**5. Conclusions**

592 A Bird's-Eye View of Veterinary Medicine

their disease potential is neither known in wild birds nor in domestic birds. It is probable that wild birds can transmit APMV-2 to -9 to domestic birds. APMV-2, -3, -4, -6, -7, -8, -9 have been isolated from domestic poultry birds and antibodies to these viruses have also been detected in domestic poultry (Alexander, 1980b; Alexander and D.J., 2003; Warke et

APMV-3 strains Netherlands and Wisconsin were first characterized by standard pathogenicity tests (MDT and ICPI). The results of the MDT test showed that APMV-3 strain Netherland was slightly pathogenic (112 hr) compared to strain Wisconsin (>168 hr). Similar findings were also observed in ICPI test: APMV-3 strain Netherland showed an ICPI value of 0.39, while the ICPI value of strain Wisconsin was zero. Although the results of pathogenicity index tests (MDT and ICPI) showed that APMV-3 strain Netherlands was slightly pathogenic to chickens, the pathogenicity of both the APMV-3 strains is similar to

The growth kinetics of APMV-3 strains in chicken brain showed that both the strains are equally competent to grow in brain tissue and the highest virus titer was observed 120 hr post inoculation. These results suggest that the low ICPI values of APMV-3 strains were due

It has been shown previously by experimental infection that APMV-3 strain Netherlands is more virulent than strain Wisconsin (Alexander, 1980b). In another study, it was shown that the extent of disease and death in the birds after infection with APMV-3 strain Netherlands depends on dose as well as route of infection (Alexander and Collins, 1982b). The clinical signs of illness were more evident in 1-day-old birds compared to 2-weeks-old birds. In chickens, both the strains of APMV-3 were also isolated from tissues of respiratory, digestive and nervous systems. Similar findings were also observed in turkeys infected with both the APMV-3 strains. However, the titers of APMV-3 strain Netherlands in different organs were higher than those of strain Wisconsin in all the infected groups of birds. These results confirmed previous findings that chickens and turkeys are susceptible to APMV-3 infection. Furthermore, younger birds are more susceptible than older birds (Alexander and

An interesting finding observed was the presence of large amounts of viral antigens at the epithelial cell linings, suggesting that these cells are highly permissive to APMV-3 replication. The study also suggested that APMV-3 has a tropism towards both epithelial and sub-epithelial cells (Kumar et al., 2010a). In addition, the detection of viral antigens, and in most cases infectious virus, in multiple internal organs of the birds indicates that both the viruses are capable of replicating in multiple organs rather than being restricted only to respiratory and alimentary tracts. Presumably, the virus reached the various internal organs through the blood stream. Nonetheless, this extensive amount of virus replication was not accompanied by severe disease in birds. These results show that APMV-3 strains are capable of infecting young and adult chickens and turkeys using an oculonasal route of infection. Serologic assays demonstrated a humoral response in all the birds inoculated with either APMV-3 strain, a further indication of successful replication. However, our findings suggest that chickens are comparatively more susceptible than

to nondestructive replication of the virus in brain tissue (Kumar et al., 2010a).

al., 2008).

that of lentogenic NDV strains (Alexander, 1998).

Collins, 1982b; Russell et al., 1989).

turkeys to APMV-3 infection.

APMV-3 is capable of infecting young and adult SPF chickens and turkeys. The disease caused by APMV-3 is more severe in younger birds than in older birds, where it is mostly inapparent. Our results also showed that APMV-3 strains vary in pathogenicity. Strain Netherlands is more virulent than strain Wisconsin. This study has demonstrated that APMV-3 has an affinity for both epithelial as well as sub-epithelial cells of respiratory and alimentary tracts. In terms of pathogenicity for poultry, APMV-3 is probably second in importance only to NDV. However, in commercial chickens and turkeys the disease picture could be quite different depending on management practices, environmental conditions and other concomitant infections. Further studies are needed to understand the disease potential of this virus to commercial poultry.
