Rezultati programa monitoringa bolesti Zapadnog Nila u Republici Srbiji u 2017 godini

Abstract

The constant circulation of Western Nile virus (VZN) has been detected in the last few years in Serbia. Bigger or smaller epidemics have been reported in human population in Serbia since 2012, until today. The veterinary service in Serbia launched a national program for WNV monitoring in June 2017, and it was continuation of the monitoring programs from 2014 and 2015. Program is funded by the Veterinary Directorate, and it is implemented on the field by veterinary service in collaboration with entomologists and ornithologists. The main objective of the monitoring program was the early detection of the presence of WNV in a certain area, and consequently timely alerting of human health services and local governments in order to control the mosquito population and to inform the local communities. The monitoring program was based on the direct and indirect monitoring of the presence of WNV in nature. Indirect monitoring of virus presence was performed by serological testing of horses on the presence of anti-WNV IgM antibodies as the confirmation of acute infection. Direct monitoring of the WNV presence in nature was done by molecular testing of WNV presence in pooled mosquito’s samples and in wild birds in active surveillance and by testing the samples of clinically suspected horses in passive surveillance. Number of tested samples is defined at the level of each district of the Republic of Serbia in relation to the risks of WNV infection. In the period June-September 2017 in Serbia, according to the program, 2457 blood sera of horses were tested, and seroconversion (IgM antibodies) was detected in only 10 (0.41%) horses. The seroconversion was in the ascendant order as the program progressed, and with increasing the activity of the vectors, positive serological response were determined in June in 0%, in July in 0.31% (2/641), in August in 0.83% (5/606), and in September in 0.50% (3/595) of tested horses. The number of districts where the positive horses were detected was: 0 in June, 2 in July, 2 in August and 2 in September. In passive surveillance, tissues samples of 2 clinically suspected horses that died in June were tested for WNV presence and negative results were obtained. In direct monitoring of virus presence, 838 pools of mosquitoes were tested from June to August 2017, and WNV was confirmed in 21 (2.51%) samples. The prevalence of WNV in mosquitoes has increased since the first positive findings detected in June (0.48%; 1/207)), 1.64% (7/426) mosquito samples were tested positive in July, and 6.37% (13/204) in August. Positive mosquito samples were detected in 5 districts: 10.14% positive / tested samples was detected in South Bačka, 9.46% in South Banat, 5.48% in North Bačka, 4.26% in Srem and 1.35% in Central Banat District. Among XX Симпозијум епизоотиолога и епидемиолога / XX Епизоотиолошки дани 95 77 samples of hunted wild birds, WNV was detected in 1 (1.30%) case – Eurasian magpie hunted near towns Kljajićevo in West Bačka District in October 2017. WNV was also detected in 1 (0.40%) out of 253 tested samples of pharyngeal swabs of live wild bird – the Great tit sampled at location Gradica (Kraljevo) in Raška District in August. Among 58 samples of found dead wild birds, from the territory of 6 districts, WNV was not detected in any of them. WNV monitoring program during 2017 was proved as successful and meaningful. At the same time it pointed on the opportunities and the need for its improvement. The reasons for this is, first of all, in the large percentage of already seropositive horses due to few years of intensive WNV circulation in the area, that rise question on usefulness of the serology testing of horses. Therefore, for the next WNV monitoring program we propose testing the possibility for including the additional domestic animals species as sentinel animals for serological surveillance (calves or finisher pigs), and further testing of IgM antibodies in horses for that purpose. Direct monitoring of the presence of WNV would be further conducted with periodical testing of pooled mosquitoes samples and wild birds.