Crimean-Congo hemorrhagic fever disease due to tick bite with very long incubation periods.

Background: Crimean-Congo hemorrhagic fever (CCHF) is a zoonotic viral disease with a high mortality rate, and is one of the viral hemorrhagic fever syndromes. The average mortality rate of CCHF is 3-30%. Research indicates that the longest incubation period after a tick bite is 12 days in CCHF disease. However, in clinical practice, we encounter patients with CCHF as a result of tick bites with much longer incubation periods (max. 53 days) than those reported in the literature. We present herein CCHF cases presumably infected through tick bites and having incubation periods longer than the upper limit reported in the literature.

Methods: We analyzed the cases of the 825 CCHF patients admitted to our hospital from 2007 to 2010 and found that 312 of them had undoubtedly been bitten by a tick. We searched the patient records for information on the incubation period and found that 12 patients had experienced an incubation period of over 12 days, which is the longest incubation period stated in the literature for patients definitely bitten by a tick.

Results: A total of 12 patients (eight males and four females, with a mean age of 45 years) were recruited into this study. Five (41.7%) of the 12 patients had positive CCHF virus-specific IgM antibodies, three (25%) had a positive reverse transcription polymerase chain reaction test for CCHF virus, and four (33.3%) had positive results in both tests during the acute and/or convalescent phase of the disease. In these cases, the interval between tick bite and the onset of symptoms was a mean of 23.6 days (range 13-53 days).

Conclusion: Physicians serving in endemic regions should be aware of these longer incubation periods after a tick bite. It is suggested that they perform more follow-ups on clinically and serologically highly suspected patients than they currently do.