Molecular characterization of endemic salmonella infections ... - Evira

1. INTRODUCTION
Zoonoses are infections that can spread from vertebrate animals to man. The most important
zoonoses in the EU by far are campylobacteriosis and salmonellosis. Salmonellosis is also one of
the most significant zoonoses in Finland. It is estimated that about 60 to 80 per cent of the reported
cases in humans are of foreign origin. The most common Salmonella enterica subsp. enterica
serovars of domestic origin being S. Infantis and S. Typhimurium definitive phage type (DT) 1. Both
are considered endemic in Finland.
Salmonella Infantis is the predominant serovar in production animals in Finland. Before the
introduction of S. Infantis into the broiler chicken production in Finland in 1971, only sporadic
isolations of S. Infantis among animals, animal-feed and humans were made. S. Infantis became
more common among cattle in the country in the 1980s, and in the 1990s it became the
predominant Salmonella serovar. In 1995, a feedstuff-related outbreak occurred among cattle
farms.
Salmonella Typhimurium DT1 spread to broiler farms in Finland in 1983, and sporadic isolations in
broilers have been made since. DT1 has become the most common S. Typhimurium phage type
among cattle farms, and has been isolated every year since 1980. Annually, DT1 also causes
outbreaks among humans.
Salmonella Agona was not frequently encountered in Finland until an increase in the number of
isolations found in animals and feed in 1994. A small outbreak of S. Agona involving eight cattle
farms was seen in 1994-1995, and S. Agona was the third most common Salmonella serovar in
cattle in Finland in 1995, after S. Infantis and S. Typhimurium. Usually more than 50 per cent of the
serovar Agona isolates from humans are of foreign origin, but in 1999 a large outbreak in humans
of domestic origin occurred.
In addition to the conventional epidemiological surveys, bacterial typing methods provide the basis
for investigations of outbreaks of human and animal salmonellosis today. Typing is also used for
surveillance to obtain baseline information and to estimate the effect of animal reservoirs in human
cases. Moreover, it is used to identify factors that contribute to the persistence and spread of
infection in endemic situations, and to monitor critical points for cross-contamination in food
production.
The present study was undertaken to obtain molecular information on the endemic Salmonella
serovars Infantis and Typhimurium DT1, in addition to the potentially emerging serovar Agona. We
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