Onset and duration of immunity against Babesia canis infection in dogs vaccinated with antigens from culture supernatants

Molecular identification and antigenic characterization of a merozoite surface antigen and a secreted antigen of Babesia canis (BcMSA1 and BcSA1)

Background

Babesia canis is an apicomplexan tick-transmitted hemoprotozoan responsible for causing canine babesiosis in Europe and west Asia. Despite its importance, there is no known rapid diagnostic kit detection of B. canis infection in dogs. The present study identified two novel antigens of B. canis and used the recombinant antigens to establish a rapid, specific and sensitive serodiagnostic technique for detection of B. canis infection.

Methods

A complementary DNA (cDNA) expression library was constructed from the mRNA of B. canis and immunoscreened using B. canis-infected dog sera. The cDNAs encoding a merozoite surface antigen and a secreted antigen protein were identified and designated as BcMSA1 and BcSA1, respectively. The recombinant BcMSA1 and BcSA1 (rBcMSA1 and rBcSA1) expressed in Escherichia coli were purified and injected into mice for production of anti-sera. The native proteins were characterized by Western blot analysis and immunofluorescence. Furthermore, indirect enzyme-linked immunosorbent assays (iELISA) and rapid immunochromatographic tests (ICT) based on rBcMSA1 or rBcSA1 were established and evaluated to test specific antibodies in consecutive plasma samples from two B. canis-infected dogs.

Results

Antiserum raised against rBcMSA1 and rBcSA1 recognized the 39 kDa and 44 kDa native proteins by Western blot analysis, respectively. In addition, immunofluorescence and confocal microscopic observations revealed that BcMSA1 was found on the surface of parasites. However, BcSA1 localized in the matrix of the merozoites. The ELISA and ICT based on rBcMSA1 or rBcSA1 could detect specific antibodies in consecutive plasma samples from two B. canis-infected dogs. They showed no cross-reactions against the serum samples collected from dogs experimentally infected with closely related parasites.

Conclusion

Taken together, the current results indicated that the rBcMSA1 and rBcSA1 are promising serodiagnostic antigens for developing iELISA and ICT to detect B. canis infection. To our knowledge, this study is the first to report BcMSA1 and BcSA1 as potential antigenic proteins for serodiagnosis of B. canis infection in dogs.

Successful vaccines for naturally occurring protozoal diseases of animals should guide human vaccine research. A review of protozoal vaccines and their designs

Effective vaccines are available for many protozoal diseases of animals, including vaccines for zoonotic pathogens and for several species of vector-transmitted apicomplexan haemoparasites. In comparison with human diseases, vaccine development for animals has practical advantages such as the ability to perform experiments in the natural host, the option to manufacture some vaccines in vivo, and lower safety requirements. Although it is proper for human vaccines to be held to higher standards, the enduring lack of vaccines for human protozoal diseases is difficult to reconcile with the comparatively immense amount of research funding. Common tactical problems of human protozoal vaccine research include reliance upon adapted rather than natural animal disease models, and an overwhelming emphasis on novel approaches that are usually attempted in replacement of rather than for improvement upon the types of designs used in effective veterinary vaccines. Currently, all effective protozoal vaccines for animals are predicated upon the ability to grow protozoal organisms. Because human protozoal vaccines need to be as effective as animal vaccines, researchers should benefit from a comparison of existing veterinary products and leading experimental vaccine designs. With this in mind, protozoal vaccines are here reviewed.

The immunopathology of canine vector-borne diseases

The canine vector-borne infectious diseases (CVBDs) are an emerging problem in veterinary medicine and the zoonotic potential of many of these agents is a significant consideration for human health. The successful diagnosis, treatment and prevention of these infections is dependent upon firm understanding of the underlying immunopathology of the diseases in which there are unique tripartite interactions between the microorganism, the vector and the host immune system. Although significant advances have been made in the areas of molecular speciation and the epidemiology of these infections and their vectors, basic knowledge of the pathology and immunology of the diseases has lagged behind. This review summarizes recent studies of the pathology and host immune response in the major CVBDs (leishmaniosis, babesiosis, ehrlichiosis, hepatozoonosis, anaplasmosis, bartonellosis and borreliosis). The ultimate application of such immunological investigation is the development of effective vaccines. The current commercially available vaccines for canine leishmaniosis, babesiosis and borreliosis are reviewed.

Clinical management of canine babesiosis

OBJECTIVE

To review and summarize current information regarding epidemiology, pathogenesis, and pathophysiology leading to the various clinical syndromes associated with canine babesiosis. Diagnosis, treatment, preventative strategies, and zoonotic implications are discussed.

ETIOLOGY

Babesiosis is caused by hemoprotozoa of the genus Babesia. Numerous species of Babesia exist worldwide. An increased incidence of babesiosis is described, especially in North America. The babesial organism spends the majority of its life cycle within the erythrocyte of the definitive host, resulting in hemolysis, with or without systemic complications.

DIAGNOSIS

Definitive diagnosis depends on direct visualization of the organism on blood smear or polymerase chain reaction. A positive serologic antibody test indicates exposure with or without active infection.

THERAPY

Antiprotozoal drugs, antimicrobials, and supportive care are the mainstays of babesiosis therapy.

PROGNOSIS

Prognosis depends on the severity of disease, which in turn depends on both organism and host factors. Clinical syndromes associated with a poorer prognosis include red biliary syndrome, acute renal failure, acute respiratory distress syndrome, neurologic dysfunction, acute pancreatitis, cardiac dysfunction, and hypoglycemia.

Attenuated vaccines for tropical theileriosis, babesiosis and heartwater: the continuing necessity

Overwhelming evidence has accumulated of the effectiveness of immunization with live attenuated vaccines to control tick-borne diseases of livestock. Despite several disadvantages, vaccination with live attenuated organisms against tropical theileriosis, babesiosis and possibly heartwater constitutes one of the most cost-effective intervention strategies. Although great advances have been made through genomics and proteomics research, this has not yet translated into effective non-living vaccines. As a result, there is a continuing necessity to use available live vaccines in tick and tick-borne disease-control strategies adapted to conditions prevailing in many parts of the world.

Safety trial using the Leishmune vaccine against canine visceral leishmaniasis in Brazil

A group of 600 healthy and asymptomatic dogs from Brazilian canine visceral leishmaniasis endemic areas was vaccinated with three sc doses of Leishmune which is the industrialized formulation of the FML-saponin, recently licensed for commercialization in Brazil, which previously showed 76-80% vaccine efficacy against canine visceral leishmaniasis. Safety evaluation was performed for 14 days after each vaccine injection and disclosed transient reactions of local pain (40.87%), anorexia (20.48%), apathy (24.17%), local swelling reactions (15.90%), vomit (2.4%) and diarrhoea (1.5%). All effects showed significantly correlating declines, from the first to the third dose (p<0.0001). Most of the noticed reactions of pain (73%), anorexia (79%) and local swelling (84.7%) were mild. No significant differences between puppies and adults dogs were found in the number of adverse reactions. Adult dogs developed however, 94.5% of the small swelling reactions (<3 cm), and indicating that they are more resistant to the inflammatory response promoted by the saponins. No dead by anaphylaxis occurred, and only two dogs (0.1%) showed allergic reactions (facial oedema and itching) after the third dose. Transient alopecia on injection site occurred in only five poodles (0.28%) with total recovery and no need of treatment. All the mild adverse events in response to Leishmune injection were transient and disappeared before the injection of the following vaccine dose, confirming the tolerability of the vaccine. The Leishmune preparation was less haemolytic (HD(50)=180 microg/ml) than expected for a QS21 saponin-containing vaccine, indicating that its formulation with the FML antigen diminished the potential in vitro toxicity.

Immunity against Babesia rossi infection in dogs vaccinated with antigens from culture supernatants

Soluble parasite antigens (SPA) from different Babesia species have been shown earlier to induce protective immunity when used as vaccine. However, initial attempts to produce such vaccine against Babesia rossi infection using SPA from B. rossi culture supernatants were not or only partially successful. Here we show that when dogs were vaccinated with a vaccine comprising SPA from B. rossi combined with SPA from Babesia canis protective immunity against experimental challenge infection was induced. Immunity was reflected in reduced clinical signs that resolved spontaneously, and reduction of parasitaemia and SPA in the blood. Not a single infected erythrocyte could be found in blood smears of dogs that had been repeatedly boosted (three vaccinations in total). In contrast, three out of four control dogs required chemotherapeutic treatment to prevent death. The fourth control dog showed a transient parasitaemia that resolved spontaneously. Vaccination did not prevent the development of a transient anaemia. It is concluded that a vaccine containing a mixture of SPA obtained from in vitro culture supernatants of B. rossi and B. canis induces protection in dogs against heterologous challenge infection with B. canis (as shown before) or B. rossi.