Pathogenicity analysis and control strategies to combat avian diseases: mechanisms of increased virulence of Marek's disease virus and the development of vaccines against poultry red mites.

The occurrence of avian diseases has been greatly reduced by improved sanitation on poultry farms and the development of prevention programs through vaccination and other measures. However, the poultry industry still faces several concerns. Marek's disease (MD) has caused significant economic losses to the poultry industry in the past; however, the introduction of vaccines has successfully contributed to a reduction in MD occurrences. Nevertheless, sporadic MD occurrences are still observed, and increased virulence has been reported owing to the changes in viral characteristics. In addition to infectious diseases, infestation with poultry red mites (PRMs; Dermanyssus gallinae), which are small hematophagous ectoparasites of poultry, has caused severe declines in productivity of the poultry industry worldwide. Furthermore, in addition to animal hygiene, problems caused by PRMs are of concern in terms of public health and animal welfare. The emergence of acaricide-resistant PRMs has made their control difficult. Therefore, the establishment of novel control strategies is eagerly awaited. Among the issues of avian diseases facing the poultry industry, this review highlights research on the mechanisms of increased virulence of MD virus and the development of a novel approach for PRM control.