Marek's disease in poultry; cause, symptom, prevention and control

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Marek's disease in poultry; cause, symptom, prevention and control

Marek disease is a highly contagious viral disease of poultry characterized by T-cell lymphomas and peripheral nerve enlargement. Although no treatme
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Standard criteria used for diagnosis include history, clinical signs, gross necropsy, and histopathology. Although no treatment is available, current vaccines are highly protective. Chickens are the most important natural host for Marek disease virus (MDV), a highly cell-associated but readily transmitted alphaherpesvirus with lymphotropic properties of gammaherpesviruses. Quail can be naturally i

nfected, and turkeys can be infected experimentally. However, severe clinical outbreaks of Marek disease in commercial turkey flocks, with mortality from tumors reaching 40%–80% between 8 and 17 weeks of age, were reported in France, Israel, and Germany. In some of these cases, the affected turkey flocks were raised in proximity to broilers. Turkeys are also commonly infected with turkey herpesvirus (HVT), an avirulent strain related to Marek disease virus that is commonly used as a Marek disease vaccine in chickens. Other birds and mammals appear to be refractory to the disease or infection. Marek disease is one of the most ubiquitous avian infections; it is identified in chicken flocks worldwide. Every flock, except for those maintained under strict pathogen-free conditions, is presumed to be infected. Although clinical disease is not always apparent in infected flocks, a subclinical decrease in growth rate and egg production may be economically important. Etiology of Marek Disease in Poultry
Marek disease virus is a member of the genus Mardivirus within the subfamily Alphaherpesvirinae. Within the genus Mardivirus are three closely related species previously designated as three serotypes of Marek disease virus. Gallid alphaherpesvirus 2 (MDV serotype 1) represents all virulent Marek disease virus strains and is further divided into pathotypes, designated as mild (m), virulent (v), very virulent (vv), and very virulent plus (vv+). Gallid alphaherpesvirus 3 (MDV serotype 2) and Meleagrid alphaherpesvirus 1 (turkey herpesvirus, MDV serotype 3) represent avirulent virus strains isolated from chickens and turkeys, respectively, and are commonly used as vaccines against Marek disease. Transmission and Etiology of Marek Disease in Poultry
Marek disease is highly contagious and readily transmitted among chickens. The virus matures into a fully infective, enveloped form in the epithelium of the feather follicle, from which it is released into the environment. It may survive for months in poultry house litter or dust. Dust or dander from infected chickens is particularly effective in transmission. Once the virus is introduced into a chicken flock, regardless of vaccination status, infection spreads quickly from bird to bird. Infected chickens continue to be carriers for long periods and act as sources of infectious virus. Shedding of infectious virus can be reduced, but not prevented, by prior vaccination. Unlike virulent strains of Marek disease virus, which are highly contagious, turkey herpesvirus is not readily transmissible among chickens (although it is easily transmitted among turkeys, its natural host). Attenuated Marek disease virus strains vary greatly in their transmissibility among chickens; the most highly attenuated are not transmitted. Marek disease virus is not vertically transmitted. Pathogenesis of Marek Disease in Poultry
Currently, four phases of infection with Marek disease in vivo are recognized:
Early cytolytic infection (productive-restrictive)
Latent infection
Second phase of cytolytic, productive-restrictive infection coincident with permanent immunosuppression
Proliferative phase, involving nonproductively infected lymphoid cells that may or may not progress to the point of lymphoma formation. Productive infection may occur transiently in B lymphocytes within a few days after infection with virulent Marek disease virus strains and is characterized by antigen production, which leads to cell death. Because few if any virions are produced, this has also been termed a restrictive-productive infection. Productive infection also occurs in the feather follicle epithelium, in which enveloped virions are produced. Latent infection of activated T cells is responsible for the longterm carrier state. No antigens are expressed, but virus can be recovered from such lymphocytes by cocultivation with susceptible cells in tissue cultures. Some T cells, latently infected with oncogenic Marek disease virus strains, undergo neoplastic transformation. These transformed cells, provided they escape the immune system of the host, may multiply to form characteristic lymphoid neoplasms. Clinical Findings of Marek Disease in Poultry
Marek disease, leg paresis, chicken
Marek disease, leg paresis, chicken
COURTESY OF DR. JEAN SANDER. The incidence of Marek disease is quite variable in commercial flocks and depends on:
strain and dose of virus
age at exposure
maternal antibody
host gender and genetics
strain and dose of vaccine virus
several environmental factors, including stress
In addition to lymphoid neoplasms, Marek disease virus can also induce other clinically distinct disease syndromes, including:
transient paralysis
early mortality syndrome
cytolytic infection
atherosclerosis
persistent neurologic disease
Typically, affected birds show only depression before death, but a transient paralysis syndrome has been associated with Marek disease; chickens become ataxic for periods of several days and then recover. This syndrome is rare in immunized birds. Death is usually the result of paralysis, rendering the birds unable to reach food and water. Lesions
Marek disease, peripheral nerve enlargement, chicken
Marek disease, peripheral nerve enlargement, chicken
COURTESY OF DR. JOHN DUNN. Marek disease, skin involvement, chicken
Marek disease, skin involvement, chicken
COURTESY OF DR. JEAN SANDER. Marek disease, eye involvement, chicken
Marek disease, eye involvement, chicken
COURTESY OF DR. JEAN SANDER. Enlarged nerves are one of the most consistent gross lesions in affected birds. Various peripheral nerves, but particularly the vagus, brachial, and sciatic, become enlarged and lose their striations. Diffuse or nodular lymphoid tumors may be seen in various organs, particularly the liver, spleen, go**ds, heart, lung, kidney, muscle, and proventriculus. Enlarged feather follicles (commonly termed skin leukosis) may be noted in broilers after defeathering during processing and are a cause for condemnation. The bursa is only rarely tumorous and more frequently is atrophic. Histologically, the lesions consist of a mixed population of small, medium, and large lymphoid cells plus plasma cells and large anaplastic lymphoblasts. These cell populations undoubtedly include tumor cells and reactive inflammatory cells. When the bursa is involved, the tumor cells typically appear in interfollicular areas. Diagnosis of Marek Disease in Poultry
Standard criteria: history and clinical signs, gross pathology, and histopathology
Advanced criteria: immunohistochemistry, standard and quantitative PCR, virus isolation, serology
For the diagnosis of Marek disease, it is critical to diagnose the tumors and not the infection because Marek disease is considered ubiquitous within commercial poultry flocks. Usually, diagnosis is based on enlarged nerves and lymphoid tumors in various viscera. The absence of bursal tumors helps distinguish this disease from lymphoid leukosis, although the presence of bursal tumors does not exclude Marek disease. Marek disease can develop in chickens as young as 3 weeks old, whereas lymphoid leukosis typically is seen in chickens >14 weeks old. Reticuloendotheliosis, although rare, can easily be confused with Marek disease, because both diseases can feature enlarged nerves and T-cell lymphomas in visceral organs. Standard criteria are often sufficient for a presumptive diagnosis, but advanced criteria are needed for a definitive diagnosis. Immunohistochemistry can be used to confirm tumors are composed of predominant T-cell populations or expressing specific MDV antigens. There is a quantitative association between viral load and Marek disease tumors; most tumor-bearing chickens have high viremia titers and are usually PCR positive. Thus, the demonstration of high quantities of virus, viral DNA, or viral antigens in tumor cells and the exclusion of other relevant tumor viruses should be sufficient for a specific diagnosis of Marek disease. Control of Marek Disease in Poultry
There is no effective treatment for Marek disease
Prevention methods include vaccination, biosecurity, and genetic resistance
Vaccination is the central strategy for the prevention and control of Marek disease, along with strict sanitation to reduce or delay exposure and by breeding for genetic resistance. The most widely used vaccines include:
Turkey herpesvirus (HVT, naturally avirulent Meleagrid alphaherpesvirus 1)
SB-1 or 301B/1 (naturally avirulent Gallid alphaherpesvirus 3)
CVI988/Rispens (attenuated Gallid alphaherpesvirus 2)
HVT vaccine has seen rapidly increased use as a backbone in recombinant vaccines featuring the insertion of genes from other poultry viruses, such as Newcastle disease virus, infectious bursal disease virus, or infectious laryngotracheitis virus. These recombinant vaccines offer protection against both Marek disease virus and the inserted virus. Bivalent vaccines consisting of HVT and either the SB-1 or 301B/1 strains of Gallid alphaherpesvirus 3 have been used to provide additional protection against challenge with virulent Marek disease virus isolates. The most protective commercial vaccine currently available appears to be CVI988/Rispens, an attenuated Marek disease virus strain that is also commonly mixed with HVT at vaccination.

13/10/2022

Marek’s disease virus, a herpesvirus that is the causative agent of Marek’s disease, is a worldwide economic burden on poultry farming. However, little is known about the prevalence and dynamics of this virus in the field. Commercial poultry farming is highly structured, and so important questions are, how does virus prevalence differ across this structure, and how does virus prevalence change within a single level of this structure over time? To answer these questions, virus prevalence across farms in Pennsylvania for three years was surveyed. This involved collecting dust samples from chicken houses and using a qPCR (quantitative polymerase chain reaction) assay specific for non-vaccine Marek’s disease virus to assess the virus’s concentration in the dust.
In total, 4448 samples were collected across 15 operations, and 106 farms. These data were analyzed with generalized linear mixed effects models fit using Bayesian methods. Virus prevalence varied considerably in the collected data. Substantial amounts of variation were attributable to between operation, between grower, and between flock effects. A smaller magnitude of variation was attributable to between house effects and between sample effects. Also, significant effects of cohort age and seasonality were identified. Researchers were unable to identify a significant effect of production type, but it is unclear whether this was due to a lack of biological importance or due to sampling constraints. Examining the data from within farms over time confirmed many of the patterns discovered by the mixed effect modeling. These data also revealed apparent patterns of virus disappearance and reemergence, where the virus concentration dropped to below detectable levels only to reappear in later samples. Whether this was due to repeated extinction and reintroduction events, or due to virus population dynamics that occurred below the qPCR limit of detection is still an open question.

21/09/2022

The most protective commercial vaccine currently available appears to be CVI988/Rispens, an attenuated Marek's disease virus strain that is also commonly mixed with HVT at vaccination.
Vaccines are administered at hatch or in ovo to embryos at the 18th day of incubation.

21/09/2022

How Does Marek’s Disease Spread?
On a bigger scale, one infected chicken is enough to cause other chickens to get sick. As we have said earlier, this disease is easy to pass from one chicken to another. The infected chicken does not even have to be there to do this.
An infected chicken can spread this disease by simply living. For one, it will unconsciously shed its dander (skin flakes) where it goes. These flakes could then be a means of infecting other chickens.

21/09/2022

Causes of Marek’s Disease
The cause of Marek’s disease is a virus. Specifically, one linked to those that bring about herpes in humans. You do not need to worry. This one will not make you sick.

23/08/2022

Morbidity is 10-50% and mortality up to 100%. Mortality in an affected flock typically continues at a moderate or high rate for quite a few weeks. In 'late' Marek's the mortality can extend to 40 weeks of age. Affected birds are more susceptible to other diseases, both parasitic and bacterial.
The route of infection is usually respiratory and the disease is highly contagious being spread by infective feather-follicle dander, fomites, etc. Infected birds remain viraemic for life. Vertical transmission is not considered to be important.
The virus survives at ambient temperature for a long time (65 weeks) when cell associated and is resistant to some disinfectants (quaternary ammonium and phenol). It is inactivated rapidly when frozen and thawed.
Signs
Paralysis of legs, wings and neck.
Loss of weight.
Grey iris or irregular pupil.
Vision impairment.
Skin around feather follicles raised and roughened.
Post-mortem lesions
Grey-white foci of neoplastic tissue in liver, spleen, kidney, lung, go**ds, heart, and skeletal muscle.
Thickening of nerve trunks and loss of striation.
Microscopically - lymphoid infiltration is polymorphic.
Diagnosis
History, clinical signs, distribution of lesions, age affected, histopathology.
Differentiate from Lymphoid leukosis, botulism, deficiency of thiamine, deficiency of Ca/Phosphorus/Vitamin D, especially at the start of lay.

Treatment
None.

Prevention
Hygiene, all-in/all-out production, resistant strains, vaccination generally with 1500 PFU of HVT at day old (but increasingly by in-ovo application at transfer), association with other strains (SB1 Sero-type 2) and Rispen's.
It is common practice to use combinations of the different vaccine types in an effort to broaden the protection achieved. Genetics can help by increasing the frequency of the B21 gene that confers increased resistance to Marek's disease challenge.
Latest information
In 2018, Aviagen published their comprehensive brief "Marek's disease control in broilers birds" on The Poultry Site. It includes details of transmission, diagnosis, vaccinations, vaccine administration and causes of the disease.

16/03/2022

Marek's Disease and the importance of either purchasing vaccinated chicks or vaccinating chicks you hatch at day one of age. Leave a comment or send an email with any questions or other poultry related topics you would like covered!
For more information on backyard poultry, poultry production, wildfire resources for farmers and ranchers, COVID-19 food safety recommendations, and more, please check out

16/03/2022

Marek's disease (MD) is a highly infectious neoplastic condition of chickens caused by a herpesvirus. The virus is cell associated in tumors and in all organs except in the feather follicle where enveloped infectious virions egress from the body. From this source, infection is spread horizontally by the airborne route to the environment and to other chickens. Vertical transmission from dam to offspring does not occur or at best is very rare. The nonpathogenic herpesvirus of turkeys (HTV) is ubiquitous in turkeys and is probably spread horizontally by the airborne route. When chickens are inoculated with this virus, they do not subsequently develop MD even after infection with virulent Marek's disease virus. The Marek's disease virus, not the HVT, will spread horizontally from dually infected birds. The HVT vaccine is safe and highly effective in preventing MD under field conditions, and most chickens throughout the world are vaccinated with this vaccine. Other vaccines that have been used but have disadvantages over HVT include the following: (a) the highly pathogenic HPRS 16 strain of Marek's disease virus was attenuated by passage in cell culture. The attenuated virus protects against MD and does not spread, but "over-attenuated" virus does not protect; (b) naturally apathogenic strains virologically, immunologically, and epizootiologically similar to pathogenic strains will protect when adminstered before infection with the virulent strains; (c) virus preparations that have been chemically treated to inactivate infectivity protect only slightly. When a candidate vaccine virus for the prevention of herpesvirus-induced cancer in humans is developed, the purity of the vaccine preparations will be easily determined by modern techniques. However, measurements of safety and effectiveness are a significant problem. If, analogous to the MD model, the vaccine will have to be administered shortly after birth and the incubation period to development of neoplasms is long, then pathogenicity tests in nonhuman primates and other animals may be of limited valued. However, biochemical demonstration that the segment of the nucleic acid responsible for oncogenesis is absent from the vaccine virus may be the major indication that the vaccine is nonocogenic and therefore safe. Because of the low incidence of neoplasia and long incubation period, the effectiveness of the vaccine will be difficult to test. The vaccine possibly will protect against an acute manifestation of viral infection. Future research on MD will be directed to determining the mechanism of protection against disease, i.e., whether immunity is mediated by thymus- or bursa-dependent systems, and to identifying the protective antigen, i.e., which cell surface or an interior antigen induces the protective immunity. The prevention of MD by vaccination may become a very fruitful area for model studies on prevention of human cancer by vaccination.

16/03/2022

Marek's disease virus (MDV), a poultry pathogen, has been increasing in virulence since the mid twentieth century. Since multiple vaccines have been developed and widely implemented, losses due to MDV have decreased. However, vaccine failure has occurred in the past and vaccine breakthroughs remain a problem. Failure of disease control with current vaccines would have significant economic and welfare consequences. Nevertheless, the epidemiology of the disease during a farm outbreak is not well understood. Here we present a mathematical model to predict the effectiveness of vaccines to reduce the outbreak probability and disease burden within a barn. We find that the chance of an outbreak within a barn increases with the virulence of an MDV strain, and is significantly reduced when the flock is vaccinated, especially when there the contaminant strain is of low virulence. With low quantities of contaminated dust, there is nearly a 100% effectiveness of vaccines to reduce MDV outbreaks. However, the vaccine effectiveness drops to zero with an increased amount of contamination with a middle virulence MDV strain. We predict that the larger the barn, and the more virulent the MDV strain is, the more virus is produced by the time the flock is slaughtered. With the low-to-moderate virulence of the strains studied here, the number of deaths due to MDV is very low compared to all-cause mortality regardless of the vaccination status of the birds. However, the cumulative MD incidence can reach 100% for unvaccinated cohorts, and 35% for vaccinated cohorts. These results suggest that death due to MDV is an insufficient metric to assess the prevalence of MDV broiler barns regardless of vaccine status, such that active surveillance is required to successfully assess the probability of MDV outbreaks, and to limit transmission of MDV between successive cohorts of broiler chickens.

16/03/2022

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, although the disease occurs rarely in some other types of birds.

04/02/2022

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.

04/02/2022

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.

03/01/2022

Marek’s disease
Occurrence: Worldwide.
Species affected: Chickens (all breeds), pheasants and occasionally quail.
Age affected: Usually under 16 weeks, but birds can die near the onset of egg production. Causes: Marek’s disease virus is a cell-associated herpes virus containing double-stranded DNA, of which there are three serotypes.
Effects: It is immunosuppressive and causes increased susceptibility to other diseases. Signs include weakness, paleness, feed refusal, diarrhoea, poor performance culls and blindness. There is paralysis or perisis (partial paralysis), which can be unilateral or bilateral in wings and/or legs, which causes one leg to stretch forward and the other backwards. Tumours and tremors occur. Mortality ensues.

13/11/2021

Methods of Spread
Marek's disease virus occurs commonly wherever chickens are raised. The virus is highly infectious and once introduced into a flock it spreads rapidly to unvaccinated birds, so that most chickens in an unvaccinated flock become infected.
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.

13/11/2021

Marek's Disease
Be it among big producers in the broiler, layer and breed segments or small farmers focused on organic production, Marek’s Disease is something many in the poultry industry have at least heard of. Easily prevented through efficient vaccination, this disease causes not only animal suffering but also severe losses to producers.
Fighting Marek’s Disease is fundamental in every farm. According to the Food and Agriculture Organization of the United Nations (FAO), global per capital consumption of poultry meat has increased fivefold since the early 1960s. Preventing a wide range of poultry diseases means ensuring healthy animals able to offer high-quality protein in order to attend growing global demands. With our focus on prevention over treatment, we are committed to ensuring animal well-being and food security for generations to come.
Learn more! Prevention is possible!
What is Marek’s Disease?
Marek’s Disease is a common viral lymphoproliferative disease affecting poultry populations worldwide. It is named after the Hungarian veterinarian József Marek, who discovered it and first described it in 1907. The disease is caused by an avian Herpesvirus that inflicts great distress to animals through several manifestations ranging from peripheral nerve lesions to lymphomas. It is widely found in chickens all over the world.
How is it transmitted and what are the symptoms?
The Marek’s Disease virus is highly contagious, transmitted between chickens through the dust and dander of infected birds, and it can survive for long periods in farm and field environments. Actually, Marek's Disease is very complex. Clinical manifestations vary widely, depending on virus strain, bird age, condition, and other factors. It can be often difficult to differentiate from other diseases because it manifests in a variety of syndromes with wide-ranging signs. The most common clinical manifestations of the disease include peripheral nerve lesions, which may cause paralysis or persistent neurologic problems, and in tumor formation in nerve, organ, muscle and epithelial tissue. In animals not protected, clinical signs could be paralysis of the legs, weight loss, blindness or other eye abnormalities, skin lesions around the feather follicles, listlessness, wasting, and early mortality. Affected birds are also immunosuppressed, and therefore more susceptible to other infectious diseases.
Which impact does the Marek’s Disease have in the poultry industry?
Marek’s Disease is capable of causing significant economic losses in commercial poultry flocks. Young chickens, whose immune systems are still under development, are most susceptible to infection. Even in the absence of clinical signs, Marek's Disease virus can significantly damage chickens' immune system as the virus attacks T lymphocytes. The resulting immunosuppression causes poor growth and performance, significantly affecting production and economics in the poultry industry. Birds are more prone to secondary infections and less responsive to other vaccines, leading to increased medication costs.
How can the disease be prevented?
Marek’s Disease cannot be treated, and the only solution is prevention through vaccination, which was introduced first in 1970, making a great contribution. Later on, during the 1980s and 1990s, new and more virulent forms of the virus appeared, pushing for the development of newer vaccines. While vaccination can prevent infection in chickens, it does not prevent the virus from being spread - vaccinated birds may still be carriers, so good hygiene practices are also very important!
What is our role in the control of Marek’s Disease?
Being the global leader in prevention of Marek’s Disease, Boehringer Ingelheim provides a wide range of innovative solutions to keep animals safe. Our comprehensive selection of vaccines and hatchery delivery systems offers protection to poultry and supports veterinarians controlling the spread of Marek’s Disease and other poultry health challenges worldwide. These include not only vaccines against Marek’s Disease, but also all the main diseases affecting the poultry industry, like Infectious Bursal Disease, Newcastle Disease, Infectious Bronchitis, Avian Influenza and many others.
Our overall aspiration is to create the future of animal well-being through preventive care. In case of poultry, we strive to help win the battle against this and other diseases, shaping the future of poultry health through safe and effective prevention.

13/11/2021

Marek's disease can be periodic because it is herpes virus, it can go into a seeming remission but the hen loses a lot of condition and never really regains their body mass. The next bout seems harder for them to recover from. Long term they develop tons of tumor that effect breathing and all their body functions. I nursing my hen but wonder whether it would be more compassionate to kill her.
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.

13/11/2021

Marek’s Disease symptoms
Some birds do not show any ‘symptoms’ of disease. They may simply be resistant to it, or the type of virus caught may be non-pathogenic (not causing disease).
It should be noted that there are four different presentations of Marek’s disease- Neurological, Visceral, Cutaneous and Ocular. The type of presentation will dictate the kind of signs that you will see.
Signs for each of these forms will vary- some birds display all signs, others not so many.
Neurological
The neurological form of the disease is the most notable and disturbing in its presentation.
The symptoms are mainly caused by lesions affecting the nervous system and several other problems usually follow.
Occasionally the affected bird will have a temporary paralysis which will resolve itself spontaneously.
The bird shows signs of progressive paralysis, usually in the legs or wings. Often the bird looks like it’s doing the splits.
Twisting of the head to one side or backwards.
Respiratory problems such as labored breathing.
Darkened or purple comb (lack of oxygen).
Diarrhea.

05/05/2021

Egg-cellent Background on Egg Color

Did you know that all eggs are white, in the beginning? It makes no difference which breed of chicken laid the egg. Also, several factors come into play which can determine or affect the color of a hen’s egg. A hen’s overall health can affect the color of her eggshell, for egg-sample, eggshells will be a paler shade if she is struggling with parasites or illness. Basking in the sun for long time periods or being without access to fresh cool water can also cause a hen’s eggs to be much lighter, even white-ish if she is a tinted egg layer.

Here’s a Trivia Tidbit you can use to quiz your family and friends. A hen’s earlobe color may be a clue as to the color of egg that she will lay. Hens with white earlobes typically lay white eggs, while hens with red earlobes usually lay tinted or brown, blue, green and pink eggs!

1. Bright White and In the Spotlight!

White eggs are simply eggs sans pigment added from the hen’s reproductive system. Even without a tint or darker “paint”, white eggs are striking like the bold full moon’s glow on a dark night and have a beauty all their own.

White Egg Layers

Leghorns, Silkies, Hamburgs, Sebrights, Polish, Lakenvelders, Minorcas, Andalusians

2. Bravo, Beautiful Brown Eggs!

Do your egg baskets hold some beautiful brown eggs? Though brown egg layers are very common in many backyard flocks, their eggs are nothing short of egg-straordinary! To get any one of the myriad shades of brown eggshells, a pigment known as protoporphyrin, from a hen’s hemoglobin, is painted on during the last few hours of the egg laying process. These masterpieces in varying shades of light browns through the spectrum to a rich chocolate brown color are determined by more than a dozen of a hen’s genes. That being said, if you dabble in a little backyard breeding, crossing a light brown egg layer with a darker brown egg layer should, for all intents and purposes, yield a hen that lays a medium brown egg. However, to add a touch of mystery to this already intricate process, some hens possess a gene which actually represses or completely prevents the brown pigment from being painted on. Wow!

Seasons come and seasons go, but did you know that brown egg color is lighter in the warmer months and darker in the colder months? And, as a hen ages, her eggs will contain less pigment and lean toward the lighter end of the brown spectrum.

Cream or Light Tan Egg Layers

Wyandottes, Faverolles, Dorkings, Buff Orpingtons, Some Easter Eggers

Brown Egg Layers

Rhode Island Reds, New Hampshire Reds, Dominiques, Delawares, Cochins, Brahmas, Plymouth Rocks, Chanteclers

05/05/2021

It’s a very common practice among backyard chicken keepers to keep LOTS of egg-exquisitely different breeds! Why? Chicken keeping is quite addictive and once bitten by the chicken keeping bug; you’ll find yourself continually quoting the old adage, “The more the merrier!” Every year when spring has sprung up all around you, you get that urge, yes, you know the one. You get the urge to add a chick, chick here and a chick chick there, and before you know it, you’ve got oodles of lovely breeds clucking about in your backyard. And, what is the absolute best thing about having a multi-colored multi-breed flock? Yes, you guessed it…LOTS of egg-straordinarily different colored eggs! Yay!

05/05/2021

Egg binding
Egg binding (a disease where the hen is unable to lay her eggs) is a condition that can cause similar symptoms to Marek’s. The main symptom that draws parallels is that the hen won’t be able to use her legs properly, and may squat or be unable to move them. This may seem like paralysis, but it is due to the hen being unable to lay her egg. Other similar symptoms include droopiness.

Issues with vitamin consumption
If your chickens are deficient in certain vitamins, the effects can look like Marek’s disease. A deficiency in Vitamin B can give your chicken’s paralysis and issues with their legs. Ensure your chickens are getting all the right vitamins through their feed!

Keep calm and keep chickens!

However dire Marek’s may seem, don’t let the disease put you off getting chickens! Many backyard flocks both rural and urban live long, happy lives without ever having to come into contact with this disease. If you’re particularly concerned, make sure you purchase chickens that have already been vaccinated against Marek’s.

As chicken keepers, we like to think that we are doing the best we can for our girls, however, there is often more we can do to prevent health issues. I highly recommend the online chicken keeping course titled Ultimate Chicken Health to all my readers! It is written by our friends over at Chickenpedia. They have compiled everything you need to keep healthy chickens through the seasons (which is more than you think!) with a great set of check-lists and downloads to keep.

05/05/2021

Marek's disease is a Herpes virus infection of chickens, and rarely turkeys in close association with chickens, seen worldwide. From the 1980s and 1990s highly virulent strains have become a problem in North America and Europe.

The disease has various manifestations: a) Neurological - Acute infiltration of the CNS and nerves resulting in 'floppy broiler syndrome' and transient paralysis, as well as more long-standing paralysis of legs or wings and eye lesions; b) Visceral - Tumours in heart, o***y, tests, muscles, lungs; c) Cutaneous - Tumours of feather follicles.

Morbidity is 10-50% and mortality up to 100%. Mortality in an affected flock typically continues at a moderate or high rate for quite a few weeks. In 'late' Marek's the mortality can extend to 40 weeks of age. Affected birds are more susceptible to other diseases, both parasitic and bacterial.

The route of infection is usually respiratory and the disease is highly contagious being spread by infective feather-follicle dander, fomites, etc. Infected birds remain viraemic for life. Vertical transmission is not considered to be important.

The virus survives at ambient temperature for a long time (65 weeks) when cell associated and is resistant to some disinfectants (quaternary ammonium and phenol). It is inactivated rapidly when frozen and thawed.

Signs
Paralysis of legs, wings and neck.
Loss of weight.
Grey iris or irregular pupil.
Vision impairment.
Skin around feather follicles raised and roughened.
Post-mortem lesions
Grey-white foci of neoplastic tissue in liver, spleen, kidney, lung, go**ds, heart, and skeletal muscle.
Thickening of nerve trunks and loss of striation.
Microscopically - lymphoid infiltration is polymorphic.
Diagnosis
History, clinical signs, distribution of lesions, age affected, histopathology.
Differentiate from Lymphoid leukosis, botulism, deficiency of thiamine, deficiency of Ca/Phosphorus/Vitamin D, especially at the start of lay.

Treatment
None.

Prevention
Hygiene, all-in/all-out production, resistant strains, vaccination generally with 1500 PFU of HVT at day old (but increasingly by in-ovo application at transfer), association with other strains (SB1 Sero-type 2) and Rispen's.

It is common practice to use combinations of the different vaccine types in an effort to broaden the protection achieved. Genetics can help by increasing the frequency of the B21 gene that confers increased resistance to Marek's disease challenge.

Latest information
In 2018, Aviagen published their comprehensive brief "Marek's disease control in broilers birds" on The Poultry Site. It includes details of transmission, diagnosis, vaccinations, vaccine administration and causes of the disease.

01/04/2021

What Are The Signs of Marek’s Disease?
Some birds do not show any ‘symptoms’ of disease. They may simply be resistant to it, or the type of virus caught may be non-pathogenic (not causing disease).
It should be noted that there are four different presentations of Marek’s disease- Neurological, Visceral, Cutaneous and Ocular. The type of presentation will dictate the kind of signs that you will see.
Signs for each of these forms will vary- some birds display all signs, others not so many.
Neurological
The neurological form of the disease is the most notable and disturbing in its presentation.
The symptoms are mainly caused by lesions affecting the nervous system and several other problems usually follow.
Occasionally the affected bird will have a temporary paralysis which will resolve itself spontaneously.
The bird shows signs of progressive paralysis, usually in the legs or wings. Often the bird looks like it’s doing the splits.
Twisting of the head to one side or backwards.
Respiratory problems such as labored breathing.
Darkened or purple comb (lack of oxygen).
Diarrhea.

28/03/2021

Affected birds can have symptoms of general depression, weight loss and lethargy due to generalized illness. There are four forms of Marek's Disease

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Marek’s virus is transmitted two main ways. The virus can be transferred by fecal droppings and by feather dander.

Marek’s virus is transmitted two main ways. The virus can be transferred by fecal droppings and by feather dander. Some symptoms of Marek’s disease can be mild and vague, some can be severe and deadly. Paralysis can occur, along with sudden death. Since Marek’s disease attacks cells that produce antibodies, the immune system is at a disadvantage. You may find that the chicken also succumbs to coccidiosis or another pathogenic, opportunistic organism found in the environment.

Marek’s Disease symptoms are caused by a particularly

Marek’s Disease symptoms are caused by a particularly strong herpes virus. Marek’s Disease can be found in the environment. The usual symptoms involve the nervous system, eyes, skin and other organ systems. A strong variation of the disease shows tumor growth. Marek’s Disease is mainly seen in young chicks and older chickens. Chicks and chickens with Marek’s Disease can show a complex set of symptoms or be totally symptom free.

Identification of marek disease in poultry

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.

Young birds are more susceptible for marek disease

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.

Marek’s disease, is a worldwide economic burden on poultry farming.

Marek’s disease virus, a herpesvirus that is the causative agent of Marek’s disease, is a worldwide economic burden on poultry farming. However, little is known about the prevalence and dynamics of this virus in the field. Commercial poultry farming is highly structured, and so important questions are, how does virus prevalence differ across this structure, and how does virus prevalence change within a single level of this structure over time? To answer these questions, virus prevalence across farms in Pennsylvania for three years was surveyed. This involved collecting dust samples from chicken houses and using a qPCR (quantitative polymerase chain reaction) assay specific for non-vaccine Marek’s disease virus to assess the virus’s concentration in the dust. In total, 4448 samples were collected across 15 operations, and 106 farms. These data were analyzed with generalized linear mixed effects models fit using Bayesian methods. Virus prevalence varied considerably in the collected data. Substantial amounts of variation were attributable to between operation, between grower, and between flock effects. A smaller magnitude of variation was attributable to between house effects and between sample effects. Also, significant effects of cohort age and seasonality were identified. Researchers were unable to identify a significant effect of production type, but it is unclear whether this was due to a lack of biological importance or due to sampling constraints. Examining the data from within farms over time confirmed many of the patterns discovered by the mixed effect modeling. These data also revealed apparent patterns of virus disappearance and reemergence, where the virus concentration dropped to below detectable levels only to reappear in later samples. Whether this was due to repeated extinction and reintroduction events, or due to virus population dynamics that occurred below the qPCR limit of detection is still an open question.

Vaccination for mareks disease

Marek's Disease and the importance of either purchasing vaccinated chicks or vaccinating chicks you hatch at day one of age. Leave a comment or send an email with any questions or other poultry related topics you would like covered! For more information on backyard poultry, poultry production, wildfire resources for farmers and ranchers, COVID-19 food safety recommendations, and more, please check out

Marek disease in chickens

Marek's disease vaccines:

Marek's disease ('MD' or 'fowl paralysis') is a very common disease of chickens

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, although the disease occurs rarely in some other types of birds.

Effect of marek disease in poultry marketing

Methods of Spread Marek's disease virus occurs commonly wherever chickens are raised. The virus is highly infectious and once introduced into a flock it spreads rapidly to unvaccinated birds, so that most chickens in an unvaccinated flock become infected. 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.

Marek disease in poultry is the major problem of production

Marek’s Disease Symptoms

Marek’s Disease symptoms Some birds do not show any ‘symptoms’ of disease. They may simply be resistant to it, or the type of virus caught may be non-pathogenic (not causing disease). It should be noted that there are four different presentations of Marek’s disease- Neurological, Visceral, Cutaneous and Ocular. The type of presentation will dictate the kind of signs that you will see. Signs for each of these forms will vary- some birds display all signs, others not so many. Neurological The neurological form of the disease is the most notable and disturbing in its presentation. The symptoms are mainly caused by lesions affecting the nervous system and several other problems usually follow. Occasionally the affected bird will have a temporary paralysis which will resolve itself spontaneously. The bird shows signs of progressive paralysis, usually in the legs or wings. Often the bird looks like it’s doing the splits. Twisting of the head to one side or backwards. Respiratory problems such as labored breathing. Darkened or purple comb (lack of oxygen). Diarrhea.