A sheeppox outbreak in Morocco: isolation and identification of virus responsible for the new clinical form of disease

Abstract

BackgroundSheeppoxvirus (SPPV) is a member of the Capripoxvirus genus of the Poxviridae family, which causes significant economic losses in Morocco. The resurgence of the sheeppox disease during 2010 was characterized by an emergence of a classical nodular form for the first time in Morocco. However, little is known about the virus strain responsible for nodular form. In this study, thirty three sheep, from the eastern region of Morocco, clinically infected were examined and dead animals were autopsied.A rapid diagnostic assay for SPPV using different type of clinical samples would be useful for outbreak management. The aim of this work was to isolate the virus strain responsible for nodular form and we identified and compared by phylogenetic analysis the field strain with Moroccan vaccine strain targeting the thymidine kinase (TK) gene and the chemokine analogue receptor of interleukin (IL8) gene. Further, it was important to investigate and validate a real-time PCR using different clinical and post-mortem samples to manage epidemic sheeppox disease.ResultsThe nodular form of sheeppox disease observed in Morocco was clinically characterized by fever, depression, lacrimation, diarrhea in lambs and nodule. At necropsy, the most affected organ was the lung. The etiological strain was successfully isolated from lung nodule in a dead lamb and was identified by using real-time PCR that has been tested and validated on different types of clinical and post mortem samples from naturally infected animals. Sequence and phylogenetic analysis of TK and IL8 gene showed that there was a very close relationship between field and vaccine strain. They were clustered within other SPPV strains.ConclusionIn the current study, we show for the first time the nodular form of sheeppox in Morocco. We demonstrate a robust real-time PCR-based diagnostic assay to detect the sheeppox virus in multiple sample that can be implemented to efficiently manage the disease outbreak. Our study also offers the prospect for future molecular studies to understand the clinical forms.

Investigation of a Possible Link Between Vaccination and the 2010 Sheep Pox Epizootic in Morocco

“…The significant differences found between the Moroccan vaccine strain and the field isolates in the present study contrasts with the findings of Zro et al. (,b). It most probably reflects the degree of conservation of the different genomic regions selected for analysis in both studies.…”

“…Supporting the findings of Zro et al. (,b), ocular swabs were found to be a useful sample type to test with a detection rate of the Haegeman PCR panel of 91%. For rectal and nasal swabs, the detection rates were noticeably lower but this was heavily influenced by negative results obtained for these types of samples in four or five flocks compared with the other swab types and suggests that the timing of sample collection relative to the course of infection may be more critical for nasal and rectal swabs than for other sample types.…”

“…Despite several vaccination campaigns, SPPV remains an important problem in Morocco which peaked in 2010 with a major epizootic (1892 outbreaks, 11 917 cases and 2978 dead sheep) (private communication from ONSSA, the Moroccan epidemiology and sanitary monitoring service). Initial reports citing similarity between the field isolates and the vaccine strain used in Morocco (Zro et al., ,b) warranted a closer investigation of the virus associated with the 2010 outbreaks. This was achieved by obtaining further clinical samples from different provinces in eastern Morocco and by sequencing and phylogenetic analysis of different regions of the viral genome.…”

“…For these reasons, SPPV is considered to be one of the most important infectious and contagious diseases in the sheep industry in Morocco (Sbihi, ; Moroccan Ministry of Agriculture Rural Development and Sea Fisheries, ). By the late 1990s, SPPV was almost eradicated from the country, but around 2002, the number of SPPV cases increased again culminating in a remarkable epizootic peak in 2010 with a clinical form of SPPV which until then had not been observed in Morocco (Zro et al., ).…”

“…Zro et al. (,b)recently reported a high degree of similarity between isolates from the SPPV epizootic of 2010 in Morocco and the live attenuated vaccine strain used in vaccination programmes. This finding might be attributable to sequencing of highly conserved parts of the Capx genome (Tulman et al., ) rather than a close relationship between both viruses.…”