7 February 2018
Vaccines are one of the greatest achievements in medical science. In recognition of their role in the control of equine disease the Equine Veterinary Journal (EVJ) has produced a special collection of articles on equine vaccine research, available free online here.
Vaccination involves the administration of a biological preparation that stimulates the immune system to fight a specific disease and recognise and destroy it in any further encounters. It is the most effective method for the control of infectious diseases in humans and animals.
Guest edited by Janet Daly, Associate Professor in Emergent Viruses, School of Veterinary Medicine and Science at the University of Nottingham and Pablo Murcia, EVJ’s Latin American Editor, based at the Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, the collection covers aspects of the control of equine influenza, immunology in young horses and herd immunity.
The first inactivated virus vaccines for the control of equine influenza became available in the late 1960s and there are now several licensed vaccines for horses. The protection induced by an equine influenza vaccine depends on the antigenic relatedness of the strain(s) included in the vaccine to circulating strains encountered by horses. However, a vaccine containing a mismatched strain can still limit clinical signs of disease. In the paper What can mathematical models bring to the control of equine influenza? Janet Daly and collaborators confirm that because a mismatched vaccine is poor at suppressing virus replication and shedding, the likelihood of a large outbreak occurring increases.
In order to ascertain whether the equine influenza vaccines in use in Japan remain appropriate, Yamanaka et al’s 2015 paper assesses The potential impact of a single amino-acid substitution on the efficacy of equine influenza vaccines and suggests that vaccine efficacy may be compromised as a result of a single amino acid change.
The importance of including a relevant strain in vaccines emphasises the need for effective surveillance strategies. In the article on the Surveillance of equine influenza viruses through the Réseau d'Epidémio-Surveillance en Pathologie Equine (RESPE) network in France from November 2005 to October 2010 Legrand and collaborators show how surveillance improved the detection of equine influenza in France and highlight the importance of training in veterinary surveillance.
In addition to vaccine composition, strategic timing of delivery of vaccines to pregnant mares, foals and youngstock is an important factor for vaccine efficacy according to Perkins and Wagner’s paper The development of equine immunity: current knowledge on immunity in the young horse. Following this, a paper by Davis et al on the characterisation of immune response in healthy foals when a multivalent vaccine was initiated at age 90 or 180 days concludes that the immunity gap could be reduced if required.
On the subject of immunity gaps Cullinane and collaborators tested three different primary vaccination schedules applicable within the racing industry in the Comparison of primary vaccination regimes for equine influenza: working towards an evidence-based regime. The longer vaccination intervals were found to increase the length of the immunity gap between the first and second and second and third vaccine doses. However, the flexibility of the horseracing authority recommendations allows for strategic vaccination to boost immune responses immediately prior to an increased risk of exposure to infection.
Strategic vaccination can also be used to control the spread of equine influenza during an outbreak. Accelerated vaccination schedule provides protective levels of antibody and complete herd immunity to equine influenza by El-Hage et al suggests that an accelerated vaccination schedule may reduce the time taken to achieve ‘herd immunity’. In the study antibody levels were ‘boosted’ by the third dose and were similar to the values obtained in other studies using standard vaccination schedules.
Mathematical models have suggested that vaccinating young racehorses at six-monthly intervals rather than annually may reduce the risk of outbreaks occurring. A study on The impact of different equine influenza vaccine products and other factors on equine influenza antibody levels in Thoroughbreds by M Ryan and collaborators implies that over-vaccination may be an issue for horses in field conditions.
Celia Marr, editor of the EVJ said: “This important collection showcases the breadth of continuing research in what is the lynchpin for disease control and preventative healthcare in all equines. We hope it will both engage and inform our readers about the essential role and function of vaccines.”
Janet Daly continued: “We are proud to have contributed to this important area of equine veterinary science and look forward to publishing more articles to help expand knowledge of equine vaccinology in future.”
The collection is available free online. It is available here.