This summer has brought extreme heatwaves, increasing demand for air conditioning and causing more than 10,000 excess deaths across Europe. Alongside these record-breaking temperatures, epidemiologists are monitoring an uptick in vector-borne diseases, illnesses caused by bacteria, viruses, or parasites carried by a vector, usually mosquitoes or ticks, and in some cases rodents. Commonly known vector-borne illnesses include Lyme disease, malaria, dengue fever, West Nile virus, and Zika virus. While many of these illnesses are endemic to parts of Africa, Southeast Asia, and Central and South America, and travellers may import them into Western countries, extreme heat and climate change are altering seasonal patterns, resulting in increased numbers of cases within the West.
A Longer Season for Ticks—and the Diseases They Carry
In the northeastern U.S. and Canada, tick populations and bites have significantly increased this summer. Infectious disease experts are seeing greater cases of alpha-gal syndrome, which causes a person to become allergic to mammalian meat and dairy products, usually after being bitten by a Lone Star tick. Lyme disease, the most common tick-borne illness, and anaplasmosis, which can cause a fever and severe head and muscle aches, can be the result of being bitten by an infected blacklegged tick.
The Expanding Mosquito Map: How Heat and Humidity Are Changing Disease Risk
Mosquito populations are also on the rise as longer periods of warm temperatures and greater humidity allow mosquito activity to start earlier in the year. Various species previously confined to tropical regions are expanding their territory. The US Centers for Disease Control’s 2026 data show that, as of July 14, 81 cases of West Nile virus were reported across 18 states, with 50 cases in Arizona alone. Of these, 57 were classified as neuroinvasive cases. Because some vector-borne illnesses can lead to cognitive impairment or organ failure if left untreated, preventing exposure is especially important.
Avoiding the Bite: How Individuals Can Reduce Their Risk
In July, the UK government advised travellers to take precautions against infections while abroad after imported cases of dengue and Zika were reported in the country.
The advisory suggests, “using insect repellent, covering exposed skin and sleeping under a treated bed net where needed, as well as practising good food and water hygiene and getting vaccinations and malaria prevention tablets where appropriate.” Though lesser-known than malaria and Lyme disease, the mosquito-borne Zika virus gained attention in 2014 and 2015, when it caused an epidemic in Brazil and spread to other parts of North and South America. The virus can cause skin rashes and microcephaly, or a condition in which babies are born with a smaller-than-expected head size, when mothers are infected during pregnancy.
According to the UK Health Alliance, “There is also an increased risk of vector-borne diseases in the UK due to the changing distribution and activity of vectors such as ticks and mosquitoes. Warmer temperatures may expand the range of tick species which transmit Lyme disease and tick-borne encephalitis.” The changing climate is altering migratory patterns for wildlife that may be infected by these illnesses, and the incubation and breeding cycles of the vectors themselves are also changing. This past winter in Europe was unseasonably warm, allowing more ticks to survive and reproduce.
Tracking the Threat: The Race to Monitor Emerging Diseases
In 2017, the World Health Organization adopted a resolution on Global Vector Control Response Through 2030, focusing on improving surveillance, clearly defining national research agendas, engaging communities, and scaling up integration tools.
The UK’s Human Animal Infections and Risk Surveillance (HAIRS) group monitors mosquito-related illnesses such as Zika virus, Chikungunya, West Nile virus, Dengue fever, and Usutu virus; and tick-borne illnesses including Crimean-Congo haemorrhagic fever, and tick-borne encephalitis. In the U.S., some federal monitoring programmes remain in place, but after sweeping cuts to the federal workforce, infectious disease monitoring and testing have faced setbacks. Universities, along with local and state governments, are left to manage the bulk of programs. In Canada, some research labs allow people to mail ticks to them for identification after they have been removed. This has proved helpful in monitoring species that have expanded into new territory, such as the Longhorned tick and Lone Star tick.
Public health experts are warning people to take extra precautions when outdoors, including using insect repellent containing DEET and regularly checking for ticks, which is easier to do when wearing lighter-coloured clothing. People should also be aware of standing water, which can become a breeding ground for mosquitoes. Symptoms of vector-borne illnesses may not appear for one to two weeks after exposure.
Sarah Sakeena Marshall, Consultant, Writer, Editor, Climate Change and National Security
