(Catarrhal fever, Sore mouth, Range stiffness in lamb, Pseudo FMD) Blue Tongue is an infectious non contagious arthropod borne virus disease of domestic and wild animals mainly affecting sheep. Disease is characterised by catarrhal stomatitis, rhinitis, enteritis and lameness due to inflammation of coronary region and sensitive lamina. Also reported from cattle and goat and these species act as reservoirs of Blue tongue disease. Word Blue Tongue originates from a Dutch word “Blaau tong” means mouth sickness. Blue Tongue is caused by RNA virus belongs to arthropod borne Orbi virus of Reoviridae family. Virus can be destroyed by 3% Sodium hydroxide solution. It can be grown in embryonated chicken egg (six day old), calf kidney and calf thyroid cells. Unweaned white mice, hamster and sheep can be used as experimental animal. Transmission: Young sheep within the age group of one year are mostly affected. Blood sucking midges of genus Culicoides are the main agents responsible for transmission. Transmission by mosquitoes and sheep ked (Melophagus ovinus) is also reported. Disease is more prevalent in late summer and early autumn. Pathogenesis: Following bite, virus multiply in the blood and viraemia happen and temperature of 105-106˚F occur. Incubation period is 6-8 days. Virus will be localised in the endothelial lining of blood vessels and get itself attached with RBCs. Along with these copious serous discharge from mucus membrane of mouth and nostrils can be noted. Extensive reddening of mucus membrane of Respiratory tract and Digestive tract also happens. Skin of eyelids, coronary band and udder also affected. Virus can also cause necrosis of skin and mucus membrane. Clinical signs: Rise in temperature, nasal discharge, salivation, lacrimation, swelling of gum, tongue and lips happen initially. This is followed by ulceration of lips, dental pad, gum and tongue, cyanotic appearance of the tongue is also observed. Virus can cause abortion and deformities like hypoplacia of the brain, large quantity of fluid in cranial cavity and severe encephalitis. Nervous symptoms are also seen. Breaking of wool from different parts or entire body, a red ring like area in coronary band and evulsion of hoof also observed. In adult dysentery is also noted. Lesions: Congestion and haemorrhage of lung tissue, hyperaemia of mouth, tongue become cyanotic and gangrenous, haemorrhage in coronary band and necrotic changes in muscles. Diagnosis: Clinical findings and history. Laboratory diagnosis is with help of AGID, CFT, FAT, NT, ELISA etc. It should be differentially diagnosed from 1. FMD (cyanotic tongue and red line on coronet are absent in FMD) 2. Malignant Catarrhal fever (extensive erosion on buccal cavity can be seen in MCF) 3. Photosensitisation (reddening and oedema can be observed in photosensitisation). Treatment: Symptomatic treatment. A course of antibiotics can be given. Control: Vector control, herd management, restriction of movement of animals, isolation of the affected and vaccination. Vaccination with avinised live virus vaccine and tissue culture vaccine can be tried. But commercially these vaccines are not available.
