GLEWS

Sheep pox and goat pox is a contagious viral disease of small ruminants, which result from infection by sheep pox virus (SPV) or goat-pox virus (GPV). The two viruses belong to the Capripoxvirus genus, Poxviridae family, which includes a third virus, causing lumpy skin disease (LSD) in cattle.

In sheep and goats, the clinical signs vary from mild to severe clinical disease, normally beginning with the onset of fever followed by erythematous macules that develop into papules (1). Lesions may also develop on the mucous membrane and on internal organs, causing systemic signs (respiratory signs, diarrhoea, depression, emaciation, abortion and sometimes death).

Sheep pox and goat pox is notifiable to the World Organisation for Animal Health (OIE) in accordance with the requirements on notification of diseases set out in Chapter 1.1. of the OIE Terrestrial Animal Health Code. The relevance of this disease for OIE notification is related to the consequences of its spread within the animal population, the resulting economic impact and international trade restrictions.

 

Human transmission

SPV and GPV affect domestic small ruminants but do not appear to infect humans. Human infections with sheep and goat pox viruses during the handling of infected animals are rarely seen but have been reported based on clinical signs. Two published articles (2, 3) suggested that capripoxviruses might be transmitted to humans and would produce eruptive skin lesions. Five people suspected of being infected had been in close contact with infected goats and recovered completely within few days. Nonetheless, such cases are extremely rare and have to be considered with caution since no virus isolation was performed to confirm the aetiology of the lesions.
SPV and GPV do not pose a risk to human health.

Impact on production

Sheep pox and goat pox causes considerable production losses in endemic areas as a result of reduced milk yields, decreased weight gain, abortion, poor quality wool and hides, increased susceptibility to pneumonia and fly strike, and mortality (4, 5). Morbidity and mortality rates may be very high, reaching 100% in naive animals. A study in India calculated that it took approximately 6 years for a flock to recover from an outbreak causing 49.5% mortality (6). Sheep pox and goat pox prevents also importation of new breeds of small ruminants into endemic regions.

With regard to disease free countries, the economic impact of the introduction of the virus would be related to the important morbidity and mortality rates observed in naïve animals, as well as the cost of the control measures to combat the disease, since many animals would be destroyed and livestock owners eventually compensated. Moreover, the introduction of the disease would have an immediate and may be a long-lasting impact on international trade.

Geographical distribution

Sheep pox virus and goat pox virus are similar in terms of their geographical distribution.
During the past 50 years, the geographical range of sheep pox and goat pox has been restricted mainly to Asia and Africa, extending from North Africa to the Equator, from West Africa to East Asia, including Turkey, the Middle East and the Southern Regions of the former Soviet Union.

The following description of the disease distribution is based on official information provided by countries to the OIE and information published in scientific papers and it is not pretended to be exhaustive.

Sheep pox and goat pox recently extended its distribution into Uganda (2000) in the south, for Africa and into Vietnam (2005, to be declared as endemic in 2008), Republic of Korea (2007) and Chinese Taipei (2008) in the east for Asia. The disease reoccurred recently in three countries after years of absence. These are Kenya that notified the reoccurrence of sheep pox and goat pox in 2003 while the previous occurrence was in 1989 (14 years ago); Mongolia , after 30 years of absence, the disease reoccurred in 2006, and remained present since that time and Azerbaijan that notified the reoccurrence of the disease in 2009 after 13 years of absence. In southern Europe, Greece reported several introductions, with the last in 2007 from Turkey (Source: WAHID).

Some European countries, namely Belarus, Belgium, Estonia, Finland, Iceland, Greenland, Latvia, Lithuania, Malta, Slovenia Switzerland and Ukraine have never reported the disease. Some other European countries have succeeded in eradicating it: Ireland in 1850, the United Kingdom in 1866, Denmark in 1879, Norway in 1882 and the Netherlands in 1893, Germany in 1920, Albania and Sweden in 1934, former Czechoslovakia and Poland in 1950, Andorra in 1952, Austria in 1954, former Republic of Yugoslavia (Bosnia and Herzegovina, Croatia, Montenegro, Serbia) in 1955, Hungary and Romania in 1957, France in 1964, Spain in 1968, Portugal in 1970, Italy in 1983, Armenia in 1987, Cyprus in 1989, Moldavia in 1994, Bulgaria in 1996 and Georgia in 1997.

The disease has never been reported in the Americas, in Oceania (Australia, Fiji, French Polynesia, New Caledonia, New Zealand, Philippines, Vanuatu) and in southern Africa (Angola, Botswana, Lesotho, Madagascar, Malawi, Reunion Island (France), South Africa, Swaziland and Zimbabwe.

Figure 1 shows the global distribution of sheep pox and goat pox.

Epidemiological information

Most isolates are host specific, SPV mainly affecting sheep and GPV goats. However, some strains can affect both species. Moreover, recombination can occur between the two viruses.
The susceptible species are domestic small ruminants.
In 2008, Sudan reported 30 cases of sheep and goat pox disease in Bohor Reedbuck (Redunca redunca) to the OIE. Bohor Reedbuck is a medium-sized, sandy coloured antelope belonging to the family Bovidae cf. figure 2. The diagnosis was based on clinical findings and on post-mortem examination (7). According to the literature, this infection has never previously been reported in wild ungulates. These findings would therefore constitute the first report of the disease in wild ungulates (1, 8, 9). However, there is no wild reservoir species for the virus (10).
 
The virus can be excreted by sick and recovered animals for several weeks and it can survive for many years in dried scabs at ambient temperatures. Virus remains viable in wool for 2 months and in premises for as long as 6 months (9).

Sensitivity differs among individuals depending on several factors (11):

• Breed: some breeds are more resistant to capripoxvirus than others;
• Sex: probably linked to their physiology, females are more sensitive than males;
• Age: young animals are more sensitive than adults;
• Husbandry conditions: parasitism, malnutrition, exhaustion, transhumance. In 2003, half of the outbreaks in Algeria occurred in Naama Wilaya, on the transhumance route for sheep flocks. Most animals were likely unvaccinated (12);
• The animal population density: in many countries, sheep pox and goat pox are present in areas with a high density of small ruminants but usually absent in isolated areas where there is less contact between animals (13).

In areas where sheep pox and goat pox are endemic, the disease is commonly first reported in young animals, whereas when the disease occurs in previously free areas usually as a result of the introduction of new animals from infected areas, animals of all age groups tend to be affected simultaneously.

Transmission of the disease between animals is mainly by direct contact and inhalation. Indirect transmission by contaminated vehicles or products (litter, fodder) or by insects (mechanical transmission) has been established but seems to play a minor role.

Transmissions via intradermal or subcutaneous inoculation as well as respiratory, transcutaneous and transmucosal routes have been reported (9).

Morbidity and mortality

Sensitivity, morbidity and mortality differ according to the animal, its age, its condition and health, and its own immunity, and the strain of the virus (some natural mild viruses have been isolated (11).

In endemic areas, the morbidity rate varies and the mortality rate is usually less than 10%. Nevertheless, case-fatality rates of nearly 100% have been reported in young animals.

In naive animals, it is more severe and the mortality and morbidity rates may reach 100%.

Seasonal variation

There are seasonal variations in sheep pox and goat pox incidence depending on the region, its climate and its most prominent livestock production system. This is in relation with closed contacts between animals in cold seasons as well as certain diet deficiencies during periods of food scarcity. These are shown in the following figures (Figs 3-5) (source: OIE, monthly data collected from 1996 to 2008).

In Asia, the highest incidence of sheep pox and goat pox is observed from November to March (figure 3).

Figure 3: Seasonal variations in Asia
   
 
In North Africa, there is also a significant increase in incidence in the winter (figure 4), from September to February, related to the lack of food reserves and the lambing period (11). In Sub-Saharan Africa two waves can be distinguished: one in February and March during the cool period and one from June to October during the rainy season (figure 5).

Figure 4: Seasonal variations in North Africa
 

 Figure 5: Seasonal variations in Sub-Saharan Africa
 

Sheep pox and goat pox surveillance and prevention in free regions

The objective in free regions is to avoid the introduction of the disease. The guidelines for avoiding such an introduction are as follows:

• Readiness and preparedness
  • Update the legislation to clarify the prevention measures to be implemented to avoid the introduction of the disease;
  • Monitor small ruminants movements, transport and trade;
  •  Ensure suitable veterinary infrastructure and financial resources;
  •  Put in place an appropriate and regular livestock census.
• Trade in animals and animal products
  • Comply with the recommendations of OIE Terrestrial Animal Health Code when importing animals and animal products from disease free or infected country/zones;
  •  Put imported animals in quarantine before their release;
  • Disinfect imported animal products (wool and hides for example).
• In the event of the disease being introduced, the following guidelines apply:
  • Culling of infected animals;
  • Disinfect the affected area(s);
  • Trace back and forward to avoid further spread of the disease.

Sheep pox and goat pox surveillance, prevention and control in endemic regions (14)

Given the socio-economic impact of sheep pox and goat pox, its potential for spread and the availability of effective and low-cost vaccines, control and even eradication of the disease is possible if there is a clear will to do so. Apply vaccination strategies would be gauged depending on an impact assessment of control measures.

Guidelines can be followed to improve surveillance in endemic regions.

These are:

• Readiness and preparedness
  • Update the legislation to clarify the conduct of animal health programmes and to define the objectives for control and eradication programmes;
  • Analyse historical data, data from surveillance activities to develop risk assessment and forecasting models according to seasonal variation, entry path of the disease into the country/zone, study of primary affected animals/flocks, etc.;
  • Improve emergency preparedness and response (emergency plans accompanied by simulation exercises);
  • Ensure suitable veterinary infrastructure and financial resources;
  • Put in place an appropriate livestock census;
  • Control animal movements and animal introduction into free flocks;
  • Avoid any facilitating factors for the expression of the disease: other infectious diseases, parasitism, malnutrition, etc.;
  • Medical prophylaxis: improve vaccination coverage (suitable vaccine supply, appropriate season to vaccinate animals). See also the following section.

• Alert: Strengthen epidemiological surveillance
  • To obtain early, accurate and complete information from the field;
  • Raise awareness of livestock owners;
  • Introduce a system of accreditation of private veterinarians for conducting surveillance, animal censuses, vaccination programmes, etc.;
  • Support targeted surveillance (flocks, markets, water points, abattoirs, and animal movement from one zone to another, etc.);
  • Support access to laboratory diagnosis in the event of suspected clinical cases;
  • Develop national/regional/international reference laboratories network for sheep and goat pox;
  • Standardise vaccination strategies and targeted vaccination campaigns in countries that are part of the same epidemiological ecosystem, especially at their borders.

• Outbreak response
  • Timely and appropriate dissemination of information within and outside the country or the region;
  • Support the isolation and quarantine of sick animals;
  • Improve tracing back in order to better understand the mechanism for the spread of sheep and goat pox in the country;
  • Improve tracing forward in order to better target the control measures to be applied;
  • Improve regional coordination for information sharing and for the harmonisation of the control programmes in each country;
  • Support a policy of compensation for livestock owners in order to encourage early notification.

International recommendations for importation of animals and animal products from sheep pox and goat pox free countries or from countries considered infected are detailed in the OIE Terrestrial Animal Health Code, 2009; Chapter 14.10. (http://www.oie.int/eng/normes/mcode/en_chapitre_1.14.10.htm)

Vaccination strategy

The most relevant strategy for controlling sheep pox and goat pox in endemic areas is mass immunisation of the susceptible population.
 
All strains of capripoxvirus of ovine, caprine or bovine origin, such as sheep and goat pox and LSD for cattle, share a major neutralising site, so that animals recovered from infection with one strain are resistant to infection with any other strain (15).

In the past, both live and inactivated vaccines were used to vaccinate against this disease (15). Nowadays, live vaccines are preferred insofar as a single dose of vaccine can generate long-lasting immunity and protection from all capripoxvirus field strains (4). In contrast, inactivated vaccines are able to generate only short-term immunity (15). Several strains of live vaccines are used in endemic areas, such as 0240 Kenya strain in sheep and goats, the Romanian and RM-65 strains in sheep and in cattle, and the Mysore and Gorgan strains used in goats. Most of them can be used in multiple species, except for 0240 Kenya which should not be administered to cattle (13). A list of countries which use, produce or commercialise sheep pox and goat pox vaccine is given in Appendix 1.

In the past, many countries were able to eradicate the disease even with vaccine of dubious efficacy. Currently, although vaccine efficacy has improved and despite the low cost of the vaccine (around USD 5/100 doses, according to the Jordanian firm JOVAC), coverage is not sufficient in some areas, mainly due to nomadism and transhumance activities, or in isolated remote farms (16).

It is recommended to vaccinate annually all sheep and goats regardless of their age. Although some young animals will have maternal derived antibodies, other will not, depending on the immune status of their mother, and considering the low cost of vaccines all young animals should be vaccinated to ensure optimal protection coverage. Those that did not generate immunity due to maternal antibodies will be vaccinated the following year (13).

Conclusion

Sheep pox and goat pox can cause considerable socio-economic losses in affected regions. There is consequently a pressing need to control this disease so as to improve food security and reduce poverty. Great strides have recently been made to improve sanitary conditions and develop effective, safe and low-cost vaccines. Sheep pox and goat pox could therefore be easy to control and even eradicate in some regions.

A national and regional political commitment is needed to provide the necessary resources to implement an efficient control programme such as to ensure an optimal vaccination strategy covering a sufficient proportion of the susceptible population. This should be backed up by adequate training in disease surveillance and vaccination. Furthermore, coordination at the regional level is absolutely essential for countries that share borders and between which there are frequent animal movements.

References

1. Spickler, AR and Roth, JA. (2008). – In Emerging and Exotic Diseases of Animals. 3rd Edition. Ames: Iowa State University.
2. Bakos, K and Brag, S. (1957). - Studies of goat pox in Sweden. Nord VetMed, 9,431-439.
3. Sawhney, A.K., Singh A.K. and Malik B.S. (1972). - Goat pox: an anthropozoonosis. The Indian Journal of Medicine Research, 60, 683-384.
4.  Babiuk, S., Bowden T.R., Boyle D.B., Wallace D.B. and Kitching R.P. (2008). - Capripoxviruses: an emerging worldwide threat to sheep, goats and cattle. Transboundary and Emerging Diseases, 55, 263–272.
5.  I. Yeruham, H., Yadin H., Van Ham M., Bumbarov V., Soham A. and Perl S. (2007). - Economic and epidemiological aspects of an outbreak of sheep pox in a dairy sheep flock. The Veterinary Record, 160 (7), 236-237.
6. Garner MG, Sawarkar S.D., Brett E.K., Edwards J.R., Kulkarni V.B., Boyle D.B. and Singh S.N. (2000). - The extent and impact of sheep pox and goat pox in the state of Maharashtra, India. Trop Anim Health Prod., 32(4), 205-223.
7. Report of the 10-th Conference of the OIE Regional Commission for the Middle-East, Doha, Qatar, October 2009
8. Robinson, A.J. and Kerr, P.J. (2001). – Poxvirus Infections. In Infectious Diseases of Wild Mammals, 3rd Ed. Iowa State University Press, Edited by Williams, E.S. and Barker I.K., Ames, Iowa, 179-201.
9. Sheep pox and goat pox. OIE Technical Disease Card. Updated in 2002. Available at: http://www.oie.int/eng/maladies/fiches/a_a100.htm
10.  Lefèvre, P.C. (1983). – In La variole ovine (clavelée) et la variole caprine. Gerdat-IEMVT, Maisons-Alfort.
11.  Fassi-Fehri M. and Lefèvre, P.C. (2003). - Clavelée et variole caprine. In Principales maladies infectieuses et parasitaires du bétail. Coordinated by Lefèvre P.C., Blancou J. and Chermette R. Editions TEC & DOC, Paris -Editions Médicales internationales, Cachan, 415-427.
12. World Organisation for Animal Health (OIE) (2004). – Algeria. In World Animal Health in 2003. OIE, Paris, 37-38
13. Aitken, I.D. (2007). – In Diseases of sheep, 4th Ed. Blackwell Publishing, Oxford, 231-235.
14. Food and Agriculture Organization of the United Nations (FAO) (2001) - RADISCON workshop on sheep pox eradication programme in Tripoli. News@Radiscon, EMRES Transboundary Animal Diseases Bulletin. No. 18/3, 17-19.
15. World Organisation for Animal Health (OIE) (2009). – Chapter 2.7.14. Sheep pox and goat pox. In Manual of Diagnostic Tests and Vaccines for Terrestrial Animals, 6th Ed. OIE, Paris, 1058-1068. Available at: http://www.oie.int/eng/normes/mmanual/2008/pdf/2.07.14_S_POX_G_POX.pd f
16. Blajan, L. (1984). - Maladies des ovins et caprins ayant une importance économique dans la zone méditerranéenne. Rev. Sci. Tech. Off. Int. Epiz., 3 (1), 191-208.

Other link: OIE’s Terrestrial Animal Health Code 2009, 18th Ed. Chapter 1.14.10.: Sheep pox and goat pox. Available at: http://www.oie.int/eng/normes/mcode/en_chapitre_1.14.10.htm