The haemoparasites Babesia bovis and Anaplasma marginale are extremely important pathogens of cattle, affecting more than 300 million animals worldwide. Species of less importance affect cattle, dogs, horses and sheep. No vaccine is available for widespread usage. This review summarises existing immunodiagnostic and immunoprophylactic methods currently available for these diseases and reports on future immunoprophylactic methods.

A Babesia parasite, isolated from the blood of a horse at Bowral, New South Wales, was identified on the basis of its morphological features, host specificity and serological reactions, as Babesia equi (Laveran 1901). The case was originally reported by Churchill and Best (1976, Aust. vet. J. 52: 487) and is the first record of equine babesiosis in Australia. In preliminary studies, the organism produced only a mild disease in an intact horse, but caused the typical clinical syndrome of acute babesiosis in a splenectomised horse, which died 19 days after the intravenous inoculation of the parasites.

Summary. Rabbits have been immunized against the effects of the paralyzing toxin of the Australian paralysis tick Ixodes holocydus by injecting them with preparations extracted from tick salivary glands. Immunized rabbits were able to withstand doses of toxin known to kill unimmunized rabbits.Neutralizing antibodies were detectable in serum after 2-4 doses of the crude extract or of the relatively pure antigenic fraction. When injections were continued at intervals of from 2-7 weeks, hyperimmunity was retained for at least 68 weeks. Hyperimmune serum, reaching a very high titre of neutralizing antibodies, was obtained after 3-6 injections. Titres tended to decline when boosting ceased, but after a 'rest period' high titres were restored by further boosting with normally lethal doses of toxin. No symptoms of tick paralysis developed despite low titres prior to boosting. Thus, once hyperimmunity had been established, high titres of circulating antibodies were not immediately essential for immunity to tick paralysis.An IgG fraction^was obtained from rabbit serum using a Protein A-Sepharose method; 33 4 Mg of IgG protein fully neutralized, and 19-5 Mg IgG half neutralized, 1 Mg of crude toxin protein. This procedure with rabbits may permit the production of a purified tick-paralysis antitoxin more suitable for human use than the existing antitoxin based on canine hyperimmune serum.

Beagles have been immunised against the paralysing effects of the Australian paralysis tick lxodes holycyclus by allowing female ticks to feed on these dogs. Complete immunity to the toxic effects of lethal numbers of feeding ticks has persisted in these beagles for at least 53 weeks and in similarly-immunised foxhounds for at least 102 weeks, during which periods the beagles and foxhounds were kept free of ticks.Serum antitoxin titres increased to a maximum value (hyperimmunity) of 46 antitoxin units/mL with a minimum number of 11 ticks feeding simultaneously. Titres declined to a low level after 12 to 14 weeks of freedom from tick infestation but increased again on reinfestation with ticks. Large numbers of ticks (up to 60) appeared to be required after several stimulation/relaxation cycles to obtain hyperimmune levels of antitoxin in serum.The serum antitoxin titre appeared to be a good indicator of effective immunity to tick paralysis during the initial development of hyperimmunity but was less indicative thereafter, as dogs whose serum antitoxin titres had reached an apparent maximum remained immune to tick paralysis after titres had decreased to low levels. There was no evidence of cutaneous hypersensitivity or any other tick rejection mechanism that could account for this effect.

The results of this paper indicate that cattle infected with B. bovis (argentina) have a markedly altered and activated coagulation system. A degree of thrombin activation occurs due partly to release of thromboplastin-like substances from lysed erythrocytes but due primarily to activation of kallikrein by babesial proteases. This produces a hyperfibrinogenaemia, particularly in intact cattle, with soluble fibrin complexes constituting up to one-third of the total fibrinogen concentration. High molecular weight non-coagulable fibrinogen-like proteins are detected terminally but more so in splenectomized cattle. Plasminogen concentration decreases in splenectomized but not intact cattle while low molecular weight fibrinogen degradation products are not easily detected. It is suggested that a hypercoagulable intermediate state with little or no fibrin deposition occurs rather than terminal disseminated intravascular coagulation.