Abstract
There has been a rapid increase in the number of scrub typhus cases in Guangdong Province, China. For this reason, an epidemiologic study was conducted to understand the characteristics of scrub typhus epidemics in Guangdong. From 2006 to 2013, the incidence of human cases increased from 0.4321 to 3.5917 per 100,000 with a bimodal peak in human cases typically occurring between May and November. To detect the prevalence of Orientia tsutsugamushi among suspected human cases and rodents, we performed ELISA tests of IgM/IgG and nested PCR tests on 59 whole blood samples from the suspected cases and 112 spleen samples from the rodents. Suspected cases tested positive for anti-O. tsutsugamushi IgM and IgG 66.1% (39/59) and 50.8% (30/59) of the time, respectively. Additionally, 20.3% (12/59) of blood samples and 13.4% (15/112) of spleen samples were positive for PCR. Phylogenetic analysis revealed that there were four definable clusters among the 27 nucleotide sequences of the 56-kDa antigen genes: 44.4% Karp (12/27), 25.9% Kato (7/27), 22.2% Gilliam (6/27) and 7.4% TA763 (2/27). We concluded many suspected cases may result in diagnostic errors; therefore, it is necessary to perform laboratory tests on suspected cases in hospitals. The high infection rate of O. tsutsugamushi among the limited rodents tested suggested that further rodent sampling throughout the province is necessary to further define high-risk areas. Furthermore, the multiple co-circulating genotypes of O. tsutsugamushi play a key role in the pervasiveness of scrub typhus in the Guangdong area.
Highlights
One billion people are affected with Scrub typhus [1]
The number of reported cases has increased yearly during surveillance periods and reached its highest peak in 2013 (Fig. 2). These reported cases were from 21 cities; of which, Guangzhou City reported the highest number of scrub typhus cases (34.3%) during the surveillance period, followed by Zhaoqing (17%), Yunfo (6.66%) and Qingyuan (5.67%)
The pathogen, O. tsutsugamushi, has been circulating among chigger mites, rodents, and humans, which has resulted in the rapid expansion of scrub typhus [15]
Summary
One billion people are affected with Scrub typhus [1]. Scrub typhus caused by O. tsutsugamushi is a major cause of acute febrile illnesses in the Asia-Pacific region. Descriptions of scrub typhus have been found in Chinese writings as early as 313 A.D. and were first described in modern literature in Japan in 1810 [2,3]. The O. tsutsugamushi strain Ikeda was originally isolated from a patient in 1979 in the Niigata Prefecture, Japan [4]. Scrub typhus is an endemic disease threatening a wide area of the Asia-Pacific rim, extending from.
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