Epidemiology of sheep pox

Detection of antibodies specific for sheeppox and goatpox viruses using recombinant capripoxvirus antigens in an indirect enzyme-linked immunosorbent assay

Viruses in the genus Capripoxvirus, family Poxviridae, cause sheeppox, goatpox and lumpy skin disease, which are the most serious poxvirus diseases of production animals. Despite the considerable threat that these viruses pose to livestock production and global trade in sheep, goats, cattle and their products, convenient and effective serodiagnostic tools are not readily available. To develop a more effective antibody detection capability, selected open reading frames from capripoxvirus DNA were amplified and expressed in Escherichia coli as His-tagged fusion proteins. By screening 42 candidate antigens, two sheeppox virus virion core proteins that were expressed efficiently, purified readily using affinity chromatography and reactive against capripoxvirus immune sera in an indirect enzyme-linked immunosorbent assay (ELISA) were identified. The ELISA performed favourably when sera from sheep and goats infected experimentally with virulent capripoxvirus isolates were tested, with sensitivity and diagnostic specificity ranging between 95 and 97%, but it was unable to detect antibodies reliably in vaccinated sheep or goats. Furthermore, no cross-reactivity with antibodies against orf virus was detected. This assay offers the prospect of a convenient and standardised ELISA-based serodiagnostic test, with no requirement for infectious reagents, that is well suited to high-throughput capripoxvirus surveillance on a flock or herd basis.

Capripoxvirus tissue tropism and shedding: A quantitative study in experimentally infected sheep and goats

Sheeppox virus and goatpox virus cause systemic disease in sheep and goats that is often associated with high morbidity and high mortality. To increase understanding of the pathogenesis of these diseases, we undertook quantitative time-course studies in sheep and goats following intradermal inoculation of Nigerian sheeppox virus or Indian goatpox virus in their respective homologous hosts. Viremia, determined by virus isolation and real-time PCR, cleared within 2 to 3 weeks post inoculation. Peak shedding of viral DNA and infectious virus in nasal, conjunctival and oral secretions occurred between 10 and 14 days post inoculation, and persisted at low levels for up to an additional 3 to 6 weeks. Although gross lesions developed in multiple organ systems, highest viral titers were detected in skin and in discrete sites within oronasal tissues and gastrointestinal tract. The temporal distribution of infectious virus and viral DNA in tissues suggests an underlying pathogenesis that is similar to smallpox and monkeypox where greatest viral replication occurs in the skin. Our data demonstrate that capripoxvirus infections in sheep and goats provide additional and convenient models which are suitable not only for evaluation of poxvirus-specific vaccine concepts and therapeutics, but also study of poxvirus-host interactions.

The current status of sheep pox disease

Sheep are the moving banks of shepherds and their economic contribution in terms of meat, wool and skin/hide is immense. Various infectious diseases jeopardize the optimum productivity; among which sheep pox is more important as the disease restricts the export of sheep and their products besides other economic losses. Although, clinical signs are indicative of the disease but a laboratory confirmation is necessary for unequivocal diagnosis and studying epidemiology. The causative agent, sheep pox virus (SPV), is antigenically and genetically closely related to goat pox virus (GPV) and lumpy skin disease virus (LSDV), the other members of the genus capripox virus. In some countries, SPV and GPV are cross infective to small ruminants posing problem in diagnosis and epidemiology. However, recent studies have showed that the viruses are phylogenetically distinct and can be differentiated by molecular tools. Prophylaxis using attenuated vaccines is the choice of control measure as the immunity is long lasting. Detailed information on isolation, identification, pathology, epidemiology, diagnosis and prophylaxis would not only help in updating the knowledge of scientific fraternity but will be useful to the policy makers in order to formulate appropriate measures for control and eradication of the disease. This synthesis is to present an up-to-date review of the disease and its control to provide the reader with an overview of the problem.