Comparison of PCR, culture and microscopy of blood smears for the diagnosis of anthrax in sheep and cattle

AIMS: To compare microscopy, culture and PCR for the diagnosis of anthrax in blood samples from sheep and cattle. METHODS AND RESULTS: Blood samples were stored at room temperature and at 37 degrees C after receipt, over a period of 15-17 days. Aliquots were plated onto blood agar and blood smears were prepared. Following microscopic examination, DNA was extracted from blood smears and subjected to a multiplex PCR assay targeting the Ba813, cap and lef markers. CONCLUSIONS: PCR provided the most reliable means for the detection of Bacillus anthracis in deteriorating blood samples (15-17 days) and was also successful in diagnosing anthrax in blood smears that had been stored for 6 years and a blood sample which had been stored for 18 months at -20 degrees C. While less successful than PCR, culture for B. anthracis on 7% sheep blood agar was typically more reliable (2-17 days) than the examination of blood smears (2-6 days) for encapsulated bacilli. SIGNIFICANCE AND IMPACT OF THE STUDY: This work demonstrated the superiority of PCR for the diagnosis of anthrax from blood smear scrapings, particularly when microscopy is unreliable.