Q&A Webinar • From Signs to Solutions: Tackling Common Infectious Diseases in Horses

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Enalees were delighted to sponsor its 1st webinar addressed to all vet teams (vets & nurses). 

The team at EIDS (Equine Infectious Disease Surveillance) discussed and informed on the most common infectious diseases seen in the UK equine population. Vets present were able to ask their questions at the end of the webinar. We’ve listed the Q&A below.

DO STRAINS OF STRANGLES CHANGE LIKE FLU?

The EIDS team responded to questions raised as follows:

Yes, there is clear evidence from Abbi’s PhD project that the bacterium, Streptococcus equi (S. equi), that causes strangles in horses does naturally change over time due to changes in it’s genetic DNA and whilst this may be happening somewhat quicker than previously thought for this pathogen, it is still at a much slower rate than is evident for equine influenza (flu), which because it is an RNA virus (not a DNA like equine herpes virus) this occurs quite commonly. However, it is important to note that the changes observed in S. equi occur at a rate that is not sufficient to majorly change the ability of the bacteria to cause strangles or to render the new strangles vaccine, Strangvac, ineffective.

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HOW DO CLINICAL SYMPTOMS OF STRANGLES DIFFER FROM DAY TO DAY. WOULD AN OWNER SEE DIFFERENT SYMPTOMS OVER TIME?

The EIDS team responded to questions raised as follows:

The clinical signs of strangles in individual horses will follow a broadly similar pattern, assuming that the animal is fully susceptible to the disease (i.e. has not encountered the infection previously or has been vaccinated against the disease) – the first signs will usually be a fever as the horse’s body temperature rises in response to the infection and this is readily detected if the animal has its temperature regularly checked and recorded, ideally twice daily. Probably depending on the infectious dose, the raised temperature will certainly be evident for a number of days and can be quite protracted in severely affected horses. The horse with a raised temperature is likely to be off its food and careful observation may show that the animal has discomfort eating due to it developing a sore throat with the lymph nodes of the head beginning to be infected with S. equi, these begin to swell and develop abscessation and they will in time ‘point’ as the skin thins and rupture, discharging characteristic pus.  There may be a slight nasal discharge also in the earlier stages although the thick and copious discharge that may be associated with strangles is usually only evident later and is often associated with the lymph nodes in the head, called retropharyngeal lymph nodes, rupturing and being discharged via the guttural pouches and down the nose when the horse lowers its head – this often brings a degree of relief for the animal.

HOW RELIABLE AT DIFFERENT DISEASE STAGES IS NASOPHARYNGEAL SWABBING FOR STREP EQUI?

The EIDS team responded to questions raised as follows:

S. equi quite quickly (within hours in fact) moves from the mucous membranes of the nose and mouth, where the initial contact with the infection is made, to the draining lymph nodes of the head and after this time swabbing of the nose and pharynx (throat) will not generally recover S. equi. This can mean that an infected horse that is incubating the disease before signs become evident, is likely to test negative for S. equi on a nasopharyngeal swab and will only test positive once the infected lymph nodes rupture to produce a nasal discharge (from ruptured retropharyngeal lymph nodes), often copious and purulent or a discharge under the jaw (from ruptured submandibular lymph nodes).

ARE DONKEYS MORE SUSCEPTIBLE TO INFLUENZA, AND ARE HORSES MORE SENSITIVE TO OTHER AGENTS?

The EIDS team responded to questions raised as follows:

It is widely considered that there is a difference in the susceptibility of donkeys and horses to different pathogens and this is evidenced from descriptions of disease in different equids, although to what extent the more stoical nature of donkeys tends to mask the true effects of infectious disease in some situations. That said it does appear that donkeys are likely to be more severely affected by influenza virus than horses and this was recently evidenced with a major outbreak of flu in west Africa in 2019. It has also been suggested that strangles may be less severe in donkeys, although a newly discovered donkey adapted strain of S. equi is known to have caused significant disease among donkeys in parts of China. African donkeys are much less susceptible to African horse sickness than horses in which it is highly fatal, unless protected by prior vaccination. Unfortunately, not much research has been conducted on demonstrating and understanding these apparent differences in susceptibility between donkeys and horses.

HAS INFLUENZA TRANSMISSION BEEN REPORTED FROM A DOG TO A HORSE?

The EIDS team responded to questions raised as follows:

We are not aware that influenza virus has been transmitted from dogs to horses, although in theory where dogs (or foxhounds as was the case in the UK around 20 years ago) are infected by horses with H3N8 equine influenza virus, infected dogs could be a source of infection for other fully susceptible horses. We are not aware of this ever being confirmed, nor are we aware that dogs in the USA, infected with a different canine influenza virus, H3N2, have acted as a source of this infection in horses either.

Key words: rapid testing, surveillance, biosafety, infectious disease, strangles (Streptococcus equi), equine herpesvirus myeloencephalopathy, equine influenza.

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