Epidemic of Salmonellosis in Passerine Birds in Switzerland With Spillover to Domestic Cats

A die-off of passerine birds, mostly Eurasian siskins (Carduelis spinus), occurred in multiple areas of Switzerland between February and March 2010. Several of the dead birds were submitted for full necropsy. Bacteriological examination was carried out on multiple tissues of each bird. At gross examination, common findings were light-tan nodules, 1 to 4 mm in diameter, scattered through the esophagus/crop. Histologically, a necroulcerative transmural esophagitis/ingluvitis was observed. Bacterial cultures yielded Salmonella enterica subsp. enterica serovar Typhimurium. At the same time, 2 pet clinics reported an unusual increase of domestic cats presented with fever, anorexia, occasionally dolent abdomen, and history of presumed consumption of passerine birds. Analysis of rectal swabs revealed the presence of S. Typhimurium in all tested cats. PFGE (pulsed field electrophoresis) analysis was performed to characterize and compare the bacterial isolates, and it revealed an indistinguishable pattern between all the avian and all but 1 of the feline isolates. Cloacal swabs collected from clinically healthy migrating Eurasian siskins (during autumn 2010) did not yield S. Typhimurium. The histological and bacteriological findings were consistent with a systemic infection caused by S. Typhimurium. Isolation of the same serovar from the dead birds and ill cats, along with the overlapping results of the PFGE analysis for all the animal species, confirmed a spillover from birds to cats through predation. The sudden increase of the number of siskins over the Swiss territory and their persistency during the whole winter of 2009-2010 is considered the most likely predisposing factor for the onset of the epidemic.

What determines the impact of alien birds and mammals in Europe?

An often-cited reason for studying the process of invasion by alien species is that the understanding sought can be used to mitigate the impacts of the invaders. Here, we present an analysis of the correlates of local impacts of established alien bird and mammal species in Europe, using a recently described metric to quantify impact. Large-bodied, habitat generalist bird and mammal species that are widespread in their native range, have the greatest impacts in their alien European ranges, supporting our hypothesis that surrogates for the breadth and the amount of resources a species uses are good indicators of its impact. However, not all surrogates are equally suitable. Impacts are generally greater for mammal species giving birth to larger litters, but in contrast are greater for bird species laying smaller clutches. There is no effect of diet breadth on impacts in birds or mammals. On average, mammals have higher impacts than birds. However, the relationships between impact and several traits show common slopes for birds and mammals, and relationships between impact and body mass and latitude do not differ between birds and mammals. These results may help to anticipate which species would have large impacts if introduced, and so direct efforts to prevent such introductions.