“…The respiratory form is characterised by pyo-granulomatous lesions within the nasal mucosa that can extend throughout the respiratory tract to the lung parenchyma Fawi, 1971;Al-Ani, 1999). Few studies have examined the equine immune response to Histoplasma and the extent and duration of immunity to natural infection, the presence of asymptomatic carriers and response to experimental vaccination are yet to be fully ascertained (Noskoav, 1960;Gabal and Khalifa, 1983;Soliman et al, 1984;Gabal and Mohammed, 1985;Soliman et al, 1985;Zhang et al, 1986;Ameni et al, 2006).…”