RESUMO
Schistosoma mansoni is the most widespread of the human-infecting schistosomes, present in 54 countries, predominantly in Africa, but also in Madagascar, the Arabian Peninsula, and the Neotropics. Adult-stage parasites that infect humans are also occasionally recovered from baboons, rodents, and other mammals. Larval stages of the parasite are dependent upon certain species of freshwater snails in the genus Biomphalaria, which largely determine the parasite's geographical range. How S. mansoni genetic diversity is distributed geographically and among isolates using different hosts has never been examined with DNA sequence data. Here we describe the global phylogeography of S. mansoni using more than 2500 bp of mitochondrial DNA (mtDNA) from 143 parasites collected in 53 geographically widespread localities. Considerable within-species mtDNA diversity was found, with 85 unique haplotypes grouping into five distinct lineages. Geographical separation, and not host use, appears to be the most important factor in the diversification of the parasite. East African specimens showed a remarkable amount of variation, comprising three clades and basal members of a fourth, strongly suggesting an East African origin for the parasite 0.30-0.43 million years ago, a time frame that follows the arrival of its snail host. Less but still substantial variation was found in the rest of Africa. A recent colonization of the New World is supported by finding only seven closely related New World haplotypes which have West African affinities. All Brazilian isolates have nearly identical mtDNA haplotypes, suggesting a founder effect from the establishment and spread of the parasite in this large country.
Assuntos
Variação Genética , Filogenia , Schistosoma mansoni/genética , África , Animais , Arábia , Região do Caribe , DNA de Helmintos/genética , DNA Mitocondrial/genética , Feminino , Geografia , Haplótipos , Humanos , Madagáscar , Masculino , Análise de Sequência de DNA , América do SulRESUMO
Species of Ribeiroia (Trematoda: Psilostomidae) are known to cause severe limb malformations and elevated mortality in amphibians. However, little is known regarding the number of species in this genus or its relation to other taxa. Species of Ribeiroia have historically been differentiated by slight differences among their larval stages. To better understand the systematics and biogeography of this genus and their potential relevance to the distribution of malformed amphibians, specimens identified as Ribeiroia were collected across much of the known range, including samples from 5 states in the United States (8 sites) and 2 islands in the Caribbean (Puerto Rico and Guadeloupe). A cercaria from East Africa identified as Cercaria lileta (Fain, 1953), with attributes suggestive of Ribeiroia (possibly R. congolensis), was also examined. The intertranscribed spacer region 2 (ITS-2) of the ribosomal gene complex was sequenced and found to consist of 429 nucleotides (nt) for R. ondatrae (United States) and 427 nt for R. marini (Caribbean), with only 6 base differences noted between the 2 species. The ITS-2 region of C. lileta (429 nt) aligned closely with those of the 2 other Ribeiroia species in a phylogenetic analysis that included related trematode genera. This evidence suggests that a third Ribeiroia species exists in tropical Africa. Variation in ITS-2 within R. ondatrae was nonexistent among the 8 populations from North America. Our study further suggests that Ribeiroia spp. originally parasitized Biomphalaria sp., and that a host switch to a closely related snail, Helisoma sp., may have occurred in the lineage represented by R. ondatrae. However, relationships within the Echinostomatidae are not understood well enough to make any robust conclusions at this time.
Assuntos
Anfíbios , Deformidades Congênitas dos Membros/veterinária , Filogenia , Trematódeos/classificação , Infecções por Trematódeos/veterinária , Anfíbios/anormalidades , Anfíbios/parasitologia , Animais , DNA de Helmintos/química , DNA Espaçador Ribossômico/química , Quênia , Funções Verossimilhança , Deformidades Congênitas dos Membros/epidemiologia , Deformidades Congênitas dos Membros/parasitologia , Reação em Cadeia da Polimerase/veterinária , Alinhamento de Sequência/veterinária , Caramujos/parasitologia , Trematódeos/genética , Infecções por Trematódeos/complicações , Infecções por Trematódeos/epidemiologia , Infecções por Trematódeos/parasitologia , Estados Unidos/epidemiologia , Índias OcidentaisRESUMO
Se determinó que M. cornuarietis, molusco que ha sido utilizado como agente de control biológico de los hospederos de esquistosomiasis, pueden constituir plaga de cultivos de arroz. Cada molusco es capaz de consumir 0,3 g de la planta en 24 h, lo que equivale a la destrucción de o,015 m* del campo de arroz. Por otra parte se observó la preferencia de B, glabrata de ingerir las heces fecales de M. cornuarietis, hecho que favorece el crecimiento del vector y su tasa de reproducción a la vez que disminuye su mortalidad44444444444444444
Assuntos
Moluscos/patogenicidade , Controle Biológico de VetoresRESUMO
Se determinó que M. cornuarietis, molusco que ha sido utilizado como agente de control biológico de los hospederos de esquistosomiasis, pueden constituir plaga de cultivos de arroz. Cada molusco es capaz de consumir 0,3 g de la planta en 24 h, lo que equivale a la destrucción de o,015 m* del campo de arroz. Por otra parte se observó la preferencia de B, glabrata de ingerir las heces fecales de M. cornuarietis, hecho que favorece el crecimiento del vector y su tasa de reproducción a la vez que disminuye su mortalidad44444444444444444