Vertical transmission of chronic wasting disease in free-ranging white-tailed deer populations

Abstract

Chronic wasting disease (CWD) is a fatal neurodegenerative disease affecting cervids across North America, Northern Europe, and Asia. Disease transmission among cervids has historically been attributed to direct animal-to-animal contact with 'secreta' (saliva, blood, urine, and feces) containing the infectious agent, and indirect contact with the agent shed to the environment in these bodily components. Mounting evidence provides another mechanism of CWD transmission, that from mother-to-offspring, including during pregnancy (vertical transmission). Here we describe the detection of the infectious CWD agent and prion seeding in fetal and reproductive tissues collected from healthy-appearing free-ranging white-tailed deer (Odocoileus virginianus) from multiple U.S. states by mouse bioassay and in vitro prion amplification assays. This is the first report of the infectious agent in multiple in utero derived fetal and maternal-fetal reproductive tissues, providing evidence that CWD infections are propagated within gestational fetal tissues of white-tailed deer populations. This work confirms previous experimental and field findings in several cervid species supporting vertical transmission as an additional mechanism of CWD transmission and may help to further explain the facile dissemination of this disease among captive and free-ranging cervid populations.

Keywords: Odocoileus virginianus; Cervid; Chronic wasting disease; Prion disease; Vertical transmission; in utero transmission.

Fig. 1

CWD detection in female white−tailed deer pregnancy microenvironment determined by RT−QuIC. Grouped based on state of collection. Amyloid seeding in one or more of the following tissues: uterus, amniotic fluid, and placentomes (a–c; Table 2) from CWD−positive dams as determined by RT−QuIC & IHC (Table 1). Amyloid formation displayed as reaction rates (1/time (t) to Thioflavin T (ThT) fluorescent threshold). Horizontal lines represent the medians with n = 8 replicates (dam tissues). Negative controls from all Georgia deer (n = 3) remained negative in all samples tested and CWD−positive controls sourced from experimentally inoculated muntjac (last data point on the right). P values as follows: * <0.05, ** <0.01, *** <0.001, ****<0.0001. Grey shaded rectangles in panels A and C denote samples utilized for bioassay inoculations (Table 3).

Fig. 2

CWD detection in white-tailed deer (WTD) fetal tissues determined by RT-QuIC. Amyloid seeding detected in fetal brain, thymus, and liver (Table 2) collected from CWD-positive dams as determined by RT-QuIC and IHC (Table 1). Amyloid formation displayed as reaction rates (1/time (t) to Thioflavin T (ThT) fluorescent threshold). Horizontal lines represent medians with n = 16 replicates (fetal tissues). Negative control fetal tissue samples from WTD collected in Georgia (n = 3) remained negative in all samples tested. P values as follows: * <0.05, ** <0.01, *** <0.001, ****<0.0001. Grey shaded rectangles denote samples utilized for bioassay inoculations (Table 4). Abbreviations represented as follows: (Th)ymus, (Br)ain, and (Liv)er.

Fig. 3

Infectious CWD prions present in white-tailed deer maternal reproductive and fetal tissues determined by mouse bioassay. Cervidized (Tg^{CerPrP−E226}5037^+/−) mice were inoculated with 10^− 4 dilutions of uterus or placentome intracranially (uterus: n = 12 mice; placentome: n = 35 mice) or fetal thymus or fetal brain intraperitoneally (thymus: n = 8 mice; brain: n = 11 mice). Terminal mouse brains were tested by conventional RT-QuIC for amyloid seeding activity. Amyloid formation displayed as reaction rates (1/time (t) to Thioflavin T (ThT) fluorescent threshold). Horizontal lines represent the median (8 replicates per mouse). Mice inoculated with tissues from free-ranging negative control deer (uterus: n = 8 mice; placentome: n = 8 mice; thymus: n = 8 mice; brain: n = 6 mice; 8 replicates each) from Georgia served as negative controls. A Mann-Whitney unpaired t-test was used against negative controls to determine statistical significance. **** indicates a P value of < 0.0001.