Detection of bluetongue virus antibodies in sheep from Paraná, Brazil

Abstract

Bluetongue (BT) is an infectious and non-contagious disease caused by bluetongue virus (BTV) belonging to the genus Orbivirus. It is transmitted by a hematophagous vector, Culicoides sp., to ruminants, particularly to sheep, which are most susceptible to this disease. The main serological tests are agar gel immunodiffusion (AGID), which is recommended by the World Organization for Animal Health (OIE), and the competitive enzyme-linked immunosorbent assay (cELISA), which has the advantage of no cross-reaction with other orbiviruses. The aim was to compare the results of these two tests by conducting them on sera collected from sheep in the state of Paraná, Brazil. From March to October 2017, serum samples were collected from 270 sheep from 10 farms in six mesoregions of Paraná. The samples were subjected to AGID and cELISA to detect antibodies against BTV. Based on the test results, we classified the sheep as low, moderate, and high occurrence. The results demonstrated that 64.81% (175/270) of the sheep were seropositive through the cELISA test, showing a high occurrence, and 41.11% (111/270) were seropositive through the AGID test, indicating a moderate occurrence. The concordance between the tests was moderate (0.51) as determined by the Kappa coefficient. Among the studied farms, 90% (9/10) presented at least one seropositive sheep, and the number of animals tested positive by the cELISA test was higher than those by the AGID test. Favorable climate, which favors the presence and multiplication of the culicoid vector and the occurrence of infection, was the biggest predominant factor responsible for the obtained results. The low occurrence in farms with milder climate suggest that the presence of antibodies also occurs due to the low pathogenicity of circulating serotypes in the different mesoregions studied. It is concluded that BTV infection is present in the sheep herds in Paraná, and the occurrence was moderate detected by AGID test and high detected by cELISA test.

Is Bluetongue Virus a Risk Factor for Reproductive Failure in Tropical Hair Sheep in Brazil?

“…Other studies carried out in the same region have shown antibody frequencies ranging from 13.4% (72/538) in young sheep [30] to 64.9% (651/1002) in adult sheep [19]. Equally, recent studies in nearby regions have also showed antibody frequencies ranging from 31.2% (34/109) to 80.4% (86/107) in sheep [16,28]. These findings demonstrated that even though the BTV has been considered endemic in tropical countries such as Brazil, there are regions or microclimates in which the virus cannot be present or in varied prevalence.…”

Serological and molecular prevalence study of bluetongue virus in small domestic ruminants in Morocco

“…BTV infection is widespread in different countries worldwide with variable seroprevalence rates, including Eastern Sudan (91.2%) 26 , Grenada (78.4%) 27 , Brazil (64.81%) 28 , southwestern Ethiopia (30.6%) 29 , Italy (19%) 30 , Kosovo (11.6%) 31 , Algeria (16.44%) 32 , and China (6.79%) 33 . Likewise, different RT-PCR studies revealed BTV viropositivity of 72.88% in Kosovo 31 , 33.6% in Zambia 34 , and 20.61% in India 35 .…”

“…This can be assigned to the breeding systems adopted and the spatial and climatic features of each region surveyed each year (given that, as mentioned before, different regions were investigated over the four years). BTV infection is widespread in different countries worldwide with variable seroprevalence rates, including Eastern Sudan (91.2%) 26 , Grenada (78.4%) 27 , Brazil (64.81%) 28 , southwestern Ethiopia (30.6%) 29 , Italy (19%) 30 , Kosovo (11.6%) 31 , Algeria (16.44%) 32 , and China (6.79%) 33 . Likewise, different RT-PCR studies revealed BTV viropositivity of 72.88% in Kosovo 31 , 33.6% in Zambia 34 , and 20.61% in India 35 .…”