Browsing by Subject "eläinlääketiede/molekyyliepidemiologia"

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  • Lindqvist, Nanna (Elintarviketurvallisuusvirasto Evira, 2008)
    Salmonellosis is one of the most significant zoonoses worldwide and also in Finland. Salmonella Typhimurium definitive phage type (DT) 1 and Salmonella Infantis are considered endemic in Finland. These serovars have frequently caused outbreaks among humans. Salmonella Agona was not frequently encountered in Finland until a small outbreak among cattle farms occurred in 1994-1995. Bacterial typing methods are used for outbreak investigations and for surveillance, where the data can be used for risk assessment calculations in addition to the future prevention of outbreaks.In particular the identification of factors that contribute to the persistence and spread of infection in endemic situations, estimations of the effect of animal reservoirs on human cases, and the identification of other risk factors for human infections are among the important reasons for typing. Salmonella Infantis became more common in cattle in the 1980s, after it established itself in the broiler chicken production in Finland in 1971. In the 1990s, S. Infantis became the predominant serovar among cattle in Finland. In 1995, a feedborne outbreak of S. Infantis in cattle occurred. By XbaI-PFGE methodology we were able to identify the feedstuff-related genotype, which contained a 60 kb plasmid. Farms infected with the feedstuff-related genotype were also identified. The stability of the feedstuff-related genotype was followed on selected farms. The plasmid was stable on the farms during the follow-up period. The feedstuff-related genotype did not persist in the cattle population. Moreover, there was a general decline in bovine salmonella infections from 1997 onwards. The genetic diversity of the S. Infantis isolates taken from Finnish cattle was also assessed. The S. Infantis infection in cattle is highly clonal as 99 per cent of the isolates had XbaI-PFGE profiles clonally related to each other. The major genotype was predominant both at the starting year of our analysis in 1985 and as the infection seemed to fade out in 2003. There is a trend towards less genetic diversity of the S. Infantis infection among domestic isolates from humans and poultry. The ribo/IS200-types and the most common XbaI-PFGE profiles determined among the analysed cattle isolates could also be detected among domestic isolates from poultry and humans. In our analysis of successive isolates from the same cattle herds, we frequently detected minor changes in banding patterns during long-lasting infections in individual herds. The sampling and testing of several isolates from a herd in outbreak investigations is therefore advisable. In 1997, another small outbreak of Salmonella Agona among cattle farms occurred. The PFGE genotype of that outbreak was possibly related to that of the first outbreak, in 1994-1995. In 1999, a large outbreak of S. Agona of domestic origin involving more than 50 human cases occurred. Despite epidemiological investigations carried out by the local authorities, the source of the outbreak remained unknown. Based on our typing data, this outbreak was unrelated to the cattle farm outbreaks, though it did occur in the same region of Finland. The outbreak profile for the 1999 outbreak could not be found in any of the older isolates. Salmonella Typhimurium DT1 has become the most common S. Typhimurium phage type among cattle farms in Finland, and has been detected annually since 1980. The infection is highly homogenous. The most common XbaI-PFGE profile can be seen in isolates from humans, domestic animals, hedgehogs and wild birds, so molecular subtyping by XbaI-PFGE alone is not discriminatory enough in analysing our endemic infection. A combination of XbaI-, BlnI-, and SpeI-PFGE can be applied in the analysis of outbreaks. Two clusters were formed by the combination of the XbaI-, BlnI-, and SpeI-PFGE profiles, IS200-profiles and possession of the serovar-specific virulence plasmid. The major cluster, typical of our endemic infection, had no virulence plasmid.