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. 2023 Jul 14:10:1151772.
doi: 10.3389/fvets.2023.1151772. eCollection 2023.

Contribution of cats and dogs to SARS-CoV-2 transmission in households

Egil A J Fischer #  1 , Els M Broens  1 , Hans S Kooistra  1 , Myrna M T De Rooij  1 , Jan Arend Stegeman  1 , Mart C M De Jong #  2
Affiliations

Contribution of cats and dogs to SARS-CoV-2 transmission in households

Egil A J Fischer et al. Front Vet Sci. .

Abstract

Introduction: SARS-CoV-2 is known to jump across species. The occurrence of transmission in households between humans and companion animals has been shown, but the contribution of companion animals to the overall transmission within a household is unknown. The basic reproduction number (R0) is an important indicator to quantify transmission. For a pathogen with multiple host species, such as SARS-CoV-2, the basic reproduction number needs to be calculated from the partial reproduction numbers for each combination of host species.

Method: In this study, the basic and partial reproduction numbers for SARS-CoV-2 were estimated by reanalyzing a survey of Dutch households with dogs and cats and minimally one SARS-CoV-2-infected human.

Results: For households with cats, a clear correlation between the number of cats and the basic reproduction number (Spearman's correlation: p 0.40, p-value: 1.4 × 10-5) was identified, while for dogs, the correlation was smaller and not significant (Spearman's correlation: p 0.12, p-value: 0.21). Partial reproduction numbers from cats or dogs to humans were 0.3 (0.0-2.0) and 0.3 (0.0-3.5) and from humans to cats or dogs were 0.6 (0.4-0.8) and 0.6 (0.4-0.9).

Discussion: Thus, the estimations of within-household transmission indicated the likelihood of transmission from these companion animals to humans and vice versa, but the observational nature of this study limited the ability to establish conclusive evidence. This study's findings support the advice provided during the pandemic to COVID-19 patients to maintain distance from companion animals as a precautionary measure and given the possibility of transmission, although there is an overall relatively limited impact on the pandemic when compared to human-to-human transmission.

Keywords: COVID-19; companion animal; final size; mathematical model; multilevel transmission; multispecies; reproduction number; zoonosis.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Graphical representation of the transmission model and the next-generation matrix (NGM). Partial reproduction numbers Rij are the number of new infectious individuals of type j (1 = human or 2 = animal) by an individual of type I (1 = human or 2 = animal). For example, R12 is the number of new infectious animals (type 2) caused by one infectious human (type 1). The actual number of new infections does also depend on the number of susceptible individuals of a certain type (S1 or S2) and the total household size H, i.e., the number of humans in the house.
Figure 2
Figure 2
Animal-to-human ratio distribution (histogram) and the basic reproduction number for these household compositions (line and bootstrap 95% confidence interval as a gray area). (A) Companion animals. (B) Only cats. (C) Only dogs. The x-axis has for dogs or companion animals to humans a maximum of 6, and for cats to humans, the maximum was 3. The y-axis represents either the household's basic reproduction number or the fraction of households with a certain ratio of animals to humans. The basic reproduction number is shown only in the range of observed values of animal-to-human ratios.
Figure 3
Figure 3
Average final size of infected humans when the infection is introduced by a cat for extreme values of ωI and ωS. Cats that do not go outside ω = 0 or are always outside ω = 1.
Figure 4
Figure 4
Average final size when the infection is introduced by a human for extreme values of ωI and ωS. Cats do not go outside ω = 0, or cats are always outside ω = 1.
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