Causative agent 
- BT virus, family Reoviridae, with 24 serotypes


Differential diagnosis 
- Contagious ecthyma
- Foot and mouth disease
- Photosensitisation
- Pneumonia
- Polyarthritis, footrot, foot abscesses
- Vesicular stomatitis
- Bovine viral diarrhea, mucosal disease in cattle


1. History taking 
- Disease in sheep
- In apparent infection in cattle, buffalo, goats
- Mortality rate 2-10%
- Infection occurs in regions where Culicoides
  vector is present
- Incubation period 5-20 days

2. Clinical examination 
Acute form (sheep)
- Fever up to 42°C, depression, emaciation
- Inflammation, ulceration, erosion and necrosis of
  the mucosa of mouth
- Swollen and sometimes cyanotic tongue
- Lameness as a result of coronitis or
  pododermatitis and myositis
- Abortion
- Complications of pneumonia
- Either death within 8-10 days or long recovery
  with alopecia, sterility and growth delay

3. Necropsy 
- Congestion, edema, hemorrhages and ulcerations
  of digestive and respiratory mucosae (mouth, tongue,   trachea, esophagus, stomach, intestine)
- Congestion of hoof laminae and coronary band
- Edematous lung (pneumonia)
- Hypertrophy of lymph nodes and splenomegaly


4. Histopathological observation 
- Arthritis
- Hyperemia of the vascular corium (hoof) with
  edema and neutrophilic infiltration
- Necrotic changes in muscle bundles
- Hemosiderosis and neutrophilic infiltration in spleen


5. Serological test 
Specimen    : paired sera
Method       : AGID test

6. Virus isolation 
Specimen    : blood, spleen, liver, semen
Method       : egg inoculation and tissue culture


7. Virus identification 
- AGID test


Control
- Control of insect vectors
- Slaughtering and destruction of infected animals
- Quarantine and serological survey (The maximum
  incubation period of Bluetongue in sheep and cattle
  was fixed at 40 days by the OIE.)