Also known as: Midges
The most important veterinary species is Culicoides
This parasite is found worldwide and attacks humans and a wide variety of animals. The only genus of the family Ceratopogonidae of current veterinary significance is Culicoides.
It causes allergic dermatitis of horses, primarily affecting the base of the tail and the withers, and induces an intermediate-type hypersensitivity reaction to the midge saliva, known as 'Sweet itch'
Culicoides are small flies 2-5mm long with a dark colouring, more commonly known as biting midges. They have a characteristic arched thorax giving a 'hump-backed' appearance. The wings are mottled.
Eggs are laid onto plants near water and the larvae fall into water and pupate. The life cycle takes 6-12 months to complete in temperate climates, but can take only 1 month in tropical climates. Females of most species are adapted to sucking blood from the host.
Culicoides take blood meals from vertebrate hosts and breed in damp, dung-enriched soil, and so are abundant in the vicinity of domestic livestock. Once eggs are laid in the soil, Culicoides larvae progress through four stages and pupate before becoming an adult midge. The lifecycle is greatly influenced by temperature: in temperate regions such as Britain, the adult midge population declines in October and is absent by December. The fourth larval stage overwinters, and adults re-appear the following April. The environmental conditions also affect the activity of midges in several ways. Culicoides survive around 10 days in warm weather but up to one month when conditions are cooler and are most active at night, from an hour before sunset to an hour after sunrise. Activity is decreased by windy conditions, and increased during the day when the weather is dull.
The Culicoides species found in the British Isles are C. pulicaris and C. obsoletus, which are also common across central and northern Europe. Knowledge of the distribution of these species in the UK is incomplete but the insects tend to gather where breeding sites and hosts occur in tandem, with the highest midge concentrations in areas containing cattle, horses and pigs. Removal of livestock decreases populations of Culicoides by a factor of 10 to 201, but some persist by feeding on wild animals and man. Hill sites have fewer midges as climatic conditions are less favourable, and the presence of sheep encourages the midge population less than that of cattle.
In Britain, studies are ongoing to determine midge distribution, seasonal incidence and the competency of the various Culicoides species to act as BTV vectors.
Classically, the major vector for BTV is Culicoides imicola. This midge is found throughout Africa, the Middle East, southern Asia, Portugal, Greece, Corsica, Sardinia, Sicily and areas of Italy1, and its distribution appears to be extending northwards. However, C. imicola has not yet been demonstrated in the United Kingdom.
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