Date Published: March 18, 2019
Publisher: Public Library of Science
Author(s): Fern Van Sant, Sayed M. Hassan, Drury Reavill, Rita McManamon, Elizabeth W. Howerth, Mauricio Seguel, Richard Bauer, Kathy M. Loftis, Christopher R. Gregory, Paula G. Ciembor, Branson W. Ritchie, Petr Heneberg.
During 2018, four free-ranging conures, from a naturalized flock in San Francisco, presented with a characteristic set of neurologic signs that had been reported in other individuals from this flock. The cause of morbidity or mortality in historic cases has not been identified. From these four subjects, fresh feces were collected during their initial days of hospitalization and submitted to the University of Georgia Infectious Diseases Laboratory and Center for Applied Isotope Studies for bromethalin and desmethyl-bromethalin quantitation. Using High Performance Liquid Chromatography, the laboratory detected bromethalin, a non-anticoagulant, single-dose rodenticide, in fecal samples from three subjects; half of these samples were also positive for desmethyl-bromethalin, bromethalin’s active metabolite. In three subjects that died, the UGA laboratory screened brain and liver samples and found bromethalin in all samples; desmethyl-bromethalin was detected in all but one brain sample, which was below the detection limit. Our findings suggest the conures are more resistant to bromethalin than are other species in which bromethalin has been studied, and/or that the conures may be ingesting the toxin at a sublethal dose. More data is needed to better assess the long-term effects of bromethalin on animals exposed at the subacute/chronic levels, and also to better understand the compartmentalization of bromethalin and desmethyl-bromethalin in a wider variety of species.
Since 1989 , a well-established flock of interbreeding feral conures has grown and extended its range both northward, along San Francisco, California, USA’s Embarcadero waterfront to the Presidio, and southward to Brisbane. The flock contains a mix of mitred (Aratinga mitrata), red-masked (also known as red-headed or cherry-head; A. erythrogenys) and red-fronted (also known as scarlet-fronted; A. wagleri) conures. The birds range in very populated areas; they commonly interact with local residents and tourists.
In 2018, San Francisco Department of Animal Care & Control transferred four recently rescued conures to For the Birds, in San Jose, California, USA, for veterinary care. To increase the likelihood of detecting bromethalin ingestion in these acute and severely affected subjects, feces was collected from each and submitted to the UGA Center for Applied Isotope Studies (CAIS), Athens, Georgia, USA, for bromethalin and desmethyl-bromethalin screening. Due to the progression of their neurologic deficits, subjects two and three were euthanized at two and three months, respectively, following initial hospitalization. Subject four died two months following initial hospitalization, after neurological signs progressed to the point that the subject could no longer self-feed. Salient histologic lesions of the CNS from the deceased subjects were consistent with those described in literature (see Figs 1–4). We detected bromethalin in samples from all four subjects from 2018. See Table 2 for all results.
The findings from our 2018 cohort suggest that conures may not metabolize bromethalin into desmethyl-bromethalin as effectively as this conversion occurs in the species studied and described in our literature review [4–5, 8–9, 15]. Because there is no pharmacokinetic data associated with bromethalin in conures, we were unable to confirm why our method detected desmethyl-bromethalin in half of the week two fecal samples from our 2018 subjects, but not in fecal samples from the other two subjects. Nor could we confirm why, weeks later, bromethalin was detected in the brains and livers from all deceased conures, and desmethyl-bromethalin was detected in all liver samples and all but one brain sample. However, variations in the concentration levels of these substances detected in our subjects would be expected to be dependent upon the time between ingestion by an individual and that individual’s presentation to the clinic. The LD50 of bromethalin varies by species with domestic felines being most susceptible and rabbits (Leporidae) being more resistant than canines or quail (Coturnix coturnix). Our data suggests that conures are more resistant to bromethalin toxicosis than rabbits, canines or quail. Whether this resistance is acquired or innate is not known, but should be better defined to understand potential ways to protect and/or treat collaterally affected species.