Warmer climates can lead to new diseases that infect humans through mosquitoes

Wednesday 29 Jun 22


Birgitte Borck Høg
Senior Academic Officer
National Food Institute
+45 35 88 70 66


Luise Müller
Statens Serum Institut
+45 32 68 85 90


René Bødker
+45 25 47 69 74
New research has mapped the risk of five mosquito-borne diseases that could potentially lead to epidemics. It is one of the topics you can read about in the Annual Report on Zoonosis, which gathers knowledge about infectious diseases that are transmitted from animals to humans.

The risk of Danes becoming ill after a mosquito bite increases. In a new study, researchers from the University of Copenhagen and the Statens Serum Institut have identified nine zoonotic infections that could potentially lead to epidemics in both the current and future warmer climates in Denmark. Five of these are so-called vector-borne, i.e. they can infect humans via mosquito bites. A future climate with higher temperatures and more cloudbursts creates good living conditions for insects, mosquitoes and ticks.

New diseases from the South and North
Some infections come with migratory birds from the South. Some of these diseases wouldn’t previously have occurred in the colder Nordic climate, but after the hot summer of 2018, for example, West Nile fever has been found in both the Netherlands and northern Germany. The disease is most commonly seen in birds, but both humans and horses have been infected through mosquito bites.
Other infections come from the North. Tularemia or hare plague is one of those now moving south in Sweden. Hare plague has been associated with hunters who have had direct contact with hares, but the bacterium is now predominantly transmitted via mosquitoes and can therefore cause more cases of disease. Hare plague can cause disease in humans, most often with mild symptoms, but requires treatment with antibiotics.

‟We are very aware of the new mosquito-borne diseases in animals, because they can have an impact on which new zoonotic epidemics we humans risk being affected by in the future," says senior researcher René Bødker from the University of Copenhagen.

Two large foodborne disease outbreaks 

The zoonosis report also provides a status on foodborne zoonoses. The number of registered cases of salmonella and campylobacter remains low due to the covid-19 pandemic. However, the number of foodborne disease outbreaks was again on the rise. In 2021, 63 food-borne outbreaks were reported. In comparison, 35 outbreaks were reported in 2020 and 51 in 2019.

“2021 was dominated by two large food-borne outbreaks in particular – one outbreak with salmonella in herbal medicine that made 54 people sick, and one with Enteroinvasive E. coli, where 48 people became ill after eating spring onions. Both outbreaks were due to imported, raw products. This emphasizes the importance of having surveillance and emergency preparedness that can detect and stop outbreaks,” epidemiologist Luise Müller from SSI says.

Monitoring and control of animals, food and the environment

In Denmark, the focus for many years has been on reducing salmonella and campylobacter through national monitoring programmes and action plans.
This year's monitoring figures show that the targets for campylobacter in chicken have been partially achieved and that salmonella in production animals, food, feed, and the environment is in line with previous years.

‟From 2022 there will be focus on further reducing campylobacter in chicken in a new action plan made in collaboration between the Danish Veterinary and Food Administration, which DTU advices, and the branches, Senior Special Advicer Birgitte Borck Høg from the DTU National Food Institute says.

Read more

The annual report presents a large amount of the data that the authorities and industry in Denmark collect on the occurrence of zoonoses in feed, animals, food, and humans. The report contains zoonosis data from a period of more than ten years. In this way, they provide an opportunity to follow trends over time. The report is published by the DTU Food Institute in collaboration with the Statens Serum Institut and the Danish Veterinary and Food Administration.
See the full report on the DTU Food Institute's website: Annual Report on Zoonoses in Denmark 2021 (pdf). It is also possible to receive the report by writing to food@food.dtu.dk.


2021 report in numbers

  • 63 foodborne disease outbreaks are registered in 2021 against 35 outbreaks in 2020
  • Norovirus is the most common cause of foodborne outbreaks. The number has increased from 6 registered outbreaks in 2020 to 14 outbreaks in 2021
  • Four bacteria have most often been responsible for registered cases of disease: Campylobacter (3,740), salmonella (692), STEC (927) and Yersinia enterocolitica (454).

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