Marek’s Disease in Chickens

There are several poultry diseases your backyard chickens can be vulnerable to, and which you need to be aware of to protect your flock and keep your birds in good health. Marek’s disease is one of these.

While many keepers of backyard chickens will never see a single case of Marek’s disease, it is, in fact, widespread and should a member of your flock become infected, the consequences can be tragic.

What is Marek’s Disease?

Chicken Health

Named after Josef Marek, a Hungarian veterinarian and the first person to identify it in 1907, Marek’s disease is a viral disease seen in chickens. It is caused by the herpes virus and there have, to date, been six mutations identified. ability to cause sickness depends on the strain.

This virus is predominantly spread through the infected skin cells (dander) of other birds. Able to survive for more than a year in coops and many years in soil, it can be transported via:

  • Clothing
  • Boots and shoes
  • Unclean hen carriers
  • Darkling beetles
  • Wild birds

The virus does not spread from hen to egg, but rather between chickens themselves. It is especially common in environments where chickens are crammed in together.

Chickens are most vulnerable to catching this disease between 5 and 25 weeks of age, though older birds are still at risk.

Symptoms in Chickens

Many birds with Marek’s disease are asymptomatic; they display no symptoms, and this may be due to having a non-pathogenic strain or the individual bird being resistant to the virus.

Those birds that do display symptoms may present in many ways and the effects may be neurological, cutaneous, visceral, and ocular. Some chickens will display all symptoms; others just a few.

At its core, Marek’s is a cancer-causing virus. It also increases the bird’s susceptibility to other diseases.

Most chickens with this disease will stop laying, and many will ultimately die.

Neurological symptoms are caused by the virus impacting the nervous system. These include:

  • Progressive paralysis, especially of the wings and legs
  • Head twisting to one side
  • Labored breathing
  • Purple, darkened comb
  • Diarrhea

Cutaneous symptoms affect the skin, such as ulcers, scabs, or other lesions around the feather follicles.

Ocular symptoms impact the eye. They include:

  • Blindness
  • Failure of the pupil to react to light
  • Greying of the eye
  • Misshapen iris

Visceral symptoms affect the internal organs and are usually identified only if a necropsy is performed after the bird has died. The bird will lose weight in life due to the development of cancer in the organs.

A vet should be called in to diagnose Marek’s disease in your flock.

Treatment for Marek’s Disease in Chickens

Silky Chickens

Currently, there is no cure or effective treatment for Marek’s disease. If the disease is not too severe, supportive care can bring chickens through without requiring them to be culled or euthanized. To protect your flock, however, diseased birds should be completely isolated and humanely euthanized if they do not recover or if symptoms are severe. Other birds will need close monitoring.

Once a bird has been infected, it will be a carrier for life. If one bird contracts the virus, it’s most likely that the entire flock will also. Birds with a strong immune system may survive but the virus will remain dormant in their systems; they may become sick if their immune system weakens at a later time.

Marek’s Vaccine for Chicks

While vaccination is available, it does not prevent chickens from catching the virus. It instead helps to minimize the severity of an outbreak, giving your chickens the best chance of recovery. This occurs by assisting the birds to build a natural immunity to the disease, minimizing its spread and symptoms, and reducing the likelihood of death if infected.

Another way to prevent an outbreak of Marek’s disease is to avoid adding hens to your existing backyard flock. If you do wish to introduce new birds, source them from a reputable supplier who practices strict quarantine measures.

Marek’s disease poses no risk to humans or other non-avian pets.

This virus is constantly mutating, and it’s crucial that you keep your flock healthy:

  1. Don’t introduce new hens to your flock without a careful selection from a reputable source and appropriate quarantine.
  2. Choose genetically resistant birds for your flock.
  3. Vaccinate your birds at one day old.
  4. Rear chicks separately from the adult flock.
  5. Clean and disinfect coops and sheds frequently.
  6. Maintain good nutrition.
  7. Treat your chickens to prevent parasites.

Caring for your backyard chickens means keeping them healthy and being aware of issues. Marek’s disease is just one of these, and being forewarned is forearmed.