Isospora rivolta (Grassi, 1879) Wenyon, 1923
ETYMOLOGY: Isospora (Iso equal; spora spore) and rivolta for Dr. Rivolta
SYNONYMS: Coccidium rivolta Grassi, 1879; Diplospora bigemina of Wasielewski (1904) in
part; Isospora rivoltae Dobell, 1919; Lucetina rivolta (Grassi, 1879) Henry and Leblois, 1926;
Isospora novocati Pellerdy, 1974; Levinea rivolta (Grassi, 1879) Dubey, 1977; Cystoisospora
rivolta (Grassi, 1879) Frenkel, 1977
GEOGRAPHIC DISTRIBUTION: Isospora rivolta is found worldwide were cats are present.
LOCATION IN HOST:
Feline definitive hosts: Asexual and sexual multiplication occurs in enterocytes
primarily in the posterior small intestine. Asexual stages are also observed in extraintestinal
Paratenic hosts: In these hosts as with Isospora felis, sporozoites will enter and persist
in cells within various lymphatic cells within the tissues of these hosts.
PARASITE IDENTIFICATION: Sporulated oocysts measure 23-29 by 20-26 m (mean,
25.4 by 23.4 m). The length width ratio is 1.08. The oocysts of Isosopora rivolta represent
the mid-range of coccidial oocysts that are passed in the feces of cats (Table 3). No micropyle
is present. Inclusions (hazy bodies) may be observed between the sporont and oocyst wall in
freshly excreted oocysts. The hazy bodies degenerate as the oocysts sporulate. No oocyst
residuum is present in sporulated oocysts. Sporulated oocysts contain 2 sporocysts. Sporocysts
measure 13-21 by 10-15 m (mean, 17.2 by 15.0 m), contain a sporocyst residuum, and 4
sporozoites but no Steida body. The sporocyst residuum is granular and may contain refractile
globules. Sporozoites are 10-14 by 2.5-3 m (mean, 12.4 by 2.8 m), and contain a single
centrally located nucleus and 2 refractile globules. Occasionally a sporulated I. rivolta oocyst
will be observed that is Caryospora-like having a single sporocyst that contains 8 sporozoites.
LIFE CYCLE: Most members of the cat family Felidae are probably suitable definitive hosts.
Levine and Ivens (1981) indicated the following were suitable definitive hosts: European
wild cat (Felis silvestris), jungle cat (Felis chaus), tiger (Leo tigris), and leopard (Leo pardus).
Oocysts of I. rivolta are excreted unsporulated. Sporulation occurs within 24 hr at 24 C, 12 hr at
30 C, and 8 hr at 37 C.
Dubey (1979) described the endogenous development of I. rivolta in kittens. Three
structural types of meronts were observed. Type 1 meronts were first observed 0.5 days PI,
divided by endodyogeny and produced up to 8 merozoites. Type II meronts were first observed
2 days PI, were multinucleated and merozoite shaped, and produced an undetermined number of
merozoites. Several divisional cycles probably occurred in the same parasitophorous vacuole.
Type III meronts were first observed 3 PI and contained 2 to 30 merozoites. Sexual stages and
oocysts were first observed 5 days PI. The prepatent period 4 to 7 days and the patent period is
greater than 2 weeks. Mice (Mus musculus), Norway rats (Rattus norvegicus), golden hamsters
(Mesocricetus auratus), cows (Bos taurus), and opossums (Didelphis viginiana, syn. D.
marsupialis) (Dubey and Frenkel, 1972; Fayer Rodents have been found to serve as paratenic
hosts in the life cycle of Isospora rivolta. The developmental cycle in kittens fed mouse tissues
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Feline Clinical Parasitology – Chapter 1
containing I. rivolta stages was similar to that in cats given oocysts but was delayed 0.5 to 2
days in the appearance of the different stages within the cat host (Dubey and Streitel, 1976).
CLINICAL PRESENTATION AND PATHOGENESIS: Experimental studies indicate that
I. rivolta is pathogenic for newborn but not weaned kittens (Dubey, 1979). Diarrhea occurs 3
to 4 days after inoculation of 1 x 105
consisting of congestion, erosion, villous atrophy, and cryptitis were seen in these kittens. No
deaths occurred. No clinical signs were observed in 10 to 13 week-old kittens given 1 x 105
TREATMENT: Coccidiosis in cats can be treated with various sulfonamides and quinacrine
EPIZOOTIOLOGY: Cats are very commonly infected with this parasite. It is unclear whether
cats are infected more commonly by oocysts or by the ingestion of paratenic hosts.
HAZARDS TO OTHER ANIMALS: None known.
HAZARDS TO HUMANS: It is possible that humans could serve as paratenic hosts. No
recorded cases of human infection exist.
Dubey JP. 1979. Life cycle of Isospora rivolta (Grassi 1879) in cats and mice. J. Protozool.
Dubey JP, Frenkel JK. 1972. Extra-intestinal stages of Isospora felis and I. rivolta
(Protozoa: Eimeriidae) in cats. J. Protozool. 19:89-92.
Dubey JP, Streitel RH. 1976. Isospora felis and I. rivolta infections in cats induced by
mouse tissue or oocysts. Br. Vet. J. 132:649-651.
Frenkel JK, Dubey JP. 1972. Rodents as vectors for the feline coccidia, Isospora felis and
Isospora rivolta. J. Infect. Dis. 125:69-72.
Levine ND, Ivens V. 1981. The Coccidian parasites (Protozoa, Apicomplexa) of
Carnivores. Illinois Biological Monographs 51, University of Illinois Press, Urbana,
Illinois. pp. 248.
to 1 x 106
oocysts in newborn kittens. Microscopic lesions