In 2014, there were more patients in the Netherlands with diseases transmitted by wild rodents than in previous years. This is especially so for leptospirosis, with cases rising from an average of 30 in previous years to 97 cases in 2014, and hantavirus infections increasing from an average of 13 cases to 36 cases in the same period. The reasons for this increase are not clear, but possibly the mild winter and hot summer have played a role. However, as the number of patients is limited, there is no cause for concern. Nevertheless, it is essential to remain alert to diseases transmitted by wild rodents and a study is being carried out on the factors that contribute to the increased incidence, as indicated in the annual Zoonotic Diseases Report prepared by RIVM and the Netherlands Food and Consumer Products Safety (NVWA).
The bacteria that cause leptospirosis are carried by rodents (such as rats) and cows and dogs. When contaminated rats urinate in surface water, the bacteria end up in places where people can come into contact with the bacteria, for instance, during recreational activities in or near surface water. The symptoms can vary considerably in humans from flu-like symptoms to serious kidney and liver failure, such as in Weil’s disease. In 2014, the incidence of leptospirosis increased in humans and also more dogs were infected than in previous years. A possible cause could be the short, mild winter of 2013-2014, during which more rats survived the winter period.
As well as flu-like symptoms, hantaviruses can cause serious kidney problems. In the Netherlands, the Puumala virus occurs and this type of hantavirus is transmitted by bank voles. Infection with the Puumala virus can lead to fever and kidney failure in humans. More bank voles were observed in 2014, possibly because of the short mild winter and thus the greater availability of food. RIVM is studying the relationships between the amount of food available, the size of the mouse population, and the number of people infected with the virus.
Zoonotic Diseases Report
The annual Zoonotic Diseases Report presents an overview of infectious diseases transmitted from animals, which are known as zoonoses. The report concerns notifiable zoonoses and their long-term trends, in terms of the number of human cases and number of animals infected.
“Our winged friends”
This year’s Zoonotic Diseases Report gave attention to zoonoses that can be transmitted by birds. This topic was also considered at the Ninth National Symposium on Zoonoses held at RIVM on 3 November 2015.