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Case 2: flu like illness

A 36 year old male who has recently returned from Southern France now presents with a flu like illness. He describes feeling exhausted with a fever, rash and vomiting. He tells you he got bitten lots by mosquitoes when in Southern France, and feels just like on his gap year when lots of his friends got unwell in South East Asia.
What are the likely or possible causes?

The best fit is probably Dengue fever, though other possibilities include malaria and zika. It is also appropriate to consider non vector illnesses (flu and covid for instance). This scenario suggests that in the same way as clinicians have adapted to include Lyme’s disease as ticks have become endemic in UK (rather than isolated to the New Forest) climate change is bringing us new diseases which will have to be part of the differential diagnosis.

Do you know which types of mosquitoes are involved in these ?

Aedes Aegypti is the main mosquito associated with Dengue (also with Zika). 

Anopheles is the group associated with Malaria.

What is the effect of planetary health changes on the distribution of mosquitoes?

Warmer temperatures are associated with an enlargement of the distribution of mosquitoes. So Aedes mosquitoes (not necessarily A Aegyptii) have developed a wider distribution over the last years. The latest data suggests it is introduced but not established in Kent and neighbouring areas in the UK and established in much of France and almost all of Germany. Data from 3-4 years earlier had a much smaller European distribution.

As many people getting dengue are asymptomatic it is likely that once Aedes is established Dengue will follow.

Malaria is not currently (2024) endemic in UK (though cases have been identified in people living close to major airports from mosquitoes imported in aircraft. There are reports of endemic malaria from France and Greece.

Virus carrying mosquitoes (Culex which is associated with West Nile virus) have been found as far north as Finland. 

Does increased heat change the speed of the reproduction of mosquitoes, or the amount that they feed/ bite?

In warmer climates mosquitoes have a faster rate of reproduction/shorter intergenerational period. The mosquitoes will also bite more actively in hotter weather (NB only female mosquitoes bite).