Hypoderma commonly known as ‘cattle grub‘ are primary parasites of bovines and have great economic importance.
Larvae of Hypoderma species have been reported also in equines, sheep, goats, and rarely in humans. Adult Hypoderma is approximately 15mm long, hairy, barrel-shaped bee-like in appearance and known as heel or gadflies.
Species; There are two species. One is H. Bovis (common cattle grub) and second is H. lineatum (northern cattle grub) the important spp.
- Distribution
The common cattle grub occurs naturally in bovines in at least 50 countries in Africa, Asia, Europe, and North America.
- Life Cycle
Hypoderms are active only in warm weather so they attach their eggs on the hair of cattle, particularly on the legs above hook joint. The eggs hatch in 3–7 days, and first-stage larvae crawl down to the base of the hair shaft and penetrate the skin by secreting proteolytic enzymes that facilitate their movement and cause considerable irritation.
When the parasites arrive under the skin of the back, swellings begin to form, measuring about 3 cm in diameter. The skin over each swelling becomes perforated and hence they play their role in degrading and condemnation of hides. During the development of the larvae, two molts occur, producing a total of three instars.
- Veterinary Significance
When they approach animals to lay eggs their characteristic buzzing noise causes the animals to panic. Cattle become anxious and attempt to escape the attack by running away, by gadding and will even go into the water.
The animals may also hurt themselves severely on posts, barbed wire, and other obstacles. H. Bovis making repeated buzzing attack due to this the animals are constantly irritated and do not feed properly, which results in an appreciable loss of weight and decrease of milk yield by dairy cows.
L3 larvae under the skin damage the adjacent flesh and this requires trimming from the carcass the greenish gelatinous tissue called butcher’s jelly. Hypoderma lineatum causes great damage to the cattle to hide and it became useless, annual loss due to this factor is very high in some countries. Young cattle and calves are more commonly and more brutally infected than older animals.
- Management
By mechanical removal of larvae: From the warble swelling mature larvae may be clutched out. This technique is more effective when the larvae are mature. Rupture of the larvae during removal may lead to local inflammation and abscess establishment.
Insecticide treatment: Hypoderma is susceptible to ivermectin and to systemically active organophosphates. By using systemic insecticides we can control larvae while they are in the early stages of migration and before they reach the backs of the animals.
Organophosphorous preparations can be given orally, sprays, bolus form but the most convenient way is to pour on. Ivermectin is given by subcutaneous injection. Severe reactions may occur due to the death of larvae in the wall of the esophagus or spinal canal that’s why these compounds should be avoided in January and February.