EVALUATE VIRAL HAEMORRHAGIC FEVER OUTBREAKS IN UGANDA TO DISTINGUISH CONTINUED HUMAN TO HUMAN TRANSMISSION VIA SURVIVORS FROM ZOONOTIC SPILLOVER EVENTS (2000-2019)

Abstract

INTRODUCTION: Uganda has experienced repeated outbreaks of viral haemorrhagic fevers (VHFs) over the last 20 years (Mbonye et al., 2012); Ebola Virus Disease (EVD) occurred in Gulu in 2000; Bundibugyo in 2007; Luweero in 2011; Luweero in 2012; and Kibaale in 2012 (Okware et al., 2015). Marburg Virus Disease (MVD) was reported in Ibanda in 2007; 2012 in Ibanda; Kampala in 2014; and Kween in 2017 (Nyakarahuka et al., 2019). Transmission dynamics of MVD are not clearly understood. Rousettus aegyptiacus bats has been linked to MVD outbreaks reported in 2007 and 2017 (Adjemian et al., 2011; Nyakarahuka et al., 2019). Furthermore, prior ecological studies indicate the geographical movement of R. aegyptiacus bats responsible for MVD infections (Towner et al., 2009). However, previous studies indicate that EVD and MVD survivors may shed virus long after recovery; suggesting possible transmission of virus via survivors (Chughtai et al., 2016). OBJECTIVE: This study investigated whether recent MVD outbreaks in Uganda are a result of continued transmission via survivors or fresh outbreaks from natural hosts. METHODOLOGY: Genomic approaches were employed; specific hypotheses were based on genetic distance and phylogenetic profiles. For the genetic distance approach, observed pairwise distances were computed using MEGA software, the calculated values were compared to expected pairwise range estimates (considering scenario of continued transmission via survivors). Possible initiation from natural host was inferred if observed pairwise values were not within the expected pairwise estimates. Furthermore, clustering of temporal samples within a clade (UFBoot >95%) was employed to establish linkages between MVD outbreaks utilizing IQ tree software. RESULTS: Pairwise results did not support the scenario of continued transmission via survivors. Expected pairwise estimate were between (0.6 -5.0) x 10-3 while observed pairwise values were between (4.8 -85.0) x 10-3. Phylogenetic results indicated true clusters segregating by outbreak time points (years) (UFBoot >95%), indicating no linkages between MVD outbreaks in Uganda. CONCLUSION: In summary, there is no evidence to support continued human to human transmission via survivors, this suggests possible initiation of MVD outbreaks from natural reservoirs.