Synonym: Isospora scorzai Arcay-de-Peraza, 1967.

Type host: Callithrix penicillata (I. Geoffroy, 1812) (syn. Hapale penicillatus), Short-tusked marmoset.

Other hosts: Other natural hosts, according to Hendricks (1974), are the marmoset, Saguinus geoffroyi (Pucheran, 1845), and capuchin monkey, Cebus capucinus (Linnaeus, 1758). Hendricks (1977), experimentally infected the night monkey, Aotus trivirgatus (Humboldt, 1811), spider monkey, Ateles fuscipes Gray, 1866, howler monkey, Alouatta pigra Lawrence, 1933 (syn. A. villosa), and the squirrel monkey, Saimiri sciureus (Linnaeus, 1758). Hendricks (1977) also reported that the domestic dog, Canis familiaris, coatimundi, Nasua nasua, kinkajou, Potos flavus, tayra, Eiria barbara, domestic cat, Felis catus (sic) and opossum, Didelphis marsupialis could serve as definitive hosts and transport hosts include the laboratory mouse, Mus musculus, and chicken, Gallus gallus. Poelma (1966) reported some isosporan oocysts "resembling I. arctopitheci" in the African bush-baby, Galago sengalensis, which died the day after its arrival in the Amsterdam Zoo. Arcay-de-Peraza (1967) found oocysts of what is likely I. arctopitheci in the feces of a Uakair monkey, Cacajao rubicundus, that was in captivity in the London Zoo. She was able to successfully infect Cebus nigrivittatus from Venezuela with these oocysts.

Type locality: Unknown (see Remarks).

Geographic distribution: EUROPE: Belgium (?), England (?), Holland (?); SOUTH AMERICA: Panama, vicinity of La Chorrera and the Canal Zone, near Cardenas Village; Venezuela (?); AFRICA (?).

Description of oocyst: Oocyst shape: subspheroid to ellipsoid; number of walls: 2; wall thickness: 1; wall characteristics: outer, colorless, smooth; inner, light yellow-brown; L x W: 27.7 x 24.3 (23-33 x 20.5-27); L/W ratio: 1.1 (1.05-1.3); M: absent; OR: absent; PG: absent. Distinctive features of oocyst: oocyst wall is easily deformed in handling.

Description of sporocysts and sporozoites: Sporocyst shape: ellipsoid; L x W: 17.6 x 12.5 (13-20.5 x 10-16); L/W ratio: 1.4 (1.2-1.6); SB: absent; SSB: absent; PSB: absent; SR: present; SR characteristics: composed of spherical, coarse granules in middle of sporocyst; SR L x W: 10.2 x 6.9; SP: with 1 large RB at narrow end. Distinctive features of the sporocyst: the voluminous SR.

Prevalence: 1/1 in the type host; from 50-100% in other naturally-infected hosts (Arcay- de-Peraza, 1967; Hendricks, 1974; Poelma, 1966).

Sporulation: Exogenous. Oocysts sporulated in 2 days in 1% chromic acid at RT in Belgium; 4 days in 2.5% aqueous potassium dichromate solution at 24ºC in Panama.

Prepatent period: Varies from 5-9 days in experimentally-infected primates (Hendricks, 1977).

Patent period: Varies from 3-55 days in experimentally-infected primates (Hendricks, 1977).

Site of infection: Presumably small intestine. Oocysts found in the posterior small intestine, but no endogenous stages were found in tissue sections.

Material deposited: Photoneotype in the USNPC, No. 87407.

Cross-transmission studies: Rodhain (1933) was unable to infect 6 young white rats or a cynocephalus monkey (presumably [?] the yellow baboon, Papio hamadryas [Linnaeus, 1758] [syn. P. cynocephalus]) with this species from C. penicillata. Hendricks (1974), however, was able to transmit this species from Cebus capucinus to 2 male S. geoffroyi, a juvenile and an adult. He also was able to transmit it to, and achieve patent infections in, 6 genera of New World primates, 5 genera of carnivores and 1 marsupial (Hendricks, 1977).

Remarks: The oocysts first seen and described by Rodhain (1933) were from a marmoset held in captivity at the Prince Leopold Institute in Antwerp, Belgium; the natural origin of this host is unknown. The description here is based on Rodhain (1933) and Hendricks (1974). Hendricks (1974) stated that the shape of sporulated oocysts was subspheroid to ellipsoid and that the SR was "equatorial" in location; however, his photomicrographs show oocysts which are clearly ovoid in shape (slightly pointed at 1 end) and sporocysts that have their SR located at 1 end, similar to that seen in I. endocallimici. Arcay-de-Peraza (1967), in a review and comparison of the Isospora spp. found in primates, described I. scorzai as a new species. However, we agree with the convincing argument of Hendricks (1974) that I. scorzai is a junior synonym of I. arctopitheci.

References: Arcay-de-Peraza (1967); Hendricks (1974, 1977); Poelma (1966); Rodhain (1933).