A new deadly “mutant” variety of blood-sucking ticks has invaded several regions in Russia, resulting in hospitals running out of vaccines.

According to reports, scientists have discovered a deadly “mutant” form that combines the “worst qualities” of two common types of ticks found in the country.

The scale of the swarm has left several hospitals without vaccines or medicines used to cure diseases caused by tick bites. Encephalitis is one such disease that can lead to permanent brain damage. Lyme disease affects the joints, heart, and nervous system.

The Sverdlovsk region is one of the worst-hit areas with around 17,242 people bitten by ticks, which includes 4,334 children. Approximately 36% of them are suspected to have Lyme disease.

Krasnoyarsk is the other worst infested region with 214 ticks per square kilometer, which is 428 times more ticks than usual. Approximately 8,215 tick bites have been reported in the region which included 2,125 cases involving children. The region has reportedly run out of immunoglobulin and encephalitis vaccine to cure the infected people.

Dr. Nina Tikhunova, of the Institute of Chemical Biology and Fundamental Medicine, Novosibirsk, confirmed the news saying a “large number inter-species hybrids which produce 'fertile offspring' have invaded Novosibirsk and Tomsk regions.”

The mutant tick “is capable of carrying infectious agents associated with both parent species,” she said, adding that the tick bites are “very unpleasant for people.”

The region has seen a huge jump in people seeking medical help after being bitten by “abnormally active” ticks. Over 20 people, suspected of encephalitis, have been hospitalized. Dr. Tikhunova has asked everyone bitten by a tick to seek medical help to check if the creature is infected.

According to reports, many other cities too have no stocks of immunoglobulin to treat people. People have been asked to stay home as the new supplies are only expected in July.

Ticks This photo taken at the Dutch National Institute for Public Health and the Environment (RIVM) in Bilthoven shows tick specimens used for a study on the new TBE tick virus, on August 18, 2016. Photo: Getty Images/ AFP/ Robin Van Lonkhuijsen