Environmental Dermatology

What’s Eating You? Sand Flies

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As thousands of Americans descended upon Brazil for the Olympic games in the summer of 2016, the mosquito-borne Zika virus became a source of great concern among the countless athletes and travelers in Rio. As is often the case, the media frenzy that ensued drew travelers’ attention away from a lesser known flying vector that often carries with it grave consequences. The Phlebotominae, commonly known as sand flies, are biting insects known for their ability to transmit the protozoa Leishmania as well as a number of other viruses and bacteria. As the impact of sand flies continues to grow in the United States and worldwide, knowledge of the vector is important for proper treatment and prevention of the diseases they carry.

Practice Points

  • Sand flies cause a wide array of cutaneous and systemic diseases worldwide.
  • Identification and treatment of leishmaniasis and other diseases transmitted by sand flies requires a high degree of clinical suspicion.
  • With the increase in global travel and the rise of autochthonous disease in the United States, American physicians must increase their awareness of diseases for which sand flies serve as vectors.


 

References

Identification

Phlebotomine sand flies are the only member of the Psychodidae family that are capable of taking blood.1 The mouthparts of the sand fly are toothed distally, and the maxilla and mandible are utilized in a sawtooth fashion to take a bloodmeal.2 The flies are very small (ie, only 1.5–3.5 mm in length), which makes their identification difficult.1 Sand flies can be distinguished by the appearance of their wings, which often are covered in hair and extend across the back in a V shape.3 The adult sand fly is hairy with a 6- to 8-segmented abdomen, and the color can range from gray to yellow to brown.2 Phlebotomine sand flies can be further identified by their long antennae, dark eyes, and small heads (Figure).2

Sand fly anatomy.

As is the case with all Diptera, the sand fly goes through 4 complete life stages from egg to larva to pupa to adult.3 Female sand flies will lay their eggs following a blood meal and have been found to take multiple blood meals in a single cycle.2 On average, the eggs will hatch in 6 to 17 days but are temperature dependent.3 The subsequent larvae and pupa stages last 20 to 30 days and 6 to 13 days, respectively.1 The larvae are white in color with short antennae and dark heads.4 Sand flies prefer to lay their eggs in areas where adequate resting places are available and where their larvae will thrive.4,5 The larvae require warm moist environments to succeed and thus are commonly found in animal burrows.3 Once fully developed, the adult sand fly can live up to 6 weeks.2

Sand Fly Vector

Although it is more common in rural forested areas, the sand fly also can be found in urban areas, including heavily populated cities in Brazil.6 Sand flies are most active during hot humid seasons but depending on the local climate may remain active year-round.1,7 For example, in tropical regions of Asia, the number of sand flies increases substantially during the monsoon season compared to the dry season.2 Phlebotomine sand flies are most active at dusk and during the night5 but may become agitated during the daytime if their environment is disturbed.1

Host selection usually is broad and includes a wide variety of vertebrates.2 In the United States, host species are thought to include small rodents, foxes, armadillos, and opossums.8 One study found that visceral leishmaniasis in foxhounds is able to develop fully in sand flies, thus posing an emerging risk to the American population.9

Distribution

The Phlebotominae family contains approximately 700 different species of sand flies but only 21 are known vectors of disease.10 The great majority belong to 1 of 3 genuses: Phlebotomus, Sergentomyia, and Lutzomyia.11 The vectors are commonly divided into Old World species, dominated by the Phlebotomus genus, and New World species, which exclusively refers to the Lutzomyia genus.3 The Old World and New World distinction helps to classify the various vectors and subsequently the diseases they transmit. Old World refers to those vectors found in Southwest and Central Asia, the Indian subcontinent, the Middle East, and East Africa, as well as Southern Europe.6 New World refers to vectors found predominantly in Brazil and other parts of Latin America but also Mexico and the United States.6 Sand flies are found to be endemic in 90 countries and on each continent, except Australia.5 Although the vector can be found in a variety of environments, sand flies prefer moist environments that typify tropical and subtropical climates, thus it is not surprising that the highest diversity of Phlebotominae in the world can be found in the Amazon basin.12

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