Eimeria Arloingi

Hosts: Sheep, goat, Rocky Mountain bighorn sheep, Ovis musimon, O. polii, Capra ibex, Hemmitragus jemlaicus, roe deer.

Location: Small intestine.

Geographic Distribution: Worldwide.

Prevalence: This is probably the most common coccidium in sheep. Christensen (1938a) found it in 90% of 100 sheep from Idaho, Maryland, New York and Wyoming. Balozet (1932) found it in 52% of 63 sheep and 56% of 41 goats in Tunisia. Jacob (1943) found it in 58% of 100 sheep and 18% of 11 goats in Germany. Svanbaev (1957) found it in 52% of 302 sheep and 52% of 48 goats in Kazakhstan.

Morphology: The oocysts are usually elongate ellipsoidal, but are sometimes asymmetrical, with one side curved more than the other, or slightly ovoid. They are 17 to 42 by 13 to 27 u with a mean of 27 by 18 u; their length-width ratio is 1.1 to 1.9 with a mean of 1.49 (Christensen, 1938a). The oocyst wall is 1.0 to 1.5 u thick, transparent, almost colorless to yellowish-brown, and composed of 2 layers, the outer one being half as thick as the inner, according to Christensen (1938a). The oocyst wall is apparently lined by a membrane. A micropyle 2 to 3 u in diameter is present. A micropylar cap is present; it varies from an inconspicuous, flat structure to a prominent, transparent, pale yellow to yellowish-green rounded cone or crescent, 0.2 to 2 u high by 3 to 8 u wide with a mean of 1.2 by 5 u. This cap is a tough, lid-like structure which is easily dislodged and may be lost in some specimens. An oocyst residuum is absent. An oocyst polar granule is present according to Balozet (1932). The sporocysts are ovoid, 13 by 6 u. A sporocyst residuum is present. The sporulation time is 1 to 2 days (Christensen, 1938a) to 3 to 4 days (Balozet, 1932).

Life Cycle: Lotze (1953a) studied the life cycle of E. arloingi in experimentally infected lambs. The sporozoites emerge from the oocysts in the small intestine, enter the crypts of Lieberkuehn, and penetrate thru the tunica propria into the interior of the villi. Here they enter the endothelial cells lining the central lacteals and grow. The host cell also grows, and its nucleus becomes very large. There is apparently only 1 generation of schizonts and merozoites. The schizonts become mature 13 to 21 days after infection. At this time they are about 122 to 146 u in diameter and contain a large number (probably millions) of merozoites about 9 u long and 2 u wide.

The merozoites break out of the schizonts and enter the epithelial cells of the small intestine. Sometimes only a small group of cells at the bottom of the crypts is parasitized, but in heavy infections practically all the epithelial cells of the villi are invaded. The infected villi are enlarged and greyish. Some of these merozoites become microgametocytes; these form many microgametes, leaving a large mass of residual material. Most of the merozoites become macrogametes, which contain large plastic granules when mature.

Following fertilization, the macrogametes turn into oocysts, which break out of the host cells and are first seen in the feces on the 20th day after infection. Their numbers increase for about 5 days and then decrease at about the same rate for the next 5 days. Thus the prepatent period is 19 days and the patent period about 10 days following a single exposure.

Pathogenesis: Lotze (1952) studied the pathogenicity of E. arloingi in 3-month-old lambs experimentally infected with 200,000 to 60 million oocysts. No visible signs were produced by infections with 1 million oocysts or less. In lambs infected with 3 or 5 million oocysts, the feces became soft on the 13th day and then returned to normal during the next 6 days. The health, general condition and weight gains of these animals were not affected.

Severe diarrhea was produced with higher doses, but none of the animals died altho one was killed in extremis. In general, the experimentally infected lambs appeared normal up to the 13th day after inoculation, when their feces became soft. In the more heavily infected lambs the feces then became watery, and diarrhea was severe beginning on the 15th day. Blood-tinged mucus was passed by affected lambs only occasionally. The feces began to return to normal on the 17th day and were usually nearly normal by the 20th day. Lambs with marked diarrhea became weak and refused feed.

At necropsy, only a few small, slightly hemorrhagic areas scattered thruout the lining of the small intestine were seen up to the 13th day. From the 13th to 19th days the small intestine was more or less thickened and edematous, and thick, white opaque patches made up of groups of heavily parasitized villi were present.

The villi containing the schizonts become thin-walled sacs and are presumably destroyed. The sexual stages are clustered in the epithelial cells of the villi and destroy these cells when they emerge. However, they do not do as much damage as the asexual stages, since the condition of affected animals appears to improve before oocysts are shed. E. arloingi is less pathogenic than E. ninakohlyakimovae.

Epidemiology: This species has been reported not only from domestic sheep and goats but also from the Rocky Mountain bighorn sheep (Ovis canadensis), moufflon (O. musimon), argali (O. ammon polii), ibex {Capra ibex), and Hemmitragus jemlaicus (see especially Yakimoff, 1933a). Ullrich (1930) found it in the roe deer. Whether the forms from all these animals are really E. arloingi remains to and cross-transmission experiments. According to Lotze (1953), no cross-transmission studies, even between domestic sheep and goats, have been reported up until the time of his paper, and he attempted none.