Vets tend not to be consulted over sweet itch in horses, pilot study finds

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A 16th-inch-long (1.6mm) female biting midge (Culicoides sonorensis) feeding on blood.
A 16th-inch-long (1.6mm) female biting midge (Culicoides sonorensis) feeding on blood. © Scott Bauer, USDA ARS

A small pilot study found a general reluctance to involve veterinarians in the treatment of horses with sweet itch, or summer eczema.

The condition, formally known as equine insect bite hypersensitivity (IBH), is a frustrating recurrent skin disease involving an immune reaction to the bites of Culicoides midges. There is no cure.

The hypersensitivity is caused by allergens in the saliva of the midges, and possibly other biting insects. This hypersensitivity leads to self-inflicted trauma that can result in bald patches, bleeding and crusting of the skin.

Currently, a combination of physical barriers and chemical repellents have been suggested to be the most effective way to control the midges and subsequent IBH.

The pony in the picture shows typical signs of sweet itch. In severe cases such as this, the scabs and sores extend all the way down the mane along the back to the base of the tail and are also seen on the flanks, belly and legs. Inset is a photograph of a typical response that occurs following an injection of Midge proteins. There is a small swelling in the area of skin that has been tested for sensitivity to midge extract in salt solution (square 2) compared to an area of skin injected with the salt solution alone (square 1).
The pony in the picture shows typical signs of sweet itch. In severe cases such as this, the scabs and sores extend all the way down the mane along the back to the base of the tail and are also seen on the flanks, belly and legs. Inset is a photograph of a typical response that occurs following an injection of Midge proteins.

“Overall, attitudes towards IBH suggested that the condition is a notable welfare and economic concern for stakeholders, but veterinary involvement tended to only be in more severe cases,” Hannah Lomas and Philip Robinson reported in the journal Veterinary Sciences.

“Further research is required in the future to improve understanding, management and potential treatment of this condition,” the pair, from Harper Adams University in Shropshire, concluded.

The pilot study involved sit-down interviews in central England with nine people involved in the horse industry across a range of roles, ranging from a veterinarian to hobbyist owners, a racing yard employee, a riding school employee, and a competition horse owner.

One respondent told Lomas, who carried out the interviews: “Because it is a well-known issue, I don’t think people do contact the vet. I’ve never contacted a vet over it because you sort of Google it … people have loads of different ideas on how to manage it.”

The interviewed veterinarian suggested that, with a wide range of possible management and treatment strategies, owners tended to use a trial and error approach to finding a successful combination that worked for them.

The vet continued: “I think there is always the temptation to try and manage it yourself, especially if you don’t know any better, and just try loads of different fly repellents and not really know the management changes like not turning them out in the morning and evening when they [the midges] are most active.”

Veterinary involvement, as far as several of the respondents were concerned, was likely only in severe cases, and when self-management had failed.

The general reluctance to involve vets arose despite the obvious welfare impact on horses, and the frustrations for owners in managing the malady, Lomas and Robinson said.

The pair’s aim in their pilot research was to gain an understanding of experiences with IBH, and to gauge opinions on the value of the various management strategies horse owners used to control it.

They found that awareness of IBH was generally high, particularly in those with experience of the condition. Indeed, six of the nine participants had previously owned a horse with IBH. Just one had no previous personal experience with the condition.

“Although the majority of participants were aware that IBH is caused by an insect, some were unaware of more specific details in relation to the fact that it is mainly caused by Culicoides midges.

“Those with previous experience of IBH commented on the significant effect on daily routines, and the associated cost implications.

“Most participants supported an integrated approach to hypersensitivity management, and this most commonly involved a combination of physical barriers and chemical repellents, but sometimes included feed supplementation.”

The use of fly rugs, moving horses into stables when the midges were most active, or moving the horses into areas the midges were less likely to inhabit, were strategies used, as well as repellents. Soothing lotions were also used on affected horses.

Three reported using dietary supplements, which included garlic, vitamin B12, Marmite and a herbal mix.

A Culicoides biting midge.
A Culicoides biting midge.

Discussing their findings, Lomas and Robinson said that while all those interviewed had some knowledge of IBH, only those with personal experience of the condition had a more advanced understanding.

Culicoides midges are recognized as poor fliers, making horses less exposed to midge bites in windy, open areas. “However, this was only mentioned once across the interviews, suggesting that it is not commonly known amongst equine stakeholders.”

“Overall, in terms of the management of IBH it was obvious that there were many different strategies available, and no consensus on what was best for a horse suffering from the condition.

“A lot of what seems to be done is based on what the individual had found to be effective in previous cases, or what other horse owners had recommended to them. The effectiveness of each strategy seemed to be dependent on individual circumstances and the severity of the case.”

The financial and time cost implications of managing IBH-affected animals may be one of the reasons associated with why some participants with previous experience with IBH would be wary of buying a horse with a history of sweet itch.

“What is significant is the general lack of veterinary involvement reported by these stakeholders, despite their frustrations about the condition and its impact on their horses.

“Instead, there was almost a resigned acceptance of the condition as a daily part of horse ownership in the spring and summer seasons, and a sense of managing as best they could, only involving veterinarians if the condition was deemed severe enough to merit the additional cost.

“It was clear that IBH can be a significant recurrent cause of suffering for susceptible horses.”

The pair suggested that a single set of recommended guidelines on IBH that provided scientific information could be beneficial. “This would not only increase knowledge of the condition across the industry, but could also make individuals better prepared when it arose in the future.”

There needed to be more collaboration between research professionals and industry stakeholders to manage IBH effectively and optimize horse welfare, they said.

A Pilot Qualitative Investigation of Stakeholders’ Experiences and Opinions of Equine Insect Bite Hypersensitivity in England
Hannah R. Lomas and Philip A. Robinson
Veterinary Sciences 2018, 5(1), 3; doi: 10.3390/vetsci5010003 

The pilot study, published under a Creative Commons License, can be read here

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