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Mareks Disease and an explanation about resistance using the Mareks vaccine available
Written by Sue @ The Cuckoo Poultry Stud
This article is only here as the Stud vaccinates all hatchlings, as such this and the following article on how to vaccinate are included on this site
from researched information and first hand knowledge of the disease after numerous discussions and comparisons with other Breeders over several years.
Mareks Disease (MD) is a common virus that kills more birds than any other disease except Coccidiosis. Mareks is so common that you have to assume that you have it in your flock, even if you detect no evidence = if there is 'air' on and around your property = you have Mareks Disease present. Do not assume otherwise as it is air borne transmitted = a strong wind can blow contaminated dander for many kilometres from one chicken pen to another.
The disease effects both commercial and backyard poultry, and has been known to result in large losses in severe ‘outbreaks’.
Mareks is a member of the Herpes Virus family and causes internal lesions (tumours), paralysis and or blindness and most often death.
It is spread through microscopic airborne feather dander and spreads easily and quickly from one flock to another via the wind. No bird or human contact is required for Mareks to spread as it travels quickly on the wind. The virus is inhaled by the birds (predominantly newly hatched chicks are most at risk on ‘infection’) and lodges in the respiratory tract before entering the blood stream. It is often also carried onto a property by people and equipment as the dander is so fine and lodges in clothing and on equipment as a fine dust.
The Mareks Virus is able to survive in the environment for many months in temperate climates but it has been reported by some Breeders that colder climates have had a marked effect on the times of outbreaks. It would appear that the cold does not agree with the virus. And the Breeders that live in colder climates have less outbreaks of the disease than those living in temperate or tropical climates.
The study of Mareks Disease in poultry has had a profound effect on cancer research. The Mareks vaccine for chickens was the first time medical science was able to produce an effective cancer vaccine for any species. Since then vaccines for a small few human cancers have been developed, thanks to the humble ‘chook’.
There are different types of Mareks in chickens. The most common are, Nerve, Ocular (eye), Visceral (tumour producing).
The Nerve (most commonly seen) type can become apparent very quickly and exhibits symptoms as slight to severe paralysis in the legs; this is often seen as a progressive paralysis. This paralysis is less often seen in the wings or neck, but can be displayed in all simultaneously. The Sciatic Nerve (the main nerve to the leg) is most commonly affected. The birds affected are unable to stand, become paralysed or appear to be uncoordinated. Often they display ‘the splits’ where one leg points to the front the other to the back. This often and usually results in death from trampling by other chickens, and/or the inability to get food and water. There can be transient paralysis that disappears after a few days. An example is a dropped wing that suddenly corrects itself. There are reports where birds with this version have survived due to extreme TLC on behalf of the owner, but these reports are few and far between.
The Ocular version can often be detected by an irregularly shaped pupil, cloudy eye (grey eye), or sensitivity to light (photosensitive) that occurs suddenly. Ocular Mareks can result in blindness.
The Visceral version should be considered when the bird appears to be just ‘wasting’ away although it is eating and drinking well, and still active almost until the ‘end’ (often within 24-48hrs of death). In this form tumours often develop on the liver, spleen, kidney and heart; also the ovaries occasionally develop tumours and more rarely the testes develop small tumours. Birds with the Visceral form may show signs of paralysis, depression, anaemia (pale combs) and dehydration (shrunken combs). Also sometimes loss of appetite, loss of weight and occasionally diarrhoea are displayed. However a large number of birds with the Visceral form just die without any obvious clinical symptoms.
Mareks is extremely contagious but does not spread vertically (to the egg), it IS inhaled and spread via the wind and humans carrying the dander in on their clothes. Unvaccinated chicks should have developed a natural immunity (age resistance) by the time they are five to six months old IF they are going to. This is one reason it is important to raise the chicks separate from the adult birds.
Any older birds that have developed Mareks and survived are carriers. New birds from elsewhere must be considered potential carriers.
Mareks usually starts to display symptoms from 5 to 25 weeks, but symptoms can appear when the bird is older (up to 12-14mths old) and is stressed or ill from other sources (latent Mareks).
However, if the bird is a few years old, one has to consider a similar disease called Avian Lymphoid Leukosis (this does pass via the egg). Both diseases will produce internal lesions (tumours), usually detectable at post mortem, but L.L. does not produce paralysis.
Since it is so difficult to control a flocks exposure to Mareks, (airborne spread, bringing in new birds, exhibiting stock) the best course is reduction/prevention. This starts with completely sanitizing your incubators and brooders and keeping your pens as clean as possible. Keeping everything as clean as possible reduces the risk but can not eliminate it.
It is recommended that diseased birds be removed from the flock and humanely destroyed. If you have one bird with Mareks you likely have others, so close monitoring of the flock/s is very important.
You may want to consider the use of the Mareks Vaccine. The vaccine is available from a number of poultry suppliers and is easy to administer to day old chicks. # contact your local supplier in your state for more details
It is an injection form of vaccine and is given just under the skin at the back of the neck (subcutaneously = under the skin. NOT intramuscular (in the muscle) it MUST be given only under the skin) you need to exhibit care when injecting as you could stick the needle through the other side of the skin and either vaccinate the floor or yourself by accident.
The vaccine alone is not enough to prevent Mareks Disease. It is important to have a good biosecurity system in place to help vaccinated chicks develop immunity before they are introduced to the challenges of adult chook life. And come into contact with the virus at that time.
How the vaccine works (basically, and in a very loose explanation) is the Mareks is a live vaccine and by having it in the chicks system as early as possible (meaning within 24hrs of hatching = NOT drying, but actual breaking the shell and taking its first breath) the immune system recognises it as something it needs to build a resistance to as that immune system is developing.
Chicks need to be raised separately so they are as free as possible from infected dander. A good hygiene regiment is also important. This must include a thorough clean out and disinfection of sheds and all equipment between batches of chicks, using a disinfectant that is effective against viruses is advised. Good nutrition is essential and as close to total reduction of exposure to other diseases and also parasites is also a must. These simple and easy practices will help maximize resistance to Mareks infection.
Breeding genetically resistant strains of birds, as well as the use of vaccines and good hygiene are of great help in the control of Mareks Disease.
There are certain ‘B factors’ contained in the blood of some chickens that make them more resistant to Mareks. If you have access to a Laboratory for ‘B type’ blood testing, ‘B factor’ birds are desirable for breeding a Mareks ‘resistant’ flock.
In flocks with a serious Mareks problem, it should be considered to totally depopulate. Clean and disinfect ALL sheds and equipment (including human clothing and bed linen/cloth furniture etc) then spell the property for the several warm months and should also include the colder months of late Autumn, Winter and early Spring. Then repopulate with vaccinated chicks/birds after this time.
# added in 2012
It is apparent, even with all the literature available, that some still do not fully understand Mareks Disease or the vaccine.
A number of reputable Breeders have recently brought to my attention an alarming situation =
Some few people talk of 'vaccinating' (using the vaccine mentioned in this article) chicks that are from one month old up to adult age birds against this Disease and they only 'vaccinate' once every month or 2 months everything that has hatched in that time as well as older birds they bring onto their property.
Understanding how a chicken acquires resistance to this disease with the help of the Mareks vaccine is important.
Hatchlings are 'born' with almost no immune system which takes the first 3 weeks to mature. Their immune system develops resistance/immunity to a number of things in this first 3 weeks; some things need extra help over a period of several weeks (medicated feed against Coccidiosis as an example).
Some vaccines are given at an older age with good reason; Mareks is not one of them.
Hatchlings are given the Mareks vaccine in the first 24 to 36hrs of life, preferably within the first 24hrs.
Any bird older than 36hrs that is given this injection rarely develops protection with the help of this vaccine as the resistance is developed from day 1 to 3 weeks of age as the hatchlings immune system develops and matures.
The injection needs to be given in this time frame so that the maturing immune system CAN develop the resistance necessary.
Hence the advice that hatchlings be kept seperate from all other birds and in a clean environment for the first three weeks.
Once a bird has been exposed to Mareks, and if it is susceptible, within a few weeks it starts to develop the tumours etc and the outward symptoms will start to show up 5 to 25 weeks later = no amount of vaccine given after the time frame mentioned is going to stop that bird displaying symptoms of the Disease, and it will not stop the bird dying from the disease, unless the bird is very strong = that bird is then a carrier.
The Mareks vaccine does not cure the disease; it affords a degree of resistance against it when given in the first 24 to 36hrs after hatching. At one month of age it is too late to vaccinate as any that are susceptible are already in the process of dying from the disease.
The Mareks Vaccine gives resistance to the Mareks Disease with an average 80 to 95% success rate against the hatchlings developing Mareks.
This is approximately the same resistance rate as for any vaccine across all mammal and avian breeds/species.
The Mareks vaccine works to give resistance not immunity as such, the word vaccine is used to simplify a sentence.
“I am giving my birds a Mareks vaccination” as opposed to “I am giving my birds a Mareks resistance injection”
Humans understand the word vaccine hence its use.
# some try to breed for resistance and do not vaccinate – this is their choice, but one has to remember that Mareks goes in a 7 year cycle so breeding for resistance is a long term project. It also requires the need for very heavy culling to keep only those birds that survive to adulthood each year.
A costly process considering feed bills etc. The Mareks vaccine is a cheaper alternative.
Also note that any bird that is not vaccinated must be considered a carrier of the disease and that if that bird is put into a Show has potentially infected the entire Pavilion with the Mareks Disease the very first time it moves and its dander starts floating around = potentially landing on another Breeders bird and then taken to that property – and so on.
# [TCB] - subject to copyright laws of Australia