PRISTINA, KOSOVO—Magnified on a monitor in Kurtesh Sherifi’s laboratory, the 6-millimeter-long, armor-plated male Hyalomma marginatum looked formidable. Even more unnerving, the tick is a hunter, says Sherifi, a veterinary parasitologist at the University of Prishtina. Unlike ticks that wait on vegetation for a passing host, Hyalomma, the principal vector of the virus that causes Crimean-Congo hemorrhagic fever (CCHF), can travel hundreds of meters in search of cattle or another animal, Sherifi says. “If we’re in the field, Hyalomma are running after us.”
Kosovo has long been one of Europe’s hot spots for CCHF, a human disease that can progress from fever and muscle pain to liver failure, severe bleeding, and death. From 2013 through 2016, some three dozen people here were hospitalized and about one-third died. But decades of confronting CCHF have also made Kosovo, Europe’s newest country, also one of its most experienced in detecting and monitoring the disease.
Now, virologists are advising other European nations to draw on that expertise as the virus gains ground across the continent. “There should be concern, especially because of climate change,” says Maryam Keshtkar-Jahromi, an infectious disease specialist at Johns Hopkins University. A review she co-authored, published in June in Virologica Sinica, concluded that CCHF could cause severe outbreaks in previously unaffected areas. Spain has recorded locally acquired CCHF since at least 2013 and continues to see sporadic infections, including three so far this year, one fatal. Portugal confirmed its first case in 2024; the patient died. And in 2023, CCHF virus turned up for the first time in ticks in France, where no locally acquired human case has yet been reported.
“My suspicion is that we will find CCHF in a lot of places we didn’t expect it,” says Jens Kuhn, an independent virologist who formerly directed virology at the U.S. National Institute of Allergy and Infectious Diseases’s Integrated Research Facility.
Hyalomma have been hitching rides into northern Europe on migrating birds for decades. But until recently, the ticks often encountered conditions too harsh to complete their life cycle. A warming European climate is changing that: Higher temperatures and longer summers now make it more likely that immature ticks will develop into adults and perhaps establish local populations, says Mohammed Parvage, an environmental scientist at the Swedish Veterinary Agency.
A 2025 review found that Hyalomma ticks had been reported at least once in 40 European countries. Finding Hyalomma doesn’t necessarily mean the CCHF virus is present. But surveillance for it remains patchy across Europe, leaving an incomplete picture. “Countries that think they don’t have a particular virus typically don’t test for the virus,” Kuhn says.
Scientists also tend to focus on pathogens only after they cause conspicuous illness, Kuhn says, rather than while they circulate quietly in animals and vectors. In parts of Europe, researchers have already found evidence of CCHF virus circulating in ticks or animals without recent human cases. Once CCHF appears on a country’s radar, diagnostic panels may expand—and suddenly more cases are detected.
Kosovo has spent decades learning how to look for CCHF. Its national public health laboratory was already performing antibody and polymerase chain reaction testing before the 2013 outbreak, often returning results the same day, says Xhevat Jakupi, a microbiologist at Kosovo’s National Institute of Public Health. Since then, its diagnostic and sequencing capabilities have expanded. Just as important, he says, is accumulated experience: “We know what works well and what doesn’t work.”
Such systems can take 10 to 20 years to mature, Keshtkar-Jahromi says. She argues that Kosovo, Albania, and Bulgaria, which have established surveillance systems, could help anchor a regional diagnostic network. This could involve broader surveillance of ticks and the pathogens they carry, Kuhn says, coupled with better tick identification and greater awareness among physicians.
A wider lens has already produced surprises. In 2022 and ’23, Sherifi and colleagues discovered two previously uncharacterized viruses in sand flies; antibodies to one, Grapi, later turned up in human blood samples, although it has not been linked to human disease. The findings hint at a much larger hidden viral diversity, says Vít Dvorák, an entomologist at Charles University who collaborated on the work. “The more you survey, the more of the viruses you’re finding.”
As other countries confront the risk of CCHF, the human disease in Kosovo has dwindled to sporadic cases. Hyalomma remains common and the virus is still turning up in ticks: In a 2024 survey, Sherifi and colleagues found CCHF viral RNA in 16 of 1301 ticks collected around the country. Yet from 2016 through 2025, Kosovo recorded a mere five human cases. “We’re feeling more relaxed compared to previous years,” Jakupi says. “But we’re not sure how long this will last.”
After the 2013 outbreak, authorities stepped up farmer education, treated livestock with tick-killing acaricides, improved diagnostics, and expanded tick surveillance. Sherifi believes those measures helped drive down cases of human disease. Fewer Kosovars now work small farms by hand, he says, and mechanization means fewer people encounter tick-infested livestock. (Livestock don’t appear to get sick from the virus.) Farmers are also more aware of the danger of pulling ticks from animals with bare hands.
Another possibility is that the virus has simply entered a lull—or that it continues to circulate, with many human infections going undetected. A 2012 survey found CCHF antibodies in 4% of 1105 Kosovars without signs of infectious illness, suggesting many infections had gone unrecognized. The unusually high mortality rate among those diagnosed with the disease could reflect an undercounting of people with mild or no symptoms, Keshtkar-Jahromi says. “They don’t come to the hospital,” she says, so confirmed cases may represent “the tip of the iceberg.”
The prospect that infections can remain undetected adds urgency to calls for better surveillance. “The first diagnosed human case may not be the beginning of the story,” Parvage says. “It may simply be the first time we notice it.”