Marek's disease in chickens: symptoms and treatment

Marek's disease is one of the common ailments among poultry, but ordinary hens and broilers suffer the most from it. Knowing how to recognize the symptoms in time, withstand quarantine, protect the livestock from death, you can protect yourself from large financial losses. The efforts spent on breeding are reduced to nothing due to the simple neglect of recommendations and non-compliance with preventive measures.

What is this disease?

Marek's disease is viral in nature, affects the tissues of internal organs and the functioning of the nervous system of birds.

There are three forms of the disease:

  1. Visceral - tumor growths on the internal tissues.
  2. Ocular (ocular) - partial loss of vision or complete blindness.
  3. Neural - consequences with paralysis and paresis in severe course.

The causative agent of Marek's disease

The causative agent of Marek's disease is the Herpes virus. The infection is high, infected chickens do not spread the infection through their external environment immediately, but 7–20 days after the virus enters their body. One individual can be a carrier from six months to two years, in some cases, a lifetime. But with the recovery of the chicken, it acquires a lifelong immunity, which it transfers to its offspring.

Did you know? There is no way to protect and prevent Marek's disease more effectively than timely vaccination.

Viral characteristics of the pathogen:

  • good adaptability to environmental conditions, at a temperature of +25 ° C it can be pathogenic for five months, preserved in litter, eggs, excrement;
  • affects at the cellular level.
Now there is no single special way to treat this disease, so when it is detected, the only thing that can be done is to conduct antiviral therapy, organize a quarantine zone, send the chickens to slaughter.

Sources and routes of infection

The route of transmission and infection is airborne. Insects: flies and ticks are especially dangerous as carriers of insects. An infected bird that exhales the virus also serves as a source of the epidemic. The virus spreads very quickly, entering the body through the respiratory tract. A bird can be a carrier, even when immune to the disease. In this case, she may not have any symptoms, she will be healthy. Therefore, to establish where it came from is not so simple.

History reference

The disease got its name in honor of the Hungarian veterinary researcher Jozsef Marek, who first described the disease in 1907. The scientist himself called it “chicken polyneuritis, ” but after the disease was still left associated with the name of its discoverer. In Russia, they learned about Marek’s disease only in 1930, taking up its study.

The development of a vaccine against the disease began only in 1970. Its basis is the use of active immunostimulants and virus strains for the production of antibodies in birds. Today, vaccination of young livestock is the main measure of its protection.

Economic damage

The rate of financial loss is quite high. Risks include:

  • large rejection of chickens;
  • tangible case of goals;
  • costs of quarantine measures;
  • spending on treatment, prevention;
  • reduced hen productivity.
For a large household, the infection can cause quite significant financial damage.

Symptoms and course of the disease in chickens

The symptomatology of the disease does not appear immediately - the incubation period can last from two to almost 22 weeks.

Factors affecting the development of the disease:

  • viral strain;
  • the number of bacteria that entered the body of an individual;
  • antibodies inherited from the mother;
  • the age of the chicken;
  • immunity.


Diagnosis consists of a number of symptoms, autopsy results, viral studies. The disease always comes in the form of an epidemic due to the rapid spread of infection. To confirm the diagnosis, the veterinarian sends the dead chickens to the laboratory. Accurate diagnosis requires five to ten dead individuals.

Important! It is important to have in mind the sensible veterinarian who can distinguish Marek's disease from leukemia, bird plague, Newcast's disease, poisoning and other related defects.

Pathogenesis and pathological changes

After the virus is in the lungs, it multiplies and travels through the body with blood flow. The peripheral lymphoid cells are affected; the brain, eyes, and muscles take very strong damage. Acute Marek's disease is more aggressive, internal organs suffer most, in the subacute type - eyes and nervous system.

External changes, except for those in the iris of the eye, with Marek's disease are rarely noticeable before an autopsy, after which the following pathological changes in the body are detected:

  • thickened nerve trunks;
  • tumor formations on internal organs (liver, pancreas, lungs, kidneys, ovaries, stomach);
  • muscle and skin deformity;
  • hemorrhage, swelling in the brain, spinal cord;
  • cell accumulation around blood vessels;
  • necrosis can be observed in the lens of the eye.
A more thorough study reveals other changes at the chemical level. About 25-30% of chickens also suffer from damage by the ovarian virus, and the heavier the course, the higher the risk of tissue dysfunction and mortality.

Forms of the course of the disease

Symptoms manifest themselves in different ways and depending on the form of the course of the disease, which has two varieties:

  1. Subacute (chronic, classical).
  2. Sharp.

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Below we consider the features of the symptoms in each of them.


A fatal outcome with a subacute type of ailment is likely no more than 30%. Damage to nerve cells, less often - to the eyes.

Symptoms of subacute Marek's disease associated with NS:

  • the chicken is limping;
  • the feathered wings sagged, the tail;
  • neck turned out;
  • semi-paralysis (usually temporary).
If the virus touches the eyes, this can be seen by the color of the iris - it becomes gray or with a blue tint. You may notice visual impairment in birds, as well as complete blindness. Changes in the pupil itself:

  • pear shape, narrow or other unnatural (not round) shape;
  • weak reaction to light or lack thereof.
A bird with eye damage dies in the period from a month to 1.5 years.


This option resembles leukemia. Young stock is more susceptible to this form, as well as chicks up to 5 months old. Since during the period of 7-20 days there may be no signs of the disease, often the entire herd of birds becomes infected.

The main symptoms are:

  • digestion is disturbed;
  • weight is reduced;
  • no appetite;
  • weakness.
Some chickens suffer from complete or partial paralysis. During the period of the disease, productivity decreases and a high mortality rate is recorded.

Quarantine and control measures

Ill chickens and roosters are isolated from healthy ones or immediately allowed for slaughter. To prevent the spread of the epidemic, disinfect the house. Chlorine, formaldehyde, phenol are suitable for this purpose. Egg incubation is possible only after the room has been treated with formaldehyde vapor four times and not earlier than a month after cleaning. There should be no litter, no litter, or even feathers or fodder from infected birds in the chicken coop.

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Methods for controlling the disease:

In normal adult chickensBroilers
Treatment with “Acyclovir” - helps only at an early stage, before signs of paralysis appear. It does not give a 100% guarantee of protection against death, it is used as antiviral therapy.The defeat of the livestock by 5-10% makes the treatment impractical for meat breeds. The bird is slaughtered, the room is being processed. To prevent the disease, broilers should be vaccinated 24 hours after hatching, with revaccination 10–20 days if necessary.

Can I eat meat and eggs from infected birds?

Marek’s disease is completely safe for people, so you don’t need to take any special precautions; you won’t get the virus. You can eat sick chicken meat and eggs if it has no signs:

  • Gospel disease (jaundice);
  • changes in muscle tissue (deformation);
  • anemia
  • noticeable internal changes.

It is advisable to heat the meat before use for 1.5 hours. Feather and fluff can also be used after thorough disinfection.

Disease Chicken Vaccine

To form an immunity against Marek’s disease in chickens, chickens should be vaccinated even at the age of one. Weakened herpes contained in the dosage provokes the production of antibodies to it. The drug is administered intramuscularly.

Important! After vaccinating chickens, do not worry if they are sleepy. Keep them warm for 2 days to prevent colds during immunity.

For vaccination use:

  • vaccines FSBI "ARRIAH";
  • strain based on turkey material;
  • "Nobilis";
  • "Intervet";
  • products of the Kursk Biofactory and Shchelkovo Biocombine;
  • Marex, Rospens, or Waxitec.
Vaccinated chickens are 90% protected against Marek's disease. Immunity is formed for ten days.

General preventive measures

In addition to vaccination, there are other preventive methods of combating the disease:

  • maintaining constant cleanliness in the house and yard for walking chickens;
  • separate keeping of adult chickens, young animals and chickens;
  • purchase of young animals, chickens, hatching eggs only from trusted, reliable breeders;
  • regular cleaning with disinfection of the house, yard;
  • washing and disinfection of feeders, drinking bowls.
The above methods will not protect against economic risks by 100%, but savings on vaccines, with a high probability, can cause serious losses and considerable problems.

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Faced with Marek’s disease in adult chickens, immediately vaccinate uninfected young individuals. Efficiency in this case will be lower than timely vaccinations, but the percentage of death will be less. Risks can always be minimized by treating farming as responsibly as possible.

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