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Received Nov 30, 2017; Accepted Jan 28, 2018
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1. Introduction
Dengue fever (DF) is a kind of acute infectious diseases caused by dengue virus (DV). Its major clinical symptoms include acute high fever, headache, generalized myalgia, ostalgia and arthralgia, rash, hemorrhagic tendency, and low white blood cell count [1]. Dengue hemorrhagic fever (DHF) is a kind of dengue fevers with more serious clinical symptoms like extremely high fever, severe hemorrhage, shock, low platelet count, pachyhematous, and high death rate [2]. A DHF accompanying with shock is called dengue shock syndrome (DSS).
Aedes aegypti and Aedes albopictus are two major vectors for transmission of dengue viruses [3]. Dengue fever is endemic in tropical and subtropical zones and has become one of the most wide-spread, infectious, and dangerous arboviral diseases. In recent years, there are several outbreaks of dengue fever and dengue hemorrhagic fever in Southeast Asia, Pacific Islands, Central America, and South America, making it a critical world-wide issue for public health [4].
Currently, there is no vaccine or antiviral treatment for dengue fever [5]. The patients are only recommended to drink plenty of fluids or take medicines like acetaminophen to avoid dehydration from vomiting and high fever [6]. Thus, it is very important to develop new antiviral drugs against dengue viruses. However, there are many difficulties in the synthesis of new compounds including high cost, low yields, and so on [7], which urges drug companies and research entities to search for antiviral drugs from natural products. It is known that traditional Chinese medicines are among the most studied natural products in curing diseases [8]. Owing to thousands of years’ clinical trials of these medicines in China, traditional Chinese doctors have plenty of experience in combining natural products to cure diseases and protect people from the invasion of many viruses. Thus, it is promising to isolate antiviral drugs from Chinese medicinal herbs.
As a type of popular traditional Chinese medicinal herb, Isatis tinctoria (woad, Brassicaceae or Ban Lan Gen) has been proven to be effective against various viruses including influenza, hepatitis A virus (HAV), and...