Increased incidence of Lyme borreliosis in southern Sweden following mild winters and during warm, humid summers

Abstract

The aim of the present study was to investigate the long-term incidence rate of Lyme borreliosis and, additionally, to determine whether a correlation exists between climatic factors and summer-season variations in the incidence of Lyme borreliosis. Climatic variability acts directly on tick population dynamics and indirectly on human exposure to Lyme borreliosis spirochetes. In this study, conducted in primary healthcare clinics in southeastern Sweden, electronic patient records from 1997-2003 were searched for those that fulfilled the criteria for erythema migrans. Using a multilevel Poisson regression model, the influence of various climatic factors on the summer-season variations in the incidence of erythema migrans were studied. The mean annual incidence rate was 464 cases of erythema migrans per 100,000 inhabitants. The incidence was significantly higher in women than in men, 505 and 423 cases per 100,000 inhabitants, respectively (p<0.001). The summer-season variations in the erythema migrans incidence rate correlated with the monthly mean summer temperatures (incidence rate ratio 1.12; p<0.001), the number of winter days with temperatures below 0 degrees C (incidence rate ratio 0.97; p<0.001), the monthly mean summer precipitation (incidence rate ratio 0.92; p<0.05), and the number of summer days with relative humidity above 86% (incidence rate ratio 1.04; p<0.05). In conclusion, Lyme borreliosis is highly endemic in southeastern Sweden. The climate in this area, which is favourable not only for human tick exposure but also for the abundance of host-seeking ticks, influences the summer-season variations in the incidence of Lyme borreliosis.

Erythema migrans nach Infektion durch Borrelia afzelii oder Borrelia garinii: Abhängigkeit des klinischen Erscheinungsbildes vom Geschlecht der Patienten

“…Most of the individuals in our study sustained their tick bites in June, corresponding well with the vacation months and with earlier European data (24,30) Distribution of the tick bites predominantly on the lower limbs agrees with earlier studies in Sweden (2,13).…”

Local landscape effects on population dynamics of Ixodes ricinus

“…It is important to notice that we did not sample for ticks in April and May. In southern Sweden tick activity can peak already in April-May (Bennet et al, 2006). Irrespective of the starting month, the peak tick activity in the area around Stockholm continues, as we can see in our data, till June.…”

Destruction of spirochete Borrelia burgdorferi round-body propagules (RBs) by the antibiotic Tigecycline

“…In central Europe and Scandinavia, the disease is highly endemic. Cases of B. burgdorferi in southern Sweden alone rose from 164 (in 1992) to 664 (in 2000) per 100,000 population (29). Over 100 strains of Borrelia sp.…”