A critical review of diagnostic methods for camel brucellosis

Brucellosis is a zoonotic disease that severely affects animal productivity and human health worldwide. Although camels are susceptible, the diagnosis of brucellosis in these animals has received limited scientifically valid attention. Most bacteriological studies in naturally infected camels present major shortcomings, including insufficient sample type, size and processing, low inoculum volumes, suboptimal culture media, inadequate growth conditions, and imperfect strain typing. Regarding serological diagnosis, the unique features of camelid antibodies and their implications for WOAH-recommended tests are insufficiently addressed, leading to questionable assumptions about immunoglobulin detection. Comparative analysis of serological data across studies reveals a marked lack of standardization. Moreover, no serological test has been properly validated for camels, and cut-off values for quantitative assays, including iELISAs and cELISAs, are commonly extrapolated from cattle recommendations by manufacturers. These limitations, together with the inappropriate use of tests incorrectly regarded as confirmatory, undermine the reliability of published seroprevalence and risk factor studies subsequent reviews and meta-analyses, hindering One Health interventions. DNA-based diagnostics that have been directly applied to animal samples thus far are similarly unreliable. There are no systematic studies addressing sampling strategies, sample processing, DNA extraction, amplification protocols, or validation for PCR, RT-PCR and qPCR assays. Available evidence indicates low sensitivity compared with well-performed bacterial culture, and studies lack appropriate specificity controls. Although the difficulties imposed by the environment where most camel reside cannot be ignored, there is an urgent need for rigorously designed diagnostic studies. This review proposes improvements based on existing camel research and established experience in domestic ruminants.