Why are bats the source of dangerous coronavirus pandemics?

Question

Why do coronaviruses come from bats?

I mean, why precisely coronaviruses and not (for instance) herpesviruses? It looks like bats host more zoonotic viruses (per species) than rodents, although they don't develop any sign of disease.

The article above says that rodents host more zoonotic viruses than bats overall (68 against 61), but at the same time most of the latest pandemics originated from bats.

It also seems that bats could be involved in the maintenance of ebola viruses.

My question is: why did these major pandemics originate from bats and not from rodents, although rodents host more zoonotic viruses overall?

We should also take into consideration that human-rodent interaction is usually more likely than human-bat interaction, except for people who consume bats (like Chinese people; this would (partially) explain why both SARS and 2019-nCoV developed in China).

Answer 1

The preponderance of links between bat and human pathogens has led to a debate about whether bats disproportionately contribute to emerging viral infections crossing the species barrier into humans (26–30). Given the diversity of the Chiroptera order (Figure ​(Figure1),1), we may simply see more bat viruses because there are so many (>1,300) species of bats (31). However, even when accounting for the fact that they make up ~20% of extant terrestrial mammals, bats are overrepresented as reservoir hosts of pathogens with a high potential for spilling into human populations (32, 33). In fact, no known predictors that have been described to impact the likelihood of crossing the species barrier, including reservoir host ecology, phylogenetic relatedness to humans or frequency of reservoir-human contact, explain this pattern (32). Thus, why bats are such a frequent source of pathogenic human viruses remains a tantalizing mystery.

--Going to Bat(s) for Studies of Disease Tolerance

Other references that debate whether bats are special, generally conclude that they might somehow be, and argue about causes, include

• Brook CE, Dobson AP. Bats as ‘special’ reservoirs for emerging zoonotic pathogens. Trends Microbiol. (2015) 23:172–80. This may be the best of the group, going into more detail and including more recent data

• Dobson AP. Virology. What links bats to emerging infectious diseases? Science (2005) 310:628–9.

• Wang LF, Walker PJ, Poon LL. Mass extinctions, biodiversity and mitochondrial function: are bats ‘special’ as reservoirs for emerging viruses? Curr Opin Virol. (2011) 1:649–57.

• Olival K, Epstein JH, Wang LF, Field HE, Daszak P. Are bats exceptional viral reservoirs? In: Aguirre AA, Ostfeld R, Daszak P, editors. editors. New Directions in Conservation Medicine. Oxford, UK: Oxford University Press; (2012). p. 195–212.

• Luis AD, Hayman DT, O'Shea TJ, Cryan PM, Gilbert AT, Pulliam JR, et al. . A comparison of bats and rodents as reservoirs of zoonotic viruses: are bats special? Proc Biol Sci. (2013) 280:20122753.

Answer 2

The following paper proposes that the bat borne viruses evolve to rapidly-transmit as a response to their robust immune systems:

We carried out virus infectivity assays on bat cell lines expressing induced and constitutive immune phenotypes, then developed a theoretical model of our in vitro system, which we fit to empirical data. Best fit models recapitulated expected immune phenotypes for representative cell lines, supporting robust antiviral defenses in bat cells that correlated with higher estimates for within-host viral propagation rates. In general, heightened immune responses limit pathogen-induced cellular morbidity, which can facilitate the establishment of rapidly-propagating persistent infections within-host. Rapidly-transmitting viruses that have evolved with bat immune systems will likely cause enhanced virulence following emergence into secondary hosts with immune systems that diverge from those unique to bats.

• Accelerated viral dynamics in bat cell lines, with implications for zoonotic emergence, eLife Sciences (2020)