Lumpy skin disease along with sheep pox and goatpox are the most serious poxvirus diseases of livestock, and are caused by viruses that belong to the genus Capripoxvirus within the subfamily Chordopoxvirinae, family Poxviridae. To facilitate the study of lumpy skin disease pathogenesis, we inoculated eight 4- to 6-month-old Holstein calves intravenously with lumpy skin disease virus (LSDV) and collected samples over a period of 42 days for analysis by virus isolation, real-time PCR and light microscopy. Following inoculation, cattle developed fever and skin nodules, with the extent of infection varying between animals. Skin nodules remained visible until the end of the experiment on day post-inoculation (DPI) 42. Viremia measured by real-time PCR and virus isolation was not observed in all animals but was detectable between 6 and 15 DPI. Low levels of viral shedding were observed in oral and nasal secretions between 12 and 18 DPI. Several tissues were assessed for the presence of virus at DPI 3, 6, 9, 12, 15, 18 and 42 by virus isolation and real-time PCR. Virus was consistently detected by real-time PCR and virus isolation at high levels in skin nodules indicating LSDV has a tropism for skin. In contrast, relatively few lesions were observed systemically. Viral DNA was detected by real-time PCR in skin lesions collected on DPI 42. Cattle developing anti-capripoxvirus antibodies starting at DPI 21 was detected by serum neutralization. The disease in this study varied from mild with few secondary skin nodules to generalized infection of varying severity, and was characterized by morbidity with no mortality.
Further advances are required in understanding protection from AIDS by T-cell immunity. We analyzed a set of multigenic simian/human immunodeficiency virus (SHIV) DNA and fowlpox virus priming and boosting vaccines for immunogenicity and protective efficacy in outbred pigtail macaques. The number of vaccinations required, the effect of DNA vaccination alone, and the effect of cytokine (gamma interferon) coexpression by the fowlpox virus boost was also studied. A coordinated induction of high levels of broadly reactive CD4 and CD8 T-cell immune responses was induced by sequential DNA and fowlpox virus vaccination. The immunogenicity of regimens utilizing fowlpox virus coexpressing gamma interferon, a single DNA priming vaccination, or DNA vaccines alone was inferior. Significant control of a virulent SHIV challenge was observed despite a loss of SHIV-specific proliferating T cells. The outcome of challenge with virulent SHIV mn229 correlated with vaccine immunogenicity except that DNA vaccination alone primed for protection almost as effectively as the DNA/ fowlpox virus regimen despite negligible immunogenicity by standard assays. These studies suggest that priming of immunity with DNA and fowlpox virus vaccines could delay AIDS in humans.
An indirect ELISA was developed to detect antibodies specific for capripoxviruses in goat, sheep and cattle sera. Heat-inactivated Nigerian sheeppox virus was used as the ELISA antigen. Sera obtained from sheep and goats that were experimentally infected with different capripoxvirus isolates were used to develop and evaluate the sensitivity of the ELISA. Virus neutralization indexes were determined for the experimental sera in OA3.Ts cells. The specificity of the ELISA was determined using 231 sera from capripoxvirus naïve sheep and goats from Canada. In addition, the ELISA was tested for cross-reactivity to anti-orf virus antibodies using orf-reactive sera and no cross-reactivity was observed. Using experimentally generated sera obtained from animals infected with virulent sheeppox or goatpox virus isolates, the diagnostic sensitivity of the ELISA was 96% with a diagnostic specificity of 95%, where the diagnostic sensitivity of the virus neutralization assay was 96% with a diagnostic specificity of 100%. Further evaluation of this ELISA, using 276 cattle serum samples that were positive by virus neutralization assays, revealed a diagnostic sensitivity of 88% with a specificity of 97%. These results indicated that the inactivated capripoxvirus ELISA can detect capripoxvirus-specific antibodies in sheep, goats and cattle that have been infected with virulent capripoxvirus isolates. Non-virulent capripoxvirus isolates, in contrast, did not elicit positive (>or=1.5 Log10 neutralization index) antibody responses.
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