Recovery of anosmia in hamsters infected with SARS-CoV-2 is correlated with repair of the olfactory epithelium

Abstract

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is responsible for a pandemic affecting billions of people worldwide. Apart from the extreme global economic impact, the pandemic will likely have a lasting impact through long-term sequelae not yet fully understood. Fully understanding the mechanisms driving the various symptoms and sequelae of SARS-CoV-2 infection will allow for the eventual development of therapeutics to prevent or treat such life-altering symptoms. In this study, we developed a behavioral test of anosmia in SARS-CoV-2-infected hamsters. We find a moderately strong correlation between the level of anosmia and the score of histological damage within the olfactory epithelium. We also find a moderately strong correlation between the level of anosmia and the thickness of the olfactory epithelium, previously demonstrated to be severely damaged upon infection. Thus, this food-searching behavioral test can act as a simple and effective screening method in a hamster model for various therapeutics for SARS-CoV-2-related anosmia.

Figure 1

Body weight and temperature change in hamsters. Weight change (A) and temperatures (B) for SARS-CoV-2-inoculated (n = 32) versus mock-inoculated (n = 4) Syrian golden hamsters were shown in average ± SEM/ SARS-CoV-2-inoculated hamsters were euthanized for sample collection at 2, 3, 5, 8, 17, 21, 35, and 42 dpi (n = 4 each). Significant differences between SARS-CoV-2- and mock-inoculated groups at each timepoint were determined by a two-way ANOVA followed by Fisher’s LSD test. *p < 0.05.

Figure 2

Time (s) taken for hamsters to find the hidden cookie. The time required for hamsters to find the hidden cookie were shown in box plots. The broken line indicates the cut off value of measurement (300 s). Significant differences compared to mock group were determined by one-way ANOVA followed by Dunnett’s post hoc test. *p < 0.05. Mock n = 8; all infected groups n = 4.

Figure 3

Virus titers in the lungs of SARS-CoV-2-inoculated hamsters. Averages and SEMs of virus titers in the lungs were plotted. The broken line indicates the limit of detection (< 1.50 log₁₀ TCID50/g). All groups n = 4.

Figure 4

Representative histology of nasal turbinate in hamsters. Significant olfactory epithelial damage and nasal discharge is evident through 8 dpi in samples. Scale bars: 1 mm (left), 100 µm (Right).

Figure 5

Histology scores of nasal turbinate. Scoring of gross histopathological changes of the olfactory epithelium in the four nasal turbinate regions: S—nasal septal, MT—medial turbinate, DT—dorsal turbinate, LT—lateral turbinate. 0—no damage (normal), 1—mild damage (damage reaches only through epithelial layer; basal layer remains untouched), 2—moderate damage (up to 75% of damage reaches basal cells), 3—severe damage (over 75% of damage reaches basal cells). Scores were averaged between two independent reviewers. 21dpi n = 3; all other groups n = 4.

Figure 6

Olfactory epithelium thickness in nasal turbinate. Box plots of the thickness (μm) of the olfactory epithelium (OE) in the four nasal turbinate regions were shown: S—nasal septal, MT—medial turbinate, DT—dorsal turbinate, LT—lateral turbinate. All results the average of two independent measurements. 21 dpi n = 3; all other groups n = 4. * = p < 0.05.