ucanr.edu/sites/poultry/type/backyard/ MAREK’S DISEASE Marek’s disease occurs most often in juvenile to young adult chickens with a peak between 3-8 months; however it can occur at any age. Classically, Marek’s disease presents with limb/wing weakness progressing to paralysis if peripheral nerves are involved (neurotropic form). It may produce enlargement of/tumor formation in internal organs such as liver and spleen (viscerotropic form), and/or involve the skin (cutaneous form). The different forms can occur separately or together. Marek's disease virus (MDV) is a highly contagious disease shed in the feather follicle dander of both sick and healthy carrier chickens. MDV is mostly transmitted by inhalation of the aerosolized virus, and, to lesser extent, by direct contact with shedding chickens. The virus is not transmitted through the egg. MDV is resistant to most disinfectants, and can survive in the environment for many months, and possibly years. Decontamination of a property is extremely difficult; however, it is beneficial to disinfect areas that can be cleaned (such as coop). There is no treatment for Marek's disease; however it can be largely prevented by vaccination of day old chicks (or embryos in ovo). Vaccination should be done at the hatchery, or by you or your veterinarian if you are hatching your own. Vaccination of older chicks/chickens is unlikely to work because most have already been exposed to the virus. HVT Marek's vaccine (see below **) is available online. To be efficacious, directions for use need to be followed closely. Double vaccination while chicks are still in the hatchery is advocated by some, and may increase efficacy of the vaccine. Others vaccinate once in the hatchery, and again 1-2 weeks later. Following vaccination, chicks should not be exposed to a MDV-contaminated environment for a minimum of 2 weeks, and preferably 4 weeks. MAREK’S VACCINES 1. Bivalent HVT/CVI 988 (Rispens) and Homologous CVI 988 (Rispens) Vaccines These vaccines can be bought from the different poultry vaccine manufacturers, and are used commonly in commercial poultry, but at the moment are not generally unavailable for use in backyard flocks. The vaccine of choice would be the bivalent HVT+CVI 988 (Rispens) which will provide the broadest spectrum of efficacy, even against very virulent strains of MD virus. These MD vaccines are in cell-associated form, which means that the vaccine virus is present in live cells and in order to maintain its infectivity, the cells have to be kept viable. The vaccine has to be transported and stored, frozen at -196ºC in liquid nitrogen in special containers. Before use, the vaccine has to be mixed in specific diluents provided by the vaccine manufacturers and must be applied in 1-2 hours by subcutaneous vaccination in the neck region of the chick in the hatchery. The minimum dose size of the commercial available MD vaccines is 1000 doses/ampoule. This might be a problem if only a small numbers of birds have to be vaccinated. After the vaccine is mixed in the diluents, it has to be used immediately and cannot be stored. It is strongly recommended to follow the instructions of transport, storage, mixing of vaccine in diluent before use, and actual vaccination as prescribed by the vaccine manufacturer. 2. SB1 (avirulent Gallid herpesvirus type 3) Vaccine This vaccine is also cell-associated, deep frozen and available from poultry vaccine producers (not via Internet); however it may be slightly easier to obtain than the above. All the above comments regarding storage and use still apply. It is considered to be less efficacious than CVI 988 (Rispens), but more efficacious than HVT (see below). 3. HVT (Turkey Herpes Virus) Vaccine ** Vaccines made available by several Internet Web suppliers are mostly in freeze-dried (lyophilized) form and contain only HVT. The freeze-dried vaccine, which needs to be stored at 2 - 7ºC until reconstitution in the diluent, will provide a lesser level of protection than the cell-associated vaccines listed above, but this may be enough for small isolated backyard flocks. The Report 4.36-CAHFS Standard Report - 11/2/2017 Page 2 of 4 CAHFS Preliminary Version 1 Accession # K1800638 March 12, 2018 vaccine cannot be stored after reconstitution and needs to be used within 1-2 hours. This is the only vaccine currently available for small backyard flocks. If buying chicks from large hatcheries, it is possible that some are using one of the cell-associated, deep frozen vaccines listed above; however the commercial poultry industry would like to limit their use (particularly Rispens), because of a legitimate con
