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.


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

(Table 4)

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 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