Newcastle Disease (ND) is a highly contagious viral disease that affects almost all avian species including poultry, cage and wild birds around the globe (Terregino et al. 2003; Vidanovic et al. 2011). ND is economically important disease and included as list-A disease of Office des International Epizootics (OIE) (Anonymous). Mortality of infected birds ranges from negligible to as high as 100 % depending on the pathotype of the virus involved and health status of the birds (Alexander and Manvell 2004). NDV is an enveloped virus with single stranded, non-segmented, negative sense RNA genome (Makoui et al. 2013). The virus belongs to Avulavirus genus of Paramyxoviridae. There exist only one serotype of NDV designated as avian paramyxovirus-1 (Kapczynski et al. 2013) however, different virus strains do vary in their pathogenicity. There are 3 pathotypes of NDV; velogenic (highly virulent), mesogenic (moderate virulent), and lentogenic (mild virulent) based upon diseases producing potential and severity of signs in the infected birds (de Leeuw and Peeters 1999).
NDV is primarily transmitted to the susceptible birds through aerosol and fecal oral route (Martin 1992). Infected birds secrete high amount of the virus in their feces, saliva, mucous and nasal secretions which might contaminate the premises. Inanimate objects or fomites are a potential reservoir of viruses outside the host and might play an important role in the transmission of pathogens (Nicas and Sun 2006). Several factors can influence the survival of viruses outside the host (Sobsey and Meschke 2003; Weber and Stilianakis 2008; Stallknecht and Brown 2009). A number of studies show that respiratory pathogens can survive from hours to months on fomites (Abad et al. 2001; Kramer et al. 2006). Certain physical factors like temperature, humidity, pH, salinity, exposure to ultraviolet (UV) rays etc drastically affects the
Introduction
2
virus persistence in the environment. Effect of such physical insults is more pronounced on enveloped viruses than non-enveloped ones (Mbithi et al. 1991; Schaap et al. 2012; Tuladhar et al. 2012). High humidity and temperatures not only reduces the survival of influenza viruses on contaminated surfaces but also modulates their transmission to the susceptible birds (Shaman and Kohn 2009; McDevitt et al. 2010; Paynter 2014). Similarly lower temperature and less humidity promote the survival of NDV in the environment (Dat and Chuc 1985; Kournikakis et al. 1988).
ND is endemic in Pakistan but since last few years several new virus strains are circulating in commercial and rural poultry of the country (Munir et al. 2012; Shabbir et al. 2013). Central Punjab region is densely populated with commercial poultry and serve as disease epicenter every year. It has been observed that the disease outbreaks usually start in December, attain peak in the late winter and spring season, start decline in June and disappear in the rainy season. Apart from several other contributing factors, environmental survival of the viruses might contribute to the disease outbreaks.