Molecular characterization of a gene encoding a 29-kDa cytoplasmic protein of Babesia gibsoni and evaluation of its diagnostic potentiality

Analysis of Genetic Diversity of cytb gene from Babesia gibsoni Isolates from Naturally Infected Dogs in Karnataka, India

PURPOSE

The study aimed to investigate genetic diversity in Babesia gibsoni, the causative agent of canine babesiosis, and to assess the presence of atovaquone-resistant isolates in naturally infected dogs.

METHODS

A total of 24 blood samples confirmed for B. gibsoni infection was subjected to PCR amplification and sequencing based on cytb gene. Genetic characterization of B. gibsoni as well as attempts to detect the point mutation rendering atovaquone resistance was carried out based on the analysis of nucleotide sequence of cytb gene using bioinformatics software.

RESULTS

The findings indicated that the B. gibsoni isolates in the investigation exhibited a high nucleotide identity with the Asian genotype, ranging from 98.41 to 98.69%. Notably, none of the isolates carried cytb gene variants associated with atovaquone resistance. Phylogenetic analysis revealed clustering of most isolates with those from Japan and China, except for one isolate forming a distinct subclade. Haplotype network analysis indicated a high diversity with 22 distinct haplotypes among the B. gibsoni isolates, emphasizing the genetic variability within the studied population.

CONCLUSION

In conclusion, the cytb gene exhibited remarkable conservation among the twenty-four B. gibsoni isolates studied and the study represents the first genetic diversity assessment of B. gibsoni using the cytb gene in dogs from India. These findings shed light on the genetic characteristics of B. gibsoni in the region and provide valuable insight for addressing the challenges posed by this life-threatening disease in dogs.

Comparison of heat shock protein 70 kDa and 18S rDNA genes for molecular detection and phylogenetic analysis of Babesia vogeli from whole blood of naturally infected dogs

A total of 300 blood samples of domiciliated dogs in rural and urban areas of southeast Rio de Janeiro State, Brazil, were used to compare the 18S ribosomal DNA region (18S rDNA) and the heat shock protein 70 kDa (hsp70) gene for molecular detection of Babesia vogeli and to perform a phylogenetic study comparing the two genes for B. vogeli classification. Using conventional polymerase chain reaction (cPCR) of 18S rDNA and hsp70 sequences, we were able to detect B. vogeli with the same sensitivity (96.15%) and specificity (99.63%). However, sequencing revealed one false positive (Rangelia sp.) for 18S rDNA that was not detected by hsp70. This is the first report of an organism closely related to the Rangelia vitalii parasite of dogs in Brazil. In the hsp70-cPCR and hsp70-qPCR comparison, 15.66% of samples were considered positive by quantitative (q)PCR, significantly more than was detected by cPCR (8.66%). In addition to the high conservation of the 18S rDNA, phylogenetic analysis showed that the hsp70 gene can be used to describe phylogenetic relationships between canine piroplasmids with more accuracy than 18S rDNA. According to these findings, the qPCR method has greater sensitivity than cPCR for detection of B. vogeli in naturally infected dogs. The hsp70-qPCR detection limit was 10 copies, with an efficiency of 100.30% and a determination coefficient (R²) of 0.998. The development of this qPCR method provides a highly sensitive approach for B. vogeli molecular detection and a tool that is capable of quantifying parasitemia levels in whole blood samples from dogs. The primers and probes were designed to be specific for B. vogeli, though analytical specificity of the assay has not been tested in vitro with DNA of certain Babesia species that infect dogs. The hsp70 gene is a precise molecular marker for Babesia phylogeny, especially species that infect dogs.

Initial development of Babesia ovata in the tick midgut

The initial development of Babesia ovata in the midgut of the vector tick Haemaphysalis longicornis has been demonstrated through in vitro and in vivo studies. Although the research on the partial developmental cycles of B. ovata in the tick midgut was performed in our previous study by using ticks fed on experimentally B. ovata-infected cattle, detailed information on the developmental stages of B. ovata in H. longicornis was limited. This report describes the sequential development of stages of B. ovata in an in vitro study using B. ovata-infected erythrocytes and tick midgut contents. The in vivo study also confirmed the developmental stages in the midgut contents of artificially B. ovata-infected ticks. In this observation, we have recognized the distinct forms of B. ovata developmental stages in the tick midgut; the aggregation forms and ray bodies with shorter spikes and light-stained cytoplasm were shown by Giemsa staining. The similarities and differences of the stages as compared to previous reports have been discussed.

Establishment of a novel tick-Babesia experimental infection model

Ticks are potent vectors of many deadly human and animal pathogens. Tick-borne babesiosis is a well-recognized malaria-like disease that occurs worldwide and recently has attracted increased attention as an emerging zoonosis. Although the proliferation of Babesia organisms is essential in the vectors, their detailed lifecycle with time information for migration in ticks remains unknown. A novel study model for the elucidation of the migration speed of Babesia parasites in their vector tick, Haemaphysalis longicornis, has been developed using an artificial feeding system with quantitative PCR method. The detectable DNA of Babesia parasites gradually disappeared in the tick midgut at 1 day post engorgement (DPE), and in contrary increased in other organs. The results indicated that the Babesia parasite passed the H. longicornis midgut within 24 hours post engorgement, migrated to the hemolymph, and then proliferated in the organs except the midgut. This time point may be an important curfew for Babesia parasites to migrate in the tick lumen. We also visualized the Babesia parasites in the experimentally infected ticks and in their eggs using IFAT for detecting their cytoskeletal structure, which suggested the successful tick infection and transovarial transmission of the parasite. This model will shed light on the further understanding of tick-Babesia interactions.

New Molecules in Babesia gibsoni and their application for diagnosis, vaccine development, and drug discovery

Babesia gibsoni is an intraerythrocytic apicomplexan parasite that causes piroplasmosis in dogs. B. gibsoni infection is characterized clinically by fever, regenerative anemia, splenomegaly, and sometimes death. Since no vaccine is available, rapid and accurate diagnosis and prompt treatment of infected animals are required to control this disease. Over the past decade, several candidate molecules have been identified using biomolecular techniques in the authors' laboratory for the development of a serodiagnostic method, vaccine, and drug for B. gibsoni. This review article describes newly identified candidate molecules and their applications for diagnosis, vaccine production, and drug development of B. gibsoni.

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.

Immunogenicity and growth inhibitory efficacy of the prime-boost immunization regime with DNA followed by recombinant vaccinia virus carrying the P29 gene of Babesia gibsoni in dogs

In recent studies, heterologous prime-boost approaches, employing plasmid DNA and viral vector pathogen-delivering sequences, have been considered an effective protection strategy for intracellular parasite infections. Here, we evaluated the efficacy of such a strategy against the canine Babesia gibsoni infection. The DNA (pCAGGS-P29) and recombinant vaccinia virus (vvP29) both encoding the P29 of B. gibsoni were used in this study. The dogs were immunized 3 times with priming DNA and boosted once with recombinant virus. The dogs immunized with P29 developed a significant level of IgG2 antibody against P29. The response was strongly boosted by the inoculation of vvP29. The peripheral IFN-gamma responses of the dogs immunized with P29 were significantly higher than those of controls after the parasite inoculation. Moreover, the P29 immunized group showed a significantly low level of parasitemia. In conclusion, this study supports the efficacy of a prime-boost strategy for dogs against canine B. gibsoni infection.

Canine babesiosis: from molecular taxonomy to control

Canine babesiosis is a clinically significant emerging vector-borne disease caused by protozoan haemoparasites. This review article considers recent literature pertaining to the taxonomic classification of Babesia and Theileria species affecting dogs and the geographical distribution of these parasites. The diagnosis of canine babesiosis by traditional, molecular and serological methods is reviewed, together with recent advances in our understanding of the pathophysiology of piroplasmosis, and of the treatment and prevention of this disease.

Babesia gibsoni rhoptry-associated protein 1 and its potential use as a diagnostic antigen

A cDNA encoding the rhoptry-associated protein 1 (RAP-1) homologue was obtained by immunoscreening an expression library prepared from Babesia gibsoni merozoite mRNA. The complete nucleotide sequence of the gene was 1740bp. Computer analysis suggested that the sequence contains an open reading frame of 1425bp encoding an expected protein with a molecular weight of 52kDa. Based on the sequence similarity, this putative protein was designated as the B. gibsoni RAP-1 (BgRAP-1). The BgRAP-1 gene was expressed in the Escherichia coli BL21 strain, and the recombinant BgRAP-1 was used as the antigen in the enzyme-linked immunosorbent assay (ELISA). The results can differentiate between the B. gibsoni-infected dog sera and the Babesia canis infected dog sera or the normal dog sera. Furthermore, the antibody response against the recombinant protein was maintained during the chronic stage of infection, indicating that the recombinant BgRAP-1 protein might be a useful diagnostic antigen for the detection of antibodies to B. gibsoni infection in dogs.

Molecular characterization of a novel 32-kDa merozoite antigen of Babesia gibsoni with a better diagnostic performance by enzyme-linked immunosorbent assay

We cloned and expressed a novel gene encoding a 32-kDa merozoite protein of Babesia gibsoni (BgP32). The length of nucleotide sequence of the cDNA was 1464 bp with an open reading frame of 969 bp. The truncated recombinant BgP32 (rBgP32) without a signal peptide and C-terminal hydrophobic sequence was expressed in Escherichia coli as a soluble glutathione-S-transferase (GST) fusion protein. Western blotting demonstrated that the native protein was 32-kDa, consistent with molecular weight of the predicted mature polypeptide. Enzyme-linked immunosorbent assay (ELISA) using rBgP32 detected specific antibodies from 8 days to 541 days post-infection in the sequential sera from a dog experimentally infected with B. gibsoni. Moreover, the antigen did not cross-react with B. canis subspecies and closely related protozoan parasites, indicating that rBgP32 is a specific diagnostic antigen. Analysis of 47 sera taken from dogs with anaemic signs revealed that rBgP32 detected a higher proportion of B. gibsoni seropositive samples (77%) than its previously identified rBgP50 (68%) homologue. These results indicate that the BgP32 is a novel immunodominant antigen of B. gibsoni, and rBgP32 might be useful for diagnosis of B. gibsoni infection.