Introduction to Special Issue on Pathogens in China

China is located in central and eastern Asia, with a land area of 9.6 million square kilometers and a cross-tropical, temperate, and cold belt region. There are not only a great variety of mosquitoes, ticks, and other hematophagous arthropods, but also a large number of wild animals in the vast region and complex natural environment in China. Furthermore, the rapid growth of the agricultural industry including the large-scale production of poultry (chickens and ducks) and livestock (pigs, cattle, sheep, etc.) also increases the number of potential host animals. The presence of numerous and widely distributed blood-feeding arthropods and animals not only provides favorable conditions for the circulation and expansion of vector-borne pathogens in nature, but also increases the prevalence of various vector-borne diseases that pose great challenges to the public health of society in China, and the world as well. Owing to the Chinese government's emphasis on public health and huge investment, the incidence of vector-borne diseases and zoonoses in China has been significantly reduced. Several vector-borne diseases such as kala-azar, schistosomiasis, and malaria have been almost eliminated in China, but there remain multiple vector-borne and zoonotic disease epidemics of public health concern. There are 39 notifiable infectious diseases in China by law, including vector-borne or zoonotic infectious diseases, such as plague, brucellosis, Japanese encephalitis (JE), dengue fever, highly pathogenic avian influenza, and rabies. These diseases not only exist, but also sometimes appear as large outbreaks in different regions in China. In addition, new pathogens and emerging infectious diseases, such as severe fever with thrombocytopenia syndrome virus, and human infection of highly pathogenic avian influenza (H7N9, H5N1), are emerging. Vector-borne and zoonotic infections remain a major public health challenge in China.

The Vector-Borne and Zoonotic Diseases Special Issue on Pathogens in China focuses on the pathogens, hosts, and as appropriate the vectors involved in the transmission cycles of vector-borne and zoonotic infections that are prevalent in China. Included are bacterial pathogens such as Borrelia burgdorferi, Yersinia pestis, and Listeria ivanovii, as well as viral pathogens such as rabies virus, and human infection caused by highly pathogenic avian influenza virus, Japanese encephalitis virus (JEV), West Nile virus (WNV), tick-borne encephalitis virus (TBEV), and Getah virus (GETV). In the articles in this issue, there are examples such as plague and rabies, prevalent in China for many years, but also new pathogens that have been discovered in recent years, such as WNV, GETV, Akabane virus (AKBV), and Kaeng Khoi virus (KKV) spread by bats. Publications here not only introduce the epidemiological status of vector-borne or zoonotic infectious pathogens in China, including seroepidemiological survey data, but also report on the isolation and identification of TBEV, AKBV, and KKV and other vector-borne and zoonotic infections detected in China

Since 2008, when the JE vaccine was included in the expanded program on immunization in China, the number of cases of JE has decreased significantly. However, there were unexpectedly twice as many JE cases in China in 2013 than in 2011 and 2012. A report by Li et al. in this issue analyzed the spatial and temporal distribution of JE cases in 2013, and found that the high incidence of JE cases in China in 2013 was mainly in the group of people >40 years old, and in north China, that includes regions where there was a relatively low prevalence of JE before. This report provides not only an introduction to the current situation of JE epidemiology in China, but also has great reference significance for the prevention and control of JE in other countries outside of China. In China, WNV was first isolated from mosquitoes and was subsequently found in Xinjiang Uygur Autonomous Region, west China, during an epidemic of adult viral encephalitis. The data presented by Cao et al. in this issue showed that no cases of WNV infection were detected in serum specimens from viral encephalitis patients with JEV or non-JEV patients except in the Xinjiang Uygur Autonomous Region in China. The study highlights the importance to detect and monitor WNV infection in the vast JEV-endemic areas of mainland China. The seroepidemiological investigation of sheep in Qinghai-Tibet plateau infected with Yersinia pestis and the human infections with H7N9 virus in China, etc., are also described in this issue.

It is well known that the bacterial or viral pathogens and related infections described in this issue are not only prevalent in China but are also prevalent in many other countries around the world. The data and discussions presented in this special issue are highly relevant. Not only do they demonstrate and communicate historical and current research results of important vector-borne diseases and zoonoses in China, but also they will be of great value to researchers, physicians, health care workers, epidemiologists, entomologists, and others who are involved in vector-borne and zoonotic diseases in other countries outside of China.