Sandfly fever Naples virus (SFNV) is an enveloped negative‑sense RNA virus of genus Phlebovirus that causes a short febrile illness known as “three‑day fever.” The virus is transmitted to humans through the bite of infected phlebotomine sand flies and belongs to the Naples serogroup of sandfly fever viruses.
Biology and Transmission
SFNV is a member of the family Phenuiviridae, genus Phlebovirus, and its genome consists of three segments of negative‑sense RNA enclosed in a lipid envelope. It circulates in natural populations of phlebotomine sand flies and is maintained by vertical transmission within these vectors. Isolation studies show that the virus infects several sand fly species including Phlebotomus papatasi, P. perniciosus, P. perfiliewi, P. longicuspis and P. sergenti, and it has also been found in Sergentomyia minuta. Humans are incidental hosts who acquire infection after being bitten by infected female sand flies; there is no evidence of long‑term vertebrate reservoirs. The virus was first isolated during World War II when outbreaks of a self‑limited febrile illness occurred among soldiers in Sicily and North Africa. Since then, SFNV has been detected across the Mediterranean basin, the Middle East and parts of Asia and northern Africa. The active season for sand fly vectors spans from spring through early autumn, and infection rates peak during the summer months when vector activity is highest. After an incubation period of about 4–8 days, patients develop an abrupt onset of fever with severe frontal headache, retro‑orbital pain, myalgia, arthralgia, abdominal discomfort and nausea. Laboratory findings may include leukopenia and thrombocytopenia, but severe disease is rare and there is usually no rash. Most patients recover within three days without specific therapy; management is supportive and includes rest, fluids and analgesics. No vaccine exists, so prevention relies on reducing contact with sand flies through insect repellents, protective clothing and vector control.
Wartime Outbreaks and Regional Trends
During World War II thousands of Allied and Axis troops stationed in Sicily and North Africa developed a sudden febrile illness later identified as sandfly fever. Investigations by Sabin and colleagues isolated two causative viruses, SFNV and the closely related Sicilian virus, from blood samples of infected soldiers and from Phlebotomus papatasi. Post‑war epidemics were reported in parts of Serbia and the Banat region where large numbers of civilians experienced similar three‑day fevers. Serological surveys have since demonstrated high levels of SFNV exposure among populations in the Mediterranean and the Near East. In Israel and neighbouring countries antibody prevalence for SFNV has been reported at up to 30 percent; studies in the former Yugoslavia found 57.6 percent of residents on the island of Brač and 27.9 percent of people in Kosovo had antibodies to the virus. These findings indicate widespread circulation of SFNV in endemic regions. Although the illness is generally mild, travellers and military personnel from non‑endemic areas can be incapacitated by infection during peak sand fly season, underscoring the need for awareness and personal protective measures. Sandfly fever Naples virus remains an important example of an arthropod‑borne virus that has co‑evolved with its sand fly hosts. While infections are usually self‑limited, the virus continues to circulate widely, and high seroprevalence in endemic areas suggests that many infections go unrecognized. Control of sandfly fever relies on vector avoidance and surveillance rather than specific medical interventions. Related Terms: Sandfly fever Sicilian virus, Toscana virus, Phlebovirus, Pappataci fever, Granada virus