Editing Canine distemper (section)

==Mechanism==
[[File:12985 2019 1136 Fig4 HTML.webp|alt=|thumb|Principal routes of canine distemper virus (CDV) infection and transmission in hosts]]
The canine distemper virus affects nearly all body systems.<ref name="Beineke 2015">{{cite journal|last1=Beineke|first1=A|last2=Baumgärtner|first2=W|last3=Wohlsein|first3=P|title=Cross-species transmission of canine distemper virus-an update|journal=One Health|date=December 2015|volume=1|pages=49–59|doi=10.1016/j.onehlt.2015.09.002|pmid=28616465|pmc=5462633}}</ref> Puppies from 3–6 months old are particularly susceptible.<ref name="remedys">{{cite web|url=http://www.healthcommunities.com/canine-distemper/canine-distemper-overview.shtml|title=Health Topics: Pet Health: Canine Distemper: Canine Distemper Overview|date=4 Nov 2014|website=HealthCommunities.com|orig-year=28 Feb 2001|url-status=live|archive-url=https://web.archive.org/web/20141220224421/http://www.healthcommunities.com/canine-distemper/canine-distemper-overview.shtml|archive-date=2014-12-20|access-date=2014-12-15}}, accessed 15 December 2014.</ref> CDV spreads through aerosol droplets and through contact with infected bodily fluids, including nasal and ocular secretions, [[feces]], and [[urine]], 6 to 22 days after exposure. It can also be spread by food and water contaminated with these fluids.<ref name="Carter">{{cite web|url=http://www.ivis.org/advances/Carter/Part2Chap18/chapter.asp?LA=1|title=Paramyxoviridae|author1=Carter, G.R.|author2=Flores, E.F.|year=2006|work=A Concise Review of Veterinary Virology|access-date=2006-06-24|author3=Wise, D.J.}}</ref><ref name="Hirsch1999">{{cite book|title=Veterinary Microbiology|author=Hirsch, D.C.|author2=Zee, C.|publisher=Blackwell Publishing|year=1999|display-authors=etal}}</ref> The time between infection and disease is 14 to 18 days, although a fever can appear from 3 to 6 days after infection.<ref name="Carmichael">{{cite web|url=http://www.ivis.org/advances/Infect_Dis_Carmichael/appel/chapter_frm.asp?LA=1|title=Canine Distemper: Current Status|author1=Appel, M.J.G.|author2=Summers, B.A.|year=1999|work=Recent Advances in Canine Infectious Diseases|url-status=live|archive-url=https://web.archive.org/web/20050901104919/http://www.ivis.org/advances/Infect_Dis_Carmichael/appel/chapter_frm.asp?LA=1|archive-date=2005-09-01|access-date=2006-06-24}}</ref>

The canine distemper virus tends to direct its infection toward the [[lymphatic system|lymphoid]], [[epithelium|epithelial]], and [[nervous system|nervous tissues]]. The virus initially replicates in the lymphatic tissue of the respiratory tract.  The virus then enters the blood stream and infects the [[respiratory]], [[gastrointestinal]], [[urogenital]], epithelial, and [[central nervous system]]s, as well as [[optic nerve]]s.<ref name="CreevyMerck" /> Therefore, the typical pathologic features of canine distemper include lymphoid depletion (causing [[immunosuppression]] and leading to secondary infections), interstitial [[pneumonia]], [[encephalitis]] with [[demyelination]], and [[hyperkeratosis]] of the nose and foot pads.

The virus first appears in bronchial lymph nodes and tonsils two days after exposure.  The virus then enters the bloodstream on the second or third day.<ref name="Hirsch1999"/>  A first round of acute fever tends to begin around 3–8 days after infection, which is often accompanied by a low white blood cell count, especially of [[lymphocytes]], as well as a low platelet count.  These signs may or may not be accompanied by [[Anorexia (symptom)|anorexia]], a runny nose, or discharge from the eye.  This first round of fever typically recedes rapidly within 96 hours, and then a second round of fever begins around the 11th or 12th day and lasts at least a week.  Gastrointestinal and respiratory problems tend to follow, which may become complicated with secondary bacterial infections.  Inflammation of the brain and spinal cord, otherwise known as [[encephalomyelitis]], either is associated with this, subsequently follows, or comes completely independently of these problems. A thickening of the footpads sometimes develops, and vesicular pustular lesions on the abdomen usually develop. Neurological signs are typically found in animals with thickened footpads from the virus.<ref name=CreevyMerck/><ref name="Jones1997"/> About half of sufferers<!-- !  check for tone !--> experience [[meningoencephalitis]].<ref name="Jones1997"/> Less than 50% of the adult dogs that contract the disease die from it. Among puppies, the death rate often reaches 80%.<ref>{{cite web|url=https://acadogs.com/Canine_Distemper.html |title=Canine Distemper |publisher=American Canine Association, Inc.|access-date=2015-04-13 |url-status=dead |archive-url=https://web.archive.org/web/20150202193246/https://acadogs.com/Canine_Distemper.html |archive-date=2015-02-02 }}</ref>