The first vaccine for CE (commonly referred to as orf, scabby mouth, sore mouth, and contagious pustular dermatitis) was developed at the Texas Agricultural Experiment Station (currently the Texas AgriLife Research Center) at Sonora, Tex, in the 1930s.1,2 The vaccine was labeled for use in sheep, but it was efficacious when used in goats. The etiologic agent that causes the disease of CE in sheep and goats is referred to as orf virus or CE virus. In the late 1990s, there were anecdotal reports of epizootics of a persistent, generalized form of CE in goats vaccinated with the vaccine labeled for use in sheep. A study3 conducted to evaluate the effectiveness of the vaccine revealed that it was ineffective for protecting goats against the strain of orf virus that caused the persistent, generalized form of CE in goats. Results of that study3 prompted development of a CE vaccine from viruses obtained during outbreaks of CE in goats.4
In Texas, the goat-derived CE vaccine was used successfully in goats for a few seasons. However, in the early and mid-2000s, outbreaks of more virulent CE, mainly in Boer goats and Boer-Spanish crossbred goats, were consistently being reported in goats vaccinated with the goat-derived CE vaccine5,a (Figure 1). The specific reasons for the vaccination failures are unknown, but variability among animals and breeds,5 nutritional differences,6 incorrect vaccine administration,7 antigenic differences in strains of the orf virus,5,8 and environmental conditions9 have been postulated.
Goats vaccinated with a goat-derived CE vaccine that developed mild (more typical) lesions of orf (A) and excessively proliferative lesions potentially attributable to the more virulent strain of the orf virus (B).
Citation: American Journal of Veterinary Research 73, 1; 10.2460/ajvr.73.1.86
Therefore, the objective of the study reported here was to determine whether young goats properly vaccinated with the goat-derived CE vaccine would be protected when challenge exposed with a field strain of the orf virus obtained from more virulent CE infections (virulent strain of orf virus). Furthermore, we evaluated whether vaccination with a vaccine developed from the virulent strain of orf virus would induce protection against challenge exposure with the strain of virus contained in the goat-derived CE vaccine.
Materials and Methods
Animals—Boer-Spanish crossbred goats (3 to 20 days old; n = 126) were used in the study. Boer-Spanish crossbred goats are a prevalent goat breed found in the goat-raising area of Texas and are the animals predominantly reported to have the more virulent form of CE. Goat kids were from dams that had been vaccinated with the CE vaccine labeled for sheep when the dams were kids. Dams and kids were pastured together on approximately 145 hectares. None of the goats had clinical signs of CE at the time of the study. The study was approved by the Institutional Animal Care and Use Committee of Texas A&M University.
Preparation of vaccine and material for challenge exposure—Two vaccine preparations were evaluated. The goat-derived CE vaccine was prepared as described elsewhere.4 The vaccine for a virulent field strain of orf virus was prepared from scabs collected from active-disease lesions located around the mouth and nares of goats that had been vaccinated with the goat-derived CE vaccine. The vaccine for the virulent field strain of orf virus was prepared by modification of a procedure described elsewhere.4 Briefly, scabs were combined and placed in a desiccator for 4 to 7 weeks. Scabs were then ground slowly in a grinding mill. The ground scabs were passed through a coarse sieve to remove hair and then were further ground manually by use of a mortar and pestle. The material was desiccated for an additional 2 to 3 weeks. Finally, the material was ground in a ball grinder. The powdered scab material was divided into 65-mg aliquots and stored in glass vials at 4°C until used. At the time of vaccination or challenge exposure, each aliquot of powdered scab material was mixed with 6 mL of 30% glycerin-saline (0.9% NaCl) solution.
Vaccination and challenge exposure—The study involved parallel groups. Goats were randomly allotted into 2 groups. Group 1 (n = 85) was vaccinated with the goat-derived CE vaccine, and group 2 (41) was vaccinated with the vaccine created from the virulent strain of orf virus. Predation loss (n = 7) and death (2) resulted in 81 goats in group 1 and 36 goats in group 2 for use in challenge exposure.
Ten weeks after vaccination, goats in each of the 2 groups were randomly allocated for challenge exposure with the strain of the goat-derived CE vaccine or the virulent strain of orf virus (every other kid in each vaccination group was assigned to the same challenge exposure). Consequently, there were 4 subgroups in the study. Group 1A (n = 41) was vaccinated with the goat-derived CE vaccine formulated for goats and subsequently challenge exposed with the strain of the goat-derived CE vaccine, group 1B (40) was vaccinated with the goat-derived CE vaccine and subsequently challenge exposed with the virulent strain of orf virus, group 2A (18) was vaccinated with the vaccine created from the virulent strain of orf virus and subsequently challenge exposed with the strain of the goat-derived CE vaccine, and group 2B (18) was vaccinated with the vaccine created from the virulent strain of orf virus and subsequently challenge exposed with the virulent strain of orf virus. Vaccination and challenge inoculation were performed on the hairless skin at the medial aspect of the right and left thigh, respectively. The skin was scarified, and approximately 0.05 mL of the reconstituted vaccine or challenge-exposure solution was applied to the scarified region.
Assessment of lesions—Lesion formation (ie, scabs) was assessed 12 days after vaccination and 10 days after challenge exposure. Scabs were graded as present or not present. If scabs were present, a lesion severity score was assigned by use of an ordinal scale from 1 to 4 (1 = formation of a few small scabs, 2 = mild scab formation, 3 = moderate scab formation, and 4 = excessive and severe scab formation).4 Assessment of goats and scoring of lesions were performed by the same investigator (JMBM).
Data analysis—Scab formation due to vaccination or challenge exposure was analyzed by use of χ2 analysis of contingency and the Fisher exact test. Lesion severity scores were analyzed by use of the Mann-Whitney rank sum test. A value of P ≤ 0.05 was considered significant for all analyses.
Results
Scab formation and lesion severity score—The number of goats that developed lesions as a result of challenge exposure with the virulent strain of orf virus did not differ significantly (P = 0.482) between the goats vaccinated with the vaccine produced from the virulent strain of orf virus (group 2) and the goats vaccinated with the goat-derived CE vaccine (group 1B). Similarly, there was no significant (P = 0.460) difference in lesion severity score between group 2 and group 1B.
The proportion of goats that developed lesions as a result of challenge exposure with the strain of virus in the goat-derived CE vaccine following vaccination with the vaccine produced from the virulent strain of orf virus (group 2A; 14/18) was significantly (P = 0.007) smaller than the proportion of goats vaccinated with the goat-derived CE vaccine (group 1; 83/85). However, there was no significant (P = 0.498) difference in lesion severity score between group 2A and group 1 (Table 1).
Lesion formation (ie, scabs) and median lesion severity score in young goats vaccinated with a goat-derived CE vaccine or a vaccine produced from a more virulent field strain of orf virus and subsequent challenge exposure (10 weeks after vaccination) with the virus strain of the goat-derived CE vaccine or the virulent field strain of orf virus.
| Group* | No. of goats† | Lesion formation‡ | Lesion severity score§ |
|---|---|---|---|
| 1 | 85 | 83/85 | 2.0 (2.0–2.0) |
| 1A | 41 | 18/41‖ | 0.0 (0.0–1.0)‖ |
| 1B | 40 | 35/40¶ | 2.0 (1.0–3.0)¶ |
| 2 | 41 | 38/41 | 2.0 (2.0–3.0) |
| 2A | 18 | 14/18#** | 2.5 (1.0–3.0)¶ |
| 2B | 18 | 8/18††‡‡ | 0.0 (0.0–1.0)††§§‖‖ |
Group 1 was vaccinated with the goat-derived CE vaccine, and group 2 was vaccinated with the vaccine created from the virulent strain of orf virus. Group 1A was vaccinated with the goat-derived CE vaccine and subsequently challenged exposed with the strain used for the goat-derived CE vaccine, group 1B was vaccinated with the goat-derived CE vaccine and subsequently challenge exposed with the virulent strain of orf virus, group 2A was vaccinated with the vaccine created from the virulent strain of orf virus and subsequently challenge exposed with the strain used for the goat-derived CE vaccine, and group 2B was vaccinated with the vaccine created from the virulent strain of orf virus and subsequently challenge exposed with the virulent strain of orf virus.
Nine goats (4 in group 1 and 5 in group 2) were found dead (n = 2 goats) or lost as a result of predation (7) sometime after vaccination but before viral challenge exposure.
Value reported is the number of goats with lesions/number of goats in the group.
Value reported is median (interquartile range). Lesion severity score was assigned by use of an ordinal scale from 1 to 4 (1 = formation of a few small scabs, 2 = mild scab formation, 3 = moderate scab formation, and 4 = excessive and severe scab formation).
Value differs significantly (P < 0.001) from the value for group 1.
Value differs significantly (P < 0.001) from the value for group 1A.
Value differs significantly (P = 0.007) from the value for group 1.
Value differs significantly (P = 0.034) from the value for group 1A.
Value differs significantly (P < 0.001) from the value for group 2.
Value differs significantly (P = 0.001) from the value for group 1B.
Value differs significantly (P < 0.001) from the value for group 1B.
Value differs significantly (P < 0.001) from the value for group 2A.
Discussion
Vaccination with the goat-derived CE vaccine did not provide heterologous protection from challenge exposure with the virulent strain of orf virus, but it did provide homologous protection from infection with the virus strain of the goat-derived CE vaccine. Clinical signs in naïve sheep and goats generally begin as localized erythema and development of pustules and vesicles at the site of infection. The pustules and vesicles rupture and form scabs. Lesions heal by 4 to 8 weeks after infection.10–16 In goats with protective immunity, infection results in lesions in fewer animals, less severe lesions, and a shorter resolution time of approximately 1 to 3 weeks.3,11,12,14–18 In goats exposed to the virulent strain of orf virus, there were no significant differences in the number of goats that developed lesions or in lesion severity between goats vaccinated with the vaccine developed from the virulent strain of orf virus (group 2) and goats vaccinated with the goat-derived CE vaccine (group 1B). These results support findings of other studies,3,5,8,19–21 which suggest that strains of orf virus antigenically distinct from those in the goat-derived CE vaccine are a cause of disease outbreaks in sheep and goats.
It did not appear that vaccination with the vaccine produced by use of the virulent strain of orf virus provided protective immunity against infection with the virus strain of the goat-derived CE vaccine. If vaccination had stimulated protective immunity, the number of goats with lesions and severity of the lesions should have been reduced.3,11,12,14,15,18 In the present study, significantly fewer goats vaccinated with the vaccine produced by use of the virulent strain of orf virus (group 2A) formed scabs following challenge exposure with the virus strain of the goat-derived CE vaccine than did goats vaccinated with the goat-derived CE vaccine (group 1). However, there were significantly fewer goats with scabs when goats were vaccinated with the goat-derived CE vaccine prior to challenge exposure (group 1A). Lesion severity scores did not differ significantly between groups 1 and 2A. These findings suggest that protection derived from vaccination with the vaccine produced by use of the virulent strain of orf virus may not have biological importance.
Reduced protection from vaccination has been attributed to physiologic variability among individual animals and breeds,5 genetic factors,22 nutritional differences,6 environmental conditions,11 the method of inoculation,20 viral titers at the time of inoculation and challenge exposure, incorrect vaccine administration,7 and antigenically distinct strains of the orf virus.5,8,20 The methods used in the present study accounted for most of these variables, except for potential antigenic differences between strains of the orf virus; thus, antigenic differences in epitope and virulence proteins likely were factors in the differences in protection and apparent vaccine failures.
Research has been conducted on neutralization epitopes and virulence proteins of the orf virus.16,23,24 The orf virus encodes a range of immunomodulatory and virulence genes for substances that interfere with host antivirus immune responses.25 These include vascular endothelial growth factor,26 interferon resistance factor,27 inhibitor of ovine granulocyte-macrophage colony-stimulation factor,28 inhibitor of interleukin-2,28 and a cytokine interleukin-10 orthologue.29 Immune responses of sheep to the orf virus involve neutrophils, dendritic cells, T cells (of which CD4+ predominate), B cells, and antibodies.16,18,28,30,31 Increases in CD4+ and CD8+ T cells, B cells, inflammatory cytokine interleukin-1β and chemokine interleukin-8, and the humoral response have been used to evaluate protection provided by a vaccine.14,16,20 Relative correlates, which are immune responses with a relationship to protection,32 are useful measures, but they do not always evaluate actual protection from disease. For example, even in animals with sufficient antibody titers, neutralizing antibodies against orf virus are rare and passive transfer with hyperimmune serum or colostrum is not protective against infection and disease.30,33,34 In the present study, the variables of interest were the clinical signs of lesion formation and lesion severity. Duration of clinical signs, which is reduced with protective vaccination,11,12,14,15 would have been useful to measure in the present study; however, pasture location and logistics precluded us from determining the duration.
In the present study, goats vaccinated with the vaccine produced by use of the virulent strain of orf virus did not develop the excessively proliferative reactions that potentially can be seen with infections attributable to the virulent strain of orf virus in field settings. However, lesion severity scores of these goats (group 2) were higher than those of goats vaccinated with the goat-derived CE vaccine (group 1). Individual susceptibility factors within animals,5 anatomic location for and method of virus introduction,35 and lack of secondary compounding infections36 may have factored into the absence of excessively proliferative lesions in the present study. Additionally, processing the virus in the scabs for use in the vaccine and for challenge exposure may have attenuated the virulence of the virus.37
In the present study, there was homologous protection after vaccination, protection against challenge exposure with the same virus strain that was used in the vaccine, which significantly reduced the number of goats with scabs and lesion severity. Nonetheless, the proportion of vaccinated goats that formed scabs after challenge exposure with the virus strain of the goat-derived CE vaccine (18/41) or the virulent strain of orf virus (8/18) was higher than that in other studies.4,11,14,34 This may reflect differences between a study conducted in a controlled laboratory environment and a study conducted in field conditions. The goats were maintained on a pasture that in previous years contained sheep and goats vaccinated with a commercial orf vaccine labeled for use in sheep. Goats in the present study could have been exposed to a virus strain unrelated to the virus strain used in the study reported here. However, this should not have biased the results or conclusions because all goats had similar potential exposure to any field strain of the orf virus. Although there is variation in protection among studies, results of the study reported here clearly indicate that the 2 strains of orf virus are not cross protective, which may be attributable to antigenic differences. This lack of protection may be a factor in CE outbreaks in vaccinated goats.
ABBREVIATIONS
| CE | Contagious ecthyma |
Musser JMB, Taylor CA, Payne SL. Comparison of orf virus interferon resistant and envelope glycoprotein genes in contagious ecthyma outbreaks (abstr), in Proceedings. 3rd Vaccine Global Cong 2009;P3.44.
References
- 1.
Boughton IB, Hardy WT. Contagious ecthyma (sore mouth) of sheep and goats. J Am Vet Med Assoc 1934; 85:150–178.
- 2.
Boughton IB, Hardy WT. Immunization of sheep and goats against soremouth (contagious ecthyma). Bull Tex Agric Exp Sta 1935; 504:5–16.
- 3.↑
de la Concha-Bermejillo A, Ermel RW, Zhang Z, et al. Contagious ecthyma (orf) virulence factors and vaccine failure, in Proceedings. 103rd Annu Meet U S Anim Health Assoc 1999;513–524.
- 4.↑
Musser JMB, Taylor CA, Guo J, et al. Development of a contagious ecthyma vaccine for goats. Am J Vet Res 2008; 69:1366–1370.
- 5.↑
de la Concha-Bermejillo A, Guo J, Zhang Z, et al. Severe persistent orf in young goats. J Vet Diagn Invest 2003; 15:423–431.
- 6.↑
Goff JP. Major advances in our understanding of nutritional influences on bovine health. J Dairy Sci 2006; 89:1292–1301.
- 8.
Beck CC, Taylor WB. Orf: it's awful. Vet Med Small Anim Clin 1974; 69:1413–1417.
- 9.↑
Webster AJF. Environmental and physiological interactions influencing resistance to infectious disease. In: Dunlop RH, Moon HW, eds. Resistance to infectious disease. Saskatoon, SK, Canada: Modern Press, 1970;61–68.
- 10.
McKeever DJ, Jenkinson DM, Hutchison G, et al. Studies of the pathogenesis of orf virus infection in sheep. J Comp Pathol 1988; 99:317–328.
- 11.↑
Yirrell DL, Reid HW, Norval M, et al. Immune response of lambs to experimental infection with orf virus. Vet Immunol Immunopathol 1989; 22:321–332.
- 12.
Pye D. Vaccination of sheep with cell culture grown orf virus. Aust Vet J 1990; 67:182–186.
- 13.
Housawi FMT, Abu Elzein EME, Gameel AA, et al. A close comparative study on the response of sheep and goats to experimental orf infection. Zentralbl Veterinarmed B 1993; 40:272–282.
- 14.
Nettleton PF, Brebner J, Pow I, et al. Tissue culture-propagated orf virus vaccine protects lambs from orf virus challenge. Vet Rec 1996; 138:184–186.
- 15.
Anderson IE, Reid HW, Nettleton PR, et al. Detection of cellular cytokine mRNA expression during orf virus infection in sheep: differential interferon-γ mRNA expression by cells in initial versus reinfection skin lesions. Vet Immunol Immunopathol 2001; 83:161–176.
- 16.
Haig DM, McInnes CJ. Immunity and counter-immunity during infection with the parapoxvirus orf virus. Virus Res 2002; 88:3–16.
- 17.
Marklew S. Assessment of liquid cell culture grown orf virus in sheep, in Proceedings. 3rd Cong Europ Soc Vet Virol 1995;520–523.
- 18.
Haig DM, McInnes C, Deane D, et al. The immune and inflammatory response to orf virus. Comp Immun Microbiol infect Dis 1997; 20:197–204.
- 19.
Horgan ES, Haseeb MA. The immunological relationships of strains of contagious pustular dermatitis virus. J Comp Pathol 1947; 57:1–7.
- 20.↑
Zamri-Saad M, Roshidah I, Al-Ajeeli KSA. Experimental cross-infection of sheep and goats with different isolates of contagious ecthyma virus. Aust Vet J 1994; 71:218–220.
- 21.
Guo J, Zhang Z, Edwards JF, et al. Characterization of a North American orf virus isolated from a goat with persistent, proliferative dermatitis. Virus Res 2003; 93:169–179.
- 22.↑
Nguyen TC. The immune response in sheep: analysis of age, sex and genetic effects on the quantitative antibody response to chicken red blood cells. Vet Immunol Immunopathol 1984; 5:237–245.
- 23.
Czerny CP, Waldmann R, Scheubeck T. Identification of three distinct antigenic sites in parapoxvirus. Arch Virol 1997; 142:807–821.
- 24.
Mercer AA, Yirrell DL, Whelan EM, et al. A novel strategy for determining protective antigens of the parapoxvirus, orf virus. Virology 1997; 229;193–200.
- 25.↑
Haig DM, Thomson J, McInnes C, et al. Orf virus immuno-modulation and the host immune response. Vet Immunol Immunopathol 2002; 87:395–399.
- 26.↑
Lyttle DJ, Fraser KM, Fleming SB, et al. Homologs of vascular endothelial growth factor are encoded by the poxvirus orf virus. J Virol 1994; 68:84–92.
- 27.↑
Haig DM, McInnes CJ, Thomson J, et al. The orf virus OV20.0L gene product is involved in interferon resistance and inhibits an interferon-inducible, double-stranded RNA-dependent kinase. Immunology 1998; 93:335–340.
- 28.↑
Deane D, McInnes CJ, Percival A, et al. Orf virus encodes a novel secreted protein inhibitor of granulocyte-macrophage colony-stimulating factor and interleukin-2. J Virol 2000; 74:1313–1320.
- 29.↑
Fleming SB, Anderson IE, Thomson J, et al. Infection with recombinant orf viruses demonstrates that the viral interleukin-10 is a virulence factor. J Gen Virol 2007; 88:1922–1927.
- 30.
McKeever DJ, Reid HW, Inglis NF, et al. A qualitative and quantitative assessment of the humoral antibody response of the sheep to orf virus infection. Vet Microbiol 1987; 15:229–241.
- 32.↑
Plotkin SA. Correlates of protection induced by vaccination. Clin Vaccine Immunol 2010; 17:1055–1065.
- 33.
Buddle BM, Pulford HD. Effect of passively-acquired antibodies and vaccination on the immune response to contagious ecthyma virus. Vet Microbiol 1984; 9:515–522.
- 34.
Zamri-Saad M, Kamal-Hizat A, Saharee AA. The efficacy of a live contagious ecthyma vaccine in kids. J Vet Malaysia 1993; 5:55–56.
- 35.↑
Housawi FMT. Severe inflammatory orf infection in fancy shami goats in Saudi Arabia. Sci J King Faisal Univ 2004; 5:115–124.
- 36.↑
Ndikuwera J, Odiawo GO, Usenik EZ, et al. Chronic contagious ecthyma and caseous lymphadenitis in two Boer goats. Vet Rec 1992; 131:584–585.
- 37.↑
Buddle BM, Dellers RW, Schurig GG. Contagious ecthyma virus-vaccination failures. Am J Vet Res 1984; 45:263–266.
