Scientists Have Discovered a New, Potentially Brain-Invading Tick Virus

Ticks may cause even more harm to humans than we knew. Scientists in China believe they’ve discovered a novel tickborne virus that can infect people and other animals. Though the scientists have only identified a handful of human cases so far, the virus does appear capable of making us sick and potentially invading our brains.

According to the findings, detailed in a New England Journal of Medicine paper published earlier this week, the first known victim of this virus was a 61-year-old man who was admitted to a hospital in the city of Jinzhou in June 2019 with fever, headache, and signs of dysfunction across multiple organs. Five days earlier, he had been bitten by ticks while visiting a wetland park in Inner Mongolia (around Northern China), suggesting a possible origin of his illness. He also didn’t respond to an initial course of antibiotics, indicating that a viral infection was to blame.

And when the scientists tested his blood, they came across a never-before-seen viral agent. Next-generation genetic sequencing revealed that their mystery virus belongs to the orthonairovirus genus in the Nairoviridae family, and is a close relative to other tickborne viruses such as the Crimean-Congo hemorrhagic fever virus. They decided to dub their find the Wetland virus, or WELV.

Following this initial case, the researchers next decided to look for the virus elsewhere, in both people and animals living near the region where the man had likely contracted the infection. They found the virus lurking in a small percentage of five different tick species, most commonly in Haemaphysalis concinna ticks, which are known to spread other tickborne diseases. They also found the virus in a small number of sheep, horses, pigs, and a kind of rodent known as the transbaikal zokor. And when they looked for the virus in the blood of patients who became feverish within a month of a tick bite, they retroactively identified 20 potential cases of acute WELV infection, including 17 where WELV was the only tickborne germ found in their bodies.

These WELV patients tended to experience a variety of nonspecific symptoms like fever, swollen lymph nodes, and dizziness. Some of these patients showed signs of tissue damage and blood clotting, and one patient slipped into a coma as a result of their illness. That patient also showed signs of a neurological infection, with increased white blood cells found in their spinal fluid. Thankfully, all of the identified patients did eventually recover. But when the researchers dosed mice with strains of WELV collected from their original patient and ticks, they found that the virus could reach the brain and cause lethal infections in these animals.

More work needs to be done to confirm the danger that WELV poses to humans and to better understand the virus, the researchers say. One hypothesis that the researchers have, for instance, is that WELV can be passed down through generations of Haemaphysalis concinna ticks through the ovaries of female ticks—a survival trick that other tickborne parasites are known to employ. The researchers also found WELV antibodies in some dogs and cattle, suggesting a larger range of animal hosts. At the same time, they identified WELV antibodies in a small percentage of seemingly healthy park rangers, possibly indicating that the virus doesn’t always sicken people who catch it (other human tickborne infections often go unnoticed for this same reason). So there’s still a lot more to be learned about this new potential tickborne foe and others like it.

“Initial symptoms of WELV infection manifest as nonspecific illness, thereby necessitating a differential diagnosis from other tickborne diseases,” the researchers wrote. “Improving surveillance and detection for emerging orthonairoviruses will allow a better understanding of the effect that these viruses have on human health.”