Avastrovirus 2, also called avian nephritis virus, is an astrovirus which causes 'avian nephritis' in chickens. Causes: Infectious Stunting Syndrome — ISS — Baby Chick Nephritis — BCN. The virus has been reported in Japan, Europe, USA and New Zealand. The disease is mainly transmitted horizontally by the oro-faecal route, but rarely vertical transmission may occur. Clinical signs of the disease are normally only seen in chicks less than two weeks old, and these signs should be mild unless the chick is immunosuppressed.