\u00a0<\/strong><\/p>\n<\/td>\n MAREK’S DISEASE CLINICAL FORMS<\/strong><\/p>\n<\/td>\n<\/tr>\n Given the ubiquity and strength of the virus, vaccination is usually performed on the 1st day of life in hatchery to prevent the infection of the chicks. However, the effectiveness of the vaccine depends on various factors:<\/p>\n \u00a0<\/strong><\/p>\n<\/td>\n FACTORS INFLUENCING VACCINE EFFICACY<\/strong><\/p>\n<\/td>\n<\/tr>\n ANTEMORTEM<\/strong>: The signs depend on the clinical condition of the animals, paralysis of the limbs or neck flaccid paralysis can be seen.<\/p>\n POSTMORTEM<\/strong>: Lesions can include thickening, usually unilateral, of the sciatic nerve, nodular lesions in the viscera, thickening of the\u00a0proventriculus\u00a0wall, splenomegaly and the presence of perifollicular skin nodules<\/strong>.<\/p>\n LABORATORY DIAGNOSIS<\/strong>: MD\u00a0diagnosis\u00a0should not only confirm the disease but must rule out other birds neoplastic syndromes such as avian leukosis. This can be done by a histopathological study<\/strong>; therefore tissues to be sent (send samples in formalin<\/strong>) should include those that allow us to distinguish between the two diseases. Samples<\/strong>: sciatic nerve, skin, brain and bursa. Also send tissues or organs that are affected (liver, spleen, proventriculus, etc).<\/p>\n Image characteristic of a chicken neck with flaccid paralysis.<\/p><\/div>\n\n \n Nervous<\/strong><\/td>\n Usually unilateral flaccid paralysis of the legs or wings is observed. In this case, tumor cells infiltrate \u00a0the peripheral nervous system, especially the sciatic nerve (neurolymphomatosis).<\/td>\n<\/tr>\n \n Visceral<\/strong><\/td>\n Mortality drip and sometimes diarrhea. At necropsy the presence of tumors in different organs\u00a0is revealed. The most common are liver, proventriculus and spleen.<\/td>\n<\/tr>\n \n Flaccid neck<\/strong><\/td>\n Transient flaccid\u00a0neck paralysis is observed on the birds. Forcing them to lay with their necks stretched on the floor. Usually associated with infection with highly virulent strains (“very virulent plus”) MDV (vv+ MDV).<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \n\n
\n \n \n \n Pathotype<\/strong><\/td>\n Different strains of Marek exist: the virulent strains (“virulent” – v MDV), the highly virulent (“very virulent” – vv MDV) and highly virulent plus (“very virulent plus” – vv+ MDV). Among other things strains \u00a0vv+ MDV\u00a0and vvMDV are characterized by being able to break the immunity generated by\u00a0Marek vaccines HVT and bivalent . Here we do not know what field pathotypes are present \u00a0but the flaccid neck clinic observed on some farms is associated with vv+ MDV strains, \u00a0therefore probably these strains are circulating.<\/td>\n<\/tr>\n \n Serotype<\/strong><\/td>\n Also there are different serotypes of Marek (1, 2 and 3). Most common vaccines are \u00a0HVT (serotype 3) or Rispens CVI988 (serotype 1) and there are some combined vaccines. CVI988 vaccine seems that yields best protection against vv+ MDV. The HVT gives good protection against virulent strains, and in combination with strains of serotype 2 strains against vvMDV.<\/td>\n<\/tr>\n \n Genetics<\/strong><\/td>\n There is also genetic genetic effect: some strains are more susceptible to Marek others.<\/td>\n<\/tr>\n \n Conservation<\/strong><\/td>\n Marek’s vaccine is stored frozen in liquid nitrogen and its management in hatchery must be very good because the title of the vaccine drops very quickly.<\/td>\n<\/tr>\n \n Regime<\/strong><\/td>\n To further complicate the issue, since birds are \u00a0nowadays slaughtered very soon, in many cases they have no time to develop disease, and it is common not to vaccinate full dose. In fact most of the Marek\u00a0cases seen in \u00a0slaughterhouse are usually\u00a0in\u00a0slower growing birds.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n ![\"Image](\"https:\/\/sesc.cat\/wp-content\/uploads\/2012\/04\/SESC-0033-09-1-800x531.jpg\" "\\"Image")
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