Melophagus ovinus, also known as the sheep ked, is a bloodsucking Dipteran insect (family Hippoboscidae) that has domestic sheep as its primary host, but can be occasionally found in goats too, especially if they graze together with sheep.
Sheep keds are native to Europe and prefer regions with cold to moderate weather. Nowadays it is found also in North and South America, parts of Asia and Africa, Australia and New Zealand. In endemic regions more than 30% of the sheep flocks may be infested with keds.
Sheep keds are obligate parasites, i.e. they cannot complete their life cycle without parasitizing their hosts.
The disease caused by Melophagus ovinus is called melophagiasis.
Sheep keds do not affect cattle, swine, poultry, dogs or cats.
Are sheep infected with Melophagus ovinus contagious for humans?
- NO. The reason is that this species is not a human parasite.
Biology and life cycle of sheep keds
Adult sheep keds are hairy insects, 3 to 6 mm long, and resemble ticks (although they have only six instead of eight legs as adult ticks). They belong to the Dipteran insects but have no wings and do not fly at all, but remain their whole life on the same host. Their legs end in strong claws that they use for firmly attaching to the host's wool. They feed on blood of their hosts. Off the host they do not survive more than 3 weeks.
Sheep keds live in the wool of sheep, preferentially on the shoulders, the neck and the belly. Adult females are viviparous, i.e. they do not lay eggs but already hatched larvae. These larvae develop individually in the female's uterus until the reach the maturity (L3-larvae), usually about 1 week after egg fertilization. Each female deposits one larva per week, and a total of 15 to 20 larvae during her lifetime (70 to 150 days). Each larva is strongly attached to a wool fiber with a sticky material secreted by the female. Soon after being deposited these larvae pupate and the adults hatch about 3 weeks later. One to two days after hatching adults reach sexual maturity and mate.
Transmission between animals in a flock is by contact: the closer the contact, the faster and efficient is transmission to other animals. Most frequent transmission is from ewes to their lambs after birth, often in spring. At this time of the year keds tend to be close to the surface of the wool. Since adult sheep are often shorn at this time of the year, keds tend to migrate to the lambs that have longer wool.
In regions with a temperate climate and cold winters sheep ked infestations have a seasonal development and are a typical winter pest, together with lice and mites. Populations peak at late winter and early spring. This is due to the fact that sheep housed during the winter offer ideal conditions for ked development (long wool, constant temperature, high humidity) and transmission (crowding).
Harm to livestock and economic loss due to sheep keds
Ked infestations can be quite harmful for sheep. Each ked bites its host repeatedly, not only once as ticks do. And these bites are very irritating. Affected animals bite themselves, scratch and rub vigorously, which damages the wool and can cause self-injuries that may become infected with bacteria. This weakens the animals and results in reduced weight gains, particularly in lambs. Milk production of dairy sheep can be significantly reduced too. Heavy infestations can also cause anemia. Deaths are uncommon, but heavily infested lambs can die if left untreated.
Ked excrements stain the wool and reduce its value. The numerous bites damage the sheepskins producing so-called cockels, a kind of pea-sized nodules. The consequence is that the hides are downgraded after slaughter.
Prevention and control of infestations with sheep keds
In many endemic regions, ked infestations drop spontaneously in spring when the flocks are shorn and leave their winter quarters for the spring or summer pastures. Shearing eliminates a large number of keds and makes the micro-environmental conditions in the wool unsuitable for ked development because it reduces humidity and temperature on the skin surface. And once on pasture crowding ends and ked transmission too. Unfortunately a few individuals may survive until the next winter and will perpetuate the infestation in the flock.
To reduce the transmission of keds to newly born lambs it is recommended to shear the pregnant ewes shortly before lambing.
Chemical control of keds is often done with the same antiparasitics that are used for lice or scab prevention in fall, which are usually effective against sheep keds too. This is often done with concentrates for spraying or dipping that contain mainly synthetic pyrethroids (e.g. cypermethrin, deltamethrin) and/or organophosphates (e.g. diazinon, ethion, phoxim, etc.). Some ready-to-use pour-ons with similar active ingredients are also effective against sheep keds. Insect development inhibitors (e.g. diflubenzuron, triflumuron) used in some countries against lice are usually not effective against sheep keds at the therapeutic dose used against lice.
However, these products will kill only the adult keds in the wool, not the pupae. This means that such products must offer enough residual effect to kill the adults hatching out of the pupae (up to 4 weeks after pupation), or the treatment must be repeated 4 to 5 weeks later when all the pupae have hatched.
Macrocyclic lactones (e.g. abamectin, doramectin, ivermectin, moxidectin) available either as injectables, pour-ons or drenches are usually also effective against sheep keds and control many other external parasites as well as a number of gastrointestinal roundworms of sheep.
There are no true vaccines against sheep keds.
So far biological control of sheep keds (i.e. using its natural enemies) is not possible. Learn more about biological control of flies and other insects.
Click here medicinal plants for controlling flies and other external parasites of livestock and pets.
Resistance of Melophagus ovinus to insecticides
So far there are no reports on resistance of Melophagus ovinus to insecticides.
This means that if a product fails to achieve the expected efficacy, chance is very high that either the product was unsuited for the control of Melophagus, or it was used incorrectly.
Ask your veterinary doctor! If available, follow more specific national or regional recommendations for sheep ked control