Serological study on WNV presence in horses in Vojvodina after the human outbreak in Serbia in 2012

Abstract

To establish the presence of West Nile virus (WNV) infection in the animal population in Serbia after the human WNV outbreak, the presence of anti-WNV IgG antibodies was examined by commercial ELISA of blood sera samples of 130 horses collected in 2012 from 6 stables and 1 settlement in Vojvodina Province, northern Serbia. During the blood sampling, hibernating mosquitoes in the vicinity of the sampled horses were collected (31 pools from 4 locations) and tested for WNV presence by real-time RT-PCR. The presence of anti-WNV antibodies was observed in 49.23% (64/130) horses. Per stable, the percent of seropositive animals ranged from 35% to 64%. All 31 analyzed pools of hibernating mosquitoes tested negative for WNV RNA. The WNV-antibody prevalence of 49.23% obtained in horses during 2012 was much higher than the prevalence (12%) found in horses during 2009/2010. These results, including the confirmed seroconversion in eight horses that tested negative in 2010, indicated an intensive WNV circulation during 2012 in Serbia, and the necessity of implementing surveillance programs. [Projekat Ministarstva nauke Republike Srbije, br. TR31084 and III43007]

Methodology and results of integrated WNV surveillance programmes in Serbia

“…All districts, except the Raška District, where WNV-positive mosquito pools were detected are in the Vojvodina Province. Such a result could be attributed to the fact that the Vojvodina Province has previously been confirmed as a region with intensive WNV circulation in past years [ 10 , 12 – 14 ]. During wild bird surveillance in 2014, WNV presence was established in only 2 birds (in the Vojvodina Province).…”

“…The same was true for the beginning of WNV surveillance in Emilia-Romagna, Italy, where animal surveillance consisted of passive and active surveillance of horses and active surveillance of wild birds and mosquitoes [ 34 ]. Based on the results of earlier studies on WNV seroprevalence in horses in Serbia [ 10 – 12 ], the initial testing for the presence of WNV IgG antibodies before the programme started in early spring 2014 encompassed a much larger horse population than was required for the surveillance, so that only seronegative horses would be included in the surveillance programme.…”

“…The districts of Vojvodina Province and the City of Belgrade have previously been identified as areas with high WNV circulation [ 10 , 12 – 14 ]. The possible explanation for that situation can be associated with geographical and climate features: the entire territory of Vojvodina Province and Belgrade City are located in the flatland area of up to 250 m altitude, characterized by a hot summer continental climate ( Dfa climates), with an average temperature in the warmest month of ≥22°C as well as many slow water flows (Danube, Tisza and Sava rivers), small lakes and swamp areas that are favourite sites for shorter or longer stays for many migratory birds on their migration routes.…”

“…In addition, just one year later, to assess WNV presence in the environment immediately after the human WNV outbreak in 2012, the presence of WNV IgG antibodies was detected in 64 (49.23%) out of 130 tested blood sera samples of horses from 6 stables and 1 settlement in Vojvodina Province. Per stable, the percentage of seropositive animals varied from 35% to 64% [ 12 ].…”

Flaviviruses at the territory of Serbia – present situation and challenges

“…96) seropositive horse blood sera were identified in tests conducted during 2012 and 2013, respectively(Medić et al, 2014;Petrović et al, 2014a;Petrović et al, 2015). Pronounced increase in the prevalence of seropositive horses strongly suggested an intensive circulation of WNV in the environment.…”