Epizootic Hemorrhagic Disease in Cattle, Western Turkey

In 2007, an outbreak of epizootic hemorrhagic disease (EHD) occurred in Turkey. On the basis of clinical investigation, 41 cattle were suspected to have EHD. Reverse transcription–PCR and sequence analyses indicated that the virus belonged to EHD virus serotype 6, thus confirming EHD virus infection of cattle in Turkey.


The Study
In July 2007, a 7-week outbreak of disease in cattle began in Mugla, Turkey. The disease was regarded as unusual or atypical for the region, and cases were reported to the Uludag University Faculty of Veterinary Medicine. Similar reports were also received from Izmir, Canakkale, and Istanbul through the end of August 2007. The cattle had stomatitis, swelling of eyelids, respiratory distress, nasal and ocular discharge, redness and scaling of muzzle and lips, lameness, and udder erythema, and some were recumbent (Table 1). Body temperatures were elevated (39.7°C-41.1°C), except for 1 animal, whose temperature was 37.5 °C, below the reference range for cattle (37.8°C-39.2°C). However, heart rates (mean 72 ± 3 beats/min) and respiratory rates (mean 24 ± 4 breaths/min) were within reference ranges of 60-80 beats/min and 10-30 breaths/min, respectively, for cattle with suspected disease. Cattle with EHD had tachycardia and tachypnea ( Table 2). Causes of mucosal disease, stomatitis, and fever, including bovine viral diarrhea, foot and mouth disease, and infectious bovine rhinotracheitis, were considered, but the rate of spread and some of the clinical signs ruled out these diseases. However, the clinical signs of the disease were consistent with either EHD or BTV infection (6,(8)(9)(10). These diseases were therefore considered as requiring further laboratory-based diagnostic assays.
A total of 41 blood samples were obtained from the affected cattle (35 Holsteins and 6 Brown Swiss, 2-5 years of age). Samples were obtained in tubes with and without EDTA. Complete blood analysis showed that 5 of the cattle with EHD had low leukocyte counts (online Appendix Table, available from www.cdc.gov/EID/content/15/2/317-appT.htm). After use for hematologic analysis, samples were stored at -30°C until virologic and serologic tests could be performed. Samples from the 41 animals were tested by ELISA for bovine viral diarrhea virus antigens; results were negative. To isolate virus, we spread unclotted blood samples onto baby hamster kidney-21 (BHK) cells.
Because EHDV had never been observed in Turkey, no diagnostic procedures were available. We therefore submitted selected samples ( (15). The 4 serum samples were also tested for EHDV-specifi c antibodies by ELISA (12); only 1 sample was found to contain antibodies to EHDV. Conventional RT-PCR of RNA extracted from the 11 original blood samples gave inconclusive results. Agarose gel electrophoresis indicated no product of the expected size. However, virus was isolated from 6 of the blood samples by using KC cells (dsRNA virus reference collection at the Institute for Animal Health, reference collection nos. TUR2007/01-06). These 6 samples and the 1 original positive cell culture were further tested by serotype-specifi c RT-PCRs that targeted segment 2 for identifi cation of EHDV serotype. This analysis identifi ed all viruses as EHDV-6, sharing 95.7% nucleotide sequence identity (segment 2, 110-670 bp) with the EHDV reference strain 318.

Conclusions
Of the selected samples submitted for BTV and EHDV testing, the positive identifi cation of EHDV RNA supports initial clinical identifi cation of an EHD outbreak in Turkey. The negative results from the blood samples may have resulted from degradation of viral RNA during transfer to the laboratory or insuffi cient sensitivity in the conventional RT-PCR. The propagation of another 6 virus isolates (TUR2007/01-06) by passage through KC cells indicates that virus was indeed present in the original blood samples, although not detected by conventional RT-PCR.
That only 1 of the 4 original serum samples was positive for EHDV antibodies by ELISA can be explained by time of sample collection. Antibodies to BTV can be detected from 8 days after infection (11); these samples may have been collected during the early stages of infection, before development of the immune response.
This study confi rms EHDV infection of cattle in Turkey. EHD needs to be considered in the differential diagnosis of cattle with clinical signs that include fever; stomatitis; lameness; salivation; redness and scaling of the nose