There have been many reports of people going out knowing they are positive for COVID, denying a known infection is COVID, etc. This is a very interesting essay on some possible mechanisms by which SARS-COV-2 may manipulate infected people's behaviour. /1link.springer.com/article/10.100…

These are potential mechanisms and are not proven to my knowledge (paper is 2021). Some of them are based on known potential effects of specific biological interactions. Social factors are likely more powerful than biological ones for explaining behaviour that transmits COVID. /2

Definitely the most important one is that COVID has several possibly mechanisms by which it can make infected people feel fine. I recall at the beginning of the pandemic, people would feel fine but have incredibly low oxygenation, meaning they were about to crash and die. /3

Also, many people who end up with Long Covid, meaning they likely had significant internal damage from the virus, feel nearly fine in the acute phase of infection. Feeling fine is a recipe for going about society transmitting everywhere during the infectious phase of disease. /4

SARS-COV-2 binds to neuropilin-1 which is known to have analgesic effects (relieves pain). I.e. it may be generating a soothing response kind of like taking Tylenol to help you feel better while it continues to infect you. Telltale fever is also often not present. /5

This hypothesis is important for people to understand because, in addition to helping explain behaviour of people who go around and spread COVID because they don't realize they are sick, it also underpins the false belief that COVID is somehow equivalent to a minor cold. /6

SARS-COV-2 also suppresses interferon production more than SARS, which can delay the immune response, increasing viral replication, and can also improve mood and increase social activity. Interferon production from infection is associated with social withdrawal and depression. /7

The authors note that SARS-COV-2 binds acetylcholine receptors, which the rabies virus also does, and this could impact behaviour, though it's highly unclear. Some receptors are nicotinic: one Long Covid hypothesis is treatment through nicotine patches. /8 bioelecmed.biomedcentral.com/articles/10.11…

Loss of sense of smell is also a behaviour modulator, but because humans have a weak sense of smell the authors hypothesize selection for this may have been adapted to the virus' origins in bats, where loss of smell would likely lead to more risky behaviour by hosts. /9

The authors note COVID is associated with impaired consciousness, vascular damage and neuroinvasion. But they have no evidence that this is adaptive to the virus or that it modulates behaviour in a useful way. Perhaps it causes failure to adhere to public health measures. /10

Obviously, COVID makes you cough and can also cause diarrhea, like many viruses, and these can be both protective responses and behaviours that facilitate viral transmission. /11

The authors suggest that asymptomatic individuals may be considered a form of deceptive mimicry on behalf of the virus to promote transmission. /12

I hope you found this as interesting as I do. I think more research needs to look into biological mechanisms which may underpin the modulation of behaviour by COVID infection. /13.