Disease Transmission
Leishmania refers to a genus of intracellular protozoa found in both the Old World and the New World that causes a variety of clinical syndromes.5 Approximately 20 Leishmania species are known to cause human disease that includes localized cutaneous, diffuse cutaneous, mucosal cutaneous, and visceral infections.13 Cases of all forms of leishmaniasis worldwide have increased rapidly over the last few decades from multiple factors including war in endemic regions, increased numbers of immunodeficient individuals, and increased travel to endemic areas.14 In the United States, leishmaniasis is caused by both imported and autochthonous forms of transmission and often mirrors recent travel and immigration patterns.14,15
Sand flies also serve as vectors for sandfly fever, also known as Pappataci fever. Although sandfly fever commonly causes a mild febrile illness, it has been shown to be a considerable cause of aseptic meningitis.16 A number of novel Phleboviruses have been isolated as causes of sandfly fever, including Massilia virus, Granada virus, and Punique virus.16-18 A form of sandfly fever caused by the Toscana virus has a predilection for the nervous system and can cause encephalitis.19 Sandfly fever can be found in both the Old World and New World and thus poses a global risk.2 Additionally, Phlebotominae also have been found to transmit the Changuinola virus, a type of bunyavirus that is known to cause febrile illness in Panama.20 Vesicular stomatitis, also carried by sand flies, is a known cause of febrile disease in North and South America, including the United States.2 In 2013, the Niakha virus, a novel type of Rhabdoviridae, was isolated from Phlebotominae in Senegal.21 The sand fly is noted to transmit another type of Rhabdoviridae in India and Africa, known as the Chandipura virus.22 Although originally thought to cause mild febrile disease, it was the primary cause of multiple outbreaks of fatal encephalitis in India in 200323,24 and again in 2012.22
Sand flies also are known to serve as vectors for the bacterium Bartonella bacilliformis, which is responsible for bartonellosis.25 The disease is divided into 2 forms, which can occur separately or in succession, and is endemic to the Andes region of Peru, Ecuador, and Colombia. The first form is Oroya fever, an acute febrile hemolytic anemia that is fatal in 40% to 88% of cases without intervention.25 This bacterium also causes verruga peruana, an endemic form of bacillary angiomatosis that can persist for years.2 Two reports suggested that bartonellosis also can be caused by Bartonella rochalimae and Candidatus Bartonella ancashi.26,27
Vector Control
Prevention is key to reducing the risk of the various diseases caused by the Phlebotominae vector. Vector control often falls into a few categories, including residual sprays, barriers, and topical repellants.3 It appears that residual sprays applied to houses and animal shelters are the most utilized and effective form of control, with the pyrethroid insecticides having the highest sand fly–specific toxicity.3,28 Insecticides also have been applied to animal burrows where sand flies are known to reproduce; one study in Kenya showed a 90% reduction in the sand fly population following treatment of termite and animal burrows with a pyrethroid spray.29 Studies by Perich et al30,31 in 1995 and 2003 showed that using barrier sprays can be an effective protective measure. The investigators applied a 100-m barrier using a pyrethroid spray on vegetation and reported a notable decrease in sand flies for over an 80-day period.30,31
For personal protection, barrier methods are important adjunct methods of preventing individual exposures. Due to the small size of sand flies, ordinary bed nets are not effective and those treated with insecticides should be used,15 which may ultimately prove to be the most sustainable way to prevent sand fly–borne disease.32 Protective attire also should be worn, as sand flies are not able to penetrate clothing.2 N,N-diethyl-meta-toluamide (DEET)–based repellants should be applied to exposed skin.15 Finally, it is important to avoid exposure from dusk to dawn when sand flies are most active.15
Rise in Autochthonous Cutaneous Leishmaniasis in the United States
With the increased amount of worldwide tourism, especially to endemic areas, providers will continue to see rising numbers of leishmaniasis in the United States. It is difficult to determine the incidence of the disease in the United States, but one study has shown that leishmaniasis accounts for 143 of every 1000 dermatologic diseases acquired by South American tourists.33,34 In addition, the number of autochthonous cases reported in the United States continues to grow. Although only 29 cases were reported between 1903 and 1996, 13 cases were reported between 2000 and 2008.35 Another report in 2013 described an additional 3 cases in the states of Texas and Oklahoma.35 The cases have continued to move in a northeasterly pattern, suggesting a possible shift in the location of sand fly populations. Each of these cases in which a specific species of Leishmania was identified showed transmission of Leishmania mexicana.35 Most cases of cutaneous disease have occurred in Texas and Oklahoma. The first known case outside of this region was reported in 2014 in North Dakota.8 Leishmania donovani, brought into the United States with European foxhounds, also is spreading.8 One species of sand fly, Leishmania shannoni, has now been discovered in 16 states,36-42 where it serves as a potential vector for L mexicana.43,44