Sheep Pox and Goat Pox (SGP)

Last updated June 24, 2003

Agent
Hosts
Epidemiology
SGP As a Biological Weapon
Clinical Features
Differential Diagnosis
Laboratory Diagnosis
Treatment
Prevention
Outbreak Control
Public Health Issues
References

Agent

Sheep pox and goat pox (collectively known as SGP) were recognized in the second century AD. However, they were not recognized as contagious diseases until 1673. SGP is a viral disease that causes the formation of generalized pox lesions and systemic illness in affected sheep and goats. Characteristics of SPG virus (SPGV) include:

Family: Poxviridae
Genus: Capripoxvirus
Cannot be serologically distinguished from the virus that causes lumpy skin disease
Has only one serotype but numerous strains that affect sheep only, goats only, or both

Environmental Survival of SGPV

Resistant to desiccation and to acidic and alkaline conditions (see References: VEIN)
Can survive for years in dried scabs; remains viable in wool for 2 months and on environmental surfaces for 6 months (see References: OIE: Technical disease card database)

Hosts

As the name implies, the primary hosts of SGP are sheep and goats. The virus can replicate in cattle but does not cause clinical disease. It has not yet been detected in wild ungulates, and there has been no evidence that SGP is infectious to humans (see References: House 1998).

Epidemiology

Transmission

SGP is transmitted through direct contact and can be passed between sheep and goats. Routes of transmission include:

Inhalation of aerosols from acutely infected animals
Inhalation of aerosols from dust contaminated by pox scabs in barns and night holding areas
Contact through skin abrasions by fomites or direct contact with a pox lesion or scab
Insect transmission (less likely)
Intravenous, intradermal, intranasal, or subcutaneous inoculation (experimental only) (see References: House 1998)

Sources

The main source of the virus is skin lesions (see References: VEIN).

Occurrence

SGP is endemic in Africa, the Middle East, the Indian subcontinent, and much of Asia. A similar disease was reported in the western United States, but it was not proven to be SGP (see References: House 1998). SPG has recently made frequent appearances in southern Europe (see References: OIE: Manual of standards). A few of the recent outbreaks are listed below:

In September 2002, an outbreak occurred in eastern Russia. There were 391 cases reported, with 66 deaths and 325 animals slaughtered (see References: OIE: Sheep pox and goat pox in Russia).
In December 2001, there were seven outbreaks of sheep pox reported in Morocco. Fifty cases were reported, with 42 deaths (see References: OIE: Sheep pox in Morocco).

SGP As a Biological Weapon

Characteristics that make SGP a potential biological weapon include:

High morbidity and extremely high mortality in young animals
Significant economic losses in terms of reduced productivity and lower quality of wool and leather (see References: Rao 2000).
Can be spread by many routes, including aerosol and fomite transmission

Clinical Features

SGP is an acute to chronic disease of sheep and goats that can manifest in a papulovesicular or nodular form. The severity of disease varies with age of the animal. Lambs and kids under 1 month of age suffer from a very severe generalized form of SGP. In older animals, clinical signs may be less severe and mortality is lower. Clinical features are outlined in the table below.

Clinical Features of Sheep Pox and Goat Pox
*Feature*	*Characteristics*
Incubation period	4 to 8 days; can be up to 3 wk
General clinical signs	Fever within 3-5 days after inoculation Depression Conjunctivitis Lacrimation Rhinitis Photophobia Generalized pox lesions throughout skin and mucous membranes within 2 days; most easily observed on hairless parts of body (perineum, inguinal area, scrotum, udder, axilla, muzzle) (see FAO figure) More severe skin lesions with more severe illness Lymphadenitis Focal viral pneumonia with lesions distributed uniformly throughout lungs (see FAO figure) Respiratory rate of up to 90/min Anorexia and emaciation Nervous signs Swollen muzzle Nares and oral mucosa may have extensive lesions Secondary bacterial infection (may interfere with healing) Disease may last 4-6 wk Full recovery after 3 mo Abortion rare Death caused by infection of internal organs, especially lungs Morbidity rate up to 80%, mortality up tp 50% (adults) Morbidity rate up to 100%, and mortality up to 95% (lambs and kids under 1 mo) Mortality rate increases to 50%-90% with peste des petits ruminants coinfection
Papulovesicular form	White-grey papules that dessicate and form easily removable crusts Papules may transform into vesicles Vesicle rupture leaves thick crust over lesion
Nodular form ("stone pox")	Nodules arise from papules Involves all layers of skin and subcutaneous tissue Necrosis and sloughing of nodules leaves hairless scar
Adapted from: House 1998; OIE: Manual of standards; OIE: Technical disease card database; Parker 1990; VEIN (see References).

The lesions in SGP involve the entire epidermis and dermis and penetrate into the subcutaneous tissue; they follow a regular development pattern (see References: House 1998):

First appears as an erythematous area (macula)
Progresses to a raised, slightly blanched erythematous lesion with edema in the central part of the lesion (papula)
If palpated, lesions feel thick
A transudate may form during the vesicular stage of the lesion
Vesicles are rarely found on the skin
Center of the lesion becomes necrotic, appearing depressed and gray, and is surrounded by an area of hyperemia
2 to 4 weeks after the first signs, a scab forms
With severe lesions, scars may form after healing

In some cases, the lesions on the eyes may be so severe that the inflammation causes the eyes to close. Lesions may also be found in the pharynx, epiglottis, trachea, vulva, prepuce, testicles, udder, teats, and the epithelium of the rumen and omasum. The lesions in the lungs may be severe, extensive, and uniformly distributed throughout owing to hematogenous infection.

The mortality rate of SGP is worsened by poor nutrition, heavy parasitism, and severe climatic conditions.

Differential Diagnosis

The following conditions should be considered in the diagnosis of SGP (see References: House 1998; VEIN):

Contagious ecthyma (contagious pustular dermatitis)
Bluetongue
Peste des petits ruminants
Photosensitization
Dermatophilosis
Sheep scab (psoroptic mange)
Insect bites
Parasitic pneumonia
Caseous lymphadenitis
Streptothricosis (Dermatophilus congolensis infection)
Mange

Laboratory Diagnosis

Samples for laboratory diagnosis should be obtained from both acute and chronic cases. The samples needed include the following (see References: House 1998):

Skin biopsies of early lesions
Aspirates from enlarged lymph nodes
Necropsy samples, including a full set of tissue samples, especially from gross lesions of the lungs, trachea, and rumen

The samples should be shipped under wet ice if they will arrive in less than 2 days and under dry ice if delivery will take longer. Samples for histopathology should be preserved in 10% buffered formalin (see References: House 1998).

The following tests can be used to identify the agent (see References: OIE: Manual of standards):

Immunofluorescence staining of intracytoplasmic inclusion bodies
Antigen detection enzyme-linked immunosorbent assay (ELISA)

Serologic tests include:

Virus neutralization
Indirect fluorescent antibody test
Western blot analysis
Agar gel immunodiffusion (AGID)
ELISA

AGID is not recommended for the diagnosis of capripox because of a cross-reaction with antibody to contagious pustular dermatitis virus (the main consideration in differential diagnosis).

Treatment

There is currently no treatment for SGP.

Prevention

Vaccination

Two effective vaccines are available for SGP. The Romanian strain has been used for many years and is the most widely used. The Kenya O 180 strain is thought to have the best safety record and highest efficacy. All known strains of capripoxvirus share a neutralization site and will therefore cross-protect (see References: OIE: Manual of standards).

Killed vaccines are also available, but they have proven impractical in the field because they fail to provide lasting immunity (see References: House 1998). There is also a new recombinant vaccine that provides protection against capripox, rinderpest, and peste des petits ruminants.

Other measures

Additional methods of prevention include:

Restrictions on movement of sheep and goats between infected and noninfected areas
Restrictions on movement of animal products

Meat
Hair
Wool
Hides

Decontamination of animal products before allowing entry into nonendemic areas

Outbreak Control

Control procedures depend on how much the disease has spread.

Before extensive spread:

Quarantine area for at least 45 days after recovery (see References: OIE: Technical disease card database).
Slaughter infected and exposed animals.
Clean and disinfect premises.
Vaccinate animals on surrounding premises.

After the disease has spread:

Vaccinate to control losses.
Consider elimination of infected and exposed flocks via slaughter.
Dispose of dead/slaughtered animals and contaminated materials.
Clean and disinfect contaminated premises, equipment, and facilities (see References: House 1998).

Public Health Issues

SGP does not cause infection in humans; therefore, there are no public health issues to be considered.

References

FAO (Food and Agriculture Organization of the United Nations). In: Specific diseases of sheep and goat. Chap 5 [Web page]

House JA. Sheep and goat pox. In: US Animal Health Association, Committee on Foreign Animal Disease. Foreign animal diseases: the gray book. Ed 6. Part IV. Richmond, VA: US Animal Health Assoc, 1998 [Full text]

OIE (Office International des Epizooties/World Organization for Animal Health). Sheep and goat pox. In: Manual of standards for diagnostic tests and vaccines 2000. Chap 2.1.10 [Full text]

OIE (Office International des Epizooties/World Organization for Animal Health). Sheep pox and goat pox in Russia. Outbreak report, Sep 2002 [Full text]

OIE (Office International des Epizooties/World Organization for Animal Health). Sheep pox in Morocco. Outbreak report, Dec 2001 [Full text]

OIE (Office International des Epizooties/World Organization for Animal Health). Sheep pox and goat pox. Technical disease card database [Web page]

Parker MT, Collier LH. Topley and Wilson's principles of bacteriology, virology, and immunity. Vol 1. Kent, England: Edward Arnold, Hodder & Sloughton, 1990: 567-8

Rao TV, Bandyopadhyay SK. A comprehensive review of goat pox and sheep pox and their diagnosis. Anim Health Res Rev 2000 Dec; 1(2): 127-36 [Abstract]

VEIN (Veterinary Education and Information Network). Dermatological diseases: sheep pox [Web page]


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