AUSTRALIAN POULTRY FORUM™

Marek's Disease

Clinical Signs
Diagnosis
Similar Disease
Methods of Spread
Treatment
Prevention
Further Information

Marek’s disease (MD or fowl paralysis) is a very common disease of chickens caused by a herpes virus. Marek’s disease affects both commercial and backyard poultry and may result in death or severe production loss. The disease causes changes in many of the nerves and may cause tumours in major internal organs.

Chickens are the main species affected. The disease occurs rarely in some other types of birds.
Clinical Signs
Young birds are most susceptible to infection. Most deaths from Marek’s disease occur between 8 and 20 weeks of age, although in some cases the disease may be seen in birds as young as 3-4 weeks of age or as old as one year of age.

Typically, Marek’s disease occurs as the nervous form, appearing as a progressive paralysis of one or more of the limbs or, less often, the neck or wings. The sciatic nerve (the main nerve to the leg) is commonly affected The birds are unable to stand, become paralysed, appear uncoordinated and slowly waste away from lack of food and water. In most cases the paralysis comes on quickly. In some cases the eyes may be affected, resulting in blindness.

In the visceral form, Marek’s disease occurs as tumours in internal organs, including the ovaries, liver, spleen, kidney and heart. Sometimes the liver and spleen are swollen without distinct tumours being present. Birds may show signs of depression, paralysis, loss of appetite, loss of weight, anaemia (pale combs), dehydration (shrunken combs), and sometimes diarrhoea. Some birds die without any clinical signs being noticed.

Most birds that develop Marek’s disease usually die.
Diagnosis
Veterinary examination is necessary to diagnose Marek’s disease. The clinical signs, combined with post-mortem findings, will confirm the diagnosis in most cases, and, most importantly, rule-out other diseases. Enlargement of nerves such as the sciatic nerve are commonly seen at post-mortem. Changes in one or more internal organs may also be observed.
Similar Disease
A different viral disease known as lymphoid leucosis also causes tumours in organs, but does not cause paralysis. It is usually seen in birds over 16 weeks of age, whereas Marek’s disease is commonly seen in younger chickens.
Methods of Spread
Marek’s disease virus occurs commonly wherever chickens are raised and most chickens probably become infected. The virus is highly infectious and once introduced into a flock, it spreads rapidly to unvaccinated birds.

Infected chickens carry the virus for life whether they develop the disease or not, and continue to shed the virus for long periods. The virus is shed from the feather follicles and spreads readily in fluff and dust, gaining entry when the bird breathes infected dust particles. This material can also be carried by people and equipment.

The virus can survive in the environment for as long as several months at room temperature. It is not spread from the hen to the chicken through the egg.
Treatment
There is no treatment for Marek’s disease.

Diseased birds should be promptly removed from the flock and humanely destroyed. Other birds in the flock are likely to be infected at this stage also, so close monitoring of all birds is important.
Prevention
Although vaccines are commonly used in the commercial poultry industry, small numbers of doses cannot be purchased for use in backyard flocks.

For backyard flocks, the best protection against Marek’s disease is obtained by buying, from a commercial source, birds that have been correctly vaccinated.

Vaccination alone will not prevent Marek's disease. Particularly for commercial flocks, it is important to have good biosecurity to ensure that vaccinated chicks will develop immunity before they are subjected to a severe challenge of virus. For example, chicks need to be reared separately so that they are free from the infected fluff and dust of older birds. Standard hygiene measures are also important, including a thorough clean-out and disinfection of sheds and equipment between batches of chicks with a disinfectant effective against viruses. Good nutrition and maintenance of freedom from other diseases and parasites are also very important. These practices will help maintain the flock’s health and to ensure that the birds have optimum resistance against Marek’s disease infection.

For general advice on biosecurity, see the biosecurity checklist for bird keepers.

The breeding of genetically resistant strains of chickens, combined with the use of vaccination and good hygiene, can also be used to help control Marek’s disease.

For flocks with a serious Marek’s disease problem, the only solution is to depopulate, clean and disinfect all sheds and equipment, and spell for several months. Vaccinated chicks from a reputable hatchery would then need to be sought as replacements.

I have just become aware of Marek's Disease, and don't know whether our older chickens have been vaccinated. I know for sure that our 10wk old silkie chicks have not, and I would hate them to get sick.

Can they be vaccinated at a later age, or do they need to be done as very young chicks?

Thanks.

Deb

Hi Debbieo4914, Mareks usually hits between 5 and 25 weeks of age so keeping your youngsters separate from the adults and away from the poultry shows until they're over 5 months old is advisable. Over the age of 5 months it is best to cull them (any with clinical symptoms) as there is technically no treatment.

Thanks
Peacocks Australia

Are victoms of Mareks disease safe for humans to eat??

Peter

Not sure about eating them I'm sure someone on here will know!

I had all of my chicks vaccinated against Marek's yesterday, thanks to a local Pekin breeder. He did all of them, from my last babies (12 hours old) to my two silkie pullets (approx 4 months).

He did say that there was no guarantee with the older ones (or, I guess, with any of them), however as our flock is small and they may not have been in contact with the disease yet I feel better having had them all done.

I am really glad he offered to do all of that needling!

Deb

Hi Peter16, There is a Withholding period for Vaccinated birds & eggs, for unvaccinated victims of Mareks the body should be incinerated (not binned or buried)



Thanks
Peacocks Australia

ahk thanks

Peter

No that's great Kai, a point well worth mentioning, as they are similar in some symptoms will post something on Rickets soon!

Foot Note for others: Rickets is NOT a Disease; it's a Vitamin D deficiency.



Thanks
P.A

hi every1 i thought about getting mi flock done for the diese as i had some chooks with it. i bought them from a market (they "were vacinated") and lost some from tht i dont think mi orginal birds have got it but would prefer to get the young ones done and im hatching some new chicks soon and was wandering if i can by the vacineen or have to take them to the vet?

cheers stuart