> Doesn't seem likely though - contagion more or less involves some kind of symptom (sneezing, coughing, etc) and it's hard to imagine a body developing a really high viral load or bacterial population without becoming feverish.
AFAIU, the profile depends on the class of virus, though obviously not all hosts behave similarly. Evolutionary strategies differ.
> evidence indicates that people who are infected with 2019-nCoV may be at their most contagious in the 48–72 hours before symptoms are noticeable. In addition, it is now estimated that up to 25 percent of infected individuals remain asymptomatic and may unwittingly infect others.
Knowing what we know now about significant aerosol transmission from merely speaking, it should be obvious now that coughing or sneezing isn't a prerequisite for highly contagious respiratory viruses. It should have been obvious before as we already knew that viral host reservoirs often remain asymptomatic. Bats, for example, are common reservoirs for respiratory viruses because a) they roost in dense groups, b) have strong selective pressure for consistently high function (flight is exhausting), and c) they've evolved immune systems that can handle a high viral load (a consequence of (a) and (b)), so don't often exhibit symptoms. I would presume many bird species make good reservoirs for similar reasons, though birds aren't mammals, which might complicate jumping to humans.
IIRC, a friend of mine, who had been researching rhinoviruses for several years at the time, explained to me that the coughing and sneezing fits from some types of cold viruses are caused by viral fragments rather than primary infection, in such cases symptoms peak at the tail-end of infection as fragments build up, and the fits might even be incidental/accidental from an evolutionary perspective. Some human cold viruses are specialized to infect children, who usually exhibit no symptoms or, at worst, a runny nose (again, latter might be incidental). Asymptomatic respiratory infections run rampant among children.
That's pretty scary. An interesting thought experiment: given a disease that was asymptomatic but after some time, deadly, do you think it would be possible to contain given current technology/social situation?
An interesting aside: I just looked it up, and it turns out that quarantine predated the germ theory of disease by many centuries. It's interesting that people can come up with effective strategies for defence against something that they both have no treatment for, and no real understanding of.
AFAIU, the profile depends on the class of virus, though obviously not all hosts behave similarly. Evolutionary strategies differ.
From the MIT COVID-19 page (https://medical.mit.edu/faqs/COVID-19):
> evidence indicates that people who are infected with 2019-nCoV may be at their most contagious in the 48–72 hours before symptoms are noticeable. In addition, it is now estimated that up to 25 percent of infected individuals remain asymptomatic and may unwittingly infect others.
Knowing what we know now about significant aerosol transmission from merely speaking, it should be obvious now that coughing or sneezing isn't a prerequisite for highly contagious respiratory viruses. It should have been obvious before as we already knew that viral host reservoirs often remain asymptomatic. Bats, for example, are common reservoirs for respiratory viruses because a) they roost in dense groups, b) have strong selective pressure for consistently high function (flight is exhausting), and c) they've evolved immune systems that can handle a high viral load (a consequence of (a) and (b)), so don't often exhibit symptoms. I would presume many bird species make good reservoirs for similar reasons, though birds aren't mammals, which might complicate jumping to humans.
IIRC, a friend of mine, who had been researching rhinoviruses for several years at the time, explained to me that the coughing and sneezing fits from some types of cold viruses are caused by viral fragments rather than primary infection, in such cases symptoms peak at the tail-end of infection as fragments build up, and the fits might even be incidental/accidental from an evolutionary perspective. Some human cold viruses are specialized to infect children, who usually exhibit no symptoms or, at worst, a runny nose (again, latter might be incidental). Asymptomatic respiratory infections run rampant among children.