SARS-CoV-2 Infection and Clinical Signs in Cats and Dogs from Confirmed Positive Households in Germany

Round 1

Reviewer 1 Report

Michelitsch and collaborators carry out an interesting epidemiological study where the antibodies against SARS-CoV-2 in pets from households with SARS-CoV-2 positive cases are tested. However, the work is irreproducible due to the lack of information provided. The Questionnaire S1 is empty.

Some parameters statistics such as a high standard deviation should be discussed and explained.  Is it a sampling problem?

Author Response

Dear reviewer 1!

Please find our response in the attached file.

Author Response File: Author Response.docx

Reviewer 2 Report

In this manuscript entitled “Evaluation of SARS-CoV-2 infection and development of clinical signs in cats and dogs kept in households with confirmed human infection in Germany”, Michelitsch et al examined the seroprevalence of SARS-CoV-2 among cats and dogs and explored the factors that may influence their infection risks through a multivariable logistic regression model. Overall, this is a well-designed research which provides a fresh perspective towards the interspecies transmission of SARS-CoV-2 between humans and their pets. However, before being considered for publication in Viruses several concerns need to be addressed, as detailed below.

1.       Although the general writing of this manuscript is fluent and readable, the title is somewhat confusing to me and maybe to the readers. A lot of information is contained in this title and comes to an inevitable loss of logic. The authors are encouraged to come up with an alternative title to better summarize the manuscript with a more concise description.

2.       The authors centered on the interaction between pet animals and hosts, but the basic information of the animals is not discussed in the manuscript, such as their ages, breeds, although the questionnaire included such information.

3.       Line 122-123: how was the 1/100 dilution of serum samples chosen for the study? Did the authors follow one particular protocol described in a previous publication?

4.       Line 274-275: please describe figure 4 in greater detail in the legends; for readers with less statistics background the figure maybe too hard to understand with the current info provided. i.e., what are the black columns in the bar chart stands for?

5.       The authors provided detailed analysis on how cats and dogs be infected with SARS-CoV-2 while interacting with their owners/other infected humans. Were there any situations where pets being in the middle of the transmission route (from animal to animal, or from animal to human)?

Author Response

Dear reviewer 2!

Please find our response in the attached file.

Author Response File: Author Response.docx

Reviewer 3 Report

This manuscript summarizes a study evaluating SARS-CoV-2 seroprevalence among cats and dogs owned by people with COVID-19 to better the transmission dynamics from people to animals and risk factors associated with transmission. The authors selected households with at least 1 PCR confirmed human COVID-19 case with pets (dogs or cats). A survey was completed by the owners, describing their timeline of infection, symptoms, clinical signs seen in their pets, and description of contact with the pets. A blood sample was collected from the animals for evaluation via ELISA. 42.5% of cats and 56.8% of dogs were seropositive for SARS-CoV-2. The authors assessed through a multivariable logistic regression risk factors for dogs and cats and concluded that interspecies transmission of SARS-CoV-2 occurs frequently, and the nature and frequency of contact is an important risk factor.

Article:

Thank you for submission of this article. This article clearly summarizes the findings of this serosurvey. The article could be strengthened by adding in additional relevant epidemiologic information, for example reporting interval between human infection and animal clinical signs to better describe the transmission.

Was a survey completed for each animal? In the event that levels of exposure were different, this would be important to evaluate. As mentioned later, the species-susceptibility of dogs and cats cannot be ignored in the discussion of seropositivity and differences between these two, rather than limiting the discussion to the nature of contact with humans in the household.

As the authors know, the ELISA results indicate exposure, but it is difficult to describe the timeline between human infection and subsequent transmission to dogs and cats without baseline values. Additionally, the possibility of transmission between dogs and cats in the same household cannot be excluded, as the authors mentioned.

For future research, the use of serologic titers to characterize immune response may be more informative than use of an ELISA, though understand that ELISAs are quite commonly used.

Review:

The authors clearly and succinctly present their findings. Background literature presented in the introduction on seroprevalence among cats and dogs could be expanded; significant research describing this has been completed to date and is described in the discussion but could be useful to set the stage earlier in the manuscript. Additionally, discussion on the species-specific susceptibility to SARS-CoV-2 (and differences between dogs and cats) could be helpful to include, particularly since these results are inconsistent with previous research that has shown an increased susceptibility of cats to SARS-CoV-2. Inclusion of FIV/FeLV status would also be useful for the sampled cats.

The identification of risk factors for transmission is important, but the recommendations based on these findings could be expanded upon. Additionally, were there any risk factors appreciated for the development of clinical signs? Sincere apologies if it was overlooked.

The finding that “no significant association was found between reported clinical signs in animals and their antibody status” warrants further discussion. Previous research suggests that a certain percentage of particularly cats do develop clinical signs (see Experimental infection of domestic dogs and cats with SARS-CoV-2: Pathogenesis, transmission, and response to reexposure in cats | PNAS) for experimental studies), but discussion of why this was not the case in this study would be a helpful addition.

A significant body of evidence exists describing transmission between humans and companion animals, and more reference to these publications and comments on similarities and differences would be helpful.

Specific Comments:

1.       Additional animal to human transmission has been described previously. Please consider:

ila T, Sunghan J, Laochareonsuk W, et al. Suspected cat-to-human transmission of SARS-CoV-2, Thailand, July–September 2021. Emerging. Infect Dis J. 2022;28(7):1485–1488. doi:10.3201/eid2807.212605

2.       Line 150- consider adding in that past medical history was included on the questionnaire, rather than introducing this in results.

3.       Line 167- consider adding in actual ages into these results, rather than dichotomizing by high and low among the sample population

4.       Line 247- recommend specifying that this is a SARS-CoV-2 diagnosis

5.       Line 265- Was the degree of interaction between the animals evaluated?

Author Response

Dear reviewer 3!

Please find our response in the attached file.

Author Response File: Author Response.docx

Reviewer 4 Report

 Michelitsch et al. confirmed the interspecies transmission of SARS-CoV-2 between humans and their pet animals, and the pets may not show any clinical signs. The antibody status of 115 cats and 170 dogs, originating from owners with SARS-CoV-2 positive was assessed by ELISA. The authors concluded that no significant association was found between reported clinical signs in animals and their antibody status. 

Please find below suggestions for improvements:

Major comments:

1.The authors tested antisera using the indirect ELISA. As this assay provided the foundation of this study, a detailed ELISA results need to be shown in a table or figure. In the figure, the absorbance value at 450nm and negative control should be shown.

2. Several studies with cats and dogs infection of COVID19 already published, which may reduce the novelty of the study.

Minor comments:

1.Line 125, page 3, what is “TBST”? Please list the full name of it.

2. line 124, page 3, the diluted serum was added to the coated and uncoated wells. What protein or peptide used to coat the plate?

Author Response

Dear reviewer 4!

Please find our response in the attached file.

Author Response File: Author Response.docx