In 2015, an outbreak of tularemia in hares occurred in the Netherlands. Between February and May, large numbers of dead hares were found in a relatively small area in the province of Friesland, near the village Akkrum. Specimen were sent to the Dutch Wildlife Health Centre (DWHC) in Utrecht to determine the cause of death.
Subsequently, material of these animals was submitted to the Central Veterinary Institute (CVI) for diagnostic testing of tularemia. The laboratory tests confirmed the disease in 11 of these cases. As only a small number of animals was tested, the total number of infected hares in the area was probably higher. This is an exceptional situation for the Netherlands, since previous findings of tularemia involved only incidental cases.
Tularemia is caused by the bacterium Francisella tularensis, which can infect many animal species, especially wild fauna. Humans can also become infected, which makes F. tularensis a zoonotic disease.
Previous cases of tularemia in the Netherlands
In 2011 screening for tularemia among hares was initiated by DWHC and CVI. In 2013, for the first time in decades, a Dutch hare tested positive for tularemia. Moreover, tularemia was also confirmed in a human patient, probably infected in the same region. In 2014, multiple cases of tularemia were detected in the Netherlands in hares (2) as well as in humans (3).
Zoonoses response team
The outbreak among hares at the beginning of 2015 led to the meeting of a zoonosis (zoonotic disease) response team. The response team includes experts from various disciplines and organizations (National Institute for Public Health and the Environment, Municipal Health Service, CVI, Animal Health Service Deventer, Faculty of Veterinary Medicine Utrecht University, Netherlands Food and Consumer Product Safety Authority) to provide sound advice to the government regarding the need for intervening measures. The response team concluded on a limited risk for public health of the outbreak.
Soon after the outbreak of tularemia in Friesland, an initiative for further research was launched. This also involved potential human exposure to the bacterium that causes tularemia. After the outbreak early 2015, the Municipal Health Service and the National Institute for Public Health and the Environment provided supportive information to GPs and specialists to help them detect possible infections in humans at an early stage.
Possible role of mice
Possible sources and transmission routes of F. tularensis were investigated. Rodents (especially voles) are considered an important reservoir for the bacterium. Since June 2014, increased populations of voles were observed in Friesland, including in the area where the dead hares were observed from February to May 2015. Because of a possible role of voles in the outbreak of tularemia among hares in the affected area, the prevalence of F. tularensis in these mice was determined. Additionally, the presence of this bacterium in various tularemia vectors (including ticks and horseflies) and in water samples was investigated. The results of the study will be reported in the course of 2016.
Other findings in 2015
Besides the surrounding area of Akkrum, in March 2015 tularemia was detected in a hare from southern Friesland and in a hare from the eastern part of Overijssel. In 2015, tularemia was also detected in a patient from the central region of the Netherlands; the source of infection cannot be determined with any certainty, but probably resulted from insect bites.
From the observations of tularemia in hares as well as in human patients in the recent years, it can be concluded that tularemia is endemic in the Netherlands.