Annual Report on Zoonoses in Denmark 2023

Starting in 1994, this year marks the 30th anniversary of the report of Annual Report of Zoonoses in Denmark 2023 and the collaboration between institutions in Denmark on reporting important information on zoonoses to the public. The collaboration continues to grow and evolve - the latest being the KOZO partnership investigating non-food-borne zoonotic outbreaks.

Campylobacter continues to be the most common bacterial foodborne illness, with 5,186 cases in 2023 in Denmark. The number of Salmonella cases continued to increase for the forth year in a row, to 1,207 cases in 2023. For both illnesses, the number of cases seems to move towards the same levels as observed before the Covid-19-epidemic in 2020-2021. The numbers of Shiga-Toxin producing Escherichia coli (STEC) cases increased from 1,330 in 2022 to 1,431 cases in 2023. This increase can be explained by a change in diagnostics.

Food and waterborne outbreaks
In total, 64 foodborne outbreaks with 1,760 patients were reported in 2023. The number of foodborne outbreaks is on the same level as in 2022, where 63 outbreaks were registered.

Norovirus (NoV) was the leading cause of foodborne outbreaks in Denmark, causing 13 outbreaks and affecting a total of 462 persons. The most common way of acquiring NoV infection was through exposure to symptomatic or healthy carriers among kitchen staff. A total of 363 persons were affected by an unknown pathogen linked to pulled pork.

Salmonella spp. caused 18 outbreaks in Denmark in 2023, with six of them being part of international outbreaks. The largest international outbreak was with Salmonella Enteritidis sequence type 11, where more than 200 cases were reported in 13 countries. The investigations are further described in Chapter 7.

Eleven Campylobacter outbreaks were reported in 2023 as in 2022, and as in 2021 sequence type ST52 was the most frequent cause. Four outbreaks of listeriosis were also reported in Denmark in 2023, but the source was not identified.

KOZO - the coordination group for zoonotic threats in Denmark
The Danish national coordination group "KOZO" was established in 2022 to address zoonotic threats. KOZO facilitates cross-sector collaboration among authorities to prepare for, assess, and manage zoonotic outbreaks. Unlike the Central Outbreak Management Group which focuses on foodborne outbreaks, KOZO covers non-food borne zoonotic diseases such as animal influenza and tickborne encephalitis. The core group includes experts from human-, animal-, wildlifehealth, and the surrounding environment. Regular meetings ensure effective communication and coordination across sectors, making KOZO an essential One Health forum.

Applied AI in food safety related to Listeria monocytogenes
Whole genome sequencing (WGS) is a powerful tool for characterizing pathogens, especially in food safety control. It's widely used for surveillance of foodborne pathogens and outbreak investigations. Countries like Denmark, France, and the United Kingdom have adopted WGS, replacing older methods. WGS, combined with machine learning, can help predict outcomes like virulence potential and disinfectant resistance. Despite its potential, adoption in the food industry remains limited. Current practices rely on conventional microbiological methods, which lack resolution to differentiate between strains. WGS technology can address these limitations and enhance food safety.

WGS is gradually replacing routine microbiological methods in the food industry. It enables faster and more precise pathogen identification. WGS generates extensive sequencing data, providing valuable insights into microorganisms. Experts can predict bacterial features like antibiotic resistance and virulence using genetic elements. Listeria monocytogenes, a common pathogen in food, challenges quality assurance systems. The chapter describes a new machine learning tool that is called ListPred look to predict the virulence potential and disinfectant tolerance, aiding risk assessment and food safety.


The Annual Report on Zoonoses presents a summary of the trends and sources of zoonotic infections in humans and animals, as well as the occurrence of zoonotic agents in food and feeding stuffs in Denmark in 2023. Greenland and the Faroe Islands are not represented. The report is based on data collected according to the Zoonoses Directive 2003/99/EC, supplemented by data obtained from national surveillance and control programmes as well as data from relevant research projects. Corrections to the data may occur after publication resulting in minor changes in the presentation of historical data in the following year’s report. The report is also available at www.food.dtu.dk.


Vector borne zoonoses
In 2023, Denmark experienced a cool season for vectors, yet an average number of mosquito genera were present. The recently discovered West Nile fever mosquito, Culex modestus, that can feed on both birds and mammals, is raising concerns about its potential to transmit West Nile Virus (WNV) and Usutu virus. Despite testing negative for these viruses, Cx. is a vector of importance. Additionally modestus, a model predicted the correlation of tick activity patterns with Lyme neuroborreliosis (LNB) incidence. Tick-borne encephalitis (TBE) cases have also increased in Denmark, with TBEV detected in ticks from Tisvilde Hegn. The virus's spread may be linked to migratory birds and deer.

In 2023, no exotic mosquitoes were recorded in Denmark. However, a Hyalomma tick, also known as the hunting tick, was found on a horse near Ringsted. These ticks, typically found in North Africa, Asia, and parts of Europe, can potentially carry the Crimean-Congo Hemorrhagic Fever virus. Despite Denmark's climate not favoring their survival, adult Hyalomma ticks emerged due to warmer springs and summers. Additionally, the Dermacentor reticulatus, or meadow tick, is expanding northward in Germany and has been observed in Denmark. Dogs in Denmark are diagnosed with severe Babesia canis infections transmitted by D. reticulatus ticks.

Denmark has amended its Executive Order on Notification of Infectious Diseases
Denmark has expanded the legal scope for using laboratory data in national infectious disease surveillance. The amended Executive Order on Notification of Infectious Diseases allows comprehensive monitoring, aiding disease control efforts. Clinicians report diseases through an electronic system, and microorganisms are monitored in laboratories. The Health Act designates Statens Serum Institut (SSI) as the data owner for the Danish Microbiology Database (MiBa), enabling better surveillance, including antimicrobial resistance monitoring. The Personal Identification Number (CPR) facilitates linking laboratory and epidemiological data. Over 90 microorganisms require reporting, with 40 necessitating individual clinician reports.

Increase in human infection of Salmonella Enteritidis
Salmonella Enteritidis is the most prevalent serotype in Denmark, accounting for about a third of human cases. Poultry and egg products are common sources. The number of cases were quite stable from 2014-2019. In 2020-2021 the number of cases decreased due to the Covid-19 pandemic, where travel-restrictions were implemented. In 2023, there were 384 registered cases, with domestic infections accounting for 48%. Whole genome sequencing identified 10 outbreaks, including one linked to pre-fried chicken kebab imported from Poland.

Denmark's Salmonella control programme, in place since 1988 for broiler production and 1996 for table egg production, ensures Salmonella-free chicken meat and eggs. In 2023 two poultry flocks were positive with Salmonella Enteritidis (one free range layer flock and one organic broiler flock). The eggs from the positive flock were sent to heat treatment and the broilers were culled. EU regulations have led to reduced Salmonella contamination in the EU. Denmark's stricter programme achieved special guarantees for table eggs (2012) and chicken meat (2018). Imported chicken meat and table eggs must be tested negative for Salmonella.