Transmission routes for nipah virus from Malaysia and Bangladesh

Abstract

Human infections with Nipah virus in Malaysia and Bangladesh are associated with markedly different patterns of transmission and pathogenicity. To compare the 2 strains, we conducted an in vivo study in which 2 groups of ferrets were oronasally exposed to either the Malaysia or Bangladesh strain of Nipah virus. Viral shedding and tissue tropism were compared between the 2 groups. Over the course of infection, significantly higher levels of viral RNA were recovered from oral secretions of ferrets infected with the Bangladesh strain. Higher levels of oral shedding of the Bangladesh strain of Nipah virus might be a key factor in onward transmission in outbreaks among humans.

Figure 1

Predicted means for detection of Nipah virus (NiV) RNA in nasal wash samples (A), oral swab samples (B,) and rectal swab samples (C) from experimentally infected ferrets over time, based on residual maximum-likelihood analysis. Black line, NiV-Bangladesh; gray line, NiV-Malaysia. NiV N gene copies per milliliter of sample were calculated from reverse transcription data, then the transformation log₁₀(x₁ + 780) was calculated, where x₁ = NiV gene copies per milliliter. Values were fitted in the residual maximum-likelihood model by using transformed data and are plotted as values relative to the original scale (y-axis; logarithmic scale). Error bars represent approximate upper and lower limits for 95% CIs for the mean (calculated as mean ± 2 SE relative to the transformed scale).

Figure 2

Oral shedding of Nipah virus (NiV) in experimentally infected ferrets. A) Results of viral RNA area under the curve (AUC) calculation. Lower margin, inner line, and upper margin of the boxes represent 25th percentiles, medians, and 75th percentiles, respectively. Whiskers show maximum and minimum values for each group. B) Comparison of mean AUC between NiV-Bangladesh and NiV-Malaysia. Mean AUC for the NiV-Bangladesh infection group was significantly higher than that for the NiV-Malaysia–infected group; p = 0.001. Interval bars represent 95% CIs for the means. BD, Bangladesh; MY, Malaysia.

Figure 3

Nipah virus (NiV) antigen in acutely inflamed tonsillar tissue and overlying epithelium (A) and nasopharyngeal epithelium (B) in 2 ferrets infected with NiV-Bangladesh. Rabbit α-NiV N protein antiserum. Original magnification ×200.

Figure 4

Olfactory epithelium of a ferret infected with Nipah virus (NiV)-Bangladesh. NiV antigen was observed in close association with submucosal nerve fibers (N). Rabbit α-NiV N protein antiserum. Original magnification ×200.

Figure 5

Nipah virus (NiV) antigen in neuron (double arrows) and capillary endothelia (single arrow) of a ferret experimentally infected with NiV-Bangladesh. Rabbit α-NiV N protein antiserum. Original magnification ×200.

Figure 6

Nipah virus (NiV) antigen in ferret infected with NiV-Malaysia. A) Choroid plexus endothelium. B) ependymal epithelium and subependymal tissue, including neurons. Rabbit α-NiV N protein antiserum. Original magnification ×200.