Mother to offspring transmission of chronic wasting disease in Reeves' Muntjac deer

The horizontal transmission of prion diseases has been well characterized in bovine spongiform encephalopathy (BSE), chronic wasting disease (CWD) of deer and elk and scrapie of sheep, and has been regarded as the primary mode of transmission. Few studies have monitored the possibility of vertical transmission occurring within an infected mother during pregnancy. To study the potential for and pathway of vertical transmission of CWD in the native cervid species, we used a small cervid model-the polyestrous breeding, indoor maintainable, Reeves' muntjac deer-and determined that the susceptibility and pathogenesis of CWD in these deer reproduce that in native mule and white-tailed deer. Moreover, we demonstrate here that CWD prions are transmitted from doe to fawn. Maternal CWD infection also appears to result in lower percentage of live birth offspring. In addition, evolving evidence from protein misfolding cyclic amplification (PMCA) assays on fetal tissues suggest that covert prion infection occurs in utero. Overall, our findings demonstrate that transmission of prions from mother to offspring can occur, and may be underestimated for all prion diseases

Infectious Prions in Pre-Clinical Deer and Transmission of Chronic Wasting Disease Solely by Environmental Exposure

Key to understanding the epidemiology and pathogenesis of prion diseases, including chronic wasting disease (CWD) of cervids, is determining the mode of transmission from one individual to another. We have previously reported that saliva and blood from CWD-infected deer contain sufficient infectious prions to transmit disease upon passage into naïve deer. Here we again use bioassays in deer to show that blood and saliva of pre-symptomatic deer contain infectious prions capable of infecting naïve deer and that naïve deer exposed only to environmental fomites from the suites of CWD-infected deer acquired CWD infection after a period of 15 months post initial exposure. These results help to further explain the basis for the facile transmission of CWD, highlight the complexities associated with CWD transmission among cervids in their natural environment, emphasize the potential utility of blood-based testing to detect pre-clinical CWD infection, and could augur similar transmission dynamics in other prion infections

B Cells and Platelets Harbor Prion Infectivity in the Blood of Deer Infected with Chronic Wasting Disease▿ †

Substantial evidence for prion transmission via blood transfusion exists for many transmissible spongiform encephalopathy (TSE) diseases. Determining which cell phenotype(s) is responsible for trafficking infectivity has important implications for our understanding of the dissemination of prions, as well as their detection and elimination from blood products. We used bioassay studies of native white-tailed deer and transgenic cervidized mice to determine (i) if chronic wasting disease (CWD) blood infectivity is associated with the cellular versus the cell-free/plasma fraction of blood and (ii) in particular if B-cell (MAb 2-104+), platelet (CD41/61+), or CD14+ monocyte blood cell phenotypes harbor infectious prions. All four deer transfused with the blood mononuclear cell fraction from CWD+ donor deer became PrPCWD positive by 19 months postinoculation, whereas none of the four deer inoculated with cell-free plasma from the same source developed prion infection. All four of the deer injected with B cells and three of four deer receiving platelets from CWD+ donor deer became PrPCWD positive in as little as 6 months postinoculation, whereas none of the four deer receiving blood CD14+ monocytes developed evidence of CWD infection (immunohistochemistry and Western blot analysis) after 19 months of observation. Results of the Tg(CerPrP) mouse bioassays mirrored those of the native cervid host. These results indicate that CWD blood infectivity is cell associated and suggest a significant role for B cells and platelets in trafficking CWD infectivity in vivo and support earlier tissue-based studies associating putative follicular B cells with PrPCWD. Localization of CWD infectivity with leukocyte subpopulations may aid in enhancing the sensitivity of blood-based diagnostic assays for CWD and other TSEs

CWD bioassay inocula sources.

a<p>Water, feed buckets and bedding from CWD+ deer suites.</p>b<p>Colorado State University deer number 112 (PO brain inoculated deer from previous study<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0005916#pone.0005916-Mathiason1" target="_blank">[27]</a>).</p>c<p>Colorado State University deer number 121 (IC brain inoculated deer from previous study <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0005916#pone.0005916-Mathiason1" target="_blank">[27]</a>).</p>d<p>Wisconsin Department of Natural Resources, Madison, WI, USA.</p>e<p>Colorado State Veterinary Diagnostic Laboratory, Fort Collins, CO, USA.</p>f<p>Transitioning from pre-clinical to clinical.</p>g<p>Contains brain tissue from deer of pre-clinical and clinical status at terminal field collection.</p

Study design to investigate CWD vertical/maternal transmission.

*<p>Dam inoculated orally (PO) only. All other dams inoculated PO and subcutaneously (SC).</p><p>Late = > ½ time to dam terminal TSE disease.</p><p>Early = < ½ time to dam terminal TSE disease.</p><p>Late gestation = >3.5 months gestation.</p><p>Early gestation = <3.5 months gestation.</p><p>NCD = No clinical disease.</p><p>dpb = days post birth.</p>1<p>Dam’s first conception.</p>2<p>Dam’s second conception.</p>3<p>Dam’s third conception.</p

Summary of naïve deer exposed to inoculum from CWD+ deer—combined with our previous published findings

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0005916#pone.0005916-Mathiason1" target="_blank">[27]</a>.</p

Amplifiable CWD prions detected in muntjac dam and fetal tissues.

<p>All panels show representative Western blot results after 5 rounds of sPMCA. Samples considered CWD positive are denoted with an asterisk (*). (A-H) Complete PK digestion of PrP^C is shown in negative deer brain controls (-C) without and with PMCA. PrP^CWD detection is shown in positive deer controls (+C) following PK digestion without and with PMCA. Tissue abbreviations are defined as follows: C = control, MED = mediastinal lymph node, PAR = parotid lymph node, POP = popliteal lymph node, MES = mesenteric lymph node, PLA = placenta, HLN = hepatic lymph node, TE = third eyelid, MAN = mandibular lymph node, TON = tonsil, ILN = ileocecocolic lymph node, RAM = recto-anal mucosa associated lymphoid tissue, SP = spleen, RLN = retropharyngeal lymph node, IL = ileum, TLN = tracheobronchial lymph node, SLN = sublumbar lymph node, OB = obex, MAM = mammary lymph node, CA = caruncle.</p

Western blot results of deer exposed to body secretions and excreta from CWD+ deer.

<p>Western blot demonstration of the typical PK digestion band shift (28–35 kD) associated with prion infection in the brain (medulla oblongata at obex) of deer receiving blood, brain, saliva or environmental exposure, but not urine and feces from CWD-infected donors. Lanes 1–4 represent CWD+/− deer controls (10% brain homogenate of medulla at obex) without and with PK digestion at 25 µg/ml. Lanes 5–12, 10% brain homogenate of blood, brain, urine/feces or saliva inoculated deer without and with PK digestion at 25 µg/ml. Lanes 13–15, brain homogenate from deer environmentally exposed to CWD+ fomites without and with PK digestion at 25 and 50 µg/ml.</p