Marek's disease

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Chicken paralyzed due to Marek's disease

The Marek's disease (also Marek's disease ) is a by Josef Marek (1868-1952) named viral disease of chickens , more rarely in other chicken birds . It is associated with an increase in T lymphocytes (lymphoproliferative) in nerves , intestines , gonads , iris , muscles and skin . Marek's disease is a notifiable animal disease in Germany under the Animal Health Act .

Pathogen

Chicken herpes virus 2
Systematics
Classification : Viruses
Area : Duplodnaviria
Empire : Heunggongvirae
Phylum : Peploviricota
Class : Herviviricetes
Order : Herpes viral
Family : Herpesviridae
Subfamily : Alphaherpesvirinae
Genre : Mardivirus
Type : Chicken herpes virus 2
Taxonomic characteristics
Genome : dsDNA linear
Baltimore : Group 1
Symmetry : icosahedral
Cover : available
Scientific name
Gallid alphaherpesvirus 2
Short name
GaHV-2
Left

The causative agent of Marek's disease is the virus species chicken herpesvirus 2 ( scientifically Gallid alphaherpesvirus 2 , GaHV-2) from the genus Mardivirus (acronym for outdated Marek's disease-like viruses ), subfamily Alphaherpesvirinae . The species occurs in different strains, which differ in their virulence .

It is related to the turkey herpes virus ( know Meleagrid alphaherpesvirus 1 , same genus), but not identical.

A disease with comparable symptoms can also be triggered by the closely related Marek's disease virus serotype 2 (MDV2), which belongs to the species chicken herpesvirus 3 ( English Gallid alphaherpesvirus 3 , GaHV-3, also in the genus Mardivirus ).

Disease origin and spread

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

Infection occurs via the airways (airborne), both through inhalation of virus-contaminated material and through animated vectors such as bird mites , fleas and ticks . Inanimate vectors such as peeling skin, feathers, animal feed, dust, and everyday objects also play a role in the spread.

From one week after infection, infected animals excrete the virus through falling feathers, feces and saliva for life. Within a herd, the virus spreads to all animals within a few weeks.

Lymphocyte infiltration of the iris in Marek's disease, left a normal eye

After the primary colonization in the lungs , it is washed out into the blood ( viraemia ) and the lymphatic organs ( thymus , spleen and bursa fabricii ) colonize . In the bursa Fabricii there is a shrinkage of the lymph follicles , in the thymus a shrinkage of the cortex . In the further course of the infection about 10 days after the infection, the feather follicles , nerves , iris and intestines are colonized by a cell-associated second virus and nodular T lymphocyte accumulations ( lymphomatosis ) are formed. The extent of the disease is also determined by the immune status and previous infections. If the animal has previously had contact with weakly virulent strains, the formation of lymphomas usually does not occur .

Clinical picture

The incubation period is 20 to 160 days. Marek's disease is very variable in its picture.

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

The acute form is epidemic in chicks up to the 8th week of life and leads to deaths especially in 18–22 week old animals. There may also be late deaths at the beginning of the first laying period. The mortality rate is up to 50%. The acute form shows up in bumps in the skin that lead to rough skin, as well as lymphomas in the bowels. The animals lose weight and die because cancerous cell growths have developed in the internal organs such as the liver, spleen or lungs.

Combat

Therapy is not possible, so control is focused on prevention. It takes place through veterinary hygiene measures. Vaccination, which usually takes place on the first day of life, is possible, but is only carried out in breeding animals and laying hens. However, this only protects against the onset of symptoms and not against the infection. The vaccine is only available in doses of 1,000 or more animals and must be used within a short time, which is why it is advisable to join forces and jointly vaccinate various hobby breeders. It is also possible to rely on the resistance of the chickens by means of breeding measures. However, it takes years for the infestation to be reduced in a farm.

In Germany, Mareksche disease is one of the notifiable animal diseases . There is no obligation to notify in Austria.

literature

  • Rolle / Mayr (ed.): Medical microbiology, infection and epidemic theory , Enke Verlag Stuttgart, 8th edition 2007. ISBN 3-8304-1060-3

Sources and individual references

  1. List at the BMEL , accessed on May 13, 2015.
  2. a b c d e ICTV: ICTV Taxonomy history: Human alphaherpesvirus 1 , EC 51, Berlin, Germany, July 2019; Email ratification March 2020 (MSL # 35)
  3. ICTV : dsDNA Viruses: Herpesviridae , in: ICTV 9th Report (2011)
  4. NCBI : Gallid alphaherpesvirus 3 (species)
  5. Jump up ↑ Wildlife - Marek's disease is treacherous. Retrieved January 5, 2020 .
  6. Jump up ↑ Wildlife - Marek's disease is treacherous. Retrieved January 5, 2020 .
  7. Annex to Section 1 of the Ordinance on Notifiable Animal Diseases (TKrMeldpflV) in the version published on February 11, 2011 ( Federal Law Gazette I p. 252 ), last amended by Article 381 of the Ordinance of August 31, 2015 ( Federal Law Gazette I p. 1474 )