Incidence and effects of West Nile virus infection in vaccinated and unvaccinated horses in California

Gardner, Ian A.; Wong, Susan J.; Ferraro, Gregory L.; Balasuriya, Udeni B. R.; Hullinger, Pamela J.; Wilson, William D; Shi, Pei Yong; Maclachlan, Nigel J

doi:10.1051/vetres:2006045

Cited by 52 publications

(43 citation statements)

References 24 publications

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“…This is in agreement with a similar percentage (19%) of neurological manifestations to infections reported for this virus strain during the 2010 epidemic in Greece (49). Interestingly, a slightly lower morbidity rate (10%) within infected horses has been reported for lineage 1 WNV strains (50)(51)(52).…”

Section: Discussionsupporting

confidence: 89%

Evaluation of Cross-Protection of a Lineage 1 West Nile Virus Inactivated Vaccine against Natural Infections from a Virulent Lineage 2 Strain in Horses, under Field Conditions

Chaintoutis

Diakakis

Papanastassopoulou

et al. 2015

Clin Vaccine Immunol

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Although experimental data regarding cross-protection of horse West Nile virus (WNV) vaccines against lineage 2 infections exist, the cross-protective efficacy of these vaccines under field conditions has not been demonstrated. This study was conducted to evaluate the capability of an inactivated lineage 1 vaccine (Equip WNV) to protect against natural infections from the Nea Santa-Greece-2010 lineage 2 strain. In total, 185 WNV-seronegative horses in Thessaloniki, Greece, were selected during 2 consecutive years (2011 and 2012); 140 were immunized, and 45 were used as controls. Horses were examined for signs compatible with WNV infection. Neutralizing antibody titers against the Greek strain and the PaAn001/France lineage 1 strain were determined in immunized horses. WNV circulation was detected during both years in the study area. It was estimated that 37% and 27% of the horses were infected during 2011 and 2012, respectively. Three control animals developed clinical signs, and the WNV diagnosis was confirmed. Signs related to WNV infection were not observed in the vaccinated animals. The nonvaccinated animals had a 7.58% ؎ 1.82% higher chance of exhibiting signs than immunized animals (P < 0.05). Neutralizing antibodies raised against both strains in all immunized horses were detectable 1 month after the initial vaccination course. The cross-protective capacity of the lowest titer (1:40) was evident in 19 animals which were subsequently infected and did not exhibit signs. Neutralizing antibodies were detectable until the annual booster, when strong anamnestic responses were observed (geometrical mean titer ratio [GMTR] for lineage 1 of 30.2; GMTR for lineage 2 of 27.5). The results indicate that Equip WNV is capable of inducing cross-protection against natural infections from a virulent lineage 2 WNV strain in horses. West Nile virus (WNV) is a single-stranded RNA virus within the Japanese encephalitis virus serocomplex, which belongs to the genus Flavivirus (family Flaviviridae) (1). WNV is maintained in nature by enzootic transmission cycles between certain bird species and ornithophilic mosquitoes (2). Mosquitoes mainly belonging to the genus Culex can also act as bridge vectors, transmitting the virus to other animal species, including incidental hosts (3-6). Humans and horses are regarded as incidental (deadend) hosts, as the virus titer developed in their blood is generally too low to infect mosquitoes (7). Nevertheless, WNV infection in susceptible hosts may eventually cause neurological disease (8). Regarding horses, the reported clinical signs may vary, and these include fever, paraparesis or tetraparesis, and ataxia, recumbency, and behavioral changes, while in many clinically affected horses muscle fasciculation and tremors are also present. It is expected that deaths will occur in a small percentage of the affected animals (9-13).Phylogenetic analyses of WNV strains isolated worldwide have resulted in the identification of 8 genetic lineages of the virus so far (14). Until 2004, only viral strains...

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Section: Discussionsupporting

confidence: 89%

Evaluation of Cross-Protection of a Lineage 1 West Nile Virus Inactivated Vaccine against Natural Infections from a Virulent Lineage 2 Strain in Horses, under Field Conditions

Chaintoutis

Diakakis

Papanastassopoulou

et al. 2015

Clin Vaccine Immunol

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“…Although attenuated and inactivated viral vaccines currently protect horses and birds against WNV infection, no vaccine is approved for human use. Formalin-treated WNV protects geese, hamsters, and horses from lethal experimental WNV challenge [13][14][15][16][17][18], and horses in field trials [16,19,20]. Although inactivated vaccines may be useful for immunocompromised individuals, repeated dosing may be required to induce durable protection.…”

Section: Introductionmentioning

confidence: 99%

The relative contribution of antibody and CD8+ T cells to vaccine immunity against West Nile encephalitis virus

Shrestha

Chu

et al. 2008

Vaccine

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West Nile virus (WNV) is a mosquito borne, neurotropic flavivirus that causes a severe central nervous system (CNS) infection in humans and animals. Although commercial vaccines are available for horses, none is currently approved for human use. In this study, we evaluated the efficacy and mechanism of immune protection of two candidate WNV vaccines in mice. A formalin-inactivated WNV vaccine induced higher levels of specific and neutralizing antibodies compared to a DNA plasmid vaccine that produces virus-like particles. Accordingly, partial and almost complete protection against a highly stringent lethal intracranial WNV challenge were observed in mice 60 days after single dose immunization with the DNA plasmid and inactivated virus vaccines, respectively. In mice immunized with a single dose of DNA plasmid or inactivated vaccine, antigenspecific CD8 + T cells were induced and contributed to protective immunity as acquired or genetic deficiencies of CD8 + T cells lowered the survival rates. In contrast, in boosted animals, WNVspecific antibody titers were higher, survival rates after challenge were greater, and an absence of CD8 + T cells did not appreciably affect mortality. Overall, our experiments suggest that in mice, both inactivated WNV and DNA plasmid vaccines are protective after two doses, and the specific contribution of antibody and CD8 + T cells to vaccine immunity against WNV is modulated by the prime-boost strategy.

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“…This preparation also contains an adjuvant. Several epidemiological studies investigating the outbreaks throughout the United States have justified the use of these commercially available vaccines as a preventative strategy (6,8,21,23,30).…”

mentioning

confidence: 99%

Comparative Efficacies of Three Commercially Available Vaccines against West Nile Virus (WNV) in a Short-Duration Challenge Trial Involving an Equine WNV Encephalitis Model

Seino

Long

Gibbs

et al. 2007

Clin Vaccine Immunol

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Incidence and effects of West Nile virus infection in vaccinated and unvaccinated horses in California

Cited by 52 publications

References 24 publications

Evaluation of Cross-Protection of a Lineage 1 West Nile Virus Inactivated Vaccine against Natural Infections from a Virulent Lineage 2 Strain in Horses, under Field Conditions

Evaluation of Cross-Protection of a Lineage 1 West Nile Virus Inactivated Vaccine against Natural Infections from a Virulent Lineage 2 Strain in Horses, under Field Conditions

The relative contribution of antibody and CD8+ T cells to vaccine immunity against West Nile encephalitis virus

Comparative Efficacies of Three Commercially Available Vaccines against West Nile Virus (WNV) in a Short-Duration Challenge Trial Involving an Equine WNV Encephalitis Model

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