Robin writes:

Overcrowding and virulence

Genes are no longer genes if they do not survive. Those that do not adapt disappear. An adaptation to high transmissibility with episodic transmission in pathogenic microbes might allow high virulence as in smallpox. But generally, decreasing virulence over the long term tends to be more adaptive, trending towards an uneasy truce or even a “peaceful coexistence”.

However there can be environmental conditions external to both the host and the pathogen that can modulate their interactions. Overcrowding of chickens in industrial farms could promote the transmission of pathogens to a degree that would compensate for the maladaptiveness of an increase in virulence, thus accounting for the increased virulence seen since the advent of industrial chicken farming. Urban overcrowding could be the setup for the emergence of novel human to human transmitted pathogens.

Jim writes:

Thank you so much for sharing that session with Dr Steitz. It was so enjoyable to hear such animated talk about big events in microbiology with insights about the work and  researchers, for a nice long period. Researchers face so many obstacles in their work, including gender discrimination, but you folks offered many positive aspects that made for a pleasant presentation. The sound quality was perfect, too. 345 is easily one of your top ten productions Prof Racaniello.  It was like sitting in on an informal discussion between Feynman, Oppenheimer, Curie, Rosalind Franklin, and Turing!

Great minds are beautiful!

Thanks again


Smithfield, VA

George writes:

Hello TWIV Professors,

I have been a faithful listener for the last one year and I have to admit I am hooked. Every Monday i download the podcast and listen while driving home. Wish you could see me driving and laughing while listening to the discussions!

I notice that very few listeners from Africa write (besides Piet in South Africa) but i am certain you have a huge fan base.

On TWIV 348 you talked about Nigeria reaching a milestone, one year since the last Polio case. This is quite commendable. My country (Kenya) has been largely polio free except some few introductions from the neighboring countries. However, this progress is now under threat from the Catholic church. The church is opposing the Polio vaccination ostensibly because the vaccine is “contaminated”. This is a dangerous position to take because as Prof Racaniello noted these are the same reasons that led to the bounce in the Polio cases in Nigeria from 2003. I just hope that religion will not be allowed to mix with health.

Keep up the great work, i learn more from you each day.



P.S It is rather cold by our standards here in Nairobi, Kenya; 18 degrees Celsius, humidity 56%, precipitation 22% and wind 11.2mph!

George Gachara, PhD

Dept of Medical Laboratory sciences

Kenyatta University

Marianne writes:

Hi TWiV team;

I just wanted to follow up on two letters from your last episode.

On the controversial ‘anti-vaccine’ course taught at UofT – the dean at U of T Scarborough has resigned after the internal investigation. The story seemed to indicate that the instructor of the course, officially called “Alternative Health: Practice and Theory,” (who was also coincidentally the resigning deans spouse) is no longer teaching there and the course has been discontinued.

As for the letter from DJ – his letter seemed to indicate that vaccines are so dogmatically entrenched in science that they are static – that they don’t change as post marketing data is collected. In fact, there have been many modifications of vaccines over time often in an effort to increase safety. A great example is the pertussis (which causes Whooping cough) vaccine. The original vaccine was a whole cell vaccine, and had been associated with increased (although still relatively mild) adverse events after vaccination. In an effort to reduce these events, there was a switch to an acellular form in the 1990s. However, this has come at a cost, with data emerging that the immunity in those vaccinated with the acellular vaccine is not as effective as the whole cell (I think you may have covered this story on a TWiV episode, however link to manuscript is below). All vaccines, and their modifications will have that risk and benefit. I think that the point is that although scientists are basically unanimous around the value of vaccines, it doesn’t mean they are blind to improvements that need to be made over time. It’s just that it’s incredibly difficult to explain how and why vaccines may change in today’s sometimes very anti-vaccine climate.  Scientists by nature speak in nuanced terms and the public sometimes (mostly) has a short attention span and an allergy to jargon. Scientists need to be consistent and approachable and relevant – science outreach is so important. That’s why I so appreciate the TWiX podcasts and all that you do as a group.



Margaret writes:

Hi Vincent et al,

This paper just came out in PNAS, and it confirms what Rich said in TWIV episode 348: the best way to convince vaccine-skeptical people about the benefits of vaccines is, basically, anecdotes about what happens to unvaccinated kids. Directly addressing anti-vax arguments about the risks of vaccines is a waste of time, as we know: it’s like playing a game of whack-a-mole (the arguments change constantly, and as soon as you’ve convinced someone that one argument is faulty, three new arguments pop up to take its place); and often it has the counterintuitive effect of actually hardening anti-vaccine beliefs. Instead, talk to the vaccine-skeptical about the dangers of the diseases that vaccines are designed to prevent. THAT, as Horne et al show, actually succeeds in increasing vaccination rates. I found it to be a rare piece of encouraging information.

I also wanted to remind Rich that Vermont (which, like CA, is quite the bastion of anti-vax sentiment) has also passed a law removing philosophical exemptions for vaccination requirements in public schools. It doesn’t address religious exemptions, and it certainly doesn’t end the battle over vaccinations in VT, but it is a huge step forward. I have many friends in VT, several of whom are immune-compromised, and I cheered this news loudly. I wanted to make sure Vermonters get the credit due them for pushing this important and politically difficult move.

Thanks for your show — I’m a genetics/evolution PhD who has moved onto toxicology for my postdoc, but I greatly enjoy getting to sit in on your virology “journal club” every week. The podcast is a good length for my bus commute (as depressing as that is) and it helps me feel like that time stuck in traffic is well-spent, at least one day a week. Keep up the great work!

Lance writes:

Dear all,

In approximately two weeks I will be headed to the CDC lab in Sierra Leone for 2-3 months to help with the Ebola effort. Working for the CDC Viral Special Pathogens Branch is something I dreamed about when I was a wee little microbiologist and sitting in my cubicle across from people who I have read about in books and science articles is really amazing.

Two thoughts:

  1. I have been and probably will remain quite critical of the phd/post doc system and training. I didn’t have a great time doing my phd and found it difficult to get employment (that I could survive on) immediately after. However, I remained flexible and have since had a couple good jobs followed by the CDC calling and offering me my dream job. So, keep your head up, stay flexible, and apply to everything!
  1. I think the TWiV crew should come to Sierra Leone. I don’t personally know yet, but I have been told the hotel is quite nice and supposedly we have wifi most of the time! I’ll keep you posted on the weather when I get there but it looks hot, humid, rainy, and floody.

Looking forward to curling up after a long day in the hot lab and listening to TWiV from inside my mosquito net.

Best wishes,


Ralph writes:


I have been listening to your podcast for about 6 months.  I am a computer scientist, not a virologist and I enjoy learning some about other fields.  As I expect is the case with a number of others, I first found you when you were doing weekly Ebola coverage.

One area where I have not understood your strong reaction was when you talk about gain of function experimentation. I get that the whole group thinks the restrictions are unproductive.  I have not decided how I come down on this issue. I probably lean towards allowing scientists to experiment, just on principles. But, there are at least 2 significant reasons I can see limiting this research (at least government funded limitations).  First, there has to be some risk that the experimental viruses could get out.  Catastrophic collapse of buildings or terrorist actions come to mind. Second, whatever function you add to the viruses would represent the experiment and may never arise in nature through random mutation.  The second factor would seem to limit the potential benefit.  I don’t see that you give any credence to those factors and that makes me think you may not be properly balancing risks and benefits.

It is currently 85 degrees Fahrenheit here in Dallas Texas.  I don’t go for those funny French units, but I think it is fine if you like them.

Have a good day,


PlutoJohnye writes:

Great minds!!

So this is high noon on Pluto. This morning I thought of sending in the NASA link as a listener pick. Good pick!

Boston Custom House, #PlutoTime 0518, 19 Jul 2015

Johnye Ballenger


JAKsCrow writes:

Hello Prof Racaniello,

Yesterday, I started listening to the TWiV podcast, entertaining! I’m also thru lect 14 on the 2015 youtube virology course. Thanks for the free and fun TWiV and lectures!

In TWiV2 polio, you mentioned people with ebola get serum from already cured ebola patients and the antibodies are sometimes able to cure the symptomatic patients. Must the donor and recipient having matching blood types for the ebola serum to not be rejected by the recipient’s immune defense?

Also, if a person is vaccinated with rabies, HepA/B, yellow fever, etc then is it possible to infect another person with the antibodies produced from said vaccinations via unprotected sex? My doctor didn’t know.


Martin writes:

Please talk about this.


Susan writes:

I think this is relevant to episode 343 or so, Snippet on CWD:

Assessment of Abilities of White-Tailed Deer to Jump Fences

ABSTRACT There is a need for insight into fence heights required for impeding white-tailed deer (Odocoileus virginianus). We evaluated the ability of wild-caught deer to jump progressively taller fences and documented deterrence rates of 0% for fences <= 1.5 m followed by increasing deterrence rates of 14% at 1.8 m, 85% at 2.1 m, and 100% at 2.4 m. We documented 100% deterrence rates during 5 additional experiments with different deer and the test fence at 2.4 m, a common height of fences at captive deer facilities. Our results will be valuable to those managing spread of wildlife diseases, deer–vehicle collisions, and agricultural damage.

Love Twiv, thanks for all your work on the show. Susan

Susan Ann Shriner, PhD

Wildlife Epidemiologist

National Wildlife Research Center

4101 LaPorte Avenue

Fort Collins, CO 80521

Christophe writes:

Hello Vinnie & the TWiV Team,

No doubt you have already been told about this, but if not, you should check out the recent Rationally Speaking podcast, episode #137

Rationally Speaking #137 – Marc Lipsitch on, “Should scientists try to create dangerous viruses?”

I would recommend the podcast series generally as they speak about many interesting subjects – this episode was not as good as usual mainly because Marc was not a particularly great speaker, I might have skipped it but felt i had to listen to it seeing as i have heard you guys (& gal of course ) talking about the gain of function brouhaha at length, and figured i should hear the other side.

I would love to hear Vincent or one of the other TWiV hosts give the other side to the Rationally Speaking listeners. I would be happy to email them suggesting you as a guest if you would rather not do it yourself 🙂

Marc even mentions TWiV  – not by name, just by allusion to a certain other podcast that has subjected him to ad hominem attack… 🙂

Still listening and enjoying TWiV  – keep up the good work.


Konrad writes:

Hey Twivome,

I’d like to share a listener pick with you all: Stated Clearly, a collection of animations that explain the basics of evolution and genetics to laypeople. I’ve found them useful as easy-to-understand introductory videos and I hope you will too!

They’re also raising funds for new videos, check them out here:



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