Human SARS-CoV infection originated from the direct contact between humans and civets in market or restaurants. Closing wet markets and cleaning civets cut off the spread chain of SARS-CoV and effectively ended the SARS epidemic. In contrast, MERS-CoV is believed to have existed in camels for a very long time and camels are widely distributed in Middle East and African countries, serving as important transport vectors and sources of meat and milk for the local population.
Comparison of transmission of MERS-CoV and SARS-CoV
Both SARS-CoV and MERS-CoV are emerging zoonotic pathogens that crossed the species barriers to infect humans. Evidence showed that SARS-CoV and MERS-CoV originated from bats, the nature reservoirs, then transmitted to human via intermediate hosts civets and camels, respectively.
It was suggested that MERS-CoV ancestors had been circulating in bats for very long time. MERS-CoV has evolved to adapt to use human receptor and the DPP4-recognizing bat coronaviruses like HKU4 may follow up, thereby posing a serious risk to human health.
Although NeoCoV is closer to MERS-CoV than other bat coronaviruses at genomic level, the phylogenetic analysis of the spike protein showed that HKU4 is the most closely related to MERS-CoV among all currently known bat coronaviruses, sharing 67% sequence identity. This is corelated with the capability of HKU4 of using DPP4 as its functional receptor. However, HKU4 preferred bat DPP4 over human DPP4, whereas MERS-CoV showed the opposite trend.
The most recent ancestor analysis speculated that MERS-CoV may have jumped from bats to camels approximately 25 years ago in Africa, with camels then being importrd into the Arabian Peninsula, while HKU5 and MERS-CoV may have diverged from their common ancestor about 400 to 500 years ago.
Seven conserved replicase domains in orf1ab of MERS-CoV related viruses were compared with MERS-CoV. The concatenated translated domains of NeoCoV shared 95% amino acid sequence identity with MERS-CoV species. Other bat coronaviruses, HKU4, HKU5 and SC2013, could be considered as different coronavirus species
By genomic analysis of lineage C betacoronaviruses, MERS-CoV derived from camels show high similarities to human MERS-CoV with>99.5% nt identities, confirming that the human and camels isolates belong to the same coronaviruses species. Bat HKU4, HKU5, NeoCoV and SC2013, shared 69.8, 70, 85.6, and 75.6%, respectively.