Some strains of human papillomavirus (HPV) can cause cervical cancer, so you often hear about it as a 'female' sexually-transmitted infection. It's not — it's a human thing, and all humans can get infected. Here's what happens when males get it.
Most of the people who are exposed to HPV fight off the virus, so it's not a simple equation of 'get infected, get cancer.' It's a cascade of bad luck: a cancer-causing strain of the virus infects a person who can't fight it off effectively. There's no way to predict ahead of time whether an individual is one of the unlucky. But a new study by Staci Sudenga and her colleagues in press at European Urology gives us a better idea of how these infections progress over time.
Their study followed 3033 healthy men between the ages of 18 and 70 living in either the United States, Mexico, and Brazil for two years. Every six months, subjects would come in for a physical exam and HPV testing to determine whether they had picked up a new infection or fought off an old one. Men who developed genital lesions had a small sample removed for genetic testing, to identify which strain of the virus was living inside it.
The study found that HPV infection was incredibly common: one or more of the 37 known strains of the virus turned up in more than half of the patients in the study — sometimes multiple strains per person. But only 5% of the men who contracted HPV developed any visible symptoms. And most of those men were infected with one or more of three strains of the virus: either HPV6, HPV11, or HPV16.
The strain mattered. The small subset of unlucky patients who showed visible symptoms over the course of the two year study mostly developed genital warts, and most of those patients were carrying either HPV6 or HPV11. Precancerous lesions were extremely rare, turning up in less than 1% of the men surveyed. But most of those men were infected with HPV16 (although some of them also carried HPV6, HPV11, or HPV73).
Fortunately for those in the US and in a preventative state of mind, the three HPV strains that were most likely to cause lesions are part of both the quadrivalent and nine-valent HPV vaccine, both of which are licensed for use.
Image from the CDC.