What is Dr. Zubair Khalid's research focus?

Dr. Zubair Khalid specializes in molecular virology, mRNA vaccine development, and computational biology, with a focus on avian pathogens like IBDV and Avian Reovirus.

Where is Dr. Zubair Khalid currently working?

Dr. Zubair Khalid is a Postdoctoral Research Associate at the University of Maryland (UMD), specifically within the Department of Animal and Avian Sciences.

Sand Fly: Biology, Diseases, and Veterinary Importance

Name: Sand Fly: Biology, Diseases, and Veterinary Importance
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-20

Sand flies are small, hairy, moth-like biting insects in the family Psychodidae that transmit some of the most important vector-borne diseases of dogs, people, and livestock. The two dominant genera are Phlebotomus in the Old World and Lutzomyia in the New World, and the females of many species take blood meals that can carry Leishmania parasites, phleboviruses, and vesicular stomatitis virus.

For pet owners and livestock keepers, the practical takeaway is that sand flies are not simply a nuisance. A single bite from an infected female can start a months-long infection in a dog, and the same insects feed on horses, cattle, and people. Understanding how sand flies live, breed, and feed is the foundation for protecting animals on your property.

What Is a Sand Fly?

A sand fly is a hematophagous (blood-feeding) fly in the subfamily Phlebotominae. Adults are much smaller than mosquitoes, typically only 2 to 4 mm long, with a body covered in dense hairs that gives them a fuzzy, moth-like appearance. When they land, they hold their wings in a characteristic V shape over the back, which is one of the easiest ways to tell them apart from mosquitoes and biting midges.

That last distinction matters. Sand flies are frequently confused with biting midges (Culicoides), which are also tiny blood-feeding flies. Biting midges transmit different pathogens, including bluetongue virus and African horse sickness, and they belong to a separate family. Confusing the two leads to the wrong control strategy, because sand fly larvae develop in moist soil and organic debris, while Culicoides larvae develop in wet mud, manure, and standing water.

There are hundreds of sand fly species worldwide. In Eastern Africa alone, a harmonized regional atlas documented 67 sand fly species from 1,745 geo-referenced records collected between 1906 and 2025, with Kenya, Ethiopia, and Sudan showing the greatest documented diversity [1]. Only a subset of these species actually transmit disease, which is why entomological surveys focus on identifying which species are present in a given area.

The Two Main Genera

Veterinary and medical importance centers on two genera.

Phlebotomus (Old World): Found across southern Europe, North Africa, the Middle East, and Asia. Phlebotomus perniciosus is the principal vector of Leishmania infantum in the western Mediterranean basin and can also transmit phleboviruses such as Toscana virus [2]. A high-quality genome assembly of P. perniciosus was recently published to support research into vector competence and host preference [2].
Lutzomyia (New World): Found across the Americas. Lutzomyia longipalpis is the main vector of Leishmania infantum and visceral leishmaniasis on the American continent [3].

Other genera, such as Migonemyia, Nyssomyia, and Pintomyia, also contain competent vectors. A survey in Santa Catarina, Brazil, identified Migonemyia migonei, Nyssomyia neivai, and Pintomyia fischeri as species with potential vector capacity [4].

Sand Fly Life Cycle

Diagram of the leishmaniasis life cycle showing sand fly and human stages — This life cycle diagram shows how Leishmania parasites develop in the sand fly and are transmitted to humans. Image: NIAID, CC BY 2.0, via Wikimedia Commons.

Sand flies undergo complete metamorphosis: egg, four larval instars, pupa, and adult. This is a terrestrial life cycle, unlike mosquitoes. Sand fly larvae do not live in water. They develop in moist, shaded soil rich in organic matter, often around animal burrows, cracks in walls, leaf litter, and the base of vegetation.

Egg. Females lay eggs in small batches in moist organic material. Eggs hatch within days to a couple of weeks depending on temperature.
Larva (four instars). The larvae are legless, worm-like, and feed on decaying organic matter and microorganisms. They pass through four molts. This stage can last from a few weeks to several months, and some species enter a dormant phase during cold or dry conditions.
Pupa. The larva pupates in the same moist substrate. The pupal stage is relatively short, typically one to two weeks.
Adult. The adult emerges, mates, and the female seeks a blood meal to develop eggs. Males do not take blood. Females require blood to complete each gonotrophic cycle, and they can lay eggs multiple times during their lifespan.

The reproductive biology of the female directly affects disease risk. In a study of P. perniciosus and P. ariasi, the probability of Leishmania infection was highest in gravid females, consistent with cumulative parasite acquisition as sand flies age and complete successive egg-laying cycles [5]. Infection probability also peaked in late summer, likely reflecting high parasite prevalence in reservoir hosts at that time [5].

Adult Sand Fly Behavior and Why It Matters

Adult sand flies are weak fliers. They typically move only short distances from their breeding sites, usually within a few hundred meters. This is why targeted environmental management around kennels, stables, and homes can meaningfully reduce exposure.

They are primarily crepuscular and nocturnal, with peak activity around dusk and dawn, though some species bite during the day in shaded areas. They rest during the day in dark, humid microhabitats: animal sheds, cracks in walls, tree holes, and dense vegetation.

Host preference varies by species. Some, like P. papatasi, feed readily on humans. Others, like P. perniciosus, feed on dogs and other mammals. This host preference determines which pathogens circulate in which hosts. Dogs are particularly important because they serve as the primary reservoir for Leishmania infantum and are frequently bitten by sand flies, making them ideal sentinel hosts for surveillance [6].

A Note on Sand Fly Saliva

When a female sand fly bites, she injects saliva that contains vasodilators and immunomodulatory proteins. These salivary proteins are not just a delivery vehicle. In a human challenge study with Lutzomyia longipalpis, repeated exposure to sand fly bites induced innate and type 1-polarized immune responses to salivary proteins, and two specific salivary proteins (LJM19 and LJL143) correlated with enhanced killing of Leishmania parasites in co-cultured macrophages [7]. This finding points to a future direction in vaccine development, but it also explains why repeated exposure to sand fly bites can alter how a host responds to infection.

Diseases Transmitted by Sand Flies

Sand flies transmit three main groups of pathogens of veterinary importance: Leishmania protozoa, phleboviruses, and vesicular stomatitis virus.

Leishmaniasis

Leishmaniasis is the most significant sand fly-borne disease worldwide. It is caused by protozoan parasites of the genus Leishmania and presents in two main clinical forms: tegumentary (cutaneous and mucosal) leishmaniasis and visceral leishmaniasis [8].

Canine leishmaniasis. Dogs are the primary reservoir for Leishmania infantum, the species that causes visceral leishmaniasis in both dogs and humans [9]. In dogs, infection can be subclinical for months or years, or it can progress to clinical disease with weight loss, enlarged lymph nodes, skin lesions, kidney disease, and eye inflammation. A One Health surveillance study in Sicily found canine seroprevalence ranging from 12 to 34 percent, with spatial overlap between canine and human case-detection patterns [9].

The geographic range of canine leishmaniasis is expanding. In southern Brazil, the first autochthonous case of canine visceral leishmaniasis was reported in Florianópolis in 2010 [4]. A 2026 study in the adjacent municipality of Biguaçu collected 367 sand flies over 12 months, identified nine species, and found one dog positive for Leishmania infantum among 235 sampled [4]. In Costa Rica, a coastal focus was investigated where four dogs were seropositive and PCR-positive, and three pools of Lutzomyia serrana sand flies tested positive for Leishmania DNA near the detection limit [10].

Human leishmaniasis. Sand flies transmit Leishmania to humans as well. In Sicily, 67 confirmed human cases were detected over a two-year surveillance period, including 50 cutaneous and 17 visceral cases [9]. Cutaneous leishmaniasis causes skin ulcers that can be disfiguring. Visceral leishmaniasis, if untreated, is fatal.

The vector life cycle inside the sand fly. Leishmania parasites undergo a complex developmental cycle in the sand fly gut before they become infectious to a vertebrate host. Recent research has shown that the parasite's life cycle involves reversible differentiation pathways and sexual recombination, generating highly virulent and drug-resistant hybrids [11]. The vector inoculum is not just parasites. It is a complex pro-infectious environment comprising saliva, exosomes, and viral endosymbionts that preconditions the host for infection [11].

The sand fly gut microbiota also influences whether Leishmania can establish an infection. A study of four sand fly species in Türkiye found that the gut microbiota was dominated by Proteobacteria (81.2 percent), with species-specific profiles: Wolbachia dominated P. papatasi, Pseudomonas was enriched in P. major, and Bradyrhizobium was abundant in P. sergenti and P. tobbi [12]. Research on P. perniciosus showed that ecdysone signaling regulates immunity and microbiota balance, directly shaping Leishmania infantum infection [13]. In another study, cultivable bacteria from P. tobbi showed anti-leishmanial activity, with Serratia liquefaciens and Micrococcus luteus producing the strongest leishmanicidal effects [14].

Sand Fly Fever Viruses (Phleboviruses)

Phleboviruses are a genus of RNA viruses in the family Phenuiviridae transmitted by sand flies. Two well-known members are Toscana virus (TOSV) and Sicilian sand fly virus (SFSV). Toscana virus is associated with meningitis and encephalitis in humans [2].

A multinational serological survey of 2,500 dogs across Portugal, Spain, Italy, Croatian Istria, Turkey, and Israel detected antibodies to TOSV and SFSV, confirming that dogs are exposed to these viruses across the Mediterranean basin [6]. In Kosovo, a novel phlebovirus called Mirusha virus was isolated from a Phlebotomus perfiliewi sand fly, and neutralizing antibodies were found in 2.0 percent of dogs and 0.8 percent of humans sampled [15]. The virus replicated in mammalian cells but not in mosquito cell lines, suggesting it is specifically adapted to sand fly transmission [15].

These findings are important because sand fly-borne phleboviruses can cause undiagnosed febrile illness during the vector-active season, and surveillance has traditionally focused on mosquitoes rather than sand flies [15]. For veterinarians, this means that dogs with unexplained fever during warm months in endemic areas may warrant consideration of phlebovirus exposure.

Vesicular Stomatitis

Vesicular stomatitis virus affects horses, cattle, and pigs, causing vesicles and erosions on the mouth, tongue, teats, and hooves. The disease is clinically indistinguishable from foot-and-mouth disease in cattle, which makes it a reportable condition in the United States. Sand flies are among the biological vectors of vesicular stomatitis virus, along with biting midges and black flies. The Merck Veterinary Manual lists sand flies among the flies of veterinary importance that transmit this virus to livestock [16].

Outbreaks of vesicular stomatitis in the United States occur sporadically, primarily in the Southwest, and are often associated with the movement of infected animals and the activity of vector populations. For livestock owners, the presence of sand flies near barns and corrals is a risk factor worth managing.

Vector-Borne Disease Table

Disease	Agent	Primary Vector	Main Hosts	Region
Visceral leishmaniasis	Leishmania infantum	Lutzomyia longipalpis, Phlebotomus perniciosus	Dogs, humans	Mediterranean basin, Middle East, South America
Cutaneous leishmaniasis	Leishmania spp.	Phlebotomus spp., Lutzomyia spp.	Humans, dogs, rodents	Middle East, Central Asia, South America, East Africa
Sand fly fever	Toscana virus, Sicilian sand fly virus	Phlebotomus spp.	Humans, dogs (seroconversion)	Mediterranean basin, Balkans
Mirusha virus infection	Mirusha virus	Phlebotomus perfiliewi	Humans, dogs	Kosovo, Balkan peninsula
Vesicular stomatitis	Vesicular stomatitis virus	Sand flies, biting midges, black flies	Horses, cattle, pigs	Americas, especially southwestern United States

How Sand Flies Spread Disease: The Transmission Cycle

The transmission cycle of sand fly-borne disease follows a consistent pattern. An infected female sand fly takes a blood meal from a reservoir host. The pathogen enters the sand fly's gut, where it must survive and develop. For Leishmania, the parasite transforms into promastigotes and migrates to the mouthparts. For phleboviruses, the virus replicates in the sand fly's tissues. When the sand fly bites again, usually a few days to a week later, it injects the pathogen into a new host.

The period between the first infectious blood meal and the ability to transmit is called the extrinsic incubation period. It varies by pathogen and temperature. Warmer temperatures generally shorten this period, which is one reason sand fly-borne diseases are expanding into new areas.

An 18-year sand fly monitoring study in Israel found that land-use change and climatic variability both shaped sand fly populations, with different species showing contrasting long-term trends [17]. Phlebotomus sergenti and P. papatasi were most abundant immediately after landscape modification and declined later, while P. tobbi and P. syriacus increased after park establishment [17]. This species-specific response means that environmental changes can shift which sand fly species dominate an area, and therefore which diseases are most likely to circulate.

flowchart TD
    A[Female sand fly takes blood meal] --> B[Pathogen enters sand fly gut]
    B --> C[Extrinsic incubation period]
    C --> D[Pathogen reaches mouthparts]
    D --> E[Sand fly bites new host]
    E --> F[Pathogen enters vertebrate host]
    F --> G[Dog or human develops infection]
    G --> H[Reservoir host amplifies pathogen]
    H --> A

Protecting Pets and Livestock from Sand Flies

Sand fly control requires a combination of strategies. No single measure eliminates risk, especially in endemic areas.

Insecticide-Treated Bedding and Resting Sites

Sand flies rest in dark, humid places during the day. Treating kennels, bedding, and resting surfaces with residual insecticides reduces adult populations and lowers biting pressure. In livestock operations, treating stall walls, feed storage areas, and shaded resting spots can reduce sand fly numbers. The Merck Veterinary Manual notes that sand flies of animals are best managed through Integrated Pest Management approaches that target both adults and breeding sites [16].

Repellents and Spatial Repellents

Volatile pyrethroid spatial repellents (VPSRs) are a newer tool. A systematic review and meta-analysis found that transfluthrin VPSR showed a protective effect of 48 percent (95% CI 26 to 63 percent) against Leishmania infection incidence in a single trial, though evidence was limited [18]. The same review found 50 percent protection against Plasmodium and 34 percent against arboviruses [18]. These products can complement other measures but should not replace environmental management.

For pets, topical repellents containing permethrin or deltamethrin are commonly used in canine leishmaniasis prevention in endemic areas. These products are not appropriate for cats, and owners should always consult a veterinarian before applying any insecticide to a pet.

Environmental Management

Sand fly larvae need moist organic matter to develop. Removing leaf litter, composting material, and decaying vegetation from around kennels and animal housing reduces breeding sites. Fixing leaky pipes and improving drainage eliminates the damp conditions that larvae require. Keeping grass short and vegetation sparse near resting areas reduces adult daytime resting sites.

In peri-domestic settings, sand fly assemblages often overlap with adjacent forested habitats, indicating pathways for sylvatic-to-peridomestic spillover [19]. This means that properties near wooded or natural areas may need more intensive management.

Host-Targeted Measures

Dogs in endemic areas can be fitted with deltamethrin-impregnated collars, which reduce sand fly bites and may lower the risk of Leishmania transmission. The Companion Animal Parasite Council recommends year-round parasite prevention for dogs in endemic regions.

Vaccination against canine leishmaniasis is available in some countries but not the United States. Owners traveling to or living in endemic areas should discuss prevention with a veterinarian.

Diagnosis and Treatment Overview

Diagnosis of leishmaniasis in dogs typically involves serology (indirect immunofluorescence antibody test or ELISA) plus PCR. A kDNA-based PCR assay targeting the Leishmania donovani complex has been developed and validated for detection of L. infantum, with sensitivity down to 100 femtograms of DNA [4]. In clinical practice, conjunctival swab sampling is a non-invasive method for detecting L. infantum in dogs [4].

Treatment of canine leishmaniasis is complex and depends on the clinical form and severity. The standard first-line treatment in many countries involves a combination of meglumine antimoniate and allopurinol, though protocols vary. Treatment does not achieve a sterile cure in most cases, and relapses are common. This is why prevention is far more effective than treatment.

For vesicular stomatitis, treatment is supportive. There is no specific antiviral therapy. Affected animals should be isolated, provided with soft feed and water, and monitored for secondary bacterial infections. Because vesicular stomatitis is clinically indistinguishable from foot-and-mouth disease, it is a reportable disease in the United States and suspected cases must be reported to state or federal animal health officials.

Limitations and When to Contact a Veterinarian

Sand fly biology and the diseases they transmit vary by region, species, and individual animal health. This article provides general information, but it cannot replace a veterinary examination.

Contact a veterinarian promptly if your dog shows any of the following:

Unexplained weight loss, especially with enlarged lymph nodes.
Non-healing skin lesions, particularly on the ear tips, nose, or around the eyes.
Recurrent fever or lethargy lasting more than a few days.
Kidney-related signs such as increased drinking and urination.
Eye inflammation, including uveitis.

For livestock, contact a veterinarian if horses, cattle, or pigs develop vesicles or erosions on the mouth, tongue, teats, or hooves. Because vesicular stomatitis is a reportable disease, do not wait to see if lesions resolve on their own.

If you live in or are traveling to an area where leishmaniasis is endemic, talk to your veterinarian about prevention before you go.

Frequently Asked Questions

What do sand flies look like?

Sand flies are much smaller than mosquitoes, usually 2 to 4 mm long, with hairy, moth-like bodies and wings held in a V shape when resting. They are often mistaken for biting midges, but sand flies have a distinct fuzzy appearance and different breeding habits.

Do all sand flies bite?

No. Only the females bite, and they do so to obtain blood for egg development. Males feed on plant sugars and do not take blood meals.

Can sand flies transmit diseases to dogs?

Yes. Sand flies transmit Leishmania infantum, the parasite that causes canine visceral leishmaniasis. Dogs are the primary reservoir for this parasite in many parts of the world, and infection can be subclinical or progress to serious disease.

Are sand flies the same as biting midges?

No. Sand flies and biting midges are different families of flies. Sand fly larvae develop in moist soil and organic debris, while biting midge larvae develop in wet mud and standing water. They transmit different diseases.

How can I protect my dog from sand flies?

Use veterinarian-recommended topical repellents or insecticide-treated collars, reduce breeding sites around your home by removing moist organic debris, and keep your dog indoors during peak sand fly activity at dusk and dawn. In endemic areas, year-round prevention is recommended.

Is there a vaccine for leishmaniasis in dogs?

Vaccines against canine leishmaniasis are available in some countries, including Brazil and parts of Europe, but are not licensed in the United States. Owners in endemic areas should discuss options with a veterinarian.

Can sand flies transmit diseases to horses and cattle?

Yes. Sand flies are among the biological vectors of vesicular stomatitis virus, which affects horses, cattle, and pigs. The disease causes vesicles and erosions on the mouth, tongue, teats, and hooves and is reportable in the United States.

What time of day are sand flies most active?

Sand flies are primarily crepuscular and nocturnal, with peak biting activity around dusk and dawn. Some species also bite during the day in shaded, humid areas.

This article is educational and is not a substitute for veterinary diagnosis or treatment.