Opinion | Herpes B: A Hidden Menace in Monkeys

Picture this scene: someone in a tropical country wants to see monkeys living wild — sitting in groups, standing, playing, swinging through trees. Then, in a flash, one free-roaming primate leaps and draws near, perhaps hoping to receive a delectable treat. In the next nanosecond, a nip, bite, or scratch exposes the human to monkey saliva.

At this point, some might think: Oh my God, what if it has rabies?

But, wearing my exotic infection hat, I would like to pose another chilling question. What if, at that particular moment, the monkey had oral blisters and was shedding macacine alphaherpesvirus 1, commonly called herpes B?

Earlier this year, events resembling my fictional opening scene are what likely led a 37-year-old man who was enjoying Hong Kong’s Kam Shan Country Park — also known as Monkey Hill — to contract this dangerous virus of macaques. A few weeks later, the man was critically ill with B virus encephalitis which, untreated, typically kills 70% of its victims.

Since early April, when Hong Kong’s Centre for Health Protection released information about the herpes B sufferer, nothing more has been shared about his clinical status or survival.

A Quick Primer

Now for a helpful hint: if you know where to look, it’s remarkably easy to learn about herpes B virus. For today’s column, I turned to a specific online chapter in the 2024 edition of CDC’s indispensable travel resource often called the Yellow Book.

Here are some of its key takeaways.

• B virus is endemic both in Asia and North Africa. Old World monkeys, also called macaques, are its only natural hosts.
• Adventure tourists, children, vets, and lab techs are at highest risk for exposure.
• Anywhere from a few days to 3 to 4 weeks post-exposure, an infected human may develop flu-like symptoms and herpetic blisters at the inoculation site. Untreated, the illness will progress to ascending encephalomyelitis.
• In this final stage — even with aggressive antiviral therapy and supportive care — death fells almost everyone with full-blown central nervous system infection.

And now for a final notable caveat. Despite the frequency with which monkeys bite humans, herpes B infections are rare, no doubt because many sero-positive monkeys — just like people with herpes simplex 1 and 2 — have virus living in their neural ganglia but, most of the time, do not actively shed. Here’s one example for context: some years back, herpes B virus was serologically detected in roughly 25% of monkeys first brought in the 1930s to Florida’s Silver Springs State Park; during their 2015 mating season, only 3-14% of those antibody-positive macaques were actively shedding virus. Nonetheless, aggressive first aid (for example, immediate washing of a monkey bite with soap, povidone iodine, or chlorhexidine, followed by 15 to 20 minutes of copious irrigation with water) is recommended, as are prophylactic antivirals.

Finally, the National B Virus Resource Center, a biosafety level 4 facility at Georgia State University, is the only U.S. laboratory that does clinical testing of human specimens. The lab’s 24/7 help line is 404-413-6550; its email address is bvirus@gsu.edu.

Another Monkey Bite Victim

Once stories hit the internet about the critically-ill man in Hong Kong, I recalled a patient of mine who visited Bali and thankfully dodged a similar fate.

As a busy ad agency manager, the young woman I’ll call Nina* couldn’t wait for her tropical escape. On Day One, she basked on a beach and napped in her bungalow. On Day Two she headed to the Sangeh Monkey Forest, one of Central Bali’s leading attractions.

Ironically, the 15-acre preserve offers little natural food for primates, but no matter. Sangeh’s long-tailed macaques are more than happy to eat bananas, peanuts, and other treats sold to tourists and Hindu worshippers. Of course, Sangeh warns visitors not to feed monkeys, but that advice is often ignored, just as it is in many other overseas monkey enclaves.

Long story short: although Nina herself did not bring snacks, she was not spared from a run-in with the macaques. As soon as she entered the forest, she spied a female macaque and her still-wet newborn, then crouched to take a photo — ka-boom! First, one monkey jumped on her back and climbed atop her head, then a second mounted her leg. Several hours later, Nina finally saw the tear in her black silk pants and the bite in her thigh, at which point she quickly sought post-exposure rabies prophylaxis, including rabies immune globulin and several rabies shots. But it was not until I was contacted a week later that she started a 2-week course of valacyclovir (Valtrex) to fight off herpes B.

Looking back, we’ll never know whether it was simply good fortune or the drug that kept Nina from serious harm. But the potential risk was certainly clear: as shown in an earlier serologic study of 38 Sangeh Forest monkeys, more than 80% were latently infected with herpesvirus B.

A Final Prescription: Teaching Science and Common Sense

The GeoSentinel Surveillance and Research Network is a program funded by CDC and other public health agencies that tracks a wide array of infections and other health events in international travelers. In a 2020 paper about travelers’ exposure to animals, GeoSentinel authors analyzing 11 years of records found that the percentage of patients bitten by monkeys was second only to those bitten by dogs.

What does this say, I wonder, not just about 21st-century travelers but 21st-century humans? Has our modern fascination with animals somehow blinded us to the fact that certain microbes they harbor can be innocuous to them but foreign enough to cause us serious, even deadly harm?

Even though our recent pandemic has upped awareness of zoonoses, I believe that all of us — doctors and patients alike — need continuing, lifelong education about these infections. After all, they’re not going away. On the contrary, as our global population continues to grow and encroach upon new habitats, these threats are often ever-closer.

*Patient’s name has been changed.

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