I have a 6 month old Bullmastiff. I was playing with him the other day and noticed a Lymph node on his left rear leg is enlarged. He was vaccinated for Rabies and also had his DA2PP booster around 11 days ago.
I was concerned if this could be an effect from the vaccines or something worse like lymphoma which I know is common in this breed.
Vaccines work by stimulating the immune system. Lymph nodes are part of the immune system. When an animal is vaccinated the nearest lymph node sometimes swells up. In dogs this almost always is harmless. (In cats, such swelling unfortunately may be a harbinger of cancers called vaccine-associated sarcomas; any post-vaccination irregularity in a cat should be assessed by a vet.)
David, the swollen lymph node probably is a harmless reaction to the vaccine that will resolve on its own within a few weeks.
Be aware, however, that other problems including infections, minor autoimmune diseases, and yes, cancer can cause swollen lymph nodes. Fortunately cancer is very rare in six-month-old dogs.
Also, vaccines most frequently cause swelling of the closest lymph node located between the site of vaccination and the heart. It’s not common for vaccines to be administered on the far-flung reaches of dogs’ legs (in cats, however, it is a recommended practice). Therefore, a swollen lymph node on the leg is not exactly typical for a canine vaccine reaction.
There is no doubt: the vet who administered the vaccines should take a look at the lymph node. It’s probably nothing serious, but it’s worth a check-up.