Page 928 - Veterinary Immunology, 10th Edition
P. 928

Several different vaccines are available against canine
  VetBooks.ir  leishmaniasis. All are designed to stimulate T cell–mediated

               responses. One such vaccine consists of a Leishmania component
               called the fucose-mannose ligand adjuvanted with saponin. This

               vaccine may also serve as an immunotherapeutic agent, producing
               clinical improvement in dogs with disseminated disease. An
               alternative vaccine containing an excretory protein of L. infantum
               promastigotes with either a muramyl dipeptide or a saponin

               adjuvant also appears to be effective. Experimental vaccines,
               including killed vaccines and DNA vaccines, have shown
               encouraging results.
                  Many factors contribute to the resistance of animals against

               babesiosis, including genetic factors (Zebu cattle are more resistant
               to disease than European cattle) and age (cattle show a significant
               resistance to babesiosis in the first 6 months of life). Animals that
               recover from acute babesiosis are resistant to further clinical

               disease. It is therefore possible to infect young calves when they are
               still relatively insusceptible to disease, so that they become resistant
               to reinfection. The organisms employed for this procedure are first
               attenuated by repeated passage through splenectomized calves and

               then administered to recipient animals in whole blood. As might be
               anticipated, the side effects of this type of controlled infection may
               be severe, and chemotherapy may be required to control them. The
               transfer of blood from one calf to another may also trigger the

               production of antibodies against the foreign red cells. These
               antibodies complicate any attempts at blood transfusion in later life
               and may provoke hemolytic disease of the newborn (Chapter 31). In
               a slightly different approach, cattle can be made resistant to East

               Coast fever (T. parva infection) by infecting them with virulent
               sporozoites and then treating them with tetracycline.
                  Since a primary infection with T. gondii will confer strong
               protective immunity on an animal, protective immunization is a

               real possibility. A live Toxoplasma vaccine containing the S48
               incomplete strain has been used successfully for the control of
               toxoplasmosis in sheep. The strain was developed by prolonged
               passage in laboratory mice and has lost the ability to develop
               bradyzoites or to initiate the sexual stages of the life cycle in cats. It

               produces protection against a severe challenge for at least 18





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