Hypodermosis

Hypodermosis is a parasitic disease of cattle and other ruminants caused by the larvae of warble flies in the genus Hypoderma, most commonly Hypoderma bovis and Hypoderma lineatum. It is a temperate-zone condition known for producing conspicuous subcutaneous nodules, or warbles, along the animal’s back and body. The condition is primarily of veterinary importance because of economic losses from reduced weight gain, diminished milk production, and damage to hides.

The life cycle begins when adult flies lay eggs on the host’s hair. After hatching, the larvae penetrate the skin and migrate through subcutaneous tissues, eventually forming large nodules that house the developing larvae. The larvae emerge through breathing holes in the skin to complete their development before dropping to the ground to pupate. Adults then emerge to repeat the cycle. The migration and development typically occur over the warmer months, with the risk of economic impact spanning several months per year.

Clinical signs include visible warbles with swelling and a characteristic breathing hole along the back, local irritation, and reduced performance. In severe infestations, weight loss, decreased feed efficiency, and hide damage can be significant. Diagnosis is mainly based on the presence of characteristic nodules and the timing of fly activity; post-mmortem examination can confirm the species involved.

Control and prevention rely on timing targeted anthelmintic treatments to kill larvae before they reach the back, often using macrocyclic lactones or other licensed repellents and larvicides. Management practices and veterinary guidance are essential to limit outbreaks and protect production and product value. Hypodermosis can occasionally affect humans through accidental human infestation, but this is rare.