Invasion of the central nervous system in a porcine host by nipah virus

Abstract

Nipah virus, a newly emerged zoonotic paramyxovirus, infects a number of species. Human infections were linked to direct contact with pigs, specifically with their body fluids. Clinical signs in human cases indicated primarily involvement of the central nervous system, while in pigs the respiratory system was considered the primary virus target, with only rare involvement of the central nervous system. Eleven 5-week-old piglets were infected intranasally, orally, and ocularly with 2.5 x 10(5) PFU of Nipah virus per animal and euthanized between 3 and 8 days postinoculation. Nipah virus caused neurological signs in two out of eleven inoculated pigs. The rest of the pigs remained clinically healthy. Virus was detected in the respiratory system (turbinates, nasopharynx, trachea, bronchus, and lung in titers up to 10(5.3) PFU/g) and in the lymphoreticular system (endothelial cells of blood and lymphatic vessels, submandibular and bronchiolar lymph nodes, tonsil, and spleen with titers up to 10(6) PFU/g). Virus presence was confirmed in the nervous system of both sick and apparently healthy animals (cranial nerves, trigeminal ganglion, brain, and cerebrospinal fluid, with titers up to 10(7.7) PFU/g of tissue). Nipah virus distribution was confirmed by immunohistochemistry. The study presents novel findings indicating that Nipah virus invaded the central nervous system of the porcine host via cranial nerves as well as by crossing the blood-brain barrier after initial virus replication in the upper respiratory tract.

FIG. 1.

Presence of Nipah virus antigen in the nasal turbinate. Positive staining in large multinucleate cells, consistent with osteoclasts, and smaller uninucleate cells (may be osteoclasts or osteoblasts) located along the margins of the bone trabeculae. Immunostaining using polyclonal guinea pig anti-Nipah virus serum. Pig 5, 6 dpi, nasal turbinate. Scale bar represents 50 μm.

FIG. 2.

Positive immunostaining for Nipah virus antigen of the axons on the cross-section of the olfactory nerve in the turbinates. Positive staining of the Schwann's cells was not observed on the sections. Immunostaining using polyclonal guinea pig anti-Nipah virus serum. Pig 5, 6 dpi, nasal turbinate. Scale bar represents 50 μm.

FIG. 3.

Presence of Nipah virus antigen in the granule cell neurons of the olfactory bulb (secondary sensory neuron). Immunostaining using polyclonal guinea pig anti-Nipah virus serum. Animal 19, 7 dpi, olfactory bulb. Scale bar represents 50 μm.

FIG. 4.

Positive immunostaining for Nipah virus N protein using mouse monoclonal anti-N antibodies in the ependymal lining of the third ventricle. Pig 5, 6 dpi. Scale bar represents 50 μm.

FIG. 5.

Nipah virus antigen detected in the smooth muscle cells and in the endothelial cells of small blood vessels in the brain using polyclonal guinea pig anti-Nipah virus serum. Pig 5, 6 dpi, cerebral cortex. Scale bar represents 50 μm.

FIG. 6.

Positive immunostaining for Nipah virus N protein, using mouse monoclonal anti-N antibodies, in brain cells, mainly in glia cells and occasionally neurons in an animal with fulminant virus-induced meningitis. Animal 19, 7 dpi, cerebral cortex. Scale bar represents 50 μm.