Observation on kinetes of Babesia ovata in the hemolymph of the vector tick Haemaphysalis longicornis

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.

Babesia ovata: Taxonomy, phylogeny and epidemiology

Babesia ovata, which is transmitted by Haemaphysalis longicornis, is an intraerythrocytic protozoan parasite of cattle. Based on its morphology, B. ovata is classified as a large-type Babesia. The developmental stages of B. ovata have been described both in cattle and the tick vector. In infected adult female ticks, the parasite is transovarially transmitted to the tick eggs. The sexual reproduction of B. ovata has been demonstrated in the tick midgut. The diagnostic tools that are currently available for the specific detection of B. ovata in cattle include microscopy and polymerase chain reaction assays. The development of improved molecular and serological diagnostic tools has been constrained by the limited availability of genetic data. B. ovata has been reported in cattle populations in Japan, Korea, China, Mongolia and Thailand. B. ovata was thought to be a benign parasite; however, infections in immuno compromised or Theileria orientalis-infected animals are clinically significant. Thus, control strategies aimed at minimizing the prevalence of B. ovata are vital. The taxonomy of B. ovata is unclear, and the phylogenetic position has not been well defined. Consequently, non-B. ovata species have sometimes been classified as B. ovata. In this review, we provide an outline of the lifecycle, geographical distribution, and control of B. ovata, and critically discuss the taxonomy and phylogeny of this bovine Babesia.

Molecular evidence of Babesia caballi (Nuttall and Strickland, 1910) parasite transmission from experimentally-infected SCID mice to the ixodid tick, Haemaphysalis longicornis (Neuman, 1901)

Molecular evidence that suggests the possible role of the ixodid tick, Haemaphysalis longicornis and its eggs in the transmission of equine Babesia caballi parasites is presented herein. Using polymerase chain reaction (PCR) to assay for DNA in parasites, presumably acquired by ticks that were allowed to feed on splenectomized-SCID mice, experimentally exposed to in vitro-cultivated B. caballi, we have obtained positive bands that corresponded to the expected B. caballi-specific 430bp gene fragment in 50% of female ticks used, and in 75 and 25% of eggs and larval progeny, respectively. Also, parasite DNA was detected in ticks, eggs and larvae as late as the 16th to the 20th day post-host infestation. Present findings support to the potential role of H. longicornis in the transmission of B. caballi parasites. Its capability, however, to successfully transmit the infection to horses under natural conditions in the field needs to be further ascertained. To our knowledge, this is the first documented study incriminating H. longicornis as a most and likely biological vector of equine babesias.