Sheep and goatpox
Sheeppox virus (SPPV) and goatpox virus (GTPV) were once believed to be strains of the same virus, but genetic sequencing has now demonstrated them to be separate viruses. They belong to the family of Poxviridae, genus Capripoxvirus.
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. SPPV and GTPV cannot be distinguished from each other with serological techniques, including viral neutralisation. SPPV and GTPV 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 and partially different geographic distribution.
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. 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. Indirect transmission by fomites occurs, indirect transmission by insects (mechanical vectors) plays a minor role. Chronically infected carriers do not occur.
Sheeppox and goatpox are endemic in Africa, north of the Equator, the Middle East and Asia, while some parts of Europe have experienced outbreaks recently. Countries that reported outbreaks of the disease between 2010 and 2015 include Bulgaria, Chinese Taipei, Israel, Kazakhstan, Kyrgyzstan, Mongolia, Morocco, Greece and Russia, with Greece, Israel and Russia having experienced recurring incidences. For the more recent, detailed information on the occurrence of this disease worldwide, see the OIE World Animal Health Information Database (WAHID) Interface. LSD is categorized on the list of notiﬁable diseases by the World Organization for Animal Health (OIE).
Morbidity rate in endemic areas vary between 70–90%, mortality rate are 5–10% in endemic areas, although it can approach 100% in imported animals. Some breeds of European sheep, such as Soay, may die of acute infection before the development of skin lesions. In other breeds there is an initial rise in temperature to above 40°C, followed in 2–5 days by the development of macules – small circumscribed areas of hyperaemia, which are most obvious on unpigmented skin – and then of papules – 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. Within 24 hours of the appearance of generalised papules, affected animals develop rhinitis, conjunctivitis and enlargement of all the superficial lymph nodes. As the papules on the mucous membranes of the eyes and nose ulcerate, so the discharge becomes mucopurulent, and the mucosae become necrotic.
Breathing may become laboured and noisy, due to the developing lung lesions. In the following 5–10 days the papules form scabs, which persist for up to 6 weeks, leaving small scars. The skin lesions are susceptible to fly strike, and secondary pneumonia is common. Anorexia is not usual unless the mouth lesions physically interfere with feeding. Abortion is rare.
The clinical signs and post-mortem lesions vary considerably with breed of host and strain of capripoxvirus. Indigenous breeds are less susceptible and frequently show only a few lesions, which could be confused with insect bites or contagious pustular dermatitis. However, lambs that have lost their maternally derived immunity, animals that have been kept isolated and animals brought into endemic areas from isolated villages can often be seen with generalised and sometimes fatal capripox. Invariably there is high mortality in unprotected imported breeds of sheep and goats following capripoxvirus infection. Capripox is not infectious to humans.
Laboratory confirmation of SPPV/GTPV is most rapid using the polymerase chain reaction (PCR) method in combination with a clinical history consistent with generalised SPPV/GTPV infection. Isolation of the virus is possible as capripoxviruses will grow on tissue culture of ovine, caprine or bovine origin, although field isolates may require up to 14 days to grow or require one or more additional tissue culture passage(s). The virus causes intracytoplasmic inclusions that can be clearly seen using haematoxylin and eosin staining. The antigen can also be detected in tissue culture using specific sera and immunoperoxidase or immunofluorescence techniques. An antigen-detection enzyme-linked immunosorbent assay (ELISA) using a polyclonal detection serum raised against a recombinant immunodominant antigen of capripoxvirus has been developed. The virus neutralisation test is the most specific serological test. The indirect immunofluorescence test is less specific due to cross-reactions with antibody to other poxviruses. Western blotting using the reaction between the P32 antigen of capripoxvirus with test sera is both sensitive and specific, but is expensive and difficult to carry out.
If culling is not possible, isolation of infected herds and sick animals for at least 45 days after recovery is necessary. If slaughtering of infected herd is possible, proper disposal of cadavers and products is required as well as stringent cleaning and disinfection of farms and equipment. New animals need to be quarantined before introduction into herds. Animal and vehicle movement should be controlled within infected areas.
Live and inactivated vaccines have been used. 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 that confer immunity up to 2 years, while inactivated vaccines give, at best, only short-term immunity. Currently, no recombinant vaccines for capripoxviruses are commercially available.
For more detailed information regarding LSD refer to Chapter 2.7.13 Lumpy skin disease in the latest edition of the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals