Salmonella prevalence among Sweden’s dairy cattle herds is low but varies across the country, according to a study.

In late 2019, the National Veterinary Institute (SVA) and Swedish Board of Agriculture (Jordbruksverket), conducted an anonymous national milk tank survey for antibodies against Salmonella.

It is the second time such a survey on milk samples from all the country’s dairy herds have been examined. The first occasion was 2013. The work contributes to regular Salmonella surveillance and means resources can be directed wher they will have the most impact.

Antibodies against Salmonella were detected in only 4 percent of samples but prevalence varied between zero and 24 percent depending on the region.

Infection spread with Salmonella to cattle herds can happen from the surrounding environment, wildlife or birds, feed or water, humans or other herds.

Explanation of high levels
The highest prevalence was found in Öland and Gotland. Öland has a recognized higher occurrence of Salmonella Dublin. However, results in Gotland differ from what was seen in the 2013 survey.

Findings for Öland are at about the same level, 24 percent, as a local survey in March 2009 but slightly higher than the national screening in 2013. Gotland saw a change from 5.5 percent positive tank milk samples in April 2013 to 22 percent in October 2019.

The difference in Öland could be explained by seasonal variation that exists with regard to antibodies against Salmonella in milk but the figures in Gotland are above what is expected in any seasonal variation.

The Swedish Food Agency (Livsmedelsverket) recommends milk is pasteurized as an effective way to kill any harmful bacteria.

Authorities and industry organizations are planning to follow-up the results in Gotland to gain a better understanding of the situation so actions can be taken. The first step in this process is a follow-up milk tank survey which is planned for this spring.

Another study, published in the journal Preventive Veterinary Medicine in March 2016, found only 3 percent of Swedish dairy herds were positive when screened for Salmonella.

Presence of positive herds within five kilometers was significantly associated to testing positive. Results highlighted differences between Salmonella Dublin and other serotypes concerning prevalence and degree of geographical clustering.