Thread by @FondOfBeetles

On Hantavirus: a (non-technical) thread.

Disclaimer: I am a biology PhD, but not virology/epidemiology. Husbandman is a virology PhD. But I’m told I’m good at communicating science, so here’s my take.

#Hantavirus

Humans get hantavirus from rodents who carry it.

Some people went to Argentina birdwatching in a landfill, and were exposed to hantavirus because rodents like landfills.

Looks like one - if not two - people brought the virus onto their cruise boat.

So now we have an isolated boat with an index case: someone who is infected.

That’s not good for the index case. Hantavirus has a high fatality rate, and that’s scary.

But fatality rate alone does not determine outbreak risk.

A virus that kills 30 % of the people who contract it but barely spreads to anyone else is less dangerous to society than one that kills 0.1 % but infects everyone.

See: COVID.

All viruses work in basically the same way:
They enter your cells>
They hijack the cellular machinery to copy themselves>
They burst out of your cells, often destroying the cell in the process.

In the meantime, your immune system is working to keep you healthy.

But: a virus replicating inside your cells is only a potential danger to you. It’s crap if the virus has a high fatality rate, obvs.

But it becomes a danger to others when it starts leaving your body: sneezing, breathing, secreting, bleeding it out.

This is called shedding. This is the virus going forth and finding a new host.

But different viruses do all this stuff differently.

Some are Door Dash - live fast or die young, sorry about all the sneezing but who needs nose cells anyway.

Some are snipers - they take their time, don’t raise eyebrows, wait for their chance.

People are worrying about long incubation periods - the time between getting infected and having symptoms.

The length isn’t the issue.

What matters is whether a person is shedding during incubation.

COVID shedded before you felt ill.

That’s why it spread so efficiently. You’re infectious before you know you’re sick.

Hantavirus doesn’t appear to shed before you have symptoms. Even if they are 2 weeks or 8 weeks after exposure.

With hantavirus, it t seems to be the case that you incubate for weeks feeling fine, and not infectious.

Then you deteriorate rapidly. And go to bed, or to hospital, or whatever.

But not to birthday parties (see later).

R0 is the average number of people one infected person passes a virus to in a susceptible population.

It’s a predictor of pandemic potential.

Measles is 12–18.
COVID v 1.0 was 2–3.
Flu is like 1.2.

For Andes hantavirus, R0 estimates from the 2018 Argentina (human-to-human) outbreak was between 1 and 2.

Above 1 means it can sustain transmission, but only just.

So now to why boats aren’t really a great indicator of what happens outside a boat.

The R0 of COVID-on-boat was much higher than COVID-on-land.

Loads of people, packed into shared buffets and cramped living spaces.

Petri dish, pressure cooker etc.

If you wanted to maximise transmission of a tricky-to-transmit virus, boats are ideal.

Maybe also all-in hotels in Cape Verde, where I shall be visiting in ten days. I’m more worried about food poisoning than floating Hanta.

Human-to-human transmission of Hanta requires close and/or prolonged contact.

You aren’t catching it walking behind an asymptomatic person in the street, or handling a symptomatic patient who is bagged up.

There’s a paper doing the rounds about ‘superspreaders’. It has beautiful figure, that should be reassuring.

The lessons from the paper is: even if you go to birthday parties while symptomatic, the virus struggles to infect others.

The same situation with COVID might have looked very different.

If the flight attendant dealing with an incredibly sick passenger spent a lot of time around the passenger, including face-to-face assessments around managing a flight - face holding, look at me, let me get you a sick bag - that’s close and/or prolonged contact with a symptomatic patient.

I know the boat didn’t really recognise they were dealing with hantavirus, and made some decisions that look poor *In hindsight*.

But this is not COVID.

Still: just don’t get on flights or go to birthday parties if you feel ill. Sometimes it’s good not to share 🤣

A few footnotes:

1. I had assumed people would know I was talking about the Andean variant, which can transmit between people.

Reports of sequencing the virus responsible for the current outbreak doesn’t flag any DNA changes (mutations) that are concerning.

2. The flight attendant who may have dealt with a very sick patient is reportedly negative for Hanta. I assume monitoring will continue is for some time.

That she has symptoms but is negative suggests it’s a standard cold.

Plenty of people who’ve been in contact with passengers and patients will get colds over the coming weeks. So these “scares” aren’t going to stop anytime soon.

3. I’ve taken a correction on the R0 for Andean variant, calculated from the Birthday Party outbreak.

The R0 before containment seems to have been slightly higher than 2.

Please remember: the index case here was ill - he had fever, tiredness, etc.

As a proportion of those around him, he infected very few people. Compare if it had been COVID or worse, measles.