Prevalence and drivers of ectoparasite abundance on Norway rats ( Rattus norvegicus ) in New York City residential complexes

BACKGROUND: Norway rats, Rattus norvegicus (Berkenhout), can carry ectoparasites of public health importance. However, this ectoparasite burden in residential complexes remains poorly characterized. This study examined ectoparasites recovered from Norway rats collected within New York City residential complexes and evaluated their associations with capture environment, host trait, and trap type. RESULTS: Six ectoparasite species were recovered. Spiny rat mites, Laelaps echidnina Berlese and Laelaps nuttalli Hirst, had the highest prevalence (56.1%), followed by the tropical rat mite, Ornithonyssus bacoti (Hirst) (40.3%), the spiny rat louse, Polyplax spinulosa (Burmeister) (39.5%), the Oriental rat flea, Xenopsylla cheopis (Rothschild) (38.4%), and the house mouse mite, Liponyssoides sanguineus (Hirst) (2.2%). Indoor-captured rats had higher abundance of X. cheopis, O. bacoti, and Laelaps spp., whereas P. spinulosa was more abundant on outdoor-captured rats. Cage-trapped rats (live rats) had higher counts of X. cheopis and Laelaps spp. than snap-trapped rats (dead rats). Among cage-trapped rats, 92.5% carried at least one species of ectoparasites and a mean number of 18.6 ectoparasites. Xenopsylla cheopis prevalence was 50.6% and the flea index was 4.1 fleas per examined live rat. Species composition varied among the four sampled New York City boroughs. CONCLUSIONS: Given the public health relevance of these ectoparasites, the detection of L. sanguineus on Norway rats in New York City, together with an increase in X. cheopis prevalence as compared with previous New York City surveillance data, highlights the need to include ectoparasite surveillance and control in urban rodent management programs. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.