Geographical factors and air raid alarms influence leptospirosis epidemiology in Ukraine (2018-2023)

Abstract

Leptospirosis, a widespread zoonotic disease caused by Leptospira spp., affects approximately 1 million people annually and causes about 58,000 deaths worldwide. This study examines the epidemiology of leptospirosis in Ukraine from 2018 to 2023, focusing on the impact of weather and geographical factors on disease transmission. Data from the Ukrainian Centre for Disease Prevention and Control, the Ukrainian Hydrometeorological Center, and the State Agency of Water Resources of Ukraine were analyzed. The country was divided into five regions: North, East, Center, South, and West. For the visualization, but not the quantitative analyses, the notification rate (NR) of leptospirosis was classified into three categories: low, moderate, and high. The highest NR were in Zakarpattia, Ivano-Frankivsk, Khmelnytskyi, Mykolaiv, and Kherson regions, with Zakarpattia having the highest rate. We analyzed whether various weather parameters-such as average annual temperature, precipitation, days with precipitation ≥1 mm, and relative humidity-were associated with the notification rate (NR) of leptospirosis, but no significant correlations were detected. However, a significant positive correlation was observed between higher density of the river network and NR (Kendall's rank correlation, r = 0.65, p = 0.0005), indicating that geographical factors may play an important role in Leptospira transmission. Additionally, we found a significant correlation between monthly air raid alarm frequency and the NR of leptospirosis cases in 2023. Case reports of individuals contracting leptospirosis in bomb shelters further support the hypothesis that air raid evacuations impact leptospirosis epidemiology. Further investigation is needed to fully understand this relationship and its implications.

Keywords: Epidemiology; Leptospirosis; Shelters; Ukraine; Weather; Zoonosis.

Fig. 1

Average annual rate of confirmed leptospirosis cases per 100,000 population, European Union/European Economic Area, 2010–2021. Adapted from ECDC. The average number of leptospirosis cases in Ukraine is one of the highest in Europe, amounting to 0.73 per 100,000 people for the period 2010–2021. For comparison, in neighboring countries, the rate is 0.1 in Poland, 0.15 in Slovakia, and 0.34 in Romania.

Fig. 2

A - Average Annual Temperature in the period 2018–2023 (light blue: less than 9.5 °C; blue: 9.5 to 10.5 °C; dark blue: greater than 10.5 °C). The average annual temperature was higher in Zakarpattia and the central-southern part of Ukraine. B - Average Annual Precipitation in the period 2018–2023 (light blue: less than 539 mm; blue: 539 to 608 mm; dark blue: greater than 608 mm). The average annual precipitation was higher in the western part of Ukraine. C - Annual Number of Days with Precipitation ≥1 mm in the period 2018–2023 (light blue: less than 93.2 days; blue: 93.2 to 113 days; dark blue: greater than 113 days). The number of days with precipitation was higher in the western part of Ukraine. D - Annual Average Relative Humidity in the period 2018–2023 (light blue: less than 73.00 %; blue: 73.00 to 75.8 %; dark blue: greater than 75.8 %). Relative humidity was higher in the western part of Ukraine, with peaks in the Volyn and Lviv regions. E - Average Density of River Network (km/km²) (light blue: less than 0.3; blue: 0.3 to 0.5; dark blue: greater than 0.5). The highest river network density was in the western part of Ukraine – Zakarpattia, Lviv, Ivano-Frankivsk, and Chernivtsi regions. F - Air Alarm Duration (light blue: less than 714.17 h; blue: 714.17 to 2254.9 h; dark blue: greater than 2254.9 h). The longest durations of air alarms were in Kharkiv (4295.15 h) and Zaporizhzhia (4067.38 h). The grey zone represents occupied territories with NA (Not Available) data. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

A - Monthly Leptospirosis Infections and Air Alarms (Blue bars represent the count of people infected with leptospirosis each month. Red line with markers represents the corresponding air alarm values for each month); B- Number of alarms announced depending on the weather: Sun – sunny weather, Moon – nighttime weather, Cloud – cloudy weather, Fog (wavy lines) – foggy weather, Partly Cloudy (sun partially covered by a cloud) – partly cloudy weather, Cloudy Night (moon with cloud) – cloudy night weather, Rain – rainy weather, Snow – snowy weather. The highest number of alarms was announced during cloudy weather, while the lowest was during foggy weather. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 4

Seasonal and Weather Distribution in 2023 in Zakarpattia Region. The top chart shows that in 2023, the majority of leptospirosis cases in Zakarpattia were concentrated in late summer and early autumn, with 25 out of 150 cases reported in August and 47 in September. The bottom chart illustrates the changes in average temperature and total monthly precipitation in 2023, alongside leptospirosis cases. The highest rainfall was recorded in June and July.