Effects of meteorological factors on scrub typhus in a temperate region of China

Abstract

Scrub typhus is emerging and re-emerging in many areas: climate change may affect its spread. To explore the effects of meteorological factors on scrub typhus, monthly cases of scrub typhus from January 2006 to December 2012 in the Laiwu district of temperate northern China were analysed. We examined the correlations between scrub typhus and meteorological factors (and their delayed effects). We built a time-series adjusted negative binomial model to reflect the relationships between climate variables and scrub typhus cases. The key determinants of scrub typhus transmission were temperature, relative humidity and precipitation. Each 1°C increase in monthly average temperature in the previous 3 months, each 1% increase in monthly relative humidity in the previous 2 months and each 1 mm increase in monthly precipitation in the previous 3 months induced 15·4%, 12·6% and 0·7% increases in the monthly number of cases, respectively. In conclusion, scrub typhus is affected by climate change in temperate regions.

Rapid increase of scrub typhus incidence in Guangzhou, southern China, 2006―2014

“…While high atmospheric pressure is thought to be adverse to mites’ survival [9]. The time lags in the effect of meteorological factors may be related to the life cycle of chigger mites as about 2–3 months [12] and the incubation period of the disease (mean of 10–12 days) [11]. Because of the nature of that a chigger normally feeds on its host only once in its life cycle and the infection transmitted by a chigger must have been derived from the female parent by transovarian transmission [12, 25], the infection rate and population density of larval trombiculid mites largely depend on those of the last generation and the habitat during the time between egg hatch and settling down on a host for a larvae, which are influenced by relative humidity and atmosphere pressure in previous about 1–2 months.…”

“…Two-sided p -values under 0.05 were considered statistically significant. Considering that the mean incubation period of scrub typhus in humans is 10–12 days [11] and that the life cycle of chigger is several months [12], we first examined possible time lags of the influence of each meteorological factor (0–3 months) on monthly incidence of scrub typhus. The most significant lag was then used in the negative binomial regression.…”

Diversification of Orientia tsutsugamushi genotypes by intragenic recombination and their potential expansion in endemic areas

“…Recent epidemiological data available in various resources (S1 Table), clearly demonstrates the gradual emergence of scrub typhus in several endemic countries (Fig 1). Even though the increasing number of reported cases of scrub typhus might be partly due to increased awareness and better surveillance systems in the developing countries [2,9], environmental change and human activity might be important factors contributing to the emerging trend [14–17]. Given that vector mites maintain the intracellular pathogen, ecological changes of the vector species in local endemic regions could be the primary cause of the emergence of scrub typhus, as recently observed in South Korea [15,16].…”

Analysis on epidemiological characteristics of 4 species natural-focal diseases in Shandong Province, China in 2009-2017: a descriptive analysis

“…Their density fluctuations are closely related to the seasonal distribution of scrub typhus cases, and the monthly distribution of scrub typhus cases was consistent with the fluctuation of Leptotrombidium scutellare[9, 30, 31]. Third, some studies have shown that meteorological factors affect the incidence of scrub typhus, such as temperature, sunlight, precipitation, etc[16, 32, 33]. The climatic conditions of Shandong Province from September to November may be most suitable for the occurrence of scrub typhus.…”