Emerging Viruses in Spain: Nile, Crimea-Congo & Dengue Cases Rise

European medical professionals are observing a concerning trend: an increase in locally acquired infections from viruses typically associated with other regions. Specifically, doctors are reporting cases of the West Nile virus, Crimea-Congo hemorrhagic fever, and dengue fever originating within Spain, prompting calls for heightened diagnostic vigilance.

Rising Concerns Over Vector-Borne Diseases

The alert stems from a session titled ‘Emerging Viruses in Europe’ held during the XVI Infectious Diseases Conference, organised by the Working Group on Infectious Diseases of the Spanish Society of Internal Medicine (SEMI) between February 19th and 20th. Participants emphasized the need for physicians to consider these diseases as potential causes even in patients without a history of travel.

The Role of Climate and Globalization

Dr. José Manuel Ramos, a member of the SEMI Working Group, highlighted the contributing factors. “Climate change and globalization are favoring the conditions for insects or vectors that cause certain infectious diseases to live better in our environment,” he stated. He further explained that imported cases from travelers could also lead to local transmission, creating new, domestically-acquired instances.

Did You Know? In 2024, Spain reported 158 autochthonous (locally acquired) cases of West Nile fever, along with two imported cases from Malta and Morocco.

Alongside increased diagnostic awareness, SEMI is urging the public to take preventative measures, focusing on protection against insect and tick bites. This is particularly important as effective vaccines are often unavailable for these emerging viruses, making prevention and symptomatic treatment the primary strategies.

Understanding the Symptoms

While some infections may be asymptomatic, most individuals experience symptoms that can range in severity. Common symptoms include general malaise, muscle aches (myalgias), and joint pain (arthralgias). West Nile virus can also manifest as a severe headache and confusion due to meningoencephalitis, with greater morbidity than mortality, particularly in older individuals.

The consequences of these infections can be significant. West Nile virus can lead to problems with attention, memory, and mobility. Crimea-Congo hemorrhagic fever carries a 20% mortality rate and can cause major organ failure, including kidney failure, jaundice, and proteinuria.

Expert Insight: The increasing prevalence of these viruses in Europe underscores the interconnectedness of global health and the impact of environmental changes on disease patterns. A proactive approach to surveillance and public health education is crucial to mitigate potential outbreaks.

Data from the European Centre for the Prevention and Disease Control (ECDC) indicates 989 cases of West Nile virus across 14 European countries in 2025, including Spain. Dengue fever, transmitted by the Aedes albopictus mosquito (also known as the tiger mosquito), saw 1,119 reported cases in Spain two years prior, with 788 confirmed. Cases of Crimea-Congo hemorrhagic fever, spread by Hyalomma ticks, have been gradually increasing in Spain since 2016.

Frequently Asked Questions

What are the peak months for dengue fever activity?

Dengue fever has its highest activity between May and October.

How is the Crimea-Congo hemorrhagic fever transmitted?

The virus causing Crimea-Congo hemorrhagic fever is transmitted through the bite of ticks of the genus Hyalomma.

What is the mortality rate associated with Crimea-Congo hemorrhagic fever?

The mortality rate for Crimea-Congo hemorrhagic fever can be as high as 20 percent.

As climate patterns continue to shift and global travel increases, these trends will continue, potentially leading to more frequent and widespread outbreaks of these and other vector-borne diseases. Continued vigilance and preventative measures will be essential. What role do you think international collaboration will play in addressing these emerging health threats?