I would suggest that if you're doing a race through the jungle your biggest problem is likely to be potential foot rot. Your feet will get very wet, both from sweat and from the high humidity.
I'd suggest having a couple of pairs of shoes which you can interchange on a daily basis to give each a chance to air and dry out (although if extremely humid there's not much chance of anything remaining totally dry). Keep all your clean socks in ziplock polythene bags to keep them dry. Use two-layer socks to stop blisters. Whenever you have the opportunity, take off your shoes and let your feet breathe. At night, slather Vaseline over your feet and sleep in thin cotton socks to allow it to be absorbed into the skin. Powder your feet with talcum powder before putting on your running socks each morning - helps to absorb moisture and keep feet fresh.
That's about all I can think of for the moment!
