Effect of breed of cattle on innate resistance to infection with Babesia bovis, B bigemina and Anaplasma marginale.
OBJECTIVE
To assess the innate resistance of naive Bos taurus, Bos taurus cross Bos indicus and Bos indicus cattle to virulent Babesia bovis, B bigemina and Anaplasma marginale parasites.


METHODS
Groups of 10, pure B indicus, 1/2 B indicus cross, 1/4 B indicus cross and pure B taurus steers were infected with virulent B bovis, B bigemina and A marginale parasites [corrected].


METHODS
Sequential infections were carried out by intravenous inoculation of infected blood containing 1 x 10(8) parasites of B bovis, followed by B bigemina and then A marginale. To assess resistance, measurements were made of parasitaemia, rectal temperature, packed cell volume and the number within a group requiring chemotherapy to control infection. There was a recovery period between each infection.


RESULTS
Infection with B bovis showed that pure B indicus steers were significantly more resistant to B bovis infection than the other groups, with none of this group requiring treatment. There was no significant difference between 1/2 B indicus cross and 1/4 B indicus cross with 30% and 20%, respectively, of steers in these groups requiring treatment [corrected]. The pure B taurus steers were significantly more affected then those in the other three groups with 80% requiring treatment. Infections of B bigemina produced a mild response in comparison to that of B bovis and none of the steers required treatment. However, the pure B taurus group was significantly more affected than the other three groups for all other measurements. After the A marginale infection, B indicus steers were moderately affected with 50% requiring treatment, whereas 70% of the 1/2 B indicus group, 80% of the 1/4 B indicus cross group and 100% of the pure B taurus group required treatment [corrected].


CONCLUSIONS
All breeds of cattle, ranging from pure B indicus to pure B taurus may be at risk of severe disease if exposed to virulent A marginale. The results confirm that pure B indicus cattle are relatively resistant to B bovis, but there could be a significant risk of severe mortalities if cross-bred herds are exposed to virulent infection.
Bock
R E
RE
Tick Fever Research Centre, Wacol, Queensland. Bockr@dpi.qld.gov.au
de Vos
A J
AJ
Kingston
T G
TG
McLellan
D J
DJ
D000709:Anaplasma / Q000472:pathogenicity*; D000822:Animal Husbandry; D000818:Animals; D001403:Babesia / Q000472:pathogenicity*; D001947:Breeding; D002417:Cattle / Q000235:genetics*; D002418:Cattle Diseases / Q000235:genetics* / Q000517:prevention & control; D005260:Female; D007113:Immunity, Innate / Q000235:genetics*; D008297:Male; D017282:Tick-Borne Diseases / Q000235:genetics / Q000517:prevention & control / Q000662:veterinary*; D014774:Virulence