Equine vaccination Flashcards
Why do we vaccinate horses
Protect individual animals
Protect groups of animals
Reduce shedding of pathogens
To comply with regulations
What makes horses different in the context of vaccination?
competition
yards
transport
the nature of equine influenza
the risk of tetanus
anatomical quirks – guttural pouches
What can we vaccinate horses against?
Licensed equine vaccines in the UK
Clostridium tetani (tetanus)
Influenza (EIV)
Streptococcus equi (strangles)
Equine herpesvirus (EHV)
West Nile virus (WNV)
Equine viral arteritis (EVA)
Rotavirus
Rabies
Equine influenza
Highly contagious viral respiratory disease – typically 100% of unvaccinated horses will be affected; milder disease where some horses only in a group vaccinated
Rapid outbreaks due to airborne route and contact-based spread including via horse handlers
Outbreaks have been exacerbated by movements of poorly vaccinated groups of animals for competition
In Australia in 2007 there was a widespread outbreak – have a look into this if you are interested
Clinical signs: lethargy, depression, loss of appetite, cough, pyrexia, dyspnoea if severely affected
Loss of respiratory mucosa leads to secondary infection as a common and serious complicating factor
Equine influenza evolution
Virus is single-stranded RNA and mutates readily – this causes antigenic drift making vaccines that are effective against newer virus types important (just as with human influenza)
The virus has two glycoproteins on its surface – haemagglutinin (H) and neuraminidase (N) hence the nomenclature, e.g., H3N8
Two original broad virus types were identified – equine 1 – an H7N7 type and equine 2 – an H3N8 type; the equine 1 type has not been isolated for several decades now so all recent outbreaks are due to H3N8
New strains (a strain is the particular virus isolated based on its genome) are named further based on where and when the outbreak was first recorded, e.g., Kentucky/98 and Newmarket/2/93 – you will notice that these are two of the world’s major centres for horse racing! The 2 of the Newmarket strain refers to the fact that this was the second outbreak in that location
From 1980 onwards there was a divergence of strain types into European-type and American-type; potentially confusingly, this did not mean that these types were only present in those locations. In 1993 there were two outbreaks on racing yards in Newmarket – Newmarket/1/93 and Newmarket/2/93. Both occurred at the same location at the same time but 1 was an American-type and 2 was a European-type
Further evolution has led
Equine influenza vaccines
All vaccines have been shown to reduce clinical signs and virus shedding
Virus shedding is particularly important
There is much discussion about which virus strains should be included although the OIE periodically update advice and is very clear that vaccine manufacturers should include the latest recommended strains in their vaccines. The current guidelines from 2016 state that this should include virus strains representative of both of the Florida Clades – 1 and 2. Only one manufacturer has done this.
Tetanus in horses
Clostridium tetani bacterial pathogen that can survive for a long time in the environment in soil, bedding, on objects such as fences and wire and nails
The bacteria produce a toxin that damages the nervous system
Horses and ponied particularly susceptible based on their environments and lifestyles – stabled, exercised, competition
They are very good at getting wounds e.g., penetrating foot injuries
Established infection is often fatal
Vaccination is highly protective
Tetanus anti-toxin can be administered and is considered useful to give whenever fresh wounds are suspected, especially in unvaccinated animals
Equine herpes virus
EHV is quite widespread and as with other herpesviruses can become persistently infected, lying dormant and re-emerging periodically
This means that vaccination is unlikely to be fully effective
Two herpesviruses are implicated in horse health: EHV 1 and EHV 4
EHV 4 can cause mild respiratory disease and occasional abortions
EHV 1 is more of a concern, causing abortion and/or neurologic disease depending on the exact strain
Vaccine efficacy claims are made for the protection of horses against EHV 1 or 4-related respiratory disease and abortion, but not neurologic disease
EHV vaccination is used largely for breeding establishments and sometimes competition yards
Strangles in horses
A bacterium, Streptococcus equi which is endemic in the UK causing outbreaks especially on yards with poor biosecurity
Clinical signs include pyrexia, cough, poor appetite, nasal discharge and swollen or abscessed lymph nodes of the head. Can be hard to manage and occasionally fatal
Spread though direct contact between infected horses and also via discharges spread through physical contact of grooms, farriers or veterinary surgeons. Survival in the environment can occur, particularly in water troughs
Good hygiene is therefore essential in controlling the disease and strict isolation should be practised in the face of an outbreak
Some horses can become persistently infected (most commonly in their guttural pouches)for months or even years. They can intermittently shed bacteria thus spreading disease
In order to manage outbreaks and declare horses free of infection, horses need to be repeatedly swabbed taking a nasopharyngeal sample and ones from both guttural pouches
A vaccine is available to reduce clinical signs and try to prevent abscessation
It is intended for use in horses where a risk of infection has been clearly identified, due to contact with horses from areas where Strangles is known to be present, e.g., stables with horses that travel to shows and/or competitions in such areas, or stables that obtain or have livery horses from such areas
Equine viral arteritis
The virus is an issue in breeding situations
It is an uncommon but very important and notifiable disease which means if suspected it must be reported to the Animal & Plant Health Agency (APHA)
Stallions can be asymptomatic and spread to mares who can become clinically affected
Mares can spread to foals and also other stallions subsequently mated
Spread is via mating, artificial insemination, contact with aborted foetuses, contaminated equipment and materials and droplets on the breath of infected animals
Clinical signs of EVA include abortion, pyrexia, lethargy, depression, swelling of the lower legs, conjunctivitis, nasal discharge, and swelling of the scrotum and mammary gland
Vaccination and strict biosecurity measures around breeding establishments and their practices are important
Stallions should be vaccinated and testing of mares is very important – certification for export is required
West Nile virus in horses
WNV is not currently present in the UK: it is a notifiable disease and should be reported to SPHA if suspect
Insect vectors are implicated in spreading the disease which suggests seasonality should it arrive in the UK
Clinical signs include pyrexia and neurological (tremors, ataxia) and mortality can be high
There is a risk of introduction from imported horses and from travelling horses and people; WNV is in southern and eastern parts of Europe and endemic in the USA
A vaccine is now licensed for use in the UK
Routine vaccination is not recommended. Horses travelling to endemic areas should be vaccinated
Rotavirus in horses
Rotavirus can cause diarrhoea in foals
Mares can be vaccinated in late pregnancy to establish good colostral and milk levels for passive transfer to the foal
Biosecurity and checking of adequate passive transfer of immunity in general in breeding establishments is very important and vaccination should augment not replace these practices
Rabies in horses
Rabies virus is not present in the UK horse population
There is a vaccine licensed for use in multiple species which may be indicated for travelling animals
Vaccine regulations
Influenza is mandatory in many competition settings
Historically the Jockey Club created rules for racehorses, more widely adopted and that have persisted for many years
A primary course of two injections given between 21 and 92 days apart
A third injection given between 150 and 215 days after the second injection
Annual boosters are required thereafter (must be given within 365 days of previous injection)
However,following the Equine Influenza outbreak in 2019, many regulatory bodies and competition centres require 6 monthly boosters, to reduce the risk of transmission at large events
In 2019 British Riding Clubs, British Dressage and British Eventing made 6 monthly influenza vaccinations mandatory even at a relatively local level
It is also important to note that horses cannot compete until 7 days after their 2nd vaccination of a course
The Fédération Équestre Internationale (FEI) has a six-monthly requirement for ‘booster’ vaccination
What should we vaccinate horses against?
As you can now appreciate, each situation requires a specific review regarding the need for vaccination and which vaccines should be used
A solitary pony will have limited risk from most infectious diseases and may require tetanus only. However, any movements, new horses being introduced nearby and contact from the owner with other horses may change the risk level
