We would like to thank S. Werner for providing the crows used in this study and USDA, APHIS, WS, NWRC animal care staff for animal care and monitoring. Mention or use of a product does not imply USDA endorsement. Funding for this study was provided by USDA, APHIS, Veterinary Services.

Our protocol is adapted from one we previously published7. All procedures involving animals were approved by the Institutional Animal Care and Use Committee of the United States Department of Agriculture (USDA), Animal and Plant Health Inspection Service (APHIS), Wildlife Services (WS), National Wildlife Research Center (NWRC).
1. Crow Gavaging
<ol>
	<li>Estimate passage time of &#39;pseudo brain material&#39; through the alimentary tract of American crows.
	<ol>
		<li>Mix 5 ml of cooked and scrambled whole egg with blue dye and gavage 1 crow using a 2 in&#160;gavage needle (Figure 1).</li>
		<li>Check crow every 30 min until blue/green-stained feces are no longer being excreted.</li>
	</ol>
	</li>
	<li>Obtain uninfected and terminally ill RML (Chandler strain) -infected C57BL/6 mouse brains.</li>
	<li>Generate a 20% wt/vol normal and infected mouse-brain homogenate in a bullet blender homogenizer with 1x phosphate buffered saline (PBS) and glass beads, then centrifuge at 3,000 x g for 1 min to remove larger particulate matter. Remove supernatant and dilute with an equal volume of 1x PBS to generate a 10% wt/vol in sterile PBS. Freeze at -80 &#176;C until needed.</li>
	<li>17 hr prior to gavage remove food, but not water, from crow pens.</li>
	<li>Randomly allocate crows to treatment groups and orally gavage each crow with 5 ml of either normal or infected mouse brain homogenate using a 2 in&#160;gavage needle.</li>
	<li>Transfer crows to individual cages and collect and pool all feces within each cage for 4 hr post gavage (Figure 2).</li>
	<li>Homogenize pooled feces for each crow in a bullet blender homogenizer with glass beads until a uniform texture is achieved. *Crow feces are mostly liquid and can be mixed easily.</li>
	<li>For each crow, dilute 500 &#181;l of fecal homogenate into 9.5 ml 1x PBS for a total volume of 10 ml.</li>
	<li>Centrifuge the fecal homogenate for 15 min at 1,400 x g and extract the supernatant.</li>
	<li>To minimize the threat of a secondary microbial infection, treat supernatant with 1 &#181;l of 100 units/ml penicillin and 100 &#181;g/ml streptomycin (Invitrogen, NY) per 100 &#181;l of homogenate then place under UV light at room temperature for 20 min to reduce risk of viral and bacterial contamination. After UV exposure, sonicate samples in a 3000 Mp sonicator at setting 70 for 30 sec to disrupt the membrane of any remaining microbes.</li>
</ol>
2. Mouse Inoculation
<ol>
	<li>Randomly allocate mice to the following treatment groups (Table 1):
	<ol>
		<li>Group 1 - Positive treatment mice inoculated intraperitoneally (IP) with 1 ml of fecal homogenate from crows orally gavaged with 5ml infected mouse brains.</li>
		<li>Group 2 - Negative treatment mice inoculated IP with 1 ml of fecal homogenate from crows orally gavaged with 5ml normal mouse brains.</li>
		<li>Dilute infected and normal mouse brain homogenate for Groups 3 and 4 to 1:100 w/v in 1x PBS.</li>
		<li>Group 3 - Positive control mice inoculated IP with 1 ml of infected mouse-brain homogenate.</li>
		<li>Group 4 - Negative control mice inoculated IP with 1 ml of normal mouse-brain homogenate.</li>
	</ol>
	</li>
</ol>
<table border="1">
	<tbody>
		<tr>
			<td></td>
			<td>Treatment Group</td>
			<td>Number of Animals</td>
		</tr>
		<tr>
			<td>Group 1</td>
			<td>Scrapie + Crow Feces</td>
			<td>100</td>
		</tr>
		<tr>
			<td>Group 2</td>
			<td>Scrapie - Crow Feces</td>
			<td>25</td>
		</tr>
		<tr>
			<td>Group 3</td>
			<td>Scrapie + Mouse Brain</td>
			<td>10</td>
		</tr>
		<tr>
			<td>Group 4</td>
			<td>Scrapie - Mouse Brain</td>
			<td>5</td>
		</tr>
	</tbody>
</table>
Table 1. Scrapie status of inoculum (positive +, negative -) and number of animals used7.
<ol start="2">
	<li>Intraperitoneally inoculate mouse:
	<ol>
		<li>Scruff mouse by dorsal neck fur with thumb and index finger and gently rotate to expose ventral side.</li>
		<li>Elevate posterior end of mouse so head is slightly lower.</li>
		<li>Insert 25 G needle 1 cm through skin, 1 cm lateral of midline, and 1-2 cm anterior to the sacroiliac joint using a needle-locking syringe.</li>
		<li>Inject 1 ml inoculate slowly into mouse body cavity.</li>
	</ol>
	</li>
</ol>
3. Mouse Monitoring
<ol>
	<li>Monitor mice daily until they express clinical signs of mouse scrapie. Clinical signs may include: kyphosis, ataxia, stiff tail, lack of grooming, emaciation, and lethargy.</li>
	<li>Score mice for each of the 6 clinical signs when visible signs are evident, where 0 = none visible, 1 = moderate, and 2 = severe.</li>
	<li>Euthanize mice when total daily scores for each sign reach &#8805;8 for 1 day, &#8805; 6 continuously for 3 days, or at 365 days post inoculation (dpi).</li>
	<li>Harvest brains immediately following euthanasia and store at -70 &#176;C.</li>
	<li>To confirm a scrapie diagnosis, digest brain samples with 3 &#181;l of a 50 &#181;g/ml of proteinase-K solution (PK) diluted as follows: 3.1. &#181;l PK, 12.5 &#181;l of 500 mM EDTA, pH 8, 109.39 &#181;l of 1x PBS for 30 min at 45 &#176;C, then inactivate the PK by adding 8 &#181;l loading buffer and incubating samples at 95 &#176;C for 5 min. Load samples onto a 12% SDS-PAGE gel, electrophorese and transfer to Immobilon PVDF membrane and block with 5% nonfat milk in 0.2% Tween 20 in PBS for 1 hr at room temperature. Then probe with Bar224 anti-PrP monoclonal antibody conjugated to Horseradish peroxidase, diluted in Superblock, for 1 hr at room temperature. Rinse membrane for 1 hr with PBS-0.2% Tween 20. To visualize, incubate Western blot 5 min with chemiluminescent substrate and image on a G-box gel documentation system.</li>
</ol>

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No conflicts of interest declared.

We demonstrate a procedure to document passage of PrPRes material through the digestive system of crows. We used conventional methods to determine if crows have the ability to translocate PrPRes material to disease-free geographic areas. Others have evaluated resistance of PrPRes to ruminant19-21 and rodent22,23 digestive fluids, both of which failed to eliminate it. Future application of these techniques should be applied to other carnivores24 as they cou...

Transmissible spongiform encephalopathies (TSE) are fatal infectious neurodegenerative disorders that affect wildlife, domestic animals, and humans. The infectious agent of TSE diseases appears to be misfolded or pathogenic isoforms (PrPRes) of prion proteins1. Animal TSE diseases include chronic wasting disease (CWD) in mule deer (Odocoileus hemionus), white-tailed deer (Odocoileus virginianus), elk (Cervus elaphus), and moose (Alces alces); scrapie in sheep and goats; bovine spongiform encephalopathy (BSE) in domestic cattle; transmissible mink encephalopathy in farmed mink; feline spongiform encephalopathy in cats; exotic ungulate spongiform encephalopathy in exotic zoo ruminates of the family Bovidae; and spongiform encephalopathy in nonhuman primates8. The single human TSE disease, variant Creutzfeldt-Jakob disease, is rare and thought to be acquired by consuming PrPRes-contaminated food9. Similarly, BSE can infect humans if contaminated beef is consumed10. Of all the TSE diseases, scrapie and CWD are the only two with self-sustaining epidemics and sources for infection are presumed to be from animal to animal2,3,11 as well as from environmental sources4-6. Research suggests that most TSE diseases require notable extended incubation periods from natural exposure events of PrPRes material to manifestation of clinical signs2-4,6,8 and apparent species barriers minimize, but do not eliminate the potential for, interspecies transmission12-14.
Identifying mechanisms for the spread of infectious prion (PrPRes) material is extremely important for answering questions about how TSE diseases move across the landscape. Experimental investigations have suggested that insects15,16, poultry and pigs17, and American crows (Corvus brachyrhynchos)7,18 are passive carriers or dispersers of PrPRes material. Passage of PrPRes material through the digestive system of crows has recently been documented, demonstrating the role they may play in dispersal of TSE diseases7. These results make it plausible that crows, a scavenger, could encounter, consume, and transport infectious material via feces deposition, to disease-free areas.
The procedures we demonstrate here were used to document passage of PrPRes material through the digestion system of crows and will greatly facilitate the application of these methods to other scavenger and carnivore species-specific models in related future research. In this study conventional methods were used to investigate an unconventional means of trafficking PrPRes material, which could contribute to the spread and overall burden of PrPRes material.

<table border="0" cellpadding="0" cellspacing="0" width="545">
	<tbody>
		<tr height="43">
			<td height="43" style="height:43px;width:217px;">RML Chandler strain mouse-adapted scrapie</td>
			<td style="width:112px;">Rocky Mountain Laboratories</td>
			<td style="width:137px;"></td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:217px;">RC57BL/6 mice</td>
			<td style="width:112px;">Hilltop Lab Animals</td>
			<td style="width:137px;"></td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:217px;">American crows</td>
			<td style="width:112px;">wild captured</td>
			<td style="width:137px;"></td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:217px;">Pen/Strep</td>
			<td>Invitrogen</td>
			<td style="width:137px;">15140-122</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:217px;">Phosphate buffered Saline</td>
			<td style="width:112px;">Invitrogen</td>
			<td style="width:137px;">70011-044</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:217px;">Sonicator</td>
			<td>Misonix</td>
			<td style="width:137px;"></td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:217px;">Proteinase-K solution</td>
			<td style="width:112px;">Roche</td>
			<td align="right" style="width:137px;">3115887001</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:217px;">Loading buffer</td>
			<td style="width:112px;">Invitrogen</td>
			<td style="width:137px;">NP0007 and 0009</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:217px;">Bis-tris SDS PAGE 12% gel</td>
			<td style="width:112px;">Invitrogen</td>
			<td style="width:137px;">NP0342</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:217px;">Immobilon PVDF membrane</td>
			<td style="width:112px;">Millipore</td>
			<td style="width:137px;">1SEQ00010</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:217px;">Tween 20</td>
			<td style="width:112px;">Sigma Aldrich</td>
			<td style="width:137px;">P2287</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:217px;">Bullet blender homogenizer</td>
			<td style="width:112px;">Braintree Scientific</td>
			<td style="width:137px;">BBX24B</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:217px;">2.3 mm Zirconia/silica beads</td>
			<td style="width:112px;">BioSpec Products</td>
			<td style="width:137px;">11079125Z</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:217px;">Bar224 anti-PrP monoclonal antibody</td>
			<td style="width:112px;">Cayman Chemical</td>
			<td align="right" style="width:137px;">10009035</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:217px;">Superblock</td>
			<td style="width:112px;">Thermo Scientific</td>
			<td align="right" style="width:137px;">37517</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:217px;">chemiluminescent substrate</td>
			<td style="width:112px;">Millipore</td>
			<td style="width:137px;">WBKLS0500</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:217px;">G-box gel documentation system</td>
			<td style="width:112px;">Syngene</td>
			<td style="width:137px;"></td>
			<td style="width:79px;"></td>
		</tr>
	</tbody>
</table>

procedures for identifying infectious prions after passage through the digestive system of an avian species

Infectious prion (PrPRes) material is likely the cause of fatal, neurodegenerative transmissible spongiform encephalopathy (TSE) diseases1. Transmission of TSE diseases, such as chronic wasting disease (CWD), is presumed to be from animal to animal2,3 as well as from environmental sources4-6. Scavengers and carnivores have potential to translocate PrPRes material through consumption and excretion of CWD-contaminated carrion. Recent work has documented passage of PrPRes material through the digestive system of American crows (Corvus brachyrhynchos), a common North American scavenger7.
We describe procedures used to document passage of PrPRes material through American crows. Crows were gavaged with RML-strain mouse-adapted scrapie and their feces were collected 4 hr post gavage. Crow feces were then pooled and injected intraperitoneally into C57BL/6 mice. Mice were monitored daily until they expressed clinical signs of mouse scrapie and were thereafter euthanized. Asymptomatic mice were monitored until 365 days post inoculation. Western blot analysis was conducted to confirm disease status. Results revealed that prions remain infectious after traveling through the digestive system of crows and are present in the feces, causing disease in test mice.

The procedures used demonstrate that the digestive system of crows does not eliminate PrPRes infectivity 4 hr after oral gavage of scrapie brain homogenate7. All twenty crows that were gavaged with PrPRes material subsequently transmitted PrPRes material via feces to mice. Diseased mice were identified by manifestation of clinical mouse-scrapie signs and disease confirmation was completed by Western blot analysis.
Investigation of the retention time ...

Watch this Scientific Journal Video about Procedures for Identifying Infectious Prions After Passage Through the Digestive System of an Avian Species at JoVE.com

Procedures for Identifying Infectious Prions After Passage Through the Digestive System of an Avian Species

Scavengers have potential to translocate infectious transmissible spongiform encephalopathy prions in their feces to disease-free areas. We detail methods used to determine if mouse-adapted scrapie prions remain infectious after passage though the digestive tract of American crows (Corvus brachyrhynchos), a common consumer of dead animals.

Infectious prion (PrPRes) material is likely the cause of fatal, neurodegenerative transmissible spongiform encephalopathy (TSE) diseases1. Transmission ...

procedures-for-identifying-infectious-prions-after-passage-through

Research

JoVE Journal

Immunology and Infection

11.0K Views.  USDA. Scavengers have potential to translocate infectious transmissible spongiform encephalopathy prions in their feces to disease-free areas. We detail methods used to determine if mouse-adapted scrapie prions remain infectious after passage though the digestive tract of American crows (Corvus brachyrhynchos), a common consumer of dead animals.