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SHEEP POX AND GOAT POX
Aetiology Epidemiology Diagnosis Prevention and Control References
AETIOLOGY
Classification of the causative agent
Virus family Poxviridae, genus Capripoxvirus
Sheep pox virus (SPV) and goat pox virus (GPV) were once believed to be strains of the same virus, but
genetic sequencing has now demonstrated them to be separate viruses. Most strains are host specific and
cause severe clinical disease in either sheep or goats, while some strains have equal virulence in both
species. Further complicating this is that recombination can occur between sheep and goat strains, which
produce a spectrum with intermediate host preference and range of virulence
SPV and GPV cannot be distinguished from each other with serological techniques, including viral
neutralisation. SPV and GPV are also closely related to lumpy skin disease virus in cattle (LSDV), but
there is no evidence LSDV causes disease in sheep and goats. It has a different transmission mechanism
(insects) and partially different geographic distribution.
Resistance to physical and chemical action
Temperature:
Susceptible to 56°C/2 hours; 65°C/30 minutes. Some isolates inactivated at
56°C/60 minutes
pH:
Susceptible to highly alkaline or acid pH (hydrochloric or sulphuric acid at 2% for
15 minutes)
Disinfectants/chemicals: Inactivated by phenol (2%) in 15 minutes. Sensitive to detergents, e.g. sodium
dodecyl sulphate. Sensitive to ether (20%), chloroform, formalin (1%), and
sodium hypochlorite (2-3%), iodine compounds (1:33 dilution), Virkon® 2%,
quarternary ammonium compounds 0.5%.
Survival:
Susceptible to sunlight, but remains viable in wool/hair and dry scabs on skin for
up to 3 months. Persists in unclean shaded pens for as long as 6 months.
Survives freeze
–thaw cycles, but infectivity may be reduced
EPIDEMIOLOGY
Morbidity rate: Endemic areas 70
–90%
Mortality rate: Endemic areas 5
–10%, although can approach 100% in imported animals
Hosts
All breeds of domestic and wild sheep and goats, although most strains cause more
severe clinical disease in only one species
Native breeds in endemic areas are far less susceptible than introduced breeds of
European or Australian origin
– morbidity and mortality may approach 100%
Transmission
Transmission is usually by aerosol after close contact with severely affected animals
containing ulcerated papules on the mucous membranes. There is no transmission in
the prepapular stage, e.g. animals early in disease or those dying peracutely (e.g. Soay
breed of European sheep). There is reduced transmission once papules have become
necrotic and neutralising antibody produced (about one week after onset). Animals with
mild localised infections also rarely transmit disease.
Infection may also occur through other mucous membranes or abraded skin
Chronically infected carriers do not occur
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Indirect transmission by contaminated implements, vehicles or products (litter, fodder)
occurs
Indirect transmission by insects (mechanical vectors) has been established (minor role)
Sources of virus
Ulcerated papules on mucous membranes prior to necrosis
Skin lesions with scabs: contain large amounts of virus in association with antibody but infectivity
is not known
Saliva, nasal and ocular secretions
Milk, urine, faeces
Semen or embryos: transmission not yet established
Occurrence
Capripox is endemic in Africa north of the Equator, the Middle East, Turkey, Iran, Iraq, Afghanistan,
Pakistan, India, Nepal, parts of the People’s Republic of China, Bangladesh.The most recent outbreaks
occurred in Vietnam in 2005, Mongolia in 2008 and 2009, and Azerbaijan in 2009. The first outbreak in
Chinese Taipei occurred in 2008 and was eradicated by stamping out and movement control.
For more recent, detailed information on the occurrence of this disease worldwide, see the OIE
World Animal Health Information Database (WAHID) Interface
[http://www.oie.int/wahis/public.php?page=home] or refer to the latest issues of the World Animal
Health and the OIE Bulletin.
DIAGNOSIS
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 diagnosis
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). Inapparent infections also occur
Early clinical signs
o
rise in rectal temperature to above 40°C
o
macules develop in 2-5 days
– small circumscribed areas of hyperaemia, most
obvious on unpigmented skin
o
papules develop from macules
– hard swellings of between 0.5 and 1 cm in
diameter
– which may cover the body or be restricted to the groin, axilla and
perineum. Papules may be covered by fluid-filled vesicles, but this is rare. 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 generalised papules
o
affected animals develop rhinitis, conjunctivitis and enlargement of all superficial
lymph nodes, especially prescapular lymph nodes
o
papules on the eyelids cause blepharitis of varying severity
o
papules on the mucous membranes of the eyes and nose ulcerate, creating
mucopurulent discharge
o
mucosae of the mouth, anus, and prepuce or vagina become necrotic
o
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
o
papules become necrotic from vascular thrombosis and ischaemic necrosis
o
papules form scabs in the next 5
–10 days, which persist for up to 6 weeks, leaving
small scars
o
skin lesions are susceptible to fly strike
o
secondary pneumonia is common
o
anorexia is unusual unless mouth lesions physically interfere with feeding
o
abortion is rare.
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Lesions
Skin lesions: congestion, haemorrhage, oedema, vasculitis and necrosis. All the layers
of epidermis, dermis and sometimes musculature are involved
Lymph nodes draining infected areas: enlargement (up to eight times normal size),
lymphoid proliferation, oedema, congestion, haemorrhage
Pox lesions: on mucous membranes of the eyes, mouth, nose, pharynx, epiglottis,
trachea, on the rumenal and abomasal mucosae, and on the muzzle, nares, in the vulva,
prepuce, testicles, udder, and teats. Lesions may coalesce in severe cases
Lung lesions: severe and extensive pox lesions, focal and uniformly distributed
throughout the lungs; congestion, oedema, focal areas of proliferation with necrosis,
lobular atelectasis. Enlargement, congestion, oedema and haemorrhages of mediastinal
lymph nodes
Differential diagnosis
The clinical signs of severe sheep pox and goat pox are highly characteristic. However, in their mild form
they can be confused with parapoxvirus causing orf or urticaria from multiple insect bites.
Contagious ecthyma (contagious pustular dermatitis or orf)
Insect bites
Bluetongue
Peste des petits ruminants
Photosensitisation
Dermatophilosis
Parasitic pneumonia
Caseous lymphadenitis
Mange
Laboratory diagnosis
Samples
Samples for virus isolation must be sent to the laboratory as soon as possible. They should be kept cold
and shipped on gel packs. If these samples must be shipped long distances without refrigeration, glycerol
(10%) can be added; tissue samples must be large enough that glycerol does not penetrate into the centre
of the tissue and destroy the virus.
Neutralising antibodies can interfere with virus isolation and some antigen-detection tests; samples for
these tests must be collected during the first week of illness. Samples for PCR can be taken after
neutralising antibodies have developed. Paired serum samples should be collected for serology.
Live animals: Full skin thickness biopsies; vesicular fluid if available; scabs; skin
scrapings; lymph node aspirates; whole blood collected into heparin or EDTA; paired
sera
Animals at necropsy: skin lesions; lymph nodes; lung lesions; histology: full set of
tissues, especially those with lesions
Procedures
Identification of the agent
Genome detection by polymerase chain reaction (PCR) using capripoxvirus-specific primers for
the attachment protein gene is described in lumpy skin disease (chapter 2.4.14) of the OIE
Terrestrial Manual
Transmission electron microscopy: rapidly identifies typical capripox virions
Virus isolation in cell culture (primary lamb testis or lamb kidney): the appearance of CPE may
take 4
–12 days, intracytoplasmic inclusions are clearly seen by haematoxylin and eosin staining,
and antigen can be detected by immunoperoxidase or immunofluorescence staining techniques
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Agar gel immunodiffusion test (AGID): tests lymph gland biopsy material taken from an early case
of capripox; cross-reacts with parapox
Capripoxvirus antigen and inclusion bodies may also be seen in stained cryostat or paraffin
sections of biopsy or post-mortem lesion material.
Inhibition of cytopathic effect using positive serum
Antigen-detection ELISA
Serological tests
Virus neutralisation: most specific serological test, but not sufficiently sensitive since
immunity to capripox infection is predominantly cell mediated
– infected animals may
only produce undetectable low levels of neutralising antibody.
Indirect fluorescent antibody test: cross reacts with other poxviruses
Agar gel immunodiffusion (AGID): cross reacts with other poxviruses
Western blotting: uses P32 antigen of capripoxvirus for reaction with test sera; sensitive
and specific, but is expensive and difficult to carry out
ELISA : P32 antigen or another appropriate antigen expressed by a suitable vector could
be used to develop an acceptable and standardised serological test
For more detailed information regarding laboratory diagnostic methodologies and vaccines, please
refer to Chapter 2.7.14 Sheep pox and goat pox in the latest edition of the OIE Manual of Diagnostic
Tests and Vaccines for Terrestrial Animals under the heading
“Diagnostic Techniques”.
PREVENTION AND CONTROL
No treatment
Sanitary prophylaxis
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
Vaccination may be considered when the disease has spread more widely
Medical prophylaxis
Live and inactivated vaccines have been used for the control of capripox. All strains of capripoxvirus so far
examined share a major neutralisation site and will cross protect.
There are several attenuated virus vaccines delivered by subcutaneous or intradermal
route; conferred immunity lasts up to 2 years
Inactivated vaccines give, at best, only short-term immunity
Currently, no recombinant vaccines for capripoxviruses are commercially available.
However, a new generation of capripox vaccines is being developed that uses the
capripoxvirus genome as a vector for the genes of other ruminant pathogens, for
instance genes of rinderpest and peste des petits ruminants (PPR) viruses.
For more detailed information regarding laboratory diagnostic methodologies and vaccines, please
refer to Chapter 2.7.14 Sheep pox and goat pox in the latest edition of the OIE Manual of Diagnostic
Tests and Vaccines for Terrestrial Animals under the heading
“Requirements for Vaccines”.
For more detailed information regarding safe international trade in terrestrial animals and their
products, please refer to the latest edition of the OIE Terrestrial Animal Health Code.
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REFERENCES AND OTHER INFORMATION
Current Animal Health Status (Disease Information)
Brown C. & Torres A., Eds. (2008). - USAHA Foreign Animal Diseases, Seventh Edition.
Committee of Foreign and Emerging Diseases of the US Animal Health Association.
Boca Publications Group, Inc.
Coetzer J.A.W. & Tustin R.C. Eds. (2004). - Infectious Diseases of Livestock, 2nd
Edition. Oxford University Press.
Fauquet C., Fauquet M. & Mayo M.A. (2005). - Virus Taxonomy: VIII Report of the
International Committee on Taxonomy of Viruses. Academic Press.
Kahn C.M., Ed. (2005). - Merck Veterinary Manual. Merck & Co. Inc. and Merial Ltd.
Spickler A.R., & Roth, J.A. Iowa State University, College of Veterinary Medicine -
http://www.cfsph.iastate.edu/DiseaseInfo/factsheets.htm
World Organisation for Animal Health (2012). - Terrestrial Animal Health Code. OIE,
Paris.
World Organisation for Animal Health (2012). - Manual of Diagnostic Tests and Vaccines
for Terrestrial Animals. OIE, Paris.
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The OIE will periodically update the OIE Technical Disease Cards. Please send relevant new
references and proposed modifications to the OIE Scientific and Technical Department
(scientific.dept@oie.int). Last updated April 2013.