Entry-competent-replication-abortive African horse sickness virus strains elicit robust immunity in ponies against all serotypes

Abstract

African horse sickness virus (AHSV) is an Orbivirus within the Reoviridae family, spread by Culicoides species of midges, which infects equids with high mortality, particularly in horses and has a considerable impact on the equine industry. In order to control the disease, we previously described Entry Competent Replication Abortive (ECRA) virus strains for each of the nine distinct AHSV serotypes and demonstrated their potential as vaccines, first in type I interferon receptor (IFNAR-/-) knockout mice, and then in ponies. In this report we have investigated whether or not a combination ECRA vaccine comprising nine vaccine strains as two different cocktails is as efficient in ponies and the duration of the immunity triggered by ECRA vaccines. In one study, a group of ponies were vaccinated with a cocktail of 4 vaccine strains, followed by a vaccination of the remaining 5 vaccine strains, mimicking the current live attenuated vaccine regimen. In the second study, ponies were vaccinated with a single ECRA-AHSV strain and monitored for 6 months. The first group of ponies developed neutralising antibody responses against all 9 serotypes, indicating that no cross-serotype interference occurred, while the second group developed robust neutralising antibody responses against the single serotype that were sustained at the same level throughout a 6-month study. The results support our previous data and further validate ECRA vaccines as a safe and efficacious replacement of current live vaccines.

Keywords: African horse sickness virus; Entry competent replication abortive; Neutralising antibody; Vaccine.

Fig. 1

a. Time course of the multivalent AHSV Trial. b. Seroconversion of animals after multivalent ECRA-AHSV vaccination. Animals were vaccinated with 2 different ECRA-AHSV cocktails 21 days apart, with ECRA-AHSV1/4/7/9 on day 0, and ECRA-AHSV2/3/5/6/8 on day 21. The induction of the immune response was monitored in vaccinated animals by VP7 group specific competitive ELISA.

Fig. 2

Serum neutralisation activity in ponies after multivalent ECRA-AHSV vaccination. Neutralizing antibody titres of vaccinated animal sera were determined by serum neutralisation assay 21 days after receipt of Cocktail 1, immediately prior to Cocktail 2, and at 42 days. Neutralising antibody was never detected in the serum of the control animal indicated in Black.

Fig. 3

Seroconversion of animals after ECRA-AHSV4 Vaccination. The induction of the immune response was monitored in vaccinated animals by VP7 group specific competitive ELISA.

Fig 4

Long term serum neutralisation activity of sera collected from ECRA-AHSV4 vaccinated ponies. Sera collected throughout the study were examined for serotype specific neutralisation by serum neutralisation assay against AHSV serotype 4. Titres are expressed as the reciprocal of the highest dilution that maintained 90% neutralisation compared to the control animal in Grey.

Fig. 5

Cytokine Analysis of ponies vaccinated with ECRA AHSV4. Sera collected throughout the study were examined for cytokine expression by Luminex Assay, to monitor (a) Th1, (b) Th2, and (c) T.Reg. response.