Anomalous morphologies in Ixodes scapularis feeding on human hosts.

Cases of anomalous morphologies in the blacklegged tick, Ixodes scapularis, have been reported in both field-collected and human-biting specimen in the Northeastern and Midwestern United States, complicating the identification of this medically important tick species. We herein describe four cases of morphological anomalies in I. scapularis females exhibiting nanism and abnormally small genital apertures. We also report a female I. scapularis displaying slight asymmetry in the lower abdomen oriented toward the right side and an abnormal anal groove completely enclosing the anus. The identity of each specimen was confirmed using taxonomic keys, high resolution light and scanning electron microscopy imaging, and DNA sequencing of the 18S rRNA gene. All specimens described in this study were found parasitizing human hosts and were submitted to the Connecticut Agricultural Experiment Station-Tick Testing Laboratory in 2021 for species identification and pathogen screening. Here, we also discuss recent reports of teratological abnormalities in I. scapularis as well as likely causes for such deformities and potential implications.