SPIROMETRA SPECIES: PROLIFERATIVE SPARGANOSIS
As with other tapeworms, the life cycle of Spirometra species is indirect. However, with Spirometra species two intermediate hosts are needed rather than just one (Table 1). Mature tapeworms live in the small intestine of the definitive host; eggs are released from the proglottid and pass in
the feces to the environment. If deposited or washed into water, the egg hatches and the ciliated form is eaten by a freshwater
copepod crustacean. The tapeworm develops into the procercoid, which is the infective form for the second intermediate host.
Table 1: Some species of Taenia, Mesocestoides, and Spirometra in domestic dogs and cats
The second intermediate host range is quite diverse and includes most vertebrates except fish. Once ingested by the vertebrate,
the tapeworm develops into another form (the plerocercoid—also called the sparganum), which is now infective to the definitive host. Conversely, if the second intermediate host is eaten by another nonfish
intermediate host, the sparganum remains viable and migrates back into tissues. Within the definitive host, the sparganum
remains in the small intestine where it attaches to the mucosa and matures. The prepatent period is as little as 10 days.
Intestinal infections with Spirometra species tend to cause few problems. Intermittent diarrhea or vomiting may occur. Owners may not associate these problems
with tapeworm infections unless long chains of senile proglottids are found. Eggs can be found on fecal flotation but are
very similar to those of Diphyllobothrium species. Praziquantel is the treatment of choice for this parasite infection.
Dogs can also act as second intermediate hosts of Spirometra species if they drink water with infected copepods. In these cases, which have mostly been reported in the Deep South, the
spargana develop within the tissues of the dog. Sparganosis can be proliferative or nonproliferative. Most infections are
nonproliferative, such that ingestion of a single procercoid results in the development of a single plerocercoid. But in proliferative
sparganosis, ingestion of a single procercoid can result in numerous spargana as a result of the asexual replication of the
larvae. The larvae grow and repeat the process, which can ultimately lead to death of the host.9
Clinical signs of nonproliferative sparganosis are the presence of subcutaneous nodules or cysts. For proliferative sparganosis,
the most recent report in a dog indicated initial signs were progressive forelimb lameness and pain associated with subcutanous
cysts.9 As the condition deteriorated, fever, dyspnea, mature neutrophilia and hypoproteinemia were present. At necropsy, numerous
cysts were found in the soft tissues of the forelimb and neck as well as within the pleural and peritoneal cavities.9
In domestic animals, no approved treatment for sparganosis is available. Various anthelmintics have been tried, most with
poor results. The lack of treatment options for proliferative sparganosis generally warrants a poor prognosis for survival.