Assessment of carvacrol for control of avian aspergillosis in intratracheally challenged chickens in comparison to voriconazole with a reference on economic impact

This study was designed to investigate the efficacy of essential oils as an alternative prophylaxis and treatment for avian aspergillosis. The in vitro susceptibility of Aspergillus fumigatus strains to antifungal drugs and carvacrol, thymol, eugenol, thymoquinone and cinnamon was determined using the macrodiffusion and microdilution methods. Carvacrol has antifungal activity in comparison to voriconazole (VCZ) (MIC 0·5, 0·25 μg ml−1 respectively). While cinnamon, euganol, thymol and thymoquinone displayed moderate to weak inhibitory activity. For the efficacy study, five groups of 10‐day‐old chicks (n = 48) were infected intratracheally either with A. fumigatus conidia or saline (negative control). Chicks in carvacrol prophylactic and treatment (CRPT) group were fed for 10 days beginning from hatch with carvacrol (200 mg kg−1 per diet) supplemented diets. VCZ (VCZT:20 mg kg−1 body weight (BW)), carvacrol treatment (CRT, CRPT) was started upon appearance of the first clinical signs and continued for 10 days. Birds were monitored for an additional 15 days following treatment. Fungal burden and therapeutic efficacy were assessed by survival, BW, quantitative (q) culture (CFU), quantitative real‐time PCR (qPCR) and histopathological changes at several time points. Serum biochemical changes were also assessed. VCZT, CRPT, CRT in comparison to the sham‐treated (SHAM) group have prolonged survival (87·5, 83·4, 79·2, 41·7% respectively). In VCZT and CRPT, a significant reduction in clinical signs, lesions, CFU and qPCR counts to the limit of detection were observed. CRPT has the lowest BW reduction, economic losses and significant low total cholesterol levels. Carvacrol has a promising potential to be used as a prophylactic and treatment against A. fumigatus. Prognosis of avian aspergillosis is often poor due to delayed diagnosis and treatment failure. However, the widespread uses of azole prophylaxis in birds are thought to be the major driver of azole resistance. These findings create a possibility to develop an effective drug‐free alternative strategy for control of avian aspergillosis.