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==Villus Atrophy==
* Commonly seen in enteric disease.
* Occurs when more enterocytes are lost than are produced in the crypts.
* Causes malabsorption of nutrients and water.
* There are two main types of villus atrophy:
===Villus atrophy with intact/hypertrophic crypt glands===
* Insult affects the villus enterocytes leading to increased loss.
** Under mild insult, villi may fully regenerate.
** Severe insult leads to immature cells on the villus.
*** Secrete water and electrolytes into lumen.
* Examples include:
** '''Rotavirus, Coronavirus'''
*** Infect villus enterocytes.
** '''Coccidia'''
*** Infect surface enterocytes.
** '''Nematodes'''
*** Abrase surface.
===Villus atrophy with damage to crypts===
* The primary insult is to crypt cells.
** Crypt cell death leads to dilated gland lumens (cysts).
** Production is impaired, eventually leading to insufficient cells for villi.
* Enterocytes lost to lumen are replaced by increasingly immature cells.
** Gives rise to severe malabsorption.
* If damage is severe, erosions/ulcers may form which may eventually heal.
** Even if there are no ulcers, damage can be long-term
*** Causes long-term malabsorption.
* Examples include:
** '''Parvovirus'''
*** Target crypt cells.
** '''Lymphoma'''
*** Numerous neoplastic lymphocytes compress crypts.
** '''Cytotoxic chemicals'''
*** Dividing crypt cells are susceptible.
==Enteritis Particularly Associated with Villus Atrophy==
===[[Reoviridae#Rotaviruses|Rotavirus]]===
===[[Cryptosporidium|Cryptosporidium]]===
* Small coccidial parasite.
* Affects calf, lamb, piglet, kitten.
* Increasingly important as part of the neonatal [[Intestine Diarrhoea - Pathology|diarrhoea]] complex in calves.
* Zoonosis.
====Pathology====
=====Gross=====
* Intestines diffusely reddened, with fluid contents.
=====Histological=====
* Tiny parasites on surface of epithelium.
* Villus atrophy and fusion.
* Iinflammation (mainly lymphoid) in crypts and lamina propria.
[[Category:Intestine_-_Inflammatory_Pathology_by_Type]]