Enzootic nasal adenocarcinoma in sheep: An update

Abstract

Enzootic nasal adenocarcinoma of sheep (ENAS) is a contagious tumor of the ethmoid turbinate mucosa. The disease occurs naturally in all continents except Australia and New Zealand. Similar disease has been described in goats. ENAS is aetiologically associated with enzootic nasal tumor virus 1 (ENTV-1) a type Beta retrovirus and closely related to jaagsiekte sheep retrovirus (JSRV) and enzootic nasal adenocarcinoma virus of goats (ENTV-2). Clinical signs include continuous nasal discharge, respiratory distress, exophtalmus and skull deformations. The tumors have been classified histologically as low grade adenocarcinoma. ENTV-1 can be demonstrated in tumors by immunohistochemistry using several antisera developed against JSRV antigens which cross-react with ENTV-1 ones. ENTV-1 shares a oncogenic mechanisms with JSRV and ENTV-2 and active replication of the virus is required because oncogenic proprieties are associated with env gene products. Information about immune reactions in relation to ENTV-1 is scarce and controversial. Some early studies indicated absence of immune reaction although more recent studies have detected the presence of neutralizing antibodies in sheep with tumors and in contact sheep. However, the sensitivity and specificity of these tests are very low to be used in field studies. Several specific PRC techniques are available to detect viral genome in tissues and tumors. ENTV-1 can be detected in nasal secretion but is rarely found out of the tumor. The utility of PCR tests in control or eradication plans is discussed.