In humans, no-see-ums can spread parasitic skin worms, an affliction primarily confined to tropical areas. A swarm of bites can lead to a high fever and the onset of itchy bumps. But the pathogens can remain active for months and can develop into a disease called leishmaniasis.

No-see-ums found in Asia and Africa (the genus Phlebotomus) and those in Latin America and the Caribbean (the genus Lutzomya) generally carry the Leishmania parasite. In fact, these bugs carry more than 20 protozoan parasites and can cause severe reactions -- fatal ones, in some cases -- caused by toxins transmitted to major body organs.

Leishmaniasis is estimated by the World Health Organization to affect up to 12 million people in 88 countries, generated an annual two million new cases. The leishmania-carrying no-see-ums are particularly entrenched in Honduras, Belize, Mexico, Hispaniola and Trinidad. In Asia, they are active in Thailand, and in the Middle East, in Egypt.

The problem for those acquiring leishmaniasis is that diagnosis is sometimes difficult. Leishmaniasis is just one of the many tropical diseases that travelers can acquire and accounts for less than 5 percent of tropical diseases. Most physicians in the United States are not particularly well-versed in tropical diseases, so a specialist might be needed to get an accurate diagnosis.

Leishmaniasis features sores that can resemble a small volcano, with a raised edge and central crater. They present with a scab but may not be painful. They may affect nearby glands, particularly if bitten under the arm.

The no-see-um is akin to a flea, in that they seem to communicate and flock to a happy hunting ground, aka you. When no-see-ums find a human with exposed skin, they will often swarm the individual. You can get several bites from an individual no-see-um and will experience several to many bites at once.