Epidemiological investigation of sheep pox outbreaks in Rajasthan

Sheep pox, a highly contagious, host specific, viral infection, causes high rate of morbidity and mortality in sheep, irrespective of age, sex and breed. In the present study, disease outbreaks in 11 sheep flocks in villages of Churu and Bikaner (Rajasthan, India) were investigated to find out the aetiology and to further examine the cause of possible sheep pox vaccine failure as suspected by the local farmers following vaccination. About 60–100% morbidity was recorded in the outbreaks, while mortality ranged from 18–50% involving suckling and young lambs, and pregnant ewes in different flocks. Pregnant ewes also aborted. Clinically, the affected sheep showed high fever, depression, prostration and different developmental stages of pox lesions such as erythema, papules, vesicles/haemorrhagic vesicles, pustules, and cicatrix scars all over the body. The nodular lesions were detectable on dental pad and lips together with encrustation of nares and lips. The lesions were also found underneath tail, while a few animals also revealed lumpy edematous swelling in the brisket region. The microscopic lesions corroborated the gross lesions and were characterized by the infiltration of lymphocytes and sheep pox cells in skin, lung, spleen and heart, while skin scabs showed acanthosis, hydropic changes and necrosis in epithelial layers infiltrated with neutrophils and mononuclear cells. The epithelial cells and sheep pox cells showed occasional intracytoplasmic inclusions. The results of CIE and PCR in clinical samples displayed sheep pox antigen/antibody and virus nucleic acid. Thus, gross and microscopic changes and CIE and PCR results confirmed the disease as sheep pox. Restricting the movement of infected sheep flocks and hygienic measures in the affected area at the farms helped in containment of the spread of infection.