One human’s harmless virus can be another animal’s worst nightmare, as a recent report well illustrates.
Veterinary researchers at the University of Florida have confirmed the first cases of herpes simplex virus type 1 (HSV-1) in lemurs, one of which may have been infected via a shared yoga class. Though the virus typically only causes mild cold sores in people, it proved fatal for all of the lemurs they tried to treat. The findings highlight the importance of being careful in how people interact with wildlife, the researchers say, especially animals that aren’t naturally immune to the viruses we carry.
“We should recognize that we can be dangerous,” senior study author Jim Wellehan, a professor at the University of Florida’s College of Veterinary Medicine, told Gizmodo.
Deadly lemur herpes
HSV-1 (also formally known as Human alphaherpesvirus 1) has been bumming a ride on humans for quite some time. Research has suggested that it first started infecting our direct ancestors about six million years ago. Today, about two-thirds of people under 50 worldwide are thought to carry HSV-1. And though it can be a life-threatening infection for certain groups, like infants, or an unseemly issue when it causes genital herpes, most people infected with HSV-1 will never experience anything more serious than cold sores.
Herpesviruses tend to be very specifically adapted to their hosts. HSV-1 has reached a sort of equilibrium with humanity, one that allows it to live in our bodies for decades without typically causing much trouble, but the same isn’t true when it ends up in some of our primate cousins, particularly primates that are less closely related to us. Studies have shown HSV-1 can be highly fatal in white-handed gibbons, common marmosets, and white-faced saki monkeys, to name a few. There have been reports of suspected HSV-1 in lemurs as well, but according to the researchers, this is the first time that veterinarians have confirmed lemur HSV-1 infections through molecular testing.
The report details four cases, all of which were privately owned and were either brought to the university’s Zoological Medicine Service for care or had a necropsy (the animal equivalent of an autopsy) performed by UF vets. Two cases involved ring-tailed lemurs (Lemur catta), one involved a black-and-white ruffed lemur (Varecia variegata), and another involved a Varecia hybrid lemur (Varecia variegata x Varecia rubra).
The sickened lemurs experienced neurological symptoms like seizures, and all had developed encephalitis, or an inflammation of the brain; some also developed ulcers along their throats. Tests found signs of the virus in all of the primates’ brains. Despite numerous treatments, including a common antiviral used for HSV-1 in people, none survived their ordeal.
The team’s findings were published last month in the Journal of Zoo and Wildlife Medicine.
Lessons to be learned
Human herpes infections do seem to be rare in lemurs, thankfully. And there are ways to further reduce this risk. The authors note that no suspected HSV-1 cases in lemurs have been documented at an accredited zoo for decades, thanks likely to the precautions that staff and researchers take when interacting with these animals, such as masking.
“I generally make it clear to our students that the main risk when working with these sorts of primates is not the primate to us, it’s us to the primate,” Wellehan said. “We need to recognize that we can carry scary stuff that can wipe out populations that are naïve to these things.”
Unfortunately, there are places where that risk might not be as recognized as it ought to be. The researchers wrote that one case involved an animal used in “lemur yoga classes for the public, which can reasonably be expected to have a high occurrence of human contact.” And this isn’t just a Florida thing either; similar programs can be found in other parts of the world.
The researchers say vets who treat human-owned lemurs should have HSV-1 on their radar, especially when the animals develop encephalitis or ulcers around their mouth and throat. And in general, “appropriate biosecurity measures and education of caretakers” who interact with lemurs should be implemented to minimize the risk of infection.
These cases might also highlight the role that viruses like HSV-1 play in the evolution of their hosts, the authors argue. Pigeons, for instance, carry a different herpesvirus that’s largely harmless to them but fatal to some of the birds-of-prey that feed on them. This reality may have helped the birds spread their wings far across the world, and it’s even possible a similar thing happened when humans and their HSV-1 started migrating out of Africa, the researchers speculate.
According to Wellehan, the mostly peaceful relationship we’ve formed with HSV-1 shows that survival-of-the-fittest often isn’t about being the faster or stronger animal around—sometimes it’s just about having the right immune response to a microbe.
