Rase Veterinary Centre

Text Box: Rase Veterinary Centre

Unit 1b Gallamore Lane
Market Rasen
Lincolnshire
LN8 3RX

Tel: 01673 842448
Fax: 01673 844430

Equine News Text Box: Issue 3

July 2006

Text Box: Sweet Itch

Sweet itch is an allergic skin condition caused by the bits of certain fly bites. It is a seasonal condition common to horses whereby the horse becomes allergic to the biting insect’s saliva. It is estimated that 3% of ponies in the UK suffer from sweet itch.
The main species of insect that causes sweet itch in horses is a midge known as Culicoides pulicaris. This type of fly tends to bite the areas around the mane and tail dock which makes these the most severely affected areas by sweet itch. The flies which cause sweet itch tend to inhabit wet, humid areas. So places such as ponds and ditches can be heavily infested with the midges. In dry regions sweet itch rarely exists as the conditions are unsuitable for the sweet itch causes insects. The most active time for the midges, and thus the time when they are most likely to bite is early evening and dusk.
Sweet itch does not develop over night; it takes a couple of summers of exposure to these biting flies to develop. Sweet itch then tends to worsen year by year. This is why younger horses, foals and yearlings very rarely suffer from sweet itch. Itchiness in younger horses is usually the result of an irritation rather than an allergy. A change in location can trigger sweet itch, otherwise sweet itch is first recognised in horses around 5 years of age. This is not to say though that it may not arise in older horses.

Sweet itch is a reoccurring disease, striking seasonally usually between the months of April and October yearly. The side-affects are hair loss, damaged hair and dandruff, usually targeting the mane and tail root areas. As the horse scratches on any available implements to help relieve the itchiness, they can often cause self-inflicted skin wounds and abrasions. As fly populations dwindle in the autumn, sweet itch cases also decrease. The colder months see the decline of sweet itch. This allows the infected horses to re-grow hair and repair damaged skin. A result of this can be that the hair on affected areas re-grows white.

It is well worth spending time and effort trying to eradicate the problem of sweet itch. And the only reliable way of preventing the disease is to ensure the horse is not bitten by flies. There are many products on the market to relieve the uncomfortable feeling sweet itch causes, but the best treatment to prevent the cause. Preventative measures include; stabling at the peak times of early evening and dusk, wearing a summer sheet, and fly repellent applied daily. Fly repellent products range from the ‘cheap and cheerful’ benzyl benzoate lotion to more modern permethrin containing repellents. More naturally based products containing garlic or citronella oil may help in some cases although there is a general impression that permetherin products are often more successful. When trying a new product it is often wise to try it out on a localised area of your horse’s skin first to make sure that you are not going to get a reaction to it.
One of the most reliable methods of sweet itch prevention though is to move the horse to an alternative location. Midges are not found everywhere, and so moving a horse to an area where there is restricted shelter and no water filled ditches may help cure the problem. Anti fly rugs/ sheets can also be useful.
Corticosteroids can be effective at reducing the itchiness sweet itch causes. One problem of using such drugs though is that they can cause laminitis as a side affect, and therefore their usage is restricted. Once bitten it can be a very time consuming process to cure sweet itch. Preventative measures once started cannot be relaxed throughout the season. Also the results of the treatment can take a long time to show up.
The satisfactory control of sweet itch is achievable in most cases but requires considerable and constant effort from the owner which is both inconvenient and time consuming.