Leishmaniasis is an arthropod-borne and zoonotic disease that infects man incidentally. It is caused by Leishmania spp. The disease has a spectrum of manifestations, from minor, self-limiting cutaneous (skin) lesions to extreme disfigurement and death. The parasite is spread to vertebrate hosts, including humans, through the bite of female sand flies. The sand fly, therefore, is the 'vector' of leishmaniasis. In the Old World, the vectors of human leishmaniasis are predominantly from the genus Phlebotomus. In the New World, all disease vectors are in the genus Lutzomyia. Parasite species also differ between the hemispheres. New World leishmaniasis is usually limited to tropical or semi-tropical environments, though a recent outbreak of cutaneous leishmaniasis in Texas demonstrates that parasites normally associated with Central America are capable of spreading into the United States. Old World parasites are well adapted to transmission in temperate areas, including parts of Iraq and Afghanistan.
Between 2001 and 2006, nearly 1300 incident diagnoses of leishmaniasis were detected in veterans of the current conflicts in Iraq and Afghanistan. Only four of these cases were the deadly visceral form, an infection that affects the intestines and other viscera. The rest showed cutaneous manifestations. The peak incidence rate was observed in the late summer and fall of 2003, but the disease rate has declined since. For the entire six year period, the incidence rate was 2.31 cases per 1,000 person-years. The highest risk of disease among American personnel was observed along the Iran-Iraq border where the rate exceeded 200 per 1000 deployed persons. Diagnosis can be difficult, especially in deployed settings. There are no available vaccines or prophylactic medications  and treatment may not eliminate all of the parasites, so infected veterans could theoretically serve as reservoirs after returning to the United States.
This paper reports part of a larger study to assess the risk of introducing Old World Leishmania parasites into the sand fly populations of the temperate New World. The study was in three parts:
1. A survey of sand fly species on American military facilities with large numbers of soldiers deploying to Iraq or Afghanistan ;
2. A feeding study to assess the ability of a New World sand fly species to become infected with an Old World Leishmania spp.;
3. An analysis of sand fly abundance to identify plant communities where the risk of sand fly bites is increased.
This paper reports on the third part of the study.
Previous studies have linked adult sand fly abundance to a variety of environmental factors. Although one study noted an association between soil chemistry and the abundance of Sergentomyia spp., most have used plant communities to identify environmental associations. In Kenya, sand fly abundance was greatest in closed canopy forests and least in thickets. New World sand fly species also tended to be associated with forests. In northern Colombia, forested reserve areas displayed both greater species diversity and abundance than the degraded habitats in the same area. However, medically important species re-colonized and exploited the degraded areas, suggesting that forest degradation could lead to greater human exposure to sand fly vectors. In northern Argentina, habitats were classified as primary forest, secondary forest and xeric woodland. The greatest abundance was detected in secondary forests.
Possibly due to the relative lack of sand fly-borne diseases in the United States, fewer studies on sand fly ecology have been performed in this country. However, a recent outbreak of canine visceral leishmaniasis has stimulated interest in the possible role of sand flies in the transmission of disease. When a focus of canine disease was investigated in upstate New York, the highest abundance of Lu. vexator (Coq.) was noted on steep slopes in mature mixed hardwood forests. However, on Ossabau Island off the coast of Georgia, Lu. shannoni Dyar was most active in established maritime live oak forests, with mixed hardwood and pine forests harboring significantly fewer sand flies. In the southwest, geographic information systems were used to analyze associations with Lu. apache, which indicated a potential range through steppe and semi-desert vegetative provinces from Arizona to Idaho.
The risk of importing exotic Leishmania spp. from the current war zones into the United States is dependent upon a variety of factors, including the susceptibility of North American sand flies to infection, the ability of the parasite to develop in the fly, and the availability of suitable vertebrate reservoirs. Environmental factors suitable for supporting large vector populations are also important variables. This part of the study attempts to identify and locate those variables in areas where returning, and possibly infected, veterans could come into contact with sand fly vectors.