Fatal toxoplasmosis in a wild snowshoe hare (Lepus americanus) and eastern gray squirrel (Sciurus carolinensis) from the eastern United States.

Toxoplasmosis is a parasitic disease that exemplifies the One Health interface due to its global distribution and diversity of hosts in which it can infect and potentially cause disease. While T. gondii, the causative agent of toxoplasmosis, has been well-described in many wildlife taxa, including wild and domestic birds and mammals, there is limited published research on clinical disease in wild lagomorphs and rodents. Furthermore, despite detection in wild lagomorphs in Europe and Australia, T. gondii as a cause of clinical disease has yet to be described in wild lagomorphs in the USA. Here, we describe acute toxoplasmosis as the cause of mortality in a snowshoe hare in West Virginia, USA and an eastern gray squirrel (Sciurus carolinensis) in South Carolina, USA. These infections manifested as severe, acute, multi-organ necrosis (liver, spleen, and lungs) with high numbers of widespread protozoal zoites within affected areas. The mode of T. gondii transmission to the hare and squirrel is unknown but likely was via ingestion of infective oocysts from the environment when foraging or grooming. The potential of wild lagomorph and squirrel populations in the USA to serve as a reservoir for T. gondii has implications for spillover to (1) humans via handling or consuming undercooked meat, and (2) other wildlife such as wild felids that could predate infected lagomorphs and squirrels.