Emergence of myxomatosis as a cause of deaths in hares in the UK

Myxomatosis has been identified as the most likely cause of a recent spike in hare deaths, which could have devastating implications for this already threatened species.

September and October 2018 have seen an unusual peak in brown hare (Lepus europaeus) deaths, particularly in the east of England, as reported by landowners, farmers and members of the public. With several possible causes, the Wildlife Trusts and University of East Anglia put out a plea for the public to report and photograph any dead or sick hares in an attempt to find the potential cause(s) of the deaths. Examination of a greater number of cases following an ‘overwhelming’ response has now strongly indicated that myxomatosis is responsible.

 The brown hare, recent deaths in this species have been associated with myxomatosis

Myxomatosis is best known as a highly pathogenic disease afflicting the European rabbit (Oryctolagus cuniculus). In this species, myxomatosis is characterised by rather distressing symptoms, including a swollen head, ears and eyelids, the latter often leading to blindness. Recent outbreaks of myxomatosis amongst rabbits in the UK have led to horrific scenes where rabbits sit listlessly in the middle of busy roads, blindness preventing them from finding their way off the busy carriageway. And the loss of vision also makes them easy targets for predators. Most cases result in death within 14 days, while some individuals can die as quickly as 2 days after infection.

A young rabbit with symptoms of myxomatosis, including swollen eyelids (image source Wikipedia)

Myxomatosis is caused by the myxoma virus, a poxvirus that naturally infects the South American tapeti rabbit. The virus is transmitted between susceptible individuals through blood-feeding arthropods, such as fleas and mosquitoes. They first acquire the virus by biting an infected individual and transmit the virus onwards upon biting a susceptible individual. While the myxoma virus is benign in the tapeti, it is highly lethal in European rabbits and is associated with very high mortality rates. This has led to myxoma virus being used as a biological control agent for rabbit populations, first in Australia in 1950 and subsequently in Europe. In these releases, as many as 99% of rabbits in the affected areas were killed, highlighting the potential of this virus to cause catastrophic declines. However, the myxoma virus is not typically associated with infections of the hare, making the current cases rather unusual.

The hare isn’t doing too well in the UK, even without any potential declines associated with myxomatosis. Thought to have first been introduced here by the Romans, hares have undergone an 80% decline over the past century, linked to changes in agricultural practices and hunting (both legal and illegal). Current estimates suggest there are roughly 817,500 hares left in the UK, which sounds like a reasonable number. However, when you consider the declines seen in European rabbits in affected areas, should similar mortality occur in hares, the survival of this species in the UK could be under threat.

Interestingly, there was also a large die off in hares in Spain due to myxomatosis earlier this year. Future research efforts will be required to determine whether the outbreaks are the result of a single viral strain that has adapted to hares and spread between the countries or whether the UK and Spain outbreaks are the result of independent cross-species transmission events.

Time will tell whether the myxoma virus continues to spread in hares and what the mortality rate will be in the species in the UK environment, but the initial signs are concerning. The Wildlife Trusts and University of East Anglia are urging anybody who sees a sick or dead hare to take photographs and send them to Dr Diana Bell (d.bell@uea.ac.uk) at the University of East Anglia.

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