What Clinicians Need to Know

Europe is experiencing increasing prevalence of arbovirus diseases — those transmitted by arthropod vectors such as mosquitoes, ticks, or sand flies. These diseases, including dengue, chikungunya, and Zika, have traditionally been endemic to the tropical and subtropical regions of South America, the Caribbean, Africa, and Asia. Their frequency and scale have increased globally in the past two decades, and the geographic range of transmission has expanded into areas previously unaffected, including non-endemic regions in Europe.

While most cases are imported, mosquito species and ticks are establishing themselves further northwards and westwards in Europe. According to the European Centre for Disease Prevention and Control (ECDC), between 2021 and 2024, the number of autochthonous (locally acquired) dengue outbreaks and cases increased considerably, and chikungunya and Zika infections have also now been reported in Mediterranean regions.

Arbovirus Diseases Becoming More Common

Tamás Bakonyi, ECDC principal expert on vector-borne and zoonotic diseases, told Medscape Medical News that arbovirus diseases have become more common in Europe due to a combination of environmental, biological, and societal factors.

Climate conditions can change the environment in which infectious diseases thrive, contributing to their increase and impact, he said. Rising temperatures, milder winters, more frequent extreme weather events, and changing rainfall patterns may create more favorable conditions for the transmission of several vector-, food-, and waterborne diseases.

“Vector-borne diseases like dengue, chikungunya virus disease, West Nile virus infections, Lyme borreliosis, and tick-borne encephalitis are particularly sensitive to changes in temperature, humidity, and rainfall,” he explained. Warmer temperatures increase mosquito and tick survival and shorten pathogen incubation times, which in turn accelerates disease transmission cycles.

Most Cases Imported

International travel has led to the importation of arboviruses from endemic regions to Europe, Bakonyi said. This underlies most reported arbovirus infections in Europe but may spark local outbreaks. The ECDC collects data on imported cases on an annual basis. Its latest interactive surveillance atlas, for the year 2023, showed across the EU:

• Dengue: 5027 travel-associated cases vs 129 locally acquired cases.
• Chikungunya: 320 imported cases including in Spain (191), Germany (44), and France (39), with no reported locally acquired cases.
• Zika virus infection: 79 travel-associated cases with none locally acquired.

In addition, the ECDC collects seasonal data over the summer on locally acquired cases of various arboviral diseases. Its latest communicable disease threats surveillance for the week ending August 01, 2025, showed:

• Locally acquired dengue in three European countries in 2025 so far: France (6, including 2 new cases since the previous week), Italy (3), and Portugal (2 in Madeira).
• Locally acquired chikungunya in France (49) and Italy (2) so far during 2025.
• Up to 30 July, Crimean-Congo hemorrhagic fever cases were reported in Greece (2) and Spain (2).
• Up to 30 July, human cases of West Nile virus infection were reported in Bulgaria, France, Greece, Italy, and Romania.

Be Alert for Symptoms

Clinicians across Europe this summer should be on the alert for symptoms of arbovirus infections, both mosquito-borne and tick-borne diseases, Bakonyi advised.

Dengue — Most cases are imported by travelers returning to the EU from endemic areas, but these may generate local, mosquito-borne transmission in areas with competent vectors and supportive climatic/weather conditions. Transmission is primarily by Aedes aegypti globally and Aedes albopictus in Europe, where the species is increasingly frequent. Symptoms include an acute, high fever, occasionally progressing to hemorrhagic fever, with headache, myalgia, arthralgia, and a maculopapular rash. Up to 5% of cases can be severe, with increased vascular permeability that can lead to life-threatening hypovolemic shock.

Chikungunya — A notifiable disease at the EU level. Around a third of cases are asymptomatic; the remainder are characterized by sudden onset fever, chills, headache, myalgia, nausea, photophobia, incapacitating joint pain, and petechial or maculopapular rash. Recovery may take months but typically occurs within 10 days and gives lifelong immunity.

Zika — Generally asymptomatic, but may cause mild fever, arthralgia, and fatigue, with a maculopapular rash, conjunctivitis, myalgia, and headache. It is usually short (2-7 days) and self-limiting, but infection during pregnancy may lead to congenital central nervous system malformations such as microcephaly, with a raised risk for fetal loss.

West Nile fever — About 80% of infections are asymptomatic but may cause fever, headache, malaise, myalgia, fatigue, and eye pain, sometimes with a rash. Some 1%-10% of cases may be severe, especially among older people. Most cases in humans occur between July and September, when mosquitoes are active.

Diagnosis More Difficult

Diagnosis should be on the basis of clinical presentation and epidemiologic context, as well as laboratory tests, which vary by disease, Bakonyi said. Testing has become more difficult recently due to the global expansion of arboviruses, leading to antibodies that cross-react on serological assays.

As for treatment, Bakonyi recommended referring to the World Health Organization (WHO), which issued its first global arbovirus guidelines in July. These also point to the difficulty in distinguishing between arboviral infections because early symptoms often overlap.

Treatment Largely Symptomatic

Treatment is largely symptomatic in mild infections. With suspected or confirmed nonsevere dengue, chikungunya, Zika, or yellow fever, the WHO recommends oral rehydration, with paracetamol or dipyrone for managing pain and fever. Corticosteroids are not recommended in nonsevere infections, and nonsteroidal anti-inflammatory drugs should be avoided in all cases.

For hospitalized patients with suspected or confirmed severe arboviral disease, the WHO recommends:

• Prefer crystalloid fluids over colloids for intravenous (IV) rehydration.
• Use capillary refill time and serum lactate levels to guide decisions on IV fluid management, with a passive leg raise test for patients in shock.
• Avoid systemic corticosteroids and immunoglobulins.
• Avoid prophylactic platelet transfusions in patients with platelet counts < 50,000/μL unless there is active bleeding.

Sheena Meredith is an established medical writer, editor, and consultant in healthcare communications, with extensive experience writing for medical professionals and the general public. She is qualified in medicine and in law and medical ethics.