Bacterial infections in pigs experimentally infected with Nipah virus

Nipah virus (NiV; Paramyxoviridae) caused fatal encephalitis in humans during an outbreak in Malaysia in 1998/1999 after transmission from infected pigs. Our previous study demonstrated that the respiratory, lymphatic and central nervous systems are targets for virus replication in experimentally infected pigs. To continue the studies on pathogenesis of NiV in swine, six piglets were inoculated oronasally with 2.5 x 10(5) PFU per animal. Four pigs developed mild clinical signs, one exudative epidermitis, and one neurologic signs due to suppurative meningoencephalitis, and was euthanized at 11 days post-inoculation (dpi). Neutralizing antibodies reached in surviving animals titers around 1280 at 16 dpi. Nasal and oro-pharyngeal shedding of the NiV was detected between 2 and 17 dpi. Virus appeared to be cleared from the tissues of the infected animals by 23 dpi, with low amount of RNA detected in submandibular and bronchial lymph nodes of three pigs, and olfactory bulb of one animal. Despite the presence of neutralizing antibodies, virus was isolated from serum at 24 dpi, and the viral RNA was still detected in serum at 29 dpi. Our results indicate slower clearance of NiV from some of the infected pigs. Bacteria were detected in the cerebrospinal fluid of five NiV inoculated animals, with isolation of Streptococcus suis and Enterococcus faecalis. Staphylococcus hyicus was isolated from the skin lesions of the animal with exudative epidermitis. Along with the observed lymphoid depletion in the lymph nodes of all NiV-infected animals, and the demonstrated ability of NiV to infect porcine peripheral blood mononuclear cells in vitro, this finding warrants further investigation into a possible NiV-induced immunosuppression of the swine host.