A100 - SHEEP POX AND GOAT POX

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A100 - SHEEP POX AND GOAT POX

Nature of the disease
Sheep pox and goat pox (SGP) are highly contagious diseases of sheep and goats characterised by fever, ocular and nasal discharges. Pox lesions appear on the skin and on the respiratory and gastro-intestinal mucosa. Mortality can be high.

The diseases are caused by a capripox viruses. This group also includes the Lumpy skin disease of cattle.

Classification
OIE List A disease
Susceptible species
Sheep pox and goat pox viruses are generally considered host specific, but different strains show different host preferences and it is not unknown for both sheep and goats to be infected by the same strain of virus.
Merino and European breeds of sheep are more susceptible than other breeds. Goat breeds also vary in susceptibility.
Distribution
SGP occurs in Africa (mainly north of the equator), the Middle East, central Asia (including south Russia and western China), and the Indian sub-continent as far east as Myanmar.
Clinical signs 
The diseases are more severe in lambs and kids than adults. Disease begins with:
  • Sudden onset of fever
  • Discharges from the nose and eyes, and salivation
  • Loss op appetite
  • Reluctance to move
  • Skin lesions appear in 1-2 days, extending all over the skin, but are most obvious on face, eyelids and ears,  perineum and tail. Lesions may also be seen on the mucous membranes of the nostrils, mouth and vulva
  • Acute respiratory distress
  • Mortality peaks about two weeks after the onset of the skin lesions

Lesions begin as an area of reddening, progressing over two weeks to a papule, vesicle, pustule with exudation and scab formation. Healing is very slow.

A nodular form of the disease (‘stonepox’) can also occur this resembles lumpy skin disease in cattle.

Post-mortem findings 
The epidermal and mucosal lesions described above will be apparent at post-mortem.

Ulcerations may be found in the lining of the trachea and gastro-intestinal tract. Lung lesions consisting of pale grey nodules may also be seen.

Differential diagnosis 
  • Contagious pustular dermatitis (scabby mouth)
  • Bluetongue
  • Mycotic dermatitis
  • Sheep scab
  • Mange
  • Photosensitisation
Specimens required for diagnosis 
SGP should be suspected when an acute disease of sheep or goats is accompanied by fever, pox-like skin lesions and high mortality.

For serological examination, paired of blood sample from animals with fever.

For virus identification, samples can be sera, vesicular fluid, scabs and skin scrapings of lesions and lesions in the respiratory and gastro-intestinal tract. Samples should be taken within the first week of apparition of the symptom and be kept fresh. OIE recommends to use the identification methods which could be cell inoculation and identification by immunofluorescence, staining of intracytoplasmic inclusion bodies, inhibition of cytopathic effect using positive serum or ELISA.

Transmission   
Capripox viruses are very resistant and remain viable for long periods, on or off the animal host e.g. they may persist for up to 6 months in shaded animal pens, and for at least 3 months in dry scabs on the fleece, skin and hair from infected animals. 

Transmission of SGP is by contact with infected animals, their aerosols, nasal secretions, saliva or dried scabs. The viruses are also readily transported on clothes and equipment. Insects e.g. the stable fly (Stomoxys calcitrans) act sometimes as mechanical vectors.

No specific information is available on transmission of SGP through semen or embryos. 

NB With lumpy skin disease in cattle, virus has been detected in semen for up to three weeks after infection.

Risk of introduction   
Movement of infected animal is the main means by which SGP is spread to new areas. Thus where there are no importations of live animals or genetic material from endemically infected countries there is little risk. 

However, the viruses can be transported on clothing, equipment and unprocessed wool products brought in by people from affected countries. Therefore the role of quarantine is of primary importance.

Control / vaccines  
In endemic areas systematic vaccination programs have provided the most effective control over the disease. 

In an outbreak situation diseased sheep or goats should be destroyed and their carcases burnt or buried. This could be supplemented by vaccination of in-contact animals, and movement controls for both animals and vehicle should be applied.

Cell-cultured attenuated and inactivated vaccines have been used to prevent disease. Inactivated vaccines provide about five months protection but there is no ready commercial source. The live attenuated vaccines give good immunity and are considered suitable in an emergency situation.

References
  • GEERING WA, FORMAN AJ, NUNN MJ, Exotic Diseases of Animals, Aust Gov Publishing Service, Canberra, 1995, 440p
  • Office International des Epizooties, 2002
  • Sheeppox and Goatpox, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 429; 622-623