Humoral immune response to repeated lumpy skin disease virus vaccination and performance of serological tests

BACKGROUND

In the presented study we investigated the development of the humoral immune response against LSDV during the process of re-vaccination of cattle over a time span of 5 months. In addition, the performance of different serological techniques for antibody detection against LSDV was compared. For sample collection, an area without previous LSD outbreak reports in Serbia was selected. Seventy-nine cattle from twenty farms vaccinated in 2016 and re-vaccinated in 2017 were included in the study. Two farms from the same area with good calving management were selected for investigation of passive LSDV antibody transfer from vaccinated mothers to new-borne calves.

RESULTS

All investigated cattle were healthy on the day of vaccination and during the whole study. Swelling at the injection site or other side effects of vaccination did not occur after re-vaccination in the study. Detection of LSD-specific antibodies was performed with the standard serological methods VNT and IFAT as well as a commercially available Capripox double antigen multi-species-ELISA. Capripoxvirus-specific antibodies were detected 46 to 47 weeks after vaccination in 2016, with VNT in 35.06% and with IFAT and ELISA in 33.77%. A secondary response was observed in all three tests 1 month after re-vaccination with a significant increase in seropositive animals compared to the results before re-vaccination. With all applied serological methods, the number of animals testing positive was significantly higher at 1 and 5 months post re-vaccination than before re-vaccination. No significant statistical difference (p > 0.05) was observed between the results of all three tests used. The sensitivity and specificity of ELISA was estimated to be SeELISA 91% and SpELISA 87% calculated by the results of VNT and SeELISA 88% and SpELISA 76% calculated by the results of IFAT. Passive antibody transfer from vaccinated mothers to new-born calves was investigated at 14 days after birth. Discrepancies for the detection of LSDV specific antibodies between cows and newborn calves at the age of 14 days were observed in VNT and IFAT, but not in ELISA.

CONCLUSION

Of all tests used the commercially available ELISA shows to be the most useful for high throughput analysis compared to VNT or IFAT.

Absence of lumpy skin disease virus in semen of vaccinated bulls following vaccination and subsequent experimental infection

Twelve serologically negative bulls were used, six were vaccinated with a modified live LSD vaccine and six unvaccinated. All were then experimentally infected with a virulent field strain of LSDV. No clinical abnormality was detected following vaccination, and mild clinical signs were seen in four vaccinated bulls following challenge. Virus was not found in semen of vaccinated bulls. Two of the unvaccinated bulls developed severe LSD and four showed mild symptoms, all excreted the virus in the semen following challenge. This study confirmed the ability of LSD vaccination to prevent the excretion of LSDV in semen of vaccinated bulls.

Comparative sequence analysis of the South African vaccine strain and two virulent field isolates of Lumpy skin disease virus

The genomic sequences of 3 strains of Lumpy skin disease virus (LSDV) (Neethling type) were compared to determine molecular differences, viz. the South African vaccine strain (LW), a virulent field-strain from a recent outbreak in South Africa (LD), and the virulent Kenyan 2490 strain (LK). A comparison between the virulent field isolates indicates that in 29 of the 156 putative genes, only 38 encoded amino acid differences were found, mostly in the variable terminal regions. When the attenuated vaccine strain (LW) was compared with field isolate LD, a total of 438 amino acid substitutions were observed. These were also mainly in the terminal regions, but with notably more frameshifts leading to truncated ORFs as well as deletions and insertions. These modified ORFs encode proteins involved in the regulation of host immune responses, gene expression, DNA repair, host-range specificity and proteins with unassigned functions. We suggest that these differences could lead to restricted immuno-evasive mechanisms and virulence factors present in attenuated LSDV strains. Further studies to determine the functions of the relevant encoded gene products will hopefully confirm this assumption. The molecular design of an improved LSDV vaccine is likely to be based on the strategic manipulation of such genes.

Vaccines for lumpy skin disease, sheep pox and goat pox

Sheep pox, goat pox and lumpy skin disease (Neethling) are diseases of sheep, goats and cattle respectively, caused by strains of poxvirus, within the genus Capripoxvirus. Strains affecting sheep and goats are not totally host-specific; some cause disease in both sheep and goats while others may cause disease in only one species. Those causing disease in cattle appear to be specific for cattle, and this is reflected in the different geographical distribution of lumpy skin disease (LSD) and sheep pox and goat pox (sheep and goat pox); LSD is confined to Africa, while sheep and goat pox are present in Africa north of the equator, and throughout West Asia and India, as far East as China and Bangladesh. Occasionally sheep and goat pox spreads from Turkey into Greece. All strains of capripoxvirus so far examined are antigenically indistinguishable, and recovery from infection with one strain provides immunity against all other strains. Because of this antigenic homology among all strains, there is the potential to use a single vaccine strain to protect cattle, sheep and goats.

Trial of a capripoxvirus-rinderpest recombinant vaccine in African cattle

Cattle were vaccinated with differing doses of an equal mixture of capripox-rinderpest recombinant viruses expressing either the fusion protein (F) or the haemagglutinin protein (H) of rinderpest virus. Animals vaccinated with 2 x 10(4) p.f.u. or greater of the combined viruses were completely protected against challenge, 1 month later, with both virulent rinderpest and lumpy skin disease viruses. Vaccination with any of the doses did not induce any adverse clinical response in the animals or transmission of the vaccine virus between animals. All cattle challenged 6 or 12 months after vaccination with 2 x 10(5) p.f.u. of the mixture of recombinant viruses were protected from severe rinderpest disease. Ten out of 18 were completely protected while the remaining 8 developed mild clinical signs of rinderpest. Cattle vaccinated with the recombinant vaccines after prior infection with the parental capripox virus showed more marked clinical signs of rinderpest after challenge with virulent rinderpest, but 9 out of 10 recovered, compared with 80% mortality in the unvaccinated controls.

The clinical response of cattle experimentally infected with lumpy skin disease (Neethling) virus

British cattle were inoculated with lumpy skin disease (Neethling) virus and their clinical signs observed over a three week period. Elevation of body temperature following infection was not found to be a consistent feature, and even in severe cases was limited to a peak temperature of 41 degrees C. Generalised lesions were seen 9-14 days post infection (p.i.), and the development of generalised infections did not appear to be dose related. Following intradermal inoculation lesions were detected from day 2 p.i. and first appearance and severity of local reaction appeared to be related to dose. Virus isolation was carried out on ocular, nasal and saliva swabs, and on buffy coat preparations. A transient viraemia was detected in two of eleven animals that did not show generalized signs; virus was not isolated from the secretions of seven animals without generalised signs. Virus was isolated from the peripheral secretions of an animal with generalised disease between 9 and 15 days p.i. and viraemia was detected in each of five animals with generalized signs. Delayed-type hypersensitivity reactions following intradermal inoculation of immune cattle with LSDV were found to be maximal at 24 h after challenge.

Recombinant capripoxvirus expressing the hemagglutinin protein gene of rinderpest virus: protection of cattle against rinderpest and lumpy skin disease viruses

A cDNA clone containing the complete coding sequence of the hemagglutinin (H) protein gene of the RBOK vaccine strain of rinderpest virus, under the control of the vaccinia late promoter p11, was inserted by homologous recombination into the thymidine kinase gene of the KS-1 strain of capripoxvirus. The recombinant virus produced authentic H protein as judged by its electrophoretic mobility, transport to the cell surface of infected lamb testis cells, and reactivity with monoclonal antibodies specific for the H protein of rinderpest virus. The recombinant virus induced significant levels of rinderpest virus neutralizing antibodies in vaccinated cattle and protected them from clinical rinderpest after challenge with a lethal dose of a highly virulent heterologous strain of the virus. Protection was achieved using vaccine doses lower than those used with a similar recombinant expressing the fusion protein gene of rinderpest. The parental KS-1 virus is widely used as a vaccine against capripox viruses and so the rinderpest recombinant acts as a dual vaccine to protect cattle against both rinderpest and lumpy skin disease.

Neutralising antibodies to lumpy skin disease virus in African wildlife

A total of 3445 sera from 44 different wild species collected between 1963 and 1982 in 11 African countries south of the Sahara, were examined for neutralising antibodies to Lumpy Skin Diseases (LSD) Virus (prototype Neethling). Antibodies were demonstrated in six species but were of low prevalence. It was concluded from the generally negative results, that wildlife in Africa probably does not play a very important part in he perpetuation and spread of LSD Virus.

A comparison in calves of the antigenicity of three strains of bovid herpesvirus 2

Three strains of bovid herpesvirus 2, viz. Allerton, bovine mammillitis and 69/1LO were used to infect calves intradermally. Twenty-eight days later the immunity of the calves was challenged by intravenous injection of a homologous or heterologous strain. Challenge control calves developed a fever (greater than 40 degrees C) lasting several days and widespread skin lesions which varied with the strain. Homologous challenge of the primary infection produced neither skin lesions nor febrile response, except in one calf in which fever was noted on one day. Heterologous challenge did not cause skin lesions but fever occurred in 8/12 calves. In particular Allerton virus failed to protect completely against heterologous challenge. Despite minor differences evident in these experiments, it is recommended that these isolates should be considered as strains of the same virus--bovid herpesvirus 2.