BLUE TONGUE

This is a viral infection of sheep and occasionally goats and cattle but mild infection. At least 16 strains of the virus are known. Disease is transmitted by culicoides. Disease is non-contagious and characterized by congestion of the hoof tissues, nasal and oral mucosae and and stiffness arising from muscle degeneration.
Distribution
Disease is endemic in many African countries like Tanzania, Morocco, South Africa, Sudan, Chad, Nigeria, Central African Republic, Zimbabwe and Kenya. Other affected countries are Cyprus, Middle East, USA and Spain.
Clinical signs
There is rise in body temperature which may be sudden or gradual. Temperature may fluctuate for a number of days. High temperature is ensued by hyperaemia of the nasal and buccal mucosae.
Later, it is accompanied by salivation and frothing at the mouth caused by peculiar and persistent licking movement of the tongue. The frothing around the lips is followed by appearance of watery discharge from the nostrils which become more prolific, mucocatarrhal and mixed with blood. Later on, the lips and tongue swell, the face only to a variable extent. The color deepens and small petechial haemorrhages appear on the mucous membrane of the mouth, muzzle and conjunctiva. This discoloration may deepen to an almost purplish blue from which the appearance of the tongue give rise to the description of the disease.
The lips or muzzle epithelium thicken and shade off. More severe changes may be observed in mouth where the gum, cheeks and tongue mucosae ulcerate leaving exposed irregular and haemorrhagic surface. As a result, saliva becomes mixed with blood and has the most offensive odour because of the presence of necrotic tissue. In a mean time, the nasal discharge has become purulent and dries leaving a crust around the nostrils.

Pain arising from the lesions in the mouth leads to loss of sensation and dejection with the result that the animals assumes recumbent position with its head bent to one side. In severe cases, enteritis with diarrhea may be observed.
Careful examination of the feet reveal reddening of the coronary brand which is more pronounce on bucks and frequently present in hind feet. This discoloration is well marked in lambs whose hooves are thin and transparent. There are varying degrees of lameness characterized by ached back, reluctance to move and stiff gait.
Inability to feed results in progressive emaciation. Animals may linger in this state for up to 10 days before dying of prostration and exhaustion.
Occasionally, animals may develop torticollis caused by severe degeneration of cervical muscles. In some cases, the disease may be mild with fever, hyperaemia of the nose and mouth.
Diagnosis
This is based on clinical signs, epidemiology including presence of vectors and susceptible sheep, post-mortem lesions.
Confirmatory diagnosis is based on biological test like serum neutralization test, CFT, isolation and recognition of the virus.
Differential diagnosis
Heart water
Sheep pox
Orf
Footh and mouth disease
Vesicular stomatitis
Rinderpest
PPR
Control
In endemic areas, all animals should be removed to the grazing area or high ground. The disease occurs seasonally. Animals should be immunized before the season.
Use of insecticides to kill the culicoides.
In non-endemic areas, there should be complete embargo on importation of susceptible sheep.
Vehicles like ship, aeroplanes, motor vehicles coming into the country should be sprayed before they land.
Treatment
There is no drug for the treatment of the disease.
Antibiotics and sulfonamides may be used against secondary bacterial infections especially those causing bronchopneumonia.
Careful nursing of affected animal is important. They should be placed in shades or stables and protected from extremes of temperatures.
Clean the lesion in mouth and feet with antiseptic and apply antibiotic powder on them.