Tularemia outbreak and after; effect of seasonal changes

Abstract

Tularemia is a zoonotic infectious disease caused by Francisella tularensis. In Yozgat, a total of 525 cases were identified between 2010 and 2016. A serious epidemic occurred with a total of 442 cases in 2010 and 2011 and the number of cases decreased in the later years. In our study, we investigated the association of seasonal factors (temperature, humidity, amount of precipitation, wind speed) with the tularemia epidemic which occurred in 2010 and 2011 and with the decrease in the number of cases in the later years. This study included tularemia cases seen in Yozgat and its districts between 2010 and 2016. Tularemia was defined as a microagglutination test (MAT) result of ? 1/160 or a 4-fold increase in MAT titer between two tests at least two weeks apart, in the presence of consistent clinical findings. Seasonal factors were recorded. The conformity of data to normal distribution was analyzed using the Shapiro-Wilk test. The Mann-Whitney U test was used with the results of Monte Carlo simulations to compare differences between two independent groups in terms of quantitative data. It was found that tularemia cases are more frequently seen in the spring and winter. Meteorological data showed that wind force was statistically significantly higher in the epidemic years than in the other years (p< 0.05). No statistically significant difference was found between mean air temperature, amount of precipitation, and humidity (p> 0.05). Our study found that wind velocity was significantly higher in the epidemic years than in the other years (p< 0.05) and this increase in wind velocity may have caused an increase in tick population and distribution. We believe that, rather than causing direct transmission of tularemia to humans, the increased tick population plays a key role in the maintenance of the life cycle of tularemia by causing transmission to rodents and domestic animals. © 2020 Ankara Microbiology Society. All rights reserved.