Babesiosis as a potential threat for bovine production in China

Abstract

Babesiosis is a tick-borne disease with global impact caused by parasites of the phylum Apicomplexa, genus Babesia. Typically, acute bovine babesiosis (BB) is characterized by fever, anemia, hemoglobinuria, and high mortality. Surviving animals remain persistently infected and become reservoirs for parasite transmission. Bovids in China can be infected by one or more Babesia species endemic to the country, including B. bovis, B. bigemina, B. orientalis, B. ovata, B. major, B. motasi, B. U sp. Kashi and B. venatorum. The latter may pose a zoonotic risk. Occurrence of this wide diversity of Babesia species in China may be due to a combination of favorable ecological factors, such as the presence of multiple tick vectors, including Rhipicephalus and Hyalomma, the coexistence of susceptible bovid species, such as domestic cattle, yaks, and water buffalo, and the lack of efficient measures of tick control. BB is currently widespread in several regions of the country and a limiting factor for cattle production. While some areas appear to have enzootic stability, others have considerable cattle mortality. Research is needed to devise solutions to the challenges posed by uncontrolled BB. Critical research gaps include risk assessment for cattle residing in endemic areas, understanding factors involved in endemic stability, evaluation of parasite diversity and pathogenicity of regional Babesia species, and estimation of whether and how BB should be controlled in China. Research should allow the design of comprehensive interventions to improve cattle production, diminish the risk of human infections, and increase the availability of affordable animal protein for human consumption in China and worldwide. In this review, we describe the current state of BB with reference to the diversity of hosts, vectors, and parasite species in China. We also discuss the unique risks and knowledge gaps that should be taken into consideration for future Babesia research and control strategies.

Keywords: Apicomplexa; Babesia spp.; Bovine babesiosis; Chinese cattle industry; P. R. China; Tick-borne diseases.

Fig. 1

Geographical distribution of Babesia species detected in bovines in China. Babesia bovis (blue square) and B. bigemina (yellow square) are the most widely distributed species, following B. orientalis (black square) mostly endemic to the south of Yangtze river; the endemic areas of other species including B. major (dark green square), B. ovata (red square), B. U sp. Kashi (light blue square), B. motasi (purple square), and B. venatorum (green square) seem limited according to the present data, which may be due to the lack of widespread sampling and detection. The pathology, tick vector transmission stage, and type of hosts are shown. NA indicates not available

Fig. 2

Giemsa-stained thin blood smear of bovine Babesia spp. Intraerythrocytic forms of B. bovis (a), B. bigemina (b), B. ovata (Wenchuan isolate) (c), B. major (Yili isolate) (d), and B. U sp. Kashi (e) were obtained from experimentally splenectomized cattle. Intraerythrocytic forms of B. orientalis (f) were obtained from an experimentally splenectomized water buffalo and B. motasi (g) from an experimentally infected sheep. Magnification ×1000