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MMTV Common Mouse Virus and Human Breast Cancer

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Post by Crabby Fri 11 Jun 2021, 3:05 am

Hello, I have keeped Fancy Mice 3 times in my life, the first time when I was 17. Now I am 36.

While searching the Internet I came across an article about zoonoses caused by mice and there was mentioned MMTV, a virus that is responsible for cancer in Fancy Mice and also in all laboratory and wild mice. Almost 96% of all wild populations and 100% of laboratory populations are infected with it and almost every breast tumor in a Fancy Mice can be traced back to this virus.
It is transmitted to the young in breast milk and eventually causes breast cancer in females, and sometimes males too.

Now studies show that spontaneous human breast cancer (Without genetic predisposition) appears to be often linked to MMTV. However, there is also an HMTV, a virus from the same lineage mainly found in humans that appears to be involved in the development of breast cancer. However, clearly mouse-related MMTV viruses have also been found in human breast cancer. It is assumed that the infection of humans with MMT viruses already took place in the Neolithic or the Copper Age, since such virus DNA was found in human skulls from this time period.
It is assumed by some researchers that spontaneous breast cancer without genetic predisposition can be transmitted from humans to humans, from mouse to human and from mouse-eating animals such as dogs and cats to humans and that this is via bacteria that are in the saliva that act as a transporter for the virus:

https://www.nature.com/articles/s41523-019-0136-4

Personally, I have strong doubts about keeping mice now, on the one hand I have spent at least 6 years with Fancy MIce and their tumor virus, of course I also had old females who clearly had breast cancer, on the other hand I was perhaps lucky enough not to catch the virus.

Nobody in our family has had breast cancer, I don't want to be the first. It would break my heart to stop keeping mice, but on the other hand i dont want to be infected with a breast cancer spreading virus and spread it even to others.

What do you think, I googled once and found US sites where mice breeders died of breast cancer at an early age, or have breast cancer. Of course I have to say that I don't know whether this women had an MMTV-dependent tumor or other one, breast cancer is very common. What do you think about it and do you know mice and rat keepers who have / died from breast cancer?

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Post by River Sun 13 Jun 2021, 6:49 pm

Wash your hands before and after handling, as I recommend doing regardless, and carry on IMO. There's risk to everything in life and with this being a new discovery, and mice keeping being an old hobby, I'm not inclined to worry. Totally up to you, though, and the decision to play it safe is absolutely respectable. It's your body. Smile

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Post by Blue79 Sun 20 Jun 2021, 11:34 am

Hello, I’ve been searching info about this and I’m really worried, I have 6 mice actually, I love love them and they’re my biggest hobby but I got worried about my health because I don’t wanna get this virus that can cause breast cancer. Does anyone have more info about this? I don’t know what to do, I want to continue keeping my mice as always but at the same time I’m so worried about my health.

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Post by Dee67 Sun 20 Jun 2021, 3:35 pm

Seriously, @Blue79 and @Crabby , I think during our lives we are exposed to hundreds of different viruses, through the air, soil, water, animals and other humans. Unless you want to stay indoors in a filtered environment and never interact with anything, you take your chances. We have immune systems for a reason and you just need to exercise fair caution in life, like looking both ways before crossing the street. You can only decide for yourself what risks you are willing to take in life.

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Post by Crabby Mon 21 Jun 2021, 3:37 am

Nobody can know, if we don't get this virus already from our mothers with breast milk, or if we have got it from someone we where in body contact with.
What if we eat contaminated raw vegetables or fruit, which contained the virus?

On the other hand, the virus is not spread 100% in the population and its noticeable that the virus is more present in breast tissue from women with breast cancer.

Yes there are always dangers in life, but it is a difference between doing things that are not avoidable like crossing the street, driving car, having contact to people, eating at foreign people/restaurant and things like smoking, extreme sports, hanging out with questionable people and eating things that are known to be harmful to your body.
If we don't earn our money as a feeder breeder for reptiles, breeding or keeping mice is not something we have to do to survive.

I did more research but didn't find any study which clearly says that there is absolutely no connection, the problem is there is no bigger study to date to clear this issue. There are also no studies about pet owners and the virus, only about lab workers who developed antibodies against the virus, after they where working with the infected mice. The longer they worked with the animals, the more they developed antibodies. The problem is, developing antibodies doesn't mean to be protected, it only means the body is fighting against it. How did the virus entered the body of workers with protective equipment?

There is one case from early 2000s where a 28 years old female lab worker developed breast cancer one year after she was exposed to mice infected with the virus. It is is not documented if her cancer was positive for MMTV so it could be a coincidence. And if she was infected, how did it happen? Was she bitten by a mice? Did she hurt herself with a contaminated scalpel at a tumor dissection?

There are very little studies about female lab workers and cancer, this study from Sweden only finds a connection to chemical labs: https://oem.bmj.com/content/74/11/823
But an older study from Israel points for biomedical labs, which where the places where mice are used more often: https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.10312
But is there even a connection with mice? This was not measured in the studies.

I personally will wait and see if new studies are published, but I don't think we will get an answer soon, because most studies are just a way to make money for the researchers and they keep their cost low with small participant sample size. A large study with 10.000 participants or more which where needed to clear the connection between MMTV infections and human breast cancer development would be very expensive and only favourable, if big pharma was interested to create a vaccine like for cervical cancer.

The most important question is: Do healthy people without familiar/genetic breast cancer which are MMTV positive in their saliva and/or body tissue develop cancer more often than MMTV negative people? And this would need a follow up study of 10-20 years.

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Post by River Mon 21 Jun 2021, 7:05 pm

Life isn't just about what we need to do to survive, though. Smile 

IMO enjoying yourself -- chasing your dreams and participating in hobbies you enjoy -- is a really necessary part of being a healthy, well-rounded individual. And this will likely always come with some risk. I'm a huge birdwatcher. My ventures into the wilderness put me into all sorts of unnecessary danger. I live in Florida, where I come within feet of alligators and snakes and yada yada yada, but all in all, it's a relatively safe hobby and I enjoy it. Mice keeping is the same. They can certainly carry diseases, that's always been true, but it's not something I've ever let get in the way of enjoying our time together. 

Not to say you can't find safer hobbies. You likely can (is there any danger in scrapbooking...?), but it may be difficult. I'm not meaning to imply you're wrong to be careful about it, you're definitely not! These are perfectly valid concerns, and it's understandable to make whatever choice you make. I hope this doesn't come off as belittling how you feel! I'm just sharing why I'm not personally concerned with the current information. Smile

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Post by Crabby Wed 14 Jul 2021, 3:53 am

I've wrote a letter to what is here the National Cancer Institute and asked for an answer about the risk of the keeping of mice and MMTV/Cancer. The response was not surprising to me.

There is ongoing research and as long as there is no clear answer about this like with the HPV, Epstein Barr Virus and others, they recommend nothing in particular. They linked me to a site with standard phrases about hygiene and animal keeping. The site was very similar to this: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/322016/Guidance_on_reducing_the_risk_of_human_infection_from_pet_rodents.pdf

But I don't think that any normal person could follow these guidelines. Washing hands after every contact, cleaning cages with gloves and face mask, don't eat in the same room with the animals, don't let them touch your mouth. The guidelines are also for dog owners and I don't believe that any dog owner will follow this. Most people don't wash their hands after every dog contact, keep the dog away from the dining and living room. Where I live it is normal for dogs to sleep in the bed with their owners, people take their dogs to the restaurant.
I mean, if you have young children or you are a teenager yourself and you live with an animal, you wont keep this guidelines, that's just the way children are.
Rats and Mice throw out their bedding very often on the floor, urinating when moving around the room and they chew on everything. It is not unusual for children to have their pet rodents in their bedroom.
I mean the most people buy rats and mice because they are animals to interact with, not for viewing them behind a glass wall and interact with them with a face mask and gloves.
In that case, buying a reptile, spider or insect would be a better pet in my opinion, because they don't need so much interaction and can be kept behind a glass wall without getting bored.

Interestingly, there are also mouse strains who have already integrated the MMTV virus in their DNA and they smell different for other mice: https://www.pnas.org/content/99/8/5612
They smell different, because their immune system is altered, which makes them more prone to various infections, mentioned in another study about mice with genetic MMTV.

A similar phenomenon is the known mice coat colour blue(blue dilution), which is caused by an insertion of a leukemia virus in their DNA: http://www.informatics.jax.org/allele/key/85

Also widespread mutation Piebald is caused by a retrovirus insertion: https://www.nature.com/articles/s42003-020-0781-z

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Post by Dee67 Wed 14 Jul 2021, 5:33 pm

Wow, that's sone pretty interesting stuff! Thanks for the post, very informative. I do try to remember to wash my hands after handling my mouse, but then again I kiss him all over and my dog too, so... Undecided

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