Direct evidence for an expanded circulation area of the recently identified Balkan virus (Sandfly fever Naples virus species) in several countries of the Balkan archipelago

Abstract

Background: Recently, Balkan virus (BALKV, family Phenuiviridae, genus Phlebovirus) was discovered in sand flies collected in Albania and genetically characterised as a member of the Sandfly fever Naples species complex. To gain knowledge concerning the geographical area where exposure to BALKV exists, entomological surveys were conducted in 2014 and 2015, in Croatia, Bosnia and Herzegovina (BH), Kosovo, Republic of Macedonia and Serbia.

Results: A total of 2830 sand flies were trapped during 2014 and 2015 campaigns, and organised as 263 pools. BALKV RNA was detected in four pools from Croatia and in one pool from BH. Phylogenetic relationships were examined using sequences in the S and L RNA segments. Study of the diversity between BALKV sequences from Albania, Croatia and BH showed that Albanian sequences were the most divergent (9-11% [NP]) from the others and that Croatian and BH sequences were grouped (0.9-5.4% [NP]; 0.7-5% [L]). The sand fly infection rate of BALKV was 0.26% in BH and 0.27% in Croatia. Identification of the species content of pools using cox1 and cytb partial regions showed that the five BALKV positive pools contained Phlebotomus neglectus DNA; in four pools, P neglectus was the unique species, whereas P. tobbi DNA was also detected in one pool.

Conclusions: We report here (i) the first direct evidence that the Balkan virus initially described in coastal Albania has a much wider dissemination area than originally believed, (ii) two real-time RT-PCR assays that may be useful for further screening of patients presenting with fever of unknown origin that may be caused by Balkan virus infection, (iii) entomological results suggesting that Balkan virus is likely transmitted by Phlebotomus neglectus, and possibly other sand fly species of the subgenus Larroussius. So far, BALKV has been detected only in sand flies. Whether BALKV can cause disease in humans is unknown and remains to be investigated.

Keywords: Arbovirus; Bunyaviridae; Emergence; Fever; Meningitis; Phlebotomus; Phlebovirus; Phylogeny; Sand fly; Toscana virus.

Fig. 1

Geographical distribution of the sand fly trapping stations. Black circles denote trapping stations. Red circles denote trapping stations in which at least one pool was found to contain Balkan virus RNA

Fig. 2

Phylogeny of the Balkan virus and closely related phleboviruses using partial nucleotide sequences of the nucleoprotein gene (572 nt). Neighbor-joining analysis (Kimura 2-parameter model) was performed using MEGA6, with 1000 bootstrap replicates

Fig. 3

Phylogeny of the Balkan virus and closely related phleboviruses using partial nucleotide sequences of the polymerase gene (525 nt). Neighbor-joining analysis (Kimura 2-parameter model) was performed using MEGA6, with 1000 bootstrap replicates