U.S. cat case links proliferative sparganosis to Spirometra sp. 3
Bottom line
A newly published case report in the Journal of Veterinary Diagnostic Investigation describes what the authors say is the first reported case of proliferative sparganosis in a domestic cat in the United States caused by Spirometra decipiens complex 2, now also referred to as Spirometra sp. 3. The report, published online March 21, 2026, links severe, disseminated disease in a cat to a parasite lineage that had not previously been associated with this presentation in domestic cats, challenging the long-standing assumption that proliferative sparganosis was tied mainly to Sparganum proliferum. The authors used molecular testing to identify larval cestode DNA with a 99% match to S. decipiens, underscoring how taxonomy and diagnostics around Spirometra are shifting. (journals.sagepub.com)
Why it matters: For veterinary professionals, the case expands the differential diagnosis for cats with unexplained granulomatous, visceral, or disseminated parasitic lesions, especially in regions where exposure to amphibians, reptiles, or infected intermediate hosts is possible. CDC guidance notes that dogs and cats become infected by eating infected second intermediate hosts, and newer U.S. molecular surveillance suggests Spirometra sp. 3 is established in North America and may have a particular association with domestic cats. That makes species-level confirmation more than an academic exercise: it can affect case recognition, epidemiology, zoonotic risk discussions with pet parents, and public health reporting. (cdc.gov)
What to watch: Expect closer scrutiny of archived and future feline sparganosis cases, with molecular testing likely to reshape how U.S. veterinary labs classify Spirometra infections and assess their pathogenic potential. (journals.sagepub.com)
A new U.S. case report is adding weight to a growing rethink of Spirometra disease in cats. In the Journal of Veterinary Diagnostic Investigation, researchers report a domestic cat with proliferative sparganosis caused by Spirometra decipiens complex 2, now called Spirometra sp. 3, and say it is the first such case documented in a U.S. domestic cat. The paper was published online March 21, 2026, and argues that a parasite lineage not previously linked to this syndrome in cats can, in fact, produce severe disseminated disease. (journals.sagepub.com)
That matters because proliferative sparganosis has historically been attributed to Sparganum proliferum or, in more recent molecular discussions, to other Spirometra lineages. In the new report’s abstract, the authors note that sparganosis in domestic cats is rare, is usually described as subcutaneous or visceral granulomatous disease, and in North America has traditionally been associated with Spirometra mansonoides. Their case broadens that picture by showing lesions across multiple tissues that resembled those classically attributed to S. proliferum, but with molecular evidence pointing instead to Spirometra sp. 3. (journals.sagepub.com)
The broader scientific backdrop has been moving in this direction. A 2025 U.S. molecular survey of Spirometra isolates reported that the lineage formerly grouped within S. decipiens complex 2 is now treated as Spirometra sp. 3 in North America, while the South American lineage is separated as S. decipiens. That same study found Spirometra sp. 3 in U.S. animals and suggested the lineage may have a host association with domestic cats. It also emphasized that proliferative sparganosis is defined by asexual larval proliferation and migration through multiple tissues, a pattern distinct from more localized non-proliferative infections. (cambridge.org)
There’s also a One Health angle. CDC describes sparganosis as infection with the plerocercoid larval stage of Spirometra or Sparganum, with canids and felids serving as definitive hosts and infection acquired through the food chain involving copepods and then second intermediate hosts such as reptiles and amphibians. In practical terms, that means outdoor hunting behavior, predation, or ingestion of infected prey remains relevant when veterinarians are assessing exposure history. The new feline case report explicitly highlights the zoonotic importance of accurate identification and surveillance. (cdc.gov)
Expert reaction in the form of adjacent literature also suggests this isn’t an isolated taxonomic footnote. A review published in 2024 described Spirometra tapeworms as zoonotic wildlife parasites with unresolved diversity and distribution, while a separate 2024 feline case report from Japan documented aberrant sparganosis caused by S. mansoni, not the lineage historically expected. And just this week, another JVDI report described proliferative sparganosis caused by Spirometra sp. 3 in a dog, reinforcing that this lineage’s pathogenic capacity may be broader than many clinicians assumed. Taken together, these reports point to a diagnostic landscape in flux rather than a single anomalous case. (pubmed.ncbi.nlm.nih.gov)
Why it matters: For veterinary professionals, the key takeaway is that unusual granulomatous, serosal, subcutaneous, or disseminated lesions in cats may warrant renewed consideration of sparganosis, even when the presentation seems atypically aggressive. Molecular confirmation is becoming central, because morphology and older naming conventions may no longer capture the clinically relevant species distinctions. That has implications for pathology workflows, referral testing, case documentation, and pet parent counseling about hunting exposure, intermediate hosts, and zoonotic context. It may also influence how veterinary diagnosticians reinterpret older U.S. cases previously labeled under broader or outdated names. (journals.sagepub.com)
What to watch: The next step is likely more molecular characterization of feline and wildlife cases across the United States, including retrospective testing of archived specimens, to clarify how common Spirometra sp. 3 really is, where it circulates, and whether it is more strongly associated with severe proliferative disease than previously recognized. (cambridge.org)