The animals most likely to carry the disease are wild hares, hence the name rabbit fever, and rodents, but it can also be transferred to humans via mosquito bites and occasionally tick bites.
It's also possible for the infection to be transmitted by inhaling dust or drinking water which is contaminated by urine or faeces from animals with the disease, according to Swedish healthcare service 1177. The disease cannot be carried from human to human.
It is too early to measure the exact extent of the disease this year, since statistics from the Public Health Agency won't be available until later.
But the Swedish Veterinary Institute has warned of several findings of dead animals which had been infected with the disease, and a “suspected outbreak”.
A total of 33 people in the Gävleborg region have been affected by rabbit fever since the start of July, according to regional healthcare authorities. In most cases, the patients had been infected in the Ljusdal area, and one case related to a patient who became sick after cleaning out a barn.
At least 12 people have been affected by rabbit fever in the Dalarna region alone, a doctor in communicable diseases told SVT Dalarna, and he said the figure was expected to increase.
“It looks like there will be a lot of cases this year, more than last year,” doctor Anders Lindblom said, adding: “Not everyone [who is affected by rabbit fever] seeks medical care and reports the illness.”
At least a further five people have confirmed cases of rabbit fever in Norrbotten too.
Symptoms of rabbit fever typically begin with swelling or tenderness in the lymph node and a skin lesion at the site of any bite or direct contact, followed occasionally by symptoms which can include a skin rash, nausea, and headaches.
Sweden had a large outbreak of rabbit fever in 2015, when 859 people across the country suffered from the illness, the majority of them in Norrbotten and Västerbotten. In 2018, 107 cases were reported across Sweden, with Dalarna the most severely affected region.
The best way to protect yourself from infection is to avoid mosquito bites as much as possible (either by using repellents, or wearing long, loose clothing when going outside between dusk and dawn), and being especially careful if you need to touch a dead animal such as a rodent or hare, using precautions such as a face mask and gloves.