In 1918, the Spanish influenza A (H1N1) virus pandemic caused 50 million deaths worldwide [
1,
2]. In 2009, influenza A virus originating in swine (H1N1) caused a pandemic, and the avian H5N1 and H7N9 influenza A viruses in China are highly pathogenic to humans [
1‐
4]. Currently, the application of three antiviral medicines known as neuraminidase (NA) inhibitors, oral oseltamivir, zanamivir, and peramivir, is recommended for the treatment of influenza. However, oseltamivir resistance has been detected in some of the 2009-derived H1N1 viruses and the seasonal H1N1 viruses between 2007 and 2009, but little in H3N2 viruses [
5]. In the future, zanamivir- and peramivir-resistant strains, similar to oseltamivir-resistant strain, will emerge. Therefore, the development of novel anti-influenza drugs to prevent and control future influenza epidemics and pandemics is desired.
Traditional medicinal plants have been recognized as a rich source of candidate compounds for the development of pharmaceuticals [
6,
7]. A large number of natural products and extracts from medicinal plants have been reported to possess anti-influenza virus activity [
8‐
10]. Therefore, many studies have focused on traditional medicinal plants as an important source of candidate compounds for the discovery of novel anti-influenza drugs.
The abundance of medicinal plants in Myanmar has enabled the population to use traditional medicines to maintain their own health and treat various diseases. Thus, to discover sources for novel anti-influenza drugs, we screened extracts from 118 medicinal plants collected in Myanmar to analyze the cell viability of influenza A H1N1 virus (A/PR/8/34)-infected MDCK cells using naphthol blue black staining. We identified six medicinal plants that promoted the survival of influenza A virus-infected cells selected by the criteria described at the Methods section. Of these six plants, the activity of extract from the stems of
Jatropha multifida Linn (
J. multifida) was strongly pronounced.
J. multifida, a member of the family Euphorbiaceae, is a tree of 2–3 m in height, and widely distributed in sub-tropical and tropical areas throughout Asia and Africa [
11]. Popularly known as “Say-ma-khan”, it is commonly used as a folk medicine in Myanmar and has been used as a purgative, and against fever, indigestion, colic, wounds, and skin infection [
11]. The seed oil, latex, and leaves are effective purgatives and abortifacients, have been used as wound dressings, and for the treatment of neurodermatitis, eczema, and itches [
11]. The roots and stems have antimicrobial, antimalarial, antitumor, antileishmanial, and antiulcer activities [
11,
12]. In addition, previous phytochemical studies on
J. multifida reported the presence of cyclic peptides, diterpenoids, and phenolic compounds [
11]. However, pharmacological and phytochemical investigations of
J. multifida stems originating from Myanmar have not yet been conducted, which attracted us to investigate whether extracts from the stems of
J. multifida, obtained using various solvents, possessed anti-influenza virus activity.