Babesia Bigemina

Synonyms: Pyrosoma bigeminum, Apiosoma bigeminum, Piroplasma bigeminum, Piroplasma australe, Babesia hudsonius bovis.

Disease: Bovine babesiosis, piroplasmosis, redwater, Texas fever.

Hosts: Ox, zebu, water buffalo, deer (Mazama americana reperticia) (syn., M. sartorii reperticia), white-tailed deer (Odocoelius virginianus chiriquensis (syn., O. chiriquensis).

Location: Erythrocytes.

Geographic Distribution: Central America, South America, Europe, North, Central and South Africa, Australia, formerly North America (U.S.).

Prevalence: This species causes one of the most important diseases of cattle in the tropics and subtropics.

Morphology: The trophozoites in the erythrocytes are piriform, round, oval or irregularly shaped. The piriform trophozoites occur characteristically in pairs, a feature which gives the species its name. B. bigemina is relatively large. The round forms are 2 to 3 u in diameter and the elongate ones 4 to 5 u long.

Life Cycle: This has been described above (p. 287). The tick vectors are Boophilus annulatus in North America, B. microplus in South and Central America, B. australis in Australia, B. calcaratus in North Africa and the USSR, B. decoloratus in South Africa, Haemaphysalis punctata in Europe, Rhipicephalus appendiculatus and R. evertsi in South Africa, and R. bursa in North Africa. Transmission takes place thru the egg in all species; stage-to-stage transmission also takes place in Haemaphysalis and Rhipicephalus. Intrauterine transmission may also take place (Enigk, 1942).

Pathogenesis: B. bigemina is highly pathogenic for adult animals but much less so for calves. The incubation period is 8 to 15 days or less. The first sign of disease is a rise in temperature to 106 to 108 F. The temperature persists for a week or more. Affected animals are dull, listless, fail to eat and stop ruminating. The feces are yellowish brown. Severe anemia is caused by the invasion and destruction of the erythrocytes; up to 75% of them may be destroyed. Hemoglobinuria is ordinarily present, but may be absent. Affected animals become thin, emaciated and icteric. In chronic cases the temperature is not very high and there is usually no hemoglobinuria, but diarrhea or constipation with hard, yellowish feces is present.

The initial febrile response is associated with the appearance of parasites in the peripheral blood. Death may occur in 4 to 8 days in acute cases. The mortality is as high as 50 to 90% in untreated cases, but treatment reduces it markedly. Calves less than a year old are seldom seriously affected. Chronically affected animals lose condition quite rapidly and remain thin, weak and emaciated for weeks before finally recovering.

The principal lesions are splenomegaly with soft, dark red splenic pulp and prominent splenic corpuscles. The liver is enlarged and yellowish brown. The gall bladder is distended with thick, dark bile. The mucosa of the abomasum and intestine is edematous and icteric, with patches of hemorrhage. The subcutaneous, subserous and intramuscular connective tissues are edematous and icteric, and the fat is yellow and gelatinous. The blood is thin and watery, the plasma may be tinged with red, and the urine in the bladder is usually red.

Immunity: As mentioned in the general discussion of immunity, recovered cattle are premunized, and premunition due to latent infection persists for life.

Diagnosis: Fever associated with hemoglobinuria, anemia and icterus is suggestive of babesiosis. The diagnosis can be confirmed by finding B. bigemina by microscopic examination of stained blood smears.

Treatment: Trypan blue was the first effective drug used against babesiosis, and is still used in some areas. It is administered intravenously in 1 to 2% aqueous solution; up to 200 ml may be given at a time. Two treatments on successive days may be needed, but 1 is often enough. The tissues turn blue, and recovery is relatively slow.

Acriflavine (trypaflavine) is also used to some extent, 50 to 100 ml of a 1% aqueous solution being given intravenously. Neither acriflavine nor trypan blue eliminates all parasites, and recovered animals remain premunized.

A number of aromatic diamidines are effective against B. bigemina. Stilbamidine was found by Adler and Tchernomoretz (1940) to be effective in calves when injected subcutaneously at a dosage of 2 to 4 mg per kg. Phenamidine is used quite widely. Randall and Laws (1947) gave 15 mg per kg phenamidine isethionate subcutaneously; the drug was well tolerated in doses up to 22.5 mg per kg. Berenil is the most recent of these drugs to be introduced (Bauer, 1955). It is injected intramuscularly at a dosage rate of 1 to 3 mg per kg body weight.

The quinoline derivative, acaprin, is also effective. The dosage for cattle is 0.02 ml per kg of a 5% aqueous solution subcutaneously.

The diamidines and acaprin eliminate all the parasites, so that treated animals are no longer premunized.

Prevention and Control: Since B. bigemina is transmitted only by ticks, infection can be prevented by tick control. This can be done by dipping the cattle regularly. This is the way in which Texas fever was eliminated from the United States. Another measure which has been used is artificial premunization of young animals with a mild strain, especially before shipping them to endemic areas.

Remarks: Spindler et. al. (1958) found a Babesia which resembled B. bigemina in a white-tailed deer (Odocoileus virginianus couesi) in New Mexico. The animal was weak and had lesions characteristic of babesiosis. Blood smears made from several other white-tailed deer, mule deer, cattle and a few antelope from the same region were negative, but this finding raises a question as to the existence of a possible reservoir of Babesia in wild deer in the southwestern states.