Everyone knows that health problems can be not only in humans, but also in animals. For farmers who decide to start breeding chickens, it is important to consider that they may be susceptible to various diseases. Therefore, it is necessary to adhere to all the required preventive measures, and in case of problems - in time to eliminate them.
In the article, we will talk about such an ailment as Marek’s disease in chickens. Consider its main features, types, methods of prevention and treatment.
General information about the disease
The disease occurs as a result of damage to the cells of the bird's body and is an acute viral disease. At the same time, the chicken itself at the time of infection becomes the carrier of the infection and, if all the necessary measures are not taken, can infect others.
The virus penetrates not only the bird's body, but also is released into the environment: feed, feathers, dust and so on - everything is infected and retains its destructive properties for a long time. For example, at a temperature of + 20-25 degrees, the virus remains active for several months, and at a temperature of up to +4 degrees - for several years.
The only thing that can at least slightly please in this situation is that the aggressive agent dies at a high level of humidity. And this means that he, most likely, is not inherited from chicken to chicken.
The causes of the disease
What contributes to the occurrence of a disease named after the scientist Marek? The disease manifests itself as a result of damage to the bird's body with a DNA-containing virus called the herpes virus. It interferes with the formation of virus-neutralizing antibodies and is characterized by interferon activity.
As mentioned above, the causative agent of the disease is able to survive in the environment within one year.
Infection pathways
Marek’s disease (she often infects domestic birds) involves infection by the airborne (aerogenic) route. The main carrier of the infection is the affected chicken, which releases the virus into the environment. This can occur both through the respiratory tract, and through the digestive tract or feather-skin follicles.
As a result, Marek’s disease can be transmitted to other birds through feathers, fluff, food, water, dust, or carried by insects.
Incubation period
At the initial stage of the disease, there are no specific signs. The appearance of the problem can be suspected only by the pallor of the crest, weakness and exhaustion of the bird, unnatural gait or posture. In addition, the chicken may begin to show anxiety. If the disease immediately affected a large number of individuals, there is a likelihood that birds will develop depression, which will entail dehydration and drastic weight loss.
After an incubation period, which can last from 2 to 15 weeks, Marek’s disease in chickens begins to manifest itself more pronounced.
The acute form of Marek's disease and its symptoms
The acute form of the disease is characterized by loss of body weight, loss of strength, refusal to feed, paralysis and paresis, improper staging of the body (head, legs, tail, wings), digestive problems. If the bird's eyes were affected by the virus, then this threatens her with a very rapid loss of vision.
The acute form is characterized by a rapid course of the incubation period and the disease itself. As a rule, a chicken dies between the ages of 1 to 5 months.
The acute form of the disease is very similar to leukemia, therefore, after the death of a bird, it is important to transfer its body to a special laboratory for examination and making an accurate diagnosis.
The classic form of Marek's disease and its symptoms
There is a classic form of such a problem as Marek’s disease. Symptoms in this case will be as follows: the iris of the eye changes its color to bluish or gray, the pupil becomes pear-shaped or multifaceted, the tail and wings sag, the neck twists, the bird begins to limp.
These changes are associated with nerve damage, which caused paralysis of the whole body or some of its parts.
The incubation period with the classic form of the disease can last within 2-3 months. Chicken dies at the age of 5 to 16 months.
In order to have an idea of how the bird’s eyes change during the diagnosis of “Marek’s disease”, the photo below will serve as a good example.
As you can see, it is very difficult to confuse this disease with any other.
Internal changes
Often there are times when chickens recover, and after some time (about 2-6 weeks) still die.
This is due to the fact that Marek’s disease is also accompanied by changes in the internal organs of the bird. You can detect them only after the death and opening of the chicken. They appear in the form of numerous foci of tumor development on a particular organ. Most often affects the heart, stomach, liver, lungs, kidneys, pancreas, ovaries and testes, fabrika bag, nerves of the brachial plexus, skin.
The acute form of the disease affects one or more vital parts of the body, resulting in the death of the bird.
In this case, the liver and spleen are usually enlarged and differ in a tuberous or smooth surface with the inclusion of focal or diffuse gray nodules on it.
Diagnosis of the disease
Marek's disease can be diagnosed in special laboratories. For this purpose, the corpses of dead birds are sent there.
In order to accurately identify the cause of death, express diagnostics is provided, which includes bioassay on chickens, chicken embryos, and cell culture tests. As for serological reactions, RNF, RDP, RIGA are used.
Additionally, it is necessary to conduct differential diagnostics, which will help to exclude the presence of hypovitaminosis B and C, leukemia, viral encephalomyelitis.
Marek's disease in chickens: treatment
Are there any ways to get rid of the problem? Unfortunately, the treatment of Marek’s disease is very rarely effective, because there are simply no special tools to help overcome the disease. Therapy includes the use of standard antiviral drugs, but the likelihood of a fatal outcome remains quite high. For example, laying hens die in 50% of cases. It is noteworthy that broilers survive much more often - in about 90% of cases.
If the bird is already affected by paralysis, the chances of its successful recovery are close to zero.
That is why a special vaccine against Marek’s disease was developed, which will help to build immunity from the virus and protect the bird. Let's talk about this in more detail.
Marek's Disease Vaccination
It’s worth starting with the fact that only a qualified specialist (veterinarian) should be vaccinated. It is impossible to do it yourself.
It is important to take into account the fact that the acquired immunity is not transmitted from chicken to chicken. Therefore, it is imperative to immunize each generation of poultry.
Typically, chickens are vaccinated with a live vaccine that contains a weakened strain of the virus. The immunity of a young organism easily copes with it and, as a result, further immunity to it is developed, which persists until the end of life.
For maximum effectiveness, it is recommended to vaccinate a chicken already in the first days of its life. After this, the procedure is repeated two weeks later (on the fifteenth day).
Consider a summary of the three best-known vaccines that can help prevent such a nuisance as Marek’s disease.
Vaksitek HVT + IBD (Vaxxiek HVT + IBD)
The vaccine goes on sale in the form of a frozen suspension. It is packaged in 1000, 2000 or 4000 doses in 2 ml glass ampoules. All of them are fixed on special tripods and placed in a Dewar vessel with liquid nitrogen, in which (according to the instructions) the medication should be transported and stored. The drug is intended for the treatment of Marek's disease and Gamboro disease in chickens.
The tool contains in its composition:
- a fibroblast cell culture of chicken SPF embryos that were infected with a recombinant turkey herpes virus;
- dimethyl sulfoxide (cryoprotectant).
Before use, the vaccine must be diluted with a special solution of the company "Merial" according to the instructions attached to it.
The tool promotes the formation of immunity to Marek's disease after a single application. The effect is maintained throughout the life of the bird.
The shelf life of the drug, subject to all necessary transport and storage measures, is 3 years (36 months). At the end of the application is prohibited.
The drug is immediately disposed of when:
- there is no labeling on the ampoule with the vaccine;
- tightness or integrity of the capping was broken;
- the content has changed its color or consistency;
- flakes or other impurities appeared in the ampoule;
- the vaccine was thawed and was not used after that for an hour after dilution with the solution.
Disinfecting means involves boiling it or treating 5% chloramine and 2% alkali solution in a ratio of 1: 1 for half an hour.
Mareks Rispens + HVT (Marek's Rispens + HVT)
This drug is packaged in 1000 or 2000 doses and is in 2 ml ampoules. As in the previous case, the product is transported and stored in a Dewar vessel with liquid nitrogen. In this case, the temperature should be -196 degrees.
The composition of the drug includes:
- a fibroblast cell culture of chicken SPF embryos that were infected with turkey herpes viruses and Marek’s disease;
- cattle serum (stabilizer);
- dimethyl sulfoxide (cryoprotectant).
After using the vaccine, immunity in chickens is formed on the sixth day and remains until the end of its productive use.
The drug does not have medicinal properties and is completely harmless.
The product must be disposed of in the same cases that were described when considering the vaccine "Vaksitek."
Rispens CVI-988 (Rispens CVI-988)
The product goes on sale in the form of a frozen suspension. In its composition it contains:
- fibroblast cells of chicken SPF embryos that were infected with Marek's disease;
- cattle serum (acts as a stabilizer);
- dimethyl sulfoxide (cryoprotectant).
The drug can be packaged in 1000 or 2000 ampoules and stored in a container with liquid nitrogen (Dewar vessel) at a temperature of -196 degrees Celsius.
Immunity after application of the vaccine is formed on the 7-14th day and lasts throughout the life of the bird.
Methods for the prevention of Marek's disease
Prevention of the disease primarily consists in the immunization, which was discussed in the previous sections of the article.
In addition, it is necessary to observe a few simple rules.
- Organize separate keeping of chickens by age groups. It is important to give special attention to chickens in their first days of life.
- Observe veterinary and sanitary rules in the chicken coop and incubators.
- If a disease is suspected, suspicious chickens should be immediately discarded and destroyed. This will help to prevent the infection of other birds.
- As you can see, preventive measures are quite simple to implement. However, their observance will prevent the occurrence of the disease and preserve the health of the entire poultry farm.
To summarize
Undoubtedly, Marek's disease is a very serious problem for poultry farmers. The disease affects chickens and causes them to blindness, paralysis, paresis and death. Another fact that significantly complicates the situation is that a cure for the disease has not yet been invented, and treatment with anti-inflammatory drugs is not very effective even in the initial stages. The only thing that farmers can do to preserve the health and life of chickens on the farm is to vaccinate on time and follow simple prevention rules.