Swedish blood donor study reveals high prevalence of undiagnosed TBE infections

It is estimated that the number of TBE infections transmitted by ticks and not detected by healthcare services is much higher than was previously believed. A new study on Swedish blood donors at Uppsala University Hospital and Uppsala University has shown this. The results were published in Eurosurveillance, which is affiliated with the EU Centre for Disease Prevention and Control.

We were surprised to see that so many blood donors had traces of previous TBE virus infections. The number of cases reported was not enough to predict the extent of this infection.

Bo Albinsson is a doctoral student from Uppsala University and one of the original authors of this article.

Tick-borne Encephalitis (TBE), a serious disease, is becoming more common in many parts of Europe. Statistics from the Public Health Agency of Sweden show that 597 cases of tick-borne encephalitis were reported in Sweden in November 2023. This is the highest number of cases ever recorded in one year.

TBE is a disease that must be reported under the Communicable Diseases Act since 2004. All cases are required to be written by the local infection control doctor as well as the Public Health Agency of Sweden. Those who have mild symptoms, or none at all, are not detected and do not appear in statistics. The relationship between the reported cases and the percentage of infected people was unknown until now.

The traditional methods used to determine if someone is infected with the virus can be unreliable, as people who have been immunized against TBE may also test positive. It is also not known how many people were vaccinated as there is no Swedish national TBE vaccination registry.

Researchers from Sweden have examined blood tests of 2,700 anonymous donors in nine regions. The TBE-SMIA method (suspension multiplex immunoassay), which was used, was developed by the Zoonosis Science Center at Uppsala University and the Clinical Microbiology Department of Uppsala University Hospital. This method allows for the first time to distinguish between the antibody response following TBE virus infection and the response following TBE vaccination. The researchers were able to determine how many people had been infected. The researchers were able to estimate how much of each region’s population is vaccinated.

The Immunology eBook is a compilation of the most important interviews, articles, and news from the past year. Download the latest version. Results showed that blood donors who had a history of TBE virus infection ranged from 1% to 7% in different regions. The researchers calculated that based on the populations of the other areas, this would correspond to more than 160,000 individuals aged 15-65. This is significantly higher than the previous estimates.

Researchers also found that in different regions, the proportion of blood donors who were vaccinated for TBE ranged between 8.7% and 57%. This translates into 1.6 million Swedes (15-65 years old) across the regions studied.

“It’s noteworthy that TBE cases are increasing in spite of relatively high vaccination rates. It is important to continue research, such as mapping the distributions of the virus among tick populations. Our results are a valuable background for future vaccine strategies. It is worth considering the establishment of a national TBE vaccination register.

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