An outbreak of a potentially deadly virus affecting cats has been detected in Mattapan, according to the Animal Rescue League of Boston.

"The Animal Rescue League of Boston became aware of this outbreak after responding to reports of sick cats in the area around Walk Hill Street in Mattapan," the agency said in a statement released this afternoon. "In conducting a full investigation of the sick animals it was determined that they had contracted this potentially fatal virus."

Panleukopenia — also called feline Distemper— affects cats only. There is a vaccine that is "highly effective" in preventing transmission.

The Animal Rescue League of Boston in collaboration with the Massachusetts Animal Fund and City of Boston Animal Care & Control will conduct a free feline distemper vaccine clinic in Mattapan on Sat., October 22 to assist the residents in this neighborhood with protecting their cats through vaccination.

The vaccinations will take place at the corner of Walk Hill Street and Harvard Street from 9:30 a.m. to 12:30 p.m. Cats must be in carriers If you do not have a carrier, please come by the clinic to pick one up and then return home for your cat.

For more information visit: www.arlboston.org/panleuk-clinic