Duration of circulating antibody and immunity following infection with equine influenza virus

Abstract

The duration of immunity as measured by virological, serological and clinical responses following infection with influenza A/equine/Newmarket/79 (H3N8) was assessed in repeated challenge experiments in which ponies were infected by exposure to aerosols of infectious virus. Previous infection stimulated complete clinical protection which persisted for at least 32 weeks as demonstrated by the absence of febrile responses and coughing in two groups of ponies infected 16 weeks or 32 weeks after the first infection. Partial clinical protection persisted for over a year as demonstrated by the absence of coughing and a reduction in the number of febrile responses in a group of ponies infected 62 weeks after their first infection. These results contrasted with those observed in immunologically naive control ponies which developed pyrexia, dyspnoea and nasal discharge and coughing. The kinetics of virus specific antibody production in primary and secondary infections with equine influenza were studied by the single radial haemolysis test and a radioisotopic antiglobulin binding assay which measured virus specific IgGab antibody isotype. Antibody to the haemagglutinin, as measured by the single radial haemolysis test, declined rapidly after primary infection whereas the IgGab responses to whole virus antigens persisted for longer. The single radial haemolysis test was therefore particularly useful for the detection of antibody responses in multiple infections or exposures to influenza antigens. The radioisotopic antiglobulin binding assay was more sensitive for identifying infections which had occurred more than six months previously, as evidenced by anamnestic IgGab responses in ponies with low levels of antibody before rechallenge.

ISCOM-based equine influenza vaccine: Duration of immunity and randomised clinical trials to assess an accelerated schedule of immunisation and efficacy

“…At this time, ponies showed little or undetectable SRH antibody titre [10]. It is likely that protection in absence of antibodies involved CMI stimulation, which efficiently supports or replaces protection induced by antibodies [10,43,44]. Stimulation of IFN gamma, a CMI marker, was previously demonstrated after immunization with ISCOM and ISCOMatrix EI [9,45,46].…”

Comparison of two modern vaccines and previous influenza infection against challenge with an equine influenza virus from the Australian 2007 outbreak

“…In man, it is thought that cellular immune mechanisms play an important role in clearance of virus from the respiratory tract [18]. Infection with EIV has been shown to induce long-term immunity independent of circulating antibodies against HA [11]. Of the previously infected ponies studied in this report, 3 of the 4 had detectable SRH antibody levels 18 months post-infection with only one above 75 mm 2 .…”

“…Natural infection with EIV confers a long-term immunity to re-infection with a homologous strain even in the absence of antibodies at the time of re-infection [11]. In order to mimic more closely the protective immunity induced by EIV, a new generation of vaccines has been designed to stimulate both antibody and cell-mediated immunity [26].…”

Cellular Immune Recognition of Influenza A Viruses in Equines: in vitro and in vivo Studies on the Immunogenicity of Equine Influenza Viruses

“…The protection of our animals against infection at 6 months post glycoprotein injection supports this view. Hannant et al (1988) similarly reported complete Clinical protection for about 32 weeks in horses following a previous exposure of the animals to an H3N8 equine influenza virus. Cellular immune response comprises a complex interaction between different cell types and molecules and induction ofT cell response requires antigen processing, presentation and recognition by Tcell receptors (Berzotsky et al 1988).…”