Lumpy skin disease (LSD) is a viral disease of cattle caused by lumpy skin disease virus (LSDV) and is included in the OIE list of notifiable animal diseases [1]. LSDV belongs to the genus Capripoxvirus of the family Poxviridae together with sheep pox (SPP) and goat pox (GTP) virus [2]. It is widely accepted that transmission of LSDV mainly takes place mechanically by blood-feeding arthropods such as mosquitoes (Aedes aegypti), stable flies (Stomoxys calcitrans) and ticks (Amblyomma hebraeum and Rhipicephalus appendiculatus) feeding on infected animals [3,4,5,6]. The disease can manifest in different forms ranging from acute to in-apparent, characterized by fever, lymphadenitis, skin nodules, lesions of the ocular, nasal and oral mucous membranes, and can in severe forms sometimes lead to death [7]. Development of nodules of different size starts after onset of fever, the number may range from a few nodules to the generalized form covering the entire body [8].
Over the past decades, LSD has spread from sub-Saharan Africa, where it is considered endemic in many countries, to the Middle East triggering concern of a further spread into Europe and Asia. In 2013, the first LSD outbreak was reported in Turkey where the disease subsequently became endemic. A further spread from Turkey into Greece was seen in 2015, followed by outbreaks in Bulgaria, the Former Yugoslav Republic of Macedonia, Serbia, Albania and Kazakhstan in 2016 [9]. On June 7, 2016 a first LSD outbreak was officially confirmed in Serbia, in the municipality of Bujanovac, Ljiljance village, near the border to the Former Yugoslav Republic of Macedonia [10].
For successful LSD control, vaccination of all susceptible animals is considered to be the main pillar, supported by other control measures such as stamping out, animal movement restrictions and vector control. For vaccination of cattle against LSD, live attenuated capripoxvirus vaccine strains were used, including the homologous LSDV Neethling strain and KSGP O-240 previously described as Kenyan sheep pox and goat pox virus, or the heterologous RM65 SPP, Romanian SPP and Gorgan GTP virus strains [11,12,13,14].
Facing the risk of a spread of LSD throughout the country, disease control measures including mass vaccination were applied in Serbia. In 2016, all susceptible animals were vaccinated using a LSDV Neethling vaccine (Onderstepoort Biological Products, South Africa) after dividing the country into three zones. Vaccination in zone one (infected zone) was done first starting from the outside and working inwards. This was followed by vaccination in the second (buffer zone) and third zone (Northern part of country). In 2017, re-vaccination of all susceptible animals was performed with BOVIVAX LSD-N Neethling vaccine (M.C.I. Sante Animale, Morocco) without zoning. Together with vaccination total stamping out was implemented in non-vaccinated herds when LSD was diagnosed, modified stamping out of only the infected animals with clinical signs and after laboratory confirmation of a field virus strain was performed when LSD occurred in vaccinated farms [10]. During the LSD epidemic in Serbia in 2016, 225 outbreaks with 267 affected animals were reported [15].
Annual re-vaccination and vaccination of calves derived from vaccinated cattle at the age of 6 months is the vaccination scheme recommended by the vaccine producer. Whilst vaccination will not induce immune response in each vaccinated animal, mass vaccination will provide good overall protection, if more than 80% of the population are vaccinated [12]. A recent immunological study following up LSD vaccination using Neethling, SPP and GTP vaccine strains has shown that vaccination equally stimulates humoral and cell-mediated immunity [16,17,18]. Although there are studies on the efficiency of vaccination after a single vaccine application, to our knowledge there are no published studies on the humoral response to the LSDV Neethling vaccine in the field after vaccination and re-vaccination.
Humoral immune response can be investigated by using virus neutralization test (VNT), indirect fluorescent antibody test (IFAT) and ELISA [1, 19]. So far, VNT is the only serological test validated by the OIE with a high specificity for detecting capripoxvirus-specific antibodies [1]. In serological investigations, IFAT should be used with caution, considering the described cross-reactivity with bovine papular stomatitis virus and other poxviruses [1]. A recently developed double antigen ELISA from ID vet® with a high specificity and sensitivity for capripoxvirus antibody detection according to the manufacturer, could fill the gap of serological tools for mass screening.
The aim of this longitudinal study was to investigate the humoral immune response of vaccinated cattle during the re-vaccination campaign as well as of newborn calves after colostrum intake. In addition, a comparison of the results obtained by standard serological methods (VNT and IFAT) with the results obtained by using a commercially available ELISA in order to prove suitability of ELISA was performed.