Light Microscopy and Ultrahistology of Intestinal Changes in Pigs Infected with Epizootic Diarrhoea Virus (EVD): Comparison with Transmissible Gastroenteritis (TGE) Virus and Porcine Rotavirus Infections

Abstract

For almost three decades, transmissible gastroenteritis virus (TGE), a coronavirus, was the only known viral agent to cause severe neonatal diarrhoea in pigs, giving rise to considerable losses (1). Recently, a number of other viruses have been shown to be involved in the aetiology of diarrhoea in pigs, namely rotaviruses (9, 1 l), the epizootic diarrhoea virus (another coronaviruslike agent not related to TGE virus,4,8,14), rotavirus-like, calici-virus-like and 23 nm virus-like particles (18). Present evidence suggests that in addition to TGE virus, rotaviruses and epizootic diarrhoea virus are widespread and of considerable economic importance. The clinical and epizootiological picture of infections with these three agents is similar (3, 5, 15) and differential diagnosis is difficult. Furthermore, histological findings in the small intestine, which is the target organ of these viruses, reveal remarkable similarities. Since the histological and ultrastructural changes of natural and experimental TGE and rotavirus infections are known from a number of studies (10, 12, 16, 17), it is of interest to investigate the pathological changes caused by epizootic diarrhoea virus and compare them with TGE and rotavirus infections. U. S. Copyright Clearance Center Code Statement: 0721-1 856/81/2807-0564$02.50/0 Light Microscopy and Ultrahistology of Intestinal Changes in Pigs Material and Methods 565 AnimalsSix naturally infected piglets (2 piglets 5-6 days, and 4 piglets 4-6 weeks old) and four piglets (2-5 days old) infected experimentally with an intestinal filtrate from a confirmed EVD field case were examined. The experimentally infected animals were sacrificed 20-24 hours and 36-48 hours after infection. Clinical and epizootiological data on the naturally infected piglets have been reported elsewhere (8).TGE lesions were studied in 5 naturally infected animals 3-9 days of age, and i n 2 newborn piglets experimentally infected with 1,000 LD 50 of an intestinal suspension from a piglet infected with the Miller strain. These piglets were sacrificed 48 hours after infection. Rotavirus infected intestines were obtained by infecting 2 piglets at 2 days of age with the field strain Munich V 1274 and harvesting the material 48 hours later. Four non-infected healthy animals at 2-4 days of age served as controls.The experimental piglets were colostrum-deprived and fed reconstituted dried cow milk supplemented with vitamins (Biofix-F, Milchhof, Munich). All infections were carried out orally. The animals were anaesthesized with Narcoren@, and jejunal tissues were taken from the cranial, middle and caudal parts. Colon tissue was sampled from the middle part. Regional lymph nodes were also investigated. Irnmunofluorescence staining (FA)Frozen sections were made from all intestinal samples for the demonstration of viral antigens by FA. The sections were fixed with acetone at 4 OC for 10 minutes and stained directly using EVD*-, TGE-, and rotavirus antibody FITC conjugates. HistologyAfter fixation in 7 O/o neutral formalin, paraffin ...

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