The human immunodeficiency virus type 1 (HIV-1) epidemic remains a major public health burden in China. By the end of 2018, it is estimated that there are approximately 1.25 [1.10–1.40] million persons living with HIV/AIDS in China. During 2018, 81 [60–105] thousand new HIV infections occurred [
1].
In early 1990s, HIV-1 Thai subtypes B′ and C were co-circulated among injection drug users (IDUs) [
2] in Yunnan province in southwestern China bordering the ‘Golden Triangle’, leading to active inter-subtype recombination which generated CRF07_BC, CRF08_BC, and a large number of unique recombinant forms [
3,
4]. In the initial period, drug trafficking activities were considered to be responsible for the rapid spread of CRF07_BC and CRF08_BC across China [
5]. From 1978, as commercial sex activity increased across the country [
6], the proportion of newly reported HIV infections/acquired immune deficiency syndrome (AIDS) patients through heterosexual transmission increased dramatically. Nowadays, CRF07_BC and CRF08_BC have become the most epidemic strains in China [
7,
8] and drug-driven epidemic has been shifting to sexually transmission-driven epidemic [
9]. There were other B/C CRFs reported in the last few years, such as CRF57_BC (identified in Baoshan, Western Yunnan) [
10], CRF62_BC and CRF64_BC (identified in Ruili/Dehong, Western Yunnan) [
11]. However, there was scarce evidence that such B/C recombinant forms had spread to other areas. In 2016, we reported a novel B/C recombinant form, CRF85_BC, among heterosexually infected patients in southern Sichuan (Yibin city) [
12]. CRF85_BC was then reported in Anhui [
13], Yunnan [
14] and Northern Sichuan [
15] (Guangyuan City). Due to lack of B or C epidemic history in the local high-risk population, the origin and the spread of CRF85_BC was still to be investigated.
Sichuan province is in the interior of Southwest China, adjacent to Yunnan and Guizhou in the South and Tibet in the West. Sichuan has a population of approximately 85 million people, and is a developing area in China. Since the initial HIV epidemic was fueled by IDU in 1990s, the HIV epidemic in Sichuan had become one of the worst in China. By 2018, there were 132, 680 HIV infections reported in Sichuan province, which ranked the first among all provinces/autonomous regions in China [
16]. Several studies have focused on the HIV epidemic in IDUs [
17,
18] and CRF07_BC [
19,
20] in Liangshan prefecture in Sichuan, and reported that the infected IDUs in this region could serve as a source of transmission to other regions of China [
20]. However, limited attention has been paid to the recent shift of the HIV-related risk behaviors from IDU to sexual contact, and also to other circulating HIV strains in this area.
Genetic and temporal dynamic analyses have been widely used to reconstruct the history of the HIV epidemic and have provided important information to aid in the development of strategies for the prevention of HIV-1 transmission. Here, we reported an investigation of the temporal and spatial dynamics of HIV CRF85_BC to give more clues about transmission of HIV strains in China.