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Rich Davis, PhD, D(ABMM), MLS 🇺🇦 Profile picture
@richdavisphd
Sep 17, 2020 • 6 tweets • 4 min read • Read on X
#MicroRounds (Day 733): Hypothetical case: a parent hears their child use the toilet but not flush (typical behavior!).

But upon entering the bathroom they're horrified to see this worm in the bowl with their kid's poop! How freaked out should they be?? #ASMClinMicro #IDTwitter A split picture: a tangled skinny worm (thinner than a stran
Cont.: Here's some additional information (from your friendly neighborhood parasitology lab).
1) Yes, it's actually a worm.
2) You zoom in close and see this on one of the ends of the worm... A split, three pronged brown worm.
#MicroRounds: If you see this worm in your toilet: relax. It didn't come from a person!

A horsehair worm. Nematomorpha (i.e. "looks like a nematode") is a phylum that infects grasshoppers, crickets & drives them to water. A common false human parasite #ASMClinMicro #IDTwitter A tangled brown worm (skinnier than spaghetti). Caption read
I left the most interesting part of Nematomorpha under-explained: how did this non-human parasite end up in your toilet?

It came from it's host!

Good news: the host wasn't a human
Bad news: it was an insect (cricket, grasshopper) and it's … disturbing
The lifecycle of horsehair worms requires eggs to be laid in fresh water. Worms (which are enormous, tangled and wriggling) produce neurotransmitters within the cricket/insect host that drives them to erratic behavior. When in water, the worm emerges! kqed.org/science/193777…
Some additional cool features of horsehair worms:
- the worms consume lipids w/in the cricket host, delaying its development
- despite the size of the worms, if they don't drown, the insect host can survive, hop away, even go on to lay eggs of its own!wired.com/2014/05/absurd…

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More from @richdavisphd

Rich Davis, PhD, D(ABMM), MLS 🇺🇦 Profile picture
Jun 26, 2020
What does a mask do? Blocks respiratory droplets coming from your mouth and throat.

Two simple demos:

First, I sneezed, sang, talked & coughed toward an agar culture plate with or without a mask. Bacteria colonies show where droplets landed. A mask blocks virtually all of them. ImageImage
What about keeping your distance?

Second demo: I set open bacteria culture plates 2, 4 and 6 feet away and coughed (hard) for ~15s. I repeated this without a mask.

As seen by number of bacteria colonies, droplets mostly landed <6 ft, but a mask blocked nearly all of them. ImageImage
I'm aware that this simple (n=1) demo isn't how you culture viruses or model spread of SARS-CoV-2.

But colonies of normal bacteria from my mouth/throat show the spread of large respiratory droplets, like the kind we think mostly spread #COVID19, and how a mask can block them! ImageImage
Read 56 tweets
Rich Davis, PhD, D(ABMM), MLS 🇺🇦 Profile picture
Apr 8, 2020
Good thread on sensitivity & specificity of first emergency use authorization (EUA) #COVID19 serology test, Cellex, means for testing a low-prevalence population: increased risk of false positives

BUT IT'S ACTUALLY WORSE THAN THIS bc these numbers =/= *clinical* sensitivity 1/
A huge question (if not THE question) in #SARSCoV2 lab diagnostics is the rate of false negatives and false positives.

This can be calculated IF (and it's a crucial "if") you know the True Disease Status of people and then test them with your test approach. Like this:
2/
BUT we don't really have a gold standard/reference method for determining True Disease Status of COVID-19 patients. But we think PCR tests are the best we have right now.

SO you contrast your NEW test vs. results against your best comparator test.

Results look like this: 3/
Read 19 tweets
Rich Davis, PhD, D(ABMM), MLS 🇺🇦 Profile picture
Feb 27, 2020
News and updates about the status of laboratory diagnostics for #COVID19 are coming thick and fast today.

A quick thread on that topic, starting with @HelenBranswell's timely article (why aren't you following her??) as a jumping off point:
1/n
First, we know that the CDC has tested few cases of possible #COVID19 patients.

In an MMWR from last week, they said they'd tested "1,007 people" but news this week is saying "<500"? I don't understand that discrepancy.

Suffice to say it's far, FAR below what is needed! 2/n Screen grab from Feb 25,2020 CDC MMWR COVID 19 Update https://www.cdc.gov/mmwr/volumes/69/wr/mm6908e1.htm
Second, the CDC's developed PCR assay (which was described w/ sequences/primers back in January) *was* distributed to some (12+) public health labs.

But some component of that gave some labs problems (1 of 3 probes? a neg control? unclear to me)
cidrap.umn.edu/news-perspecti…

3/n
Read 16 tweets
Rich Davis, PhD, D(ABMM), MLS 🇺🇦 Profile picture
Feb 13, 2019
HOO BOY I just read the "Harvard Study Proves 'Unvaccinated Children Pose No Risk'" garbage, bunk, actually-just-an-open-letter-from-an-antivax-immunologist and I am DANGEROUSLY INFURIATED.

I will NOT be linking to this article. But it is garbage. *RAGE SCREAM* #VaccinesWork
What is notable is the approach: Consistently demonstrating that vaccines are 1) effective and thereby 2) changing the landscape of commonly seen infections to prove that vaccines DON'T prevent spread of disease??

It's a baffling strategy that doesn't work.
#VaxFactsFebruary
It turns out there's a rather good Snopes article debunking a lot of the scientific claims. If you MUST read this thing (which again I wont' link to) you can find it here: snopes.com/fact-check/har…

But since I'm already riled up, here are a few points from me… #VaccinesWork
Read 17 tweets
Rich Davis, PhD, D(ABMM), MLS 🇺🇦 Profile picture
Oct 12, 2018
Antibiotic testing. Let's go.

Tentatively calling this #tweetorial "Antibiotic testing: why and how and huh?"

Important caveat: this is a HUGE topic. I’m mostly going to focus on 1) basic rationale and 2) laboratory methods. And 3) try not to say anything wrong/misleading!
Question #1: Why would a person want to know if bacteria A is resistant to antibiotic B?
And the answer is ...

All are legit answers! But it's very situation dependent and you'd have different reasons for each. Let’s go through them.
#tweetorial #pathtweet #asmclinmicro
Read 28 tweets

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