Hypodermatosis

It is a parasitic disease caused by subcutaneous larvae of gadflies. Cattle and red deer are affected. Annual losses from under-receipt of milk, meat and reduction of quality (often culling) as a result of hypodermatosis constitute a huge economic loss.

Hypodermatoses of cattle

Hypodermatoses of cattle are caused by gadfly larvae:

- Hypoderma bovis (common scutellum, string) - when the adult gadfly flies up, the animals are disturbed, which causes the gadfly to attach one egg at a time

- H. lineatum (oesophagus) - approaches on grass, does not cause strong disturbance, and therefore attaches 5 to 20 eggs.

Developmental biology of bovine hypodermatosis

After the attachment of Hypoderma bovis or H.lineatum eggs to the hair, the formation of the larva inside the egg begins and continues for 3-7 days. Then the larva of Hypoderma bovis hatched from the egg penetrates through the skin, into the body of the host, migrate along the large vessels and nerves to the spine, and through the intervertebral foramen enter the spinal canal. The larva of H.lineatum hatched from the egg penetrates through the skin, into the body of the host, migrate towards the oesophagus and localise in its submucous layer.
 
The first-stage larvae of Hypoderma bovis and H.lineatum stay in the spinal canal and oesophagus for 5-6 months, after which they migrate again to the back and lumbar region. For further development, the larvae need oxygen, for which they form fistulae in the skin. Then they moult twice and as 3rd stage larvae exit through the fistula holes, fall to the ground, where they pupate. The duration of pupation is 20-40 days.

Sick animals are the source of infection. Young animals are infested (infected) more intensively than adults, with fistula capsules appearing 1 month earlier.

Larvae of the 1st stage, penetrating through the skin, cause pain and restlessness of the animal. A wound is formed at the site of penetration, from which a serous exudate (a clear liquid similar to blood) flows. Migrating in the body, the larvae cause tissue damage and inflammation develops. Later, the damaged areas are replaced by connective tissue. 

Large numbers of larvae in the oesophagus can impair its patency and in the spinal canal cause paralysis of the hind limbs. Larvae of stage 2 and 3 cause chronic inflammation, with connective tissue overgrowth around the fistula capsules, which leads to culling of the tannery raw material. In addition, the products of larvae lead to intoxication, emaciation and reduced productivity.
Symptoms of hypodermatosis

The main symptoms of hypodermatosis include itching, swelling of the subcutaneous fatty tissue, which is painful on palpation. At first, faintly visible seals appear, then they turn into tubercles with a hole in the centre. As the larva grows, there is an increase in the discharge from the fistula hole, which glues the hair.

Diagnosis is based on clinical examination and palpation of the skin. Early diagnosis of hypodermatosis is carried out in October-November using special diagnostic methods (ELISA ELISA).

Hypodermatosis of red deer

Maral hypodermatosis is caused by the larvae of gadflies

H.diana is a fly of medium size, up to 12 mm. Larvae of the 3rd stage differ in structure from larvae of this stage in cattle.

Developmental biology of hypodermatosis of red deer

Flies lay eggs on the thin summer hair of red deer. After 5-7 days larvae emerge, which penetrate the skin and within 2-3 months migrate to the intermuscular connective tissues towards the sacrum, back and lumbar region. Once development is complete, stage 1 larvae return under the skin and transform into stage 2 larvae, a connective tissue capsule is formed around them, and a fistulous opening is formed in the skin. In these capsules, second-stage larvae develop for 2.5 to 4.5 months, then moult and become third-stage larvae. The entire developmental cycle is completed in 8 to 10 months. Larval shedding and pupation occurs in spring. The pupal stage lasts 56-72 days.

Symptoms of red deer hypodermatosis

As the larvae traumatise tissues at the site of infiltration and migration routes, inflammation develops. Inflammation is particularly severe during the development of 2nd and 3rd stage larvae in fistula capsules. Tubercles (jaundices) with fistulous openings are clearly visible in the skin. In March-April, the hair of sick red deer is ruffled and contaminated with secretions from fistula capsules. When heavily infected, the animals are emaciated and sedentary.

Diagnosis is made on the basis of examination and palpation of the skin.

Treatment of hypodermatosis

For treatment in the early and late stages of hypodermatosis, injections of drugs based on ivermectin, eprinomectin and other preparations of this group are recommended