In 2014 and the first quarter of 2015, a total of 72 hares were submitted to the Dutch Wildlife Health Centre (DWHC) for post-mortem investigation. Causes of death identified in these animals included trauma and a range of infectious diseases, three of which can affect humans (zoonoses); tularemia, toxoplasmosis and pseudotuberculosis.
Over the last few months, tularemia, caused by the bacteria Francisella tularensis, has received a lot of attention in the Dutch wildlife press after being identified as the cause of an increased number of deaths in hares, particularly in the province of Friesland.
information about this condition in humans and animals is available on the website of the OIE.
This year toxoplasmosis was identified as the cause of death in two hares submitted to the DWHC for post-mortem exam. Toxoplasmosis is caused by infection with the Toxoplasma gondii parasite. The life cycle of this parasite involves definitive (felids that have not previously been infected) and intermediate (all warm-blooded animals, including humans) hosts. Only in the definitive host are eggs (oocysts) produced and these are excreted by the million in the feces and can survive for up to 1.5 years in the environment. These oocysts are the source of infection of intermediate hosts in which motile forms of the parasite leave the oocyst and migrate through the body forming cysts in muscle and nervous tissue (tissue cysts). Cats or other predatory animals can become infected upon consumption of tissue cysts in their prey.
The DWHC has also published cases of toxoplasmosis in other wildlife species in the Netherlands (squirrels, fox).
Further information about this condition in humans and animals is available on the website of the OIE.
Pseudotuberculosis is caused by the bacteria Yersinia pseudotuberculosis. In 2014 it was identified in seven hares submitted to the DWHC for post-mortem investigation but has not yet been seen in 2015. A thesis entitled ‘Hares in the Netherlands’ describes Yersinia as occurring extensively in wildlife species, particularly in voles and musk rats, though only tending to cause disease when the host is in poor condition. Between 1966 and 1974, pseudotuberculosis was identified as the cause of death in 62% and 29% of investigated hares dying during autumn and winter months in the Noordoostpolder (n=45) and other areas of the Netherlands (n=481), respectively.
Toxoplasma and Yersinia are ubiquitous in the wild; whether or not this is the case for F. tularensis is not yet known. As to why the incidence of certain diseases varies from one year to the next is not well understood although, in the case of Yersinia it is thought that wet and cold conditions may play a role.
For more information about toxoplasmosis in people visit the website of the OIE
The DWHC will continue to monitor the health status, and in particular, the occurrence of toxoplasma in the Dutch hare population and you can help by reporting finding a dead animal via the submission form on our website. For microscopic examination of these animals it is essential that the cadavers are in a fresh state i.e. not dead for more than one day; cadavers should not be frozen. It is therefore preferable to report dead hares as soon as possible and to keep the cadaver in a cool (not frozen) place until it can be collected. After submitting your form you will be contacted by the DWHC who will help decide whether the animal is suitable for submission and advise you on how to package the cadaver and arrange collection of the packaged hare from your home or place of work. The consumption of dead hares by pets or people should be avoided and gloves should be worn if handling cadavers.
1 Broekhuizen, S. 1982. Hazen in Nederland. Proefschrift Landbouwhogeschool Wageningen.