Experimental infection model for Sin Nombre hantavirus in the deer mouse (Peromyscus maniculatus)

Abstract

The relationship between hantaviruses and their reservoir hosts is not well understood. We successfully passaged a mouse-adapted strain of Sin Nombre virus from deer mice (Peromyscus maniculatus) by i.m. inoculation of 4- to 6-wk-old deer mouse pups. After inoculation with 5 ID(50), antibodies to the nucleocapsid (N) antigen first became detectable at 14 d whereas neutralizing antibodies were detectable by 7 d. Viral N antigen first began to appear in heart, lung, liver, spleen, and/or kidney by 7 d, whereas viral RNA was present in those tissues as well as in thymus, salivary gland, intestine, white fat, and brown fat. By 14 d nearly all tissues examined displayed both viral RNA and N antigen. We noted no consistent histopathologic changes associated with infection, even when RNA load was high. Viral RNA titers peaked on 21 d in most tissues, then began to decline by 28 d. Infection persisted for at least 90 d. The RNA titers were highest in heart, lung, and brown fat. Deer mice can be experimentally infected with Sin Nombre virus, which now allows provocative examination of the virus-host relationship. The prominent involvement of heart, lung, and brown fat suggests that these sites may be important tissues for early virus replication or for maintenance of the virus in nature.

Figure 1

Sera from all SNV-inoculated animals at days 7, 14, and 28 pi were examined for reactivity to the SNV N antigen by strip immunoblot assay (central band). In addition to the viral band, a Coomassie blue (CB) band was loaded for orientation, as well as high-intensity (3+) and low-intensity (1+) bands of deer mouse serum. Animals at 14 d were undergoing seroconversion, whereas the 28-d specimens were fully reactive.

Figure 2

Localization of SNV N antigen in acutely infected deer mice by immunohistochemistry. Selected samples are shown at ×400. (A) Mouse no. 5139 heart, 21 d. (B) Heart of sham-injected mouse, 21 d. (C) Mouse no. 2450 lung, 21 d. (D) Mouse no. 5139 kidney. (E) Mouse no. 2468 liver, 14 d. (F) Mouse no. 2450, brown fat. Arrows indicate the borders of a glomerulus.

Figure 3

TaqMan quantitative RT-PCR analysis. The RNA copy number is expressed as the mean of all tissues with detectable signal at each time point. The number of tissues positive/tissues tested is expressed above each time point bar. Error bars indicate the SEM for three replicates. Threshold sensitivity was 1,000 copies/mg.