Marek's disease

The Marek 's disease is a named after Joseph Marek (1868-1952) viral disease of chickens, rare other gallinaceous birds. It is accompanied by a proliferation of T lymphocytes ( lymphoproliferativ ) in nerves, intestines, gonads, iris, muscles and skin. The Marek 's disease is a notifiable disease.

Pathogen

The causative agent of Marek's disease is the chicken herpes virus 2 ( GaHV -2) from the Alphaherpesvirinae subfamily. It occurs in various strains that differ in their virulence. It is related to the turkey herpes virus, but not identical.

Disease emergence and spread of

The disease manifests itself mainly in young animals, from the 13th week of life, morbidity decreases significantly. Old animals (after the first laying period ) may remain without clinical symptoms.

Infection occurs via the airways (via air ), both by breathing the virus on material as well as through busy vectors like bird mites, fleas and ticks. Even inanimate vectors such as skin scales, feathers, feed, dust, and everyday objects play a role in the spread.

Infected animals shed the virus from one week after the infection on failing feathers, feces and saliva of a lifetime. Within a herd, the virus spread within weeks all animals.

After the primary colonization in the lungs, there is a washout in the blood ( viremia ) and the colonization of lymphoid organs ( thymus, spleen and bursa of Fabricius ). In the bursa of Fabricius there is a loss of lymphoid follicles in the thymus to a shrinkage of the cortex (cortex ). Later in the feather follicles, nerves, iris (Iris ) and intestines are colonized about 10 days after infection, a cell-associated second Viräme and leads to the formation of nodular lymphocyte accumulations T ( lymphomatose ). The extent of the disease is also determined by immune status and previous infections. Had the animal before contact with weakly virulent strains remains mostly under the formation of lymphomas.

Clinical picture

The incubation period is 20 to 160 days. The Marek 's disease is highly variable in their image.

In the classic form dominates the colonization of the nerves and leads to paralysis in 12 to 16 -week-old animals. It occurs sporadically and the mortality is below 10 %.

The acute form occurs liable to disease in chicks up to the 8th week of life and leads to death, especially at 18-22 weeks old animals. There may also be late death at the beginning of the first lay. The mortality rate is up to 50%. The acute form manifests itself in skin elevations, leading to a rough skin, and lymphoma in the intestines.

Combat

No treatment is possible, which is why the fight focused on prevention. It is carried out by sanitary measures. A vaccination on the first day of life is possible, but is performed only in breeding and laying hens. Also the breeding of resistant chickens is attempted.

The Marek 's disease is notifiable.