INFECTIVITY AND CROSS IMMUNITY STUDIES OF COLOMBIAN BOVINE BABESIA SPECIES

BABESIOSIS IS AN INFECTIOUS CATTLE DISEASE ENDEMIC TO MANY AREAS OF THE GLOBE. IT IS ONE OF THE MOST COSTLY CATTLE AFFLICTIONS IN THE WORLD. THE PROBLEM OF HOW TO IMMUNIZE CATTLE AGAINST BABESIOSIS HAS PERPLEXED SCIENTISTS FOR DECADES. WHEN CATTLE ARE PRE-IMMUNIZED WITH BLOOD CONTAINING CONTROLLED AMOUNTS OF VIABLE INFECTIOUS BABESIA ORGANISMS, THEY RESIST FUTURE EXPOSURE BUT BECOME CARRIERS OF THE INFECTION. AN EXPERIMENT WAS CONDUCTED TO ASCERTAIN THE FEASIBILITY OF USING MACERATED TICKS, INFECTED WITH BABESIA ARGENTINA, AS A SOURCE OF INFECTIOUS MATERIAL. A COLONY OF BOOPHILUS MICROPLUS TICKS WAS INFECTED WITH BABESIA BY PERMITTING THEM TO FEED ON INFECTED CATTLE. THE EGGS, LARVAE, AND NYMPHS FROM THE INFECTED TICKS WERE MACERATED AND INJECTED SUBCUTANEOUSLY INTO SPLENECTOMIZED CALVES. THE EXPERIMENT WAS NOT SUCCESSFUL; NONE OF THE CALVES SHOWED SIGNS OF INFECTION, AND THEY PROVED TO BE FULLY SUSCEPTIBLE WHEN CHALLENGED WITH B. ARGENTINA. IN A SECOND EXPERIMENT, BABESIA BIGEMINA WAS ISOLATED FROM OTHER BOVINE HEMOTROPIC AGENTS BY RAPID SERIAL PASSAGE THROUGH SPLENECTOMIZED CALVES. A SECOND GROUP OF EIGHT CALVES WAS INJECTED WITH A STRAIN PREVIOUSLY ISOLATED FROM A DIFFERENT GEOGRAPHIC REGION OF COLOMBIA. A THIRD GROUP OF CALVES SERVED AS CONTROLS. AFTER 28 DAYS, FOUR CALVES IN EACH OF THE THREE GROUPS WERE CHALLENGED WITH B. BIGEMINA ORGANISMS OF EACH ISOLATE. THE CHALLENGE GROUPS WERE HOMOLOGOUS, HETEROLOGOUS, AND CONTROL. BOTH THE HOMOLOGOUS AND HETEROLOGOUS GROUPS DEMONSTRATED IMMUNITY TO CHALLENGE. NO DIFFERENCES IN THE VIRULENCE OF THE TWO ISOLATES WERE DEMONSTRATED.