NiV is part of the new Henipavirus genus within the Paramyxovirinae subfamily (Wang et al. 2001). Pneumovirinae and Paramyxovirinae comprise family Paramyxoviridae. The three other genera within Paramyxovirinae are Respirovirus (e.g. parainfluenza 3 virus), Morbillivirus (e.g. rinderpest virus), and Rubulavirus (e.g. Newcastle disease virus).
NiV is antigenically, ultrastructurally, serologically, and molecularly similar to HeV (Field et al. 2001). NiV contains a single-stranded nonsegmented RNA genome (18.2 kb) of negative polarity that is fully encapsulated by protein (Chua et al. 2001). It lacks the double fringe characteristic of HeV (Daniels et al. 2001) and contains inclusions of smooth, curvilinear membranes not found in other Paramyxoviridae. These membranes are potentially analogous to the “replication complexes” of positive-stranded RNA viruses (Goldsmith et al. 2002). NiV can form large syncytia more quickly than HeV, and the distribution of nuclei within syncytia differ between the two viruses (Daniels et al. 2001). Like other paramyxoviruses, NiV is easily destroyed by heat, lipid solvents, non-ionic detergents, formaldehyde, and oxidizing agents (Barclay and Paton 2000).
Antibodies to NiV react with cells infected with HeV (Wang et al. 2001), though there is an 8- to 16-fold difference in antibody levels (Lam and Chua 2002). Serum neutralization tests were used in initial studies on pigs and humans, and the sera often had HeV antibodies at low titers (Daniels et al. 2001). The ELISA (98.4% specificity) was then used in conjunction with neutralization under BSL4 conditions. NiV grows well in Vero cells, and identification methodologies for virus isolates include immunostaining of fixed, infected cells, neutralization with specific antisera, PCR of culture supernatants, electron microscopy, and immunoelectron microscopy (Daniels et al. 2001). Recently, a rapid immune plaque assay has been developed that accepts smaller serum samples and can be used to corroborate ELISA results without the BSL4 constraint (Crameri et al. 2002).
Author: S. Cobey.