Proliferative sparganosis caused by Spirometra sp. 3 in a dog.

Here, we report a case of proliferative sparganosis caused by Spirometra sp. 3 infection in a domestic dog in Pennsylvania, USA. Proliferative sparganosis is an unusual and often fatal condition caused by the multiplication of the larval cestode stage, Spirometra spp., within various organs and tissues of intermediate hosts, including humans, dogs, and cats. Although domestic dogs and cats are often definitive hosts of Spirometra spp., they can also act as paratenic or second intermediate hosts. These animals may develop high parasite burdens within muscle, connective tissue, or visceral organs after ingesting the cestode plerocercoid larvae through predation, scavenging, or contaminated water or food. As a zoonotic agent with potentially devastating consequences, accurate species identification through molecular and phylogenetic analysis is imperative for a better understanding of the Spirometra genus and other poorly understood parasites.