Cats can serve to also support the plerocercoid larval stage of Spirometra spp. acting in this case as the paratenic host rather than the final host of the infection. Infection with this larval stage often goes by the name sparganosis. Plerocercoids or spargana are white, ribbon-like structures that usually occur subcutaneously in the tissues of the second intermediate host. These larval tapeworms may reach several centimeters in length. Like the adult tapeworms, the spargana selectively absorb large quantities of vitamin B12, giving the head of the larva a characteristic pinkish color . Mueller (1974) states that the appearance of the plerocercoid of Spirometraerinaceieuropaei is more robust than the slender plerocercoid of Spirometramansonoides. Another form of spargana that has bee reported from humans is a plerocercoid that seems to reproduce inside the host and has been called sparganum proliferum or the proliferating sparganum. A case of proliferating sparganosis has been reported from a cat from Florida, USA.
Cats infected with the plerocercoids of Spirometraerinaceieuropaei have been reported in China (Tang, 1935), Japan (Uga et al., 1986), and in a cat from Taiwan that was purchased in Cambodia and brought to the United States (Schmidt et al., 1968). Uga et al. (1986) found that 10 of 1880 cats were infected with this parasite in the Hyogo Prefecture of Japan with cats harboring between 1 and 166 spargana each. The average length of the plerocercoids was 11.5 cm (2.0-28.0 cm) and they had the thickened body with a distinct cup shaped groove in the scolex described by Mueller (1974) for the plerocercoids of Spirometra erinaceieuropaei. Some of these plerocercoids were fed to dogs that developed patent infections with Spirometra erinaceieuropaei. From the cats, the plerocercoids were recovered from the inguinal and cervical regions, fatty tissue around the kidneys, on the chest, and in both femoral regions. All the cats harboring the plerocercoids were also found to be infected with the adults of Spirometraerinaceieuropaei; however, only 0.5% of the cats in the survey harbored plerocercoids while 39% of the cats in the survey harbored the adult tapeworm. There have been no studies describing the clinical signs of infection in cats or the attempted treatment of the infections with either anthelminthics or via surgical removal of the worms.
There have been rare reports of humans infected with plerocercoids that seem to proliferate unchecked in the tissues of the human host. Some of these cases have been from Japan, one has been from Florida, USA, and one from Venezuela (Beaver and Rolon, 1981; Moulinier et al., 1982). There has been one such case reported from a cat in Florida USA where proliferating plerocercoids were found in the abdominal cavity of a 6-year-old, male, domestic long-haired cat that had lived its entire life in Florida. The cat developed a painful abdomen over a two month period at the end of which it was noted to have a palpable abdominal mass and was euthanatized. Necropsy revealed that the spleen, liver, and stomach wall had numerous plerocercoids that appeared to be budding.
The plerocercoids of Spirometramansonoides are capable of persisting in the tissues of cats as was noted by Mueller (1938) who reported the presence of an active larva being recovered from as cysts on the external wall of the duodenum of a cat from Rome, NY, USA. Cats can be infected with spargana by feeding procercoids to young kittens. The cysts appear in the flat muscles of the body wall or under the skin (Mueller, 1974). There has been very little description of the clinical signs associated with potential plerocercoid infection in cats.
Beaver PC, Rolon FA. 1981. Proliferating larval cestode in a man in Paraguay. a case report and review. Am J Trop Med Hyg 30:635-637.
Moulinier R, Martinez E, Torres J, Noya O, de Noya BA, Reyes O. 1982. Human proliferative sparganosis in Venezuela. Report of a case. Am J Trop Med Hyg 31:358-363.
Mueller JF. 1938. The life history of Diphyllobothriummansonoides Mueller, 1935, and some considerations with regard to sparganosis in the United States. Am J Trop Med 18:41-58.
Mueller JF. 1974. The biology of Spirometra. J Parasitol 60:3-14.
Schmidt RE, Reid JS, Garner FM. Sparganosis in a cat. J Sm Anim Pract 9:551-553.
Tang CC. 1935. a survey of helminth fauna of cats in Foochow. Pek Nat Hist Bull 10:223-231.
Uga Sm Goto M, Matsumura T, Kagei N. 1986. Natural infection of sparganum mansoni in cats captured in Hyogo Prefecture, Japan. Jap J Parastiol 35:153-159.