Mapping the Distribution of Anthrax in Mainland China, 2005-2013

Abstract

Background: Anthrax, a global re-emerging zoonotic disease in recent years is enzootic in mainland China. Despite its significance to the public health, spatiotemporal distributions of the disease in human and livestock and its potential driving factors remain poorly understood.

Methodology/principal findings: Using the national surveillance data of human and livestock anthrax from 2005 to 2013, we conducted a retrospective epidemiological study and risk assessment of anthrax in mainland China. The potential determinants for the temporal and spatial distributions of human anthrax were also explored. We found that the majority of human anthrax cases were located in six provinces in western and northeastern China, and five clustering areas with higher incidences were identified. The disease mostly peaked in July or August, and males aged 30-49 years had higher incidence than other subgroups. Monthly incidence of human anthrax was positively correlated with monthly average temperature, relative humidity and monthly accumulative rainfall with lags of 0-2 months. A boosted regression trees (BRT) model at the county level reveals that densities of cattle, sheep and human, coverage of meadow, coverage of typical grassland, elevation, coverage of topsoil with pH > 6.1, concentration of organic carbon in topsoil, and the meteorological factors have contributed substantially to the spatial distribution of the disease. The model-predicted probability of occurrence of human cases in mainland China was mapped at the county level.

Conclusions/significance: Anthrax in China was characterized by significant seasonality and spatial clustering. The spatial distribution of human anthrax was largely driven by livestock husbandry, human density, land cover, elevation, topsoil features and climate. Enhanced surveillance and intervention for livestock and human anthrax in the high-risk regions, particularly on the Qinghai-Tibetan Plateau, is the key to the prevention of human infections.

Fig 1. Temporal distribution and demographic profile of anthrax cases in mainland China during 2005–2013.

(A) Temporal distribution of human and livestock cases of anthrax. (B) Average human anthrax incidences stratified by gender and age group.

Fig 2. Standardized average annual incidences and spatial-temporal clusters of human anthrax at the county level.

The cumulative numbers of livestock anthrax cases at the provincial level during 2005–2013 are overlapped.

Fig 3. Predicted risks of human anthrax at the county level in China based on the BRT model and covariates for the period of 2012–2013.

The BRT model was created and validated based on the data from 2005 to 2011, and the red circles represent the reported human anthrax cases from 2012 to 2013.