RESUMO
The dynamics of dissemination of the environmental human pathogen Vibrio parahaemolyticus are uncertain. The O3:K6 clone was restricted to Asia until its detection along the Peruvian coasts and in northern Chile in 1997 in phase with the arrival of El Niño waters. A subsequent emergence of O3:K6 strains was detected in austral Chile in 2004. The origin of these 1997 and 2004 population radiations has not yet been conclusively determined. Multiple loci VNTR analysis using seven polymorphic loci was carried out with a number of representative strains from Asia, Peru and Chile to determine their genetic characteristics and population structure. Asian and Chilean subpopulations were the most genetically distant groups with an intermediate subpopulation in Peru. Population structure inferred from a minimum-spanning tree and Bayesian analysis divided the populations into two genetically distinct groups, consistent with the epidemic dynamics of the O3:K6 clone in South America. One group comprised strains from the original Asiatic population and strains arriving in Peru and Chile in 1997. The second group included the remaining Peruvian Strains and Chilean strains obtained from Puerto Montt in 2004. The analysis of the arrival of the O3:K6 clone at the Pacific coasts of South America has provided novel insights linking the origin of the invasion in 1997 to Asian populations and describing the successful establishment of the O3:K6 populations, first in Peru and subsequently in the South of Chile owing to a possible radiation of Peruvian populations.
Assuntos
Variação Genética , Repetições Minissatélites , Vibrio parahaemolyticus/genética , Algoritmos , Ásia , Teorema de Bayes , Chile , Análise por Conglomerados , DNA Bacteriano/genética , Genética Populacional , Genótipo , Desequilíbrio de Ligação , Repetições de Microssatélites , Modelos Genéticos , Peru , Filogenia , Análise de Sequência de DNA , Vibrio parahaemolyticus/classificaçãoRESUMO
BACKGROUND: The seventh pandemic of Vibrio cholerae unexpectedly reached the coast of Peru in 1991, causing an explosive emergence of infections throughout the American continents. The origin and routes of dissemination are as yet unknown. A new Vibrio epidemic arose in 1997 in South America (northern Chile) when the pandemic clone of Vibrio parahaemolyticus was for the fist time detected outside of Asia. These 2 cases were concurrent with 2 episodes of El Niño. METHODS: We carried out a survey of records of V. parahaemolyticus infection and of strains existing in the Instituto Nacional de Salud of Peru between 1994 and 2005. Association between the El Niño event and the V. parahaemolyticus disease was analyzed through generalized additive models applied to time-series data with negative binomial response, selecting some oceanographic factors distinctive of the movement of the El Niño waters. RESULTS: Epidemiologic data and laboratory investigations of the strains showed that V. parahaemolyticus infections caused by the pandemic clone emerged in the coasts of Peru linked to the 1997 El Niño episode. The epidemic dissemination of this clone matched the expansion and dynamics of the poleward propagation and the receding of the El Niño waters. This pattern was similar to previously reported onset of cholera epidemic in 1991. CONCLUSIONS: These findings identify the El Niño episodes as a reliable vehicle for the introduction and propagation of Vibrio pathogens in South America. The movement of oceanic waters seems to be one of the driving forces of the spread of Vibrio diseases.