Theileriosis in Multiple Neonatal White-tailed Deer (Odocoileus virginianus) in Delaware, USA

Abstract

Postmortem examination of 21 neonatal white-tailed deer ( Odocoileus virginianus) from Delaware, US identified six fawns with Theileria spp. organisms or suspected infection.

White‐tailed deer neonate survival in the absence of predators

“…These diagnoses often require histological analyses, which researchers seldom conduct in neonatal survival studies, and are likely frequently misattributed during field necropsies. Theileria cervi is particularly difficult to identify even with histological examination, meaning disease prevalence was likely greater than our findings suggest (Haus et al 2018). Emaciation often occurred secondarily to a disease diagnosis, and without histological analyses, we would have likely misattributed these mortality events to starvation.…”

“…Necropsy and histological analyses identified several different diseases as primary causes of mortality, including bacterial sepsis, pneumonia, encephalitis, hepatic necrosis, and Theileria cervi parasitism. Lone star ticks (Amblyomma americanum) are the definitive vector for Theileria cervi, which commonly infects healthy individuals but can lead to death at high levels of infestation or in nutritionally stressed individuals (Yabsley et al 2005, Haus et al 2018). These diagnoses often require histological analyses, which researchers seldom conduct in neonatal survival studies, and are likely frequently misattributed during field necropsies.…”

The impact of vector control on the prevalence of Theileria cervi in farmed Florida white-tailed deer, Odocoileus virginianus

“…Fawns in particular are susceptible to the development of disease caused by T. cervi infection. The development of improved technologies such as vaginal implant transmitters has allowed researchers to gain a better idea of the causes of wild fawn mortality, and T. cervi infection might play a larger role in fawn mortality than previously thought [17]. Additionally, the relocation of species for farming or for other management scenarios can facilitate transmission of vector-borne diseases to new geographical areas, particularly when the receiving population is naïve to the pathogen [2].…”

“…Nonetheless, infection with T. cervi on the farm remained relatively high (~40%) and the nearly 100% infection rate of nearby wild deer suggests that the risk of infection is high in this geographical region. While exposure to T. cervi did not appear to have negative health effects on this cervid livestock species, neonates may be particularly at risk due to their susceptibility to disease [17]. If further tick control is needed to reduce tick populations and resultant tick-borne disease on these farms, acaracide application during spring or autumn may decrease the risk infection, but the increased exposure of deer to chemical vector control agents should be taken into consideration.…”

“…In cases where T. cervi has been linked to disease, the host was malnourished and co-infected with other parasites, or the host was translocated into an infected herd from a non-endemic area [15, 16]. Additionally, T. cervi was found to cause mortality in white-tailed deer fawns in Delaware, USA, and may be a more important parasite affecting the health of wild deer than previously thought, especially with the increase in abundance and range of the vector, lone star ticks [17]. Despite this, disease caused by T. cervi infection has not been well-documented.…”