Characterization of a Novel Murine Model to Study Zika Virus

Abstract

The mosquito-borne Zika virus (ZIKV) is responsible for an explosive ongoing outbreak of febrile illness across the Americas. ZIKV was previously thought to cause only a mild, flu-like illness, but during the current outbreak, an association with Guillain-Barré syndrome and microcephaly in neonates has been detected. A previous study showed that ZIKV requires murine adaptation to generate reproducible murine disease. In our study, a low-passage Cambodian isolate caused disease and mortality in mice lacking the interferon (IFN) alpha receptor (A129 mice) in an age-dependent manner, but not in similarly aged immunocompetent mice. In A129 mice, viremia peaked at ∼10(7) plaque-forming units/mL by day 2 postinfection (PI) and reached high titers in the spleen by day 1. ZIKV was detected in the brain on day 3 PI and caused signs of neurologic disease, including tremors, by day 6. Robust replication was also noted in the testis. In this model, all mice infected at the youngest age (3 weeks) succumbed to illness by day 7 PI. Older mice (11 weeks) showed signs of illness, viremia, and weight loss but recovered starting on day 8. In addition, AG129 mice, which lack both type I and II IFN responses, supported similar infection kinetics to A129 mice, but with exaggerated disease signs. This characterization of an Asian lineage ZIKV strain in a murine model, and one of the few studies reporting a model of Zika disease and demonstrating age-dependent morbidity and mortality, could provide a platform for testing the efficacy of antivirals and vaccines.

Figure 1.

CD1 infected with Zika virus (ZIKV) strain FSS13025 do not show signs of disease. Groups of 3-week-old CD1 mice were infected with 1 × 10⁴ plaque-forming units subcutaneously and weighed daily. Mice MOCK infected with phosphate-buffered saline (N = 2) are shown by a dashed line, whereas FSS13025-infected mice (N = 6) are shown by a solid line. The percent of initial weight is shown, and bars denote standard errors of the means.

Figure 2.

A129 mice show disease in an age-dependent manner. Groups of A129 mice aged 3 weeks (N = 5), 5 weeks (N = 6), and 11 weeks (N = 3) were infected with 1 × 10⁵ plaque-forming units of FSS13025 IP. (A) Percent of initial weight is shown. Each age has 1–2 mice MOCK infected with phosphate-buffered saline. (B) Levels of viremia in serum are shown. # Sample not taken and * samples lower than the limit of detection. (C) The mortality (natural or euthanized) after infection is shown. Error bars in all panels denote standard errors of the means.

Figure 3.

FSS13025 is lethal in AG129 by intraperitoneal (IP) or intradermal (ID) inoculation. Groups of three mice aged 3 weeks were weighed daily, and percent of initial weight is reported (A). * Significance between percent of initial weights from MOCK vs. infected groups on day 5 (P = 0.0006) by one-factor analysis of variance with Tukey–Kramer post hoc test. (B) Viremia titers are shown (N = 1 for each route for each day except ID inoculated on day 6, N = 3). (C) Percent survival is shown.

Figure 4.

Viral loads in individual 3-week-old A129 mice. Organs were homogenized and titrated on Vero cell monolayers. Below each day, the observations, average titer for the group, and if the mouse was perfused with phosphate-buffered saline before necropsy are listed. Bars denote standard error. BAR = bright, alert, and reactive to stimuli. # Sample not taken and * no detectable titer.

Figure 5.

Viral loads in individual intradermal-infected AG129 mice. Moribund mice on day 6 were necropsied and organs were harvested, triturated, and titrated. Below each day, observations and viremia titers are listed.