Application of a competitive ELISA for the detection of bluetongue virus antibodies in llamas and wild ruminants.

A competitive enzyme-linked immunosorbent assay (C-ELISA), using a group-specific monoclonal antibody against bluetongue virus (BTV), was applied to detect anti-BTV antibodies in serum samples from two llamas (Llama glama) experimentally infected with BTV serotype 10. Antibodies were detected in both llamas by 1 wk or 2 wk post-infection. Antibodies to BTV increased exponentially during the first 4 wk in both llamas and stabilized at an elevated level during the remaining 5-wk-period of the experiment. We evaluated the C-ELISA for 1,442 field sera from bluetongue-free areas, collected from 398 llamas in New Zealand as well as 451 elk (Cervus elaphus canadensis), 323 bison (Bison bison) and 270 reindeer (Rangifer tarandus tarandus) in Canada. Based on the frequency distribution of the C-ELISA values, we propose that the current negative cut-off value of 50% inhibition established for bovine field sera also can be applied to the sera from these wild ruminants. The C-ELISA values for other wild ruminant field sera collected in bluetongue-free areas of Canada from 98 native caribou (Rangifer tarandus caribou), 32 white-tailed deer (Odocoileus virginianus), 14 moose (Alces alces), and nine musk-oxen (Ovibos maschatus) and 15 yak (Bos grunniens) also were less than 50%, with the exception of three caribou samples. Based on our results, we propose that the C-ELISA be used as a rapid and specific test for serodiagnosis of BTV infection in llamas and possibly other wild ruminants.