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TWiV 77

Wladimir writes:

In regard to your question as to cases of known alteration of host behavior by virus that increases the rate of contact among hosts (Twiv 70), the most dramatic example is given by rabies. This extraordinary virus can convert a neurologically and behaviorally complex organism like a dog (or a person) into a vehicle that is behaviorally dedicated to increase the transmission of the virus. This seems to be done mainly by a sophisticated process of selective infection of particular neural structures that makes the host more aggressive and cause it to salivate more (increasing the load of viruses to be transmitted in the bite of the so-converted furious animal). I am copying to you below a fragment of the paper by Dr. Benjamin Hart "Behavioral adaptations to pathogens and parasites - 5 strategies" published Neuroscience and Biobehavioral Reviews in 1990, in case you want to provide to listeners further details of the elegantly macabre transmission tricks of the rabies virus.

all the best,
Wladimir

Effects of rabies virus on mammals. This is probably the most well-known example of a virus altering animal behavior. The virus infects domestic dogs and other canids and can turn a calm and placid animal into a wandering and vicious animal that attacks almost any target in sight. The rabies virus cannot survive except in living organisms, yet it is virtually always lethal in man, canids and many other hosts. In these instances, to be propagated the virus must be transferred to another animal before the host dies. In the furious or vicious form of rabies the virus usually enters a wound through a bite by an infected animal. The virus, which is in the attacker's saliva, enters the open wound created by the bite, moves into exposed peripheral nerves and then travels up inside peripheral nerves to the brain. The virus then multiplies in several areas of the brain of the new host, but particularly in limbic system structures such as the amygdala, hippocampus and pyriform lobes. The limbic system is known to control emotional behavior, including aggressive and feeding behavior and damage or experimental electrical stimulation of this area can lead to rage and undirected, unprovoked attacks. The greater localization and multiplication of the virus in the limbic system compared with the neocortex is apparently what causes abnormal behavior, including wandering aimlessly and attacking and biting anything encountered. While the virus is multiplying in the brain, it is also descending back down peripheral nerves including those innervating the salivary glands. The virus enters the salivary gland tissue and saliva. The nerves supplying the laryngeal and pharyngeal muscles are often affected as well and the ensuing paralysis of these muscles makes swallowing difficult. This causes pooling of saliva, and when the infected animal bites a new victim the pooled saliva is a reservoir of virus to be injected into the new victim. When transmission of the rabies virus does not depend upon abnormal viciousness for transmission, such as in vampire bats where the animals naturally bite each other rather frequently, or where the virus may be transmitted by the airborne route, abnormal viciousness for transmission from neurological alteration does not occur. In vampire bats the rabies virus reportedly does not necessarily produce acute death and may not be fatal.


from HART, B. L. (1990). Behavioral adaptations to pathogens and parasites - 5 strategies, Neuroscience and Biobehavioral Reviews 14(3): 273-294

Jessica writes:

Regarding the question you received in TWIV #70 about why a person might get a cancer-causing virus, such as HPV, but not actually develop cancer, I thought I might add a bit to your discussion. It is generally believed that 5-7 events are required for a cell to become cancerous. There are many checks and balances present in our cells designed to prevent the formation of wacky cells, and generally when a cell starts displaying bad behavior, such as uncontrolled growth, it will go through apoptosis. In the case of HPV infection, the presence of the virally-encoded oncogenes contribute to cancer formation by counteracting these checks and balances. However, infection alone is not sufficient for cervical cancer formation, and many cofactors have been demonstrated to contribute, such as age, smoking, parity (the number of times a woman gives birth), and other genital infections. Without such cofactors, the virus can lay dormant in the cells, causing no apparent disease. Additionally, as you mentioned, a large portion of HPV infections are initially cleared by the immune system.

Why do I know all this? Well, I did my graduate work on papillomaviruses--not the cancer part per se, but I listened to enough seminars on it to pick up this much at least. I have since moved on to work on flaviviruses, including (gasp!) West Nile virus. I am an avid listener of your show, it helps me through my daily public transit commute. Thanks and keep them coming.

Jessica
PS I also love TWIP, can I put my vote in for higher frequency here?

Sophie writes:

Still love your show, but I have a question about the discussion about viruses and their status: Why is it so important wether they are alive or not? I don't think many people really know when something can be called alive and would it actually make a difference if it was alive? As far as I know it would not make a difference (it's not like bacteria has rights), so why is everybody so interested in this question, when people cannot even agree on a definition of life?

Thanks for all the information.
-Sophie

Christine writes:

I was listening to podcast #69 today and was interested in the comments about mmr vaccine and it's effectiveness wearing off over time. I am in Australia and being 35 I got 2 doses of mmr as an infant and a rubella vaccination at 13. At 25 when I had my first child my immunity to rubella was considered "equivocal" or something like that and so after her birth I was again given a dose of mmr. Before getting pregnant with my second I was tested again and was "eqivocal" again and given another vaccination (less than 2 years since my last). When I came to have my third child, same thing with a gap of three years. My best understanding is that although I have some immunity it is not sufficient for protection from this disease. My doctor was concerned about me returning to teaching high school while preg. Luckily I was probably not exposed in my first preg and was kept too busy in later pregs to fit in work and kid(s).

I wonder how many other people there are like me out there contributing to outbreaks.

Christine
Avid twiv and twip listener.

Kurt writes:

I’m surprised at how few comments there are on iTunes. I’ve been listening for a long time, and figured huge numbers of others listen too. I gave you a nice review, but don’t know how to twitter. I hope your next contest has rules suitable for a technophobe. I came to you from iTunes, and never got around to looking at your website. The contest got me there, and I really like some of the links. Good work.

Your podcast is pitched over my head, but like any technical topic, just hearing the words lead to some level of understanding. The jokes need some work. I sometimes feel punished. Overall fun to listen to.

I appreciate what you are trying to do with distance learning. I listen to podcasts as I drive around Florida selling paint. I enjoy science, and lately have been listening to Physiology lectures by Gerald R. Cizadlo, Ph.D. Department of Biology The College of St. Scholastica. Take a look at http://faculty.css.edu/gcizadlo/ his lectures are on podcasts, and he puts his blackboard notes up on his website. That’s what I’d hoped for in your Virology 101 classes, since they are too dense for idle listening. I expect you will get to putting up lecture notes sometime. I like the pretty pictures of viruses.

Thanks for your good work. If I knew some arcane question I’d ask it, but, well, I don’t.
Kurt

Gary writes:

Just in case you haven't seen this yet: here is an article describing measurement of the driving energy released as individual bacteriophages inject genetic material into bacterial hosts -- I.e., the kinetic energy driving the process has now been quantified!!

http://pda.physorg.com/_news184588836.html

All the best,
Gary
PS: Again thanks for all your instruction. Your enthusiasm for, and love of virology is - without question - infectious.

Subbaro writes:

It was a good program on Reverse transcription of retro viruses. At least in a simplified way most of the aspects of it were explained. I would like to add that in addition to Cauliflower Mosaic Virus (CaMV), a plant Pararetrovirus of caulimoviridae, there are 20 different plant viruses belonging to BADNAVIRUS (Bacilliform virus with a dsDNA genome) group which show (para)retrovirus characters. Half of them are fully characterized now.

The following: Banana streak virus (BSV); Cacao Swollen Shoot Virus (CSSV); Citrus yellow mosaic virus (CYMV); Pineapple bacilliform virus (PBV); Rice tungro bacilliform virus (RTBV); Sugarcane bacilliform virus (ScBV) are economically very important viruses, especially RTBV which is associated with tungro disease of rice causing loss of millions of dollars. RTBV along with RTSV (Rice tungro spherical virus) a picorna virus produces lethal symptoms

Thanks
Subbarao

Jaturong writes:

I am a Thai doctor who is now doing Ph.D. study in Molecular Virology and Microbiology program at Baylor College of Medicine, Houston, TX. I know the show year ago from my fellow graduate student who sent out an e-mail to recommending TWiV to all students in our department and since then, I have become a big fan of the show. I am working on a mouse model system using mouse gammaherpesvirus to study the role of promyelocytic leukemia nuclear bodies (PML NBs) as host intrinsic immunity in acute infection and viral latency and the mechanism that the gammaherpesvirus uses to counteract these nuclear bodies.

Everything relates to viruses is always interesting to me, so I love every topic that has been discussed on the show. The show also encourages me to keep on working on my experiments even on days that things in the lab seem not to turn out as I expected. I also use the questions asked in the show to test my knowledge about virology by comparing mine with yours and the show’s guesses and I realized that there are many things I am supposed to know but I do not know. I do not have specific virology question right now but just wonder how do you manage your time to keep update of all virus-related articles and news, teach in classes, projects in lab, recording TWiV and response to those e-mails? After I graduate, I will be having my own lab and teaching virology in the medical school in Thailand as well.

Thank you for having a fantastic show for us and please keep it up. I really appreciate your input to educate people about viruses and am always looking forward to the next episode of TWiV.

Regards,
Jaturong

 

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