemic increase in postcolonization population size. Herein, we estimate the introduction into South America to have occurred within the last 9,000-140,000 years. This range increase parallels that of Homo sapiens. Because of known associations between Amerindians and this fungus, we suggest that the colonization of South America by C. immitis represents a relatively recent and rapid codispersal of a host and its pathogen.
Assuntos
Coccidioides/isolamento & purificação , Migrantes , Sequência de Bases , Portador Sadio , Coccidioidomicose/epidemiologia , Primers do DNA , Geografia , Humanos , Repetições de Microssatélites/genética , América do Norte/epidemiologia , América do Sul/epidemiologiaRESUMO
In this Round Table, the application of several methods of molecular typing were discussed in reference to four important pathogenic fungi: Coccidioides immitis, Histoplasma capsulatum, Candida albicans and Paracoccidioides brasiliensis. Among the different methods the following were discussed: restriction fragment length polymorphisms (RFLP), single nucleotide polymorphisms, random amplified polymorphic DNA (RAPD), polymerase chain reaction (PCR)-RFLP and microsatellites. By means of these methods, several important biological questions related to speciation, mode of reproduction and population genetics could be approached. The basic information obtained from this approach has implications in the understanding of these pathogenic fungi in relation to their behavior and the development of pathogenic features, such as resistance to antimicrobials and virulence factors used for colonization of mammalian hosts. The knowledge obtained from these studies could also be used for the development of innovative diagnostic methods, as well as for novel therapeutic approaches and production of vaccines.
Assuntos
Fungos Mitospóricos/classificação , Micoses/microbiologia , Técnicas Genéticas , Humanos , Fungos Mitospóricos/genética , Fungos Mitospóricos/patogenicidade , Técnicas de Tipagem MicológicaRESUMO
The phylogeny of 46 geographically diverse Histoplasma capsulatum isolates representing the three varieties capsulatum, duboisii, and farciminosum was evaluated using partial DNA sequences of four protein coding genes. Parsimony and distance analysis of the separate genes were generally congruent and analysis of the combined data identified six clades: (i) class 1 North American H. capsulatum var. capsulatum, (ii) class 2 North American H. capsulatum var. capsulatum, (iii) Central American H. capsulatum var. capsulatum, (iv) South American H. capsulatum var. capsulatum group A, (v) South American H. capsulatum var. capsulatum group B, and (vi) H. capsulatum var. duboisii. Although the clades were generally well supported, the relationships among them were not resolved and the nearest outgroups (Blastomyces and Paracoccidioides) were too distant to unequivocally root the H. capsulatum tree. H. capsulatum var. farciminosum was found within the South American H. capsulatum var. capsulatum group A clade. With the exception of the South American H. capsulatum var. capsulatum group A clade, genetic distances within clades were an order of magnitude lower than those between clades, and each clade was supported by a number of shared derived nucleotide substitutions, leading to the conclusion that each clade was genetically isolated from the others. Under a phylogenetic species concept based on possession of multiple shared derived characters, as well as concordance of four gene genealogies, H. capsulatum could be considered to harbor six species instead of three varieties.
Assuntos
Genes Fúngicos , Histoplasma/classificação , Histoplasma/genética , Histoplasmose/microbiologia , Filogenia , Infecções Oportunistas Relacionadas com a AIDS/microbiologia , Animais , Sequência de Bases , DNA Fúngico/genética , DNA Fúngico/isolamento & purificação , Proteínas Fúngicas/genética , Genótipo , Geografia , Histoplasma/isolamento & purificação , Histoplasmose/etiologia , Humanos , Dados de Sequência Molecular , América do Norte , Panamá , Reação em Cadeia da Polimerase , Alinhamento de Sequência , Homologia de Sequência do Ácido Nucleico , Microbiologia do Solo , América do SulRESUMO
A set of eleven biallelic and three multiallelic molecular markers have been developed to analyze populations of Histoplasma capsulatum. All markers are amplified by polymerase chain reaction (PCR) and can be readily scored using minimal amounts of template DNA. The 11 biallelic loci have polymorphic restriction endonuclease sites or small insertions or deletions which may be assessed by agarose gel electrophoresis. These markers are inherited in an unambiguous manner and are ideal for assessing structure and gene flow within US populations of H. capsulatum, but are monomorphic in non-US populations. Both length and sequence variation are present in the multiallelic loci, which can be scored by direct sequencing, polyacrylamide gel electrophoresis, or single-strand conformation polymorphism (SSCP): As they are hypervariable, the multiallelic loci can be used to type isolates and to assess the level of genetic variation within populations. Preliminary results indicate that the three multiallelic markers presented are sufficient to distinguish isolates at the individual level and are polymorphic in both US and non-US populations. This collection of molecular markers will be a useful tool in population and epidemiology studies of H. capsulatum.
Assuntos
Eletroforese em Gel de Ágar , Marcadores Genéticos , Histoplasma/classificação , Histoplasma/genética , Alelos , Sequência de Bases , Mapeamento Cromossômico , Colômbia , DNA Fúngico , Variação Genética , Genótipo , Histoplasma/isolamento & purificação , Humanos , Dados de Sequência Molecular , Sequências Repetitivas de Ácido NucleicoRESUMO
Simple cladogenetic theory suggests that gene genealogies can be used to detect mixis in a population and delineate reproductively isolated groups within sexual taxa. We have taken this approach in a study of Coccidioides immitis, an ascomycete fungus responsible for a recent epidemic of coccidioidomycosis (Valley fever) in California. To test whether this fungus represents a single sexual species throughout its entire geographic range, we have compared genealogies from fragments of five nuclear genes. The five genealogies show multiple incompatibilities indicative of sex, but also share a branch that partitions the isolates into two reproductively isolated taxa, one centered in California and the other outside California. We conclude that coccidioidomycosis can be caused by two distinct noninterbreeding taxa. This result should aid the future study of the disease and illustrates the utility of the genealogical approach in population genetics.
Assuntos
Coccidioides/enzimologia , Coccidioides/genética , Genes Fúngicos , Polimorfismo de Fragmento de Restrição , Sequência de Aminoácidos , Animais , Sequência de Bases , California , Quitina Sintase/genética , Quitinases/genética , Coccidioides/isolamento & purificação , Sequência Consenso , Sequência Conservada , Geografia , Humanos , México , Serina Endopeptidases/genética , TexasRESUMO
In a large-scale study in the Miragoane Valley of Haiti, designed to test the effects of aerial ultralow volume (ULV) malathion on epidemic Plasmodium falciparum malaria, spray operations resulted in an immediate and sharp decline in numbers of the vector, Anopheles albimanus. The adult population of this mosquito remained at less than 1% of previous levels until several weeks after a 50-day spray period (27 October-16 December 1972) during which six cycles were completed. The study area offered ideal conditions of wind, temperature, humidity, and mountain barriers. Mosquitoes in the area were highly susceptible to malathion. Results indicated that aerial ULV treatment with malathion can reduce A. albimanus populations rapidly and effectively when applications are made over an area as large as 20,000 acres. Preliminary results showed that effective control was not achieved in areas one-quarter that size; these areas were not sufficiently large, and infiltration of mosquitoes from adjacent untreated areas was possible.