DOI: 10.7589/2015-11-298 Journal of Wildlife Diseases, 52(4), 2016, pp. 912–915 Ó Wildlife Disease Association 2016 Removal of Lipid from Serum Increases Coherence between Brucellosis Rapid Agglutination Test and Enzyme-linked Immunosorbent Assay in Bears in Alaska, USA Jacques Godfroid, 1 Kimberlee Beckmen, 2 and Ingebjørg Helena Nymo 1,3 1 UiT – The Arctic University of Norway, Arctic Infection Biology, Postboks 6050 Langnes, N-9010 Tromsø, Norway; 2 Alaska Department of Fish and Game, 1300 College Road, Fairbanks, Alaska 99701-1551, USA; 3 Corresponding author (email: ingebjorg.h.nymo@uit.no) ABSTRACT: In cases of chronic Brucella spp. infection, results of the rose bengal plate test (RBPT) and indirect enzyme-linked immunosor- bent assay (ELISA) should be coherent, as reported in controlled conditions in the literature. We compared RBPT and ELISA results in 58 Alaska grizzly bears (Ursus arctos horribilis), eight Kodiak brown bears (Ursus arctos middendorffi), and six Alaska Peninsula brown bears (Ursus arctos gyas). Of the 72 bears tested, 42 (58%) were ELISA positive and 53 (73%) were RBPT positive. However, the coherence between the tests was only fair (K ¼ 0.37, SE ¼ 0.11), suggesting that either the serologic results were not compat- ible with Brucella spp. infection or that there was a technical problem with the tests. To address a potential technical problem, we performed a 30- min chloroform/centrifugation cleanup. Following cleanup, the ELISA identified 43 positives (59%) and the RBPT identified 47 (65%), and the coherence between the tests was much improved (K ¼ 0.80, SE ¼ 0.07). We recommend cleaning wildlife sera with a high lipid content before performing RBPT and performing RBPT and ELISA in parallel to assess coherence. Our results suggest that Alaskan brown bears have been exposed to Brucella spp. Key words: Alaska grizzly bear, Alaska Penin- sula brown bear, Brucella spp., bear, brucellosis, Kodiak brown bear, lipemic serum, serum cleanup. Classically, serologic tests for detecting antibodies against a specific etiologic agent or group of agents are the first screening tools used in humans, livestock, and wildlife. The presence of antibodies indicates exposure to an agent, which may be due to a current infection or an earlier infection. To make sound inferences based on serologic test results, there are two prerequisites: 1) the biology of the infection needs to be under- stood (e.g., if the host species is a reservoir or a spillover host; Godfroid et al. 2014), and 2) the test, often developed for use in a livestock species, needs to be validated when used in other species (World Organisation for Animal Health [OIE] 2015a). These prerequisites are especially important when studies rely solely on serologic results, which is often the case in wildlife disease studies (OIE 2015b). Serolog- ic tests can be classified into species-specific (e.g., brucellosis indirect enzyme-linked im- munosorbent assay [ELISA], although such tests may be used in different species with an appropriate conjugate) or species-nonspecific (e.g., agglutination tests like the rose bengal plate test [RBPT] commonly used in humans, livestock, and wildlife; Godfroid et al. 2010, 2014). The serologic tests recommended by the OIE for detecting exposure to Brucella spp. use antigens derived from Brucella abortus (OIE 2015c). This is because the immunodo- minant antigens of Brucella spp. are associat- ed with the smooth lipopolysaccharide (S- LPS) and are shared to a very large extent by the smooth Brucella species. Consequently, it is impossible to ascribe to which smooth Brucella species the antibodies detected in a host are directed (Godfroid et al. 2014). Another problem with brucellosis serology is cross-reactivity. Some Gram-negative bac- teria (the most important being Yersinia enterocolitica O:9) have an S-LPS bearing some of the same immunodominant antigens as Brucella S-LPS. In case of exposure to Y. enterocolitica O:9, using multiple brucellosis serologic tests will not solve the problem (Godfroid et al. 2014). Indeed, all validated and recommended brucellosis serologic tests use antigens derived from B. abortus biovar 1, which shares the A epitope associated to the 912 Downloaded from http://meridian.allenpress.com/doi/pdf/10.7589/2015-11-298 by guest on 11 October 2021