Human babesiosis, an emerging tick-borne disease in the People's Republic of China

Abstract

Babesiosis is a typical zoonotic, emerging disease caused by a tick-borne intraerythrocytic protozoan of Babesia spp. that also can be transmitted by blood transfusion. Babesiosis imposes an increasing public-health threat. We reviewed and mapped epidemiological studies on Babesia in vectors and/or rodents in the People's Republic of China (P.R. China) and found that B. microti was the predominant species detected in the investigated regions such as Heilongjiang, Zhejiang, Fujian provinces and Taiwan island. We reviewed a series of sporadic human babesiosis cases collected from 1940's to 2013, in Yunnan, Inner Mongolia, Taiwan and Zhejiang and other regions including a main endemic area of malaria on the China-Myanmar border areas in P.R. China. Clinical manifestations of human babesiosis were also reviewed. Human babesiosis may have previously been overlooked in P.R. China due to a lack of medical awareness and the limitation of clinical diagnostic methods.

Figure 1

Giemsa-stained thin blood smears showing the similarities of the intraerythrocytic ring form stages of B. microti and P. falciparum , showing an intraerythrocytic ring form stage of B. microti (thick arrow) and ring form stage of P. falciparum (thin arrow); Original magnification × 1,000. (A. Ring form stage of B. microti, B. Ring form stage of P. falciparum).

Figure 2

Geographic areas where endemic areas of human babesiosis and ixodes tick vectors or wild rodents infected with B. microti in China. Light green colors denote areas where the rodents that acted as the reservoir hosts in transmitting Babesia were detected; Pink colors denote areas where ixodes tick vectors transmitting Babesia were detected; Red pillars denote areas where human babesiosis reported, height of the pillars denote the number of reported babesiosis cases. White colors designate areas where no survey been carried on Babesia in ticks or rodents, despite some areas with reported human babesiosis cases.

Figure 3

Human babesiosis cases reported in China from 1930s up to 2013. Tread fitting curve denotes the development of human babesiosis cases from 1930s to 2014. Totally, assuming the cases reported by Hung et al. were human babesiosis, about 27 babesiosis cases that have been reported in China. About a third of the 27 babesiosis cases that have been reported in China were occurred before 1980 which were focused during 1940s and two thirds thereafter.

Figure 4

Phylogenetic relationships of B. microti strains using maximum-likelihood analysis by MEGA 5.0. Distances were estimated by the Kimura 2-parameter model and the numbers above the branch demonstrate bootstrap support from 1000 replications. The 18S rRNA gene and beta-tubulin gene sequence of P. falciparum fragile (JQ627152 and M31205) were included in the trees as outgroups. A. based on sequences coding 18S rRNA gene of B. microti; B. based on sequences coding beta-tubulin gene of B. microti, (originated from Goethert HK and Telford SR, 3rd [59], and modified from Zhou X et al. [58].