Theileria orientalis Ikeda Genotype in Cattle, Virginia, USA

Abstract

Theileria orientalis Ikeda genotype is a parasite that causes a disease in cattle that results in major economic issues in Asia, New Zealand, and Australia. The parasite is transmitted by Haemaphysalis longicornis ticks, which have recently been reported in numerous states throughout the eastern United States. Concurrently, cattle in Virginia showed clinical signs consistent with a hemoprotozoan infection. We used amplicons specific for the major piroplasm surface protein and small subunit rDNA of piroplasms to test blood samples from the cattle by PCR. Bidirectional Sanger sequencing showed sequences with 100% identity with T. orientalis Ikeda genotype 2 sequences. We detected the parasite in 3 unrelated herds and from various animals sampled at 2 time points. Although other benign T. orientalis genotypes are endemic to the United States, detection of T. orientalis Ikeda genotype might represent a risk for the cattle industry in Virginia.

Keywords: Haemaphysalis longicornis; Ikeda genotype; Ixodidae; Theileria orientalis; United States; Virginia; anemia; cattle; infectious disease; parasites; theileriosis; tick-borne infections; ticks; vector-borne infections; zoonoses.

Figure 1

Blood smear of an animal from a farm in Albemarle County, Virginia, USA, that was infected with Theileria orientalis Ikeda genotype. There is evidence of a regenerative response to anemia (anisocytosis and polychromasia) and intracellular piroplasms within erythrocytes. Scale bar indicates 10 µm.

Figure 2

DNA sequences from 10 cattle from a farm in Albemarle County, Virginia, USA, infected with Theileria orientalis Ikeda genotype aligned with 3 GenBank sequences of T. orientalis genotype 2 for the major piroplasm surface protein. Alignment shows 100% consensus. Samples represent cattle from 6 different herds, and 2 samples were obtained at 2 time points. Pink indicates adenine, yellow indicates guanine, green indicates thymine, and purple indicates cytosine. Nucleotides at the top indicate the consensus sequence. The GenBank sequence THEPMiPI is RNA with uracil substituted for thymine.

Figure 3

Phylogenetic tree showing major piroplasm surface unit gene sequences for Theileria species. The tree uses reference sequences from the major genotypes for T. orientalis (4). Sequences from infected cattle in Virginia, USA, cluster with genotype 2 sequences. Numbers along branches are bootstrap values. Scale bar indicates nucleotide substitutions per site.

Figure 4

Phylogenetic tree showing small subunit rDNA gene sequences for Theileria species. Representative samples from cattle in 6 herds in Virginia, USA, cluster with the reference sequences for the Ikeda genotype. The next most closely related branch is composed of T. orientalis Chitose genotype and then T. orientalis Buffeli genotype. The outgroup is composed of a single reference sequence each for T. parva and T. annulata. Small subunit rDNA sequences for I4 and Al1 were of low quality (6.4% and 3.9%, respectively). Numbers along branches are bootstrap values. Scale bar indicates nucleotide substitutions per site.