Mother to offspring transmission of chronic wasting disease in reeves' muntjac deer

Abstract

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.

Figure 1. PrP^CWD detection in CerTgPrP mice inoculated with muntjac CWD.

Western blot detection of PrP^CWD in brains of CerTgPrP mice (n = 9) IC-inoculated with obex from a CWD+ white-tailed deer (lane 2) or CWD+ muntjac (lanes 4–12) following PK digestion. Complete PK digestion of PrP^C is shown in a mouse inoculated with negative deer obex (lane 2).

Figure 2. PrP^CWD detection in CWD-inoculated dams.

(A) IHC PrP^CWD is demonstrated (red deposits) in a tonsilar lymphoid biopsy collected at 4 mpi (A3) and in the obex of a terminal TSE diseased dam at 23 mpi (A1). Absence of red deposits is shown in negative control tonsil (A4) and obex (A2). Picture objective is 20X (scale bar = 200 µm). (B) Western blot detection of PrP^CWD in obex tissue of a CWD-inoculated dam at 23 mpi (B lane 5) following PK digestion. Complete PK digestion of PrP^C is shown in negative control deer obex (B lane 3). PrP^CWD detection is demonstrated in CWD positive control deer obex (B lane 2).

Figure 3. IHC PrP^CWD detection in viable muntjac fawns born to CWD+ dams.

PrP^CWD is demonstrated (red deposits) in tonsilar biopsies collected at 40 days post birth (dpb, A), 465 dpb (C) and 504 dpb (E) and RAMALT biopsies collected at 103 dpb (B), 386 dpb (D) and 504 dpb (F) and confirmed in the terminal tissues of 1 fawn (G, H, I). Absence of PrP^CWD is shown in negative control tissues (J, K, L). Picture objective is 40X (scale bar = 100 µm) with insets at 20X (scale bar = 200 µm).

Figure 4. Amplifiable CWD prions detected in muntjac dam and fetal tissues.

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.

Figure 5. CWD detection in tissues harvested from offspring of CWD+ dams.

Tonsilar and RAMALT biopsies harvested from viable (v) offspring were analyzed for PrP^CWD by IHC. All tissues from nonviable (NV) and in utero (IU) derived tissues were analyzed for amplifiable CWD prions by 5 rounds of sPMCA. Tissues from mock-inoculated offspring were IHC and or sPMCA negative.