Sporadic outbreaks of sickly hares with unusual behaviour have been reported over recent years. The symptoms included lack of fear, jumping into the air, circling, convulsing and staggering before death.
The odd behaviour is quite distinct from the normal sexually inspired 'madness' usually seen in March. According to the latest issue of Veterinary Record, vets at the Ministry of Agriculture have found that the dead and demented hares have been killed by a virus that attacks the liver and poisons the brain. They have also shown that the virus is not the same as the one that causes a similar infection in rabbits.
The mystery of European Brown Hare Syndrome - as the disease is called - first came to scientists' attention in the late 1980s. Because its appearance coincided with the growing on the Continent of a new variety of oil seed rape, scientists thought the problem may be due to a change in the hare's diet.
Other researchers suggested the hares may have been poisoned with agricultural chemicals, although there was little evidence.
In 1984, a few years prior to the appearance of the syndrome in European hares, Chinese scientists reported an outbreak of a disease in rabbits that had killed an estimated 500,000, prompting speculation that the infection may have spread from rabbits.
But scientists at the Government's Veterinary Investigation Centre and Central Veterinary Laboratory found that a virus present in hares long before the 1984 outbreak in Chinese rabbits is responsible for the disease in British hares. They say that it is not possible to identify when the virus came to Britain, but it may have been before the 1965 law banning the import of live hares from the Continent.