Structure Avian influenza A virus
Influenza viruses are spherical or filamentous enveloped particles 80 to 120 nm in diameter. The helically symmetric nucleocapsid consists of a nucleoprotein and a multipartite genome of single-stranded antisense RNA in seven or eight segments. The envelope carries a hemagglutinin attachment protein and a neuraminidase

Classification and Antigenic Types
Influenza viruses are members of the family Orthomyxoviridae (the Greek root myxo-, mucus, attests to the respiratory ramifications of disease caused by these viruses). These viruses are further classified, on the basis of antigenic properties of the nucleoprotein and matrix proteins, as influenza A, B, or C. Influenza A viruses have been isolated from various animal species, including birds, pigs,horses, and humans, where as influenza B and C viruses are primarily human pathogens. Influenza A viruses have much more variable surface glycoproteins than either B or C viruses, yet phylogenetic analyses show that influenza A and B viruses are more closely related to each other than to influenza C.
In wild aquatic birds and poultry around the world, influenza A viruses carrying 15 antigenic subtypes of hemagglutinin (HA) and 9 antigenic subtypes of neuraminidase (NA) have been described. Here we describe a previously unidentified antigenic subtype of HA (H16)

Introduction
The microorganisms of the class Mollicutes (Mycoplasma) were first identified in 1898 as the etiologic agent of the bovine contagious pleuropneumonia (BCPP) and thereafter, all similar agents were named pleuropneumonia-like (PPLO-like) organisms
Avian Mycoplasmosis is caused principally by three species of Mycoplasma organisms. Mycoplasma gallisepticum (MG), Mycoplasma synoviae (MS) occur in chickens and turkeys. Mycoplasma meleagridis (MM) occurs in turkeys. Mycoplasma meleagridis may be seen in other species such as pheasant, quail, guineas, and pigeons. Mycoplasma synoviae causes infectious synovitis where as Mycoplasma gallisepticum causes chronic respiratory disease (CRD), which is a serious problem, particularly in chicken flocks.
Since 1994, Mycoplasma. gallisepticum conjunctivitis has become an emerging disease in finches. This disease has been responsible for major declines in house finch populations in the eastern U.S., and was recently reported in western house finch populations. Mycoplasma gallisepticum can also affect other finch species, although its impact has not been as severe.

Introduction
The microorganisms of the class Mollicutes (Mycoplasma) were first identified in 1898 as the etiologic agent of the bovine contagious pleuropneumonia (BCPP) and thereafter, all similar agents were named pleuropneumonia-like (PPLO-like) organisms
Avian Mycoplasmosis is caused principally by three species of Mycoplasma organisms. Mycoplasma gallisepticum (MG), Mycoplasma synoviae (MS) occur in chickens and turkeys. Mycoplasma meleagridis (MM) occurs in turkeys. Mycoplasma meleagridis may be seen in other species such as pheasant, quail, guineas, and pigeons. Mycoplasma synoviae causes infectious synovitis where as Mycoplasma gallisepticum causes chronic respiratory disease (CRD), which is a serious problem, particularly in chicken flocks.
Since 1994, Mycoplasma. gallisepticum conjunctivitis has become an emerging disease in finches. This disease has been responsible for major declines in house finch populations in the eastern U.S., and was recently reported in western house finch populations. Mycoplasma gallisepticum can also affect other finch species, although its impact has not been as severe.

Introduction
Marek's disease (MDV) is a naturally occuring disease of young chickens but older birds can also be affected. In contrast to the lymphoid leukosis tumor response, Marek's disease (MDV) may be observed in more diverse locations. Marek's disease is caused by a widespread, higly contagious, cellassociated, oncogenic herpes virus. virus belonging to the Herpes virus group. Much is known about the transmission of the virus; however, it appears that the virus is concentrated in the feather follicles and shed in the dander (sloughed skin and feather cells). The virus has a long survival time in dander since viable virus can be isolated from houses that have been depopulated for many months.

Hospes
Chicken of all age are susceptible. Other avian spesies, including turkey, quail and duck, can either be infected experimentally or have natural antibodie to Marek's disease (MDV).