Compellingly high SARS-CoV-2 susceptibility of Golden Syrian hamsters suggests multiple zoonotic infections of pet hamsters during the COVID-19 pandemic

Abstract

Golden Syrian hamsters (Mesocricetus auratus) are used as a research model for severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2). Millions of Golden Syrian hamsters are also kept as pets in close contact to humans. To determine the minimum infective dose (MID) for assessing the zoonotic transmission risk, and to define the optimal infection dose for experimental studies, we orotracheally inoculated hamsters with SARS-CoV-2 doses from 1 * 10⁵ to 1 * 10^-4 tissue culture infectious dose 50 (TCID₅₀). Body weight and virus shedding were monitored daily. 1 * 10^-3 TCID₅₀ was defined as the MID, and this was still sufficient to induce virus shedding at levels up to 10^2.75 TCID₅₀/ml, equaling the estimated MID for humans. Virological and histological data revealed 1 * 10² TCID₅₀ as the optimal dose for experimental infections. This compelling high susceptibility leading to productive infections in Golden Syrian hamsters must be considered as a potential source of SARS-CoV-2 infection for humans that come into close contact with pet hamsters.

Figure 1

Orotracheal SARS-CoV-2 inoculation results in increased weight loss and viral shedding. (A) Body weight curves of uninfected control group (grey), groups infected by the nasal (green) and orotracheal (red) routes; (B) Nasal shedding between 1 and 13 dpi after intranasal (green) and orotracheal (red) inoculation.

Figure 2

Cumulative mean and standard deviation of three experiments of body weight per infection dose groups. Changes in body weight (%) in relation to 0 dpi. Statistically significant differences in daily body weight changes are marked by an asterisk. P = 0.0001 for all days. Further details on statistical analysis are shown in Table S1.

Figure 3

Levels of lung affection after challenge with different infection doses. (A) Macroscopically determined level of lesion-affection (%) of whole lung during autopsy at 7 dpi and (B) at 10 dpi displayed as the mean value and standard deviation for each group. (C, D) Histopathology of hamster lungs, 10 days after orotracheal SARS-CoV-2 infection. Pneumonia-associated consolidation (C) and representative overviews (D) of the entire left lung lobe of (i) uninfected control; (ii) high dose control; (iii) infected with 1 * 10² TCID₅₀; (iv) infected with 1 * 10⁰ TCID₅₀; (v) infected with 1 * 10⁻¹ TCID₅₀; (vi) infected with 1 * 10⁻² TCID₅₀; (vii) infected with 1 * 10⁻³ TCID₅₀; (viii) infected with 1 * 10⁻⁴ TCID₅₀. (B)–(D) (n = 3).

Figure 4

Detailed histopathology of hamster lungs, 10 days after orotracheal SARS-CoV-2 infection. Hematoxylin and eosin staining, bar 50 µm. (A) Uninfected control, no lung lesion, (B) after 1 * 10^4.5 TCID₅₀ infection, showing vasculitis (arrow), type 2 pneumocyte hyperplasia and bronchialisation of alveoli (arrowhead), intra-alveolar erythrocytes (asterisk), (C) after 1 * 10² TCID₅₀ infection, with vasculitis (arrow), type 2 pneumocyte hyperplasia and bronchialisation of alveoli (arrowhead) and perivascular infiltrates (asterisk), (D) after 1 * 10⁰ TCID₅₀ infection exhibiting perivascular (arrow) and alveolar (asterisk) infiltrates, type 2 pneumocyte hyperplasia and bronchialisation of alveoli (arrowhead), (E) after 1 * 10⁻¹ TCID₅₀ infection, showing alveolar infiltrates (asterisk), type 2 pneumocyte hyperplasia and bronchialisation of alveoli (arrowhead), (F) after 1 * 10⁻² TCID₅₀ infection, with focal alveolar infiltrates (arrow) and edema (asterisk), (G) after 1 * 10⁻³ TCID₅₀ infection, exhibiting focal hypertrophy/hyperplasia of bronchial epithelium (arrow), (H) after 1 * 10⁻⁴ TCID₅₀, with focal alveolar infiltrates (arrow), (I) after 1 * 10⁻⁴ TCID₅₀ showing focal perivascular infiltrates (arrow).

Figure 5

Viral shedding in oral swab samples. (A) Genome copy number (Log₁₀) of viral RNA and (B) replication competent virus (Log₁₀ TCID₅₀/ml) detected in the oral swab samples of all hamsters. All groups were analysed, negative results are not shown. p-values are indicated for statistically significant differences in RNA levels. Details on statistical analysis are shown in Table S1. Colors match and represent results from the same hamsters as shown before and following.

Figure 6

Viral shedding in nasal washes. (A) Genome copy number (Log₁₀) of SARS-CoV-2 RNA and (B) replication competent virus (Log₁₀ TCID₅₀/ml) detected in the nasal wash samples of all hamsters 2, 4 and 7 dpi. All groups were analysed, negative results are not shown. Details on statistical analysis are shown in Table S1. Colors match and represent results from the same hamsters as shown before and following.

Figure 7

Time-dependent shedding of replication competent virus and change in body weight after infection with decreasing SARS-CoV-2 doses. Body weight development is shown by arrows; ↑ increasing from 1 to 7 or 10 dpi; ↓ decreasing from 1 to 7 or 10 dpi; ↓↑ decrease until 7 dpi followed by increase; ↑↓ increase until 4 dpi, followed by decrease until 10 dpi. Colors match and represent results from the same hamsters as shown before and following.

Figure 8

Genome copy number (Log₁₀) of SARS-CoV-2 RNA and replication competent virus (Log₁₀ TCID₅₀/ml) detected in the respiratory tract. (A) Genome copy number (Log₁₀) of viral RNA and (C) replication competent virus (Log₁₀ TCID₅₀/ml) detected in the respiratory tract samples at 7 dpi. (B) Genome copy number (Log₁₀) of viral RNA and (D) replication competent virus (Log₁₀ TCID₅₀/ml) detected in the respiratory tract samples at 10 dpi. Statistically significant differences in RNA levels were determined at 7 dpi. Further details on statistical analysis are shown in Table S1. Colors match and represent results from the same hamsters as shown before.