We investigated the current molecular epidemiological status of HIV-1 in Mongolia, a country with very low incidence of HIV-1 though with rapid expansion in recent years. HIV-1 pol (1065 nt) and env (447 nt) genes were sequenced to construct phylogenetic trees. The evolutionary rates, molecular clock phylogenies, and other evolutionary parameters were estimated from heterochronous genomic sequences of HIV-1 subtype B by the Bayesian Markov chain Monte Carlo method. We obtained 41 sera from 56 reported HIV-1-positive cases as of May 2009. The main route of infection was men who have sex with men (MSM). Dominant subtypes were subtype B in 32 cases (78%) followed by subtype CRF02_AG (9.8%). The phylogenetic analysis of the pol gene identified two clusters in subtype B sequences. Cluster 1 consisted of 21 cases including MSM and other routes of infection, and cluster 2 consisted of eight MSM cases. The tree analyses demonstrated very short branch lengths in cluster 1, suggesting a surprisingly active expansion of HIV-1 transmission during a short period with the same ancestor virus. Evolutionary analysis indicated that the outbreak started around the early 2000s. This study identified a current hot spot of HIV-1 transmission and potential seed of the epidemic in Mongolia. Comprehensive preventive measures targeting this group are urgently needed.

Thirty-six HIV-1 cases had been reported by December 2007 in Mongolia. Therefore, Mongolia has been regarded as a very low HIV-1 epidemic country, although the surveillance system is not fully developed. The aim of this study was to evaluate the risk status of HIV-1 infection in Mongolia. A total of 1415 blood samples from high-risk populations including female sex workers, men who have sex with men, mobile men, tuberculosis patients and male sexually transmitted infection (STI) clinic clients and 1050 samples from healthy controls were collected. The seroprevalences of anti-HIV-1/2, anti-Treponema pallidum, hepatitis B surface antigen (HBs Ag), anti-hepatitis C virus and hepatitis B surface antibody in the high-risk populations were 0%, 23.1%, 15.5%, 8.0% and 48.2%, and those in the controls were 0%, 3.1%, 14.7%, 4.4% and 44.4%, respectively. HIV-1 prevalence is currently low. However, according to the high prevalence of STIs in the high-risk populations, the risk status for HIV-1 infection is estimated to be high.

This study describes HIV and syphilis bio-behavioral survey conducted among 200 men who have sex with men (MSM) recruited via respondent-driven sampling (RDS) between January 4 and February 1, 2012 in Ulaanbaatar, Mongolia. Participants were administered a structured questionnaire and data were analyzed with RDS-network program in STATA. Of 196 participants who agreed to be tested for HIV and syphilis, 21 (10.7 %; weighted 7.5; 95 % CI: 4.9, 11.4) and 8 (4.1 %; weighted 3.4; 95 % CI: 1.7, 6.7) were positive for HIV and syphilis, respectively. Exposure to HIV prevention programs in the last 12 months was reported by 51.8 % (weighted 33.6; 95 % CI: 27.6, 40.1) of participants. This study found high HIV prevalence and limited uptake of HIV prevention services among MSM in Mongolia. Given the concentrated HIV epidemic among MSM in Mongolia, HIV prevention, treatment and care services should focus on MSM as the population group most affected by HIV.