Epidemic typhoid in Chile: analysis by molecular and conventional methods of Salmonella typhi strain diversity in epidemic (1977 and 1981) and nonepidemic (1990) years.

From 1977 to 1986, Chile experienced an important typhoid fever epidemic, despite statistics that indicated apparently improving levels of sanitation of drinking water and sewage disposal. The lack of antibiotic resistance among the Salmonella typhi strains isolated during this period, the mild clinical presentation of the disease, and the initially low level of efficacy of the S. typhi Ty21a vaccine in the population exposed to the epidemic suggested that this epidemic might have resulted from the dissemination of S. typhi strains with unique characteristics. To investigate this hypothesis, we used conventional methods (bacteriophage typing and biotyping) and molecular methods (restriction fragment length polymorphism analysis, ribotyping, IS200 typing, and PCR amplification of the fliC-d gene) to study a population of 149 S. typhi isolates during 1977, 1981, and 1990, the years that included periods with low (when the disease was endemic) and high (when the disease was epidemic) morbidities. Our results indicate that these S. typhi isolates in Chile represent a number of highly diverse variants of the clone of S. typhi with a worldwide distribution described by Selander et al. (R. K. Selander, P. Beltran, N.H. Smith, R. Helmuth, F.A. Rubin, D.J. Kopecko, K. Ferris, B.D. Tall, A. Cravioto, and J.M. Musser, Infect. Immun. 58:2262-2275, 1990). For example, we detected 26 PstI and 10 ClaI ribotypes among 47 and 16 S. typhi strains belonging to this clone, respectively. These results suggest that the Chilean epidemic was probably produced by multiple sources of infection because of deficient sanitary conditions. These findings illustrate the usefulness of molecular methods for characterizing the potential causes of the typhoid epidemics and the possible routes of transmission of S. typhi strains in typhoid epidemics.

[Genetic, molecular, and immunologic aspects of Vibrio cholerae infection]. / Aspectos genéticos, moleculares e inmunológicos de la infección por Vibrio cholerae.

The deterioration of the economical and social conditions of the majority of the population in the Americas the last 20 years has generated several epidemics of enteric infections in the region, dramatically manifested by the current massive and widespread cholera outbreak. The absence of cholera from the continent for more than 100 years, the worsening environmental conditions, the biological peculiarities of Vibrio cholerae El Tor such as decreased virulence, which generates increased number of carriers, and its improved ability to thrive in the environment are probably responsible for the rapid dissemination of the disease through out the continent. Genetic and molecular studies of the biology of V cholerae have permitted identification of a variety of new virulence factors besides the enterotoxin, and are also helping to unravel the exquisite mechanisms that regulate the expression of these virulence factors in response to different stimuli. Molecular studies of V cholerae chromosomal and plasmid DNA, and of chromosomal and plasmid gene products, with techniques such as DNA hybridization and multilocus enzyme analysis are improving the characterization of V cholerae strains, resulting in progress in understanding their epidemiology in different communities. The non-invasive character of V cholerae infections, epidemiological and immunological studies suggest that the disease and current vaccines fail in providing an effective and long lasting immunity, and that the control of the disease in endemic areas by the use of vaccines may therefore be unfeasible. Similar studies indicate that the provision of safe drinking water, adequate sewage disposal, sufficient nutrition, and education remain the most effective measures for controlling the disease.