Sheep pox and goat pox are viral diseases of sheep and goats characterized by fever, generalized papules or nodules, vesicles (rarely), internal lesions (particularly in the lungs), and death.
Sheep pox and goat pox result from infection by sheep pox virus (SPV) or goat-pox virus (GPV), closely related members of the Capripox genus in the family Pox-viridae. Most isolates are host specific, with SPV mainly causing disease in sheep and GPV predominantly affecting goats.
All breeds of domestic and wild sheep and goats. Native breeds in endemic areas are far less susceptible than introduced breeds of European or Australian. Morbidity rate: Endemic areas 70-90%. Mortality rate: Endemic areas 5-10%, although can approach 100% in imported animals
Capripox is endemic in Africa north of the Equator, the Middle East, Turkey, Iran, Afghanistan, Pakistan, India, and Nepal; parts of the Peoples Republic of China, Bangladesh and Vietnam. Recently, it has made frequent incursions into southern Europe.
SPV and GPV are often transmitted by the respiratory route during close contact, but they may also enter the body through other mucous membranes or abraded skin. These viruses can be found in saliva, nasal and conjunctival secretions, milk, urine and feces, as well as in skin lesions and their scabs. Ulcers on the mucous membranes are important sources of virus. Whether SPV and GVP can be transmitted in semen or embryos has not been established. Animals are most contagious before neutralizing antibodies develop, which occurs approximately a week after the onset of clinical signs. Experimentally infected sheep and goats can shed poxviruses in nasal, conjunctival and oral secretions for 1 to 2 months, but shedding peaks during the second week after inoculation, then declines rapidly. Chronically infected carriers are not seen.
SPV and GPV can also be spread by fomites or transmitted mechanically by insects such as stable flies (Stomoxys calcitrans), although the latter route may be un-common. These viruses can remain infectious for up to six months in shaded sheep pens. They may also be found on the wool or hair for as long as three months after infection, and possibly longer in scabs. Whether the viruses in scabs are infectious is unknown; these viruses are complexed with antibodies and can be difficult to recover on tissue culture media.
Incubation period is 8-13 days. It may be as short as 4 days following experimental infection by intradermal inoculation or mechanical transmission by insects. Clinical signs vary from mild to severe, depending on host factors (e.g. age, breed, immunity) and viral factors (e.g. species predilection and virulence of viral strain). In apparent infections also occur.
Early clinical signs include a rise in rectal temperature to above 40°C, development of macules (small circumscribed areas of hyperaemia) in 2-5 days and later papules (hard swellings of between 0.5 and 1 cm in diameter) develop from macules. A flat haemorrhagic form of capripox has been observed in some breeds of European goat, in which all the papules appear to coalesce over the body; this form is always fatal.
Acute phase: within 24 hours after appearance of generalized papules
- Affected animals develop rhinitis, conjunctivitis and enlargement of all superficial lymph nodes, especially prescapular lymph nodes
- Papules on the eyelids cause blepharitis of varying severity
- Papules on the mucous membranes of the eyes and nose ulcerate, creating mucopurulent discharge
- Mucosae of the mouth, anus, and prepuce or vagina become necrotic
- Breathing may become laboured and noisy due to pressure on the upper respiratory tract
- from the swollen retropharyngeal lymph nodes draining developing lung lesions.
If animal survives acute phase
- Papules become necrotic from vascular thrombosis and ischaemic necrosis
- Papules form scabs in the next 5-10 days, which persist for up to 6 weeks, leaving small scarsskin lesions are susceptible to fly strike
- Secondary pneumonia is common
- Anorexia is unusual unless mouth lesions physically interfere with feeding
- Abortion is rare.
By symptoms and serological tests like Virus neutralization, indirect fluorescent antibody test, Agar gel immunodiffusion (AGID), Western blotting and ELISA can be used. Specific detection of viral genome can be done by polymerase chain reaction (PCR) and virions can be identified by Transmission electron microscopy.
Vaccination is the best method to prevent the disease in susceptible animals. There are live and inactivated vaccines are available. Sheep Pox Vaccine containing cell cultures derived live attenuated strain of Sheep Pox virus belonging to Kenyan or â€œRomanianâ€ strain provides good immunity. The vaccination is done every year in healthy sheep of above 3 months of age.
If culling is not possible, isolation of infected herds and sick animals for at least 45 days after recovery
- Slaughtering of infected herd if possible
- Proper disposal of cadavers and products – burning or burial is often used
- Stringent cleaning and disinfection of farms and equipment
- Quarantine of new animals before introduction into herds
- Animal and vehicle movement controls within infected areas.