A record number of rabies-infected bats have been discovered living near millions of Americans, and wildlife officials warn they have started infecting other animals.

Rabies is a viral disease that attacks the brain and nervous system. It is almost always fatal once symptoms begin in both animals and people, and there is no effective treatment after that point. 

Officials in California revealed this month that a raccoon in Los Angeles County tested positive for the deadly viral disease, marking the first rabid raccoon sighting in the area in over 50 years.

The LA County Department of Public Health said on Tuesday that it found 76 rabid bats within the county, breaking the previous record of 69 set last year.

The county warned in a statement: 'Rabid bats have been found in every part of Los Angeles County, from suburban areas such as the San Fernando Valley to urban areas like downtown Los Angeles, in office buildings, parks, schools, businesses and residential backyards.'

Public Health officials added that the raccoon was found in the wealthy community of Westlake Village.

It tested positive for a strain of rabies carried by bats commonly found in Los Angeles, suggesting that the animal was bitten nearby and carried it into the neighborhood.

A dog that encountered the raccoon and four people at a nearby worksite were immediately treated for possible rabies exposure.

The surge in rabies cases among local bats began in January, with one bat 'found alive on the ground in a backyard near a dog' in the northern LA County city of La Cañada Flintridge.

Since then, 75 other bats were found near local homes, in swimming pools, in driveways, sitting on patio furniture or hiding inside residences every month this year.

The majority would be discovered on the ground or dead, with many being discovered by pet cats or dogs – leading to an emergency call to have the pets treated for rabies exposure.

The illness can be prevented if a person gets special shots as soon as possible once they have been bitten, scratched or exposed to the saliva of a rabid animal. Saliva entering an open wound, the eyes, nose or mouth can lead to a rabies infection.

The Department of Public Health said in a statement: 'Bats have tiny teeth, and a bite or scratch from a tooth may not leave a lasting mark but may still transmit rabies. Exposure risk to humans and pets can be ruled out if a bat tests negative for rabies.'

The first symptoms in people are usually fever, weakness and headache, and these can appear days or even weeks after exposure.

Later symptoms include tingling at the bite site, anxiety, agitation, unusual behavior, hallucinations and difficulty swallowing. Once it reaches this stage, rabies treatments will not cure the infection.

In animals, early signs are often nonspecific, including vomiting or breathing problems, before more obvious neurologic signs appear.

LA County Board Chair and First District Supervisor Hilda Solis said in a statement: 'With a recently confirmed rabies case, pet owners are strongly encouraged to keep their pets away from wildlife and ensure their rabies vaccinations are up to date.'

There has been a steady rise in the number of rabid bats being found in the county that is home to nearly 10 million people, but the cause of the record-breaking rabies rates remains a mystery.

However, officials noted that the majority of the rabid bats have been found in the Santa Clarita Valley, a suburban area in northern Los Angeles County.

Two-thirds of the rabies cases this year have been found in this part of Southern California, and the public health department stated that rabies 'may be circulating more intensely within that local bat population.'

The public health department added that anyone finding a dead or living bat indoors or in an area near pets should immediately call animal control so experts can test it for rabies.

They urged everyone in the county not to let these bats back outside if they were still alive or throw them in the garbage if dead.

'Either contain the bat in a room if indoors or cover it with a box or bucket until animal control arrives.'

Among the bats that wildlife experts recover to be tested each year, nearly one in five are said to test positive for rabies.