Field observations and experiences gained from the implementation of control measures against lumpy skin disease in South-East Europe between 2015 and 2017

The first epidemics of lumpy skin disease (LSD) reported in Europe in 2015 severely affected the cattle farming sector in several Balkan countries. After the first incursion into Greece in 2015, the disease quickly spread across the Balkan region with over 7000 outbreaks reported by the end of 2016. Thanks to a coordinated regional control and eradication policy, the spread of the disease was halted by the end of 2017. Regional large-scale vaccination campaign with effective homologous vaccines and high vaccination coverage revealed to be essential for the successful control the disease, supported by other measures such as early detection of outbreaks, total or partial stamping out and restrictions on cattle movements. The aim of this paper is to discuss the field observations, challenges and lessons learnt while dealing with the first LSD epidemics in Europe. The cross-border collaboration by the veterinary authorities of all affected countries, coordinated by the European Commission and the technical support provided by many other international organizations played a fundamental role in stopping the spread of a disease that otherwise could have expanded further to the European territory causing a large damage to the whole European cattle farming industry. The experience obtained during the control of LSD epidemics indicates that in the future LSD spread can be effectively halted, provided that appropriate surveillance plans and vigilance remains in place in the areas at risk of re-incursion, especially those bordering endemic countries.

Serological and clinical evaluation of the Yugoslavian RM65 sheep pox strain vaccine use in cattle against lumpy skin disease

Lumpy skin disease (LSD) is an emerging infectious disease of cattle. Since 2012, it has been seen throughout the Middle East region. The aim of this study was to compare the humoral response of three different dosages of the RM65 sheep pox (SPP) vaccine to assess the use of ten times sheep dose of the RM65 vaccine against lumpy skin disease, and to explore the possible causes of, and characterize the side effects caused by the RM65 vaccine. A blinded randomized collected study comprised 57 clinically normal, Holstein Friesian cattle which were randomly assigned into three experimental groups of 17 cattle according to the vaccine dose used (one, five and ten times the dose used for sheep in the field, and a control group of six cattle that did not receive the vaccine. Experimental animals were monitored closely for the development of any abnormality or side effects. Serum samples were collected for 6 weeks and were tested using serum neutralization assay. Decrease in total milk production was observed a week after vaccination and by the fifth week of the experiment, it had returned to prevaccination levels. Clinical side effects were seen in five animals that belong only to the group that received ten times of the SPP vaccine dose. Observed side effects included fever, decreased feed intake and milk production, as well as skin lesions. Skin nodules appeared between 7 and 17 days postvaccination, and remained for 11-17 days. Systemic reactions were likely to be associated with higher dosage and all affected cattle recovered uneventfully. Animals that received the highest dose (ten times the sheep dose) showed the best humoral response. The actual efficacy of the different concentration of the SPP RM65 should be evaluated based on a challenge experiment in a controlled environment.

Detection of Capripoxvirus DNA Using a Field-Ready Nucleic Acid Extraction and Real-Time PCR Platform

Capripoxviruses, comprising sheep pox virus, goat pox virus and lumpy skin disease virus cause serious diseases of domesticated ruminants, notifiable to The World Organization for Animal Health. This report describes the evaluation of a mobile diagnostic system (Enigma Field Laboratory) that performs automated sequential steps for nucleic acid extraction and real-time PCR to detect capripoxvirus DNA within laboratory and endemic field settings. To prepare stable reagents that could be deployed into field settings, lyophilized reagents were used that employed an established diagnostic PCR assay. These stabilized reagents demonstrated an analytical sensitivity that was equivalent, or greater than the established laboratory-based PCR test which utilizes wet reagents, and the limit of detection for the complete assay pipeline was approximately one log₁₀ more sensitive than the laboratory-based PCR assay. Concordant results were generated when the mobile PCR system was compared to the laboratory-based PCR using samples collected from Africa, Asia and Europe (n = 10) and experimental studies (n = 9) representing clinical cases of sheep pox, goat pox and lumpy skin disease. Furthermore, this mobile assay reported positive results in situ using specimens that were collected from a dairy cow in Morogoro, Tanzania, which was exhibiting clinical signs of lumpy skin disease. These data support the use of mobile PCR systems for the rapid and sensitive detection of capripoxvirus DNA in endemic field settings.

Review: Capripoxvirus Diseases: Current Status and Opportunities for Control

Lumpy skin disease, sheeppox and goatpox are high-impact diseases of domestic ruminants with a devastating effect on cattle, sheep and goat farming industries in endemic regions. In this article, we review the current geographical distribution, economic impact of an outbreak, epidemiology, transmission and immunity of capripoxvirus. The special focus of the article is to scrutinize the use of currently available vaccines to investigate the resource needs and challenges that will have to be overcome to improve disease control and eradication, and progress on the development of safer and more effective vaccines. In addition, field evaluation of the efficacy of the vaccines and the genomic database available for poxviruses are discussed.

Lumpy skin disease: attempted propagation in tick cell lines and presence of viral DNA in field ticks collected from naturally-infected cattle

Lumpy skin disease (LSD) is of substantial economic importance for the cattle industry in Africa and the Near and Middle East. Several insect species are thought to transmit the disease mechanically. Recent transmission studies have demonstrated the first evidence for a role of hard (ixodid) ticks as vectors of lumpy skin disease virus (LSDV). The aim of this study was to attempt in vitro growth of the virus in Rhipicephalus spp. tick cell lines and investigate in vivo the presence of the virus in ticks collected from cattle during LSD outbreaks in Egypt and South Africa. No evidence was obtained for replication of LSDV in tick cell lines although the virus was remarkably stable, remaining viable for 35 days at 28 °C in tick cell cultures, in growth medium used for tick cells and in phosphate buffered saline. Viral DNA was detected in two-thirds of the 56 field ticks, making this the first report of the presence of potentially virulent LSDV in ticks collected from naturally infected animals.

Characterization of sheep pox virus vaccine for cattle against lumpy skin disease virus

Lumpy skin disease is of significant economic impact for the cattle industry in Africa. The disease is currently spreading aggressively in the Near East, posing a threat of incursion to Europe and Asia. Due to cross-protection within the Capripoxvirus genus, sheep pox virus (SPPV) vaccines have been widely used for cattle against lumpy skin disease virus (LSDV). In the Middle East and the Horn of Africa these vaccines have been associated with incomplete protection and adverse reactions in cattle post-vaccination. The present study confirms that the real identity of the commonly used Kenyan sheep and goat pox vaccine virus (KSGP) O-240 is not SPPV but is actually LSDV. The low level attenuation of this virus is likely to be not sufficient for safe use in cattle, causing clinical disease in vaccinated animals. In addition, Isiolo and Kedong goat pox strains, capable of infecting sheep, goats and cattle are identified for potential use as broad-spectrum vaccine candidates against all capripox diseases.

Adverse Reactions to Field Vaccination Against Lumpy Skin Disease in Jordan

Lumpy skin disease (LSD) is an emerging disease in the Middle East region and has been recently reported in Jordan. The aim of this study was to investigate the adverse reactions that were reported after vaccine administration. Geographical areas enrolled in the study were free of the disease and away from the outbreak governorate. Sixty-three dairy cattle farms, with a total of 19,539 animals, were included in the study. Of those, 56 farms reported adverse clinical signs after vaccine administration. The duration between vaccine administration and appearance of adverse clinical signs ranged from 1 to 20 days (Mean = 10.3, SD ± 3.9). Clinical signs were similar to those observed with natural cases of lumpy skin disease. These were mainly fever, decreased feed intake, decreased milk production and variable sized cutaneous nodules (a few millimetres to around 2 cm in diameter) that could be seen anywhere on the body (head, neck, trunk, perineum), udder, and/or teats. Nodules were raised and firm initially and then formed dry scabs that could be peeled off the skin. The characteristic deep 'sit fast' appearance was rarely seen and most lesions were superficial. Some cattle had swollen lymph nodes, while a few pregnant animals aborted. The percentage of affected cattle ranged from 0.3 to 25% (Mean = 8, SD ± 5.1). Fever, decreased feed intake, and decreased milk production were seen in 83.9, 85.7, and 94.6% in cattle on the affected farms, respectively. All affected cattle displayed skin nodules over their entire bodies, while 33.9 and 7.1% of the affected farms reported nodular lesions present on the udders and teats, respectively. No mortalities were reported due to vaccine adverse reactions. Duration (course) of clinical signs ranged from 3 to 20 days (Mean = 13.7, SD ± 4.1). Two types of LSD vaccines were used by the farmers in this study. The first one was a sheep pox virus (SPPV) vaccine derived from the RM65 isolate [Jovivac, manufactured by Jordan Bioindustries Centre (JOVAC)] and the other an unlabelled one, which was later identified using PCR as a strain of lumpy skin disease virus (LSDV). Blood and skin samples collected from cattle vaccinated with the LSDV vaccine were positive for LSDV using both general and species-specific PCR primers, whereas those from cattle vaccinated with the Jovivac vaccine were negative. Adverse reactions observed in cattle after administration of the LSDV vaccine were reported to be more severe than those seen after Jovivac vaccine administration and were comparable with clinical signs observed in natural infections.

Evidence of lumpy skin disease virus over-wintering by transstadial persistence in Amblyomma hebraeum and transovarial persistence in Rhipicephalus decoloratus ticks

Lumpy skin disease is a debilitating cattle disease caused by the lumpy skin disease virus (LSDV), belonging to the genus Capripoxvirus. Epidemics of the disease usually occur in summer, when insect activity is high. Limited information is available on how LSDV persists during inter-epidemic periods. Transmission of LSDV by mosquitoes such as Aedes aegypti has been shown to be mechanical, there is no carrier state in cattle and the role of wildlife in the epidemiology of the disease seems to be of minor importance. Recent studies in ticks have shown transstadial persistence of LSDV in Rhipicephalus appendiculatus and Amblyomma hebraeum as well as transovarial persistence of the virus in Rhipicephalus decoloratus, R. appendiculatus and A. hebraeum. The over-wintering of ticks off the host as part of their life cycles is well known: A. hebraeum and R. appendiculatus over-winter, for example, on the ground as engorged nymphs/unfed (emergent) adults while R. decoloratus over-winters on the ground as engorged females. In this study, transstadial and transovarial persistence of LSDV from experimentally infected A. hebraeum nymphs and R. decoloratus females after exposure to cold temperatures of 5 °C at night and 20 °C during the day for 2 months was reported. This observation suggests possible over-wintering of the virus in these tick species.

Transovarial passage and transmission of LSDV by Amblyomma hebraeum, Rhipicephalus appendiculatus and Rhipicephalus decoloratus

Lumpy skin disease (LSD), an acute, sub-acute or inapparent disease of cattle, is caused by lumpy skin disease virus (LSDV), a member of the genus Capripoxvirus in the family Poxviridae. LSD is characterised by high fever, formation of circumscribed skin lesions and ulcerative lesions on the mucous membranes of the mouth, respiratory and digestive tracts. It is an economically important disease due to the permanent damage to hides, the reduction in productivity and trade restrictions imposed on affected areas. Transmission has been associated with blood-feeding insects such as stable flies (Stomoxysis calcitrans) and mosquitoes (Aedes aegypti). Mechanical (intrastadial) and transstadial transmission by Amblyomma hebraeum and Rhipicephalus appendiculatus as well as transovarial transmission by R. decoloratus have been reported. In this study transovarial passage of LSDV to larvae and subsequent transmission to recipient animals were demonstrated. The finding of transovarial passage of LSDV in female ticks shows the potential for A. hebraeum, R. appendiculatus and R. decoloratus to be reservoir hosts for LSDV.

Demonstration of lumpy skin disease virus infection in Amblyomma hebraeum and Rhipicephalus appendiculatus ticks using immunohistochemistry

Lumpy skin disease (LSD) is caused by lumpy skin disease virus (LSDV), a member of the genus Capripoxvirus. Transmission of the virus has been associated with haematophagous insects such as Stomoxys calcitrans as well as Aedes and Culex species of mosquitoes. Recent studies have reported the transmission of the virus by Amblyomma hebraeum, Rhipicephalus appendiculatus, and Rhipicephalus decoloratus ticks and the presence of LSDV in saliva of A. hebraeum and R. appendiculatus ticks. The aim of this study was to determine which tick organs become infected by LSDV following intrastadial infection and transstadial persistence of the virus in A. hebraeum and R. appendiculatus ticks. Nymphal and adult ticks were orally infected by feeding them on LSDV-infected cattle. Partially fed adult ticks were processed for testing while nymphs were fed to repletion and allowed to moult to adults before being processed for testing. The infection in tick organs was determined by testing for the presence of the viral antigen using monoclonal antibodies with immunohistochemical staining. The viral antigen was detected in salivary glands, haemocytes, synganglia, ovaries, testes, fat bodies, and midgut. Since the virus was shown to be able to cross the midgut wall and infect various tick organs, this may indicate potential for biological development and transmission of LSDV in ticks. This study strengthens the previously reported evidence of the occurrence of LSDV in tick saliva.

Development of a cost-effective method for capripoxvirus genotyping using snapback primer and dsDNA intercalating dye

Sheep pox virus (SPPV), goat pox virus (GTPV) and lumpy skin disease virus (LSDV) are very closely related viruses of the Capripoxvirus (CaPV) genus of the Poxviridae family. They are responsible for sheep pox, goat pox and lumpy skin disease which affect sheep, goat and cattle, respectively. The epidemiology of capripox diseases is complex, as some CaPVs are not strictly host-specific. Additionally, the three forms of the disease co-exist in many sub-Saharan countries which complicates the identification of the virus responsible for an outbreak. Genotyping of CaPVs using a low-cost, rapid, highly specific, and easy to perform method allows a swift and accurate identification of the causative agent and significantly assists in selecting appropriate control and eradication measures, such as the most suitable vaccine against the virus during the outbreaks. The objective of this paper is to describe the design and analytical performances of a new molecular assay for CaPV genotyping using unlabelled snapback primers in the presence of dsDNA intercalating EvaGreen dye. This assay was able to simultaneously detect and genotype CaPVs in 63 samples with a sensitivity and specificity of 100%. The genotyping was achieved by observing the melting temperature of snapback stems of the hairpins and those of the full-length amplicons, respectively. Fourteen CaPVs were genotyped as SPPVs, 25 as GTPVs and 24 as LSDVs. The method is highly pathogen specific and cross platform compatible. It is also cost effective as it does not use fluorescently labelled probes, nor require high-resolution melting curve analysis software. Thus it can be easily performed in diagnostic and research laboratories with limited resources. This genotyping method will contribute significantly to the early detection and genotyping of CaPV infection and to epidemiological studies.

Detection of lumpy skin disease virus in saliva of ticks fed on lumpy skin disease virus-infected cattle

Lumpy skin disease is an economically important disease of cattle that is caused by the lumpy skin disease virus (LSDV), which belongs to the genus Capripoxvirus. It is endemic in Africa and outbreaks have also been reported in the Middle-East. Transmission has mostly been associated with blood-feeding insects but recently, the authors have demonstrated mechanical transmission by Rhipicephalus appendiculatus as well as mechanical/intrastadial and transstadial transmission by Amblyomma hebraeum. Saliva is the medium of transmission of pathogens transmitted by biting arthropods and, simultaneously, it potentiates infection in the vertebrate host. This study aimed to detect LSDV in saliva of A. hebraeum and R. appendiculatus adult ticks fed, as nymphs or as adults, on LSDV-infected animals, thereby also demonstrating transstadial or mechanical/intrastadial passage of the virus in these ticks. Saliva samples were tested for LSDV by real-time PCR and virus isolation. Supernatants obtained from virus isolation were further tested by real-time PCR to confirm that the cytopathic effects observed were due to LSDV. Lumpy skin disease virus was detected, for the first time, in saliva samples of both A. hebraeum and R. appendiculatus ticks. At the same time, mechanical/intrastadial and transstadial passage of the virus was demonstrated and confirmed in R. appendiculatus and A. hebraeum.

Evidence of transstadial and mechanical transmission of lumpy skin disease virus by Amblyomma hebraeum ticks

Lumpy skin disease (LSD) is an economically important disease caused by LSD virus (LSDV), a Capripoxvirus, characterized by fever and circumscribed skin lesions. It is suspected to be transmitted mechanically by biting flies. To assess the vector potential of Amblyomma hebraeum in transmission of LSDV, mechanical/intrastadial and transstadial modes of transmission of the virus by this tick species were investigated. Two cattle were artificially infected as sources (donors) of infection to ticks. Ticks were infected as either nymphs or adults. Male A. hebraeum ticks were partially fed on donor animals and transferred to recipient animals to test for mechanical/intrastadial transmission. Nymphal A. hebraeum were fed to repletion on donor animals. The emergent adult ticks were placed on recipient animals to test for transstadial transmission of the virus. Successful transmission of LSDV infection was determined in recipient animals by monitoring development of clinical signs, testing of blood for the presence of LSDV by real-time PCR, virus isolation and the serum neutralization test. This report provides further evidence of mechanical/intrastadial and, for the first time, transstadial transmission of LSDV by A. hebraeum. These findings implicate A. hebraeum as a possible maintenance host in the epidemiology of the disease.

Detection of capripoxvirus DNA using a novel loop-mediated isothermal amplification assay

BACKGROUND

Sheep poxvirus (SPPV), Goat poxvirus (GTPV) and Lumpy skin disease virus (LSDV) are the most serious poxviruses of ruminants. They are double stranded DNA viruses of the genus Capripoxvirus, (subfamily Chordopoxvirinae) within the family Poxviridae. The aim of this study was to develop a Loop-mediated isothermal AMPlification (LAMP) assay for the detection of Capripoxvirus (CaPV) DNA.

RESULTS

A single LAMP assay targeting a conserved region of the CaPV P32 gene was selected from 3 pilot LAMP assays and optimised by adding loop primers to accelerate the reaction time. This LAMP assay successfully detected DNA prepared from representative CaPV isolates (SPPV, GTPV and LSDV), and did not cross-react with DNA extracted from other mammalian poxviruses. The analytical sensitivity of the LAMP assay was determined to be at least 163 DNA copies/μl which is equivalent to the performance reported for diagnostic real-time PCR currently used for the detection of CaPV. LAMP reactions were monitored with an intercalating dye using a real-time PCR machine, or by agarose-gel electrophoresis. Furthermore, dual labelled LAMP products (generated using internal LAMP primers that were conjugated with either biotin or fluorescein) could be readily visualised using a lateral-flow device.

CONCLUSIONS

This study provides a simple and rapid approach to detect CaPV DNA that may have utility for use in the field, or in non-specialised laboratories where expensive equipment is not available.

Review: lumpy skin disease: an emerging threat to Europe, the Middle East and Asia

Lumpy skin disease (LSD) is an economically devastating emerging viral disease of cattle. Lumpy skin disease is currently endemic in most African countries and has recently spread out of Africa into the Middle East region. In this article, we review the putative mechanisms of spread of LSD into the Middle East and the risks of further spread into Turkey, Europe and Asia. We also review the latest findings on the epidemiology of LSD, its mechanisms of transmission, the potential role of wildlife in its maintenance and spread and the diagnostic tests and control methods currently available.

A potential role for ixodid (hard) tick vectors in the transmission of lumpy skin disease virus in cattle

Lumpy skin disease (LSD) is an economically important cattle disease. The disease is endemic in many African countries, but outbreaks have also been reported in Madagascar and the Middle East. The aim of this study was to investigate the potential role of ixodid (hard) ticks in the transmission of the disease. Cattle were infected with a virulent, South African field isolate of lumpy skin disease virus (LSDV). Three common African tick species (genera Rhipicephalus, Amblyomma and Rhipicephalus (Boophilus)) in different life cycle stages were fed on the infected animals during the viraemic stage and on skin lesions. Post-feeding, the partially fed male ticks were transferred to the skin of non-infected 'recipient' animals, while females were allowed to lay eggs that were then tested using the polymerase chain reaction (PCR) method and virus isolation. Nymphs were allowed to develop for 2-3 weeks after which time they were tested. The non-infected 'recipient' cattle were closely monitored, both skin and blood samples were tested using PCR and virus isolation, and serum samples were tested by the serum neutralization test. This is the first report showing molecular evidence of potential transmission of LSDV by ixodid ticks. The study showed evidence of transstadial and transovarial transmission of LSDV by R. (B.) decoloratus ticks and mechanical or intrastadial transmission by R. appendiculatus and A. hebraeum ticks.

The detection of lumpy skin disease virus in samples of experimentally infected cattle using different diagnostic techniques

Lumpy skin disease (LSD) is a disease of cattle, primarily in Africa and Madagascar and rarely in the Middle East. It is caused by a capripoxvirus that belongs to the family Poxviridae. The disease is of economic importance in endemic areas. Effective control of LSD requires accurate and rapid laboratory techniques to confirm a tentative clinical diagnosis. Comparative studies on different diagnostic tests used at different stages of the disease have not been done. The aim of this study was to compare several of these tests. Six seronegative bulls, between 11 and 20 months of age, were infected intravenously and kept in an insect-free facility. The course of the infection was monitored. During a 3-month period blood samples and skin biopsies were collected for virus isolation and polymerase chain reaction (PCR). Skin biopsies were also examined using transmission electron microscopy (TEM). The incubation period in infected animals varied from 4-5 days. The length of the viraemic period did not correlate with the severity of clinical disease. Viraemia was detected from 1-12 days using virus isolation and from 4-11 days using the PCR, which is longer than has previously been reported. Virus was isolated from skin biopsies until Day 39 post infection (p.i.) and PCR could demonstrate viral DNA until Day 92 p.i. Transmission electron microscopy of negatively stained skin biopsies detected LSD virus only in one of the four bulls that developed skin lesions until Day 33 p.i. The PCR was a fast and sensitive method to demonstrate viral DNA in blood and skin samples. It could detect viral nucleic acid in skin lesions 53 days longer than virus isolation. Virus isolation from blood and skin samples was sensitive and reliable, but as a single test it may be too time-consuming to use although this depends on how rapidly the diagnosis must be confirmed. In conclusion, this study showed the PCR to be superior in detecting LSD virus from blood and skin samples. However, virus isolation is still required when the infectivity of the LSD virus is to be determined.

Excretion of lumpy skin disease virus in bull semen

This work was done to establish the incidence and duration of excretion of lumpy skin disease virus (LSDV) in semen of experimentally infected susceptible bulls. Six serologically negative bulls 11-20 months of age were experimentally infected with a virulent field isolate (strain V248/93) of LSDV. Animals were observed for the development of clinical signs, blood was collected until day 90 after infection, and semen was collected every second day until day 18, then twice a week till day 63 and twice a month until three consecutive samples were negative when tested for LSDV by polymerase chain reaction (PCR). An aliquot of each sample which tested positive using PCR was inoculated onto cell monolayers for the recovery of virus. Two bulls developed severe lumpy skin disease (LSD), two bulls showed mild signs and two bulls showed a transient fever only. Multiple samples were positive on PCR from both of the severely affected bulls and one of the mildly affected bulls; between days 10 and 159, days 8 and 132, and days 10 and 21 respectively. Only one sample from each of the other three bulls was positive on PCR. Virus was only isolated from two samples from one of the severely affected bulls and from five semen samples from the other. This study confirmed the excretion of LSDV in bovine semen for prolonged periods, even when obvious clinical signs of the disease were no longer apparent.