Synonyms: Coccidium bovis, Eimeria canadensis (pro parte), Eimeria smithi, Eimeria thianethi, Globidium fusiformis (?).
Hosts: Ox, zebu, water buffalo. Wilson (1931) was unable to infect pigs or goats with this species.
Location: The schizonts are mostly in the small intestine and the sexual stages in the cecum, colon and terminal ileum.
Geographic Distribution: Worldwide.
Prevalence: This is one of the commonest coccidia of cattle. Boughton (1945) found it in 41% of 2492 bovine fecal samples in south-eastern U.S. Hasche and Todd (1959) found it in 41% of 355 cattle in Wisconsin. Supperer (1952) found it in 66% of 130 cattle in Austria. Cordero del Campillo (1960) reported it and other bovine species in Spain. Torres and Ramos (1939) found it in 49% of 136 cattle in Brazil. Yakimoff, Gousseff and Rastegaieff (1932) found it in 40% of 126 cattle in Uzbekistan. Yakimoff (1933) found it in 47% of 17 zebus, 23% of 30 water buffaloes and 39% of 44 cattle in Azerbaidzhan. Marchenko (1937) found it in 54% of 137 cattle in the North Caucasus. Rao and Hiregaudar (1954) stated that it is common in Bombay State, India. Ruiz (1959) found it in 7% of 100 adult cattle in the San Jose, Costa Rica abattoir.
Morphology: The oocysts of E. bovis were described by Christensen (1941). Five hundred oocysts measured 23 to 34 by 17 to 23 u with a mean of 27.7 by 20.3 u. Their length-width ratios ranged from 1.1 to 1.8 with a mean of 1.37. They are typically stoutly ovoid and somewhat blunted across the narrow end, but vary considerably in shape, especially in heavy infections, subellipsoidal, asymmetrical and elongated, tapered oocysts also occurring. The micropyle is a lightened area at the small end. The oocyst wall is smooth, homogeneous, transparent, pale cloudy, greenish brown to yellowish brown, and slightly thinner toward the micropylar end. The wall is not so delicate as that of E. alabamensis. It is darker than that of E. alabamensis and lighter than that of E. auburnensis. Christensen (1941) illustrated the wall as composed of a heavy inner layer and a very thin, transparent outer layer, but he did not mention layers in his description. An oocyst residuum and polar granule are absent. A sporocyst residuum is present. The sporulation time is 2 to 3 days.
Life Cycle: Hammond et al. (1946) described the endogenous stages of the life cycle of E. bovis in detail. There is a single asexual generation. The sporozoites invade the endothelial cells of the lacteals of the villi in the posterior half of the small intestine. These cells become detached from the lacteal lining and lie free and greatly swollen in the lumens of the lacteals. The schizonts are first found 5 days after infection. They grow to giant size, becoming mature 14 to 18 days after infection. A few may still be found as long as 30 days after inoculation, but most of these are degenerate. The mature schizonts measure 207 to 435 by 134 to 267 u with a mean of 281 by 303 u and contain 55,000 to 170,000 (mean, 120,000) merozoites. They are easily visible to the naked eye as whitish balls, and their presence was first pointed out by Boughton (1942) as a macroscopic lesion which could be used in diagnosing coccidiosis.
The merozoites are 9 to 15 u (mean, 11.6 u) long and about 2 u wide. They are rounded at one end and taper abruptly to a point at the other. The nucleus is near the pointed end.
The sexual stages usually occur only in the cecum and colon, but in heavy infections they may be found in the terminal 2 or 4 feet of the small intestine. They occur in the epithelial cells of the intestinal glands. The cells at the base of the glands are invaded first, and later the rest of the gland becomes involved. The first sexual stages appear 17 days after inoculation. The macrogametes contain plastic granules in their cytoplasm, there being 1 layer of small granules near the surface and a less distinct layer of larger granules beneath it. Fertilization was not seen, but 2 stages in the union of nuclei were seen before formation of the oocyst wall.
According to Walton (1959), the haploid number of chromosomes in E. bovis is 2.
Oocysts appear 16 to 21 days after experimental infection. Large numbers are discharged for 5 to 7 days, and smaller numbers are present in the feces for 2 to 3 weeks. In 28 calves studied by Senger et al. (1959), oocysts were discharged for 7 to 15 days with a mean of 11.5 days.
Pathogenesis: E. bovis is one of the 2 most pathogenic of the bovine coccidia. Hammond, Davis and Bowman (1944) studied its effects in experimentally infected calves. An infective dose of 125,000 oocysts or more was generally needed to cause marked signs. These appeared about 18 days after infection, and consisted of diarrhea and/or bloody diarrhea, tenesmus, and temperatures as high as 106.6° F. One of 4 calves given 125,000 oocysts become moribund due to coccidiosis, while single calves given 250,000 to 1,000,000 oocysts all died or became moribund 24 to 27 days after infection.
The most severe pathologic changes occur in the cecum, colon and terminal foot of the ileum. They are due to the sexual stages of the coccidia. At first the mucosa is congested, edematous and thickened, with petechiae or diffuse hemorrhages. Its lumen may contain a large amount of blood. Later, the mucosa is destroyed and sloughed, and a patchy or continuous membrane forms over its surface. The submucosa may also be destroyed. If the animal survives, both mucosa and submucosa are later replaced.
Immunity: Senger et al. (1959) found that inocula of 10,000, 50,000 or 100,000 oocysts of E, bovis produced a good deal of immunity to reinfection. The immunity developed rapidly, calves being resistant to challenge 14 days after immunization. Immunity persisted to a moderate degree for 2 to 3 months in young calves, and in one group of yearlings there was apparently a high degree of immunity 7 months after the last inoculation. An inoculum of 10,000 oocysts did not produce as great an immunity as 50,000 or 100,000 oocysts; there was no significant difference in the degree of immunity produced by the higher doses. All these immunizing doses caused diarrhea and bloody feces; the greater the number of oocysts administered, the more severe and longer-lasting the resultant disease.
Hammond et al. (1959) found that this immunity was not directed against the schizonts but against the sexual stages or merozoites. They found no significant differences in numbers or size of schizonts between immunized and non-immunized calves, but the latter had many more sexual stages than the former.
Remarks: Hassan (1935) described the sporozoites and schizonts of an organism which he named Globidium fusiformis from 5 zebus with dysentery and rinderpest in India. The schizonts were found in the abomasum, duodenum and ileum; they often occurred anterior to the ileocecal valve, but were not found in the large intestine. They were whitish and measured 0.4 to 1.0 by 0.8 mm. The merozoites were elongate, spindle-shaped, slightly curved; with one end bluntly rounded and the other finely pointed, 13 by 2 to 2.5 u. This form may well be Eimeria bovis. However, the fact that schizonts were found in the abomasum as well as in the small intestine made Hammond et al. (1946) hesitate to assign it to this species, since they never found schizonts of E. bovis in the abomasum.