Mosquitoes are present on equine premises in the UK with horses at risk of attack, say scientists in a study funded by The Horse Trust.
The team, who studied the number of mosquitoes present in 32 equine sites – including riding schools and livery yards – around the UK, found the most abundant was a species called Ochlerotatus detritus, and was most commonly found on yards located near salt marsh.
The most widespread species of mosquito found in the study was a species called Culiseta annulata. It was recorded in more than three-quarters of the study sites and researchers say that Cs. annulata’s widespread presence and ability to breed in a variety of water sources makes it an important species for future research.
The paper, published in the Veterinary Record, concludes: “This work has shown that horses in the UK are at risk of attack from a wide variety of mosquito species, several of which are known to be vectors of equine arboviruses [viruses that are transmitted by arthropods] in affected countries.”
While there’s currently no likelihood of an outbreak of mosquito-transmitted viruses to horses in the UK, the scientists say their research shows that mosquito species which transmit viruses to horses in other countries are present here. Such species could pose a risk to horses in the future, should an arbovirus be introduced. The risk is expected to increase as climate changes occur and mosquito numbers rise in the UK as the insects thrive in warm conditions.
Gail Chapman, lead author of the paper, says: “The main relevance of this is in demonstrating that further research is required to see if there is potential for disease transmission in the UK situation, as horses are exposed to mosquitoes and exposure is likely to increase with increased abundance [of mosquitoes] with climate change.
“I think that the important thing for horse owners to know is that, at present, we have no evidence that there has been a significant increase in the risk of an outbreak of mosquito-borne disease. However, it would still be a good idea for horse owners to be aware of the importance of picking up any outbreaks early, for mosquito-borne disease.”
Both Oc. detritus and Cs. annulata are species that have the potential to carry a number of viruses including West Nile virus.
West Nile virus leads to encephalitis (a condition that causes inflammation of the brain) and can affect horses and humans. The virus is transmitted from birds by mosquitoes, but it’s not contagious from horse to horse or horse to human.
An outbreak of West Nile Virus was seen in horses in North America in the late nineties, but it’s unclear whether a similar situation could arise here in the UK.
Gail explains: “Presumably, if WNV can travel to America, it can travel to the UK so there is some risk of introduction of this virus – but this doesn’t necessarily mean an outbreak can occur. It should also be noted that some of these diseases have very complicated transmission cycles and therefore risk of introduction of virus into the country is very difficult to assess.
“There are several reasons why the UK is far less likely to have an outbreak (particularly of WNV) of the scale of the one seen in America. Birds are the main hosts that can infect mosquitoes, and many of our migratory birds may have been exposed to WNV in southern Europe or Africa, and therefore will be immune and no longer produce virus in the blood, and will not infect mosquitoes in the UK. In the US, the bird population was naïve to the virus and didn’t have immunity, meaning there were a high proportion of birds with virus in the blood in outbreak areas.”
“While we cannot say that there will never be an outbreak of WNV in the UK (with regards to climate change), it would seem likely that we would perhaps see increased outbreaks in other European countries before the UK – for example outbreaks in southern France would spread further north in France as temperatures and vector populations increased with climate change, before reaching the UK.”