Does bestiality increase your risk of penile cancer?

Aah, the things one learns when awake at 3AM on a Saturday night. Via a few different Tweeps, I ran across this article from Men's Health magazine, titled "Urgent Warning: Sex with Animals Causes Cancer."

I probably should have just stopped there.

But no, I read the magazine article, which states:

Brazilian researchers polled nearly 500 men from a dozen cities, and found that--we're not joking around here--roughly 35 percent of the men had "made it" with an animal. That's a problem, because screwing a horse, donkey, pig, or any other animal was found to up your likelihood of developing cancers of the penis by 42 percent.

Of course, this meant that now, I had to go dig up the actual journal manuscript. Though nothing is cited by Men's Health, a quick PubMed search using the terms "sex with animals" and "Brazil" turned up Sex with Animals (SWA): Behavioral Characteristics and Possible Association with Penile Cancer. A Multicenter Study, published last month in The Journal of Sexual Medicine.

Though the MH write-up makes the research sound ridiculous, it's not a bad paper overall. Starting out with the observation that penile cancer is common in impoverished regions in the world but relatively rare in developed areas, the authors wanted to examine one possible difference in this urban/rural divide: bestiality. So they enrolled 492 individuals who had spent their childhood in rural areas: 118 cases who had penile cancers and 374 controls who were seen at the same clinics for other issues, including check-ups and "cancer prevention" (though it's not really defined what's included in that catch-all). All participants were asked a variety of questions about their sexual history, including sex with animals and humans (frequency, number of partners, the usual drill), circumcision status, as well as other factors that might influence cancer outcomes, such as smoking status and history of sexually transmitted diseases and other health conditions.

The authors did find in the univariate analysis (basically, looking at one factor at a time) that there were several statistically significant differences between the cancer group and the control group. These included smoking, a history of sex with prostitutes, the presence of penile premalignant lesions (not surprising) and phimosis (NSFW), a condition where "the foreskin cannot be fully retracted over the glans penis." As the title suggests, they also found that having sex with animals was significantly higher in the case than the control group (44.0 vs 31.6 percent, p<.008>

When they combined risk factors into their multivariate analysis, a few factors still remained in the model. Phimosis was the big one, with an odds ratio of 10.41; SWA was down the list at 2.07 (95% CI: 1.21-3.52, p=0.007). Penile premalignant lesions and smoking also remained, with odds ratios in the middle of the other two.

Finally, just because I know many of you out there are curious, they also break down those who have SWA by types of animals they, um, frequent:

The animal types most often cited were mares (N = 80), followed by donkeys (N = 73), mules (N = 57), goats (N = 54), chickens (N = 27), calves (N = 18), cows (N = 13), dogs (N = 10), sheep (N = 10), pigs (N = 6), and other species (N = 3).

Yes, chickens for 27 of them. I don't even want to know, but I'm sure if I did, I could find out somewhere on the Internets. Please, don't educate me on that one. They also note that almost a third of the men reported "SWA with a group of men." I'm leaving that one alone as well (especially as that one wasn't any different between cases and controls, so it didn't seem to be an important variable for penile cancer development).

So how do they explain these findings? Their discussion is a bit odd, in my opinion, and narrows in on the SWA finding to the exclusion of their other significant risk factors. Of course, coming from my background, my first thought regarding SWA and cancer jumps to infectious agents. They acknowledge in the introduction that the human papillomavirus (HPV) is associated with about half of penile cancers. Other species of animals can also be infected with papillomaviruses, such as the rabbit of jackalope mythology. A previous study identified five potentially novel papillomaviruses in Australia, just by doing skin swabbing. As such, it's certainly safe to say that we know very little about the diversity of these viruses that exist in other animal species, much less their cancer-causing potential. It would be fascinating to look at tumor samples from the men in this group who were known to have sex with animals, and see if any novel viruses (papillomas or otherwise) could be identified.

However, they don't limit their suggestion to only zoonotic infections. That's when it gets a bit weird to me, as they say things like:

Speculation exists regarding cancer status as an infectious disease in humans [24,25], as studies have suggested that tumor cells can be transmitted from one mammal host to another within the same species [26,27]. PC is frequent in equines [28], but transmission of malignancies between animals and humans has not been reported.Virology does not consider possible viral movement from animals to humans except in cases of zoonosis, such as rabies or pandemic forms of bird or swine flu. However, the hypothesis that the HIV epidemic resulted from simian-human virus transmission has not been fully explored.

Um, huh? First, the citation they use for the HIV claim is from 1999--indeed, at that point there was still a lot that was unknown about cross-species HIV transmission, but that was 12 years ago! The field has moved on since then. I'm baffled as to what they mean by their first sentence--as far as I know, "Virology" doesn't consider anything--"Virologists" do, and why would this not be a zoonosis? Though I think direct transmission of cancer cells (like in the case of the Tasmanian devil transmissible cancer) would be unlikely, transmission of microbes which could lead to cancer development is certainly plausible and well within the realm of virology/bacteriology/etc. In my opinion, it's infinitely more likely than the idea they also suggest of more directly carcinogenic animal secretions.

There were also a number of limitations in the paper. Though they grouped frequency of sex with prostitutes into a "more/less than ten times" dichotomous variable, I don't see any similar "dose" analysis for the frequency of SWA in their models, even though they did ask the men about this. They make one statement that "long-term SWA (>3 years) was reported by 64% of the PC patients and 46.6% of the controls (P = 0.044)." This difference was statistically significant at the usual cutoff (p

Anyway, with these limitations in mind, it does appear that Men's Health got it mostly right: don't have sex with animals if you value your penis. But it's unfortunate that they just go for the sensationalism and ignore the more important variables from a public health standpoint, like "don't smoke" and "if you have abnormal penile conditions, you may want to get those checked out, k?"


Zequi SD, Guimarães GC, da Fonseca FP, Ferreira U, de Matheus WE, Reis LO, Aita GA, Glina S, Fanni VS, Perez MD, Guidoni LR, Ortiz V, Nogueira L, de Almeida Rocha LC, Cuck G, da Costa WH, Moniz RR, Dantas Jr JH, Soares FA, & Lopes A (2011). Sex with Animals (SWA): Behavioral Characteristics and Possible Association with Penile Cancer. A Multicenter Study. The journal of sexual medicine PMID: 22023719

Antonsson and McMillan, 2006. Papillomavirus in healthy skin of Australian animals.

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I love what the title "Urgent Warning" suggests. It strikes me as the type of title you'd use for approaching hurricanes or if aspirin made your eyeballs explode. I cherish the idea that Men's Health readers specifically needed that warning urgently.

Thanks for the summary. Do you have any thoughts on the actually prevalence of bestiality in this population? 35% seems very very high to me.

I am a doctoral student in epidemiology working with some US based observational studies involving individuals with high rates of HIV and HPV. I would surmise that the individuals in our studies may often be often be offended if they were asked questions related to bestiality. This could potentially affect future retention, etc. I guess I'm wondering if there are is qualitative or quantitative evidence that this behavior is going on in even a small subset of individuals in the developed world (1%+). I would probably want at least qualitative evidence before asking about it in large observational study..

It seems high to me as well, but it's definitely not my area of expertise. According to the paper, Kinsey found that 8% of American men admitted to such behavior, so I guess I wouldn't be too surprised that it would be higher in rural/farming areas than in the population in general. And if they're doing it in groups, perhaps there is less of a taboo in certain areas of the country? All just speculation, but there's probably other research out there if one digs through pubmed...

I'm surprised the good doctor was surprised. She does after all reside in Iowa. As a life long resident of Illinois I can attest to the notion that Iowa appears to be an area frequented by those who would be more likely to engage in this activity, as well as being potentially populated by human/animal chimeras. A very scary place indeed.

By Mike Olson (not verified) on 13 Nov 2011 #permalink

I'm surprised 35% of men admitted that they had sex with animals. Even if 100% of those polled actually did, I'd be amazed if up to 35% actually said so. Is bestiality stigmatized to a lesser degree in Brazil than in the US?

By Walter Brameld IV (not verified) on 13 Nov 2011 #permalink

Thanks for the reply Dr. Smith. I took a quick look and that paper by Kinsely was published in 1948 and I didn't see anything about sex with animals at first glance.

My guess is that some studies must have asked about bestiality during the beginning of the HIV epidemic...I may look further I have the time.

Given the trouble they've got with men remembering how many human sex partners they've had, why would they think this kind of self-reporting was credible to the extent that they could get reliable statistics on it? What number of men lie about their having sex with animals? I'd guess there would be a significant amount of lying on that question leading to under reporting.

I agree re: self-reporting, but if anything, you'd think the issue would be with under-reporting--so the odds ratios found here would likely be the lower end of "reality." It also depends on how they gathered the info. Because of low literacy rates, they used interviews rather than written questionnaires. If the interviewers were from the same areas/backgrounds as the participants, that may make them more likely to be truthful and open up about sexual history. But I agree, it's still going to be dicey--which is why some molecular data supporting this would be a helpful addition. If they could find animal-source viral markers in penile cancer tissue, that would open up all sorts of new avenues...

I was told about this second hand. A colleague encountered a group of armed men out in the Venezuelan coastal deserts. He was told they were from the ministry of health and were killing wild donkeys because they were a reservoir for syphilis. I have read there is some evidence that syphilis in humans originated from contact with llamas in the Peruvian Andes, and then made its way to Europe. I've been told that fishermen in Venezuela, when they catch a female river dolphin, will have sex with her before releasing her back to the river.

By Jim Thomerson (not verified) on 13 Nov 2011 #permalink

Ladies and gentlemen, I give you... next year's Ig Nobel Prize winners.

Heck, lets give them the prize for the year after that too. They've earned it.

Hm, I had never heard the llama-syphilis thing before, but from what I can find in the literature, it's an urban legend and llamas aren't susceptible to syphilis (Medicine and surgery of South American camelids: llama, alpaca, vicuña, guanaco by Murray E. Fowler). Donkeys, I don't know.

I heard Kinsey found than one in four american males who'd lived or stayed on a farm had a big tick in the bestiality box!

Not if you're a woman.

Pretty certain about that one.

Sex with chickens?
That's foul!

It could be bull...

While the conclusions seem at first blush a bit of a reach, one should remember HIV was initially contracted from human/primate contact, as ebola and a few other unpleasant virii through exposure to the animals blood.
Then, there is the Xenotropic murine leukemia virus-related virus link with human prostate cancer, though German researchers were unable to detect the virus (US researchers did).
THAT said, I'd consider carcinogenic compounds in the animals, as you have suggested. A virus wouldn't typically remain at the point of introduction to the body.
Only time, research and diligence will tell.

Actually, my money would be more on the viruses. Something like HPV can certainly remain in the epithelial surfaces for months/years (in humans, at least; no idea of duration in animals), and blood-borne viruses such as HIV that persist in secretions could enter via microtears.

There are two things I would like to say about the incidence of bestiality

1. If X% of men claim to have bestiality and if X is as high as 35, then it is very likely that bestiality may be the "natural" order of things. So it is not inconceivable that an average healthy man should be having "bestial fantasies" X% of the time (relative to the time he has sexual fantasies, not his total living time), even if he is not into bestiality. This argument does hold much less water if X is very low.

2. 35% is way higher than homosexuality. Is it really likely that bestiality would be more prevalent than homosexuality ?

I personally feel those Brazilians are lying ... maybe pulling the leg of someone doing such stupid surveys

"one should remember HIV was initially contracted from human/primate contact"

Although one method of transfer was via bushmeat, but under a meaning of "protein-rich flesh" as opposed to anything naughty.

Rogering a chimp would be rather dangerous.

"So it is not inconceivable that an average healthy man should be having "bestial fantasies" X% of the time "

I'm remembering "Halfway Up Virginia" by Ivor Biggun. One verse goes:

I'll give those cows a miss
'cos you feel such a cnt
rushing 'round to the front
to give those critters a kiss

PS Hopefully it was a *leg* they were pulling...

There are zoosexuals who have sex with animals and bestialists who have sex with animals.

In Brazil there are MANY bestialists for these reasons: sex with animals is more tolerated, is also believed that it will make your penis bigger, it is also used as an initiation ritual to have sex with an animal before even trying sex with a human, it is also used as a way of masturbation, also as a way of social bonding (instead of going with the friend to a bar for drinks, they go with friends to a barn to screw a mare)it is not like homosexuality at all.

They pretty much, they use animals sexually in the same way we use animals for their meat.

Zoosexuality (sexual orientation for animals) is rare, you can't turn poeple into zoosexuals, but you can turn people into bestialists.

PS: I'm a zoosexual and I know a lot about the subject, if anyone has any questions, you can find me on my youtube channel.