Protection against bovine babesiosis with a mixed in vitro culture-derived Babesia bovis and Babesia bigemina vaccine under field challenge. Immunization in a disease-free area

Abstract

IN MEXICO, THERE IS AN ATTENUATED LIVE VACCINE AGAINST BOVINE BABESIOSIS THAT HAS BEEN SHOWN TO CONFER PROTECTION TO SUSCEPTIBLE CATTLE IMMUNIZED AND CHALLENGED UNDER CONTROLLED CONDITIONS. IMMUNIZED CATTLE SURVIVE A CHALLENGE USING KNOWN NUMBERS OF VIRULENT PARASITES OF BOTH BABESIA BOVIS AND BABESIA BIGEMINA. HOWEVER, STRESS-INDUCING FIELD SITUATIONS SUCH AS TRANSPORTATION OR TICK-TRANSMITTED INFECTION HAVE NOT BEEN TAKEN INTO ACCOUNT. THE OBJECTIVE OF THIS STUDY WAS TO EVALUATE THE PROTECTIVE CAPACITY OF THE COMBINED VACCINE IN CATTLE IMMUNIZED IN A TICK-FREE AREA AND THEN TRANSPORTED TO AN ENDEMIC AREA. TEN, 18 MONTH OLD, SUSCEPTIBLE CHAROLAIS STEERS WERE DIVIDED INTO TWO GROUPS: ONE GROUP WAS IMMUNIZED WITH 1 €” 107 ERYTHROCYTES INFECTED WITH IN VITRO CULTURE-DERIVED BABESIA BOVIS AND BABESIA BIGEMINA PARASITES; WHILE THE SECOND GROUP WAS IMMUNIZED WITH UNINFECTED BOVINE ERYTHROCYTES. TWO MONTHS LATER, BOTH GROUPS WERE TRANSFERRED TO A BOVINE BABESIOSIS ENDEMIC AREA AND ALLOCATED IN A CORRAL INFESTED WITH BABESIA-INFECTED BOOPHILUS MICROPLUS TICKS. ANIMALS REMAINED THERE FOR THE REST OF THE EXPERIMENT AND NEVER RECEIVED IXODICIDE TREATMENT. EIGHTEEN DAYS POST-ALLOCATION, ALL FIVE CONTROL ANIMALS PRESENTED WITH SEVERE CLINICAL SIGNS CHARACTERISTIC OF ACUTE BOVINE BABESIOSIS, INCLUDING A RECTAL TEMPERATURE (RT) GREATER THAN 40.5OC FOR SEVERAL DAYS AND A DECREASED PACKED CELL VOLUME (PCV) OF 48%. BOTH PROTOZOAN SPECIES WERE FOUND IN BLOOD SMEARS AND ALL ANIMALS IN THE CONTROL GROUP HAD TO BE TREATED IN ORDER TO AVOID THEIR DEMISE. THE IMMUNIZED CATTLE ALSO PRESENTED BOTH BABESIA SPECIES IN PERIPHERAL BLOOD SAMPLES, INCREASED RT AND A 37% PCV REDUCTION, BUT REMAINED IN GOOD CORPORAL CONDITION AND DID NOT REQUIRE TREATMENT. THIS STUDY SHOWS THE PROTECTIVE CAPACITY CONFERRED TO CATTLE BY THE COMBINED VACCINE WHEN IMMUNIZED IN A BABESIA-FREE AREA AND THEN TRANSPORTED TO AN ENDEMIC AREA.