Spirometra spp.

Species

Spirometra mansonoides

Spirometra proliferum

Spirometra erinaceieuropaei

Other Spirometra spp.

Overview of Life Cycle

• Spirometra spp. have indirect life cycles that require two intermediate hosts before becoming infectious to the definitive host.
• Adult Spirometra spp. in the small intestine of infected cats or dogs release operculate eggs from a midventral genital pore; these eggs are then passed in the feces.
• When the egg contacts water, a ciliated embryo (coracidium) hatches and is ingested by a copepod, the first intermediate host, where it develops into a procercoid.
• When the copepod is consumed by a second intermediate host, the next larval form develops (plerocercoid, also called a sparganum) in muscle and connective tissue. A number of different non-fish vertebrates may serve as interemediate host.
• If an infected second intermediate host is eaten by another non-fish vertebrate, the spargana of Spirometra spp. transfer to the tissues of the new paratenic host and are capable of infecting the dog or cat that ingests these infected animals.
• Cats and dogs are infected when they ingest the larval spargana when consuming infected second intermediate host or paratenic hosts during predation or scavenging

Stages

• Eggs of Spirometra spp. are operculate, ovoid, and measure 55-76 x 30-43 µm.
  • Eggs of Spirometra spp. may be confused with trematode eggs due to the presence of a distinct operculum, or to those of Diphyllobothrium spp. due to the similar size (D. latum 67-71 x 40-50 µm). However, Spirometra spp. eggs are more likely to float in sugar or zinc solutions than Diphyllobothrium spp., and Spirometra spp. eggs are narrower at the anterior end than those of Diphyllobothrium spp.
• The ciliated first stage, termed a coracidium, emerges from the egg in the presence of water.
• A procercoid develops in a copepod, the first intermediate host, after it ingests the coracidium.
• A plerocercoid, often referred to as a sparganum, develops in the second intermediate host after it ingests the copepod. Common second intermediate hosts of Spirometra spp. include amphibians, reptiles, birds, and mammals.
• Adult Spirometra spp. are found in the small intestine of dogs, cats, and other mammals.
• The scolex of adult Spirometra spp. do not have hooks or suckers like those found in cyclophyllidean tapeworms. The worms attach to the mucosa of the small intestine with dorsal and ventral longitudinal groves on the scolex called bothria.

Spirometra mansonoides eggs, cat fecal flotation

Spirometra mansonoides, cat fecal flotation in Sheather's sugar solution

Disease

• Unlike cyclophyllidean cestodes, adults of which are widely regarded as almost nonpathogenic to the dog or cat definitive host, infection with adult Spirometra spp. can be associated with gastrointestinal disease in dogs and cats. Clinical signs reported include diarrhea, weight loss, and vomiting which usually resolve following appropriate anthelmintic therapy.
• More serious disease can occur when dogs and cats ingest an infected copepod and become the second intermediate host and the plerocercoids proliferate in the canine or feline host. This condition is referred to as proliferative sparganosis and is associated with a poor prognosis.

Prevalence

• Spirometra spp. is more common in dogs and cats in the southeastern and Gulf Coast states but infections also have been reported in Hawaii, New Jersey, New York, and Pennsylvania.
• In one survey, free roaming cats in New York and New Jersey had a Spirometra spp. infection prevalence of 3% and 1%, respectively.

Host Associations and Transmission Between Hosts

• Dogs and cats become infected with Spirometra spp. when they ingest an infected vertebrate. Spirometra spp. larvae have a broad host range; infective spargana may develop in amphibians, reptiles, birds, or mammals that ingest an infected copepod first intermediate host or a paratenic host.

Prepatent Period and Environmental Factors

• Dogs and cats may begin shedding eggs of Spirometra spp. eggs as soon as 10-30 days following infection. Infections will occur only when dogs and cats ingest spargana in prey species or in undercooked animal tissue in an area where infection is cycling in nature.

Site of Infection and Pathogenesis

• Adult Spirometra spp. are found in the small intestine of cats and dogs. Although not all infections result in overt clinical disease, vomiting, diarrhea, and weight loss that resolve following treatment have been reported.
• Proliferative sparganosis has also been rarely reported in dogs in the United States and Australia and usually results in euthanasia.

Diagnosis

• Diagnosis of infection with adult Spirometra spp. in the small intestine is made by recognizing the characteristic operculate eggs on fecal flotation or sedimentation.
• Chains of segments may also be identified in vomit or feces of an infected dog or cat. The proglottids are wider than long with a medial genital pore. These expelled segments are senile and have already shed their eggs when seen in feces or vomitus.
• Proliferative sparganosis is usually confirmed at surgery upon removal of the affected tissues and associated metacestodes.

Treatment

• No products have been approved for treatment of Spirometra spp. infections in dogs and cats.
• Praziquantel has been used successfully; however, a higher-than-labeled dose (25 mg/kg orally) and extended duration of treatment (2 consecutive days) is usually required to eliminate the infection.
• Treatment of Spirometra spp. in dogs and cats must be combined with prevention of ingestion of prey species (see Control and Prevention) or reinfection is likely to occur.

Control and Prevention

• Preventing predation and scavenging activity by keeping cats indoors and dogs confined to a leash or in a fenced yard will limit the opportunity for dogs and cats to acquire infection with Spirometra spp.
• Dogs and cats should not be fed raw or undercooked vertebrate tissue.

Public Health Considerations

• Dogs and cats infected with Spirometra spp. do not create an immediate zoonotic risk because the stage (coracidium) that hatches from the eggs shed in pet feces are infectious only to the copepod first intermediate host.
• People who inadvertently ingest Spirometra spp.-infected copepods in water or plerocercoid larvae (spargana) in the tissue of an infected second intermediate or paratenic host can develop a larval infection in their tissues. When poultices of infected animal tissues are applied directly to a wound or a mucous membrane, the spargana can also migrate directly into the human tissue. In both cases, the human becomes a paratenic host with Spirometra spp. larvae in the tissues.
• Sparganosis is most commonly seen in people in Southeast Asia. Zoonotic infections with Spirometra spp. are considered rare in North America and usually present as a flocculent subcutaneous mass; larvae may also develop in ocular tissue and in the central nervous system.

Selected References

• Conboy G. Cestodes of dogs and cats in North America. Vet Clin North Am Small Anim Pract 39:1075-1090, 2009.
• Little S. and Ambrose D. 2000. Spirometra infections in cats and dogs. Compendium on Continuing Education for the Practicing Veterinarian 22, 299–305, 2000.