While previous infection may provide some level of immunity, dogs can still be reinfected if exposed to infected ticks again. Therefore, tick prevention remains crucial even for dogs previously diagnosed with anaplasmosis. If your dog was on a tick preventative and became infected with anaplasmosis, see your vet to discuss compliance or switching to another preventative. While previous infection may provide some level of immunity, dogs can still be reinfected if exposed to infected ticks again. Therefore, tick prevention remains crucial even for dogs previously diagnosed with anaplasmosis. If your dog was on a tick preventative and became infected with anaplasmosis, see your vet to discuss compliance or switching to another preventative.