Everyone knows that he alth 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, eliminate them in time.
In the article we will talk about such an ailment as Marek's disease in chickens. Consider its main signs, 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 becomes a carrier of the infection at the time of infection and, if all necessary measures are not taken, it can infect the rest.
The virus not only enters the body of the bird, but is also released into the environment: food, feathers, dust, and so on - everything is infected and retains its destructive properties for a long time. For example, at a temperature+20-25 degrees, the virus remains active for several more months, and at temperatures up to +4 degrees - for several years.
The only thing that can please at least a little in this situation is that an aggressive agent dies at a high level of humidity. This means that it is most likely not inherited from chicken to chicken.
Causes of disease
What contributes to the occurrence of the disease named after the scientist Marek? The disease manifests itself as a result of the defeat of the bird's body by a DNA-containing virus, which is called "herpesvirus". It interferes with the formation of virus-neutralizing antibodies and is distinguished by interferonic activity.
As mentioned above, the causative agent of the disease is able to survive in the external environment within one year.
Routes of infection
Marek's disease (it often affects domestic birds) involves infection by airborne droplets (aerogenic). 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 skin-feather follicles.
As a result, Marek's disease can be transmitted to other birds through feathers, down, food, water, dust, or spread by insects.
Incubation period
At the initial stage of the disease, there are no specific signs. The appearance of a problem can be suspected only by the pallor of the crest, weakness and exhaustion of the bird, unnatural gait or posture. In addition, the chickenstart to worry. If the disease affected a large number of individuals at once, there is a possibility of depression in birds, which will lead to dehydration and rapid weight loss.
After an incubation period that can last from 2 to 15 weeks, Marek's disease in chickens begins to manifest itself more pronounced.
Acute Marek's disease and its symptoms
The acute form of the disease is characterized by weight loss, loss of strength, refusal to feed, paralysis and paresis, incorrect body positioning (head, legs, tail, wings), digestive problems. If the bird's eyes were affected by the virus, then this threatens it with a very rapid loss of vision.
The acute form is characterized by a rapid incubation period and the disease itself. Typically, a chicken dies between 1 and 5 months of age.
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 accurate diagnosis.
Classic form of Marek's disease and its symptoms
There is also a classic form of such a problem as Marek's disease. Symptoms in this case will be as follows: the iris of the eyes changes its color to bluish or gray, the pupil becomes pear-shaped or multifaceted, the tail and wings hang down, the neck twists, the bird begins to limp.
These changes are associated with nerve damage, which caused paralysis of the entire body or some of its parts.
The incubation period for the classic form of the disease can last within 2-3 months. The hen dies between 5 and 16 months of age.
In order to have an idea of how the eyes of a bird change when a diagnosis of Marek's disease is made, 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
There are often cases when chickens recover, and after some time (about 2-6 weeks) they 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 only find them after the death and opening of the chicken. They appear in the form of numerous foci of tumor development on a particular organ. The most commonly affected are the heart, stomach, liver, lungs, kidneys, pancreas, ovaries and testes, bursa of Fabricius, 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 have a bumpy or smooth surface with the inclusion of focal or diffuse gray nodules on it.
Diagnosis of 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 a bioassay onchickens, chicken embryos, analyzes in cell culture. As for serological tests, RNF, RDP, RIGA are used.
Additionally, it is necessary to conduct a differential diagnosis, which will help to exclude the presence of hypovitaminosis B and C, leukemia, viral encephalomyelitis.
Marek's disease in chickens: treatment
Are there ways to get rid of the problem? Unfortunately, the treatment of Marek's disease is very rarely effective, since there are simply no special remedies that will help defeat 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 has already been paralyzed, the chances of a successful recovery are close to zero.
That is why a special vaccine against Marek's disease was developed, which will help build immunity from the virus and protect the bird. Let's talk about this in more detail.
Vaccination against Marek's disease
It's worth starting with the fact that only a qualified specialist (veterinarian) should vaccinate. It is impossible to do this on your own.
It is also important to take into account the fact that acquired immunity is not transmitted from chicken to chicken. Therefore, it is mandatory to carry out immunization of each generation of poultry.
Chickens are usually vaccinated with a live vaccine that containscomposed of a weakened strain of the virus. Immunity of a young organism easily copes with it and, as a result, further immunity to it is developed, which lasts until the end of life.
For maximum efficiency, it is recommended to vaccinate a chicken during the first day of its life. After that, the procedure is repeated two weeks later (on the fifteenth day).
Let's take a look at a brief summary of the three most well-known vaccines that will help avoid such a nuisance as Marek's disease.
Vaxxiek HVT+IBD (Vaxxiek HVT+IBD)
The vaccine is available as 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 Gumboro disease in chickens.
The product contains:
- SPF fibroblast cell culture of chicken embryos that were infected with recombinant turkey herpes virus;
- dimethyl sulfoxide (cryoprotectant).
Before use, the vaccine must be diluted with a special solution from Merial according to the instructions attached to it.
Means contributes to the formation of immunity to Marek's disease after a single application. The effect lasts throughout the life of the bird.
Shelf life of the drug, subject to allnecessary transportation and storage measures is 3 years (36 months). Upon completion, the use of the product is prohibited.
The drug is subject to immediate disposal in cases where:
- no marking on the vaccine ampoule;
- the tightness or integrity of the closure was broken;
- content has changed its color or texture;
- flakes or other impurities appeared in the ampoule;
- vaccine was thawed and not used for one hour after reconstitution.
Disinfection of the agent involves boiling it or treating it with 5% chloramine and 2% alkali solution in a 1:1 ratio 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:
- SPF fibroblast cell culture of chicken embryos infected with turkey herpes virus and Marek's disease;
- bovine 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 has no medicinal properties and is completely harmless.
The product is subject to disposal in the same cases that were described whenreview of Vaxitec vaccine.
Rispens CVI-988 (Rispens CVI-988)
The product goes on sale in the form of a frozen suspension. In its composition it contains:
- SPF fibroblast cells from chicken embryos that were infected with Marek's disease;
- bovine 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) at a temperature of -196 degrees Celsius.
Immunity after the application of the vaccine is formed on the 7-14th day and persists throughout the life of the bird.
Methods for the prevention of Marek's disease
Prevention of the disease primarily consists in immunization, which was discussed in the previous sections of the article.
Besides this, you need to follow a few more simple rules.
- Organize separate keeping of chickens by age groups. It is important to pay 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 culled and destroyed. This will help avoid infecting other birds.
- As you can see, preventive measures are quite simple to implement. At the same time, their observance will prevent the occurrence of the disease and maintain the he alth of the entire poultry farm.
Summing up
Undoubtedly, Marek's disease is a very serious problem for poultry farmers. The disease affects chickens and causes them blindness, paralysis, paresis and death. Another fact that greatly complicates the current situation is that a cure for the disease has not yet been invented, and treatment with anti-inflammatory drugs is not very effective even at the initial stages. The only thing farmers can do to preserve the he alth and life of chickens on the farm is to carry out timely vaccination and follow simple prevention rules.
