This study reports an outbreak of oriental theileriosis in dairy cattle imported to Vietnam from Australia. Following clinical and pathological diagnoses, a total of 112 cattle blood samples were divided into three groups and tested using multiplexed tandem PCR. Group 1 were from aborted heifers in Vietnam; group 2 were from cattle before shipment from group 1 cattle and group 3 were from the same batch of cattle but transported to Taiwan. Theileria orientalis DNA was detected in 72·3% cattle. The prevalences of T. orientalis in groups 1, 2 and 3 were 77·6, 86·9 and 57·5%, respectively, and the difference in prevalence was significant between groups 1 and 3 (P < 0·0001). The infection intensities of genotypes chitose and ikeda of T. orientalis were higher in groups 1 (57 721 and 33 709, respectively) and 3 (5897 and 61 766, respectively) than those in group 2 (2071 and 6331, respectively). Phylogenetic analyses of the major piroplasm surface protein sequences revealed that genotypes chitose and ikeda determined herein were closely related to those previously reported from Australia. This first report of an outbreak of oriental theileriosis in imported cattle emphasizes improved measures for the export and import of cattle infected with T. orientalis.

Currently, prevention of canine Dirofilaria immitis infection relies on use of therapeutic agents that effectively eliminate infective larvae inoculated by mosquitoes. 5 These agents also kill circulating D. immitis microfilariae. 5 Because adverse reactions may occur in microfilaremic dogs given larvacides, it is important to determine that dogs are parasite free prior to beginning seasonal prophylactic medication. 5 For many years, the modified Knotts test, a procedure to detect microfilariae, has been used as a screening test to determine if dogs could be given prophylactic treatment for D. immitis. 5,6 Because of concern for sterile or unisexual infections, in which no microfilariae are produced, serologic tests to detect antigens produced by adult D. immitis were developed. 2,3,6,8,9 The serologic test kits, using enzyme-linked immunosorbent assay (ELISA) techniques, are commercially available. They are considered specific for D. immitis somatic antigen and are reported to be a sensitive indicator of infection in dogs having worm burdens > 10. 3,5,6,9 Most testing of the commercially available kits has been done under laboratory conditions or in regions considered hyperendemic for D. immitis infection. 1-3,6,8,9 A more recent survey has been done in a hypoendemic region. 7 In lowincidence areas, D. immitis may still cause serious clinical disease in infected animals. Additionally, apparently healthy dogs harboring D. immitis may serve as a reservoir of infection for other animals. During the height of the 1991 heartworm testing season in the northeastern United States (March-July) 0.41% (13/3,148) of dogs tested for the presence of D. immitis microfilariae in the Clinical Laboratory at Angell Memorial Animal Hospital were positive. Occult heartworm tests were not done routinely, but 4 of 45 serum samples tested were positive for adult D. immitis antigen. Microfilariae were detected in none of these. Only 1 of these dogs was treated with D. immitis adulticide. The other 3 were considered clinically healthy and given monthly doses of ivermectin or milbemycin oxime throughout the summer and early fall. These data prompted a more systematic assessment of occult heartworm testing in this non hyperendemic area, which was done during part of the 1992 heartworm season. All blood samples submitted to the Clinical Pathology Laboratory at Angell Memorial Animal Hospital for "heartworm checks" between May and July 1992 were evaluated for microfilariae by filtration techniques and for adult D. immitis antigen using 2 commercially available kits. a,b Samples from 1,359 dogs were tested, and the results were compared. If discrepancies among test results occurred or a positive result