Strange allergy

Hi Superkev
This is something that I am battling with at this very moment, so I'm interested to hear if anyone else has experienced this and what they think it is. My husband also suggested yesterday that it might be an allergy.
I don't know if you've ever travelled to Mozambique, but specifically near the mangrove swamps in Inhambane, you get bitten by what they call "palm flies". You don't see them at all (they're tiny), or hear them, or feel them biting you, until you start to itch like crazy. Of course, you scratch yourself raw and then the bites ooze and form scabs. The itching flares up every few days for a good couple of weeks at a time.
My husband and I both experienced this at our home in South Africa as well, which was on the banks of a river full of plane trees, which also host these flies.
Here, we live in central Lisbon, not much vegetation around us and I'm being plagued with exactly the same "bites" - my husband and my daughter not at all! 

Apart from antihistamines, what really helps is to use the same prevention techniques as you would for mosquitoes: from late afternoon/early evening, cover up your feet and legs and wear long sleeves, and smear yourself with anti-mozzie cream! I've been doing that for the last couple of nights and haven't experienced any new "bites".

Hoping someone else can weigh in here!